Light-induced structural changes in photosynthetic reaction centres studied by ESEEM of spin-correlated D+QA− radical pairs

AbstractZn-substituted Rhodobacter sphaeroides R26 reaction centres (RCs) frozen in the dark and under illumination exhibit quite different recombination kinetics of the D+QA− radical pairs [Kleinfeld et al., Biochemistry, 23 (1984) 5780]. We have applied electron spin echo envelope modulation (ESEEM) of the spin-correlated D+QA− radical pairs to assess a possible light-induced change in the distance between the D and QA cofactors. The recombination kinetics and the field-swept spin-polarized EPR signal for the two preparations have been monitored by time-resolved EPR spectroscopy. For the samples frozen under illumination, a slight increase in the distance, 0.4±0.2 Å, has been detected

Distance between a native cofactor and a spin label in the reaction centre of Rhodobacter sphaeroides by a two-frequency pulsed electron paramagnetic resonance method and molecular dynamics simulation

Biological and Soft Matter Physic

Use of spin labels to study membrane proteins by high-frequency electron nuclear double resonance spectroscopy

The applicability of spin labels to study membrane proteins by high-frequency electron nuclear double resonance spectroscopy is demonstrated. With the use of bacteriorhodopsin embedded in a lipid membrane as an example, the spectra of protons of neighboring amino acids are recorded, electric field gradients at the membrane surface are detected, and the constant of hyperfine interaction with the chlorine nucleus at the site of ion trapping is measured

Magnetophotoselection study of the lowest excited triplet state of the primary donor in photosynthetic bacteria

The first time-resolved magnetophotoselection study of the primary donor tripler state (P-3) in bacterial reaction centers from Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis is reported. With direct excitation of the primary donor, this approach provides the orientation (spherical coordinates delta, colatitude, and gamma, longitude) of the excited optical transition moment in the principal triplet axis system. It is essentially free from the effects of spin-lattice relaxation of P-3, enabling magnetophotoselection measurements over a wide temperature range. Two independently measured triplet-state spectra, excited with light polarized parallel and perpendicular to the EPR magnetic field, are simulated with the same set of parameters. This procedure results in a high precision (ca. +/-5 degrees with sufficient signal/noise ratio) of the obtained spherical coordinates of the optical transition moment vector. We find delta = 80 +/- 5 degrees, gamma = 70 +/- 5 degrees and delta = 75 +/- 5 degrees, gamma = 70 +/- 5 degrees for Rb. sphaeroides R26 and Rps. viridis, respectively. We demonstrate that excitation of the sample with nonpolarized light is essentially nonisotropic, Neglect of this effect in spectral simulations of light-induced signals may lead to considerable error in the parameters determined

Spin polarization induced by optical and microwave resonance radiation in a Si Vacancy in SiC: a promising subject for the spectroscopy of single defects

Depending on the temperature, crystal polytype, and crystal position, two opposite schemes have been observed for the optical alignment of the populations of spin sublevels in the ground state of a Si vacancy in SiC upon irradiation with unpolarized light at frequencies of zero-phonon lines. A giant change by a factor of 2¿3 has been found in the luminescence intensity of zero-phonon lines in zero magnetic field upon absorption of microwave radiation with energy equal to the fine-structure splitting of spin sublevels of the vacancy ground state, which opens up possibilities for magnetic resonance detection at a single vacancy

The specifications of maintenance and repair of automotive engineering of military unit during combat actions in the antiterrorist operation

В статье проанализированы особенности использования подвижных ремонтных средств войскового звена по проведению технического обслуживания и текущего ремонта автомобильной техники воинских частей Вооруженных Сил Украины, принимающих участие в антитеррористической операции.У статті проаналізовані особливості використання рухомих ремонтних засобів військової ланки по проведенню технічного обслуговування й поточного ремонту автомобільної техніки військових частин Збройних Сил України, що брали участь в антитерористичній операції.The peculiarities of using mobile repair facilities of military unit of carrying out repairs and maintenance of motor vehicles of military units of the Ukrainian Armed Forces, participating in the anti-terrorist operation were analyzed in the article