RESONANCE RAMAN-SPECTROSCOPY OF METAL-SUBSTITUTED BACTERIOCHLOROPHYLLS - CHARACTERIZATION OF RAMAN BANDS SENSITIVE TO BACTERIOCHLORIN CONFORMATION

Fourier transform (FT) preresonance Raman spectra of Mg-containing bac teriochlorophyll a (BChla) and the metal-substituted Zn-, Ni-, Cu- and Co-bactleriopheophytins a (BPhea) allowed the characterization of tho se vibrational modes sensitive to the nature of the central metal, thr ough its effect on the core size of these molecules. Six of the Raman modes active in the excitation conditions used (1064 nm, in preresonan ce with the Q(y) transition of the metal-bacteriopheophytin molecules) are shown to be sensitive to the conformation of the dihydrophorbin r ing. Comparison of the FT-Raman spectra of BChla under conditions wher e the central Mg ion is either five-or six-coordinate show that these modes may he used to distinguish modifications of the dihydrophorbin c ore size as small as 1 pm, and thus that they may be used for characte rizing conformational strains on BChla molecules both in vitro and in vivo. (C) 1997 John Wiley & Sons, Ltd.