Aggregation of chlorophylls in monolayers. VI. Infrared study of the CH stretching bands of chlorophyll a and of chlorophyll b in monolayers.
The CH vibrational stretch bands of chlorophyll (Chl) in monolayers, obtained by the Langmuir-Blodgett technique have been studied by infrared spectroscopy. Compared to a solution or to a multilayer which shows three to four bands, the spectra of Chl a or Chl b molecules in monolayers have revealed more than seven bands, which are assigned to the various CH groups in the molecule. In contrast to solutions or to multilayer samples which give featureless bands, each band of the monolayers is composed of many components which are modified when the system is perturbed either by drying or by hydration techniques. The separation between the components of the CH aliphatic bands is typical of crystalline field splitting and the modification of the intensities of these components is associated with the movement of the phytyl chain of the chlorophyll molecules. The CH aromatic stretch bands have been observed; the displacement and variation of the intensities of these bands are associated with deformation of the porphyrin ring. The CH band of the formyl group on Chl b has also been observed. The displacement and variation of the intensity of this band are related to the association that this group makes with the surrounding molecules and with the displacement of the porphyrin ring.
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Centre de recherche en photobiophysique, Université du Québec à Trois - Rivières, Trois - Rivières, Québec G9A 5H7, Canada.