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Hydrogenase from Thiocapsa roseopersicinaadsorbed on TiO 2particles, using electrons photogenerated in the conduction band of the semiconductor, in the presence of an organic electron donor, carries out hydrogen production with the rate comparable to that obtained with reduced methyl viologen as the substrate. Under conditions of the efficient hydrogenase adsorption on TiO 2(1.6 mM CaCl 2, 0.05 M Tris buffer, pH 7.2) the quantum efficiency of hydrogen photoproduction is up to 10%. Coupling of inorganic semiconductors with bacterial hydrogenase may be regarded as a way to the development of artificial photocatalytic systems of light energy conversion.

A new emission band at 673 nm was detected in the low-temperature fluorescence spectrum of dark-adapted cyanobacteria Gloeotrichia raciborski. The excitation spectrum of this band was close to the absorbance of the isolated reaction centre of photosystem II. The relative intensities of the bands of chlorophyll and pheophytin in this spectrum showed the relative concentrations of these pigments to be about 3:1. The intensity of the band increased with darkness (half-time about 2 h). Under illumination the band rapidly disappeared (half-time about 60 s). The appearance of a 673 nm band in the dark and its disappearance in the light were accompanied by a decrease, and, respectively, an increase in the fluorescence of the PS II band at 697 nm.

Photoreduction of NAD has been accomplished by a system consisting of the NAD‐dependent hydrogenase from Alcaligenes eutrophusimmobilized on CdS particles with formate as artificial electron donor. Enzymatically active NADH is formed under illumination of this system by visible light. Accumulation of the coenzyme dimer (NAD)2was not detected. NAD photoreduction is supposed to proceed via the direct electron transfer from the semiconductor to the enzyme electron transport chain. However, NADH formation as a result of hydrogenase interaction with anion‐radicals (CO.−2)‐formed in the course of formate photooxidation cannot at present be excluded.

Hydrogenase from Thiocapsa roseopersicinaadsorbed on TiO2particles, using electrons photogenerated in the conduction band of the semiconductor, in the presence of an organic electron donor, carries out hydrogen production with the rate comparable to that obtained with reduced methyl viologen as the substrate. Under conditions of the efficient hydrogenase adsorption on TiO2(1.6 mM CaCl2, 0.05 M Tris buffer, pH 7.2) the quantum efficiency of hydrogen photoproduction is up to 10%. Coupling of inorganic semiconductors with bacterial hydrogenase may be regarded as a way to the development of artificial photocatalytic systems of light energy conversion.

Both photogeneration and quenching of singlet oxygen by monomeric and aggregated (dimeric and oligomeric) molecules of bacteriochlorophyll (BChl) d have been studied in solution and in chlorosomes isolated from the green photosynthetic bacterium Chlorobium vibrioforme f. thiosulfatophilum. The yield of singlet-oxygen photogeneration by pigment dimers was about 6 times less than for monomers. Singlet oxygen formation was not observed in oligomer-containing solutions or in chlorosomes. To estimate the efficiency of singlet oxygen quenching an effective rate constant for 1O2 quenching by BChl molecules (kqM) was determined using the Stern-Volmer equation and the total concentration of BChl d in the samples. In solutions containing only monomeric BChl, the kqM values coincide with the real values for 1O2 quenching rate constants by BChl molecules. Aggregation weakly influenced the kqM values in pigment solutions. In chlorosomes (which contain both BChl and carotenoids) the kqM value was less than in solutions of BChl alone and much less than in acetone extracts from chlorosomes. Thus 1O2 quenching by BChl and carotenoids is much less efficient in chlorosomes than in solution and is likely caused primarily by BChl molecules which are close to the surface of the large chlorosome particles. The data allow a general conclusion that monomeric and dimeric chlorophyll molecules are the most likely sources of 1O2 formation in photosynthetic systems and excitation energy trapping by the long wavelength aggregates as well as 1O2 physical quenching by monomeric and aggregated chlorophyll can be considered as parts of the protective system against singlet oxygen formation.

The assignment is presented for the principal phosphorescence bands of protochlorophyll(ide), chlorophyllide and chlorophyll in etiolated and greening bean leaves measured at -196°C using a mechanical phosphoroscope. Protochlorophyll(ide) phosophorescence spectra in etiolated leaves consist of three bands with maxima at 870, 920 and 970 nm. Excitation spectra show that the 870 nm band belongs to the short wavelength protochlorophyll(ide), P627. The latter two bands correspond to the protochlorophyll(ide) forms, P637 and P650. The overall quantum yield for P650 phosphorescence in etiolated leaves is near to that in solutions of monomeric protochlorophyll, indicating a rather high efficiency of the protochlorophyll(ide) triplet state formation in frozen plant material. Short-term (2–20 min) illumination of etiolated leaves at the temperature range from -30 to 20°C leads to the appearance of new phosphorescence bands at about 990–1000 and 940 nm. Judging from excitation and emission spectra, the former band belongs to aggregated chlorophyllide, the latter one, to monomeric chlorophyll or chlorophyllide. This indicates that both monomeric and aggregated pigments are formed at this stage of leaf greening. After preillumination for 1 h at room temperature, chlorophyll phosphorescence predominates. The spectral maximum of this phosphorescence is at 955–960 nm, the lifetime is about 2 ms, and the maximum of the excitation spectrum lies at 668 nm. Further greening leads to a sharp drop of the chlorophyll phosphorescence intensity and to a shift of the phosphorescence maximum to 980 nm, while the phosphorescence lifetime and a maximum of the phosphorescence excitation spectrum remains unaltered. The data suggest that chlorophyll phosphorescence belongs to the short wavelength, newly synthesized chlorophyll, not bound to chloroplast carotenoids. Thus, the phosphorescence measurement can be efficiently used to study newly formed chlorophyll and its precursors in etiolated and greening leaves and to address various problems arising in the analysis of chlorophyll biosynthesis.

By the use of photosensitized luminescence of singlet oxygen (1O2) in CCl4, the rate constants for quenching 1O2by saturated and unsaturated fatty acids were determined. The experimental data suggest that saturated fatty acids quench 1O2via a physical mechanism, presumably as a result of energy transfer to the vibrational sublevels of CH‐ and COOH‐groups. Unsaturated fatty acids are predominantly chemical quenchers. The relative contribution of the physical quenching depends on the number of double bonds in fatty acid molecules. It was found that the quenching activity of egg phosphatidylcholine is approximately equal to the sum of quenching activities of the lipid fatty acids. The data obtained may be used for prediction of the efficiency of singlet oxygen quenching by any lipids whose fatty acid composition is known.

Considering the evolutionary pathways of solar energy conversion, we suggested that some mineral components of the earth's crust might have been capable of electron phototransfer coupled to the metabolic chains of primary heterotrophic cells. We observed a peculiar type of this process when light‐exposed particles of titanium dioxide or some other minerals initiated an electron transfer from organic electron donors to Clostridium butyricumbacterial cells, with hydrogen being evolved as a result of intra‐ and extracellular activity of hydrogenase. The coupling of mineral photocatalysts to bacterial cells may be regarded as a way to create a new type of photobiocatalytic system.