Long Range Electron Tunneling in Biological and Model Systems

Abstract

Abstract-This review paper reports the data on the role of long range electron tunneling in photosynthetic and model systems. The main papers concerned with elucidation mechanisms and kinetical peculiarities of electron transfer in reaction centers of bacteria and green plants are considered. The paper reviews the articles on long range electron transfer in reactions of metalloporphyrinssynthetic analogs of the main natural pigment of photosynthesis, chlorophyll. Liquid and solid phase redox reactions of electronically excited porphyrin molecules, intramolecular and photosensitized electron transfer processes are considered.

Hole-Burning Study of Primary Photochemistry of Metalloporphyrins in Reactive Solvent Glasses

“…Spectrophotometric Study of MgOEP in the Presence of Electron Acceptors. Photooxidation of metalloporhyrins in solvent glasses containing electron acceptors at 77 K have been used as a model reaction of primary processes in photosynthesis. ,, It has been concluded that photoionization of Zn tetraphenylporphine in C 2 H 5 OH/1 M CCl 4 2 or 2-chlorobutane/CCl 4 (1:1 v/v) 11 and similar vitreous systems at 77 K takes place in the first excited singlet state as a result of the absorption of a single quantum. On the contrary, the photon-gated HB experiments suggest that the efficient electron ejection should occur from the highly excited triplet state, i.e., after absorption of a second light quantum by the molecule in the T 1 state.…”

“…The incorrect assumption that the relatively long-lived S 1 state participates in adiabatic electron transfer 2 has been unfortunately used later by the same authors 4 for calculating electron tunneling parameters. (See also reviews of the topic in refs −8).…”

Rotaxanation as a sequestering template to preclude incidental metal insertion in complex oligochromophores

“…multisite catalysts, mimics of biochemically important species (e.g., cytochrome c oxidase), sensors, molecular electronics and/or solar-energy conversion. [1][2][3][4][5][6][7][8][9][10][11][12][13] An intensively studied area of application involves the use of porphyrinoids as components of artificial photosynthetic system models [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] with corroles making up a significant class of compounds used for this purpose. [30][31][32][33][34][35] We have previously contributed to this field with our work on corrole-porphyrin dendritic conjugates synthesized by using copper-mediated click reaction.…”

Diels-Alder reactions of 7-azalumazines. Synthesis of condensed lumazines and 8-deazalumazines

“…On the other hand, in DM-2 the change of the resonance scale and the shift of pR toward negative values suggest (i) remarkable analogies with methyl benzoates 3 and DM-3 and (ii) a prevalence of -polarization over through-conjugation in determining the C(a) chemical shift also in DM-2. The analogies between the DM-2 and 3 series find strong substantiation in the comparison of the plots of the C(a) chemical shifts of 3 vs those of 2 or DM-2: while scattering of points is observed in the former case (r = 0.550), a satisfactory linear correlation (r = 0.972, slope = 0.89 ± 0.08) is obtained between the C(a) chemical shifts of Finally, the behavior of benzonitriles 1 and DM-1, characterized by a reverse resonance effect of 4-substitudeazapteridines and lumazines.1,2 Analogous intermolecular inverse electron demand Diels-Alder reactions of 6-azapteridines with enamines have also been described that similarly provide a wide selection of 5-deazapteridines (Scheme I).1 23 Derivatives of this latter ring system are of intense current interest as antimetabolites of the folate family of enzyme cofactors,4 and some (e.g., DDATHF5) (1) Taylor, E. C.; Pont, J. L; Warner, J. C. Tetrahedron 1987, 43, 5159.…”

“…The products were combined to give 0.37 g (82%) of a tan solid: mp 298-300 °C; NMR (CDClg) 8.26 (d, J = 8. 1 Hz, 1 H), 7.82-7.73 (m, 2 H), Introduction Even though the transfer of electrons occurs in almost all chemical reactions, the dynamics of electron transfer are probably the least understood of all chemical processes. Given the importance of electron-transfer processes in a large variety of chemical reactions such as photosynthesis1 and bond-cleavage reactions,2 a great deal of theoretical3 and experimental work4 has been directed toward a better understanding of the relative rates of electron-transfer processes and the chemical processes that occur around them.5…”