Harry B. Gray

California Institute of Technology, Pasadena, California, United States

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Publications (724)2471.47 Total impact

  • [Show abstract] [Hide abstract]
    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; · 10.68 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; · 6.38 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; · 10.68 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; · 11.65 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 08/2014; · 3.35 Impact Factor
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    ABSTRACT: Fluorescence of 2-(N,N-dimethyl)aminonaphthalene-6-propionyl dyes Badan and Prodan is quenched by tryptophan in Brij 58 micelles as well as in two cytochrome P450 proteins (CYP102, CYP119) with Badan covalently attached to a cysteine residue. Formation of nonemissive complexes between a dye molecule and tryptophan accounts for about 76% of the fluorescence intensity quenching in micelles, the rest is due to diffusive encounters. In the absence of tryptophan, fluorescence of Badan-labeled cytochromes decays with triexponential kinetics characterized by lifetimes of about 100 ps, 700-800 ps, and 3 ns. Site mutation of a histidine residue in the vicinity of the Badan label by tryptophan results in shortening of all three decay lifetimes while the relative amplitude of the fastest component increases at the expense of the two slower ones. The average quenching rate constants are 4.5x10^8 s-1 (CYP102) and 3.7x10^8 s-1 (CYP119), at 288 K. Cyclic voltammetry of Prodan in MeCN shows a reversible reduction peak at -1.85 V vs. NHE that becomes chemically irreversible and shifts positively upon addition of water. A quasireversible reduction at -0.88 V was observed in an aqueous buffer (pH 7.3). The excited-state reduction potential of Prodan (and Badan) is estimated to vary from about +0.6 V (vs NHE) in polar aprotic media (MeCN) to approximately +1.6 V in water. Tryptophan quenching of Badan/Prodan fluorescence in CYPs and Brij 58 micelles is exergonic by <0.5 V and involves tryptophan oxidation by excited Badan/Prodan, coupled with a fast reaction between the reduced dye and water. Photoreduction is a new quenching mechanism for 2-(N,N-dimethyl)aminonaphthalene-6-propionyl dyes that are often used as solvatochromic polarity probes, FRET donors and acceptors, as well as reporters of solvation dynamics.
    The journal of physical chemistry. B. 07/2014;
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    ABSTRACT: Silicon(111) surfaces have been functionalized with mixed monolayers consisting of submonolayer coverages of immobilized 4-vinyl-2,2'-bipyridyl (, vbpy) moieties, with the remaining atop sites of the silicon surface passivated by methyl groups. As the immobilized bipyridyl ligands bind transition metal ions, metal complexes can be assembled on the silicon surface. X-ray photoelectron spectroscopy (XPS) demonstrates that bipyridyl complexes of [Cp*Rh], [Cp*Ir], and [Ru(acac)2] were formed on the surface (Cp* is pentamethylcyclopentadienyl, acac is acetylacetonate). For the surface prepared with Ir, X-ray absorption spectroscopy at the Ir LIII edge showed an edge energy as well as post-edge features that were essentially identical with those observed on a powder sample of [Cp*Ir(bpy)Cl]Cl (bpy is 2,2'-bipyridyl). Charge-carrier lifetime measurements confirmed that the silicon surfaces retain their highly favorable photoelectronic properties upon assembly of the metal complexes. Electrochemical data for surfaces prepared on highly doped, n-type Si(111) electrodes showed that the assembled molecular complexes were redox active. However the stability of the molecular complexes on the surfaces was limited to several cycles of voltammetry.
    Dalton Transactions 07/2014; · 3.81 Impact Factor
  • ChemInform 04/2014; 45(15).
  • Jay R Winkler, Harry B Gray
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    ABSTRACT: Electrons have so little mass that in less than a second they can tunnel through potential energy barriers that are several electron-volts high and several nanometers wide. Electron tunneling is a critical functional element in a broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic and respiratory charge transport chains. Prior to the 1970s, chemists generally believed that reactants had to collide in order to effect a transformation. Experimental demonstrations that electrons can transfer between reactants separated by several nanometers led to a revision of the chemical reaction paradigm. Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance. Theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers. Kinetics measurements have shown that electrons can tunnel about 2.5 nm through proteins on biologically relevant timescales. Longer-distance biological charge flow requires multiple electron tunneling steps through chains of redox cofactors. The range of phenomena that depends on long-range electron tunneling continues to expand, providing new challenges for both theory and experiment.
    Journal of the American Chemical Society 02/2014; · 10.68 Impact Factor
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    ABSTRACT: Fluorescence (shown in red) from the corrole nanoconjugate 1-Al–TiO2 internalized in the glioblastoma U87-Luc cell.
    Journal of Inorganic Biochemistry. 01/2014; 140:39–44.
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    ABSTRACT: We present a new approach to visualizing and quantifying the displacement of segments of Pseudomonas aeruginosa azurin in the early stages of denaturation. Our method is based on a geometrical method developed previously by the authors, and elaborated extensively for azurin. In this study, we quantify directional changes in three α-helical regions, two regions having β-strand residues, and three unstructured regions of azurin. Snapshots of these changes as the protein unfolds are displayed and described quantitatively by introducing a scaling diagnostic. In accord with molecular dynamics simulations, we show that the long α-helix in azurin (residues 54-67) is displaced from the polypeptide scaffolding and then pivots first in one direction, and then in the opposite direction as the protein continues to unfold. The two β-strand chains remain essentially intact and, except in the earliest stages, move in tandem. We show that unstructured regions 72-81 and 84-91, hinged by β-strand residues 82-83, pivot oppositely. The region comprising residues 72-91 (40 % hydrophobic and 16 % of the 128 total residues) forms an effectively stationary region that persists as the protein unfolds. This static behavior is a consequence of a dynamic balance between the competing motion of two segments, residues 72-81 and 84-91.
    European Journal of Biochemistry 12/2013; · 3.42 Impact Factor
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    ABSTRACT: We report the redox properties of Si(111) surfaces functionalized with a mixed monolayer of vinylferrocenyl and methyl moieties that have been characterized using spectroscopic, electrical, and electrochemical techniques. The silicon was functionalized using reaction conditions analogous to those of hydrosilylation, but instead of a H-terminated Si surface, a chlorine-terminated Si precursor surface was used to produce the linked vinyl-modified functional group. The functionalized surfaces were characterized by time-resolved photoconductivity decay, X-ray photoelectron spectroscopy, electrochemical measurements, and photoelectrochemical measurements. The functionalized Si surface was well passivated, exhibited high surface coverage and few remaining reactive Si atop sites, had a very low surface recombination velocity, and displayed little initial surface oxidation. The surface was stable toward atmospheric and electrochemical oxidation. The surface coverage of vinylferrocene (or fluorostyrene) was controllably varied from 0 up to 30% of a monolayer. Interfacial charge transfer to the attached ferrocene group was relatively rapid, and a photovoltage of 0.4 V was generated upon illumination of functionalized n-type silicon surfaces in CH3CN.
    The Journal of Physical Chemistry C. 12/2013; 117(51):27012–27022.
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    ABSTRACT: Earth-abundant metals are attractive alternatives to the noble metal composite catalysts that are used in water electrolyzers based on proton-exchange membrane technology. Ni–Mo alloys have been previously developed for the hydrogen evolution reaction (HER), but synthesis methods to date have been limited to formation of catalyst coatings directly on a substrate. We report a method for generating unsupported nanopowders of Ni–Mo, which can be suspended in common solvents and cast onto arbitrary substrates. The mass-specific catalytic activity under alkaline conditions approaches that of the most active reported non-noble HER catalysts, and the coatings display good stability under alkaline conditions. We have also estimated turnover frequencies per surface atom at various overpotentials and conclude that the activity enhancement for Ni–Mo relative to pure Ni is due to a combination of increased surface area and increased fundamental catalytic activity.
    ACS Catalysis 12/2013; 3(2):166. · 5.27 Impact Factor
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    ABSTRACT: Atomic-layer deposition (ALD) of thin layers of cobalt oxide on n-type BiVO4 produced photoanodes capable of water oxidation with essentially 100% faradaic efficiency in alkaline, pH = 13 electrolytes. By contrast, under the same operating conditions, BiVO4 photoanodes without the Co oxide catalytic layer exhibited lower faradaic yields, of ca. 70%, for O2 evolution and were unstable, becoming rapidly photopassivated. High numbers (>25) of ALD cycles of Co oxide deposition gave electrodes that displayed poor photoelectrochemical behavior, but 15–20 ALD cycles produced Co oxide overlayers 1 nm in thickness, with the resulting photoelectrodes exhibiting a stable photocurrent density of 1.49 mA cm–2 at the oxygen-evolution potential and an open-circuit potential of 0.404 V versus the reversible hydrogen electrode, under 100 mW cm–2 of simulated air mass 1.5 illumination.
    Journal of Physical Chemistry Letters 11/2013; 4(23):4188–4191. · 6.59 Impact Factor
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    ABSTRACT: We show that molecular catalysts for fuel-forming reactions can be immobilized on graphitic carbon electrode surfaces via noncovalent interactions. A pyrene-appended bipyridine ligand (P) serves as the linker between each complex and the surface. Immobilization of a rhodium proton-reduction catalyst, [Cp*Rh(P)Cl]Cl (1), and a rhe-nium CO2-reduction catalyst, Re(P)(CO)3Cl (2), afford electrocatalytically active assemblies. X-ray photoelectron spectroscopy and electrochemistry confirm catalyst immobilization. Reduction of 1 in the presence of p-toluenesulfonic acid results in catalytic H2 production, while reduction of 2 in the presence of CO2 results in catalytic CO production.
    Journal of the American Chemical Society 11/2013; · 10.68 Impact Factor
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    ABSTRACT: Through decades of sustained effort, researchers have made substantial progress on developing technologies for solar-driven water splitting. Nevertheless, more basic research is needed before prototype devices with a chance for commercial success can be demonstrated. In this Perspective, we summarize the major design constraints that motivate continued research in the field of solar-driven water splitting. Additionally, we discuss key device components that are now available for use in demonstration systems and prototypes. Finally, we highlight research areas where breakthroughs will be critical for continued progress toward commercial viability for solar-driven water-splitting devices.
    ChemInform 10/2013; 26(1):407–414.
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    ABSTRACT: Surfactant-free, size- and composition-controlled, unsupported, <5-nm, quantum-confined cobalt oxide nanoparticles with high electrocatalytic oxygen-evolution activity were synthesized by pulsed laser ablation in liquids. These crystalline Co3O4 nanoparticles have a turnover frequency per cobalt surface site among the highest ever reported for Co3O4 nanoparticle oxygen evolution catalysts in base and overpotentials competitive with the best electrodeposited cobalt oxides, with the advantage that they are suitable for mechanical deposition on photoanode materials and incorporation in integrated solar water-splitting devices.
    ACS Catalysis 10/2013; 3(11):2497–2500. · 5.27 Impact Factor
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    ABSTRACT: In the design of molecular sensors, researchers exploit binding interactions that are usually defined in terms of topology and charge complementarity. The formation of complementary arrays of highly cooperative, noncovalent bonding networks facilitates protein-ligand binding, leading to motifs such as the "lock-and-key". Synthetic molecular sensors often employ metal complexes as key design elements as a way to construct a binding site with the desired shape and charge to achieve target selectivity. In transition metal complexes, coordination number, structure and ligand dynamics are governed primarily by a combination of inner-sphere covalent and outer-sphere noncovalent interactions. These interactions provide a rich variable space that researchers can use to tune structure, stability, and dynamics. In contrast, lanthanide(III)-ligand complex formation and ligand-exchange dynamics are dominated by reversible electrostatic and steric interactions, because the unfilled f shell is shielded by the larger, filled d shell. Luminescent lanthanides such as terbium, europium, dysprosium, and samarium display many photophysical properties that make them excellent candidates for molecular sensor applications. Complexes of lanthanide ions act as receptors that exhibit a detectable change in metal-based luminescence upon binding of an anion. In our work on sensors for detection of dipicolinate, the unique biomarker of bacterial spores, we discovered that the incorporation of an ancillary ligand (AL) can enhance binding constants of target anions to lanthanide ions by as much as two orders of magnitude. In this Account, we show that selected ALs in lanthanide/anion systems greatly improve sensor performance for medical, planetary science, and biodefense applications. We suggest that the observed anion binding enhancement could result from an AL-induced increase in positive charge at the lanthanide ion binding site. This effect depends on lanthanide polarizability, which can be established from the ionization energy of Ln(3+) → Ln(4+). These results account for the order Tb(3+) > Dy(3+) > Eu(3+) ≈ Sm(3+). As with many lanthanide properties, ranging from hydration enthalpy to vaporization energy, this AL-induced enhancement shows a large discrepancy between Tb(3+) and Eu(3+) despite their similarity in size, a phenomenon known as the "gadolinium break". This discrepancy, based on the unusual stabilities of the Eu(2+) and Tb(4+) oxidation states, results from the half-shell effect, as both of these ions have half-filled 4f-shells. The high polarizability of Tb(3+) explains the extraordinarily large increase in the binding affinity of anions for terbium compared to other lanthanides. We recommend that researchers consider this AL-induced enhancement when designing lanthanide-macrocycle optical sensors. Ancillary ligands also can reduce the impact of interfering species such as phosphate commonly found in environmental and physiological samples.
    Accounts of Chemical Research 09/2013; · 20.83 Impact Factor
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    ABSTRACT: Re126W122CuI Pseudomonas aeruginosa azurin incorporates three redox sites, ReI(CO)3(4,7-dimethyl-1,10-phenanthroline) covalently bound at H126, the W122 indole side chain, and CuI, which are well separated in the protein fold: Re-W122(indole) = 13.1 Å; dmp-W122(indole) = 10.0 Å, Re-Cu = 25.6 Å. In view of the long intramolecular Re-Cu distance, it is surprising that CuI is oxidized in less than 50 ns after near-UV excitation of the Re chromophore. Back electron transfer (BET) regenerating CuI and ground-state ReI takes much longer (220 ns and 6 us). We show that these ET reactions occur in protein dimers, (Re126W122CuI)2, which are in equilibrium with unreactive monomers. In support of this interpretation, ET yields and kinetics are concentration-dependent and solution mass spectrometry (LILBID-MS) confirms the presence of a broad oligomer distribution with prevalent monomers and dimers; in the crystal structure, two Re126W122CuII molecules are oriented in such a way that the redox cofactors Re(dmp) and W122-indole belonging to different monomers are located at a protein-protein interface (//), where the intermolecular ET-relevant distances (Re-W122(indole) = 6.9 Å, dmp-W122(indole) = 3.5 Å, and Re-Cu = 14.0 Å) are much shorter than intramolecular ones. We propose that forward ET is accelerated by intermolecular electron hopping through a surface tryptophan: *Re//<-W122<-CuI; our kinetics analysis indicates that an equilibrium (K = 0.8-0.9) between *Re and charge-separated Re(dmp•-)(W122•+), which is established in a few ns, stores part of the excitation energy. The second ET step, intramolecular CuI oxidation, CuI->W122•+, occurs in 30 ns. The system is well coupled for forward ET but not for ReI(dmp•-)->CuII BET. Our work on interfacial electron hopping in (Re126W122CuI)2 sheds new light on redox-unit placements required for functional long-range charge separation in protein complexes.
    Journal of the American Chemical Society 09/2013; · 10.68 Impact Factor
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    ABSTRACT: We have investigated intrachain contact dynamics in unfolded cytochrome cb562 by monitoring heme quenching of excited ruthenium photosensitizers covalently bound to residues along the polypeptide. Intrachain diffusion for chemically denatured proteins proceeds on the microsecond time scale with an upper limit of 0.1 μs. The rate constants exhibit a power-law dependence on the number of peptide bonds between the heme and Ru complex. The power-law exponent of -1.5 is consistent with theoretical models for freely jointed Gaussian chains, but its magnitude is smaller than that reported for several synthetic polypeptides. Contact formation within a stable loop was examined in a His63-heme ligated form of the protein under denaturing conditions. Loop formation accelerated contact kinetics for the Ru66 labeling site, owing to reduction in the length of the peptide separating redox sites. For other labeling sites within the stable loop, quenching rates were modestly reduced compared to the open chain polymer.
    The Journal of Physical Chemistry B 08/2013; · 3.61 Impact Factor

Publication Stats

7k Citations
2,471.47 Total Impact Points


  • 1970–2014
    • California Institute of Technology
      • • Division of Chemistry and Chemical Engineering
      • • Beckman Institute
      • • Arthur Amos Noyes Laboratory of Chemical Physics
      Pasadena, California, United States
  • 2006–2012
    • University of Southern California
      • • Department of Biomedical Engineering
      • • Department of Chemistry
      Los Angeles, CA, United States
    • University of Zurich
      Zürich, Zurich, Switzerland
    • Queen Mary, University of London
      • School of Biological and Chemical Sciences
      London, ENG, United Kingdom
  • 2011
    • IT University of Copenhagen
      København, Capital Region, Denmark
    • Universitetet i Tromsø
      • Department of Chemistry
      Tromsø, Troms Fylke, Norway
    • Goethe-Universität Frankfurt am Main
      • Institut für Physikalische und Theoretische Chemie
      Frankfurt am Main, Hesse, Germany
    • Beckman Research Institute
      Duarte, California, United States
  • 2009–2011
    • Cedars-Sinai Medical Center
      • Cedars Sinai Medical Center
      Los Angeles, CA, United States
    • Lake Tahoe Community College
      South Lake Tahoe, California, United States
    • DePaul University
      • Department of Chemistry
      Chicago, IL, United States
  • 2005–2011
    • University of Rochester
      • Department of Chemistry
      Rochester, NY, United States
  • 2000–2011
    • Technion - Israel Institute of Technology
      • • Schulich Faculty of Chemistry
      • • Department of Pharmacology
      H̱efa, Haifa District, Israel
    • University of North Texas
      • Department of Chemistry
      Denton, Texas, United States
  • 2004–2009
    • University of London
      Londinium, England, United Kingdom
    • Pennsylvania State University
      • Department of Chemistry
      University Park, MD, United States
    • University of Western Australia
      • School of Chemistry and Biochemistry
      Perth, Western Australia, Australia
    • University of California, Santa Barbara
      • Department of Chemistry and Biochemistry
      Santa Barbara, CA, United States
  • 2008
    • NASA
      • Section of Planetary Sciences
      Washington, WV, United States
    • University of Bologna
      • "Giacomo Ciamician" Department of Chemistry CHIM
      Bologna, Emilia-Romagna, Italy
  • 2007–2008
    • National Heart, Lung, and Blood Institute
      Maryland, United States
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 2005–2007
    • Occidental College
      • Department of Chemistry
      Los Angeles, CA, United States
  • 2003–2004
    • The Scripps Research Institute
      • Department of Cell and Molecular Biology
      La Jolla, CA, United States
    • University of Montana
      • Division of Biological Sciences
      Missoula, MT, United States
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States
  • 1995–2004
    • University of Florence
      • CERM - Centro di Ricerca di Risonanze Magnetiche
      Florence, Tuscany, Italy
  • 1998
    • Wabash College
      Pasadena, Texas, United States
  • 1996
    • Los Alamos National Laboratory
      Los Alamos, California, United States
  • 1992–1995
    • University of California, San Diego
      • Department of Physics
      San Diego, CA, United States
  • 1993
    • University of Pittsburgh
      • Department of Chemistry
      Pittsburgh, PA, United States
  • 1988
    • The Chinese University of Hong Kong
      Hong Kong, Hong Kong
  • 1987
    • The University of Hong Kong
      Hong Kong, Hong Kong
  • 1964–1967
    • Columbia University
      • Department of Chemistry
      New York City, NY, United States