[ { "id": "authors:w4qh6-j9e64", "collection": "authors", "collection_id": "w4qh6-j9e64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170516-072216755", "type": "article", "title": "Cobalt(III) Corroles as Electrocatalysts for the Reduction of Dioxygen: Reactivity of a Monocorrole, Biscorroles, and Porphyrin\u2212Corrole Dyads", "author": [ { "family_name": "Kadish", "given_name": "Karl M.", "clpid": "Kadish-K-M" }, { "family_name": "Fr\u00e9mond", "given_name": "Laurent", "clpid": "Fr\u00e9mond-L" }, { "family_name": "Ou", "given_name": "Zhongping", "clpid": "Ou-Zhongping" }, { "family_name": "Shao", "given_name": "Jianguo", "clpid": "Shao-Jianguo" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Burdet", "given_name": "Fabien", "clpid": "Burdet-F" }, { "family_name": "Gros", "given_name": "Claude P.", "clpid": "Gros-C-P" }, { "family_name": "Barbe", "given_name": "Jean-Michel", "clpid": "Barbe-J-M" }, { "family_name": "Guilard", "given_name": "Roger", "clpid": "Guilard-R" } ], "abstract": "Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me_4Ph_5Cor)Co, one a face-to-face biscorrole linked by an anthracene (A), biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or dibenzothiophene (S) bridge, (BCY)Co_2 (with Y = A, B, X, O or S), and one a face-to-face bismacrocyclic complex, (PCY)Co_2, containing a Co(II) porphyrin and a Co(III) corrole also linked by one of the above rigid spacers (Y = A, B, X, or O). Cyclic voltammetry and rotating ring\u2212disk electrode voltammetry were both used to examine the catalytic activity of the cobalt complexes in acid media. The mixed valent Co(II)/Co(III) complexes, (PCY)Co_2, and the biscorrole complexes, (BCY)Co_2, which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O_2 to H_2O in aqueous acidic electrolyte when adsorbed on a graphite electrode, with the most efficient process being observed in the case of the complexes having an anthracene spacer. A relatively small amount of hydrogen peroxide was detected at the ring electrode in the vicinity of E_(1/2) which was located at 0.47 V vs SCE for (PCA)Co_2 and 0.39 V vs SCE for (BCA)Co_2. The cobalt(III) monocorrole (Me_4Ph_5Cor)Co also catalyzes the electroreduction of dioxygen at E_(1/2) = 0.38 V with the final products being an approximate 50% mixture of H_2O_2 and H_2O.", "doi": "10.1021/ja0501060", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2005-04-20", "series_number": "15", "volume": "127", "issue": "15", "pages": "5625-5631" }, { "id": "authors:qz4e9-f9z91", "collection": "authors", "collection_id": "qz4e9-f9z91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170420-115314999", "type": "article", "title": "Targeted Proton Delivery in the Catalyzed Reduction of Oxygen to Water by Bimetallic Pacman Porphyrins", "author": [ { "family_name": "Chang", "given_name": "Christopher J.", "clpid": "Chang-Christopher-J" }, { "family_name": "Loh", "given_name": "Zhi-Heng", "clpid": "Loh-Zhi-Heng" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Nocera", "given_name": "Daniel G.", "orcid": "0000-0001-5055-320X", "clpid": "Nocera-D-G" } ], "abstract": "A combined experimental and theoretical investigation of the role of proton delivery in determining O_2 reduction pathways catalyzed by cofacial bisporphyrins is presented. A homologous family of dicobalt(II) Pacman porphyrins anchored by xanthene [Co_2(DPX) (1) and Co_2(DPXM) (3)] and dibenzofuran [Co_2(DPD) (2) and Co_2(DPDM) (4)] have been synthesized, characterized, and evaluated as catalysts for the direct four-proton, four-electron reduction of O_2 to H_2O. Structural analysis of the intramolecular diiron(III) \u03bc-oxo complex Fe_2O(DPXM) (5) and electrochemical measurements of 1\u22124 establish that Pacman derivatives bearing an aryl group trans to the spacer possess structural flexibilities and redox properties similar to those of their parent counterparts; however, these trans-aryl catalysts exhibit markedly reduced selectivities for the direct reduction of O_2 to H_2O over the two-proton, two-electron pathway to H_2O_2. Density functional theory calculations reveal that trans-aryl substitution results in inefficient proton delivery to O_2-bound catalysts compared to unsubstituted congeners. In particular, the HOMO of [Co_2(DPXM)(O_2)]+ disfavors proton transfer to the bound oxygen species, funneling the O\u2212O activation pathway to single-electron chemistry and the production of H_2O_2, whereas the HOMO of [Co_2(DPX)(O_2)]+ directs protonation to the [Co_2O_2] core to facilitate subsequent multielectron O\u2212O bond activation to generate two molecules of H_2O. Our findings highlight the importance of controlling both proton and electron inventories for specific O\u2212O bond activation and offer a unified model for O\u2212O bond activation within the clefts of bimetallic porphyrins.", "doi": "10.1021/ja049115j", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2004-08-18", "series_number": "32", "volume": "126", "issue": "32", "pages": "10013-10020" }, { "id": "authors:tgh0n-6et57", "collection": "authors", "collection_id": "tgh0n-6et57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170427-103551816", "type": "article", "title": "Attachment of Cobalt \"Picket Fence\" Porphyrin to the Surface of Gold Electrodes Coated with 1-(10-Mercaptodecyl)imidazole", "author": [ { "family_name": "Zou", "given_name": "Shouzhong", "clpid": "Zou-Shouzhong" }, { "family_name": "Clegg", "given_name": "Robert S.", "clpid": "Clegg-R-S" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Self-assembled monolayers of 1-(10-mercaptodecyl)imidazole on Au electrodes were used to bind cobalt \"picket fence\" porphyrin (cobalt 5,10,15,20-tetrakis(\u03b1,\u03b1,\u03b1,\u03b1-2-pivalamidophenyl)porphyrin) to the electrode surface. The binding involved coordination of the cobalt center of the porphyrin to the pendant imidazole groups in the monolayer coating. Attempts to coordinate the Co(II) oxidation state of the porphyrin to the coatings were not successful. However, with the Co(III) oxidation state, substantial binding was achieved which persisted even when the Co(III) was reduced to Co(II). Absorption spectra of the attached porphyrin were obtained for both oxidation states of the cobalt center. The remaining axial coordination site on the attached cobalt porphyrin is accessible to ligands, for example, imidazole, in aqueous solution.", "doi": "10.1021/la011444r", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "2002-04-16", "series_number": "8", "volume": "18", "issue": "8", "pages": "3241-3246" }, { "id": "authors:jmyy1-xgp60", "collection": "authors", "collection_id": "jmyy1-xgp60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-150552429", "type": "article", "title": "Catalysis of the Electro-Oxidation of Carbon Monoxide by Cobalt Octaethylporphyrin", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The electro-oxidation of cobalt (II) octaethylporphyrin adsorbed on graphite electrodes, Co^(II)(OEP)_(ads') to Co^(III)(OEP) ^+_(ads), in the presence of aqueous solutions of CO leads to catalytic oxidation of CO to CO_2. No such oxidation occurs with Co^(II)(OEP) and CO dissolved in nonaqueous solvents. Coordination of the CO to Co^(III)(OEP)^+ is the first step in the catalytic mechanism. Nucleophilic attack on the coordinated CO by H_2O is the probable rate-limiting step in the catalytic oxidation. A pseudo first-order rate constant of 0.3 s^(-1) was estimated for this reaction.", "doi": "10.1021/ic010530b", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2001-11-05", "series_number": "23", "volume": "40", "issue": "23", "pages": "5829-5833" }, { "id": "authors:gy0j0-1xf64", "collection": "authors", "collection_id": "gy0j0-1xf64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170516-073937933", "type": "article", "title": "Rates of Electron-Transfer Across Liquid/Liquid Interfaces. Effects of Changes in Driving Force and Reaction Reversibility", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Rates of electron-transfer between redox reactants located on opposite sides of the interface between thin layers of organic solvents on graphite electrode and aqueous solutions were measured by means of steady-state electrochemistry. Changes in the overall driving forces for irreversible reactions produced changes in rate that fit no simple behavioral pattern. For reversible reactions, a regular increase in rate with driving force was obtained. Evidence for a significant effect of diffuse-layer potentials on reaction rates was not found.", "doi": "10.1021/jp010465r", "issn": "1520-6106", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry B", "publication_date": "2001-09-20", "series_number": "37", "volume": "105", "issue": "37", "pages": "8963-8969" }, { "id": "authors:ecwhk-m7713", "collection": "authors", "collection_id": "ecwhk-m7713", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170424-125035745", "type": "article", "title": "Schiff Base Complexes of Vanadium(III, IV, V) as Catalysts for the Electroreduction of O_2 to H_2O in Acetonitrile", "author": [ { "family_name": "Liu", "given_name": "Zenghe", "clpid": "Liu-Zenghe" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Fifteen Schiff base ligands were synthesized and used to form complexes with vanadium in oxidation states III, IV, and V. Electrochemical and spectral characteristics of the complexes were evaluated and compared. In acidified solutions in acetonitrile the vanadium(IV) complexes undergo reversible disproportionation to form V(III) and V(V) complexes. With several of the ligands the V(III) complexes are much more stable in the presence of acid than is the previously studied complex with salen, an unelaborated Schiff base ligand (H_2 salen = N,N'-ethylenebis(salicylideneamine)). Equilibrium constants for the disproportionation were evaluated. The vanadium(III) complexes reduce dioxygen to form two oxo ligands. The reaction is stoichiometric in the absence of acid, and second-order rate constants were evaluated. In the presence of acid some of the complexes investigated participate in a catalytic electroreduction of dioxygen.", "doi": "10.1021/ic0010407", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2001-03-12", "series_number": "6", "volume": "40", "issue": "6", "pages": "1329-1333" }, { "id": "authors:a5m7e-gdh90", "collection": "authors", "collection_id": "a5m7e-gdh90", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-154112820", "type": "article", "title": "Selecting Experimental Conditions for Measurement of Rates of Electron-Transfer at Liquid/Liquid Interfaces by Thin-Layer Electrochemistry", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The use of thin layers of water-immiscible organic solvents on electrode surfaces to evaluate rates of electron-transfer across liquid/liquid interfaces requires that reactant concentrations in the two adjacent phases be selected to minimize the effects of mass transfer on the measured currents. A general inequality is derived which provides a guide to the selection of suitable concentrations of the coreactants. Experimental tests of the inequality demonstrated its utility and should allay recently expressed concerns about the reliability of the thin-layer methodology.", "doi": "10.1021/jp003741v", "issn": "1520-6106", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry B", "publication_date": "2001-02-08", "series_number": "5", "volume": "105", "issue": "5", "pages": "1047-1049" }, { "id": "authors:gwrta-zrc20", "collection": "authors", "collection_id": "gwrta-zrc20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160727-100827075", "type": "article", "title": "Electrochemical Monitoring of Proton Transfer across Liquid/Liquid Interfaces on the Surface of Graphite Electrodes", "author": [ { "family_name": "Chung", "given_name": "Taek Dong", "clpid": "Chung-Taek-Dong" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Equilibrium partitioning of HClO_4 between aqueous solutions and benzonitrile (BN) or nitrobenzene (NB) was measured and used to evaluate the pKa of the acid in the two organic solvents. The potential drop across the BN/H_2O interface was evaluated from the known potential drop across the NB/H_2O interface and the voltammetrically measured formal potential of a ferrocenium/ferrocene redox couple confined within thin layers of the two organic solvents. The voltammetric reduction of tetrachloro-1, 4-benzoquinone in thin layers of BN was used to monitor changes in the concentration of protons in the layer during proton-consuming faradaic reactions. The rate of proton transfer from the aqueous to the nonaqueous phase across the BN/H_2O interface was shown to be adequate to sustain proton-consuming reactions at the electrode/BN interface.", "doi": "10.1021/ac0009447", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "2001-01-15", "series_number": "2", "volume": "73", "issue": "2", "pages": "337-342" }, { "id": "authors:n27t8-1n652", "collection": "authors", "collection_id": "n27t8-1n652", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170425-063336725", "type": "article", "title": "Examination of Cobalt \"Picket Fence\" Porphyrin and Its Complex with 1-Methylimidazole as Catalysts for the Electroreduction of Dioxygen", "author": [ { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The electrochemical behavior of cobalt 5,10,15,20-tetrakis(\u03b1,\u03b1,\u03b1,\u03b1-2-pivalamidophenyl)porphyrin (Co^(II)TpivPP) was examined in benzonitrile solutions. The electrochemical responses were changed significantly by the addition of 1-methylimidazole which coordinates once to the Co(II) and twice to the Co(III) porphyrin. The corresponding equilibrium binding constants were estimated as 2.9 \u00d7 10^3 M^(-1) and 1.7 \u00d7 10^(20) M^(-2). The cyclic voltammetric responses were affected by the rates of the ligand association/dissociation reactions. Formation of the O_2 adduct of the Co(II) porphyrin resulted in only small changes in the cyclic voltammetric pattern. Comparison between Co^(II)TpivPP and cobalt tetraphenylporphyrin (Co^(II)TPP) as catalysts for the electroreduction of O_2 showed the latter to be the superior catalyst both when adsorbed on graphite electrodes and when dissolved in thin layers of acidified benzonitrile where Co^(II)TpivPP exhibited unimpressive catalytic activity compared with Co^(II)TPP, which appeared to catalyze the reduction of O_2 by significantly more than 2 electrons per molecule.", "doi": "10.1021/ic000537d", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2000-10-02", "series_number": "20", "volume": "39", "issue": "20", "pages": "4579-4585" }, { "id": "authors:ztzc8-dtf25", "collection": "authors", "collection_id": "ztzc8-dtf25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHAcc00", "type": "article", "title": "Electrocatalytic four-electron reduction of oxygen to water by a highly flexible cofacial cobalt bisporphyrin", "author": [ { "family_name": "Chang", "given_name": "Christopher J.", "clpid": "Chang-Christopher-J" }, { "family_name": "Deng", "given_name": "Yongqi", "clpid": "Deng-Yongqi" }, { "family_name": "Nocera", "given_name": "Daniel G.", "orcid": "0000-0001-5055-320X", "clpid": "Nocera-D-G" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Chang", "given_name": "C. K.", "clpid": "Chang-C-K" } ], "abstract": "Dicobalt(II) cofacial bisporphyrins anchored by dibenzofuran (DPD) and xanthene (DPX) are efficient electrocatalysts for the four-electron reduction of oxygen to water despite their ca. 4 \u00c5 difference in metal\u2013metal distances, suggesting that the considerable longitudinal Pac-Man flexibility of the pillared platforms is the origin for the similar catalytic reactivity of these structurally disparate systems.", "doi": "10.1039/b001620i", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2000-08-01", "series_number": "15", "volume": "2000", "issue": "15", "pages": "1355-1356" }, { "id": "authors:0y2y2-bvb61", "collection": "authors", "collection_id": "0y2y2-bvb61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-094651903", "type": "article", "title": "Electrochemical Properties of Vanadium(III,IV,V)\u2212Salen Complexes in Acetonitrile. Four-Electron Reduction of O_2 by V(III)\u2212Salen", "author": [ { "family_name": "Liu", "given_name": "Zenghe", "clpid": "Liu-Zenghe" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The coordination chemistry and electrochemistry of complexes of vanadium(III,IV,V) with salen (H_2 salen = N,N'-ethylenebis(salicylideneamine) were reexamined in an attempt to uncover the origin of puzzling results reported in a previous study (Inorg. Chem. 1994, 33, 1056). Microelectrodes were utilized to allow measurements in the absence of supporting electrolyte. The source of the puzzling results was identified and the modifications required in the previous interpretations are specified. Corrected values of formal potentials and diffusion coefficients are also given. The acid-induced disproportionation of V^(IV)O(salen), as originally proposed by Bonadies et al. (J. Chem. Soc., Chem. Commun. 1986, 1218; Inorg. Chem. 1987, 26, 1218), was largely supported by the present results. The equilibrium constant for this disproportionation reaction was measured. The stoichiometry and kinetics of the reaction between O_2 and the V(III)\u2212salen complex were examined, and a possible mechanism for this four-electron reduction of O_2 is suggested.", "doi": "10.1021/ic990958z", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2000-01-24", "series_number": "2", "volume": "39", "issue": "2", "pages": "274-280" }, { "id": "authors:g3kh2-n2c10", "collection": "authors", "collection_id": "g3kh2-n2c10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160819-142157037", "type": "article", "title": "Femtosecond Dynamics of Dioxygen - Picket-Fence Cobalt Porphyrins: Ultrafast Release of O_2 and the Nature of Dative Bonding", "author": [ { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Baskin", "given_name": "J. Spencer", "clpid": "Baskin-J-S" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Zewail", "given_name": "Ahmed H.", "clpid": "Zewail-A-H" } ], "abstract": "The ultrafast release of O_2 from the O_2 adduct of picket-fence cobalt porphyrin (see picture) has been probed in real time, and has a total reaction time of 2 ps, without subsequent recombination over several nanoseconds. The dynamics of this ultrafast release of O_2 shows that relaxation within the porphyrin system (200 fs) precedes porphyrin-to-metal electron transfer, but the latter occurs at an enhanced rate (500 fs as opposed to the more usual 1\u2009\u2013\u20092 ps) because of the dative bonding of cobalt and O_2, which gives the adduct ground state significant Co^(III)\u2212O_2^\u2212 character.", "doi": "10.1002/(SICI)1521-3773(20000103)39:1<257::AID-ANIE257>3.0.CO;2-3", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2000-01-03", "series_number": "1", "volume": "39", "issue": "1", "pages": "257-260" }, { "id": "authors:s4m9f-w8k08", "collection": "authors", "collection_id": "s4m9f-w8k08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160823-144513594", "type": "article", "title": "Femtosecond Dynamics and Electrocatalysis of the Reduction of O_2: Tetraruthenated Cobalt Porphyrins", "author": [ { "family_name": "Yu", "given_name": "Hua-Zhong", "clpid": "Yu-Hua-Zhong" }, { "family_name": "Baskin", "given_name": "J. Spencer", "clpid": "Baskin-J-S" }, { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Zewail", "given_name": "Ahmed H.", "clpid": "Zewail-A-H" } ], "abstract": "Recently we reported the femtosecond dynamics of some porphyrin molecules. These studies elucidated the elementary steps involved in intramolecular relaxation and charge transfer (CT) in cobalt tetraphenylporphyrin (CoTPP) from the porphyrin \u03c0 (a_(2u)) system to the Co(d_z^2). Our interest in the dynamics of intramolecular electron transfer stems from recent studies of cobalt porphyrins that were modified by attachment of Ru(II) or Os(II) complexes to the periphery of the porphyrin ring. These modified cobalt porphyrins exhibit high catalytic activity for the electroreduction of O_2 directly to H_2O, a process that most monomeric cobalt porphyrins are unable to accomplish. The mechanism by which the modified cobalt porphyrins achieve the direct, four-electron reduction of O_2 has been suggested to involve back-bonding interactions among the attached Ru(II) and Os(II) centers, the porphyrin ring, and the Co(II) ion at its center.", "doi": "10.1021/ja983532c", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "1999-01-20", "series_number": "2", "volume": "121", "issue": "2", "pages": "484-485" }, { "id": "authors:qrp0m-dnp64", "collection": "authors", "collection_id": "qrp0m-dnp64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160823-144514367", "type": "article", "title": "Femtosecond dynamics of metalloporphyrins: electron transfer and energy redistribution", "author": [ { "family_name": "Yu", "given_name": "H. Z.", "clpid": "Yu-H-Z" }, { "family_name": "Baskin", "given_name": "J. S.", "clpid": "Baskin-J-S" }, { "family_name": "Steiger", "given_name": "B.", "clpid": "Steiger-B" }, { "family_name": "Wan", "given_name": "C. Z.", "clpid": "Wang-C-Z" }, { "family_name": "Anson", "given_name": "F. C.", "clpid": "Anson-F-C" }, { "family_name": "Zewail", "given_name": "A. H.", "clpid": "Zewail-A-H" } ], "abstract": "Femtosecond-resolved, real-time dynamics of the low-lying excited state ^2Q(\u03c0,\u03c0^*) of cobalt(II) tetraphenylporphyrin are reported in different solvents of varying polarity and structure. The dependence of the dynamics on the probing wavelength and on the metal and porphyrin substitution was also investigated. The decay in the \u03c0 system of the porphyrin occurs with a lifetime of 220 fs in benzene, while a second process with a lifetime of 1.8 ps is consistent with a proposed model for intramolecular charge separation: porphyrin a_(2u)(\u03c0)\u2192Co(d_z^2). The dynamics of the charge transfer state is influenced by the solvents' polarity and coordination ability.", "doi": "10.1016/S0009-2614(98)00753-2", "issn": "0009-2614", "publisher": "Elsevier", "publication": "Chemical Physics Letters", "publication_date": "1998-08-21", "series_number": "1-2", "volume": "293", "issue": "1-2", "pages": "1-8" }, { "id": "authors:2845h-nte07", "collection": "authors", "collection_id": "2845h-nte07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170915-082322991", "type": "article", "title": "A Simple Method for Examining the Electrochemistry of Metalloporphyrins and Other Hydrophobic Reactants in Thin Layers of Organic Solvents Interposed between Graphite Electrodes and Aqueous Solutions", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "A method is described for the preparation of stable, adherent, thin layers of organic solvents interposed between the surfaces of graphite electrodes and aqueous supporting electrolytes in which they are immersed. The electrochemistry of reactants dissolved in the thin layers is examined and utilized to evaluate surface coverages and formal potentials for molecules, such as cobalt tetraphenylporphyrins, that do not exhibit useful electrochemical responses when adsorbed on graphite. The thin layers of organic solvent can be used to concentrate analytes by extracting them from dilute aqueous solutions to produce enhanced sensitivity in electroanalytical applications. Electron transfer across the liquid/liquid interface created by the presence of the thin layer of immiscible organic solvent is also demonstrated.", "doi": "10.1021/ac980426k", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1998-08-01", "series_number": "15", "volume": "70", "issue": "15", "pages": "3114-3118" }, { "id": "authors:88prs-y2p61", "collection": "authors", "collection_id": "88prs-y2p61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180719-161207344", "type": "article", "title": "Comparison of the Behavior of Several Cobalt Porphyrins as Electrocatalysts for the Reduction of O_2 at Graphite Electrodes", "author": [ { "family_name": "Song", "given_name": "Euihwan", "clpid": "Song-Euihwan" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Four cobalt porphyrins were adsorbed on graphite electrodes and used to catalyze the electroreduction of O_2. The two porphyrins without substituent groups in the meso positions of the porphyrin ring operated at the most positive potentials and catalyzed the reduction of O_2 to both H_2O_2 and H_2O, but the H_2O did not result from significant reduction of H_2O_2. The porphyrins containing meso substituents catalyzed only the reduction of O_2 to H_2O_2. The catalysts that accomplish the four-electron reduction of O_2 are argued to consist of dimeric (or higher oligomeric) forms of the adsorbed porphyrins. The present results and those of two recent related studies indicate that the presence of only hydrogen or small alkyl groups in the meso positions of porphyrin rings facilitates the spontaneous formation of van der Waals dimers with greater catalytic activity for the reduction of O_2 by four electrons. Such cobalt porphyrins were also found to be unusually active catalysts for the electro-oxidation of H_2O_2.", "doi": "10.1021/la980084d", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "1998-07-21", "series_number": "15", "volume": "14", "issue": "15", "pages": "4315-4321" }, { "id": "authors:zdb09-9gw24", "collection": "authors", "collection_id": "zdb09-9gw24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170913-084950345", "type": "article", "title": "Adsorption/Deposition of the Ligands 9,10-Phenanthroline-5,6-dione and 9,10-Phenanthroline-5,6-diol and Their Metal Complexes on Pyrolytic Graphite Electrodes", "author": [ { "family_name": "Shi", "given_name": "Minglian", "clpid": "Shi-Minglian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Metal complexes of the electroactive ligand 9,10-phenanthroline-5,6-dione (pdon) are receiving extensive study because of their demonstrated potential as electrocatalysts for the oxidation of NADH and other substrates. In aqueous media, the reduced ligand, 9,10-phenanthroline-5,6-diol (pdol), and its complexes with transition metals are only slightly soluble and tend to accumulate on the surfaces of electrodes, where they are generated by reduction of pdon. The adsorbed (or precipitated) molecular layers can interfere with the continued electroreduction of the more soluble, oxidized precursors from which they are generated. The use of freshly cleaved basal plane pyrolytic graphite electrodes allowed the surface coordination chemistry and electrochemistry of pdon, pdol, and their complexes to be inspected in more detail than in previous studies. The results revealed several general trends:\u2009 (i) Coordination of pdon to transition metals shifts its reduction potential to more positive values. (ii) The affinity of the dipositive form of transition metal redox couples for pdon is greater than that of the tripositive form by a factor that exceeds the corresponding affinities for 9,10-phenanthroline. (iii) Pdol and its complexes are much less soluble in aqueous media than are pdon and its complexes. (iv) Complexes of pdon are much less strongly adsorbed on graphite than is the free ligand in both its protonated and unprotonated forms.", "doi": "10.1021/ac971234c", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1998-04-15", "series_number": "8", "volume": "70", "issue": "8", "pages": "1489-1495" }, { "id": "authors:e8ytp-qzq08", "collection": "authors", "collection_id": "e8ytp-qzq08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180525-140420261", "type": "article", "title": "(5,10,15,20-Tetramethylporphyrinato)cobalt(II):\u2009 A Remarkably Active Catalyst for the Electroreduction of O_2 to H_2O", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Unlike most simple, monomeric cobalt porphyrins, the cobalt tetramethylporphyrin identified in the title catalyzes the electroreduction of O_2 to H_2O instead of H_2O_2. On graphite electrodes, coatings of the porphyrin prepared by irreversible adsorption from chloroform solutions catalyze the electroreduction of O_2 in aqueous HClO_4 at unusually positive potentials. Both the title porphyrin and the corresponding unsubstituted cobalt porphine are argued to derive their activity as four-electron reduction catalysts from their propensity to form dimers (or higher aggregates) in solution and, presumptively, on the surface of graphite electrodes.", "doi": "10.1021/ic971255p", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1998-03-09", "series_number": "5", "volume": "37", "issue": "5", "pages": "1037-1043" }, { "id": "authors:jhn9q-s4t68", "collection": "authors", "collection_id": "jhn9q-s4t68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171122-083839178", "type": "article", "title": "Novel Multinuclear Catalysts for the Electroreduction of Dioxygen Directly to Water", "author": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" } ], "abstract": "The electroreduction of O_2 to H_2O in aqueous acid at\npotentials close to the thermodynamically permitted value\nremains a daunting challenge for designers of superior fuel\ncells and batteries that utilize dioxygen as the reducible\nreactant. The four-electron reduction of O_2, which involves\nthe rupture of the O-O bond and the formation of four O-H bonds, requires the use of catalysts to obtain useful rates at cathode potentials of interest in practical applications. The standard potential of the O_2/H_2O couple in solutions containing 1 M H^+ and saturated with O_2 at\n1 atm is ca. 1.0 V (vs the saturated calomel electrode, SCE), but the highest cathode potentials achievable with currently available catalysts are closer to 0.55 V. (Molecules, functional groups, or metallic deposits that accelerate the rates of electrode reactions when they are confined to the surfaces of electrodes are often called electrocatalysts, a terminology that will be adopted in this Account.) Finely divided platinum supported on high area carbon is the electrocatalyst employed most frequently to achieve the electroreduction of O_2 to H_2O in presently available fuel cells. However, this type of electrocatalyst suffers from the disadvantages of high cost and gradual loss in catalytic activity as the surface area of the active platinum particles decreases because of sintering, dissolution, physical dislodgment, and/or adsorption of impurities. Searches for superior electrocatalysts for the reduction of O2 have often focused on cobalt porphyrins which are well-known to exhibit electrocatalytic activity toward the reduction of O_2, although H_2O_2 instead of H_2O is the usual product. However, it was discovered in recent years that a variety of molecular catalysts consisting of dimeric cofacial cobalt porphyrins adsorbed on the surface of graphite electrodes are able to catalyze the direct four-electron electroreduction of O_2 without passing through H_2O_2 as an intermediate. Both dimeric and monomeric iridium por phyrins have also been found to accomplish the electroreduction of O_2 to H_2O at unusually positive potentials. The mechanisms through which dimeric electrocatalysts are believed to operate involve the simultaneous interaction of both metal centers with the two\noxygen atoms of the O_2 molecule as the O-O bond is severed. The ideas and strategies that underlay the\ndevelopment of these electrocatalysts have been described.", "doi": "10.1021/ar960264j", "issn": "0001-4842", "publisher": "American Chemical Society", "publication": "Accounts of Chemical Research", "publication_date": "1997-11", "series_number": "11", "volume": "30", "issue": "11", "pages": "437-444" }, { "id": "authors:59mgt-7b067", "collection": "authors", "collection_id": "59mgt-7b067", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180523-110226758", "type": "article", "title": "Electroreduction of O_2 to H_2O at Unusually Positive Potentials Catalyzed by the Simplest of the Cobalt Porphyrins", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Yuasa", "given_name": "Makoto", "clpid": "Yuasa-Makoto" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Simple cobalt porphine, adsorbed on graphite electrodes, catalyzes the direct reduction of O_2 to H_2O, while most other monomeric cobalt porphyrins do not. The surprising behavior of cobalt porphine suggests possible new strategies for the design of electrocatalysts for the reduction of O_2 to H_2O using structurally similar but more oxidation-resistant analogs.", "doi": "10.1021/ic970516s", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1997-09-24", "series_number": "20", "volume": "36", "issue": "20", "pages": "4294-4295" }, { "id": "authors:ez3vv-8ws48", "collection": "authors", "collection_id": "ez3vv-8ws48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-110358826", "type": "article", "title": "[5,10,15,20-Tetrakis(4-((pentaammineruthenio)- cyano)phenyl)porphyrinato]cobalt(II) Immobilized on Graphite Electrodes Catalyzes the Electroreduction of O_2 to H_2O, but the Corresponding 4-Cyano-2,6-dimethylphenyl Derivative Catalyzes the Reduction Only to H_2O_2", "author": [ { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Cobalt porphyrins in which Ru(NH_3)_5^(2+) groups are coordinated to four cyanophenyl ligands pendant to the porphyrin ring act as catalysts for the electroreduction of O_2 when adsorbed on the surface of graphite electrodes. The parent 4-cyanophenyl derivative catalyzes the four-electron reduction of O_2 to H_2O, but the 4-cyano-2,6-dimethylphenyl derivative catalyzes only the two-electron reduction of O_2 to H_2O_2.", "doi": "10.1021/ic970275o", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1997-08-27", "series_number": "18", "volume": "36", "issue": "18", "pages": "4138-4140" }, { "id": "authors:rstze-2js37", "collection": "authors", "collection_id": "rstze-2js37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170905-092129135", "type": "article", "title": "Non-Steady-State Rotating Disk Voltammetry of Redox Couples Incorporated in Perfluorsulfonated Ionomer Coatings on Electrodes", "author": [ { "family_name": "Shi", "given_name": "Minglian", "clpid": "Shi-Minglian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The differences in the affinity of Nafion coatings for Ru(NH_3)_6^(3+/2+) and Os(bpy)_3^(3+/2+) counterions and the difference in the mobilities of the two types of cations within Nafion are used to explain the differences in the voltammetric signatures that they exhibit. A new method is proposed with which to determine whether apparent diffusion coefficients of electroactive counterions in electrode coatings differ when they are evaluated in transient or in steady-state experiments. The utility of non-steady-state cyclic voltammetry with Nafion-coated rotating disk electrodes to separate the contribution to the observed current from dissolved and Nafion-confined reactants is demonstrated.", "doi": "10.1021/ac9701389", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1997-07-15", "series_number": "14", "volume": "69", "issue": "14", "pages": "2661-2668" }, { "id": "authors:mmxrb-s4597", "collection": "authors", "collection_id": "mmxrb-s4597", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171120-141114122", "type": "article", "title": "Some Consequences of the Significantly Different Mobilities of Hydrophilic and Hydrophobic Metal Complexes in Perfluorosulfonated Ionomer Coatings on Electrodes", "author": [ { "family_name": "Shi", "given_name": "Minglian", "clpid": "Shi-Minglian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Thin coatings of Nafion on glassy carbon rotating disk electrodes were saturated with hydrophilic [Ru(NH_3)_6^(3+), Co(NH_3)_6^(3+)] or hydrophobic [Ru(bpy)_3^(2+)] counterions. With both types of counterions, the plateau currents obtained when the electrodes were rotated in solutions of the cations matched the currents obtained with the uncoated electrodes in the same solutions at all accessible rotation rates. The high rates of cross-coating charge propagation demonstrated by these results involved physical diffusion of the hydrophilic complexes and electron hopping between adjacent, immobile pairs of the hydrophobic complexes. The approximate concentration profiles that develop within, and just outside of, Nafion coatings on disk electrodes that are rotated in solutions of electroactive counterions are depicted.", "doi": "10.1021/ac970137g", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1997-07-15", "series_number": "14", "volume": "69", "issue": "14", "pages": "2653-2660" }, { "id": "authors:t7k0y-73h39", "collection": "authors", "collection_id": "t7k0y-73h39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-110854891", "type": "article", "title": "Electrochemical Assessment of the Stability of [Os(NH_3)_5(OH_2)]^(2+) in Aqueous Solutions", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The [Os(NH_3)_5(OH_2)]^(2+) complex in aqueous acid has been widely regarded as short-lived on the basis of results reported in an early pioneering electrochemical study.1 More recently, a much longer-lived Os(II) species generated by reduction of [Os(NH)3))5(OH)2)]^(3+) but of uncertain composition has been reported. In the present study the lifetime of [Os(NH_3)_5(OH_2)]^(2+) in aqueous acid was determined by steady-state voltammetry at a carbon microelectrode and by comparing experimental with simulated cyclic voltammograms obtained for solutions of [Os(NH_3)_5(OH_2)]^(3+). Rate constants for the oxidation of [Os(NH_3)_5(OH_2)]^(2+) by H^+, CH_3COOH (HA), and H_2O were evaluated as k_H = 17 M^(-1) s^(-1), k_(HA) = 1.2 M^(-1) s^(-1), and k_(H_2O) = 4.1 \u00d7 10^(-4) s^(-1). These values are shown to be compatible with the data in ref 1 and come close to accounting for the long-lived species described in ref 6 which may be [Os(NH_3)_5(OH_2)]^(2+) itself. A revised value of 4.85 was measured for the pKA of [Os(NH_3)_5(OH_2)]^(3+). Adsorption of an Os complex on the surface of mercury, but not glassy carbon, electrodes is shown to enhance greatly the rate with which protons undergo direct electroreduction.", "doi": "10.1021/ic961522b", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1997-06-04", "series_number": "12", "volume": "36", "issue": "12", "pages": "2682-2687" }, { "id": "authors:q622r-6pz07", "collection": "authors", "collection_id": "q622r-6pz07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180525-133925688", "type": "article", "title": "Cobalt meso-Tetrakis(N-methyl-4-pyridiniumyl)porphyrin Becomes a Catalyst for the Electroreduction of O_2 by Four Electrons When [(NH_3)_5Os]^(n+) (n = 2, 3) Groups Are Coordinated to the Porphyrin Ring", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "In a series of recent reports evidence has been offered to support the proposal that coordination of (NH_3)_5Ru^(2+) groups to ligand sites introduced on the meso positions of certain cobalt porphyrins enhances their abilities to act as electrocatalysts for the reduction of O_2 to H_2O. The enhancement is believed to be the result of back-bonding by the Ru(II) centers into the pendant ligands and the cobalt porphyrin to which they are linked. The catalytic mechanism that has been proposed leaves the coordinated Ru centers in their +2 oxidation state as the O_2 molecule coordinated to the Co(II) center of the porphyrin in the activated complex is reduced via electron-transfer from the electrode surface. Intramolecular electron-transfer from the Ru(II) centers to the coordinated O_2 is not consistent with the experimental data. To obtain additional information about the importance of back-bonding in enhancing the catalytic activity of these cobalt porphyrins, we sought to use Os(III) in place of Ru(II) as the source of the back-donation. Os(III), unlike Ru(III), exhibits substantial back-bonding capabilities, but Os(III) is a much weaker thermodynamic reductant than Ru(II). Thus, we reasoned that any increase in the catalytic activity of cobalt porphyrins that might result from the attachment of Os(III) centers to the porphyrin ring could be confidently attributed to back-bonding effects free of any contributions from intramolecular electron-transfer. The results of experiments designed to test this speculation are described in this report.", "doi": "10.1021/ic9607189", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1996-12-18", "series_number": "26", "volume": "35", "issue": "26", "pages": "7928-7931" }, { "id": "authors:r4nnn-79s79", "collection": "authors", "collection_id": "r4nnn-79s79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180514-153140758", "type": "article", "title": "Enhancement of the Catalytic Activity of a Macrocyclic Cobalt(II) Complex for the Electroreduction of O_2 by Adsorption on Graphite", "author": [ { "family_name": "Bhugun", "given_name": "Iqbal", "clpid": "Bhugun-I" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "In solution, the [(tim)Co]^(2+) complex (tim = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) reacts only slowly with O_2, but upon adsorption on graphite electrodes it becomes an active catalyst for the reduction of O_2 to H_2O_2. The remarkable enhancement in catalytic activity is attributed to a higher affinity for O_2 of the adsorbed complex as a result of its interaction with functional groups on the surface of roughened or oxidized graphite. A possible catalytic mechanism is proposed.", "doi": "10.1021/ic9608399", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1996-12-04", "series_number": "25", "volume": "35", "issue": "25", "pages": "7253-7259" }, { "id": "authors:5780t-p8n22", "collection": "authors", "collection_id": "5780t-p8n22", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170808-160245451", "type": "article", "title": "Adsorption of Monolayers of P_2Mo_(18)O_(62)^(6-) and Deposition of Multiple Layers of Os(bpy)_3^(2+)\u2212P_2Mo_(18)O_(62)^(6-) on Electrode Surfaces", "author": [ { "family_name": "Kuhn", "given_name": "Alexander", "clpid": "Kuhn-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The unusually strong, irreversible adsorption of monolayer quantities of the P_2Mo_(18)O_(62)^(6-) anion on glassy carbon, highly ordered pyrolytic graphite, indium tin oxide, and gold-coated quartz electrodes was examined by electrochemical, spectroelectrochemical, and quartz crystal microgravimetric techniques. A very simple method was developed to deposit multiple layers of composites consisting of alternating layers of the P_2Mo_(18)O_(62)^(6-) anion and large, multiply-charged cations such as Os(bpy)_3^(2+). The resulting deposit is stable and exhibits electroactivity from both of the components that reflects the structure and ionic conductivity of the solid multilayer.", "doi": "10.1021/la960461r", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "1996-10-30", "series_number": "22", "volume": "12", "issue": "22", "pages": "5481-5488" }, { "id": "authors:k5snm-9xp72", "collection": "authors", "collection_id": "k5snm-9xp72", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120209-110217213", "type": "article", "title": "Calculation of cyclic voltammetric responses for the reductive\n formation of catalyst-substrate adducts on electrode surfaces", "author": [ { "family_name": "Xie", "given_name": "Yuanwu", "clpid": "Xie-Y" }, { "family_name": "Kang", "given_name": "Chang", "clpid": "Kang-C" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Electrocatalysts based on monolayers of transition-metal complexes attached to electrode surfaces frequently follow mechanisms in which a chemical step is interposed between the first and subsequent electron-transfer steps. The cyclic voltammetric responses to be anticipated for such systems were calculated using finite difference procedures to solve the relevant differential equation. The calculated variation of the peak currents and peak potentials with the kinetic parameters governing the three steps in the mechanistic scheme are presented in graphical form. Application of the results to a specific experimental system, the catalysis of the electroreduction of O_2 by a macrocyclic complex of Co^(III) adsorbed on graphite electrodes, produced reasonable agreement between calculated and observed cyclic voltammograms.", "doi": "10.1039/ft9969203917", "issn": "0956-5000", "publisher": "Royal Society of Chemistry", "publication": "Journal of the Chemical Society. Faraday Transactions", "publication_date": "1996-10-21", "series_number": "20", "volume": "92", "issue": "20", "pages": "3917-3923" }, { "id": "authors:prw36-0nz75", "collection": "authors", "collection_id": "prw36-0nz75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180719-162726781", "type": "article", "title": "Factors Responsible for the Unusually Strong Adsorption of [Os(bpy)_2(Cl)L_1]^+ (L_1 = 1,2-bis(4-pyridyl)ethane) and Related Complexes on Metal and Graphite Electrode Surfaces", "author": [ { "family_name": "Campbell", "given_name": "John L. E.", "clpid": "Campbell-J-L-E" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The extent and dynamics of the adsorption on gold and pyrolytic graphite electrodes of four complexes of Os(II) were compared with the previously reported adsorption of similar complexes on Pt (Acevedo, D.; Abru\u00f1a, H. D. J. Phys. Chem. 1991, 95, 9590). The complexes investigated were [Os(bpy)_2(Cl)L]^+ with bpy = 2,2'-bipyridine and L = 1,2-bis(4-pyridyl)ethane, 4-phenylpyridine, 4-(1-n-butylpentyl)pyridine, and pyridine. Spontaneous, strong adsorption of all four complexes occurred on graphite electrodes and, except for the complex with L = pyridine, on gold electrodes. The presence of a pendant pyridine site on ligand L is not required for strong adsorption to occur. Replacement of the [Os(bpy)_2(Cl)]^+ center by Ru(NH_3)_5^(2+) also led to a strongly adsorbing complex. The adsorption appears to be driven by hydrophobic interactions of the organic ligands with the electrode surface and with each other as well as specific surface\u2212ligand bond formation when a pendant pyridine group is present. Although the concentration dependence of the quantities of the complexes adsorbed could be fit to a Langmuir isotherm, the dynamics of the adsorption and desorption reactions were not consistent with Langmuirian adsorption. Stabilizing intermolecular electronic interactions among the adsorbed molecules are suggested as a possible explanation for the observed behavior.", "doi": "10.1021/la960278y", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "1996-08-07", "series_number": "16", "volume": "12", "issue": "16", "pages": "4008-4014" }, { "id": "authors:jvxbw-50w68", "collection": "authors", "collection_id": "jvxbw-50w68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180720-144653154", "type": "article", "title": "Diffusion Coefficients of Intrinsically Electroactive Polyelectrolytes and of Counterions Bound to Them", "author": [ { "family_name": "Hatozaki", "given_name": "Osamu", "clpid": "Hatozaki-Osamu" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "An electroactive label was attached to poly(acrylic acid) (molecular weight = 5000) by reaction with ferrocenylethanol. The resulting ferrocene label was stable when the polymer was dissolved in aqueous solutions, and the diffusion coefficient of the labeled polymer was estimated from the currents obtained as the ferrocene was oxidized at a rotating disk electrode. Although strong adsorption of the polymer on the electrode surfaces depressed the oxidation currents below the convection\u2212diffusion controlled values at rotating disk electrodes, it was still possible to estimate diffusion coefficients by appropriate analysis of the rotation rate dependences of the measured currents. At pH values where the labeled polymer became a polyanion, its diffusion coefficient was also estimated from the reduction currents for Ru(NH_3)_6^(3+) or Co(NH_3)_6^(3+) counterions bound electrostatically to the polyelectrolyte. Good agreement was obtained between the diffusion coefficients estimated by the two independent routes.", "doi": "10.1021/jp953740g", "issn": "0022-3654", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry", "publication_date": "1996-05-16", "series_number": "20", "volume": "100", "issue": "20", "pages": "8448-8453" }, { "id": "authors:5k6v0-05w84", "collection": "authors", "collection_id": "5k6v0-05w84", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-115958777", "type": "article", "title": "Effects of Coordination to Transition Metals on the Hydration and Electroactivity of the Chelating Ligand 1,10-Phenanthroline-5,6-dione", "author": [ { "family_name": "Lei", "given_name": "Yanbin", "clpid": "Lei-Yanbin" }, { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The intrinsically electroactive ligand in the title was coordinated to Co^(2+), Fe^(2+), Ni^(2+), Zn^(2+), and Cu^+, and the resulting hydration of the carbonyl groups of a portion of the coordinated ligand eliminated its electroactivity. The extent of hydration of the coordinated ligand was evaluated by means of rotating disk voltammetry. Estimates were obtained for the equilibrium constants governing the hydration reaction. The hydration induced by coordination of the ligand to the metal cations varied in parallel with the magnitude of the first association constant for the metal\u2212ligand coordination.", "doi": "10.1021/ic951569h", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1996-05-08", "series_number": "10", "volume": "35", "issue": "10", "pages": "3044-3049" }, { "id": "authors:4smbf-j6d97", "collection": "authors", "collection_id": "4smbf-j6d97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180719-163135834", "type": "article", "title": "Rapid Oxidation of Ru(NH_3)_6^(3+) by Os(bpy)_3^(3+) within Nafion Coatings on Electrodes", "author": [ { "family_name": "Shi", "given_name": "Minglian", "clpid": "Shi-Minglian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The oxidation of Ru(NH_3)_6^(3+) by Os(bpy)_3^(3+) is a very slow process in aqueous acid. The rate increases with pH but the reaction remains slow at pH 7. However, when the two reactants are incorporated in Nafion coatings on electrodes the oxidation can proceed much more rapidly, especially with Nafion coatings that are not fully hydrated. Rotating disk and cyclic voltammetry were employed to determine the stoichiometry of the reaction and to measure its kinetics both in solution and in Nafion coatings. The Ru(NH_3)_6^(3+) is oxidized to Ru(VII) at a rate that is first order in Ru(NH_3)_6^(3+) and Os(bpy)_3^(3+) and inverse first order in H^+. The reaction rate constant evaluated in solution was similar to that evaluated in Nafion. The higher reaction rate obtained when the reactants are incorporated in Nafion results from their higher concentrations, not from significant enhancement of their reactivities. The higher reaction rate obtained from partially dehydrated Nafion coatings is believed to result from a breakdown in cation permselectivity that permits the ionic current inside the coating during anodic current flow to be carried by anions instead of by the ejection of Ru(NH_3)_6^(3+) cations from the Nafion.", "doi": "10.1021/la950863j", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "1996-04-17", "series_number": "8", "volume": "12", "issue": "8", "pages": "2068-2075" }, { "id": "authors:mfdmq-zx575", "collection": "authors", "collection_id": "mfdmq-zx575", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180720-151111313", "type": "article", "title": "Association of Electroactive Counterions with Polyelectrolytes. 6. Electrostatic and Coordinative Binding of Ru^(3+/2+) Centers to a Copolymer of Acrylic Acid and Acrylonitrile", "author": [ { "family_name": "Yoshikawa", "given_name": "Masaki", "clpid": "Yoshikawa-Masaki" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "A random copolymer of acrylic acid and acrylonitrile was prepared in which the functionality on the polymer chain consisted of 93% carboxylic acid groups, 4.1% nitrile groups, and 2.9% acid anhydride groups. The nitrile groups were used to coordinate Ru(NH_3)_5^(2+) centers to the copolymer. The anionic carboxylate groups produced at pH values above \u223c3.5 were used to bind Ru(NH_3)_6^(3+) counterions to the resulting polyanionic copolymer. The electrochemical oxidation or reduction of the two redox centers bound to the copolymer were used to estimate diffusion coefficients for the copolymer. Reasonable agreement was obtained between the values obtained from both electroactive redox groups. The diffusion coefficient exhibited a strong dependence on pH that reflected changes in the structure of the copolymer as it was converted from its neutral to its polyanionic form. The rate of the reaction between the Ru(NH_3)_5OH_2^(2+) complex and the nitrile groups of the copolymer increased significantly with pH because electrostatic binding of the cation to the polyanionic copolymer increased the concentration of the complex in the vicinity of the nitrile groups. Adsorption of the copolymer on the surface of the electrodes interfered with the oxidation of Ru(NH_3)_5^(2+) groups coordinated to the dissolved copolymer but not with Ru(NH_3)_6^(3+) counterions electrostatically bound to the polyanion. A possible explanation for the contrasting behavior is suggested.", "doi": "10.1021/jp952831a", "issn": "0022-3654", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry", "publication_date": "1996-03-07", "series_number": "10", "volume": "100", "issue": "10", "pages": "4199-4204" }, { "id": "authors:nbrw4-hdh64", "collection": "authors", "collection_id": "nbrw4-hdh64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120702-110414259", "type": "article", "title": "High Sensitivity of Electron Transfer Rates within Nafion\n Coatings Saturated with Os(bpy)^(2+)_3 to the Extent of\n Hydration of the Coating", "author": [ { "family_name": "Shi", "given_name": "Minglian", "clpid": "Shi-M" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The sensitivity of the electrochemical responses obtained from electroactive counterions incorporated in Nafion coatings to the extent of hydration of the coatings^(27-38) is shown to be enhanced significantly when the electroactive ion is the only counterion present in the coating. Nafion coatings fully saturated with Os(bpy)^(2+)_3 exhibit unusually narrow and sharply peaked anodic currents in first-scan oxidative voltammograms. This voltammetric feature is accompanied by the\nexpulsion of one-third of the Os complex from the coating. The counterion actually ejected is primarily Os(bpy)^(3+)_3. As the Os(bpy)^(3+)_3 counterions are ejected, H_2O molecules enter the coatings. The quantity of H_2O molecules incorporated is so large that the mass of the coating (monitored with a quartz crystal microbalance) increases despite the ejection of the heavy Os(bpy)^(3+)_3 cations. After several voltammetric cycles, normally shaped voltammograms are obtained that are relatively\ninsensitive to the initial state of hydration of the coatings. The contrasting behaviors of hydrated and unhydrated coatings are compared, and possible explanations are offered for the differences observed.", "doi": "10.1149/1.2048485", "issn": "0013-4651", "publisher": "The Electrochemical Society, Inc.", "publication": "Journal of the Electrochemical Society", "publication_date": "1995-12", "series_number": "12", "volume": "142", "issue": "12", "pages": "4205-4214" }, { "id": "authors:kq2cw-7fp26", "collection": "authors", "collection_id": "kq2cw-7fp26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180801-112457194", "type": "article", "title": "Comparison of the catalytic reduction of oxygen by [5,10,15,20-tetrakis((pentaammineruthenio(II)-4-pyridyl)porphyrinato]cobalt(II) in solution and on graphite electrode surfaces", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The [5, 10, 15,20-tetrakis((pentaammineruthenio(II))-4-pyridylporphinato ]cobalt(II) complex that catalyzes the fourelectron reduction of O_2 at graphite electrode surfaces on which it has been assembled has now been prepared in homogeneous solution. The preparative procedure for the catalyst is described, and the kinetics of its catalysis of the reduction of O_2 by chemical reductants in homogeneous solution are reported. In solution, only twoelectron reductions of O_2 are obtained and the rate of intramolecular electron-transfer from the four Ru(NH_3)_(5-)py^(2+) centers on the periphery of the catalyst molecule to an O_2 molecule coordinated to the Co(II) center in the porphyrin ring is shown to be quite slow. Possible reasons for the contrasting mechanistic behavior of the catalyst in solution and on graphite electrodes are suggested.", "doi": "10.1021/ic00122a010", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1995-08-30", "series_number": "18", "volume": "34", "issue": "18", "pages": "4554-4561" }, { "id": "authors:z47z1-bht69", "collection": "authors", "collection_id": "z47z1-bht69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140129-132432696", "type": "article", "title": "Linus Pauling Teaching at Caltech", "author": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Throughout several decades Linus Pauling gave two lectures per week in the Chemistry Course\nrequired of all Caltech freshman. His style was unique and contrasted with that employed by the\nlecturers in the simultaneously required courses in Physics and Mathematics. A typical lecture by\nPauling was stimulating and entertaining and often seemed to be impromptu. The reactions of the\nfreshmen to the Pauling style were overwhelmingly positive and lasting. Some recollections by a former\nfreshman student, professorial colleague and personal friend of Linus Pauling will be offered.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "1995-04-02", "volume": "209", "pages": "477-CHED" }, { "id": "authors:862zz-7rd38", "collection": "authors", "collection_id": "862zz-7rd38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180809-152106160", "type": "article", "title": "Coordination chemistry in electrocatalysis", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Steiger", "given_name": "Beat", "clpid": "Steiger-B" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Superior electrocatalysts for the reduction of O_2 by four-electrons in one step have been prepared by coordinating ammine complexes of Ru(II) to the pyridine ligand sites in cobalt tetrakis(4-pyridyl) porphyrin. At least three coordinated Ru(II) centers appear to be required to obtain the four-electron reduction. When fac-Ru(NH_3)_3(OH_2)_3^(2+) was used to ruthenate the porphyrin, a network structure was obtained in which both terminal and bridging ruthenium centers were present.", "doi": "10.1351/pac199567020319", "issn": "0033-4545", "publisher": "International Union of Pure and Applied Chemistry", "publication": "Pure and Applied Chemistry", "publication_date": "1995-02", "series_number": "2", "volume": "67", "issue": "2", "pages": "319-322" }, { "id": "authors:9e6nc-0ap35", "collection": "authors", "collection_id": "9e6nc-0ap35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-153402798", "type": "article", "title": "Simplified Preparations and Electrochemical Behavior of Two Chromium-Substituted Heteropolytungstate Anions", "author": [ { "family_name": "Rong", "given_name": "Chaoying", "clpid": "Rong-Chaoying" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Simplified preparative procedures are described for the generation of \u03b1-[PW_(11)O_(39)Cr^(III)(OH_2)]^(4-) and \u03b12-[P_2W_(11)O_(61)Cr^(III)(OH_2)]^(7-) anions which can be readily oxidized, chemically or electrochemically, to \u03b1-[PW_(11)O_(39)Cr^(V)O]^(4-) and \u03b12-[P_2W_(17)O_(61)Cr^(V)O]^(7-). The oxidized complexes are stable in aqueous solutions. They react with benzyl or ethyl\nalcohol, but the rates of the oxidations are too slow to make the Cr(V) derivatives attractive as electrocatalysts. The voltammetry of the Cr^(V)/Cr^(III) couples is only quasi-reversible, but approximate formal potentials with their pH\ndependencies are reported. Diffusion coefficients evaluated for the polyanions show the larger anion to diffuse more\nslowly and neither anion to be highly hydrated.", "doi": "10.1021/ic00084a016", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1994-03-16", "series_number": "6", "volume": "33", "issue": "6", "pages": "1064-1070" }, { "id": "authors:agr5s-3xv98", "collection": "authors", "collection_id": "agr5s-3xv98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180319-154249507", "type": "article", "title": "Electrocatalysis of the reduction of O_2 to H_2O by tetraruthenated cobalt meso-tetrakis(4-pyridyl)porphyrin adsorbed on graphite electrodes", "author": [ { "family_name": "Shi", "given_name": "Chunnian", "clpid": "Shi-Chunnian" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Coordination of Ru(NH_3)_5 groups to the four pyridine sites in cobalt meso-tetrakis(4-pyridyl)porphyrin adsorbed\non pyrolytic graphite electrodes produces the tetraruthenated complex which acts as a catalyst for the four-electron reduction of O_2 to H_2O. The adsorbed catalyst, prepared by this heterogeneous coordination reaction, yields higher catalytic reduction rates than those obtained previously when the same catalyst was prepared within Nafion coatings on electrodes. The coordination chemistry used in the preparation of the adsorbed catalyst and its behavior as an electrocatalyst are described.", "doi": "10.1021/ic00050a029", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "1992-11-01", "series_number": "24", "volume": "31", "issue": "24", "pages": "5078-5083" }, { "id": "authors:w1sb7-d3v39", "collection": "authors", "collection_id": "w1sb7-d3v39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170915-084856218", "type": "article", "title": "Application of scanning electrochemical microscopy to studies of charge propagation within polyelectrolyte coatings on electrodes", "author": [ { "family_name": "Jeon", "given_name": "Il Cheol", "clpid": "Jeon-Il-Cheol" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The technique of scanning electrochemical microscopy is used\nto examine the properties of polyelectrolyte coatings on\nelectrodes. Coatings of protonated poly(4-vinytpyridine)\nexhibit time dependences of their redox conductivities with\nFe(CN)_6^(3-) or IrCl_6^(2-) as counterions incorporated in the coatings. By contrast, responses obtained from coatings of Nafion show no comparable time dependence. A possible reason for the difference is suggested. Images of the two types of coatings obtained with the scanning electrochemical microscope include apparent topological features in the poly(4-vinytpyridine) coatings which are shown to arise from significant variations in redox conductivity across the surface of aged coatings\nrather than from true changes in the coating's dimension. In\nthe case of Nafion coatings, only smooth surfaces are observed in scanning electrochemical microscope images whether they are recorded under conditions of positive or negative feedback. The absence of significant spatial variations in redox conductivity is believed to be responsible for the featureless images obtained with Nafion coatings.", "doi": "10.1021/ac00042a003", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1992-09-15", "series_number": "18", "volume": "64", "issue": "18", "pages": "2021-2028" }, { "id": "authors:kah5a-sn720", "collection": "authors", "collection_id": "kah5a-sn720", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180130-090151012", "type": "article", "title": "Use of Electrochemical Microscopy to Examine Counterion Ejection from Nafion Coatings on Electrodes", "author": [ { "family_name": "Lee", "given_name": "Chongmok", "clpid": "Lee-Chongmok" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The ideal cation permselectivity exhibited by electrode\ncoatings prepared from the polyelectrolyte Nafion leads to\nejection of countercatlons from the coatings during electrochemical oxidation of Os(bpy)_3^(2+) counterions incorporated in the coatings. If the coatings are saturated with Os(bpy)_3^(2+) so that these are the only counterions present, one-third of the incorporated cations are ejected during the oxidation of Os(bpy)_3^(2+) to Os(bpy)_3^(3+). The cyclic voltammetry of the incorporated Os(bpy)_3^(3+/2+) couple is altered substantially in the absence of additional counterions. The changes are attributed to contributions to the voltammetric potentials from the free energy of transfer of these strongly bound counterions. Microtip electrodes positioned just above Nafion-coated electrodes were used to monitor the ejection of both Os(bpy)_3^(3+) and Os(bpy)_3^(2+) from Nafion coatings. Much more of the former complex lo ejected from saturated coatings which is believed to be the result of electric field-assisted ejection.", "doi": "10.1021/ac00029a015", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1992-03-01", "series_number": "5", "volume": "64", "issue": "5", "pages": "528-533" }, { "id": "authors:r3d0x-wjb14", "collection": "authors", "collection_id": "r3d0x-wjb14", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180130-083252099", "type": "article", "title": "Monitoring the Ejection and Incorporation of Ferricyanide Fe(CN)_6^(3-) and Ferrocyanide Fe(CN)_6^(4-) Counterions at Protonated Poly(4-vinylpyridine) Coatings on Electrodes with the Scanning Electrochemical Microscope", "author": [ { "family_name": "Kwak", "given_name": "Juhyoun", "clpid": "Kwak-Juhyoun" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The precise positioning of microtlp electrodes close to the\nsurface of substrate electrodes, as practiced in scanning\nelectrochemlcal microscopy, was exploited to monitor the\nconcentrations of Fe(CN)_6^(-3) and Fe(CN)_6^(-4) anions at the surfaces of protonated poly(4-vinylpyridine) coatings on glassy-carbon electrodes. Positive feedback, which enhanced the magnitude of currents at the monitoring tip electrode, gave way to negative feedback when reactant concentrations were increased to the point that electron propagation through the polyectrolyte coatings became the curent-limiting step. The election of counterions when cathodic currents were passed through coatings which were saturated with Fe(CN)_6^(3-) was readily detected, especially when current steps were applied to the coated substrate electrode. Delayed arrival of counterions at the monitoring tip could be associated with the time required for the ions to traverse the coatings before they were ejected. Reincorporation of multiply-charged counterions inmediately following their ejection appeared to be favored over the incorporation of singly charged anions present at much higher concentrations.", "doi": "10.1021/ac00027a003", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1992-02-02", "series_number": "3", "volume": "64", "issue": "3", "pages": "250-256" }, { "id": "authors:6prqf-sa826", "collection": "authors", "collection_id": "6prqf-sa826", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170830-144806113", "type": "article", "title": "Application of scanning electrochemical microscopy to generation/collection experiments with high collection efficiency", "author": [ { "family_name": "Lee", "given_name": "Chongmok", "clpid": "Lee-Chongmok" }, { "family_name": "Kwak", "given_name": "Juhyoun", "clpid": "Kwak-Juhyoun" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The technique of scanning electrochemical microscopy (SECM) was introduced by Bard and co-workers (1) who have utilized it in a variety of experiments (2). The use of a microelectrode placed close to a substrate electrode to detect electroactive products generated at the latter, as described by Engstrom and co-workers (3,4),is one attractive application of the SECM technique (1). In previous studies, this type of generation/detection experiment has usually been carried out with the microelectrode used as the detector electrode (1-5).\nIn the present study, a larger (100 \u00b5m diameter) substrate electrode is used to detect and collect electrode reaction\nproducts generated at a microtip electrode positioned at\nvarious distances above the substrate electrode. The collection efficiency (in the sense employed for rotating ring-disk electrodes (6)) of such an arrangement is virtually 100% at easily achievable separation distances. The advantages of carrying out generation/collection experiments with the present apparatus are exemplified with some simple experimental systems. Comparisons with similar recent experiments in which arrays of microband electrodes are utilized (7,8) are also provided.", "doi": "10.1021/ac00014a030", "issn": "0003-2700", "publisher": "American Chemical Society", "publication": "Analytical Chemistry", "publication_date": "1991-07", "series_number": "14", "volume": "63", "issue": "14", "pages": "1501-1504" }, { "id": "authors:1py12-j4p95", "collection": "authors", "collection_id": "1py12-j4p95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180720-112442312", "type": "article", "title": "Time-resolved measurement of equilibrium surface tensions at the electrified mercury-aqueous sodium fluoride interphase by the method of Wilhelmy", "author": [ { "family_name": "Montgomery", "given_name": "Donald D.", "clpid": "Montgomery-D-D" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The Wilhelmy plate technique for measuring static and dynamic surface tensions was extended to the electrified mercury-aqueous electrolyte interphase. Several modifications to a conventional Wilhelmy plate are described, which were necessary to implement the technique within an electrochemical environment. Proper isolation of the Wilhelmy plate and associated instrument from vibration allowed sensitivities to be reached that were about 5 times greater than those attainable with maximum bubble pressure measurements. The surface tensions at the electrified mercury-aqueous NaF interphase measured with the modified Wilhelmy plate instrument agreed well with literature values. The capability of the instrument described for making rapid measurements of surface tensions was exploited to observe intrinsic fluctuations in the equilibrium surface tensions. The importance of intrinsic fluctuations and time-averaging for precise evaluation of the equilibrium surface tension are discussed.", "doi": "10.1021/la00053a031", "issn": "0743-7463", "publisher": "American Chemical Society", "publication": "Langmuir", "publication_date": "1991-05", "series_number": "5", "volume": "7", "issue": "5", "pages": "1000-1004" }, { "id": "authors:hbw2w-ant22", "collection": "authors", "collection_id": "hbw2w-ant22", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180316-141224548", "type": "article", "title": "Association of electroactive counterions with polyelectrolytes. 2. Comparison of electrostatic and coordinative bonding to a mixed polycation-polypyridine", "author": [ { "family_name": "Kobayashi", "given_name": "Junya", "clpid": "Kobayashi-Junya" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "A soluble polysiloxane containing 4,4'-bipyridine as a singly quaternized pendant group was synthesized and allowed to interact with Fe(CN)_6^(4-), Fe(CN)_5(OH_2)^(3-), and Ru(edta)OH_2^- as counterions. The electrochemical responses (formal potentials and mass-transfer-limited oxidation or reduction currents) of the electroactive counterions were utilized to evaluate diffusion coefficients and equilibrium binding constants. The latter were also measured by equilibrium dialysis. The moderate agreement between the equilibrium constants obtained by the two independent methods lent support to the general procedures employed in analyzing the electrochemical data, although some of the assumptions required for the data analysis may not be fully\njustified. The results obtained indicate that the polyelectrolyte-counterion binding equilibrium is static rather than dynamic on the electrochemical time scale of a few hundred milliseconds.", "doi": "10.1021/j100159a089", "issn": "0022-3654", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry", "publication_date": "1991-03-01", "series_number": "6", "volume": "95", "issue": "6", "pages": "2595-2601" }, { "id": "authors:rmfze-1fk61", "collection": "authors", "collection_id": "rmfze-1fk61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:TSOjes84", "type": "article", "title": "Shifts in Redox Formal Potentials Accompanying the Incorporation of Cationic Complexes in Perfluoro Polycarboxylate and Polysulfonate Coatings on Graphite Electrodes", "author": [ { "family_name": "Tsou", "given_name": "Yu-Min", "clpid": "Tsou-Y-M" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The formal potentials of several redox couples incorporated in coatings of a perfluoropolycarboxylate on graphite electrodes were measured and compared with the formal potentials of the same couples in homogeneous solution. The differences observed agreed with those calculated from the Nernst equation with the independently measured incorporationcoefficients for both halves of the redox couples. The dependences of the shifts in formal potentials on the nature of theincorporating complex ion, the ionic strength, and the temperature were determined and indicated that the incorporationequilibrium is governed by electrostatic and hydrophobic interactions that act in opposite directions. The incorporation ofmost cations examined was driven by large increases in entropy which overcame the usually unfavorable enthalpy changes.", "doi": "10.1149/1.2115632", "issn": "0013-4651", "publisher": "Journal of the Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1984-03-01", "series_number": "3", "volume": "131", "issue": "3", "pages": "595-601" }, { "id": "authors:rqfv1-rsg83", "collection": "authors", "collection_id": "rqfv1-rsg83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160921-131026889", "type": "article", "title": "Laser Spectroelectrochemistry of a Ruthenium(II) Tris(bipyridyl) Derivative Adsorbed on Graphite Electrodes", "author": [ { "family_name": "Perry", "given_name": "Joseph W.", "clpid": "Perry-J-W" }, { "family_name": "McQuillan", "given_name": "A. James", "clpid": "McQuillan-A-J" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Zewail", "given_name": "Ahmed H.", "clpid": "Zewail-A-H" } ], "abstract": "The luminescence spectra of laser-excited films of [Ru(bpy)_2pbpy]Cl_2 (bpy = 2,2'-bipyridine; pbpy = 4 4'bis(2-(diphenylamino)ethyl)-2,2'-bipyridine) adsorbed on pyrolytic graphite electrode surfaces are reported. The graphite electrode surface is shown to be effective in quenching the excited state and the resulting decay of the luminescence ls analyzed. The intensity of the luminescence from the molecules in the film can be modulated by controlling the potential of the underlying electrode. It is shown that the emitting molecules are in electronic contact with the electrode.", "doi": "10.1021/j100232a005", "issn": "0022-3654", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry", "publication_date": "1983-04-28", "series_number": "9", "volume": "87", "issue": "9", "pages": "1480-1483" }, { "id": "authors:7c0gs-5zm43", "collection": "authors", "collection_id": "7c0gs-5zm43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:TANpnas82.968", "type": "article", "title": "Temperature dependence of the reduction potential of blue copper in fungal laccase", "author": [ { "family_name": "Taniguchi", "given_name": "Vernon T.", "clpid": "Taniguchi-Vernon-T" }, { "family_name": "Malmstr\u00f6m", "given_name": "Bo G.", "clpid": "Malmstr\u00f6m-B-G" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "abstract": "Thin-layer spectroelectrochemical methods have\nbeen employed to measure the reduction potentials of the blue copper in Polypors veruicolor laccase (EC 1.10.3.2) between 7\u00b0C and 41\u00b0C (0.2 M sodium phosphate, pH 5.4). Thermodynamic parameters are: \u0394S\u00b0 = -13.9 \u00b1 2 cal/mol-K; \u0394H\u00b0 = -22.1 \u00b1 0.5 kcal/mol; E\u00b0 (25\u00b0C) = 780 \u00b1 3 mV vs. the normal hydrogen electrode. Comparison of the \u0394S\u00b0 and \u0394H\u00b0 values with those for single-site proteins suggests that the high potential of the blue copper in fungal laccase is attributable mainly to stabilization of the copper (I) center by enhanced ligand binding interactions and that protein solvation effects play a lesser role.", "pmcid": "PMC346421", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "1982-05-15", "series_number": "10", "volume": "79", "issue": "10", "pages": "3387-3389" }, { "id": "authors:pkqxp-j2g83", "collection": "authors", "collection_id": "pkqxp-j2g83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120717-132826689", "type": "article", "title": "Electrochemistry and Adsorption of Bis 2,2\u2032\u2010Bipyridinecobalt(I) and Bis 6,6\u2032\u2010Dimethyl\u20102,2\u2032\u2010Bipyridinecobalt(I) in Acetonitrile", "author": [ { "family_name": "Willett", "given_name": "Brian C.", "clpid": "Willett-B-C" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Cyclic voltammetry, coulometry, and chronocoulometry were used to examine the reduction of \nbis\u20102,2\u2032\u2010bipyridinecobalt(II), Co(bipy)^(2+)_2 , and \nbis\u20106,6\u2032\u2010dimethyl\u20102,2\u2032\u2010bipyridinecobalt(II), Co(dmbp)^(2+)_2 in acetonitrile solution. Both of the cobalt(I) reduction products, Co(bipy)^(+)_2 and Co(dmbp)^(+)_2 , adsorb on mercury but not on graphite or platinum electrodes. Formula decomposes at a modest rate while Formula is much more stable. Neither reduced complex proved effective as a catalyst for the electroreduction of nitrous oxide or alkyl halides.", "doi": "10.1149/1.2124098", "issn": "0013-4651", "publisher": "The Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1982", "series_number": "6", "volume": "129", "issue": "6", "pages": "1260-1266" }, { "id": "authors:vgez6-2vk65", "collection": "authors", "collection_id": "vgez6-2vk65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ANSjes80", "type": "article", "title": "Roger Parsons\u2014Olin Palladium Award Medalist", "author": [ { "family_name": "Anson", "given_name": "F. C.", "clpid": "Anson-F-C" } ], "abstract": "The Olin Palladium Medal of this Society has such a distinguished set of former awardees that I suspect the person who has been asked to introduce each of the medal winners has probably felt as superfluous as I do today. \n\nRoger Parsons has played so prominent a role in the development of fundamental electrochemistry in the last thirty years that his name and his ideas constantly pop up in discussions among electrochemists in Moscow and Buenos Aires, Delhi and Paris, College Station and Pasadena.", "doi": "10.1149/1.2129754", "issn": "0013-4651", "publisher": "Journal of the Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1980-04-01", "series_number": "5", "volume": "127", "issue": "5", "pages": "175C" }, { "id": "authors:9mbrn-kjp34", "collection": "authors", "collection_id": "9mbrn-kjp34", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:OYAjes80c", "type": "article", "title": "Factors Affecting the Electrochemical Responses of Metal Complexes at Pyrolytic Graphite Electrodes Coated with Films of Poly(4-Vinylpyridine)", "author": [ { "family_name": "Oyama", "given_name": "Noboru", "clpid": "Oyama-N" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Electrochemical responses from the reduction of RuIII (edta) coordinatedto films of high molecular weight poly(4-vinylpyridine) on pyrolytic graphiteelectrodes were studied as functions of film thickness, temperature, supportingelectrolyte composition, and solvent. Responses at filmed electrodes from metalcomplexes that do not coordinate to the films were also examined. With filmsthicker than ca. 1000\u00c5, the current responses are limited by the rates of molecularmotions within the films. Penetration of counterions, segmental motion ofsections of the polymer chains, and juxtapositioning of pairs of attached metalcomplexes to facilitate intercomplex electron transfer within the film or combinationsof the three are suggested as likely current limiting processes.", "doi": "10.1149/1.2129725", "issn": "0013-4651", "publisher": "Journal of the Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1980-03-01", "series_number": "3", "volume": "127", "issue": "3", "pages": "640-647" }, { "id": "authors:1c493-67h85", "collection": "authors", "collection_id": "1c493-67h85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:OYAjes80a", "type": "article", "title": "Electrostatic Binding of Metal Complexes to Electrode Surfaces Coated with Highly Charged Polymeric Films", "author": [ { "family_name": "Oyama", "given_name": "Noboru", "clpid": "Oyama-N" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "Previous reports in which metal complexes have been attached to electrode surfaces coated with polymeric molecules have depended upon the formation of covalent or coordination bonds in the attachment procedure (1-4). Such schemes can be quite successful but depending, as they do, on rather specific surface chemistry, they are not applicable to as wide a variety of metal complexes as might be desirable. We have observed that coating graphite electrodes with polymers bearing charged ionic groups produces surfaces which strongly bind multiply-charged metal complexes bearing charges opposite to that on the attached ionic polymer. By exploiting this observation it is entirely possible that virtually any desired metal ion can be attached in large quantities to electrode surfaces by coordinating the metal ion with ligands that produce a multiply-charged complex ion.", "issn": "0013-4651", "publisher": "Ellectrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1980-01", "series_number": "1", "volume": "127", "issue": "1", "pages": "247-250" }, { "id": "authors:kpgw9-sbk58", "collection": "authors", "collection_id": "kpgw9-sbk58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120802-082030036", "type": "article", "title": "Catalysis of the Electroreduction of Allyl Chloride by\n Cobalt 2,2'-Bipyridine Complexes", "author": [ { "family_name": "Margel", "given_name": "Shlomo", "clpid": "Margel-S" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The electrochemical reduction of allyl chloride is strongly catalyzed in the presence of cobalt complexes of 2,2\u2032\u2010bipyridine. A prominent reaction product of the catalyzed reduction is 1,5\u2010hexadiene. Voltammetry, coulometry, and gas chromatographic data are presented and analyzed and a mechanistic scheme proposed to account for the catalytic action of the cobalt\u20102,2\u2032\u2010bipyridine complexes.", "doi": "10.1149/1.2131655", "issn": "0013-4651", "publisher": "Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1978-08", "series_number": "8", "volume": "125", "issue": "8", "pages": "1232-1235" }, { "id": "authors:g6wfp-xfj67", "collection": "authors", "collection_id": "g6wfp-xfj67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120802-075025406", "type": "article", "title": "Electrochemistry of 2,2'-Bipyridine Complexes of Cobalt in the Presence of Acrylonitrile", "author": [ { "family_name": "Margel", "given_name": "Shlomo", "clpid": "Margel-S" }, { "family_name": "Smith", "given_name": "Wayne", "clpid": "Smith-W" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "The previously claimed (1) catalysis of the electroreduction of acrylonitrile by means of a complex of Co(I) and 2,2\u2032\u2010bipyridine is shown to be erroneous. The \"catalytic currents\" result instead from the two\u2010electron reduction of a mixed complex of Co(I) acrylonitrile and 2,2\u2032\u2010bipyridine. The equilibrium and forward rate constants for the formation of the mixed complex have been estimated and its spectrum is given. The behavior of a number of other vinyl monomers, which mimic acrylonitrile, is described.", "doi": "10.1149/1.2131421", "issn": "0013-4651", "publisher": "Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "1978-02", "series_number": "2", "volume": "125", "issue": "2", "pages": "241-246" }, { "id": "authors:3nw80-j7f38", "collection": "authors", "collection_id": "3nw80-j7f38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160305-125750662", "type": "teaching_resource", "title": "Electroanalytical Chemistry", "author": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "[no abstract]", "publisher": "American Chemical Society", "publication_date": "1976" }, { "id": "authors:m8mzd-fhf03", "collection": "authors", "collection_id": "m8mzd-fhf03", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161021-152450326", "type": "article", "title": "Electrochemistry", "author": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "abstract": "[No abstract]", "doi": "10.1146/annurev.pc.19.100168.000503", "issn": "0066-426X", "publisher": "American Chemical Society", "publication": "Annual Review of Physical Chemistry", "publication_date": "1968-10", "volume": "19", "pages": "83-110" } ]