2D ESEEM of the [sup 15]N-labeled radical cations of bacteriochlorophyll a and of the primary donor in reaction centers of Rhodobacter sphaeroides
- Technische Universitaet Berlin (Germany)
- Bruker Analytische Messtechnik, Rheinstetten (Germany)
The radical cations of [[sup 15]N]bacteriochlorophyll a and of the primary donor P[sub 865] in [sup 15]N-labeled reaction centers of Rhodobacter spaeroides R-26.1 were investigated in frozen solutions using two-dimensional ESEEM methods. Both three-pulse (stimulated echo) and four-pulse (HYSCORE) sequences were employed to avoid ambiguities in data analysis. Computer simulations of the experimental powder spectra were performed, yielding a complete set of nitrogen hyperfine coupling tensors for both systems. The obtained tensor values are compared with those from ENDOR measurements and from semiempirical INDO-type MO calculations. The results obtained from 2D stimulated echo ESEEM and HYSCORE for P[sub 865][sup [center dot]+] are interpreted in terms of an asymmetric spin density distribution over the halves of the bacteriochlorophyll dimer ([open quote]special pair[close quote]) in the reaction center with a ratio of approximately 5:1. This asymmetry is considerably larger at low temperatures in the frozen state than at room temperature. It is postulated that two different conformational states of the dimer exist at these temperatures with different spin density distributions. 60 refs., 9 figs., 4 tabs.
- OSTI ID:
- 6620044
- Journal Information:
- Journal of Physical Chemistry; (United States), Vol. 99:1; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
CATIONS
SPECTROSCOPY
CHLOROPHYLL
RADICALS
COMPILED DATA
COMPUTERIZED SIMULATION
LABELLED COMPOUNDS
MATHEMATICAL MODELS
NITROGEN 15
PHOTOSYNTHETIC BACTERIA
BACTERIA
CARBOXYLIC ACIDS
CHARGED PARTICLES
DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
IONS
ISOTOPES
LIGHT NUCLEI
MICROORGANISMS
NITROGEN ISOTOPES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
SIMULATION
STABLE ISOTOPES
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