LASER SPECTROSCOPY LABORATORY

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The funds requested in this proposal will support the development of a laser spectroscopy laboratory at the Beckman Institute. Instrumentation in the laboratory will provide for the measurement of time-resolved absorption and emission spectra on timescales from 10-11 to 102 s. Three research programs, currently supported by NIH, will directly benefit from this instrumentation: (i) studies of long-range electron transfer in metalloproteins; (ii) investigations of proton pumping in cytochrome c oxidase; and (iii) examinations of metal probes and drug binding to DNA. Electron-transfer (ET) reactions are the elementary chemical steps underlying a vast array of biochemical transformations. These transfers frequently occur over seemingly long distances with remarkable efficiencies. The goal of the ET research is to test the validity of current ET theories, and to identify the chemical and physical properties of ET systems that regulate their efficiencies. Cytochrome c oxidase is the oxygen-activating enzyme of cellular respiration. It has been estimated that nearly 90% of the 02 consumed by aerobic organisms participates in the dioxygen chemistry of cytochrome c oxidase and becomes reduced to water in the terminal step of respiration. The proton-pumping activity of cytochrome oxidase is linked to its electron-transfer reactivity, and considerable effort is directed toward identifying the site of redox linkage and unraveling the mechanism of the redox-linked proton translocation reaction. Transition metal complexes are promising new tools in biotechnology owing to their ability to recognize and react with nucleic acids. It has been demonstrated that tris(phenanthroline) metal complexes readily bind to double-stranded DNA, and some of these complexes will cleave DNA upon irradiation. The goal of this research is the development of new metal complexes which bind to different sites on DNA and new probes for nucleic acid structure. Time-resolved laser spectroscopy is a vital tool in all three of these research programs. The kinetics of photoinduced electron transfer and recombination are directly measured by transient absorption spectroscopy. Conformational changes in cytochrome oxidase have been observed by transient emission spectroscopy, complemented by transient absorption. The determination of DNA binding modes, enantiomeric preferences, and binding orientation of mixed ligand complexes has been accomplished through time-resolved emission measurements on ruthenium(II) complexes. The pulsed-laser instrumentation described in this proposal will provide the capabilities necessary to pursue this research. In the 20-ps to 20-ns time window, transient absorption measurements will be performed by conventional pump-probe spectroscopy with tunable excitation and a white-light continuum as a probe. On longer timescales, an excimer-pumped dye laser will be used as the excitation source for transient absorption and time-resolved emission experiments.