Ab initio modeling of the solvent influence on the azo-hydrazone tautomerism

The solvent effect on the azo (A) -hydrazone (H) tautomeric equilibrium of 1-phenylazo-4-naphthol is modeled by using ab initio quantum-chemical calculations. It was found that in methanol, methylene chloride and water there exists a strong hydrogen bonding between the particular tautomer and solvent, as well as dipole–dipole dye-solvent interactions. The results show that the H-form is more stable in water and methylene chloride, while methanol and i-octane stabilize the A-form. The calculational results obtained are in very good agreement with the experimental data in these solvents published previously.     

Theoretical description of solvent effects. X. Theoretical investigation of the Tautomerism of Nucleic Acid Bases of biological importance in the gas phase and in solution

The tautomerism of the nucleic acid bases cytosine and adenine and some of their derivatives is investigated by means of semiempirical MO methods. The influence of the solvent is estimated using various versions of the reaction field model. In the cases under investigation here, the medium influence does not favour “rare” tautomeric forms having other coding properties in DNA replication process than the “normal” nucleic acid base tautomers. Thus, the probability of their participation in spontaneous mutations seems to be very low.     

A reaction density functional theory study of solvent effects on keto-enol tautomerism and isomerization in pyruvic acid

It is important to study the solvent effect on keto-enol tautomerism that has applications in many areas of chemical engineering. In this work, we use a multiscale reaction density functional theory (RxDFT) to study the keto-enol tautomerism and isomerization of pyruvic acid. The results show that both effects of solvation and water assistance could reduce the reaction barriers. The water molecule participates the reaction as a catalyst to accept/give the protons with forming a hexagonal ring in the transition state. As a result of this temporary and intermediate hexagonal ring, the solute configuration undergoes a small variation during the reaction, giving a diminished contribution to the intrinsic reaction free energy. The solvent distribution shows a local ordering behavior near the solute that also reduces the contribution of solvation effect to the reaction barrier. Water assistance plays a major role in both pre-reaction and post-reaction process. In terms of the driving force for the reaction, the effects of both solvation and water assistance are important.     

Precipitate flotation. V. Extractive solvent sublation

The new technique of precipitate flotation of the second kind is unique amongst flotation processes in that it requires no surfactant. This does have the disadvantage that the floated material is not supported on the surface and tends to redisperse into the solution. A layer of immiscible organic solvent containing either a surfactant, a complexing agent, or the original precipitant, leads to solubilisation and retention of the floated material. As this is quantitative, spectrophotometric examination of the organic layer may provide a means of analysis for the ion originally precipitated. Complete removal from solutions as dilute as 10^?5 M is possible.     

The influence mechanism of solvent on the hydrogenation of dimethyl oxalate

The hydrogenation of dimethyl oxalate(DMO) for the producing of C2-C4 alcohols with methanol as solvent was researched at the temperature of 270 °C to 310 °C. Ethylene glycol(EG) was the main product at low temperature and the selectivity of which was 61.9% at 230 °C. However, EG selectivity decreased sharply with the increase of temperature while ethanol became the main liquid products with the selectivity of 43.5% at 270 °C. It can be ascribed to a thorough hydrogenation of DMO at a high temperature. In addition, the promotion of Guerbet reaction led to the production of propanol and butanol. Simultaneously, the amount of gas products including CO, CO_2 and dimethyl ether(DME) also increased, which became a competition factor in the conversion of DMO to liquid products including C2-C4 alcohols. The blank test was carried out with pure methanol as feedstock with and without Cu/SiO_2 catalyst, which revealed that methanol was involved in the formation of gas products and higher alcohols on Cu-based catalyst, and the main gas product was CO.     

The influence of solvent type on the viscosity of concentrated polymer solutions

The viscosity of concentrated (17.5 g/dl) solutions of cellulose acetate in 11 single solvents and in four binary solvent mixtures was related to a thermodynamic measure of solvent power. In single solvents, the specific viscosity varied from 4600 in dimethyl sulfoxide to 78,000 in diacetone alcohol, with the specific viscosity increasing with decreasing abolute value of the partial molar free energy of dilution. This behavior can be accounted for by the hypothesis that the number of chain entanglements increases with decreasing solvent power. In solvent mixtures, the specific viscosity often attains a minimum value at a composition where the average solubility parameter locus is near the center of the solubility region of the polymer.     

Theoretical description of shock-wave formation in a spatially inhomogeneous combustible medium for chain-branching combustion kinetics

For combustion reactions with chain-branching kinetics, the time scales of induction and heat release vary independently and can be significantly different as well as comparable, depending on the initial conditions. A theoretical study was performed to investigate the influence of the heat-release rate and kinetics on the mechanisms and conditions of shock-wave formation in a spatially inhomogeneous combustible medium — the first step of detonation initiation in systems with an induction time gradient. The study used the transport equation method developed by the authors previously.     

Theoretical description of the interface electrode-electrolyte solution

The interface: electrode-electrolyte solution is considered as a supersition of monoatomic layers interacting among them. An electrode is treated as a thin film with some crystallographic structure, while an electrolyte solution is described as a medium of ions and molecules with random structure approximated by that like to disordered samples. Applying the Green function technique the local density of states is calculated as a basic function for determining characteristic parameters in electrochemistry. In particular the properties of the work function for electrons into an electrolyte solution are discussed.     

2—羟基吡啶的合成及溶剂对反应的影响

本文主要对在２－羟基吡啶的合成中，２－氯吡啶在不同溶剂中的亲核性水解反应进行了讨论，从中掌握了这类反应的特点，从结构上分析了影响反应的原因，并提出了在分离阶段应注意的问题     

The flow of suspensions through tubes: V. Inertial effects

The behavior of particles undergoing Couette and Poiseuille flows at rates when inertial effects become significant was investigated. The rotation of rigid particles was similar to that in the Stokes flow regime, except for a drift of cylinders to limiting rotational orbits corresponding to the maximum energy dissipation. In Poiseuille flow, rigid particles migrated to an equilibrium radial position which depended on the density difference of two phases, the directions of sedimentation velocity and flow, and the ratio of particle to tube radius. Neutrally buoyant deformable particles always migrated to the tube axis. In concentrated suspensions a plasmatic layer developed near the tube wall as a consequence of radial migration. The formation of this layer modified the velocity profile and caused a reduction in the apparent viscosity coefficient.     

The influence of dietary medium chain triglycerides on rat mammary tumor development

The N-nitrosomethylurea rat mammary tumor model was used to compare the tumor-promoting effects of a highfat (HF) diet containing a 3:1 mixture of medium chain triglycerides (MCT) and corn oil with that of a HF and a low-fat (LF) corn oil diet. The serum and tumor lipid content and fatty acid (FA) composition were also determined in the three dietary groups. It was found that the MCT-containing diet failed to promote tumor development compared with the HF corn oil group. Tumor incidence in the HF-MCT group was similar to that of the LF corn oil group (5% fat, w/w), but significantly decreased compared to the HF corn oil group. Total serum cholesterol levels were significantly depressed in the HF corn oil group compared to the HF-MCT and LF corn oil groups. Analysis of serum and tumor FA profiles indicated that the HF corn oil group exhibited approximately twice the amount of linoleic acid (LA) as the other two treatment groups. Differences among the three groups in the major FA metabolite of LA, arachidonic acid, were minimal. These results are consistent with the hypothesis that tumor promotion by dietary fat is more a function of the type than the amount of fat ingested. In addition, they indicate that MCT, due at least in part to their unique structural and physiological properties, exert markedly different effects on mammary tumor development than conventional long chain unsaturated fatty acids. Presented at the symposium on “Specialty Lipids and Their Biofunctionality” at the annual meeting of the American Oil Chemists' Society, Philadelphia, May 1985.     

Radiation-induced cationic polymerization of vinyl ethers in solution: 3. The influence of monomer and solvent concentrations on the rate of polymerization of ethyl vinyl ether in ether solvent

The influence of the monomer concentration on the rate of propagation of the radiation-induced polymerization of super-dry ethyl vinyl ether has been examined in detail in two ether solvents, diethyl ether and diglyme, chosen for their different dielectric constants and their different abilities to solvate ions. Estimations of the rate of initiation and of the rate of termination have made possible the evaluation of the rate constants of polymerization. Very similar values were obtained in both ethers. Experiments were also performed in benzene-diglyme and diglyme-methylene chloride mixtures. The results are in good agreement with the previous studies, made in benzene and methylene dichloride, and confirm the important role of the solvation of the free propagating species concerning the reactivities observed in the radiation-induced polymerization of EVE in solution.     

Theoretical estimation of the effect of solvent on unperturbed dimensions: 1. Isotactic poly(vinyl alcohol)

The effect of the quality of solvent on the unperturbed chain dimensions $\text{r}{}_0{}^2$ of perfectly isotactic poly(vinyl alcohol) (iso-PVA) was studied by means of some model calculations according to the matrix method of Flory et al. These investigations were based on the assumption that the quality of solvent affected mainly the energy of the intramolecular hydrogen bond, while the magnitude of the interactions between other groups, hardly varied with the change of solvent. The individual conformation energies in a chain of iso-PVA were estimated from the analysis of structurally similar polymers, as well as the results obtained with 2,4-pentanediol. It was found that the characteristic ratio $\text{C =}\text{r}{}_0{}^2\text{nl}{}^2$ increased in non-polar solvents, with energy of the intramolecular hydrogen bond stabilizing the stretched zig-zag conformation of chain. Conversely, the characteristic ratio, monotonously decreased with increasing polarity of solvent to the value of about 6, typical of a flexible random coil. The existence of an analogous relationship, valid for other polymers, able to form an intramolecular hydrogen bond in the chain, was also discussed.     

Liquefied petroleum gas as solvent medium for the treatment of immobilized inulinases

BACKGROUND: The main goal of this work is to assess the influence of pressurized liquefied petroleum gas (LPG) treatment on the enzymatic activity of immobilized inulinases. The effects of process variables were evaluated through 2³ experimental design. RESULTS: Inulinase from Klyveromyces marxianus NRRL Y‐7571 presented an increase of 163% in residual activity using LPG at 30 bar during 1 h exposure using a depressurization rate of 20 bar min^?1. For Aspergillus niger commercial inulinase, an increment of 129% in residual activity was observed at 30 bar for 1 h treatment at the highest depressurization rate (20 bar min^?1). Enzymatic activities changed significantly depending on the enzyme source and the experimental treatment conditions investigated, such as exposure time, depressurization rate and pressure. CONCLUSION: Hence, compressed LPG appears to be a promising technique with practical relevance as a preparation step to improve enzyme activity, thus helping the development of new biotransformation processes. © 2012 Society of Chemical Industry     

The influence of montmorillonite concentration and solvent polarity on the synthesis of benzoxazine monomers in the presence of montmorillonite

The synthesis of 3,3′-(hexane-1,6-diyl)bis-(3,4-dihydro-2H-1,3-benzoxazine) was done in the absence and in the presence of 10, 30, 50 and 100 wt.% montmorillonite (MMT). The MMT exhibits a significant catalytic effect on the ring-opening reaction of the benzoxazine monomer, increasing of MMT amount influences the oligomeric structures in the polybenzoxazine precursor composition according to ¹H NMR, ¹³C NMR and SEC data. The influence of solvent polarity and temperature was also studied especially in correlation with possible interactions between solvent and MMT. The influence of the polybenzoxazine precursor composition on the polymerization behaviour was investigated by DSC. The thermostability of the obtained polybenzoxazines was studied by TGA and DMA method was involved to determine the glass transition temperature.     

Reflection on medium effects on photochemical reactivity

In reexamining medium effects on photochemical reactions, we have emphasized those on unequilibrated excited species such as the Franck-Condon species. Despite recent advances in femtochemistry, such a discussion in molecular photochemistry is uncommon, and the problem remains challenging on account of the extremely short-lived excited species. However, in such cases, a small perturbation resulting from, for example, weak guest-host interactions could turn into a determining factor in dictating the course of a photochemical channel of deactivation. Examples of medium-directed diabatic processes have been examined with this idea in mind. A modified view on rhodopsin photoisomerization is presented along with the consideration that confinement does not necessarily lead to inhibition of reactions of the trapped substrate.