Preparation of multilayers containing chlorophylla and/or phosphatidylcholine and chemical stability of chlorophylla molecules in the multilayers

Abstract

Summary. The Langmuir-Blodgett films consisting of mixed monolayers containing chlorophyll a (Cht-a) and/or phosphatidylcholine with various molar ratios could be well prepared on glass plates previously covered with three monolayers of cadmium eicosanate. Thin-layer and high-performance liquid chromatographic examinations revealed that the photostability of Chl-a molecules in various media is in the following order: the mixed mono-or multilayers > pure Chl-a mono-or multilayers >> organic solvents.It has generally been recognized that photosynthesis is carried out in the chloroplast where chlorophyll (Chl) molecules and all other photosynthetic materials are incorporated into highly organized lamellar structures. The concept of Chl aggregate with the layered structure has induced numerous studies on the Langmuir-Blodgett films of Chl as a biomimetic membrane system [11]. The aggregation of Chl molecules in vitro should be quite different from that of Chl molecules in vivo. Nevertheless, a detailed knowledge of the two-dimensionaUy packed aggregate forms in vitro would be neccessary to gain insight into the stability of Chl molecules and also to elucidate the relationship between the state and role of Chl in photosynthesis.The present series of work [1,2,7,8] was designated to investigate the properties of Chl in closely packed layers (Langmuir-Blodgett films). Recently, we have re-examined and have established methods for the preparation of chlorophyll a (Chl-a) monolayers [7] and multilayers [8] and have also developed a method for the preparation of phosphatidylcholine (PC) multilayers [5]. In this article, the chemical stability of Chl in multilayers as well as the method for the preparation of the mixed multilayers consisting of Chl-a and PC monolayers will be reported. Materials and MethodsAll the experiments were performed at 20_+ 2 ~ in total darkness or under dim green light unless otherwise stated.Chl-a was carefully prepared from fresh spinach leaves according to the method of Iriyama, Shiraki and Yoshiura [91 or from Porphyra yezoensis according to the method of Iriyama [6]. The molar extinction coefficients of Comar and Zscheile [4] were used in the determination of the concentrations of Chl-a. The purity and chemical stability of Chl-a were examined by thin-layer chromatography [16] and by high-performance Iiquid chromatography [10, 19]. Thin-layer and high-performance liquid chromatographic analyses revealed that Chl-a preparations used did not contain any teal yellow pigments, chlorophyll b or degradation products of Chl. Absorption spectra of the Chl-a preparations dissolved in diethyl ether did not show any significant differences in comparison with the literature [18] within experimental error; the ratio of absorbance of the Soret peak at 427.0 (+_1.0)nm to the red peak at 660 (_+0.5)nm was 1.30 (+0.01). The purity of Chl-a preparations was 99.0 100% on dry wt basis. Pheophytin a (Pheoa), and chlorophyll a' (Chl-a') used in thin-layer chromatographic analysis as standard materials were prepared...

Control of Molecular Arrangement in Langmuir−Blodgett Films of Chlorophyll a Prepared in Various Gas Phases Studied by Ultraviolet−Visible and Infrared Spectroscopies and Atomic Force Microscopy,

“…Investigations on LB films of Chl- a may be classified into four categories: studies on their structure, stability, morphology, and function. Iriyama , examined the stability of Chl- a in multilayer LB films and suggested preferable conditions for fabricating high-quality LB films of Chl- a . Iriyama and Yoshiura explored morphological properties of LB films of Chl- a by electron microscopy combined with a plasma replica method.…”