The effect of some antiseptic drugs on the energy transfer in chromatophore photosynthetic membranes of purple non-sulfur bacteria Rhodobacter sphaeroides

Photosynthesis Research - Chromatophores of purple non-sulfur bacteria (PNSB) are invaginations of the cytoplasmic membrane that contain a relatively simple system of light-harvesting...     

The rate of Q(x)→Q(y) relaxation in bacteriochlorophylls of reaction centers from Rhodobacter sphaeroides determined by kinetics of the ultrafast carotenoid bandshift

Transient absorption changes induced by excitation of isolated reaction centers (RCs) from Rhodobacter sphaeroides with 600nm laser pulses of 20fs (full width at half maximum) were monitored in the wavelength region of 420-560nm. The spectral features of the spectrum obtained are characteristic for an electrochromic band shift of the single carotenoid (Car) molecule spheroidene, which is an integral constituent of these RCs. This effect is assigned to an electrochromic bandshift of Car due to the local electric field of the dipole moment formed by electronic excitation of bacteriochlorophyll (BChl) molecule(s) in the neighborhood of Car. Based on the known distances between the pigments, the monomeric BChl (B(B)) in the inactive B-branch is inferred to dominate this effect. The excitation of B(B) at 600nm leads to a transition into the S(2) state (Q(x) band), which is followed by rapid internal conversion to the S(1) state (Q(y) band), thus leading to a change of strength and orientation of the dipole moment, i.e., of the electric field acting on the Car molecule. Therefore, the time course of the electrochromic bandshift reflects the rate of the internal conversion from S(2) to S(1) of B(B). The evaluation of the kinetics leads to a value of 30fs for this relaxation process. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Comparison of tryptophan fluorescence lifetimes in cyanobacterial photosystem I frozen in the light and in the dark

Photosynthesis Research - The dependence on temperature of tryptophan fluorescence lifetime in trimeric photosystem I (PSI) complexes from cyanobacteria Synechocystis sp. PCC 6803 during the...     

The rate of Qx→Qy relaxation in bacteriochlorophylls of reaction centers from Rhodobacter sphaeroides determined by kinetics of the ultrafast carotenoid bandshift

Transient absorption changes induced by excitation of isolated reaction centers (RCs) from Rhodobacter sphaeroides with 600 nm laser pulses of 20 fs (full width at half maximum) were monitored in the wavelength region of 420–560 nm. The spectral features of the spectrum obtained are characteristic for an electrochromic band shift of the single carotenoid (Car) molecule spheroidene, which is an integral constituent of these RCs. This effect is assigned to an electrochromic bandshift of Car due to the local electric field of the dipole moment formed by electronic excitation of bacteriochlorophyll (BChl) molecule(s) in the neighborhood of Car. Based on the known distances between the pigments, the monomeric BChl (B_B) in the inactive B-branch is inferred to dominate this effect. The excitation of B_B at 600 nm leads to a transition into the S₂ state (Q_x band), which is followed by rapid internal conversion to the S₁ state (Q_y band), thus leading to a change of strength and orientation of the dipole moment, i.e., of the electric field acting on the Car molecule. Therefore, the time course of the electrochromic bandshift reflects the rate of the internal conversion from S₂ to S₁ of B_B. The evaluation of the kinetics leads to a value of 30 fs for this relaxation process. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Temperature dependence of tryptophan fluorescence lifetime in aqueous glycerol and trehalose solutions

The temperature dependences of tryptophan fluorescence decay kinetics in aqueous glycerol and 1 M trehalose solutions were examined. The fluorescence decay kinetics were recorded in the spectral region of 292.5–417.5 nm with nanosecond time resolution. The kinetics curves were approximated by the sum of three exponential terms, and the spectral distribution (DAS) of these components was determined. An antisymbatic course of fluorescence decay times of two (fast and medium) components in the temperature range from –60 to +10°C was observed. The third (slow) component showed only slight temperature dependence. The antisymbatic behavior of fluorescence lifetimes of the fast and medium components was explained on the assumption that some of the excited tryptophan molecules are transferred from a short-wave-length B-form with short fluorescence lifetime to a long-wavelength R-form with an intermediate fluorescence lifetime. This transfer occurred in the indicated temperature range.     

Disproportionate effect of cationic antiseptics on the quantum yield and fluorescence lifetime of bacteriochlorophyll molecules in the LH1-RC complex of R. rubrum chromatophores

Photosynthesis Research - Photosynthetic membrane complexes of purple bacteria are convenient and informative macromolecular systems for studying the mechanisms of action of various physicochemical...