Harry B. Gray

California Institute of Technology, Pasadena, California, United States

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Publications (852)6121.58 Total impact

  • Journal of Physical Chemistry Letters 05/2015; 6(9):1679-1683. DOI:10.1021/acs.jpclett.5b00495 · 6.69 Impact Factor
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    ABSTRACT: The mechanistic features of oligomerization and oxidative cyclization steps in the synthesis of tris(pentafluorophenyl)corrole (1) have been thoroughly studied. Separation of the intermediates by preparative HPLC and analysis by NMR spectroscopy and high resolution mass spectrometry allowed for the identification of product-forming intermediates and monitoring of undesired byproducts. Conditions for complete end-capping with pyrrole were optimized for improved yields of oligomers leading to the desired corrole 1. A yield of 84 % was achieved during oxidation of an isolated precursor; the overall yield of 1 was 17.0 %.
    European Journal of Organic Chemistry 04/2015; 2015(14). DOI:10.1002/ejoc.201500276 · 3.15 Impact Factor
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    ABSTRACT: A scanning probe image of single-layer MoS2 trapping water on a mica surface is depicted on the left, with its corresponding photoluminescence image depicted on the right. The trapped water strongly quenches the fluorescence of single-layer MoS2 and distinctly affects its optical properties. The work by J. R. Heath and co-workers on page 2734 highlights the significance of the local chemical environment in determining the opto-electronic properties of 2D materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 03/2015; 27(17). DOI:10.1002/adma.201500555 · 15.41 Impact Factor
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    ABSTRACT: [Pt2(μ-P2O5H2)4](4-) (Pt(pop)) and its perfluoroborated derivative [Pt2(μ-P2O5(BF2)2)4](4-) (Pt(pop-BF2)) are d(8)-d(8) complexes whose electronic excited states can drive reductions and oxidations of relatively inert substrates. We performed spin-orbit (SO) TDDFT calculations on these complexes that account for their absorption spectra across the entire UV-vis spectral region. The complexes exhibit both fluorescence and phosphorescence attributable, respectively, to singlet and triplet excited states of dσ*pσ origin. These features are energetically isolated from each other (∼7000 cm(-1) for (Pt(pop-BF2)) as well as from higher-lying states (5800 cm(-1)). The lowest (3)dσ*pσ state is split into three SO states by interactions with higher-lying singlet states with dπpσ and, to a lesser extent, pπpσ contributions. The spectroscopically allowed dσ*pσ SO state has ∼96% singlet character with small admixtures of higher triplets of partial dπpσ and pπpσ characters that also mix with (3)dσ*pσ, resulting in a second-order (1)dσ*pσ-(3)dσ*pσ SO interaction that facilitates intersystem crossing (ISC). All SO interactions involving the dσ*pσ states are weak because of large energy gaps to higher interacting states. The spectroscopically allowed dσ*pσ SO state is followed by a dense manifold of ligand-to-metal-metal charge transfer states, some with pπpσ (at lower energies) or dπpσ contributions (at higher energies). Spectroscopically active higher states are strongly spin-mixed. The electronic structure, state ordering, and relative energies are minimally perturbed when the calculation is performed at the optimized geometries of the (1)dσ*pσ and (3)dσ*pσ excited states (rather than the ground state). Results obtained for Pt(pop) are very similar, showing slightly smaller energy gaps and, possibly, an additional (1)dσ*pσ - (3)dσ*pσ second order SO interaction involving higher (1)dπpσ* states that could account in part for the much faster ISC. It also appears that (1)dσ*pσ → (3)dσ*pσ ISC requires a structural distortion that has a lower barrier for Pt(pop) than for the more rigid Pt(pop-BF2).
    Inorganic Chemistry 03/2015; 54(7). DOI:10.1021/acs.inorgchem.5b00063 · 4.79 Impact Factor
  • Jay R Winkler, Harry B Gray
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    ABSTRACT: Single-step electron tunnelling reactions can transport charges over distances of 15-20 Åin proteins. Longer-range transfer requires multi-step tunnelling processes along redox chains, often referred to as hopping. Long-range hopping via oxidized radicals of tryptophan and tyrosine, which has been identified in several natural enzymes, has been demonstrated in artificial constructs of the blue copper protein azurin. Tryptophan and tyrosine serve as hopping way stations in high-potential charge transport processes. It may be no coincidence that these two residues occur with greater-than-average frequency in O2- and H2O2-reactive enzymes. We suggest that appropriately placed tyrosine and/or tryptophan residues prevent damage from high-potential reactive intermediates by reduction followed by transfer of the oxidizing equivalent to less harmful sites or out of the protein altogether. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 03/2015; 373(2037). DOI:10.1098/rsta.2014.0178 · 2.86 Impact Factor
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    ABSTRACT: fac-[(L)Mn(CO)3]- , where L = bis alkyl-substituted bipyridine, catalyzes electrochemical reduction of CO2 to CO in the presence of trifluoroethanol (TFEH). Here we report the atomistic level mechanism of complete catalytic cycles for this reaction, using DFT methods (B3LYP-d3 with continuum solvation) to compute free energies of reaction and activation, as well as reduction potentials for all catalytically relevant elementary steps. In the catalytic cycle for CO formation, CO2 coordinates to fac-[(L)Mn(CO)3]- (1) (L = bpy), and the adduct (2) is protonated to form [(L)Mn(CO)3(CO2H)] (3). 3 reacts to form [(L)Mn(CO)4]0 (5) via one of two pathways: TFEH-mediated dehydroxylation to [(L)Mn(CO)4]+ (4), followed by one-electron reduction to 5; or, under more reducing potentials, one electron reduction to [(L)Mn(CO)3(CO2H)]- (3’), followed by dehydroxylation to 5. The latter pathway has a lower activation energy yielding higher reaction rates at higher overpotentials. Finally 5 is reduced upon CO dissociation to regenerate 1. The highly exergonic homoconjugation and carbonation of TFE- play a critical role in reaction thermodynamics and kinetics. Based on the analogous free energy surface for L = bipyrimidine (not yet studied experimentally), we predict the faster CO2 reduction pathway (via dehydroxylation of 3’ to 5) dominates even at zero overpotential, albeit at the expense of a somewhat higher kinetic barrier (by ca. 2 kcal mol-1). The various factors contributing to product selectivity (CO over H2) are discussed.
    ACS Catalysis 02/2015; 5(4):150216174835004. DOI:10.1021/cs501963v · 7.57 Impact Factor
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    ABSTRACT: Modular syntheses of oligoarylisocyanide ligands that are derivatives of 2,6-diisopropylphenyl isocyanide (CNdipp) have been developed; tungsten complexes incorporating these oligoarylisocyanide ligands exhibit intense metal-to-ligand charge-transfer visible absorptions that are red-shifted and more intense than those of the parent W(CNdipp)6 complex. Additionally, these W(CNAr)6 complexes have enhanced excited-state properties, including longer lifetimes and very high quantum yields. The decay kinetics of electronically excited W(CNAr)6 complexes (*W(CNAr)6) show solvent dependences; faster decay is observed in higher dielectric solvents. *W(CNAr)6 lifetimes are temperature dependent, suggestive of a strong coupling nonradiative decay mechanism that promotes repopulation of the ground state. Notably, *W(CNAr)6 complexes are exceptionally strong reductants: [W(CNAr)6](+)/*W(CNAr)6 potentials are more negative than -2.7 V vs [Cp2Fe](+)/Cp2Fe.
    Journal of the American Chemical Society 01/2015; 137(3). DOI:10.1021/ja510973h · 11.44 Impact Factor
  • Journal of Visualized Experiments 01/2015; DOI:10.3791/52355
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    ABSTRACT: Transient absorption decay rate constants (kobs) for reactions of electronically excited zinc tetraphenylporphyrin (3ZnTPP*) with triruthenium oxo-centered acetate-bridged clusters [Ru3(µ3-O)(µ-CH3CO2)6(CO)(L)]2(µ-pz), where pz = pyrazine and L = 4-cyanopyridine (cpy) (1), pyridine (py) (2), or 4-dimethylaminopyridine (dmap) (3), were obtained from nanosecond flash-quench spectroscopic data (quenching constants, kq, for 3ZnTPP*/1 - 3 are 3.0 × 109, 1.5 ×109, and 1.1 × 109 M-1s-1, respectively). Values of kq for reactions of 3ZnTPP* with 1 - 3 and Ru3(µ3-O)(µ-CH3CO2)6(CO)(L)2 [L = cpy (4), py (5), dmap (6)] monomeric analogues suggest that photoinduced electron transfer is the main pathway of excited-state decay; this mechanistic proposal is consistent with results from a photolysis control experiment, where growth of characteristic near-IR absorption bands attributable to reduced (mixed-valence) Ru-cluster products were observed.
    The Journal of Physical Chemistry B 12/2014; DOI:10.1021/jp511213p · 3.38 Impact Factor
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    ABSTRACT: Bismuth vanadate is a promising photoanode material, but recent reports on undoped BiVO4 without sublayers and co-catalysts showed large variations in photocurrent generation. We addressed this issue by correlating photoelectrochemical performance with physical properties. We devised a novel anodic electrodeposition procedure with iodide added to the aqueous plating bath, which allowed us to prepare BiVO4 photoanodes with virtually identical thicknesses but different morphologies, and we could control surface Bi content. Morphologies were quantified from SEM images as distributions of crystallite areas and aspect-ratio-normalised diameters, and their statistical moments were derived. We could obtain clear photocurrent generation trends only from bivariate data analysis. Our experimental evidence suggests that a combination of low Bi/V ratio, small aspect-ratio-normalised diameters, and crystallites sizes that were small enough to provide efficient charge separation yet sufficiently large to prevent mass transport limitations led to highest photoelectrochemical performance.
    12/2014; 2(3). DOI:10.1039/C4MH00156G
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    ABSTRACT: Over the last 5 years, researchers at the California Institute of Technology and several partner institutions have been executing a set of public outreach programs unified under the name “The Solar Army.” These programs involve students of all ages, from those in primary school to adults, in the enterprise of cutting-edge solar energy research. Herein we present our experience as a case study, outlining the context, history, and structure of the Solar Army and providing perspectives from many of its leaders on their experiences in the program.
    12/2014; 3(4). DOI:10.1166/rase.2014.1076
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    ABSTRACT: We report syntheses and structures of pentamethylcyclopentadienyl (Cp*) rhodium(III) and rhodium(I) complexes. Dicationic rhodium(III) complexes, [Cp*Rh(bpy)(MeCN)](PF6)(2) and [Cp*Rh(vbpy)(MeCN)](PF6)(2) (bpy = 2,2'-bipyridyl and vbpy = 4-vinyl-2,2'-bipyridyl), were prepared by treatment of [Cp*Rh(MeCN)(3)](PF6)(2) with bpy and vbpy, respectively. The monocationic rhodium(III) complex, [Cp*Rh(Me(4)phen)Cl]Cl (Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline), was prepared by treatment of the chloride-bridged rhodium dimer, [Cp*RhCl2](2), with Me(4)phen. Two rhodium(I) complexes were synthesized via reduction of their rhodium(III) counterparts using two different methods: Cp*Rh(bpy) was produced via a new route involving treatment of [Cp*Rh(bpy)Cl]Cl with thallium formate in dry acetonitrile, whereas [Cp*Rh(Me(4)phen)Cl]Cl was reduced with Na(Hg) to give Cp*Rh(Me(4)phen). The colors of the Rh(I) complexes are attributable to relatively intense visible-region MLCT absorptions.
    Polyhedron 12/2014; 84:14-18. DOI:10.1016/j.poly.2014.05.022 · 2.05 Impact Factor
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    ABSTRACT: We report the preparation of a dicobalt compound with two singly proton-bridged cobaloxime units linked by a central [BO4] bridge. Reaction of a doubly proton-bridged cobaloxime complex with trimethyl borate afforded the compound in good yield. Single-crystal X-ray diffraction studies confirmed the bridging nature of the [BO4] moiety. Using electrochemical methods, the dicobalt complex was found to be an electrocatalyst for proton reduction in acetonitrile solution. Notably, the overpotential for proton reduction (954 mV) was found to be higher than in the cases of two analogous single-site cobalt glyoximes under virtually identical conditions.
    Inorganic Chemistry 11/2014; 53(24). DOI:10.1021/ic501804h · 4.79 Impact Factor
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    ABSTRACT: We are investigating the biological and biomedical imaging roles and impacts of fluorescent metallocorrole-TiO2 nanoconjugates as potential near-infrared optical contrast agents in vitro in cancer and normal cell lines. The TiO2 nanoconjugate labeled with the small molecule 2,17-bis(chlorosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato aluminum(III) (1-Al-TiO2) was prepared. The nanoparticle 1-Al-TiO2 was characterized by transmission electron microscopy (TEM) and integrating-sphere electronic absorption spectroscopy. TEM images of three different samples of TiO2 nanoparticles (bare, H2O2 etched, and 1-Al functionalized) showed similarity in shapes and sizes with an average diameter of 29 nm for 1-Al-TiO2. Loading of 1-Al on the TiO2 surfaces was determined to be ca. 20-40 mg 1-Al/g TiO2. Confocal fluorescence microscopy (CFM) studies of luciferase-transfected primary human glioblastoma U87-Luc cells treated with the nanoconjugate 1-Al-TiO2 as the contrast agent in various concentrations were performed. The CFM images revealed that 1-Al-TiO2 was found inside the cancer cells even at low doses (0.02-2 mu g/mL) and localized in the cytosol. Bioluminescence studies of the U87-Luc cells exposed to various amounts of 1-Al-TiO2 showed minimal cytotoxic effects even at higher doses (2-2000 mu g/mL) after 24 h. A similar observation was made using primary mouse hepatocytes (PMH) treated with 1-Al-TiO2 at low doses (0.0003-3 mu g/mL). Longer incubation times (after 48 and 72 h for U87-Luc) and higher doses (>20 mu g/mL 1-Al-TiO2 for U87-Luc and >3 mu g/mL 1-Al-TiO2 for PMH) showed decreased cell viability.
    Journal of Inorganic Biochemistry 11/2014; 140:39–44. DOI:10.1016/j.jinorgbio.2014.06.015 · 3.27 Impact Factor
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    ABSTRACT: The reduced CoI states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we analyze the low-energy electronic absorption bands of two cobaloxime systems experimentally and use a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.
    ChemPhysChem 10/2014; 15(14). DOI:10.1002/cphc.201402398 · 3.36 Impact Factor
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    ABSTRACT: Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450-550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16-0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10(-3), in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0-5.5 ps and then decays via recombination to the triplet or ground states in 0.9-3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11-22 ps.
    The Journal of Physical Chemistry C 09/2014; 118(38):21834-21845. DOI:10.1021/jp506855t · 4.84 Impact Factor
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    ABSTRACT: Surfactant-free mixed-metal hydroxide water oxidation nanocatalysts were synthesized by pulsed-laser ablation in liquids. In a series of [Ni-Fe]-layered double hydroxides with intercalated nitrate and water, [Ni1-xFex(OH)2](NO3)y(OH)x-y•nH2O, higher activity was observed as the amount of Fe decreased to 22%. Addition of Ti4+ and La3+ ions further enhanced electrocatalysis, with a lowest overpotential of 260 mV at 10 mA cm-2. Electrocata-lytic water oxidation activity increased with the relative pro-portion of a 405.1 eV N 1s (XPS binding energy) species in the nanosheets.
    Journal of the American Chemical Society 09/2014; 136(38). DOI:10.1021/ja506087h · 11.44 Impact Factor
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    ABSTRACT: We have synthesized and characterized a water-soluble gold(III) corrole (1-Au) that is highly toxic to cisplatin-resistant cancer cells. Relative to its 1-Ga analogue, axial ligands bind only weakly to 1-Au, which likely accounts for its lower affinity for human serum albumin. We suggest that the cytotoxicity of 1-Au may be related to this lower HSA affinity.
    Chemical Communications 09/2014; 50(89). DOI:10.1039/C4CC06577H · 6.72 Impact Factor
  • Peter Agbo, James R Heath, Harry B Gray
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    ABSTRACT: We report a general kinetics model for catalytic dioxygen reduction on multicopper oxidase (MCO) cathodes. Our rate equation combines Butler-Volmer (BV) electrode kinetics and the Michaelis-Menten (MM) formalism for enzymatic catalysis, with the BV model accounting for interfacial electron transfer (ET) between the electrode surface and the MCO type 1 copper site. Extending the principles of MM kinetics to this system produced an analytical expression incorporating the effects of subsequent intramolecular ET and dioxygen binding to the trinuclear copper cluster into the cumulative model. We employed experimental electrochemical data on Thermus thermophilus laccase as benchmarks to validate our model, which we suggest will aid in the design of more efficient MCO cathodes. In addition, we demonstrate the model's utility in determining estimates for both the electronic coupling and average distance between the laccase type-1 active site and the cathode substrate.
    Journal of the American Chemical Society 09/2014; 136(39). DOI:10.1021/ja5077519 · 11.44 Impact Factor
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    ABSTRACT: Although II-VI semiconductors such as CdS, CdTe, CdSe, ZnTe, and alloys thereof, can have nearly ideal band gaps and band-edge positions for the production of solar fuels, II-VI photoanodes are well-known to be unstable towards photocorrosion or photopassivation when in contact with aqueous electrolytes. Atomic-layer deposition (ALD) of amorphous, “leaky” TiO2 films coated with thin films or islands of Ni oxide has been shown to robustly protect Si, GaAs, and other III-V materials from photocorrosion and therefore to facilitate the robust, solar-driven photoelectrochemical oxidation of H2O to O2(g). We demonstrate herein that ALD-deposited 140-nm thick amorphous TiO2 films also effectively protect single crystalline n-CdTe photoanodes from corrosion or passivation. An n-CdTe/TiO2 electrode with a thin overlayer of a Ni-oxide based oxygen-evolution electrocatalyst produced 435 ± 15 mV of photovoltage with a light-limited current density of 21 ± 1 mA cm-2 under 100 mW cm-2 of simulated Air Mass 1.5 illumination. The ALD-deposited TiO2 films are highly optically transparent and electrically conductive. We show that an n-CdTe/TiO2/Ni oxide electrode enables the stable solar-driven oxidation of H2O to O2(g) in strongly alkaline aqueous solutions, where passive, intrinsically safe, efficient systems for solar-driven water-splitting can be operated.
    Energy & Environmental Science 08/2014; 7(10). DOI:10.1039/C4EE01914H · 15.49 Impact Factor

Publication Stats

26k Citations
6,121.58 Total Impact Points

Institutions

  • 1970–2015
    • California Institute of Technology
      • • Beckman Institute
      • • Division of Chemistry and Chemical Engineering
      • • Jet Propulsion Laboratory
      • • Arthur Amos Noyes Laboratory of Chemical Physics
      Pasadena, California, United States
  • 2002–2012
    • Technion - Israel Institute of Technology
      • Schulich Faculty of Chemistry
      H̱efa, Haifa, Israel
    • The Chinese University of Hong Kong
      • Department of Physics
      Hong Kong, Hong Kong
    • Universität Witten/Herdecke
      Witten, North Rhine-Westphalia, Germany
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel
    • University of Padova
      Padua, Veneto, Italy
    • Yale University
      • Department of Chemistry
      New Haven, Connecticut, United States
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada
    • Massachusetts Institute of Technology
      • Department of Chemistry
      Cambridge, Massachusetts, United States
    • University of California, Davis
      • Department of Chemistry
      Davis, California, United States
    • Washington State University
      • Department of Chemistry
      پولمن، واشینگتن, Washington, United States
    • University of California, Santa Cruz
      Santa Cruz, California, United States
    • University of Texas at Austin
      • Department of Chemistry and Biochemistry
      Austin, Texas, United States
  • 2011
    • Beckman Research Institute
      Duarte, California, United States
  • 1962–2011
    • Columbia University
      • Department of Chemistry
      New York, New York, United States
  • 1992–2010
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States
    • University of California, San Diego
      • Department of Physics
      San Diego, CA, United States
  • 2009
    • Lake Tahoe Community College
      South Lake Tahoe, California, United States
  • 2008
    • University of Bologna
      • "Giacomo Ciamician" Department of Chemistry CHIM
      Bologna, Emilia-Romagna, Italy
  • 2002–2008
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Ángeles, California, United States
  • 2007
    • Occidental College
      • Department of Chemistry
      Los Angeles, California, United States
  • 2006
    • University of Zurich
      • Institut für Anorganische Chemie
      Zürich, Zurich, Switzerland
    • Queen Mary, University of London
      • School of Biological and Chemical Sciences
      London, ENG, United Kingdom
  • 2005
    • The University of Arizona
      Tucson, Arizona, United States
    • University of Rochester
      • Department of Chemistry
      Rochester, NY, United States
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, California, United States
  • 1981–2005
    • Stanford University
      • • Department of Biochemistry
      • • Department of Chemistry
      Palo Alto, California, United States
  • 2004
    • University of London
      Londinium, England, United Kingdom
  • 2003
    • Iowa State University
      Ames, Iowa, United States
    • Cornell University
      • Department of Chemistry and Chemical Biology
      Итак, New York, United States
    • Polytechnic University of Puerto Rico
      San Juan, San Juan, Puerto Rico
  • 2002–2003
    • Northwestern University
      • • Department of Cell and Molecular Biology
      • • Department of Chemistry
      Evanston, Illinois, United States
  • 1995–2003
    • University of Florence
      • CERM - Centro di Ricerca di Risonanze Magnetiche
      Florence, Tuscany, Italy
  • 1992–2002
    • University of Pittsburgh
      • Department of Chemistry
      Pittsburgh, Pennsylvania, United States
  • 1987–2002
    • Los Alamos National Laboratory
      Лос-Аламос, California, United States
  • 1976–2002
    • Pennsylvania State University
      • Department of Chemistry
      University Park, Maryland, United States
  • 1974–2002
    • Pasadena City College
      Pasadena, Texas, United States
  • 1998
    • Wabash College
      Pasadena, Texas, United States
  • 1996–1998
    • University of Gothenburg
      Goeteborg, Västra Götaland, Sweden
    • Université de Montréal
      Montréal, Quebec, Canada
  • 1986
    • Carleton University
      Ottawa, Ontario, Canada