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Titolo: HOLE LOCALIZATION AND SPIN COUPLING IN PIMONOCATIONS AND PIDICATIONS OF MUOXOPORPHYRIN DIMERS  RELEVANCE TO STRUCTURE OF OXIDIZED SPECIAL PAIR IN PHOTOSYNTHETIC REACTION CENTERS
Autore: BINSTEAD RA; HUSH NS;
 Indirizzi:
 UNIV SYDNEY,DEPT THEORET CHEM SYDNEY NSW 2006 AUSTRALIA UNIV SYDNEY,DEPT THEORET CHEM SYDNEY NSW 2006 AUSTRALIA UNIV SYDNEY,DEPT BIOCHEM SYDNEY NSW 2006 AUSTRALIA
 Titolo Testata:
 Journal of physical chemistry
fascicolo: 50,
volume: 97,
anno: 1993,
pagine: 13172  13179
 SICI:
 00223654(1993)97:50<13172:HLASCI>2.0.ZU;2S
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 BISPORPHYRINATE DOUBLEDECKERS; TETRAPYRROLE LIGANDS; METALCOMPLEXES; PORPHYRIN SANDWICH; OXIDATIONPRODUCTS; FERRIC PORPHYRINS; CRYSTALSTRUCTURE; REDOX POTENTIALS; RADICAL CATIONS; BACTERIOCHLOROPHYLL;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Science Citation Index Expanded
 Citazioni:
 52
 Recensione:
 Indirizzi per estratti:



 Citazione:
 R.A. Binstead e N.S. Hush, "HOLE LOCALIZATION AND SPIN COUPLING IN PIMONOCATIONS AND PIDICATIONS OF MUOXOPORPHYRIN DIMERS  RELEVANCE TO STRUCTURE OF OXIDIZED SPECIAL PAIR IN PHOTOSYNTHETIC REACTION CENTERS", Journal of physical chemistry, 97(50), 1993, pp. 1317213179
Abstract
The antiferromagnetically coupled cofacial muoxoiron(III) dimers of octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) can be oxidized in two oneelectron steps to yield pimonocations and pidications. Hitherto unreported absorption bands are observed in the midinfrared region in the spectra of the monocations. These are identified as intervalence transitions of dynamically trapped holes. The electronphononcoupling energies (CH2Cl2 solution, 295 K) are 0.31 +/ 0.04 eV, and the interring, predominantly throughspace, electronic coupling constants J are 0.07 and 0.03 eV, respectively. The small values of J are aconsequence of the large mean plane separation of the porphyrin rings(4.53 angstrom). Since it is improbable that the electronphonon coupling energies will vary greatly between cofacial porphyrin dimers, it is suggested that absorption bands around 1 eV in the pimonocations of 'sandwich'' compounds such as M(III)P2 or M(IV)P2+, where P is a porphyrin and M are lanthanide, actinide, or transition metals (312) observed under similar conditions will have electronic ground states thatare delocalized on at least the vibrational time scale, with frequency maxima equal to 2J in the tightbinding approximation. The thermal interring holetransfer times in the muoxo dimer monocations are estimated to be approximately 1 ps. The relevance of these results to the problem of the structure of the oxidized 'special pair'' in the photosynthetic reaction center is briefly discussed. The pidications exhibit a band in the nearinfrared region which is attributed to a transition between antiferromagnetically coupled pistates, from which, using the Hubbard hamiltonian, interring exchange integrals K are calculated to be 0.39 +/ 0.02 eV, and the singlettriplet separations (S)DELTA(T) calculated to be 0.025 and 0.0024 eV, respectively. The monocations are stable to disproportionation in CH2Cl2 solution (K(com) (295 K) = 3 X 10(5) and 2 x 10(4), respectively).
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Documento generato il 24/11/20 alle ore 10:44:13