Ld. Sparks et al., RAMAN-SPECTROSCOPIC CHARACTERIZATION OF ISOMERS OF COPPER AND ZINC N-PHENYLPROTOPORPHYRIN IX DIMETHYL ESTER, Inorganic chemistry, 32(14), 1993, pp. 3153-3161
The reaction of certain heme-containing proteins with phenylhydrazine
results in N-phenylprotoporphyrin formation. N-substituted porphyrins
are known to inhibit ferrochelatase and to be formed in the inactivati
on of hepatic cytochrome P450 by various agents. These molecules there
fore play an important role in understanding the biological function o
f these enzymes. We have used molecular modeling in conjunction with r
esonance Raman and UV-visible absorption spectroscopies to investigate
the structure of the four distal regioisomers of N-phenylprotoporphyr
in IX dimethyl ester (NPhPPDME) metal derivatives. Regardless of which
pyrrole ring (A, B, C, or D) bears the N-phenyl substituent, a novel
distortion from planarity of the protoporphyrin macrocycle results fro
m addition of the phenyl group. The molecular mechanics calculations f
or various isomers and conformers of copper(II)N-phenylprotoporphyrin
IX predict structures similar to the structure reported for zinc N-phe
nyltetraphenylporphyrin (Kuila, D.; et al. J. Am. Chem Soc. 1984, 106,
448), with the major distortion from planarity occurring for the N-su
bstituted pyrrole ring. Although the four isomers of CuNPhPPDME are al
l similar when contrasted with CuPPDME, closer examination of the vibr
ational structure allowed the isomers to be separated into two groups.
Differences among pairs of isomers are apparent primarily in the viny
l vibrational modes and vinyl-sensitive porphyrin modes. Even more sub
tle spectral differences distinguish all of the isomers. We present ar
guments suggesting that the spectral characteristics are the result of
electronic rather than kinematic effects.