Paramagnetic transition metal complexes can serve as quantum bits, storing phase information through unpaired electrons. Despite their promise, these systems often require low temperatures and tend to rapidly decohere. Recent efforts have sought to improve longitudinal relaxation (T1), which provides an upper limit for phase coherence (Tm), by investigating existing literature compounds with reduced vibrational coupling and orbital angular momentum. However, synthetic strategies for improving T1 through novel ligand design have remained scant. Here, we disclose the synthesis of a new modular macrocyclic ligand framework with four nitrogen donors (N4) derived from phenanthroline that supports room-temperature coherent Cu(II) spin centers. The optimized complex more than doubles the T1 over the next best Cu(II)-N4 compound and exhibits a room temperature coherence time (Tm) of 0.28 μs, close to previously reported values. This performance enhancement arises from a tight binding site with short Cu–N distances, resulting in a stronger ligand field and reduced thermal accessibility of symmetric vibrational modes. This work demonstrates a practical approach to enabling spin coherence at room temperature, a factor critical to accessing relevant quantum bits and biological sensors, through a designer macrocyclic ligand platform.
", "doi": "10.1021/jacs.5c00803", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2025-04-18" }, { "id": "authors:15yt7-nbt40", "collection": "authors", "collection_id": "15yt7-nbt40", "cite_using_url": "https://authors.library.caltech.edu/records/15yt7-nbt40", "type": "article", "title": "Molybdenum\u2013Iron\u2013Sulfur Cluster with a Bridging Carbide Ligand as a Partial FeMoco Model: CO Activation, EPR Studies, and Bonding Insight", "author": [ { "family_name": "Le", "given_name": "Linh N. V.", "orcid": "0000-0003-1451-2675", "clpid": "Le-Linh-N-V" }, { "family_name": "He", "given_name": "Tianyi", "orcid": "0000-0002-8191-188X", "clpid": "He-Tianyi" }, { "family_name": "Joyce", "given_name": "Justin P.", "orcid": "0000-0002-8287-622X" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "DeBeer", "given_name": "Serena", "orcid": "0000-0002-5196-3400" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "Nitrogenase enzymes catalyze the reduction of N2 to NH3 at a complex Fe-M (M = Mo, Fe, or V) cofactor (FeMco), which displays eight metal centers and sulfide and carbide bridges with a MFe7S8C composition. The role of the unusual μ6-carbide ligand and its effects on the metal centers remain unclear. Here, we describe the transfer of a carbide ligand to a MoFe3S3 cluster supported by a bisphenoxide ligand from a previously reported terminal Mo carbide complex to yield a pentametallic cluster of MoS3Fe3CMo composition, which also displays a bridging CO that resembles the lo-CO form of nitrogenase. This cluster has an S = 1/2 spin state amenable to studies by pulse EPR spectroscopy, revealing a significantly larger carbide 13C hyperfine interaction (aiso(13C) = 12.5 MHz) than any observed for various states of FeMoco studied by EPR thus far (|aiso(13C)| = 0.89 to 2.7 MHz). This report provides a strategy for the synthesis of carbide-containing iron-sulfur clusters relevant to nitrogenase cluster modeling, as well as benchmarking information for the metal-carbon interactions by EPR methods.
", "doi": "10.1021/jacs.4c17893", "pmcid": "PMC11969536", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2025-04-02", "series_number": "13", "volume": "147", "issue": "13", "pages": "11216-11226" }, { "id": "authors:52fva-q2753", "collection": "authors", "collection_id": "52fva-q2753", "cite_using_url": "https://authors.library.caltech.edu/records/52fva-q2753", "type": "article", "title": "Probing Bioinorganic Electron Spin Decoherence Mechanisms with an Fe\u2082S\u2082 Metalloprotein", "author": [ { "family_name": "Totoiu", "given_name": "Christian A.", "orcid": "0009-0004-5437-4339", "clpid": "Totoiu-Christian-A" }, { "family_name": "Follmer", "given_name": "Alec H.", "orcid": "0000-0002-6244-6804", "clpid": "Follmer-Alec-H" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-R-G" } ], "abstract": "Recent efforts have sought to develop paramagnetic molecular quantum bits (qubits) as a means to store and manipulate quantum information. Emerging structure–property relationships have shed light on electron spin decoherence mechanisms. While insights within molecular quantum information science have derived from synthetic systems, biomolecular platforms would allow for the study of decoherence phenomena in more complex chemical environments and further leverage molecular biology and protein engineering approaches. Here we have employed the exchange-coupled ST = 1/2 Fe2S2 active site of putidaredoxin, an electron transfer metalloprotein, as a platform for fundamental mechanistic studies of electron spin decoherence toward spin-based biological quantum sensing. At low temperatures, decoherence rates were anisotropic, reflecting a hyperfine-dominated decoherence mechanism, standing in contrast to the anisotropy of molecular systems observed previously. This mechanism provided a pathway for probing spatial effects on decoherence, such as protein vs solvent contributions. Furthermore, we demonstrated spatial sensitivity to single point mutations via site-directed mutagenesis and temporal sensitivity for monitoring solvent isotope exchange. Thus, this study demonstrates a step toward the design and construction of biomolecular quantum sensors.
", "doi": "10.1021/acs.jpcb.4c06186", "issn": "1520-6106", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry B", "publication_date": "2024-10-24", "series_number": "42", "volume": "128", "issue": "42", "pages": "10417\u201310426" }, { "id": "authors:ewx6y-yaa26", "collection": "authors", "collection_id": "ewx6y-yaa26", "cite_using_url": "https://authors.library.caltech.edu/records/ewx6y-yaa26", "type": "article", "title": "Highly Activated Terminal Carbon Monoxide Ligand in an Iron\u2013Sulfur Cluster Model of FeMco with Intermediate Local Spin State at Fe", "author": [ { "family_name": "Le", "given_name": "Linh N. V.", "orcid": "0000-0003-1451-2675", "clpid": "Le-Linh-N-V" }, { "family_name": "Joyce", "given_name": "Justin P.", "orcid": "0000-0002-8287-622X", "clpid": "Joyce-Justin-P" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "DeBeer", "given_name": "Serena", "orcid": "0000-0002-5196-3400", "clpid": "DeBeer-Serena" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "Nitrogenases, the enzymes that convert N2 to NH3, also catalyze the reductive coupling of CO to yield hydrocarbons. CO-coordinated species of nitrogenase clusters have been isolated and used to infer mechanistic information. However, synthetic FeS clusters displaying CO ligands remain rare, which limits benchmarking. Starting from a synthetic cluster that models a cubane portion of the FeMo cofactor (FeMoco), including a bridging carbyne ligand, we report a heterometallic tungsten–iron–sulfur cluster with a single terminal CO coordination in two oxidation states with a high level of CO activation (νCO = 1851 and 1751 cm–1). The local Fe coordination environment (2S, 1C, 1CO) is identical to that in the protein making this system a suitable benchmark. Computational studies find an unusual intermediate spin electronic configuration at the Fe sites promoted by the presence the carbyne ligand. This electronic feature is partly responsible for the high degree of CO activation in the reduced cluster.
\nNitrogenase is an active target of heterologous expression because of its importance for areas related to agronomy, energy, and environment. One major hurdle for expressing an active Mo-nitrogenase in Escherichia coli is to generate the complex metalloclusters (P- and M-clusters) within this enzyme, which involves some highly unique bioinorganic chemistry/metalloenzyme biochemistry that is not generally dealt with in the heterologous expression of proteins via synthetic biology; in particular, the heterologous synthesis of the homometallic P-cluster ([Fe\u2088S\u2087]) and M-cluster core (or L-cluster; [Fe\u2088S\u2089C]) on their respective protein scaffolds, which represents two crucial checkpoints along the biosynthetic pathway of a complete nitrogenase, has yet to be demonstrated by biochemical and spectroscopic analyses of purified metalloproteins. Here, we report the heterologous formation of a P-cluster-containing NifDK protein upon coexpression of Azotobacter vinelandii nifD, nifK , nifH , nifM, and nifZ genes, and that of an L-cluster-containing NifB protein upon coexpression of Methanosarcina acetivorans nifB, nifS, and nifU genes alongside the A. vinelandii fdxN gene, in E. coli. Our metal content, activity, EPR, and XAS/EXAFS data provide conclusive evidence for the successful synthesis of P- and L-clusters in a nondiazotrophic host, thereby highlighting the effectiveness of our metallocentric, divide-and-conquer approach that individually tackles the key events of nitrogenase biosynthesis prior to piecing them together into a complete pathway for the heterologous expression of nitrogenase. As such, this work paves the way for the transgenic expression of an active nitrogenase while providing an effective tool for further tackling the biosynthetic mechanism of this important metalloenzyme.
", "doi": "10.1073/pnas.2314788120", "pmcid": "PMC10622910", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences", "publication_date": "2023-10-31", "series_number": "44", "volume": "120", "issue": "44", "pages": "e2314788120" }, { "id": "authors:fkwtj-ts532", "collection": "authors", "collection_id": "fkwtj-ts532", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230710-599244800.25", "type": "article", "title": "Coordination Number in High-Spin\u2013Low-Spin Equilibrium in Cluster Models of the S\u2082 State of the Oxygen Evolving Complex", "author": [ { "family_name": "Shiau", "given_name": "Angela A.", "clpid": "Shiau-Angela-A" }, { "family_name": "Lee", "given_name": "Heui Beom", "clpid": "Lee-Heui-Beom" }, { "family_name": "Oyala", "given_name": "Paul H.", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "The S\u2082 state of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) shows high-spin (HS) and low-spin (LS) EPR signals attributed to distinct structures based on computation. Five-coordinate Mn^(III) centers are proposed in these species but are absent in available spectroscopic model complexes. Herein, we report the synthesis, crystal structure, electrochemistry, SQUID magnetometry, and EPR spectroscopy of a Mn^(III)Mn^(IV)\u2083O\u2084 cuboidal complex featuring five-coordinate Mn^(III). This cluster displays a spin ground state of S = 5/2, while conversion to a six-coordinate Mn upon treatment with water results in a spin state change to S = 1/2. These results demonstrate that coordination number, without dramatic changes within the Mn\u2084O\u2084 core, has a substantial effect on spectroscopy.
", "doi": "10.1021/jacs.3c04464", "pmcid": "PMC10575483", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2023-07-12", "series_number": "27", "volume": "145", "issue": "27", "pages": "14592-14598" }, { "id": "authors:aqptv-k3b45", "collection": "authors", "collection_id": "aqptv-k3b45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230725-856902000.17", "type": "article", "title": "Photogenerated Ni(I)\u2013Bipyridine Halide Complexes: Structure\u2013Function Relationships for Competitive C(sp\u00b2)\u2013Cl Oxidative Addition and Dimerization Reactivity Pathways", "author": [ { "family_name": "Cagan", "given_name": "David A.", "orcid": "0000-0002-4719-2789", "clpid": "Cagan-David-A" }, { "family_name": "B\u00edm", "given_name": "Daniel", "orcid": "0000-0003-3100-4293", "clpid": "B\u00edm-Daniel" }, { "family_name": "McNicholas", "given_name": "Brendon J.", "orcid": "0000-0002-3654-681X", "clpid": "McNicholas-Brendon-J" }, { "family_name": "Kazmierczak", "given_name": "Nathanael P.", "orcid": "0000-0002-7822-6769", "clpid": "Kazmierczak-Nathanael-P" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-R-G" } ], "abstract": "We report the facile photochemical generation of a library of Ni(I)–bpy halide complexes (Ni(I)(Rbpy)X (R = t-Bu, H, MeOOC; X = Cl, Br, I) and benchmark their relative reactivity toward competitive oxidative addition and off-cycle dimerization pathways. Structure–function relationships between the ligand set and reactivity are developed, with particular emphasis on rationalizing previously uncharacterized ligand-controlled reactivity toward high energy and challenging C(sp2)–Cl bonds. Through a dual Hammett and computational analysis, the mechanism of the formal oxidative addition is found to proceed through an SNAr-type pathway, consisting of a nucleophilic two-electron transfer between the Ni(I) 3d(z2) orbital and the Caryl–Cl σ* orbital, which contrasts the mechanism previously observed for activation of weaker C(sp2)–Br/I bonds. The bpy substituent provides a strong influence on reactivity, ultimately determining whether oxidative addition or dimerization even occurs. Here, we elucidate the origin of this substituent influence as arising from perturbations to the effective nuclear charge (Zeff) of the Ni(I) center. Electron donation to the metal decreases Zeff, which leads to a significant destabilization of the entire 3d orbital manifold. Decreasing the 3d(z2) electron binding energies leads to a powerful two-electron donor to activate strong C(sp2)–Cl bonds. These changes also prove to have an analogous effect on dimerization, with decreases in Zeff leading to more rapid dimerization. Ligand-induced modulation of Zeff and the 3d(z2) orbital energy is thus a tunable target by which the reactivity of Ni(I) complexes can be altered, providing a direct route to stimulate reactivity with even stronger C–X bonds and potentially unveiling new ways to accomplish Ni-mediated photocatalytic cycles.
\nThirteen boronated cyanometallates [M(CN-BR3)6]3/4/5– [M = Cr, Mn, Fe, Ru, Os; BR3 = BPh3, B(2,4,6,-F3C6H2)3, B(C6F5)3] and one metalloboratonitrile [Cr(NC-BPh3)6]3– have been characterized by X-ray crystallography and spectroscopy [UV–vis–near-IR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t2g)5 electronic configurations, the lowest-energy ligand-to-metal charge-transfer (LMCT) absorptions and MCD C-terms in the spectra of boronated species have been assigned to transitions from cyanide π + B–C borane σ orbitals. CASSCF+NEVPT2 calculations including t1u and t2u orbitals reproduced t1u/t2u → t2g excitation energies. Many [M(CN-BR3)6]3/4– complexes exhibited highly electrochemically reversible redox couples. Notably, the reduction formal potentials of all five [M(CN-B(C6F5)3)6]3– anions scale with the LMCT energies, and Mn(I) and Cr(II) compounds, [K(18-crown-6)]5[Mn(CN-B(C6F5)3)6] and [K(18-crown-6)]4[Cr(CN-B(C6F5)3)6], are surprisingly stable. Continuous-wave and pulsed electron paramagnetic resonance (EPR; hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, 14N hyperfine splittings are greater for (Ph4As)3[Cr(NC-BPh3)6] than for (Ph4As)3[Cr(CN-BPh3)6].
", "doi": "10.1021/acs.inorgchem.2c03066", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2023-02-20", "series_number": "7", "volume": "62", "issue": "7", "pages": "2959-2981" }, { "id": "authors:827q0-52b18", "collection": "authors", "collection_id": "827q0-52b18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221110-430801400.14", "type": "article", "title": "\u00b9\u2077O Electron Nuclear Double Resonance Analysis of Compound I: Inverse Correlation between Oxygen Spin Population and Electron Donation", "author": [ { "family_name": "Field", "given_name": "Mackenzie J.", "clpid": "Field-Mackenzie-J" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Green", "given_name": "Michael T.", "orcid": "0000-0001-8658-8420", "clpid": "Green-Michael-T" } ], "abstract": "Although the activation of inert C\u2013H bonds by metal-oxo complexes has been widely studied, important questions remain, particularly regarding the role of oxygen spin population (i.e., unpaired electrons on the oxo ligand) in facilitating C\u2013H bond cleavage. In order to shed light on this issue, we have utilized \u00b9\u2077O electron nuclear double resonance spectroscopy to measure the oxygen spin populations of three compound I intermediates in heme enzymes with different reactivities toward C\u2013H bonds: chloroperoxidase, cytochrome P450, and a selenolate (selenocysteinyl)-ligated cytochrome P450. The experimental data suggest an inverse correlation between oxygen spin population and electron donation from the axial ligand. We have explored the implications of this result using a H\u00fcckel-type molecular orbital model and constrained density functional theory calculations. These investigations have allowed us to examine the relationship between oxygen spin population, oxygen charge, electron donation from the axial ligand, and reactivity.", "doi": "10.1021/jacs.2c05459", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2022-10-26", "series_number": "42", "volume": "144", "issue": "42", "pages": "19272-19283" }, { "id": "authors:e2q6b-bk387", "collection": "authors", "collection_id": "e2q6b-bk387", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220817-897514000", "type": "article", "title": "Characterization of a Proposed Terminal Iron(III) Nitride Intermediate of Nitrogen Fixation Stabilized by a Trisphosphine\u2010Borane Ligand", "author": [ { "family_name": "Schild", "given_name": "Dirk J.", "orcid": "0000-0003-0179-6023", "clpid": "Schild-Dirk-J" }, { "family_name": "Nurdin", "given_name": "Lucie", "clpid": "Nurdin-Lucie" }, { "family_name": "Moret", "given_name": "Marc-Etienne", "orcid": "0000-0002-3137-6073", "clpid": "Moret-Marc-Etienne" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "Terminal iron nitrides (Fe\u2261N) have been proposed as intermediates of Fe-mediated nitrogen fixation, and well-defined synthetic iron nitrides have been characterized in high oxidation states, including Fe(IV), Fe(V), and Fe(VI). This study reports the generation and low temperature characterization of a terminally bound iron(III) nitride, P\u2083\u1d2eFe(N) (P\u2083\u1d2e = tris(o-diisopropylphosphinophenyl)borane), which is a proposed intermediate of iron-mediated nitrogen fixation by the P\u2083\u1d2eFe-catalyst system. CW- and pulse EPR spectroscopy (HYSCORE and ENDOR), supported by DFT calculations, help to define a 2A ground state electronic structure of this C\u2083-symmetric nitride species, placing the unpaired spin in a sigma orbital along the B-Fe-N vector; this electronic structure is distinct for an iron nitride. The unusual d\u2075-configuration is stabilized by significant delocalization (~50%) of the unpaired electron onto the axial boron and nitrogen ligands, with a majority of the spin residing on boron.", "doi": "10.1002/anie.202209655", "pmcid": "PMC9588675", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2022-08-17", "series_number": "43", "volume": "61", "issue": "43", "pages": "e202209655" }, { "id": "authors:06n2q-96t82", "collection": "authors", "collection_id": "06n2q-96t82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220714-369441000", "type": "article", "title": "Mn\u1d35\u2c7d\u2084O\u2084 Model of the S\u2083 Intermediate of the Oxygen-Evolving Complex: Effect of the Dianionic Disiloxide Ligand", "author": [ { "family_name": "Shiau", "given_name": "Angela A.", "orcid": "0000-0003-4395-9847", "clpid": "Shiau-Angela-A" }, { "family_name": "Lee", "given_name": "Heui Beom", "orcid": "0000-0002-9550-2649", "clpid": "Lee-Heui-Beom" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "Synthetic complexes provide useful models to study the interplay between the structure and spectroscopy of the different Sn-state intermediates of the oxygen-evolving complex (OEC) of photosystem II (PSII). Complexes containing the Mn\u1d35\u2c7d\u2084 core corresponding to the S\u2083 state, the last observable intermediate prior to dioxygen formation, remain very rare. Toward the development of synthetic strategies to stabilize highly oxidized tetranuclear complexes, ligands with increased anion charge were pursued. Herein, we report the synthesis, electrochemistry, SQUID magnetometry, and electron paramagnetic resonance spectroscopy of a stable Mn\u1d35\u2c7d\u2084O\u2084 cuboidal complex supported by a disiloxide ligand. The substitution of an anionic acetate or amidate ligand with a dianionic disiloxide ligand shifts the reduction potential of the Mn\u1d35\u1d35\u1d35Mn\u1d35\u2c7d\u2083/Mn\u1d35\u2c7d\u2084 redox couple by up to \u223c760 mV, improving stability. The S = 3 spin ground state of the siloxide-ligated Mn\u1d35\u2c7d\u2084O\u2084 complex matches the acetate and amidate variants, in corroboration with the MnIV4 assignment of the S\u2083 state of the OEC.", "doi": "10.1021/acs.inorgchem.2c01612", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2022-07-14" }, { "id": "authors:sxpwn-sqd83", "collection": "authors", "collection_id": "sxpwn-sqd83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220705-671808000", "type": "article", "title": "Chemical control of spin\u2013lattice relaxation to discover a room temperature molecular qubit", "author": [ { "family_name": "Amdur", "given_name": "M. Jeremy", "clpid": "Amdur-M-Jeremy" }, { "family_name": "Mullin", "given_name": "Kathleen R.", "clpid": "Mullin-Kathleen-R" }, { "family_name": "Waters", "given_name": "Michael J.", "orcid": "0000-0001-6425-4331", "clpid": "Waters-Michael-J" }, { "family_name": "Puggioni", "given_name": "Danilo", "orcid": "0000-0002-2128-4191", "clpid": "Puggioni-Danilo" }, { "family_name": "Wojnar", "given_name": "Michael K.", "orcid": "0000-0003-2556-7014", "clpid": "Wojnar-Michael-K" }, { "family_name": "Gu", "given_name": "Mingqiang", "orcid": "0000-0002-2889-2202", "clpid": "Gu-Mingqiang" }, { "family_name": "Sun", "given_name": "Lei", "orcid": "0000-0001-8467-6750", "clpid": "Sun-Lei" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Rondinelli", "given_name": "James M.", "orcid": "0000-0003-0508-2175", "clpid": "Rondinelli-James-M" }, { "family_name": "Freedman", "given_name": "Danna E.", "orcid": "0000-0002-2579-8835", "clpid": "Freedman-Danna-E" } ], "abstract": "The second quantum revolution harnesses exquisite quantum control for a slate of diverse applications including sensing, communication, and computation. Of the many candidates for building quantum systems, molecules offer both tunability and specificity, but the principles to enable high temperature operation are not well established. Spin\u2013lattice relaxation, represented by the time constant T\u2081, is the primary factor dictating the high temperature performance of quantum bits (qubits), and serves as the upper limit on qubit coherence times (T\u2082). For molecular qubits at elevated temperatures (>100 K), molecular vibrations facilitate rapid spin\u2013lattice relaxation which limits T\u2082 to well below operational minimums for certain quantum technologies. Here we identify the effects of controlling orbital angular momentum through metal coordination geometry and ligand rigidity via \u03c0-conjugation on T\u2081 relaxation in three four-coordinate Cu\u00b2\u207a S = \u00bd qubit candidates: bis(N,N\u2032-dimethyl-4-amino-3-penten-2-imine) copper(II) (Me\u2082Nac)\u2082 (1), bis(acetylacetone)ethylenediamine copper(II) Cu(acacen) (2), and tetramethyltetraazaannulene copper(II) Cu(tmtaa) (3). We obtain significant T\u2081 improvement upon changing from tetrahedral to square planar geometries through changes in orbital angular momentum. T\u2081 is further improved with greater \u03c0-conjugation in the ligand framework. Our electronic structure calculations reveal that the reduced motion of low energy vibrations in the primary coordination sphere slows relaxation and increases T\u2081. These principles enable us to report a new molecular qubit candidate with room temperature T\u2082 = 0.43 \u03bcs, and establishes guidelines for designing novel qubit candidates operating above 100 K.", "doi": "10.1039/d1sc06130e", "pmcid": "PMC9200133", "issn": "2041-6520", "publisher": "Royal Society of Chemistry", "publication": "Chemical Science", "publication_date": "2022-07-07", "series_number": "23", "volume": "13", "issue": "23", "pages": "7034-7045" }, { "id": "authors:cwedr-ptb50", "collection": "authors", "collection_id": "cwedr-ptb50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220606-736150000", "type": "article", "title": "Copper(II) Binding to the Intrinsically Disordered C-Terminal Peptide of SARS-CoV-2 Virulence Factor Nsp1", "author": [ { "family_name": "Morales", "given_name": "Maryann", "orcid": "0000-0002-1778-8901", "clpid": "Morales-Maryann" }, { "family_name": "Ravanfar", "given_name": "Raheleh", "orcid": "0000-0003-2992-0575", "clpid": "Ravanfar-Raheleh" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Winkler", "given_name": "Jay R.", "orcid": "0000-0002-4453-9716", "clpid": "Winkler-J-R" } ], "abstract": "The first encoded SARS-CoV-2 protein (Nsp1) binds to the human 40S ribosome and blocks synthesis of host proteins, thereby inhibiting critical elements of the innate immune response. The final 33 residues of the natively unstructured Nsp1 C-terminus adopt a helix-turn-helix geometry upon binding to the ribosome. We have characterized the fluctuating conformations of this peptide using circular dichroism spectroscopy along with measurements of tryptophan fluorescence and energy transfer. Tryptophan fluorescence decay kinetics reveal that copper(II) binds to the peptide at micromolar concentrations, and electron paramagnetic resonance spectroscopy indicates that the metal ion coordinates to the lone histidine residue.", "doi": "10.1021/acs.inorgchem.2c01329", "pmcid": "PMC9195567", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2022-06-20", "series_number": "24", "volume": "61", "issue": "24", "pages": "8992-8996" }, { "id": "authors:zpda7-k2k63", "collection": "authors", "collection_id": "zpda7-k2k63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220323-704268000", "type": "article", "title": "Heterometallic uranium/molybdenum nitride synthesis via partial N-atom transfer", "author": [ { "family_name": "Barluzzi", "given_name": "Luciano", "orcid": "0000-0001-6682-342X", "clpid": "Barluzzi-Luciano" }, { "family_name": "Jori", "given_name": "Nadir", "orcid": "0000-0002-9375-894X", "clpid": "Jori-Nadir" }, { "family_name": "He", "given_name": "Tianyi", "orcid": "0000-0002-8191-188X", "clpid": "He-Tianyi" }, { "family_name": "Rajeshkumar", "given_name": "Thayalan", "clpid": "Rajeshkumar-Thayalan" }, { "family_name": "Scopelliti", "given_name": "Rosario", "orcid": "0000-0001-8161-8715", "clpid": "Scopelliti-Rosario" }, { "family_name": "Maron", "given_name": "Laurent", "orcid": "0000-0003-2653-8557", "clpid": "Maron-Laurent" }, { "family_name": "Oyala", "given_name": "Paul", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Mazzanti", "given_name": "Marinella", "orcid": "0000-0002-3427-008X", "clpid": "Mazzanti-Marinella" } ], "abstract": "The reaction of a Mo(ii) terminal nitride with U(iii) generates the first example of a transition metal capped uranium nitride. The nitride is triply bonded to U(v) and singly bonded to Mo(0) with a U\u2013Mo interaction and reacts with CO to yield cyanate.", "doi": "10.1039/d2cc00473a", "issn": "1359-7345", "publisher": "Royal Society of Chemistry", "publication": "Chemical Communications", "publication_date": "2022-04-14", "series_number": "29", "volume": "58", "issue": "29", "pages": "4655-4658" }, { "id": "authors:6570f-zs409", "collection": "authors", "collection_id": "6570f-zs409", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220307-188438000", "type": "article", "title": "Photoinduced, Copper-Catalyzed Enantioconvergent Alkylations of Anilines by Racemic Tertiary Electrophiles: Synthesis and Mechanism", "author": [ { "family_name": "Cho", "given_name": "Hyungdo", "orcid": "0000-0001-6109-5742", "clpid": "Cho-Hyungdo" }, { "family_name": "Suematsu", "given_name": "Hidehiro", "orcid": "0000-0002-9444-7254", "clpid": "Suematsu-Hidehiro" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" } ], "abstract": "Transition-metal catalysis of substitution reactions of alkyl electrophiles by nitrogen nucleophiles is beginning to emerge as a powerful strategy for synthesizing higher-order amines, as well as controlling their stereochemistry. Herein, we report that a readily accessible chiral copper catalyst (commercially available components) can achieve the photoinduced, enantioconvergent coupling of a variety of racemic tertiary alkyl electrophiles with aniline nucleophiles to generate a new C\u2013N bond with good ee at the fully substituted stereocenter of the product; whereas this photoinduced, copper-catalyzed coupling proceeds at \u221278 \u00b0C, in the absence of light and catalyst, virtually no C\u2013N bond formation is observed even upon heating to 80 \u00b0C. The mechanism of this new catalytic enantioconvergent substitution process has been interrogated with the aid of a wide array of tools, including the independent synthesis of proposed intermediates and reactivity studies, spectroscopic investigations featuring photophysical and EPR data, and DFT calculations. These studies led to the identification of three copper-based intermediates in the proposed catalytic cycle, including a chiral three-coordinate formally copper(II)\u2013anilido (DFT analysis points to its formulation as a copper(I)\u2013anilidyl radical) complex that serves as a persistent radical that couples with a tertiary organic radical to generate the desired C\u2013N bond with good enantioselectivity.", "doi": "10.1021/jacs.1c12749", "pmcid": "PMC9239302", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2022-03-16", "series_number": "10", "volume": "144", "issue": "10", "pages": "4550-4558" }, { "id": "authors:pdg32-gfd78", "collection": "authors", "collection_id": "pdg32-gfd78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220216-527740512", "type": "article", "title": "Investigation of the C\u2013N Bond-Forming Step in a Photoinduced, Copper-Catalyzed Enantioconvergent N\u2013Alkylation: Characterization and Application of a Stabilized Organic Radical as a Mechanistic Probe", "author": [ { "family_name": "Lee", "given_name": "Heejun", "orcid": "0000-0002-0439-3863", "clpid": "Lee-Heejun" }, { "family_name": "Ahn", "given_name": "Jun Myun", "clpid": "Ahn-Jun-Myun" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Citek", "given_name": "Cooper", "orcid": "0000-0001-9376-8200", "clpid": "Citek-Cooper" }, { "family_name": "Yin", "given_name": "Haolin", "orcid": "0000-0002-2063-8605", "clpid": "Yin-Haolin" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "Whereas photoinduced, copper-catalyzed couplings of nitrogen nucleophiles with alkyl electrophiles have recently been shown to provide an attractive approach to achieving a variety of enantioselective C\u2013N bond constructions, mechanistic studies of these transformations have lagged the advances in reaction development. Herein we provide mechanistic insight into a previously reported photoinduced, copper-catalyzed enantioconvergent C\u2013N coupling of a carbazole nucleophile with a racemic tertiary \u03b1-haloamide electrophile. Building on the isolation of a copper(II) model complex whose EPR parameters serve as a guide, we independently synthesize two key intermediates in the proposed catalytic cycle, a copper(II) metalloradical (L*Cu^(II)(carb\u2032)\u2082) (L* = a monodentate chiral phosphine ligand; carb\u2032 = a carbazolide ligand), as well as a tertiary \u03b1-amide organic radical (R\u00b7); the generation and characterization of R\u00b7 was guided by DFT calculations, which suggested that it would be stable to homocoupling. Continuous-wave (CW) and pulse EPR studies, along with corresponding DFT calculations, are among the techniques used to characterize these reactive radicals. We establish that these two radicals do indeed combine to furnish the C\u2013N coupling product in good yield and with significant enantiomeric excess (77% yield, 55% ee), thereby supporting the chemical competence of these proposed intermediates. DFT calculations are consistent with R\u00b7 initially binding to copper(II) via a dative interaction from the closed-shell carbonyl oxygen atom of the radical, which positions the \u03b1-carbon for direct reaction with the copper(II)-bound carbazole N atom, to generate the C\u2013N bond with enantioselectivity, without the formation of an alkylcopper(III) intermediate.", "doi": "10.1021/jacs.1c13151", "pmcid": "PMC9269863", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2022-03-09", "series_number": "9", "volume": "144", "issue": "9", "pages": "4114-4123" }, { "id": "authors:1928r-60f66", "collection": "authors", "collection_id": "1928r-60f66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220114-12550000", "type": "article", "title": "Structure and Magnetism of Few-Layer Nanographene Clusters in Carbon Microspheres", "author": [ { "family_name": "Manukyan", "given_name": "Aram", "clpid": "Manukyan-Aram" }, { "family_name": "Gyulasaryan", "given_name": "Harutyun", "clpid": "Gyulasaryan-Harutyun" }, { "family_name": "Kocharian", "given_name": "Armen", "orcid": "0000-0003-4974-7562", "clpid": "Kocharian-Armen" }, { "family_name": "Oyala", "given_name": "Paul", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Chumakov", "given_name": "Ratibor", "clpid": "Chumakov-Ratibor" }, { "family_name": "Avramenko", "given_name": "Marina", "clpid": "Avramenko-Marina" }, { "family_name": "Sanchez", "given_name": "Carlos", "clpid": "Sanchez-Carlos" }, { "family_name": "Bernal", "given_name": "Oscar O.", "clpid": "Bernal-Oscar-O" }, { "family_name": "Bugaev", "given_name": "Lusegen", "clpid": "Bugaev-Lusegen" }, { "family_name": "Sharoyan", "given_name": "Eduard", "clpid": "Sharoyan-Eduard" } ], "abstract": "The solid-phase pyrolysis method was used to synthesize carbon microspheres, consisting of clusters of few-layer nanographene and amorphous carbon. Powders of metal-free phthalocyanine and polyethylene served as precursors of the synthesized carbon microspheres. The pyrolysis products of metal-free phthalocyanine samples S_(Pc)(700) and S_(Pc)(900) contained 4 and 1 atom % nitrogen, respectively, replacing carbon in the graphene lattice in pyrrolic and pyridinic coordination. There are no impurity nitrogen atoms in the products of the pyrolysis of polyethylene. The S_(Pc)(700) sample showed strong paramagnetism with a concentration of paramagnetic centers of \u223c5 \u00d7 10\u00b9\u2079 spin g\u207b\u00b9 and a temperature-independent diamagnetism susceptibility of \u03c7_(Dia) = \u22121 \u00d7 10\u207b\u00b9\u2076 emu g\u207b\u00b9 Oe\u207b\u00b9. In a temperature range of 5\u2013300 K, ferromagnetism was also revealed with a temperature dependence similar to that of ferromagnetic cluster spin glasses, with maximum saturation magnetization, M_S^(FM) = 3 \u00d7 10\u207b\u00b2 emu g\u207b\u00b9, and coercive force, H_c = 400 Oe, at T_(sg) = 25 K. It was shown that the ferromagnetism in the S_(Pc)(700) sample is due to \u03c0(p)-electrons of zigzag-type edge states as well as nitrogen impurity atoms. The experimental results are interpreted based on the temperature dependence of the spin correlation length. It was revealed that the temperature dependence of the integral of the magnetic resonance absorption intensity closely resembles the temperature behavior of the saturation magnetization of the ferromagnetic component.", "doi": "10.1021/acs.jpcc.1c06748", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2022-01-13", "series_number": "1", "volume": "126", "issue": "1", "pages": "493-504" }, { "id": "authors:4mcqw-kak78", "collection": "authors", "collection_id": "4mcqw-kak78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211201-162456410", "type": "article", "title": "Probing Redox Non-Innocence in Iron\u2013Carbene Complexes {Fe=C(H)Ar}\u00b9\u2070\u207b\u00b9\u00b9 by ^(1,2)H and \u00b9\u00b3C Pulse Electron Paramagnetic Resonance", "author": [ { "family_name": "Arnett", "given_name": "Charles H.", "orcid": "0000-0002-1272-3797", "clpid": "Arnett-Charles-H" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "We report the synthesis and spectroscopic characterization of a series of iron-carbene complexes in redox states {Fe=C(H)Ar}\u00b9\u2070\u207b\u00b9\u00b9. Pulse EPR studies of the ^(1,2)H and \u00b9\u00b3C isotopologues of {Fe=C(H)Ar}\u00b9\u00b9 reveal the high covalency of the Fe\u2013carbene bonding, leading to a more even spin distribution than commonly observed for reduced Fischer carbenes.", "doi": "10.1002/anie.202110704", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2021-12-20", "series_number": "52", "volume": "60", "issue": "52", "pages": "27220-27224" }, { "id": "authors:q9rjh-5yb85", "collection": "authors", "collection_id": "q9rjh-5yb85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210831-200226268", "type": "article", "title": "Terminal, Open-Shell Mo Carbide and Carbyne Complexes: Spin Delocalization and Ligand Noninnocence", "author": [ { "family_name": "Bailey", "given_name": "Gwendolyn A.", "orcid": "0000-0002-6636-4128", "clpid": "Bailey-Gwendolyn-A" }, { "family_name": "Buss", "given_name": "Joshua A.", "orcid": "0000-0002-3347-8583", "clpid": "Buss-Joshua-A" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "Open-shell compounds bearing metal\u2013carbon triple bonds, such as carbides and carbynes, are of significant interest as plausible intermediates in the reductive catenation of C\u2081 oxygenates. Despite the abundance of closed-shell carbynes reported, open-shell variants are very limited, and an open-shell carbide has yet to be reported. Herein, we report the synthesis of the first terminal, open-shell carbide complexes, [K][1] and [1][BAr^F\u2084] (1 = P2Mo(\u2261C:)(CO), P2 = a terphenyl diphosphine ligand), which differ by two redox states, as well as a series of related open-shell carbyne complexes. The complexes are characterized by single-crystal X-ray diffraction and NMR, EPR, and IR spectroscopies, while the electronic structures are probed by EPR studies and DFT calculations to assess spin delocalization. In the d\u2081 complexes, the spin is primarily localized on the metal (\u223c55\u201377% Mo d_(xy)) with delocalization on the triply bonded carbon of \u223c0.05\u20130.09 e\u207b. In the reduced carbide [K][1], a direct metal\u2013arene interaction enables ancillary ligand reduction, resulting in reduced radical character on the terminal carbide (\u2a7d0.02 e\u207b). Reactivity studies with [K][1] reveal the formation of mixed-valent C\u2013C coupled products at \u221240 \u00b0C, illustrating how productive reactivity manifolds can be engendered through the manipulation of redox states. Combined, the results inform on the electronic structure and reactivity of a new and underrepresented class of compounds with potential significance to a wide array of reactions involving open-shell species.", "doi": "10.1021/jacs.1c03806", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2021-08-25", "series_number": "33", "volume": "143", "issue": "33", "pages": "13091-13102" }, { "id": "authors:xxmcb-70q98", "collection": "authors", "collection_id": "xxmcb-70q98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210527-093456375", "type": "article", "title": "CaMn\u2083^(IV)O\u2084 Cubane Models of the Oxygen Evolving Complex: Spin Ground States S < 9/2 and the Effect of Oxo Protonation", "author": [ { "family_name": "Lee", "given_name": "Heui Beom", "orcid": "0000-0002-9550-2649", "clpid": "Lee-Heui-Beom" }, { "family_name": "Shiau", "given_name": "Angela A.", "orcid": "0000-0003-4395-9847", "clpid": "Shiau-Angela-A" }, { "family_name": "Marchiori", "given_name": "David A.", "orcid": "0000-0001-9738-3674", "clpid": "Marchiori-David-A" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Yoo", "given_name": "Byung-Kuk", "orcid": "0000-0002-2610-6685", "clpid": "Yoo-Byung-Kuk" }, { "family_name": "Kaiser", "given_name": "Jens T.", "orcid": "0000-0002-5948-5212", "clpid": "Kaiser-Jens-T" }, { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Britt", "given_name": "R. David", "orcid": "0000-0003-0889-8436", "clpid": "Britt-R-David" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "We report the single crystal XRD and MicroED structure, magnetic susceptibility, and EPR data of a series of CaMn\u2083^(IV)O\u2084 and YMn\u2083^(IV)O\u2084 complexes as structural and spectroscopic models of the cuboidal subunit of the oxygen-evolving complex (OEC). The effect of changes in heterometal identity, cluster geometry, and bridging oxo protonation on the spin-state structure was investigated. In contrast to previous computational models, we show that the spin ground state of CaMn\u2083^(IV)O\u2084 complexes and variants with protonated oxo moieties need not be S = 9/2. Desymmetrization of the pseudo-C\u2083-symmetric Ca(Y)Mn\u2083^(IV)O\u2084 core leads to a lower S = 5/2 spin ground state. The magnitude of the magnetic exchange coupling is attenuated upon oxo protonation, and an S = 3/2 spin ground state is observed in CaMn\u2083^(IV)O\u2083(OH). Our studies complement the observation that the interconversion between the low-spin and high-spin forms of the S\u2082 state is pH-dependent, suggesting that the (de)protonation of bridging or terminal oxygen atoms in the OEC may be connected to spin-state changes.", "doi": "10.1002/anie.202105303", "pmcid": "PMC8319083", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2021-08-02", "series_number": "32", "volume": "60", "issue": "32", "pages": "17671-17679" }, { "id": "authors:1zydc-45893", "collection": "authors", "collection_id": "1zydc-45893", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200825-115712108", "type": "article", "title": "Hydrazine Formation via Coupling of a Nickel(III)\u2013NH\u2082 Radical", "author": [ { "family_name": "Gu", "given_name": "Nina X.", "orcid": "0000-0002-4637-8418", "clpid": "Gu-Nina-X" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "M(NH\u2093) intermediates involved in N\u2212N bond formation are central to ammonia oxidation (AO) catalysis, an enabling technology to ultimately exploit ammonia (NH\u2083) as an alternative fuel source. While homocoupling of a terminal amide species (M\u2010NH\u2082) to form hydrazine (N\u2082H\u2084) has been proposed, well\u2010defined examples are without precedent. Herein, we discuss the generation and electronic structure of a NiIII\u2010NH\u2082 species that undergoes bimolecular coupling to generate a Ni^(II)\u2082(N\u2082H\u2084) complex. This hydrazine adduct can be further oxidized to a structurally unusual Ni\u2082(N\u2082H\u2082) species; this releases N\u2082 in the presence of NH\u2083, thus establishing a synthetic cycle for Ni\u2010mediated AO. Distribution of the redox load for H\u2082N\u2010NH\u2082 formation via NH\u2082 coupling between two metal centers presents an attractive strategy for AO catalysis using Earth\u2010abundant, late first\u2010row metals.", "doi": "10.1002/anie.202013119", "pmcid": "PMC7902478", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2021-02-19", "series_number": "8", "volume": "60", "issue": "8", "pages": "4009-4013" }, { "id": "authors:2qrdb-75657", "collection": "authors", "collection_id": "2qrdb-75657", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201201-075016332", "type": "article", "title": "Characterization of Cr-Hydrocarbyl Species via Pulse EPR in the Study of Ethylene Tetramerization Catalysis", "author": [ { "family_name": "Hirscher", "given_name": "Nathanael A.", "clpid": "Hirscher-Nathanael-A" }, { "family_name": "Arnett", "given_name": "Charles H.", "orcid": "0000-0002-1272-3797", "clpid": "Arnett-Charles-H" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "The characterization of complexes involved in chromium catalysis is challenging due to the paramagnetism of Cr in its common oxidation states. Here, we demonstrate the utility of pulse electron paramagnetic resonance (pulse EPR) techniques in assigning structural features of Cr organometallic complexes relevant to ethylene tetramerization. An S = 3/2, Cr(III) bisaryl-methyl ethylene tetramerization precatalyst (1) has been selected for characterization by CW and pulse EPR spectroscopies. Using an isotopically labeled Cr-CD\u2083 complex (1-d\u2083), the methyl ligand was confirmed to remain bound to Cr in solution by detection of \u00b2H couplings in X-band hyperfine sublevel correlation (HYSCORE) spectroscopy. Protonolysis of 1-d\u2083 led to an S = 3/2, Cr(III) product (2-d\u2083) that maintained spectroscopic features in HYSCORE for the CD\u2083 group, indicative of retention of the Cr-alkyl bond. Following protonolysis of 1-h\u2083 and subsequent reaction with ethylene, an S = 1/2 Cr(I) species with an ethylene-derived ligand was generated, supporting a mechanism involving this Cr oxidation state. Additionally, the pulse EPR characterization of a Cr(I) allyl-diene complex was performed for comparison. This is the first direct observation of hydrocarbyl ligands on Cr using pulse EPR methods. The methods described here are broadly applicable to Cr, first-row transition metals and other open-shell organometallic catalytic systems.", "doi": "10.1021/acs.organomet.0c00521", "issn": "0276-7333", "publisher": "American Chemical Society", "publication": "Organometallics", "publication_date": "2020-12-28", "series_number": "24", "volume": "39", "issue": "24", "pages": "4420-4429" }, { "id": "authors:q92rt-vf471", "collection": "authors", "collection_id": "q92rt-vf471", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200929-105404784", "type": "article", "title": "Exploring the Limits of Dative Boratrane Bonding: Iron as a Strong Lewis Base in Low-Valent Non-Heme Iron-Nitrosyl Complexes", "author": [ { "family_name": "Dong", "given_name": "Hai T.", "orcid": "0000-0002-8914-3045", "clpid": "Dong-Hai-T" }, { "family_name": "Chalkley", "given_name": "Matthew J.", "orcid": "0000-0002-0484-7335", "clpid": "Chalkley-Matthew-J" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Zhao", "given_name": "Jiyong", "orcid": "0000-0002-0777-3626", "clpid": "Zhao-Jiyong" }, { "family_name": "Alp", "given_name": "E. Ercan", "orcid": "0000-0002-4803-8863", "clpid": "Alp-Esen-Ercan" }, { "family_name": "Hu", "given_name": "Michael Y.", "orcid": "0000-0002-3718-7169", "clpid": "Hu-Michael-Y" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Lehnert", "given_name": "Nicolai", "orcid": "0000-0002-5221-5498", "clpid": "Lehnert-Nicolai" } ], "abstract": "We previously reported the synthesis and preliminary characterization of a unique series of low-spin (ls) {FeNO}\u2078\u207b\u00b9\u2070 complexes supported by an ambiphilic trisphosphineborane ligand, [Fe(TPB)(NO)]^(+/0/\u2212). Herein, we use advanced spectroscopic techniques and density functional theory (DFT) calculations to extract detailed information as to how the bonding changes across the redox series. We find that, in spite of the highly reduced nature of these complexes, they feature an NO+ ligand throughout with strong Fe\u2212NO \u03c0-backbonding and essentially closed-shell electronic structures of their FeNO units. This is enabled by an Fe\u2212B interaction that is present throughout the series. In particular, the most reduced [Fe(TPB)(NO)]\u2212 complex, an example of a ls-{FeNO}\u00b9\u2070 species, features a true reverse dative Fe \u2192 B bond where the Fe center acts as a strong Lewis-base. Hence, this complex is in fact electronically similar to the ls-{FeNO}\u2078 system, with two additional electrons \"stored\" on site in an Fe\u2212B single bond. The outlier in this series is the ls-{FeNO}\u2079 complex, due to spin polarization (quantified by pulse EPR spectroscopy), which weakens the Fe\u2212NO bond. These data are further contextualized by comparison with a related N\u2082 complex, [Fe(TPB)(N\u2082)]\u207b, which is a key intermediate in Fe(TPB)-catalyzed N\u2082 fixation. Our present study finds that the Fe \u2192 B interaction is key for storing the electrons needed to achieve a highly reduced state in these systems, and highlights the pitfalls associated with using geometric parameters to try to evaluate reverse dative interactions, a finding with broader implications to the study of transition metal complexes with boratrane and related ligands.", "doi": "10.1021/acs.inorgchem.0c01686", "pmcid": "PMC7640944", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2020-10-19", "series_number": "20", "volume": "59", "issue": "20", "pages": "14967-14982" }, { "id": "authors:zfspq-qva07", "collection": "authors", "collection_id": "zfspq-qva07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200713-085326752", "type": "article", "title": "A Super-Oxidized Radical Cationic Icosahedral Boron Cluster", "author": [ { "family_name": "Stauber", "given_name": "Julia M.", "orcid": "0000-0001-9783-907X", "clpid": "Stauber-Julia-M" }, { "family_name": "Schwan", "given_name": "Josef", "orcid": "0000-0002-1086-6698", "clpid": "Schwan-Josef" }, { "family_name": "Zhang", "given_name": "Xinglong", "orcid": "0000-0003-1698-692X", "clpid": "Zhang-Xinglong" }, { "family_name": "Axtell", "given_name": "Jonathan C.", "orcid": "0000-0002-5579-4296", "clpid": "Axtell-Jonathan-C" }, { "family_name": "Jung", "given_name": "Dahee", "orcid": "0000-0003-1863-0193", "clpid": "Jung-Dahee" }, { "family_name": "McNicholas", "given_name": "Brendon J.", "orcid": "0000-0002-3654-681X", "clpid": "McNicholas-Brendon-J" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Martinolich", "given_name": "Andrew J.", "orcid": "0000-0002-7866-9594", "clpid": "Martinolich-Andrew-J" }, { "family_name": "Winkler", "given_name": "Jay R.", "orcid": "0000-0002-4453-9716", "clpid": "Winkler-Jay-R" }, { "family_name": "See", "given_name": "Kimberly A.", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly-A" }, { "family_name": "Miller", "given_name": "Thomas F., III", "orcid": "0000-0002-1882-5380", "clpid": "Miller-T-F-III" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Spokoyny", "given_name": "Alexander M.", "orcid": "0000-0002-5683-6240", "clpid": "Spokoyny-Alexander-M" } ], "abstract": "While the icosahedral closo-[B\u2081\u2082H\u2081\u2082]\u00b2\u207b cluster does not display reversible electrochemical behavior, perfunctionalization of this species via substitution of all 12 B\u2013H vertices with alkoxy or benzyloxy (OR) substituents engenders reversible redox chemistry, providing access to clusters in the dianionic, monoanionic, and neutral forms. Here, we evaluated the electrochemical behavior of the electron-rich B\u2081\u2082(O-3-methylbutyl)\u2081\u2082 (1) cluster and discovered that a new reversible redox event that gives rise to a fourth electronic state is accessible through one-electron oxidation of the neutral species. Chemical oxidation of 1 with [N(2,4-Br\u2082C\u2086H\u2083)\u2083]\u00b7\u207a afforded the isolable [1]\u00b7\u207a cluster, which is the first example of an open-shell cationic B\u2081\u2082 cluster in which the unpaired electron is proposed to be delocalized throughout the boron cluster core. The oxidation of 1 is also chemically reversible, where treatment of [1]\u00b7\u207a with ferrocene resulted in its reduction back to 1. The identity of [1]\u00b7\u207a is supported by EPR, UV\u2013vis, multinuclear NMR (\u00b9H, \u00b9\u00b9B), and X-ray photoelectron spectroscopic characterization.", "doi": "10.1021/jacs.0c06159", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2020-07-29", "series_number": "30", "volume": "142", "issue": "30", "pages": "12948-12953" }, { "id": "authors:j065k-kt261", "collection": "authors", "collection_id": "j065k-kt261", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190820-134220046", "type": "article", "title": "Mononuclear Fe(I) and Fe(II) Acetylene Adducts and their Reductive Protonation to Terminal Fe(IV) and Fe(V) Carbynes", "author": [ { "family_name": "Citek", "given_name": "Cooper", "orcid": "0000-0001-9376-8200", "clpid": "Citek-Cooper" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "The activity of nitrogenase enzymes, which catalyze the conversion of atmospheric dinitrogen to bioavailable ammonia, is most commonly assayed by the reduction of acetylene gas to ethylene. Despite the practical importance of acetylene as a substrate, little is known concerning its binding or activation in the iron-rich active site. \"Fischer\u2013Tropsch\" type coupling of non-native C1 substrates to higher-order C_(\u22652) products is also known for nitrogenase, though potential metal\u2013carbon multiply bonded intermediates remain underexplored. Here we report the activation of acetylene gas at a mononuclear tris(phosphino)silyl-iron center, (SiP_3)Fe, to give Fe(I) and Fe(II) side-on adducts, including S = 1/2 Fe^I(\u03b7^2-HCCH); the latter is characterized by pulse EPR spectroscopy and DFT calculations. Reductive protonation reactions with these compounds converge at stable examples of unusual, formally iron(IV) and iron(V) carbyne complexes, as in diamagnetic (SiP_3)Fe\u2261CCH_3 and the paramagnetic cation S = 1/2 [(SiP_3)Fe\u2261CCH_3]^+. Both alkylcarbyne compounds possess short Fe\u2013C triple bonds (approximately 1.7 \u00c5) trans to the anchoring silane. Pulse EPR experiments, X-band ENDOR and HYSCORE, reveal delocalization of the iron-based spin onto the \u03b1-carbyne nucleus in carbon p-orbitals. Furthermore, isotropic coupling of the distal \u03b2-CH_3 protons with iron indicates hyperconjugation with the spin/hole character on the Fe\u2261CCH_3 unit. The electronic structures of (SiP_3)Fe\u2261CCH_3 and [(SiP_3)Fe\u2261CCH_3]^+ are discussed in comparison to previously characterized, but heterosubstituted, iron carbynes, as well as a hypothetical nitride species, (SiP_3)Fe\u2261N. Such comparisons are germane to the consideration of formally high-valent, multiply bonded Fe\u2261C and/or Fe\u2261N intermediates in synthetic or biological catalysis by iron.", "doi": "10.1021/jacs.9b06987", "pmcid": "PMC6800224", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2019-09-25", "series_number": "38", "volume": "141", "issue": "38", "pages": "15211-15221" }, { "id": "authors:7gekq-day65", "collection": "authors", "collection_id": "7gekq-day65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190503-131410286", "type": "article", "title": "Characterization of the earliest intermediate of Fe-N\u2082 protonation: CW and Pulse EPR detection of an Fe-NNH species and its evolution to Fe-NNH\u2082\u207a", "author": [ { "family_name": "Nesbit", "given_name": "Mark A.", "orcid": "0000-0002-5642-9303", "clpid": "Nesbit-Mark-A" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "Iron diazenido species (Fe(NNH)) have been proposed as the earliest intermediates of catalytic N\u2082-to-NH\u2083 conversion (N\u2082RR) mediated by synthetic iron complexes and relatedly as intermediates of N\u2082RR by nitrogenase enzymes. However, direct identification of such iron species, either during or independent of catalysis, has proven challenging owing to their high degree of instability. The isolation of more stable silylated diazenido analogues, Fe(NNSiR\u2083), and also of further downstream intermediates (e.g., Fe(NNH\u2082)), nonetheless points to Fe(NNH) as the key first intermediate of protonation in synthetic systems. Herein we show that low-temperature protonation of a terminally bound Fe-N\u2082\u2013 species, supported by a bulky trisphosphinoborane ligand (^(Ar)P\u2083^B), generates an S = 1/2 terminal Fe(NNH) species that can be detected and characterized by continuous-wave (CW) and pulse EPR techniques. The \u00b9H-hyperfine for ^(Ar)P\u2083^BFe(NNH) derived from the presented ENDOR studies is diagnostic for the distally bound H atom (a_(iso) = 16.5 MHz). The Fe(NNH) species evolves further to cationic [Fe(NNH\u2082)]\u207a in the presence of additional acid, the latter being related to a previously characterized [Fe(NNH\u2082)]\u207a intermediate of N\u2082RR mediated by a far less encumbered iron tris(phosphine)borane catalyst. While catalysis is suppressed in the present sterically very crowded system, N\u2082-to-NH\u2083 conversion can nevertheless be demonstrated. These observations in sum add support to the idea that Fe(NNH) plays a central role as the earliest intermediate of Fe-mediated N\u2082RR in a synthetic system.", "doi": "10.1021/jacs.8b12082", "pmcid": "PMC6636918", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2019-05-22", "series_number": "20", "volume": "141", "issue": "20", "pages": "8116-8127" }, { "id": "authors:dwnx0-jbv96", "collection": "authors", "collection_id": "dwnx0-jbv96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-104228298", "type": "article", "title": "Electronic Structures of an [Fe(NNR_2)]^(+/0/\u2013) Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation", "author": [ { "family_name": "Thompson", "given_name": "Niklas B.", "orcid": "0000-0003-2745-4945", "clpid": "Thompson-Niklas-B" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Dong", "given_name": "Hai T.", "orcid": "0000-0002-8914-3045", "clpid": "Dong-Hai-T" }, { "family_name": "Chalkley", "given_name": "Matthew J.", "orcid": "0000-0002-0484-7335", "clpid": "Chalkley-Matthew-J" }, { "family_name": "Zhao", "given_name": "Jiyong", "orcid": "0000-0002-0777-3626", "clpid": "Zhao-Jiyong" }, { "family_name": "Alp", "given_name": "E. Ercan", "orcid": "0000-0002-4803-8863", "clpid": "Alp-Esen-Ercan" }, { "family_name": "Hu", "given_name": "Michael", "orcid": "0000-0002-3718-7169", "clpid": "Hu-Michael-Y" }, { "family_name": "Lehnert", "given_name": "Nicolai", "orcid": "0000-0002-5221-5498", "clpid": "Lehnert-Nicolai" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "The intermediacy of metal\u2013NNH_2 complexes has been implicated in the catalytic cycles of several examples of transition-metal-mediated nitrogen (N_2) fixation. In this context, we have shown that triphosphine-supported Fe(N_2) complexes can be reduced and protonated at the distal N atom to yield Fe(NNH_2) complexes over an array of charge and oxidation states. Upon exposure to further H^+/e^\u2013 equivalents, these species either continue down a distal-type Chatt pathway to yield a terminal iron(IV) nitride or instead follow a distal-to-alternating pathway resulting in N\u2013H bond formation at the proximal N atom. To understand the origin of this divergent selectivity, herein we synthesize and elucidate the electronic structures of a redox series of Fe(NNMe_2) complexes, which serve as spectroscopic models for their reactive protonated congeners. Using a combination of spectroscopies, in concert with density functional theory and correlated ab initio calculations, we evidence one-electron redox noninnocence of the \"NNMe_2\" moiety. Specifically, although two closed-shell configurations of the \"NNR_2\" ligand have been commonly considered in the literature\u2014isodiazene and hydrazido(2\u2212)\u2014we provide evidence suggesting that, in their reduced forms, the present iron complexes are best viewed in terms of an open-shell [NNR_2]^\u2022\u2013ligand coupled antiferromagnetically to the Fe center. This one-electron redox noninnocence resembles that of the classically noninnocent ligand NO and may have mechanistic implications for selectivity in N_2 fixation activity.", "doi": "10.1021/acs.inorgchem.9b00133", "pmcid": "PMC6598684", "issn": "0020-1669", "publisher": "American Chemical Society", "publication": "Inorganic Chemistry", "publication_date": "2019-03-04", "series_number": "5", "volume": "58", "issue": "5", "pages": "3535-3549" }, { "id": "authors:ampwf-dav07", "collection": "authors", "collection_id": "ampwf-dav07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181113-112610015", "type": "article", "title": "Tetranuclear [Mn^(III)Mn_3^(IV)O_4] Complexes as Spectroscopic Models of the S_2 State of the Oxygen Evolving Complex in Photosystem II", "author": [ { "family_name": "Lee", "given_name": "Heui Beom", "orcid": "0000-0002-9550-2649", "clpid": "Lee-Heui-Beom" }, { "family_name": "Shiau", "given_name": "Angela A.", "clpid": "Shiau-Angela-A" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Marchiori", "given_name": "David A.", "orcid": "0000-0001-9738-3674", "clpid": "Marchiori-David-A" }, { "family_name": "Gul", "given_name": "Sheraz", "orcid": "0000-0001-8920-8737", "clpid": "Gul-Sheraz" }, { "family_name": "Chatterjee", "given_name": "Ruchira", "orcid": "0000-0002-0865-061X", "clpid": "Chatterjee-Ruchira" }, { "family_name": "Yano", "given_name": "Junko", "orcid": "0000-0001-6308-9071", "clpid": "Yano-Junko" }, { "family_name": "Britt", "given_name": "R. David", "orcid": "0000-0003-0889-8436", "clpid": "Britt-R-David" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "abstract": "Despite extensive biochemical, spectroscopic, and computational studies, the mechanism of biological water oxidation by the oxygen evolving complex (OEC) of Photosystem II remains a subject of significant debate. Mechanistic proposals are guided by the characterization of reaction intermediates such as the S_2 state, which features two characteristic EPR signals at g = 2 and g = 4.1. Two nearly isoenergetic structural isomers have been proposed as the source of these distinct signals, but relevant structure\u2013electronic structure studies remain rare. Herein, we report the synthesis, crystal structure, electrochemistry, XAS, magnetic susceptibility, variable temperature CW-EPR, and pulse EPR data for a series of [Mn^(III)Mn_3^(IV)O_4] cuboidal complexes as spectroscopic models of the S_2 state of the OEC. Resembling the oxidation state and EPR spectra of the S_2 state of the OEC, these model complexes show two EPR signals, a broad low field signal and a multiline signal, that are remarkably similar to the biological system. The effect of systematic changes in the nature of the bridging ligands on spectroscopy were studied. Results show that the electronic structure of tetranuclear Mn complexes is highly sensitive to even small geometric changes and the nature of the bridging ligands. Our model studies suggest that the spectroscopic properties of the OEC may also react very sensitively to small changes in structure; the effect of protonation state and other reorganization processes need to be carefully assessed.", "doi": "10.1021/jacs.8b09961", "pmcid": "PMC6574184", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2018-12-12", "series_number": "49", "volume": "140", "issue": "49", "pages": "17175-17187" }, { "id": "authors:k4n2j-kcv87", "collection": "authors", "collection_id": "k4n2j-kcv87", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180827-094622072", "type": "article", "title": "Nitric Oxide Modulates Endonuclease III Redox Activity by a 800 mV Negative Shift upon [Fe\u2084S\u2084] Cluster Nitrosylation", "author": [ { "family_name": "Ekanger", "given_name": "Levi A.", "orcid": "0000-0001-8131-1641", "clpid": "Ekanger-Levi-A" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Moradian", "given_name": "Annie", "orcid": "0000-0002-0407-2031", "clpid": "Moradian-Annie" }, { "family_name": "Sweredoski", "given_name": "Michael J.", "orcid": "0000-0003-0878-3831", "clpid": "Sweredoski-Michael-J" }, { "family_name": "Barton", "given_name": "Jacqueline K.", "orcid": "0000-0001-9883-1600", "clpid": "Barton-J-K" } ], "abstract": "Here we characterize the [Fe\u2084S\u2084] cluster nitrosylation of a DNA repair enzyme, endonuclease III (EndoIII), using DNA-modified gold electrochemistry and protein film voltammetry, electrophoretic mobility shift assays, mass spectrometry of whole and trypsin-digested protein, and a variety of spectroscopies. Exposure of EndoIII to nitric oxide under anaerobic conditions transforms the [Fe\u2084S\u2084] cluster into a dinitrosyl iron complex, [(Cys)_2Fe(NO)_2]\u2212, and Roussin's red ester, [(\u03bc-Cys)_2Fe_2(NO)\u2084], in a 1:1 ratio with an average retention of 3.05 \u00b1 0.01 Fe per nitrosylated cluster. The formation of the dinitrosyl iron complex is consistent with previous reports, but the Roussin's red ester is an unreported product of EndoIII nitrosylation. Hyperfine sublevel correlation (HYSCORE) pulse EPR spectroscopy detects two distinct classes of NO with ^(14)N hyperfine couplings consistent with the dinitrosyl iron complex and reduced Roussin's red ester. Whole-protein mass spectrometry of EndoIII nitrosylated with ^(14)NO and ^(15)NO support the assignment of a protein-bound [(\u03bc-Cys)_2Fe_2(NO))_4] Roussin's red ester. The [Fe\u2084S\u2084]^(2+/3+) redox couple of DNA-bound EndoIII is observable using DNA-modified gold electrochemistry, but nitrosylated EndoIII does not display observable redox activity using DNA electrochemistry on gold despite having a similar DNA-binding affinity as the native protein. However, direct electrochemistry of protein films on graphite reveals the reduction potential of native and nitrosylated EndoIII to be 127 \u00b1 6 and \u2212674 \u00b1 8 mV vs NHE, respectively, corresponding to a shift of approximately \u2212800 mV with cluster nitrosylation. Collectively, these data demonstrate that DNA-bound redox activity, and by extension DNA-mediated charge transport, is modulated by [Fe\u2084S\u2084] cluster nitrosylation.", "doi": "10.1021/jacs.8b07362", "pmcid": "PMC6186442", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2018-09-19", "series_number": "37", "volume": "140", "issue": "37", "pages": "11800-11810" }, { "id": "authors:24k4c-8z842", "collection": "authors", "collection_id": "24k4c-8z842", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180813-133514351", "type": "article", "title": "Structural and mechanistic analysis of the arsenate respiratory reductase provides insight into environmental arsenic transformations", "author": [ { "family_name": "Glasser", "given_name": "Nathaniel R.", "orcid": "0000-0002-2833-5166", "clpid": "Glasser-Nathaniel-R" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Osborne", "given_name": "Thomas H.", "clpid": "Osborne-Thomas-H" }, { "family_name": "Santini", "given_name": "Joanne M.", "clpid": "Santini-Joanne-M" }, { "family_name": "Newman", "given_name": "Dianne K.", "orcid": "0000-0003-1647-1918", "clpid": "Newman-D-K" } ], "abstract": "Arsenate respiration by bacteria was discovered over two decades ago and is catalyzed by diverse organisms using the well-conserved Arr enzyme complex. Until now, the mechanisms underpinning this metabolism have been relatively opaque. Here, we report the structure of an Arr complex (solved by X-ray crystallography to 1.6-\u00c5 resolution), which was enabled by an improved Arr expression method in the genetically tractable arsenate respirer Shewanella sp. ANA-3. We also obtained structures bound with the substrate arsenate (1.8 \u00c5), the product arsenite (1.8 \u00c5), and the natural inhibitor phosphate (1.7 \u00c5). The structures reveal a conserved active-site motif that distinguishes Arr [(R/K)GRY] from the closely related arsenite respiratory oxidase (Arx) complex (XGRGWG). Arr activity assays using methyl viologen as the electron donor and arsenate as the electron acceptor display two-site ping-pong kinetics. A Mo(V) species was detected with EPR spectroscopy, which is typical for proteins with a pyranopterin guanine dinucleotide cofactor. Arr is an extraordinarily fast enzyme that approaches the diffusion limit (K_m = 44.6 \u00b1 1.6 \u03bcM, k_(cat) = 9,810 \u00b1 220 seconds^(\u22121)), and phosphate is a competitive inhibitor of arsenate reduction (K_i = 325 \u00b1 12 \u03bcM). These observations, combined with knowledge of typical sedimentary arsenate and phosphate concentrations and known rates of arsenate desorption from minerals in the presence of phosphate, suggest that (i) arsenate desorption limits microbiologically induced arsenate reductive mobilization and (ii) phosphate enhances arsenic mobility by stimulating arsenate desorption rather than by inhibiting it at the enzymatic level.", "doi": "10.1073/pnas.1807984115", "pmcid": "PMC6140538", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2018-09-11", "series_number": "37", "volume": "115", "issue": "37", "pages": "E8614-E8623" }, { "id": "authors:dm1gs-kxk98", "collection": "authors", "collection_id": "dm1gs-kxk98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180424-082955413", "type": "article", "title": "An S = \u00bd iron complex featuring N\u2082, thiolate, and hydride ligands: Reductive elimination of H\u2082 and relevant thermochemical Fe-H parameters", "author": [ { "family_name": "Gu", "given_name": "Nina X.", "orcid": "0000-0002-4637-8418", "clpid": "Gu-Nina-X" }, { "family_name": "Oyala", "given_name": "Paul H.", "orcid": "0000-0002-8761-4667", "clpid": "Oyala-Paul-H" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "abstract": "Believed to accumulate on the Fe sites of the FeMo-cofactor (FeMoco) of MoFe-nitrogenase under turnover, strongly donating hydrides have been proposed to facilitate N\u2082 binding to Fe and may also participate in the hydrogen evolution process concomitant to nitrogen fixation. Here, we report the synthesis and characterization of a thiolate-coordinated Fe^(III)(H)(N\u2082) complex, which releases H\u2082 upon warming to yield an Fe^(II)\u2013N\u2082\u2013Fe^(II) complex. Bimolecular reductive elimination of H\u2082 from metal hydrides is pertinent to the hydrogen evolution processes of both enzymes and electrocatalysts, but well-defined examples are uncommon and usually observed from diamagnetic second- and third-row transition metals. Kinetic data obtained on the HER of this ferric hydride species are consistent with a bimolecular reductive elimination pathway, arising from cleavage of the Fe\u2013H bond with a computationally determined BDFE of 55.6 kcal/mol.", "doi": "10.1021/jacs.8b02603", "pmcid": "PMC6592702", "issn": "0002-7863", "publisher": "American Chemical Society", "publication": "Journal of the American Chemical Society", "publication_date": "2018-05-23", "series_number": "20", "volume": "140", "issue": "20", "pages": "6374-6382" } ]