[Molecular organization of aggregated forms of chlorophyll and its analogs].

Infrared spectra (in the region of 1800-1600 cm-1) of aggregated protochlorophyll, chlorophyll a and b, bacterioviridin, protopheophytin, pheophytin a (in the solid films) with different absorption spectra were studied. The formation of various types of aggregates is due to the realization of different modes of intermolecular bonding. The mode of interaction depends upon the chemical structure of the pigment and upon the inclusion of low-molecular addenda into the structure of aggregates. The forms 677 nm of chlorophyll a and 658 nm of chlorophyll b appear when the coordination bonds between the keto groups of the cyclopentanone ring and central magnesium atom are formed. The longwave forms of chlorophyll a (745 nm) and chlorophyll b (675 nm, 725 nm) are formed when methanol molecules are involved in the intermolecular bonds. The coordination bonds between C=O and magnesium atom in the longwave aggregate of bacterioviridin (750 nm) are observed without participation of the low-molecular addenda, The formation of the protochlorophyl 635 nm form and aggregated forms of magnesium-free pigments occurs without participation of carbonyl groups probably by direct interaction between the eta-electron systems of molecules. The frequencies of carbonyl groups of the solid films in dioxane vapours causing absorption maxima at 690 nm (chlorophyll a) and 670 nm (chlorophyll b) are not shifted as compared to the dissolved pigments. Thipoints to the intermolecular interaction without participation of C=O groups.