Reactions on polymers with amine groups. V. Addition of pyridine and imidazole groups with acetylenecarboxylic acids

Unsaturated macromolecular carboxybetaines were obtained by reaction of poly(4-vinylpyridine) and poly(N-vinylimidazole) with propiolic acid. A kinetic model was presented for 4-methylpyridine. It consists of three coupled reactions: neutralization, addition which involves two molecules of acid and leads to a cation–anion pair structure, where the cation results from the addition of the amine nitrogen to the triple bond of acid, and an equilibrium reaction between the ion-pair structure and the betaine structure. The addition rate was found to be higher for poly(4-vinylpyridine) than for poly(N-vinylimidazole); it was also higher in water than in a water–methanol mixture. The reaction with acetylenedicarboxylic acid was carried out on poly(N-vinylimidazole), but the transformed units showed the structure that results from propiolic acid. The betaine products from 4-methylpyridine did not polymerize by radical initiation. The polymeric products show characteristics of photocrosslinking polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1615–1623, 1998     

Sebestyén moment problem: The multi-dimensional case

Given a family of vectors in a Hilbert space we characterize the existence of a family of commuting contractions on having regular dilation and such that

The theorem is a multi-dimensional analogue for some well-known operator moment problems due to Sebestyén in case or, recently, to Gavruta and Paunescu in case .

     

Preparation of Bi2Fe4O9 particles by hydrothermal synthesis and functional properties

In the present study, particles with different Bi₂Fe₄O₉ micro/nanostructures with a few particular morphologies (flower-like nanoplatelets, hierarchical microstructures, perfectly square platelets single crystals, etc.) obtained under specific hydrothermal synthesis conditions were investigated. The role of the processing parameters (such as NaOH concentration, reaction temperature, and reaction duration time) on the phase formation mechanism and on the microstructural characteristics was investigated. All the Bi₂Fe₄O₉ morphologies showed orthorhombic symmetry with space group Pbam. The photocatalytic properties and magnetic behavior as a function of the micro/nanostructural characteristics of various Bi₂Fe₄O₉ powders were determined. In the presence of Bi₂Fe₄O₉, a degradation rate of Rose Bengal in the range of 52–61% was determined after 180?min under UV light irradiation (λ?=?254?nm). Magnetic activity with antiferromagnetic behavior and a transition at ～240?K slightly dependent on the microstructures was found. The role of Bi₂Fe₄O₉ microstructures in the photocatalytic activity and magnetic properties was discussed.     

Pd-catalysed amidation of 2,6-dihalopurine nucleosides. Replacement of iodine at 0 °C

Pd-catalysed reactions of 2-Cl, 2-Br and 2-I derivatives of a 6-chloropurine nucleoside with benzamide have been compared, using Pd₂dba₃, Xantphos and Cs₂CO₃ in toluene, between 20 and 80 °C. The reactivity order was 2-I > 2-Br > 6-Cl ? 2-Cl. The 2-I substituent could be replaced even at 0 °C, under conditions disclosed here for the first time. On the other hand, the replacement of the chlorine atom at position 2 (2-Cl) required 110 °C.     

Precautions in using global kinetic and thermodynamic models for characterization of drug release from multivalent supports

Building-up a detailed kinetic model for drug release from various supports is a difficult task, especially when chemical reactions take place, accompanied by adsorption-desorption and diffusion steps. Often, semi-empirical release models derived from theoretical formulations of the transport process and system characteristics are employed. Their parameters have limited validity as they are dependent on the support, drug-ligand properties, and release conditions. However, they are often used for a quick simulation and design of drug delivery systems with a controlled release correlating the model parameters with the system characteristics and release conditions. Detailed information allows elaboration of an extended mechanistic model; the bias in the predictions introduced on various levels of model simplification is presented in this paper. A case study of a chemically activated ligand release in human plasma from a multivalent dendrimeric support is approached, pointing out the imprecision introduced by the gradual simplification of an extended model as well as the low reliability of the prediction when using various semi-empirical global models.     

Experimental evaluation of electrical conductivity of ionanofluids based on water–[C2mim][CH3SO3] ionic liquids mixtures and alumina nanoparticles

Journal of Thermal Analysis and Calorimetry - Ionic liquids are one of the recent options for heat transfer enhancement due to their excellent features; nevertheless, their thermophysical and...