Chlorophyll and pheophytin derivatives in geochemical transformation pathways: A surface-enhanced resonance Raman spectroscopic study

Protected surface-enhanced resonance Raman spectroscopy (PSERRS) has been used to study a number of chlorophyll transformation products that have been suggested as intermediates in the so-called Treibs hypothesis which describes the transformation of ancient chlorophyll a (chla) in the biosphere into desoxophylloerythroetioporphyrin (DPEP) found in sedimentary environments. Both Soret- and Q_y-resonant PSERR spectra have been recorded, providing two-dimensional structural fingerprints containing a number of bands which enable the presence of specific peripheral substituents to be identified. Some of these marker bands can be assigned directly to vibrational modes of the particular substituents. This has allowed further characterization of the vibrational spectrum of chl a; in particular, a vinyl mode has been identified which previously was thought to be Raman silent. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 147–159, 1998