The model of cage reactions proceeding through the metastable term

A model of cage reactions in the solid state is examined in which the Franck-Condon prohibition is overcome by crossing two parabolic terms of the same curvature. Since the final term is considered to be of short half life, its width is significant and there exists a transition probability. The effects on the reaction kinetics by the Markovian migration over the initial terms modulating resonance detuning and therefore the transition probability has been studied (the interaction is considered to be independent of the reaction coordinate). The case where the point of term crossing coincides with the minimum of the initial term is examined in detail. The reaction kinetics passes three stages with increasing migration frequency. The process develops non-exponentially in the slowest, quasi-static stage. The reaction kinetics and rate depend on the manner of migration in the migration-accelerated stage. Only in the kinetic stage when the migration is very fast does the traditional quasi-classical theory of electron migration hold which implies exponential reaction kinetics with the rate being independent of the energy migration.     

The effects of third elements on the kinetics of order change in Ni3Al under H.V.E.M. irradiation

The effects of boron, cobalt or titanium additions on the kinetics of order changes in Ni₃Al under irradiation were investigated in a HVEM. The long-range order (LRO) parameter was determined by measuring the intensities of superlattice spots on the diffraction patterns. Order-variation kinetics was investigated by using a previously proposed theoretical model. The number of replacements per displacement ɛ and the steady-state LRO parameter S^∞ were directly deduced by fitting a kinetic law to experimental data ; a good agreement was generally found. A weak effects of the above third elements on the disordering efficiency was observed whereas the effect of stoichiometry appeared to be more important. Reordering was found to be controlled by long-range vacancy migration with a migration enthalpy of 0.9 to 1.0 eV ; this was deduced from a comparison between the experimental temperature dependence of the steady — state LRO parameter with calculated curves. The effects of third elements on the reordering kinetics is clearly revealed : compared to binary alloys, a decrease of the effective reordering rate is generally observed.     

Simulation of Kinetics of Stabilizer Migration from Polyolefins to Air and Water

The applicability of the model for prediction of the kinetics of stabilizer migration from polyolefins to air and water was analyzed.     

Sorption of Radiocobalt on Bentonite and Kaolinite

The factors affecting the sorption of radiocobalt by bentonite and kaolinite were studied with the aim to assess important factors which should be included in modelling radiocobalt migration in soils and waters. The distribution coefficients of radiocobalt sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were insensitive to the loading, the initial pH, the ionic strength, the humic substance and the sorption direction. Thus, the sorption characteristics of radiocobalt on bentonite and kaolinite facilitated the mathematical modelling of radiocobalt migration. In addition, the sorption kinetics and the sorption mechanism of radiocobalt on bentonite and kaolinite were also examined.     

Ligand migration in nonsymbiotic hemoglobin AHb1 from Arabidopsis thaliana

AHb1 is a hexacoordinated type 1 nonsymbiotic hemoglobin recently discovered in Arabidopsis thaliana. To gain insight into the ligand migration inside the protein, we studied the CO rebinding kinetics of AHb1 encapsulated in silica gels, in the presence of glycerol. The CO rebinding kinetics after nanosecond laser flash photolysis exhibits complex ligand migration patterns, consistent with the existence of discrete docking sites in which ligands can temporarily be stored before rebinding to the heme at different times. This finding may be of relevance to the physiological NO dioxygenase activity of this protein, which requires sequential binding of two substrates, NO and O2, to the heme.     

Structure-properties correlations in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)/nanosilica mixtures: Interrelationship among phase behavior,morphology and non-isothermal crystallization kinetics

In this work, the effects of amorphous poly(styrene-co-acrylonitrile) (SAN) chains and hydrophilic and hydrophobic nanosilica at different loadings on the non-isothermal crystallization kinetics of PCL phase have been evaluated using different theoretical models including Avrami, modified Avrami, Ozawa and Mo equations. Using microscopic observations, the interrelations among the changes in the kinetics parameters and the morphology and phase behavior of PCL/SAN and PCL/SAN/nanosilica mixtures have been thoroughly investigated. Microscopic observations on the nanocomposites showed differences in the nanofiller dispersion and distribution state as well as preferential migration and localization state. These differences lead to contradictory trends in the effects of hydrophilic and hydrophobic nanosilica on the crystallization kinetics of pure PCL and PCL/SAN blends. The nanoparticle migration during non-isothermal DSC tests in PCL/SAN blends, the formation of nanoparticle agglomerates at higher loadings, the restrictions imposed on the molecular movements in the crystallization growth stage and slower phase separation and dissolution of PCL/SAN/silica mixtures result in the cooling rate dependence of the kinetics parameters.     

Singlet exciton energy transfer in tetracene-doped p-terphenyl single crystals

A picosecond laser system has been employed to study the kinetics of singlet exciton energy transfer in p-terphenyl single crystals doped with tetracene over the temperature range 77–300 K. First-order kinetics prevail and exciton migration from host to guest is controlled by thermal activation over a potential energy barrier.     

Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake and release of radiocesium by bottom sediment and suspended solids from a small stream were studied as a function of contact time during the uptake and releases, of concentration of the solid phases and of temperature, using laboratory model experiments. Kinetics of the uptake were found to be singificantly affected by temperature and concentration of the solid phase. The kinetics and the concentration effect can be quantitatively described using kinetic model of two parallel or consecutive reactions. Kinetic parameters for the model were determined. Distribution coefficient K_d is independent of sediment concentration in the range of 20–70 mg·dm^?3 but passes through a maximum at higher concentration values. Release of radiocesium adsorbed on the freshwater solids was found to be quite rapid and a simple kinetics of the release from freshwater solids was observed. The amount released decreased with increasing contact time of radiocesium with solid phase. Quantitative evaluation of the release revealed partial irreversibility of radiocesium uptake on the solids studied. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modeling of radiocesium migration in rivers.     

Moment equations for partial filling capillary electrophoresis

Moment equations were developed for partial filling CE systems, in which solute dissolution phenomena by spherical molecular assemblies or intermolecular interactions take place. Because experimental conditions of partial filling CE are divided into five categories on the basis of the magnitude relationship between the migration velocity of solute molecules and that of molecular assemblies or ligand molecules, the moment equations were systematically developed for each case by using the Einstein equation for diffusion and the random walk model. In order to demonstrate the effectiveness of the moment equations, they were applied to the analysis of partial filling CE behavior, which is correlated with dissolution phenomena of small solute molecules into spherical molecular assemblies as specific examples. Simulation results only in the case that the migration velocity of solute molecules is faster than that of molecular assemblies were represented in this paper. Detailed explanations about the derivation procedure of the moment equations and the simulation results in other cases can be found in the Supporting Information. The moment equations are theoretical bases for applying partial filling CE to the study on solute permeation kinetics at the interface of spherical molecular assemblies and on reaction kinetics of intermolecular interactions.     

Thermal isomerization of 3,3-dihalo-1,2-diphenylaziridines

The kinetics of thermal isomerization of 3,3-dihalo-1,2-diphenylaziridines containing fluorine, chlorine, or bromine atoms in the ring were studied, and the activation parameters of the reaction were determined. A concerted mechanism for the formation of imidoyl halides from haloaziridines that includes conrotatory opening of the aziridine ring with halogen migration of the 1,2 type is proposed on the basis of the data obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 48–53, January, 1978.     

可聚合二苯甲酮类光引发剂的合成及其光聚合性能研究

以4-(2,3-环氧丙氧基)二苯甲酮(EBP)和丙烯酸为原料,通过开环反应合成了含有不饱和双键的可聚合光引发剂4-(丙烯酸-2-羟基丙酯-3-氧基)二苯甲酮(AEBP).采用红外光谱(FT-IR)、核磁共振氢谱(¹HNMR)对其结构进行表征,利用紫外吸收光谱对AEBP的紫外吸收波长进行表征,通过实时红外(RT-IR)研究了AEBP引发丙烯酸酯单体的光聚合动力学.采用萃取法对比了BP与AEBP引发固化体系后的迁移性.结果表明,随AEBP浓度增加,单体最终转化率增加;当助引发剂N,N-二甲氨基苯甲酸-乙酯(EDAB)浓度为1.2%时,单体最终双键转化率最高;AEBP对双官能度单体的引发效率较之三官能度单体的好;聚合速率随光照强度的增强而变快;固化后AEBP的迁移性比传统的BP大大降低.     

Microextraction across supported liquid membranes forced by pH gradients and electrical fields

The present work has for the first time compared extraction of basic analytes across a supported liquid membrane (SLM) based on (1) passive diffusion in a pH gradient sustained over the SLM and (2) electrokinetic migration in an electrical field sustained over the SLM. For the passive diffusion experiments, performed as liquid-phase microextraction (LPME), five basic drugs were extracted under strong agitation from alkaline samples (10mM NaOH), through 2-nitrophenyl octylether immobilized in the pores of a porous hollow fibre of polypropylene (SLM), and into 25 microl of 10mM HCl as the acceptor solution. The experiments based on electrokinetic migration, performed as electro membrane isolation (EMI), were conducted under strong agitation from acidic samples (10mM HCl), through the same SLM as in LPME, and into 25 microl of 10mM HCl as the acceptor solution. Whereas LPME relied on diffusion and to some extent also convection as the principal mechanisms of mass transfer, mass transfer in EMI also included a strong contribution from electrokinetic migration. Thus, extraction kinetics was improved by a factor between 6 and 17 utilizing EMI instead of LPME. This major difference in terms of speed was especially pronounced from small sample volumes (150 microl), and suggest that EMI may be a very interesting future concept for miniaturized sample preparation. In addition to improved extraction kinetics, extraction rates were strongly compound dependent in EMI, opening the possibility to control the extraction selectivity by the extraction time.     

Origin and Regulation of Interface Fusion during Synthesis of Single-Crystal Ni-Rich Cathodes

Interface fusion plays a key role in constructing Ni-based single-crystal cathodes, and is governed by the atomic migration related to kinetics. However, the interfacial atom migration path and its control factors are lack of clearly understanding. Herein, we systematically probe the solid-state synthesis mechanism of single-crystal LiNi_0.92Co_0.04Mn_0.04O₂, including the effects of precursor size, Li/transition metal (TM) ratio and sintering temperature on the structure. Multi-dimensional analysis unravels that thermodynamics drives interface atoms migration through intermediate state (i.e., cation mixing phase) to induce grain boundary fusion. Moreover, we demonstrate that smaller precursor size (<6 μm), lager Li/TM ratio (>1.0) and higher temperature (≥810 °C) are conducive to promote the growth of the intermediate state due to reaction kinetics enhancement, and ultimately strengthen the atomic migration-induced interface fusion.     

Die identifizierung und untersuchung von isomeren O-acylribonucleosiden mit hilfe des circulardichroismus

The CD spectra of benzoyl, p-nitrobenzoyl and anisoyl derivatives of adenosine, uridine, 1-methylriboside and 1-D-ribofuranosylbenzimidazole are registrated. The possibility of identification of 2′-, 3′-O-acylribonucleosides and observation of acyl groups isomerisation kinetics is shown. The kinetics of 2′?3′ migration of a number of 2′(3′)-O-derivatives, the dependence of kinetic constants on the pH are studied. The features of acyl derivated ribonucleosides CD spectra are discussed.     

羧酸冠醚的合成

羧酸冠醚的合成吴琳，王志林，卞清，张进琪，朱春生（南京大学化学系南京２１００９３）曹建国（盐城师专化学系）关键词冠醚，离子迁移羧酸冠醚环上的羧基，对冠醚环的选择输送金属离子起着协同的作用。近十余年来，将羧酸冠醚选择萃取金属离子的能力应用于金属离子的液...     

Dsc Evaluations in F.c.c. Solid Solutions of Short-range-order Kinetics As Influenced by Bound Vacancies

A modified first order kinetic law, which describes the roles of bound and unbound vacancies, is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. The model has been applied to differential scanning calorimetry (DSC) curves of Cu–5 at%Zn quenched from different temperatures. Activation energy for migration of solute-vacancy complexes was also assessed from the kinetics of short-range-order using DSC traces. A value of 89.5±0.32 kJ mol^–1 was obtained. The relative contribution of bound and unbound vacancies to the ordering process as influenced by quenching temperature was determined. In conjunction, a parametric study of the initial total defect concentration and effective energy for defect migration was performed in order to envisage their influence on the calculated DSC profiles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Functional film of ethylene vinyl acetate and co‐polyamide compound containing “Nisin” active substance

This study deals with flexible films incorporating nisin for antibacterial active packaging purposes. A novel approach was used to gain control over nisin release profile from a thermoplastic film in order to enhance its antibacterial efficiency. This approach involves polymer blends of ethylene vinyl acetate copolymer and co‐polyamide at various ratios. It was shown that the release profile of an antibacterial substance from active packaging to foodstuff is a key factor concerning the antibacterial efficiency. Samples of 400[μm] were produced by using a laboratory twin screw compounder and a laboratory hot press. Samples were characterized for their migration kinetics, molecular interactions, mechanical properties, and water swelling properties. Antibacterial activity tests show that nisin incorporated films reduced bacterial count by different extents. Listeria ATCC 33090 was used as target bacteria (data not shown). Nisin migration profile to water medium was determined by Lowry's protocol. Scanning electron microscopy images and thermal analysis indicated that no significant molecular interactions occurred. Furthermore, droplet and co‐continues like morphology were seen at different polymer blend ratios. Osmotic pressure driven release mechanism appears to be the dominant migration mechanism, and diffusion kinetics was dominant. Results show that morphology of the polymer blend matrix alters the diffusion coefficient. In addition, water swelling characterization of different samples was done in order to reveal the relations with the diffusion coefficient. It seems that there is an inverse resemblance between water swelling and the diffusion coefficient trends.     

Time-resolved optical absorption spectroscopy of molten polyethylene blends

By means of pulse radiolysis and laser photolysis experiments with detection by optical absorption spectroscopy short-living radical transients in pure PE and in PE doped with additives (e.g. di->tert-butyl-p-cresol, diphenylamine, benzophenone and carbon tetrachloride) were characterized by their optical absorption spectra and kinetics. It was found that the additive radicals were formed in a very fast process probably via exciton migration and subsequent energy transfer and dissociation reactions.     

A density functional theory study of alkyl group migration in RMn(CO)5 complexes

The kinetics of alkyl group migration in RMn(CO)₅ complexes ( R=CH₃, C₂H₅ and C₃H₇) were studied. Isomers of CH₃Mn(CO)₅ with an agostic structure, an η¹ structure, and an η² structure were found to be local minima on the system's potential energy surface. Transition states for the inter-conversion of these species were also located. The activation free energy for this migration reaction was compared with experimental data and provides insights into the important steps in the overall reaction mechanism.     

Determination of antigen—antibody affinity by immuno-capillary electrophoresis

The use of affinity capillary electrophoresis for the characterization of antigen—antibody interactions (immuno-capillary electrophoresis) is shown using monoclonal antibodies against phosphotyrosine as a model system. The influence of the interaction kinetics on the peak profiles was demonstrated in experiments with addition of phosphotyrosine to the electrophoresis buffer. One of the two antibodies that were tested exhibited peak broadening while the other showed no change in peak shape but had a decreased mobility proportional to the amount of phosphotyrosine present. The migration shifts which were of the order 0.05 to 0.15 min at 439 V/cm were a consequence of the antibody—antigen complexes having a slower mobility than the non-complexed antibody. On the basis of measurement of migration shifts at different antigen concentrations, dissociation constants were estimated and shown to be independent on the applied field strength. Thus, when certain requirements are fulfilled, immuno-capillary electrophoresis is a fast and simple method for establishing binding characteristics of unlabelled antigen and antibody molecules under non-denaturing conditions and consumes minute amounts of sample.