A5003268863- Photosynthetic Processes and Mechanisms
- Photochemistry and Electron Transfer Studies
- X-ray Diffraction in Crystallography
- Molecular Junctions and Nanostructures
- Metal-Catalyzed Oxygenation Mechanisms
- Crystallization and Solubility Studies
- Electrochemical Analysis and Applications
- Protein Structure and Dynamics
- Porphyrin and Phthalocyanine Chemistry
- CO2 Reduction Techniques and Catalysts
- Spectroscopy and Quantum Chemical Studies
- Hemoglobin structure and function
- Metalloenzymes and iron-sulfur proteins
- Electrocatalysts for Energy Conversion
- Enzyme Structure and Function
- Metal complexes synthesis and properties
- Porphyrin Metabolism and Disorders
- Radical Photochemical Reactions
- Organometallic Complex Synthesis and Catalysis
- Electrochemical sensors and biosensors
- Magnetism in coordination complexes
- Photoreceptor and optogenetics research
- Lanthanide and Transition Metal Complexes
- Pharmacogenetics and Drug Metabolism
- Mass Spectrometry Techniques and Applications
California Institute of Technology
2015-2024
University of Michigan–Ann Arbor
2023
Dow Chemical (United States)
2020
California NanoSystems Institute
2020
University of California, Los Angeles
2020
Pasadena City College
2014-2019
Division of Chemistry
2011-2019
Occidental College
2003-2013
Czech Academy of Sciences, J. Heyrovský Institute of Physical Chemistry
2011
Queen Mary University of London
2008-2011
Natural photosynthesis uses sunlight to drive the conversion of energy-poor molecules (H2O, CO2) energy-rich ones (O2, (CH2O)n). Scientists are working hard develop efficient artificial photosynthetic systems toward “Holy Grail” solar-driven water splitting. High on list challenges is discovery that efficiently catalyze reduction protons H2. In this Account, we report one promising class molecules: cobalt complexes with diglyoxime ligands (cobaloximes). Chemical, electrochemical, and...
Recent investigations have shed much light on the nuclear and electronic factors that control rates of long-range electron tunneling through molecules in aqueous organic glasses as well bonds donor–bridge–acceptor complexes. Couplings covalent hydrogen are stronger than those across van der Waals gaps, these differences coupling between bonded nonbonded atoms account for dependence structure media redox sites Ru-modified proteins protein–protein
Splitting water to hydrogen and oxygen is a promising approach for storing energy from intermittent renewables, such as solar power. Efficient, scalable solar-driven electrolysis devices require active electrocatalysts made earth-abundant elements. In this mini-review, we discuss recent investigations of homogeneous heterogeneous evolution electrocatalysts, with emphasis on our own work cobalt iron complexes nickel-molybdenum alloys.
Water oxidation activity of nickel–iron layered double hydroxide ([NiFe]-LDH) nanosheet electrocatalysts is a function interlayer anion basicity.
Energy flow in biological structures often requires submillisecond charge transport over long molecular distances. Kinetics modeling suggests that charge-transfer rates can be greatly enhanced by multistep electron tunneling which redox-active amino acid side chains act as intermediate donors or acceptors. We report transient optical and infrared spectroscopic experiments quantify the extent to an intervening tryptophan residue facilitate transfer between distant metal redox centers a mutant...
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 Fe decreased to 22%. Addition Ti(4+) La(3+) ions further enhanced electrocatalysis, lowest overpotential 260 mV at 10 mA cm(-2). Electrocatalytic increased relative proportion 405.1 eV N 1s (XPS binding energy)...
Electrons have so little mass that in less than a second they can tunnel through potential energy barriers are several electron-volts high and nanometers wide. Electron tunneling is critical functional element broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic respiratory charge transport chains. Prior 1970s, chemists generally believed reactants had collide order effect transformation. Experimental demonstrations electrons transfer between separated by...
Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms these transformations remain unresolved, largely owing to fact that key reactive intermediates have eluded detection. One method stabilizing involves minimizing overall reaction free-energy change. Here, we report a new cobalt(I) complex reacts with tosylic acid evolve driving force just 30 meV/Co. Protonation Co I produces transient III...
Living organisms have adapted to atmospheric dioxygen by exploiting its oxidizing power while protecting themselves against toxic side effects. Reactive oxygen and nitrogen species formed during oxidative stress, as well high-potential reactive intermediates enzymatic catalysis, could rapidly irreversibly damage polypeptides were protective mechanisms not available. Chains of redox-active tyrosine tryptophan residues can transport potentially damaging equivalents (holes) away from fragile...
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 have a turnover frequency per surface site among the highest ever reported for nanoparticle oxygen evolution catalysts base overpotentials competitive best electrodeposited oxides, advantage that they are suitable mechanical deposition on photoanode...
Electron coupling through a β strand has been investigated by measurement of the intramolecular electron-transfer (ET) rates in ruthenium-modified derivatives barrel blue copper protein Pseudomonas aeruginosa azurin. Surface histidines, introduced on methionine-121 mutagenesis, were modified with Ru(2,2′-bipyridine) 2 (imidazole) 2+ complex. The Cu + to Ru 3+ rate constants yielded distance-decay constant 1.1 per angstrom, value close 1.0 angstrom predicted for electron tunneling an...
Rapid photochemical electron injection into unfolded ferricytochrome c titrated with 2.3 to 4.6 M guanidine hydrochloride (GuHCl) at pH 7 and 40°C produced ferrocytochrome, which then converted the folded protein. Two folding phases were observed: a fast process time constant of 40 microseconds (4.6 GuHCl), slower phase rate 90 ± 20 per second (2.3 GuHCl). The activation free energy for slow step varied linearly GuHCl concentration; constant, extrapolated aqueous solution, was 7600 second....
The electron transfer dynamics in solar cells that utilize sensitized nanocrystalline titanium dioxide photoelectrodes and the iodide/triiodide redox couple have been studied on a nanosecond time scale. ruthenium osmium bipyridyl complexes Ru(H2L')2(CN)2, Os(H2L')2(CN)2, Ru(H2L')2(NCS)2, Os(H2L')2(NCS)2, where H2L' is 4,4'-dicarboxylic acid 2,2'-bipyridine, inject electrons into semiconductor with rate constant >108 s-1. effects of excitation intensity, temperature, applied potential...
Ferrocytochrome c (Fe(II)cyt c) is ∼10 kcal/mol (410 meV) more stable toward unfolding than Fe(III)cyt c, owing mainly to the stabilization of ferroheme by hydrophobic encapsulation and enhanced iron−methionine bonding. To determine magnitudes these two components, we have measured binding constants N-acetylmethionine (AcMet) imidazole ferric ferrous N-acetylmicroperoxidase-8 (AcMP8), a heme-containing proteolytic fragment cyt c. Our results show that AcMet affinity heme significantly...
Distant Fe(2+)-Ru(3+) electronic couplings have been extracted from intramolecular electrontransfer rates in Ru(histidine(x)) (where X = 33, 39, 62, and 72) derivatives of cytochrome c. The increase according to 62 (0.0060) < 72 (0.057) 33 (0.097) 39 (0.11 per wave numbers); however, this order is out line with the histidine heme edge-edge distances [62 (14.8) > (12.3) (11.1) (8.4 angstroms)]. (and couplings) correlate lengths sigma-tunneling pathways comprised covalent bonds, hydrogen...
Variations in tryptophan fluorescence intensities confirm that copper(II) interacts with α-synuclein, a protein implicated Parkinson's disease. Trp4 decay kinetics measured for the F4W show Cu(II) binds tightly (Kd ∼ 100 nM) near N-terminus at pH 7. Work on F4W/H50S mutant indicates histidine imidazole is not ligand this high-affinity site.