RESONANCE RAMAN-SPECTRA OF METALLO-TRANS-OCTAETHYLCHLORINS AND THEIR MESO-GAMMA, DELTA-DEUTERATED AND N-15 SUBSTITUTED DERIVATIVES

As models of the chromophore of chlorophyll and heme d, metallo-trans-octaethylchlorin [M(OEC), M = Cu2+ and Ni2+], Fe3+(OEC)L (L = F and CI, high spin), Fe3+(OEC)L2(L = imidazole (Im), low spin], and meso-7, 6-deuteratcd and 15N-isotope-substituted Cu(OEC) were investigated by resonance Raman spectroscopy. Upon 15N substitution of four pvrrolic nitrogens of Cu(OEC), an isotopic frequency shift was observed for several Raman lines, which reasonably corresponded to the 15N-sensitive Raman lines of chlorophyll a reported by Lutz et al. The vibrational displacements of the pyrrolic nitrogens were calculated from the observed frequency shifts. The frequencies of methine-bridge stretching vibrations were shifted by ca. 5 cm-2upon meso-7,£-deuteration and found to be utilizable as a spin-state indicator of the iron ion of Fe(OEC) derivatives and likewise for iron octaethvlporphyrin [Fe(OEP)] derivatives. The Fe-L stretching mode of Fe(OEC)L was observed at 608 cm-1for L = F and at 361 cm-1for L = CI and the L-Fe-L symmetric stretching mode of Fe(OEC)L2was at 303 cm-1for L = Im, in good agreement with the corresponding frequencies of Fe(OEP) derivatives. The Raman lines of M(OEC) were more intensified upon excitation at 568.2 nm than at shorter wavelengths presumably due to resonance with Q band near 600 nm. The intensity enhancement was pronounced for Raman lines around 1100-1300 cm-1for M(OEC) derivatives in contrast with the case of M(OEP) derivatives. © 1979, American Chemical Society. All rights reserved.