Optical activity of films based on chitosan of various molecular masses and modifications

The effect of chemical (polysalt → polybase reaction) and physicochemical (heat and vapor processing) modifications of the films of chitosan of various molecular masses and prehistories on the optical activity of the polysaccharide is studied. For both of the chitosan chemical modifications, the following dependence that is nontrivial for high-molecular compounds is established: [α] = f(log\({\bar M_\eta }\)); as the degree of polymerization decreases, the modulus of [α] of the films increases. The X-ray diffraction study shows that the differences in the optical activity of the samples with different \({\bar M_\eta }\) are caused by a restriction in the mobility of the macromolecular sections upon formation of the films of high-molecular chitosan and incompleteness of the relaxation processes of the film systems to the state with energetically favorable conformations. The comparison of humidity and optical and biological activities of the initial and dehydrated chitosan films is performed. The chitosan films in the salt modification feature moderate bactericidal activity, which decreases with an increase in \({\bar M_\eta }\) of the polymer. The thermal processing of the salt modification reduces the antibacterial action; a conversion to the base form is accompanied by the loss of bactericidal activity.     

A statistical procedure for the assessment of bias in analytical methods using conditional probabilities

Accreditation and Quality Assurance - A new approach is described for the simultaneous treatment of bias and imprecision in clinical chemistry. The approach makes use of the general law of...     

Uncatalyzed synthesis of new substituted dihydro-2H-dipyrimido[1,2-a,4,5-d]pyrimidine-2,4(3H)-dione

Research on Chemical Intermediates - A convenient and new method has been developed for the synthesis of highly substituted dihydro-2H-dipyrimido[1,2-a,4,5-d]pyrimidine-2,4(3H)-dione derivatives by...     

Coupling and exponential ergodicity for stochastic differential equations driven by Lévy processes

We present a novel idea for a coupling of solutions of stochastic differential equations driven by Lévy noise, inspired by some results from the optimal transportation theory. Then we use this coupling to obtain exponential contractivity of the semigroups associated with these solutions with respect to an appropriately chosen Kantorovich distance. As a corollary, we obtain exponential convergence rates in the total variation and standard $L^1$-Wasserstein distances.     

A splitting algorithm for the wavelet transform of cubic splines on a nonuniform grid

For cubic splines with nonuniform nodes, splitting with respect to the even and odd nodes is used to obtain a wavelet expansion algorithm in the form of the solution to a three-diagonal system of linear algebraic equations for the coefficients. Computations by hand are used to investigate the application of this algorithm for numerical differentiation. The results are illustrated by solving a prediction problem.     

Changes in luminescence of semiconductor colloidal quantum dots CdSe@CdS by replacement of hydrophobic ligands with 1-thioglycerol

Luminescent properties of CdSe@CdS colloidal quantum dots upon replacement of hydrophobic stabilizing ligands with water-soluble 1-thioglycerol have been studied. The data obtained have made it possible to optimize the ligand replacement procedure and significantly decrease the loss of the fluorescence quantum yield of the resulting hydrophilic quantum dots.     

Experimental study of gasification of vacuum residue in metal melt by alternating reactor feeding with carbonaceous feedstock and oxidant

Processes occurring in a metal melt during plasma-assisted melt gasification of carbonaceous feedstock have been studied in the mode of alternating feeding the reactor with the carbonaceous feedstock and oxidant. Vacuum residue was used as an oxygen-free carbonaceous material, and air and steam were used as an oxidant. The results of the study show that by alternating the carbonaceous-feedstock pyrolysis step and the step of carbon oxidation in the metal melt, it is possible to produce synthesis gas with any desired H₂/CO ratio.     

Phase equilibria in the Cu–Cu<Subscript>2</Subscript>Se–As system

Phase equilibria in the Cu–Cu₂Se–As were investigated by differential thermal analysis and X-ray powder diffraction analysis. Informative plots describing this system were constructed, viz., the polythermal sections Cu_0.667Se_0.333–As, Cu_0.667Se_0.333–Cu_0.735As_0.265, and Cu_0.8Se_0.2–As, the isothermal section of the phase diagram at 300 K, and the projection of the liquidus surface. The obtained results differ from the published data in length of fields of primary crystallization of phases and in coordinates of a number of invariant equilibrium points.