[Molecular organization of pheophytin a in aqueous solutions of detergents]

Absorption, fluorescence and excitation fluorescence spectra of pheophytin a have been measured in aqueous solutions of nonionic (Triton X-100), anionic (sodium lauryl sulphate) and cationic (Cetyl pyridinium chloride) detergents at different concentrations and pH after system relaxation. By measuring the second derivative and differential spectra, it has been shown, that if detergent concentrations are lower than critical micelles concentration, or if the detergent is completely absent, the pigment forms conglomerates containing both dimeric and monomeric forms with an efficient energy transfer between them. If detergent concentrations are higher than critical micelles concentration, pheophytin a localizes in detergent micelle in monomeric form at neutral and acidic pH, and allomerizes at alkaline pH. The spectral characteristics of pheophytin a dimers in the conglomerate and its monomers in micelles poorly (if at all) depend on the sign of the detergent molecule charge.