IDENTIFICATION OF METALLOPORPHYRINS BY 3RD-DERIVATIVE UV VIS DIODE-ARRAY SPECTROSCOPY

Qualitative analysis of organic compounds is expedited by third-derivative processing of diode array UV/vis spectra which can locate lambda(max) with +/-0.02 nm precision, or 1/100 of the present diode interval. The technique was applied to over 50 metalloporphyrins, primarily geological residues of ancient chlorophyll, and the results suggest broader applicability. Among metalloporphyrins, the Soret band wavelength, lambda(Soret), varies with the type of functional group structure on the periphery of the 20-carbon porphyrin chromophore. Distinctive lambda(Soret) ranges are defined by exocyclic structure (butano, propano, ethano), or lack thereof (etio). Among etioporphyrins lambda(Soret) varies with the number of alkyl substituents. Etio- and ethanoporphyrin isomers with the same alkyl groups are least differentiated. Fifty or more spectral classes can be specified by including lambda(alpha) and lambda(beta), or higher than that when other data, i.e., molecular mass or chromatographic data, are added. Moreover, such results can be obtained 1000-fold faster than conventional NMR and MS structure determinations. The new technique allows one to differentiate quickly among congeners, homologues, and isomers, to use wavelength data to guide chemical isolations of known components from mixtures, and to expedite the isolation of unknowns or new structures when the technique is adjoined to HPLC separations.