Enthalpy, activation energy, and rate constant of 9 alkyl, 3 acyl, 3 alkoxyl, and 9 peroxyl radicals with alkanethiols, benzenethiol, and L-cysteine are calculated. The intersection parabolas model is used for activation energy calculations. Depending on the structure of attacking radical, the activation energy of reactions with alkylthiols varies from 3 to 43 kJ mol −1 for alkyl radicals, from 7 to 9 kJ mol −1 for alkoxyl, and from 18 to 35 kJ mol −1 for peroxyl radicals. The influence of adjacent π -bonds on activation energy is estimated. The polar effect is found in reactions of hydroxyalkyl and acyl radicals with alkylthiols. The steric effect is observed in reactions of alkyl radicals with tert-alkylthiols. All these factors are characterized via increments of activation energy. Quantum chemical calculations of activation energy and geometry of transition state were performed for model reactions: C

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A reversible fragmentation of the polyimide chain with N–N bond rupture occurs under 2-electron reduction and lithium insertion.

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A new procedure for the preparation of biocompatible gold nanoparticles using biofla vonoids: rutin, quercetin, and luteolin as reducing agents and stabilizers was proposed. On varying the bioflavonoid concentration, nanoparticles of different size are formed. By the combined use of spectroscopy and atomic force microscopy, the nanoparticle size was estimat ed (40-50 nm). Uniform and highly dispersed gold nanoparticles were obtained at Au : rutin ratios of 1 : 1, 2 : 1, and 4 : 1 and Au : quercetin ratios of 2 : 1 and 4 : 1. The nanoparticle yield remains almost constant as the Au : rutin ratio varies over a broad range from 1 : 1 to 12 : 1. It was suggested that complete reduction of Au III to Au 0 with a large excess of Au is accompanied by extensive oxidation of bioflavonoid involving an intermediate oxidant formed in the system due to the high oxidative capacity of Au III . For elucidating the catalytic role of bioflavonoids in the formation of gold nanoparticles, quantum chemical modeling of the process was performed.

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Solutions of the basic form of polyaniline in m cresol were studied by ESR and optical spectroscopy in the visible region. m Cresol can slowly (during one month) protonate polyaniline. For the first time characteristic features of spin crossover were found: sharp changes in the magnetic susceptibility and the ESR line width of polyaniline at ~200 and 250 K, a smooth decrease in the susceptibility and absorption with the temperature increase from 293 to 423 K, and the temperature hysteresis. The temperature induced structural rear rangements of polyaniline are caused, most likely, by singlet triplet transitions in relatively short sections of the polymer chain. The model of short sections permits to explain the origin of the temperature independent part of susceptibility. Quantum chemical calculations for the aniline dimers and tetramers describe correctly the singlet triplet splitting value, thermo chromism, and HFS constants in the spectrum of polyaniline.The term "spin crossover" (SC) or "spin transition" is used for the description of characteristic phenomena in samples, where transitions between the high and low spin states of the centers of the sample occur upon the temperature change or under pressure or irradiation and lead to the structural rearrangement of the sample.Most systems manifesting SC contain iron(II). 1,2 The systems containing no iron but including, for example, Cu atoms and nitroxy radicals are also known. 3 The energy of low spin states of the centers is usually lower than that of the high spin states and, hence, the fraction of the low spin states increases with the temperature decrease. The geometry of the low spin and high spin centers is differ ent and, therefore, strains accelerating the conversion of the high spin to low spin states increase with an increase in the fraction of the low spin states in the samples, and the phase transition occurs at some temperature. The sharpness of the transition is determined by the degree of cooperativity of the system and, as a rule, the temperature hysteresis is observed. Investigation of the nature of this phenomenon, including establishing conditions for the appearance of cooperativity and the mechanism of an irradiation effect and search for new systems manifest ing SC is the matter of numerous studies. The high sensi tivity of parameters of the systems under study, especially absorption in the visible region and magnetic susceptibil ity, to slight changes in the temperature, pressure, and irradiation makes it possible to use them as sensors, dis plays, and information storage devices. To increase the sharpness of the transition, the centers are bound through ligands into polymer structures; however, no true poly mers exhibiting SC are known. The SC term is applied to both solid state systems with sharp temperature induced transitions and solutions with smooth transitions reflect ing the change in the Boltzmann populations of spin states. The systems manifesting SC are rather few, because they need to fulfill several conditions; in particular, t...