Theoretical models of electrochromic and environmental effects on bacterio-chlorophylls and -pheophytins in reaction centers
The primary charge separation in photosynthetic reaction centers (RC) is carried out by an array of (bacterio)chlorophylls arranged in close proximity. The recent x-ray structures of the RC complexes from Rhodopseudomonas viridis and Rhodobacter sphaeroides reveal two possible electron pathways for purple bacteria, only one of which is active. We have calculated the effects of hydrogen bonding and chemical modification (enolization) by nearby residues upon the optical spectra, reduction potentials, unpaired spin density distributions and charge densities of bacterio-chlorophylls (BChl) and -pheophytins (BPh). In addition, we have calculated the effect of generating the primary cation and anion products on the spectra of the accessory BChl and BPh pigments in the RC. At the present levels of refinement, x-ray structures of Rb. sphaerides, which contains BChls a, reveal a molecular architecture analogous to that of R. viridis, which is comprised of BChls b. Similar electrochromic shifts are thus predicted for the two species. 28 refs., 4 figs., 4 tabs.
- Research Organization:
- Brookhaven National Lab., Upton, NY (USA); Florida Univ., Gainesville (USA)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 5455062
- Report Number(s):
- BNL-40539; CONF-8709222-1; ON: DE88004441
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ABSORPTION SPECTRA
ALCOHOLS
ANIONS
BACTERIA
CARBOXYLIC ACIDS
CATIONS
CHARGE DENSITY
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL REACTIONS
CHLOROPHYLL
COLOR
CRYSTAL STRUCTURE
ELECTRO-OPTICAL EFFECTS
ELECTROCHROMISM
ELECTRON TRANSFER
ELEMENTS
ENOLS
ENVIRONMENTAL EFFECTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN
HYDROXY COMPOUNDS
IONS
MATHEMATICAL MODELS
MICROORGANISMS
MOLECULAR STRUCTURE
NONMETALS
OPTICAL PROPERTIES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOLEPTIC PROPERTIES
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHESIS
PHOTOSYNTHETIC REACTION CENTERS
PHYSICAL PROPERTIES
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
RHODOPSEUDOMONAS
SPECTRA
SPECTROSCOPY
SYNTHESIS
X-RAY SPECTROSCOPY