Abstract
The environmental effects in electronic and vibrational spectra of chlorophyll a are investigated. The red-shifts of the absorption maximum of chlorophyll a are analyzed using an approach based on separate evaluation of nonspecific (solvatochromic) and specific effects of the solvent. They are correlated with the frequency of the keto C = O group vibration determined by resonance Raman spectroscopy. This correlation shows that hydrogen bonding may quantitative account for spectral shifts in protic solvents. Noticeable extra red-shifts related to coordination appear only in chlorophyll six-coordinated with nitrogen ligands. Resonance Raman spectra at 77 K indicate that the formation of six-coordinated chlorophyll depends in a conspicuous way on the structure of the ligand's lone-pair orbitals. In nonprotic solvents, the free keto group frequency (at least 1686 cm −1 is a function of both the refractive index and dielectric permittivity of the solvent and is remarkably dependent on temperature. The comparison of these data with absorption wavelengths and with resonance Raman frequencies of the keto C = O group of chlorophyll in vivo confirms a significant contribution of hydrogen bonding and nonspecific interactions to spectral shifts in vivo.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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