Electron-Transfer Reorganization Energies of Isolated Molecules

Author: Amashukeli, Xenia

Year: 2002

Degree: Dissertation (Ph.D.)

Advisor: Gray, Harry B.

Committee Members: Lewis, Nathan Saul; Blake, Geoffrey A.; Goddard, William A., III; Gray, Harry B.; Winkler, Jay Richmond

Option: Chemistry

Abstract

Electron-transferreorganization energies of isolated organic molecules and biologically relevant porphyrins are obtained from analyses of their photoelectron spectra. The assignments of experimental ionization energies are aided by ab initio calculations, and comparisons between He I and He II ionization data. It is established that in unsymmetrically substituted metalloporphyrins, i.e., Zn(II) protoporphyrin IX, the highest occupied molecular orbital has appreciable nitrogen character (Chapter 3).Quantum-mechanical and semiclassical analyses of vibrational progressions observed in photoelectron spectra yield gas-phase reorganization energies. Favorable agreement is reached between experimental and calculated values of reorganization energies (Chapters 2 and 3). This observation is not surprising, however, since density functional theory calculations, employed in this thesis, are successful at reproducing experimental molecular geometries. Indeed, X-ray structural parameters of dibenzo[a,c]phenazine are in excellent agreement with calculated results (Chapter 6). Vibrational frequencies of organic molecules are also calculated (Chapter 5) to aid mode-specific quantum mechanical analyses of fine structure observed in photoelectron spectra. Given the success of ab initio calculations of reorganization energies of organic molecules, the same computational approach is employed to obtain reorganization energies of six-coordinate metalloporphyrin model systems (Chapter 4). The results show that large reorganization energies are associated with charged ligands, which are most frequently found in protein redox catalytic sites; small reorganization energies, on the other hand, are calculated for the molecules with neutral ligands, commonly located in the protein active sites that facilitate electron transfer.

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