Fluorescence, absorption and electron spin resonance study of bacteriochlorin a incorporation into membrane models

Analysis of the bacteriochlorin a absorption spectra suggests the existence of a monomer-dimer equilibrium, particularly intense in phosphate buffer a nd favored by a decrease of the pH. The dye in methanolic solution is predo minantly in monomeric form. Fluorescence and electron spin resonance nitrox ide spin labeling measurements indicate that incorporation into the lipid p hase of dimyristoyl-L-alpha-phosphatidylcholine liposomes induces dye monom erization. Moreover, the molecules are bound in the external surface of the vesicles and a complete incorporation is ensured by a lipid-to-dye ratio g reater than 125. (C) 1999 Elsevier Science B.V. All rights reserved.