[ { "id": "authors:t56n7-zsz63", "collection": "authors", "collection_id": "t56n7-zsz63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170911-105731907", "type": "conference_item", "title": "Chemistry on a slide: Hydration gradient effects on rates and mechanisms at the air-water interface", "author": [ { "family_name": "Colussi", "given_name": "Agust\u00edn J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "Online electrospray pneumatic ionization mass spectroscopy of aq. microjets exposed to reactive gases has\nprovided unprecedented insights on the unique chem. that takes place in the outermost water layers of water.\nAfter describing essential tech. features, I will illustrate how water's steep interfacial d. gradient affects the\nrates and mechanisms of reactive interfacial events. Fenton chem. in O_3 (g) or H_2O_2(g) collisions with the\nsurface of aq. Fe^(2+) microjets proceeds \u223c10^3 times faster than in bulk water satd. with these gases, and\ngenerates mono- and poly-iron, high-valent, high-spin Fe(II/III)_n \u00b7Fe(IV)=O metal-oxos in high yields. The\nincomplete hydration shell of interfacial Fe^(2+) appears to support the barrierless approach of O_3/H_2O_2, and,\nhence, facilitate 2-e- O-atom over 1-e- transfers. The unambiguous mass-specific identification of metal-oxos let\nus characterize the higher reactivity of interfacial poly-iron species as O-atom donors. The ozonolysis of\nsesquiterpene solutes by O_3(g) yields Criegee intermediates at the interface, which react at similar rates with\nmM alkyl-C(O)OH acids and 23 M H_2O in MeCN:H O::4:1. Since both reactions proceed at very similar rates in\nthe gas-phase, our finding is consistent with interfacial H_2O concns. that are significantly lower than in bulk\nwater. In the oxidn. of aq. (H_2O, D_2O) benzoate-h5 and -d5 by .bul.OH(g), isotopic labeling lets us identify the\nphenyl-peroxyl radicals that ensue H-abstraction by .bul.OH and establish a lower bound (\u223c26%) for this\nprocess in interfacial water. This finding stands in marked contrast with the negligible extent of H-abstraction\nby .bul.OH both in the gas-phase and bulk water. The enhancement of H-atom abstraction in interfacial water\nis consistent with the relative destabilization of the more polar transition state for .bul.OH addn. vs. Habstraction\ndue to incomplete solvation at the low interfacial water densities.", "publisher": "Caltech Library", "publication_date": "2017-08" }, { "id": "authors:qfw2j-jnz10", "collection": "authors", "collection_id": "qfw2j-jnz10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170911-111125979", "type": "conference_item", "title": "Processing of unsaturated carboxylic acids by ozone at the air-water interface: Implications for aerosol aging", "author": [ { "family_name": "Li", "given_name": "Lijie", "orcid": "0000-0002-7988-6208", "clpid": "Li-Lijie" }, { "family_name": "Colussi", "given_name": "Agust\u00edn J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" }, { "family_name": "Enami", "given_name": "Shinichi", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Org. matter contributes 20% to 90% of PM_(2.5) mass concns. in the troposphere. Unsatd. carboxylic acids are widespread in org. aerosols. Double bonds (C=C) in unsatd. species are generally oxidized by electrophilic ozone. In contrast with the ozonation of unsatd. species in the gas phase, the mechanism and products of their ozonation on the surface of aq. org. aerosols are unknown. In the gas-phase, O_3 adds to olefinic double bonds generating chem. activated ozonides, which rapidly decomp. into carbonyl oxide Criegee (CIs) intermediates. The fate of gas-phase Criegee intermediates (CIs) in the troposphere is detd. by their reactions with water and water clusters. Our recent studies on the CIs produced on air-water interfaces (AWIs) by the\nin situ ozonation of sesquiterpenes have showed that millimolar n-alkyl-COOH acids are able to compete for CIs\nwith water. In this work, we investigate the ozonation of unsatd. carboxylic acids at air-water interface.\nOur work focuses on the impacts of mol. structure on the products of the interfacial ozonation of unsatd.\ncarboxylic acid by O_3(g). Our studies were conducted by means of our online electrospray mass spectrometry\n(o-ESI-MS), which probes the compn. of reactive interfacial layers within 1 ms. We have used o-ESI-MS to investigate for the first time the ozonation of various aerosol components at the AWIs, such as phenol, \u03b1-humulene and \u03b2-caryophyllene. In this study, we explore the intramol. and intermol. products from reactions of the CIs derived from the interfacial ozonation of various unsatd. carboxylic acids. We present results on how products depend on the alkene structure (cyclic or linear) and the sepn. of olefinic double bonds from the -COOH functionality. The competition between intramol. and intermol. addn. of -COOH and the reaction of CIs with H_2O is discussed. This work evaluates the contribution of different unsatd. carboxylic acids to aerosol aging and the potential pathways to extremely low volatility org. compds. (ELVOCs) through multiphase reactions.", "publisher": "Caltech Library", "publication_date": "2017-08" }, { "id": "authors:3gyzf-rbm55", "collection": "authors", "collection_id": "3gyzf-rbm55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140815-092403688", "type": "conference_item", "title": "Working hypothesis on the mechanism of the synergic adverse effects of ambient ozone and PM2.5 particulates", "author": [ { "family_name": "Colussi", "given_name": "Agust\u00edn J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" }, { "family_name": "Enami", "given_name": "Shinichi", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "The pulmonary epithelium is protected against atm. ozone O_3(g) by a fluid film (ELF) contg. ascorbic acid (AH2) and related antioxidants. This mechanism of protection however fails if co-pollutants redirect AH_2 and O_3(g) into species that can transduce oxidative damage to underlying tissues. We have shown (Enami et al., PNAS 2008) that, whereas the ozonation of ascorbate AH-[pK_a(AH_2) = 4.1] under physiol. conditions yields innocuous dehydroascorbic acid, the ozonation of AH_2 in pH < 5 acidic media generates a cytotoxic ozonide. On this basis we speculated that acidic particulates, by acidifying ELF below its normal pH = 6.9 value, would disable its protective antioxidant function. Here we refine our proposal by showing that the typical buffer capacities of ELF's (\u223c 10 mM/pH) prevent their direct (chem.) acidification by the inhalation of polluted ambient air contg. representative acidic particulate loadings (< 100 mg/m^3). We propose instead, on the basis of extensive clin. and physiol. studies on the innate lung host defense response, that ELF acidification is mediated by inflammatory reaction to acidic particulates. On this basis, ultrafine particulates, which reach the alveoli whose ELF is \u223c 50 times thinner than that of the airways, are expected to be pose a particularly aggressive challenge to underlying alveolar macrophages.", "publisher": "Caltech Library", "publication_date": "2014-08" }, { "id": "authors:bne8q-a6j30", "collection": "authors", "collection_id": "bne8q-a6j30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140815-093148885", "type": "conference_item", "title": "Fenton oxidation of gaseous isoprene nonaqueous aerosol surfaces", "author": [ { "family_name": "Colussi", "given_name": "Agust\u00edn J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" }, { "family_name": "Kameel", "given_name": "Rifkha", "clpid": "Kameel-R" }, { "family_name": "Friboni", "given_name": "Francesca", "clpid": "Friboni-F" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "We report that gas-phase isoprene ISO(g) is oxidized upon impacting the surface of aq. FeCl_2 solns. simultaneously exposed to H_2O_2(g). Expts. involve exposing microjets of micromolar FeCl_2 solns. at pH < 4 to ISO(g) + H_2O_2(g) mixts. for \u223c 10 \u03bcs within the spraying chamber of an electrospray ionization mass spectrometer (ESI-MS). Products are analyzed online in the pos. and neg. ion modes. We detect protonated monomer and oligomer species (ISO)_(1-8)H+, in accord with our previous report (J. Chem. A, 116 2012 6027), plus myriad (m/z) > 150 oxidn. products whose combined yields amt. to \u223c 5% of (ISO)_(1-8)H+. MS/MS anal. reveals that pos. ions typically split H_2O and O neutrals, whereas the less abundant neg. ions undergo CO, H_2O and CO_2 losses. All products are inhibited by the addn. of excess t-butanol to FeCl_2 solns. as \u00d7OH scavenger. These results implicate an oxidn. process initiated by the addn. of interfacial OH and/or HO_2 to ISO leading to poly-alcs., carbonyls, hydroperoxides and carboxylic acids. We infer that gaseous olefins can be oxidized upon impacting the surface of Fe-contg. aq. environmental surfaces, including those of aerosols.", "publisher": "Caltech Library", "publication_date": "2014-08" }, { "id": "authors:bmzfq-tec61", "collection": "authors", "collection_id": "bmzfq-tec61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130729-103126540", "type": "conference_item", "title": "First principles based theory complemented with electrospray ionization mass spectrometry to address environmental abiotic and biotic reactions", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Mishra", "given_name": "Himanshu", "clpid": "Mishra-Himanshu" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" }, { "family_name": "Pascal", "given_name": "Tod A.", "orcid": "0000-0003-2096-1143", "clpid": "Pascal-T-A" }, { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-R-J" } ], "abstract": "We will summarize recent advances in First-principles based methods for predicting interfacial entropy and free energy with\napplications to reactions at surfaces of water contg. various electrolytes. At Caltech, we have recently adapted an electrospray\nionization mass spectrometer to selectively probe physicochem. phenomena on liq. surfaces. Thus, together with theory and\nexpts. we have demonstrated that (1) anions present at air-water interface can electrostatically preorganize surrounding water\nmols. to facilitate proton transfer events, (2) the neg. charge of the air-water interface is due to the presence of excess OH- at\nthe aerial interface with a point-of-zero-charge at pH \u223c 3, and (3) rate enhancements obsd. in the proton catalyzed reactions at\nfluctuating aq. interfaces is due to inadequate hydration of hydronium, H_3O+. These findings should further our understanding\nof atm. chem., colloidal science, 'on-water' and enzymic catalysis and proton transfer reactions along and across membranes,\nincluding fuel cells and cellular processes.", "publisher": "Caltech Library", "publication_date": "2013-04" }, { "id": "authors:zhjtw-3f798", "collection": "authors", "collection_id": "zhjtw-3f798", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120816-084429838", "type": "conference_item", "title": "Proton availability at the air/aerosol/water interface", "author": [ { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" } ], "abstract": "The acidity of the water surface of aquated aerosols is examd. in expts. in which the uptake of gaseous trimethylamine,\nTMA, as TMAH+ on the surface of aquated aerosols is monitored via online electrospray mass spectrometry as a\nfunction of bulk pH, pHb. TMAH+ signal intensities track pHb along a titrn. curve displaying an equivalence point at pHb\n= 3.2, instead of the pKa(TMA) = 10.0 value measured on aq. TMA-HCl microdroplets. Inert X+ (X = Li, Na) cations,\nhowever, catalyze TMA uptake at pHb 4. The direct kinetic hydrogen isotope effects (1 < TMAH+/TMAD+ < 3.5 on\nH2O/D2O microdroplets) assocd. with TMA uptake enhancements reveal that they are driven by the competitive\nprotonation (vs. desorption) of interfacial TMA. These outcomes are consistent with thermochem. data on gas-phase\nclusters showing that TMA can be protonated by the stronger acid H2O only after extensive solvation, but readily so by\nH3O+ or small (H2O)n.4Li+ clusters at the interface. We infer that protons become available at the aerial interface of\nneat water about its isoelec. point pIw = 3.2 rather than below pHb 7, and over broader pHb ranges in the presence of\nother cations.", "publisher": "Caltech Library", "publication_date": "2010-12" }, { "id": "authors:zknyk-5yb09", "collection": "authors", "collection_id": "zknyk-5yb09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120816-083912624", "type": "conference_item", "title": "Experimental acidity of the water surface", "author": [ { "family_name": "Colussi", "given_name": "A. J.", "orcid": "0000-0002-3400-4101", "clpid": "Colussi-A-J" }, { "family_name": "Enami", "given_name": "S.", "orcid": "0000-0002-2790-7361", "clpid": "Enami-Shinichi" }, { "family_name": "Hoffmann", "given_name": "M. R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "The acidity experienced by gases colliding with the water surface is herein investigated in expts. where the protonation of\ngaseous trimethylamine on water microjets is monitored by online electrospray mass spectrometry as a function of pH of\nthe bulk liq. (pHBLK). Trimethylammonium (TMAH+) signal intensities track pHBLK along a titrn. curve displaying an\nequivalence point at pHBLK ~ 3.8 that is significantly smaller than the acidity const. pKA(TMAH+) = 9.8 in bulk soln. The\nprotonation of TMA above pHBLK 4 is strongly enhanced by the addn. of up to ~ 1 mM inert Li+ or Na+, and weakly\ninhibited at higher concns. Enhanced TMA protonation is always accompanied by direct kinetic solvent hydrogen isotope\neffects. Since TMA(g) can be protonated by bare H3O+, and by H2O only upon extensive solvent participation, we infer\nthat H3O+ emerges and becomes available at the surface of neat water below pHBLK 4.", "publisher": "Caltech Library", "publication_date": "2010-12" } ]