Spectral properties of bacteriochlorophyll c in organisms and in model systems

Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell f ragments embedded in stretched polymer film were measured. In pigment sampl es the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and ether forms of this pigment and bacteriopheophytin (with absor ption at 670 nm) were present. Tn bacteria samples, embedded in polymer, ol igomers were in high degree disaggregated and as a result the absorption ab out 670 nm was observed. Previously for similar sets of samples the decay o f fluorescence excited only at one wavelength was analyzed on three exponen tial components, but exact lifetime values of these components for various samples were different, The aim of present paper was to check if these diff erences occur because of various contributions to decay from three well def ined forms or if they were related to the existence of several pigment form s with slightly different lifetimes, The global analysis of data obtained f or various excitation and observation wavelengths of fluorescence were done . From this analysis it follows that the second situation occurs. For a mod el system containing artificial oligomers the largest component of decay ha s tau (4) of about 0.183 ns or 0.136 ns depending an observation wavelength . For the bacteria sample, in which the emission at 680 nm is the superposi tion from various pigments, global analysis done for various excitation wav elengths shows also that the tau values differ depending on the regions of fluorescence observation. From polarized spectra, it follows that in the mo del system the pigments absorbing at 670 nm are randomly distributed wherea s oligomers are highly oriented, In bacteria fragments absorbing at 670 nm pigment molecules can be divided into two groups: one oriented along the ax is of film stretching and the second practically randomly distributed. In l iving organisms, under some conditions, small amount of 670 nm pigments can be present and can work as excitation energy traps or as antenna transferr ing the excitation. Present results show that the role of various pools of 670 nm absorbing pigments can be different because of their differing orien tation.