Recent structural data for (bacterio)chlorophylls and chlorins as isolated molecule^^-^ and in proteinsb8 demonstrate the skeletal (17) Norris, J. R.; Budil, D. E.; Crespi, H. L.; Bowman, M. K.; Cast, P.; Lin, C. P.; Chang, C. H.; Schiffer, M. in ref 5c, p 147. (18) Lendzian, F.; Lubitz, W.; Scheer, H.; Hoff, A. J.; Plato, M.; Trankle, E.; Mobius, K. Tronrud et aL6 note that the seven BChls that comprise the BChl a antenna protein of P . aestuarii fall into two distinct conformational classes.Calculations for the seven individual BChls, based on these crystallographic data, indeed yield low-energy absorption maxima that parallel the conformational variations (Gudowska-Nowak, E.; Fajer, J., unpublished results). Obviously, these calculations, by themselves, do not account entirely for the experimental spectrum of P. aestuarii because excitonic interactions between close neighbors in the protein are not included.Photosynthetic reaction centers use light to generate energetic, long-lived charge-separated states by employing a series of short-range electron-transfer steps to achieve overall long-range charge separation across a lipid bilayer membrane. We have previously shown that covalently linked carotenoid-porphyrinquinone (C-P-0) triadsl-I0 and a carotenoid-porphyrindiquinone
with the known properties of Compounds I of catalase and peroxidase leads us to propose that these forms of the enzymes contain a ir-cation radical of the heme prosthetic group.
METHODSThe techniques for bromine oxidations, controlled potential electrolysis, coulometry, and for optical and esr measurements (as well as for purification and preparation of materials) have been described (4). For anion-transfer reactions, a quartz esr tube was attached to an ampoule with two side arms, one of which contained a degassed solution of [Co(III) (Et)8P]2+ 2Br-in chloroform and the other dry AgCl04 isolated by a fritted disc. After the spectrum of the bromide salt was obtained, the solution was shaken in the AgCl04 compartment to form the [Co(III)(Et)8P]2+ 2C104-salt. Relative concentrations of free radicals were determined by double integration by computer of the first-derivative spectra obtained under comparable experimental conditions. The mass spectrum was recorded on an AEI MS-9 mass spectrometer operating at 70 eV, and a source temperature of 2500C. The nuclear magnetic resonance (nmr) spectra were measured in chloroform and recorded on a Varian HA-100 spectrometer, with tetramethylsilane as internal reference. Attempts to oxidize ferric porphyrins to a formal Fe(V) oxidation state were unsuccessful due to solvent breakdown encountered at the high potentials required [>1.5 V vs. aqueous saturated calomel electrode (see) ]. RESULTS
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.