[Spectral properties and structure of bacteriopheophytin a dimer]

Abstract

In alcohol-glycerol solutions of bacteriopheophytin alpha takes place dimer formation with a long wave absorption band at 857 nm, the dimerization constant enhances with glycerol content increasing in solution. The measurement of absorption, fluorescence and CD spectra allowed to characterize the main electronic transitions (Qy, Qx, Bxy) of the dimer. For the first electronic transition (Qy) of the dimer as compared to the monomer the same oscillator strength, spectral bands narrowing of splitting components and significant increase of rotation strength in CD spectrum were found. The structural model of bacteriopheophytin a dimer is suggested on the basis of the data obtained. Coincidence of the values of the long wave shift and exitonic splitting of Qy transition for the dimer investigated and antennae bacteriochlorophylls shows that the appearance of these properties does not require pigment protein interaction. Significant (20--30 times) exceeding of the rotation strength of Qy transition of the bacteriopheophytin dimer as compared ato the antennae complex pigments can indicate the absence of this dimer in intact structures.