ATR FT-IR STUDY OF A MONOLAYER FILM OF CHLOROPHYLL-A ON A GERMANIUM PLATE

Infrared spectra of one-monolayer Langmuir-Blodgett (LB) films of chlorophyll-a (Chl-a) can be obtained with a high signal-to-noise ratio by using the attenuated total reflection (ATR) technique. The observed spectra indicate that Chl-a assumes a five-coordinated monomer in the LB films; it seems that both the ester and keto C=O groups are free from any interactions, and a water molecule coordinates to the Mg atom. Comparison of the spectra of the one-monolayer LB films with those of the cast films shows that the structure of Chl-a is quite different between the two kinds of films; in contrast to the LB films the cast films are liable to have the dimer or oligomer of Chl-a. The fact that the five-coordinated monomer is predominant in the LB films suggests that Chl-a molecules are highly oriented in the one-monolayer LB films.