Adsorption Of Chlorophyll Research Articles

Electrochemistry and photoelectrochemistry of chlorophyll on a metallic electrode: Part I. properties of chlorophyll adsorption films on metals

According to absorption and fluorescence spectra, chlorophyll solubilized in aqueous solution exists in these systems in monomeric form. It adsorbs on an amalgamated gold electrode firmly and irreversibly. Two redox reactions of adsorbed chlorophyll can be observed at −0.5 and −1.0 V (vs. SHE). The first reaction is accompanied by protonation and is ascribed to the reduction of the carbonyl group of the cyclopentanone ring. The second reaction does not involve proton consumption and is due to the addition of one electron to the porphyrin ring. The irreversible “adsorption isotherm” reveals a phenomenon similar to surface condensation. The limiting coverage corresponds to a monolayer of chlorophyll molecules adsorbed in a flat orientation. The absorption spectra of adsorbed chlorophyll at its low coverages are fairly similar to its spectrum in monomeric solution. At high coverages, a long wave shift of the red maximum typical of strong intermolecular interaction of pigment molecules is observed. Spectra in s-polarized light confirm the flat orientation of the adsorbed molecules. The extinction coefficient of adsorbed chlorophyll exceeds the same in solution by two orders of magnitude. Unusually firm adsorption taking place without any destruction of the organic molecule, formation of the chlorophyll radical anion in aqueous solution without proton attachment, an abnormally high extinction coefficient — all these peculiarities can be explained by a very strong interaction of the π-electrons of the porphyrin ring with the metal.

ChemInform Abstract: MODEL SYSTEMS FOR CHLOROPHYLL PHOTOCHEMISTRY: RETENTION OF FLUORESCENCE AT HIGH CHLOROPHYLL DENSITY AT A HYDROPHOBIC‐HYDROPHILIC INTERFACE

Many model systems containing chlorophyll show concentration quenching of fluorescence at quite moderate occupancies of the available phase space. A new kind of model system has been introduced, involving adsorption of chlorophyll and certain other amphiphilic substances to particles of polyethylene swollen with hydrocarbons, in which fluorescence is retained at coverages approaching a monolayer. In the example illustrated, the fluorescence lifetime is undiminished in spite of evidence for the prescence of associated chlorophyll species along with the monomer. The preservation of fluorescence is probably owing to a combination of high viscosity in the swollen polyethylene phase and the presence of a surfactant to keep the chlorophyll in monomeric and well-defined associated forms.

Model systems for chlorophyll photochemistry: retention of fluorescence at high chlorophyll density at a hydrophobic-hydrophilic interface

Many model systems containing chlorophyll show concentration quenching of fluorescence at quite moderate occupancies of the available phase space. A new kind of model system has been introduced, involving adsorption of chlorophyll and certain other amphiphilic substances to particles of polyethylene swollen with hydrocarbons, in which fluorescence is retained at coverages approaching a monolayer. In the example illustrated, the fluorescence lifetime is undiminished in spite of evidence for the prescence of associated chlorophyll species along with the monomer. The preservation of fluorescence is probably owing to a combination of high viscosity in the swollen polyethylene phase and the presence of a surfactant to keep the chlorophyll in monomeric and well-defined associated forms.

236 - Electrochemical study of chlorophyll adsorption layers

Chlorophyll adsorption on an amalgamated gold electrode was studied and found to be irreversible. Two-dimensional condensation occurs from the solution resulting in the formation of a monolayer. At chlorophyll concentrations higher than 10 −6 M, polylayer condensation is observed. Chlorophyll in the monolayer is reduced reversibly. Its reduction involves proton addition. The reduction of the polylayer film is strongly retarded.

Electrochemical study of chlorophyll adsorption layers

Chlorophyll adsorption on an amalgamated gold electrode wasstudied and found to be irreversible. Two-dimensional condensation occurs from the solution resulting in the formation of a monolayer. At chlorophyll concentrations higher than 10−6 M, polylayer condensation is observed. Chlorophyll in the monolayer is reduced reversibly. Its reduction involves proton addition. The reduction of the polylayer film is strongly retarded.

Some properties of chlorophyll a at hydrocarbon-water interfaces and in black lipid membranes.

Chlorophylla is very surface active in the system 2,2,4-trimethylpentanewater. The standard free energy of adsorption may be as high as 10.6 kcal/mole. However, chlorophyll adsorption at this interface is unable to stabilize black membranes. Black films formed from solutions of glyceryl monooleate and chlorophylla exhibit a weak fluorescence which indicates that a small amount of pigment, ca. 1 to 2% by area, may be contained in the membranes. Calculations based on adsorption data show that inclusion of somewhat more chlorophylla than this might be expected. However, interfacial tension data for mixed solutions do not support this expectation.