Molecular modeling of the influence of complex formation on the conformation and electronic absorption spectra of crown-containing styryl dyes

The conformation and electronic absorption spectra of crown-containing styryl dyes and their complexes with metal salts have been calculated. The long-wave absorption bands have been assigned. It was shown that the observed large hypsochromic shift of the absorption spectra during the formation of complexes of the cis-form of the dyes under consideration with alkaline earth ions is due to a change in the conformation of the chromophore and the resultant approximate prohibition with respect to symmetry of the long-wave electronic transition.Institute of Chemical Physics, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 39–45, March–April, 1993.     

A spectrofluorimetric study of the interaction of myosin with ATP

Formation of the enzymatically active rnyosin-ATP complex produces a reversible change in the fluorescence of the tryptophan residues, which may be interpreted in terms of a structural rearrangement causing the tryptophan to enter a more hydrophobic environment. Fluorescence is used to follow the kinetics of the formation and decomposition of the enzyme-substrate complex.     

A modified model of diffusion-controlled reactions

The treatment used for diffusion-controlled reactions is extended to the case when the final jumplike step of the reagent approach differs essentially from the preceding diffusion. In terms of the model proposed it is possible to take into account, in a simple way, chemical inhomogeneity of the reagents when the in-cage reaction rate depends on the pair state (for example, on the molecular orientation). In this connection the reaction can be controlled either by the reagent intrusion into the solvation shell of the partner, or by the in-cage relaxation.     

Resonance Raman spectroscopy of polyene compounds (multimode systems). Polyacetylene synthesized from cyclooctatetraene

Specific features of the excitation spectra of resonance Raman (RR) lines in multimode systems were characterized. Based on this, the spectra, the structure, and the composition of polyacetylene (PA) synthesized by polymerization of cycloocta-1,3,5,7-tetraene in the presence of metathesis catalysts were investigated. A dependence of frequencies and intensities of the C-C and C=C stretching lines on the exciting light wavelength was found and explained by broad distribution of defect-free conjugated polymer segments in the PA samples studied on the number of double bonds incorporated in them. A procedure for the calculation of the distribution functions and of the shapes of RR lines was proposed. These functions are bimodal. A reversiblecis-trans-transition was discovered in the PA samples not subjected to heat treatment, which was attributed to the presence of macrocyclic polyene structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2016–2020, August, 1996.     

Nitro derivatives of the thiophene series. 3. Study of the nitration of thiophene α,β-unsaturated ketones in the presence of protic and aprotic acids

The nitration of 4-(5-R-2-thienyl) but-3-en-2-ones (R = H, CH₃, C₂H₅) with a nitrating mixture and group I and III metal nitrates in concentrated sulfuric and trifluoroacetic acids, as well as in the presence of aluminum chloride, was investigated. Nitration with a nitrating mixture and potassium, sodium, lithium, copper, and aluminum nitrates in sulfuric acid takes place in the heterocyclic ring to give a mixture of nitro ketones. Nitration in trifluoroacetic acid and in the presence of aluminum chloride proceeds with the formation of a single -nitro ketone. The structures of the substances obtained were proved by means of the IR and PMR spectra. A possible mechanism of the reaction is discussed.See [1] for Communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 753–757, June, 1981.