Russian Journal of Physical Chemistry B最新文献

Modeling the optical response of photosynthetic pigments is an integral part of the study of fundamental physical processes of interaction between multi-atomic molecules and the external electromagnetic field. In contrast to ab initio methods for calculating the ground and excited states of a molecule, the use of semiclassical quantum theories allows us to use characteristic functions, such as spectral density, to calculate absorption spectra rather than considering the full set of electron and atom configurations. The main disadvantage of this approach is the comparison of calculated and experimental spectra and, as a consequence, the need to justify the uniqueness of the obtained parameters of the system under study and to evaluate their statistical significance. In order to improve the quality of the optical response calculation, a heuristic evolutionary optimization algorithm was used in this work, which minimizes the difference between the measured and theoretical spectra by determining the most appropriate set of model parameters. It is shown that, using as an example the spectra of photosynthetic pigments measured in different solvents, the optimization of modeling allowed us to obtain a good agreement between the calculated and experimental data and to unambiguously determine the electron-phonon interaction coefficients for the electronic excited states of chlorophyll, lutein and β-carotene.

The relaxation dynamics of “hot” and band-edge excitons in ZnCdS (2.8 eV edge exciton) and ZnCdS/ZnS (2.7 eV) quantum dot alloys was studied using femtosecond pump (360 nm, 3.44 eV, 25 fs)— probe (380–700 nm) laser spectroscopy. Transients were studied as a function of the pump pulse energy, which changes the number of excitons. The relaxation of the “hot” exciton is controlled by the Auger mechanism. The decay time of a “hot” exciton depends very weakly on the pump energy and is in the range of 140–190 fs. The decay of a band-edge exciton depends significantly on the pump energy, which suggests an Auger recombination mechanism. The multiexponential transient decay is well described within the stochastic model with only two constants (k_{i}^{{Auger}}) and (k_{i}^{1} = {i mathord{left/ {vphantom {i {{{tau }_{1}}}}} right. kern-0em} {{{tau }_{1}}}}).

The azobisisobutyronitrile (AIBN)-initiated oxidation of soy lecithin (RH) is studied in a wide range of RH (0.027−0.4 mol/L) and AIBN (0.01–0.043 mol/L) concentrations. It is found that at high concentrations of lecithin the oxidizability parameter a = k_p/(2k_t)^0.5, where k_p and k_t are the constants of the rate of chain propagation and termination, is significantly reduced, while regardless of the concentration of lecithin, a linear dependence of the initiation rate on (W_i)^0.5 is maintained. The antiradical activity of antioxidants (AOs) of different classes at [RH] = 0.4 mol/L is assessed, showing that the antiradical activity of phenols in lecithin is significantly lower than in hydrocarbons. The antiradical activity and inhibitory effects in the oxidation of lecithin decrease in the following order: α-tocopherol > 3,6-di-tert.butyl-1,2-benzoquinone > quercetin > 2,4,6-tri-tert.butylphenol.

In this paper, the mechanisms of the formation of the bisretinoid oxidation products in lipofuscin granules (LGs) isolated from the retinal pigment epithelium cells of the human eye are studied. The physicochemical characteristics of the bisretinoid photooxidation products are described. The methods of IR spectroscopy, Raman spectroscopy, fluorescence spectroscopy, scanning confocal microscopy, time-of-flight mass spectrometry of secondary ions, and high-performance liquid chromatography are used for the study. The properties of the products of photooxidation and degradation of the fluorophore of LGs, including synthetic N-retinylidene-N-retinylethanolamine (A2E), are described in detail. It is shown that the products of oxidative degradation of LGs are similar to the products of photooxidation of the main bisretinoid of LGs: A2E. These data are important both for understanding the mechanisms of the formation of cytotoxic products in LGs and for establishing their chemical nature.

Mixed phosphonium-iodonium ylides are of interest as reactants for the synthesis of new heterocyclic compounds. Recently it has been shown that under irradiation the reactions of phosphonium-iodonium ylides occur with the formation of radicals. The radicals generated in the photolysis of the ylide itself and its fragments, diphenyliodonium salt and triphenylphosphine, or compounds participating in its reactions, dichloromethane and phenylacetylene, are studied with the use of PBN and DMPO spin traps. The obtained results confirm the radical mechanism of the ylide photodecomposition and have allowed us to specify the composition of the primary radicals generated in the photolysis. The unknown EPR parameters of spin adducts are determined for some radicals.

The kinetics of singlet fission (SF) (i.e., spontaneous splitting of the excited singlet state into a pair of triplet (T) excitons (TT-pair)) is known to be significantly affected by TT-annihilation (TTA), which manifests itself in magnetic field effects on the TTA and, in particular, in the magnetic-field dependence of the SF-kinetics. In this study, in the two-state model (TSM), a method is proposed for treating the magnetic field effects on the SF-kinetics, which allows for the correct description of the manifestation of the stochastic migration of T-excitons assuming that the manifestation results from the transition from two states of coupled and freely diffusing T-excitons. In the TSM, the analytical expression for the magnetic-field-dependent part of the SF-kinetics is derived. This expression is applied to the analysis of the SF-kinetics measured in amorphous rubrene films in the absence of a magnetic field and in the field B = 8 kGs.

The fragmentation processes of adenine (Ade, C₅H₅N₅) and cyclodiglycine (DKP, C₄H₆N₂O₂) ions formed in capturing a single electron during the interaction of molecules in the gas phase with C²⁺ and O²⁺ ions with an energy of 12 keV are studied by time-of-flight mass spectrometry. The experimentally observed dependence of the relative fragmentation cross section of molecular ions on the type of projectile is qualitatively explained within the framework of the quasi-molecular model. Using the multiconfiguration method of a self-consistent field in a complete active space (CASSCF), the fragmentation reaction paths of Ade⁺ and DKP⁺ ions are calculated. The calculated energy values of the appearance of fragments are in close agreement with the available experimental data.

Stepwise fourfold addition reactions of allyl chloride (AC) growth radicals of the vinyl type to fullerene C₆₀ leading to the formation of practically all possible types of adducts are considered. The structures of the reaction products are analyzed and the thermal characteristics, such as thermal effects and enthalpies of activation, are calculated. In the radical-initiated interaction of AC and fullerene C₆₀, up to three AC growth radicals can be added. In this case, the trisadducts are stable allyl-type radicals, to which a fourth AC radical can be attached to form molecular products.