Early Stages of Interchange Reactions in Polymer Blends

Summary: Simple models are studied for better understanding of the early stages of interchange reactions in polymer blends. For a homogeneous blend of homopolymers A and B, parameters of copolymer AB formed at the reaction beginning are explicitly calculated. It is shown that the analysis of the copolymer composition can help to establish the prevailing interchange mechanism. For a bilayer blend of immiscible homopolymers A and B, the reactive compatibilization through interchange is studied by continual Monte Carlo modeling. The analysis of the local distribution in block length shows that the interdiffusion of blend components may start only after the formation of rather short copolymer blocks in the course of interchange.     

Abnormally slow reaction of oppositely charged ions: The kinetics of dopamine hydrochloride oxidation by ammonium peroxydisulfate

The kinetic curves for oxidation of dopamine hydrochloride in aqueous solution in the presence of ammonium peroxydisulfate were obtained by UV–vis spectroscopy and potentiometry. It was shown that the reaction follows the first-order kinetic equation and proceeds at a low rate. The values for the activation energy and the preexponential factor were determined as 75 kJ × mol⁻¹ and 4 × 10⁸ s⁻¹, respectively. The activation entropy was found having a negative value of −89 J × mol⁻¹ × K⁻¹. The first reaction order, the low preexponential factor and the negative activation entropy value for the reaction between the 2-(3,4-dihydroxyphenyl)ethanammonium cation and the peroxydisulfate anion were explained by the formation of ionic associates, which slowly enter into the internal redox reaction.     

A one-dimensional local tuning algorithm for solving GO problems with partially defined constraints

Lipschitz one-dimensional constrained global optimization (GO) problems where both the objective function and constraints can be multiextremal and non-differentiable are considered in this paper. Problems, where the constraints are verified in a priori given order fixed by the nature of the problem are studied. Moreover, if a constraint is not satisfied at a point, then the remaining constraints and the objective function can be undefined at this point. The constrained problem is reduced to a discontinuous unconstrained problem by the index scheme without introducing additional parameters or variables. A new geometric method using adaptive estimates of local Lipschitz constants is introduced. The estimates are calculated by using the local tuning technique proposed recently. Numerical experiments show quite a satisfactory performance of the new method in comparison with the penalty approach and a method using a priori given Lipschitz constants.This research was supported by the following grants: FIRB RBNE01WBBB, FIRB RBAU01JYPN, PRIN 2005017083-002, and RFBR 04-01-00455-a. The authors would like to thank anonymous referees for their subtle suggestions.     

An algorithm for solving global optimization problems with nonlinear constraints

In this paper we propose an algorithm using only the values of the objective function and constraints for solving one-dimensional global optimization problems where both the objective function and constraints are Lipschitzean and nonlinear. The constrained problem is reduced to an unconstrained one by the index scheme. To solve the reduced problem a new method with local tuning on the behavior of the objective function and constraints over different sectors of the search region is proposed. Sufficient conditions of global convergence are established. We also present results of some numerical experiments.     

Structural study and magnetic properties of copper(II) thiophene-2-carboxylate with 4-pyridinemethanol and isonicotinamide

The synthesis and characterization of [Cu(5-Me-2-tpc)₂(4-pyme)₂] (I), [Cu(3-Me-2-tpc)₂(4-pyme)₂] (II), [Cu(2-tpc)₂(4-pyme)₂] (III), [Cu(2-tpc)₂(isonia)₂(2-tpcH)] (IV), [Cu(5-Me-2-tpc)₂(isonia)₂(5-Me-2-tpcH)] (V), [Cu₂(2-tpc)₄(4-pyme)₂] (VI), [Cu₂(3-Me-2-tpc)₄(isonia)₂] (VII) (where 2-tpc is 2-thiophenecarboxylate, 3-Me-2-tpc is 3-methyl-2-thiophenecarboxylate, 5-Me-2-tpc is 5-methyl-2-thiophenecarboxylate and 4-pyme is 4-pyridinemethanol and isonia is isonicotinamide) are reported. The complexes under study were characterized by electronic, IR and EPR spectroscopy, magnetic susceptibility over the temperature range and X-ray structure analysis. Structural studies revealed a distorted tetragonal-bipyramidal environment around the copper ion for monomeric complexes I–V. The structure of dimeric complexes VI and VII consists of units of the known paddle-wheel dicopper(II) tetracarboxylates, which are made up of four thiophene-2-carboxylate ions thus bridging the two copper atoms. The complex molecules of all compounds are connected through H-bonds into supramolecular chains or frameworks. The spectral and magnetic properties are discussed with regard to X-ray data.     

Study of the binding sites in the biomass of <Emphasis Type="Italic">Aspergillus niger</Emphasis> wild-type strains by FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy studies were performed to confirm and to provide information on the identity and binding characteristics of the chemical groups responsible for the binding of elements using Aspergillus niger (A. niger) wild-type strains. Two absorption bands in the 3690–3615 and 2970–2895 cm^?1 regions can characterize stretching vibrations OH and CH groups in fatty acids, respectively, and intensive bands around of 1600 cm^?1 and by 1048 cm^?1 correspond to stretching vibrations of C=O groups of amides (amide I) or stretching vibrations ν(C–N). The FTIR results confirmed that no extra differences between IR spectra of A. niger in raw biomass and in solid rest after extraction with chloroform were observed. The small differences were observed in IR spectra of A. niger in chloroform after extraction.     

The effect of Cd(II) complexes with nicotinamide (NA) on microalgae growth,production of chlorophylls,oxygen evolution and Cd adsorption

The effects of Cd [Cd(NO₃)₂] and its complexes with nicotinamide (NA) [Cd(ac)₂(NA)₂, Cd(NCS)₂(NA)₂, Cd(NCSe)₂(NA)₂] were examined by using the algae Scenedesmus quadricauda and Chlorella vulgaris as a function of Cd speciation in a well-defined aqueous medium. The parameters observed during the experiments were algal growth inhibition, chlorophyll a and b content, oxygen evolution and Cd adsorption by algal cells. With regard to growth and production of chlorophylls (Chla, Chlb), the most toxic compound was Cd(NO₃)₂. On the basis of EC50 values for these parameters, the following rank order can be arranged for both algae: Cd(NO₃)₂?>?Cd(ac)₂(NA)₂?>?Cd(NCS)₂(NA)₂?>?Cd(NCSe)₂(NA)₂. While Cd(NO₃)₂ in EC50 concentration for algal growth also reduced oxygen evolution nearly by half, all Cd(II) complexes used in EC50 concentrations for the same parameter reduced oxygen evolution less. When a comparison was done for Cd(NO₃)₂, all Cd(II) complexes stimulated oxygen evolution in both algal species. Base on the adsorbed Cd quantity, the tested compounds for both algae could be arranged in the following sequence: Cd(NO₃)₂?>?Cd(ac)₂(NA)₂?>?Cd(NCS)₂(NA)₂?>?Cd(NCSe)₂(NA)₂. The results confirmed that the adsorbed Cd amount markedly exerted its influence on algal growth and intensity of their physiological processes. Higher sensitivity was confirmed for alga S. quadricauda, which adsorbed a higher amount of Cd, and reduction of all observed parameters in this alga was more intensive than in C. vulgaris. As less toxic for both algae was confirmed the complex Cd(NCSe)₂(NA)₂.     

Three‐Component Gallium(III)‐Promoted Addition of Halide Anions and Acetylenes to Donor–Acceptor Cyclopropanes

A new strategy for the three‐component addition of halide anions and acetylenes to donor–acceptor cyclopropanes (DACs) is presented. This reaction, which occurs with high E selectivity, is promoted by gallium(III) salts and based on the 1,2‐zwitterionic reactivity of DACs. It opens up a new group of processes involving DACs. The reaction occurs readily with a broad range of substrates and is tolerant of various functional groups. This methodology makes it possible to assemble highly functionalized vinyl halides, which are very convenient building blocks in organic synthesis. A possible mechanism of this reaction and its stereochemical aspects are discussed in detail.