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Donor properties of the three carbonyl groups of chlorophyll a: ab initio calculations and 13C magnetic resonance studies.

Authors :
Shipman, L L
Janson, T R
Ray, G J
Katz, J J
Source :
Proceedings of the National Academy of Sciences of the United States of America; August 1975, Vol. 72 Issue: 8 p2873-2876, 4p
Publication Year :
1975

Abstract

The relative donor properties of the three carbonyl groups of chlorophyll a have been studied theoretically by a series of ab initio molecular fragment, floating spherical Gaussian orbital, self-consistent field calculations on ethyl chlorophyllide a and experimentally through a 13C magnetic resonance study on chlorophyll a. The approximate ground state electronic wavefunction of ethyl chlorophyllide a was perturbed by monopole and dipole point charges whose signs, magnitudes, and positions were chosen to mimic the coulombic interactions associated with carbonyl coordination to Mg. Because the polarizability of the ring V keto carbonyl binding site is substantially greater than that for the ester carbonyl binding sites, the ring V keto binding site binds with smallest binding energy for weak perturbations and with largest binding energy for strong perturbations. A comparison of 13C magnetic resonance chemical shifts in chlorophyll a monomer and dimer provides new experimental evidence that the donor-acceptor interactions that bind the chlorophyll dimer together involve a substantial participation by the ring V keto carbonyl and minimal participation by the two ester carbonyl groups, and thus are in agreement with conclusions derived from the ab initio calculations.

Details

Language :
English
ISSN :
00278424 and 10916490
Volume :
72
Issue :
8
Database :
Supplemental Index
Journal :
Proceedings of the National Academy of Sciences of the United States of America
Publication Type :
Periodical
Accession number :
ejs60428433
Full Text :
https://doi.org/10.1073/pnas.72.8.2873