Depolymerization of chitin and chitosan in the course of base deacetylation

Depolymerization of chitin and chitosan in the course of deacetylation in an alkaline medium was studied, and the influence exerted on the process by the nature and concentration of the alkali (NaOH, KOH) and salts (NaCl, NaI, KI) was examined.     

On the term “pH of the precipitation onset of heavy metal hydroxides”

It is suggested to take as pH of the precipitation onset of metal hydroxides the pH at which 10% of the initial amount of metal ions has precipitated. An equation for calculating this quantity is presented.     

Specific features of separate and joint mastication of natural and 1,4-cis-butadiene rubbers in the presence of dibenzoylaminodiphenyl disulfide

Variation of the molecular structure characteristics and properties of natural and 1,4-cis-polybutadiene rubbers (gel content, molecular weight, degree of branching of macromolecules, viscosity) in the course of their separate and joint mastication in the presence of dibenzoylaminodiphenyl sulfide as mastication accelerator or without it was studied.     

Deuteron structure and diffractive deuteron-nucleus interaction

A nonrelativistic deuteron wave function involving the D-wave state and having a correct asymptotic behavior is constructed on the basis of the experimentally measured deuteron charge form factor G _C(q) and deuteron structure function A(q). The differential cross section for elastic deuteron-nucleus scattering is calculated by using this wave function and is found to agree with experimental data at an energy of 110 MeV. Integrated cross sections for various processes involving deuteron-nucleus interactions are also calculated. The distribution in the emission angle of the center of mass of the neutron-proton system produced in the diffractive dissociation of 110-MeV deuterons in the field of ²⁰⁸Pb nuclei is obtained.     

Investigation into the dielectric relaxation of vinylidene fluoride copolymers with hexafluoropropylene

Four relaxation processes and one ferroelectric-paraelectric phase transition are revealed in vinylidene fluoride-hexafluoropropylene copolymers with different ratios of the components in the temperature range from ?100 to 150°C. The relaxation process occurring at the lowest temperature is associated with the local mobility of the chains, whereas the relaxation process at a higher temperature is due to micro-Brownian motion of segments in the amorphous phase in the glass transition range. A smeared relaxor phase transition from the polar modification of the α phase of vinylidene fluoride units to the paraelectric phase is observed in the temperature range 50–70°C. At higher temperatures, there occurs an intensive relaxation process that can be attributed to space-charge relaxation or manifestation of the normal relaxation mode.     

Influence of cobalt(III) dimethyldithiocarbamate complexes on styrene polymerization initiated by tert-butyl perbenzoate

Kinetic features of radical polymerization of styrene initiated by tert-butyl perbenzoate in the presence of tris(N,N-dimethyldithiocarbamato)cobalt(III) (CoL₃) and its adduct with iodine (CoL₃ · 2I₂) were studied. The optimal concentration ratios of the activators and tert-butyl perbenzoate, providing fast styrene polymerization at 338–368 K, were determined.     

Hydrophobicity and thermal stability of fluorinated pentaerythritol esters

Wetting angles and limits of thermal stability of esters derived from pentaerythritol and perfluoro-, ω-chloropolyfluoro-, and perfluoropolyethercarboxylic acids were studied.     

Conformational implications of some nucleotide sequences

The conformational properties of some nucleotide sequences result in their ability to bind specifically some ligands or tobe recognized by specific proteins. In order to investigate the dependence of conformational behavior of the DNA duplex on nucleotide sequence, we analyzed the interaction energy of nucleic acid bases as a function of conformational parameters and base sequence. Extended regions of minimum energy values were found for different sequences. Although these regions (valleys) largely overlap, each one shows specificity for a particular sequence. This suggests that a specific pathway of changes in conformational parameters exists for each sequence. the changes may be accompanied by considerable shifts (2–3 Å) of the atom positions and an only slight variation (1–2 kcal/mol) of energy. Even small shifts in other directions can cause a drastic energy increase. For some nucleotide sequences, the energetically preferable conformations are the B-like ones (e.g., ApA, TpA), whereas for others the A-like ones are preferable (e.g., GpG, ApT). IN general, Pyr-Pur sequences have a tendency to a larger τ and smaller H and D than Pur-Pyr sequences. A large body of experimental data on nucleic acid structure in fibers and in solutions can be explained by results obtained.