THE BACTERIOCHLOROPHYLL A CATION-RADICAL REVISITED - AN ENDOR AND TRIPLE-RESONANCE STUDY

The bacteriochlorophyll (BChl) a cation radical is studied by cw-EPR a nd multinuclear ENDOR/TRIPLE resonance techniques in liquid solution y ielding the hyperfine coupling constants (hfcs) for 12 protons, all 4 nitrogens and the central magnesium nucleus. The H hfcs are assigned t o specific molecular positions by various experimental techniques incl uding isotope substitution, H/D exchange experiments and comparison wi th bacteriochlorophyll derivatives. The determined temperature depende nces of the H hfcs are measured and related to dynamical properties of the molecule in solution. The experimental hfcs compare well with tho se obtained from semiempirical molecular orbital calculations of the R HF-INDO/SP type. The importance of these results for BChl species in v ivo, i.e., in the protein matrix, is discussed.