Mechanism Of Solvent Effect Research Articles

Solvent Effect Inside the Nanocage of Zeolite Catalysts: A Combined Solid-State NMR Approach and Multiscale Simulation

Solvent effect plays an important role in manipulating the chemical reactivity, equilibrium constant, and reaction rate. Such effect is observed in heterogeneous catalysis, especially for the acidic zeolite catalyst with molecularly size pores (≤1 nm). Nevertheless, it is a great challenge to systematically investigate the intermolecular interaction and the mechanism of solvent effect on the catalytic performance inside the acidic zeolite nanocages. Here, we used the state-of-the-art solid-state NMR (SSNMR) experimental techniques combined with multiscale theoretical simulations to quantitatively investigate the solvent effect on the reactant electronic property and reaction activity. In particular, a series of 13C CP/MAS solid-state NMR experiments with acetone probe for H-ZSM-5 zeolite were performed via changing the coadsorption amount of nitromethane solvent. It is found that the solvent effect accounts for the enhancement of the apparent Bronsted acidic strength of zeolite catalysts, and thus promote...

Effects of solvent and supersaturation on crystal morphology of cefaclor dihydrate: a combined experimental and computer simulation study

The modified attachment energy model was employed to predict cefaclor dihydrate morphology. Meanwhile, the mechanism and the effect of solvent and supersaturation on the crystal morphology were also proposed. A molecular dynamics simulation was applied to investigate the interactions of cefaclor dihydrate crystal faces with the pure solvent model and the solution model. The mechanism of solvent effects on the different faces was elaborated by discussing the surface structure and the adsorption of the crystal, while the effect of supersaturation was considered from the aspect of molecular recognition. The radial distribution function analysis was introduced to explore the adsorption behaviors of solvent and solute molecules. From the mean square displacement of solvent and solute molecules, the growth shape was affected by the solvent and solute diffusion capacity. The results suggested that the morphology evolution is due to the subtle competition of the molecular adsorptions between the solute and solvent.

Growth and morphology of 1,3,5,7-tetranitro-1,3,5,7-tetraazacy-clooct ane (HMX) crystal

Cutting explosive single crystals and obtaining oriented crystal wafers (particularly crystal surfaces) are significant to research microscopic changes in highly explosive crystal wafers in various mechanical response mechanisms. Crystals have been cultivated to investigate the basic characteristics of explosives. In this study, the attachment energy (AE) model was employed to predict 1,3,5,7-tetranitro-1,3, 5,7-tetraazacy-clooct ane (HMX) crystal morphology. The gradient cooling method was used to cultivate HMX crystal in acetonitrile solution. The face of the HMX crystal was defined via X-ray diffraction pattern analysis. Simulation result shows that the predicted morphology of the HMX crystal in acetonitrile solution is dominated by the (0 1 1), (1 1 −1), and (1 0 0) faces calculated via solvent-affected AE using the AE model. The predicted HMX morphology is reasonably consistent with the observed experimental result. The mechanism of solvent effects on the structure of crystal surfaces during the process of cultivating crystals was explained by discussing binding energy and adsorption sites. Molecular modeling (MD) simulation was employed to demonstrate the interaction on the solvent surface. The MD method provides guidance to cultivate HMX crystals with various crystal faces in different solvents and under varying experimental conditions.

Solvent effect on hydrogenolysis of glycerol to 1,2-propanediol over Cu–ZnO catalyst

The present work aimed to investigate the effect of solvent on the catalytic performance of glycerol hydrogenolysis to 1,2-propanediol over a Cu–ZnO catalyst prepared by a coprecipitation method. The as-prepared Cu–ZnO particles were spherical in shape with needle-like structure formed by nanoscale particles, and had a specific surface area of 23m2/g. The solvents used in this work had an obvious influence on the hydrogenolysis of glycerol. Glycerol conversion increased gradually while the selectivity to 1,2-propanediol changed oppositely with water, ethanol and methanol as a solvent, respectively. The mechanism of solvent effect was analyzed in detail through characterizing the physicochemical properties of recovered Cu–ZnO catalyst by NH3-TPD, XRD, SEM and N2O, etc. The larger surface tension of water brought about the serious aggregation of Cu nanoparticles, leading to less active sites and lower glycerol conversion. The catalytic hydrogen transformation from ethanol or methanol to glycerol could also be responsible for the higher glycerol conversion. The higher polarity of water facilitated the removal of 1,2-propanediol from the catalyst surface, contributing to higher selectivity to 1,2-propanediol.

Mechanism of Solvent Effect in Polymorphic Crystallization of BPT

The effect of solvent on the crystallization behavior of the polymorphs of 2-(3-cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazolecarboxylic acid (BPT) was investigated under rapid cooling. From methanol (MeOH) and ethanol (EtOH) solutions, only the solvated crystals of the D forms of methanol (D(MeOH)) and ethanol (D(EtOH)) crystallized. Both D forms are stable and have similar crystal structures. However, the solubility of the D(EtOH) form is 1.5 times higher than that of the D(MeOH) form. With the release of alcohol molecules, both D forms transformed to the C form with an increase in temperature for the DSC measurement. After that, the C form transformed to the A form via a melt-mediated mechanism. The release temperature of alcohol was higher for D(EtOH) than for D(MeOH). When the crystallization was performed in 1-propanol (1-PrOH) and 2-propanol (2-PrOH), the metastable A form preferentially crystallized. On the other hand, in acetonitrile (MeCN) solutions the stable C form was selectively obtained. Th...

The mechanism of solvent effect on the positional selectivity of Candida antarctica lipase B during 1,3-diolein synthesis by esterification

We investigated the influence of solvent on the positional selectivity of Novozym 435 which was the immobilized Candida antarctica lipase B (CALB) during the esterification of oleic acid with glycerol for 1,3-diolein preparation previously. Herein, molecular modeling was used to elucidate the underlying mechanism of the solvent effect on the positional selectivity of the enzyme. The results showed that the binding energy of sn-1 hydroxyl of glycerol molecular with CALB became higher, and the binding energy of sn-2 hydroxyl of glycerol molecular with CALB became lower along with the increase of the solvent log P. It was demonstrated that, increasing log P of the solvent, the enzyme selectivity to sn-1 hydroxyl of glycerol molecular grew weaker, and the selectivity to sn-2 hydroxyl of glycerol molecular grew stronger.

Relationship between Fermi Resonance and Solvent Effects

We theoretically and experimentally study the relationship between Fermi resonance and solvent effects and investigate the Fermi resonance of p-benzoquinone and cyclopentanone in different solvents and the Fermi resonance of CS2 in C6H6 at different concentrations. Also, we investigate the Fermi resonance of C6H6 and CCl4 in their solution at different pressures. It is found that solvent effects can be utilized to search Fermi resonance parameters such as coupling coefficient and spectral intensity ratio, etc., on the other hand, the mechanism of solvent effects can be revealed according to Fermi resonance at high pressure.

Theoretical Investigation of Solvent Effects on Glycosylation Reactions: Stereoselectivity Controlled by Preferential Conformations of the Intermediate Oxacarbenium-Counterion Complex.

The mechanism of solvent effects on the stereoselectivity of glycosylation reactions is investigated using quantum-mechanical (QM) calculations and molecular dynamics (MD) simulations, considering a methyl-protected glucopyranoside triflate as a glycosyl donor equivalent and the solvents acetonitrile, ether, dioxane, or toluene, as well as gas-phase conditions (vacuum). The QM calculations on oxacarbenium-solvent complexes do not provide support to the usual solvent-coordination hypothesis, suggesting that an experimentally observed β-selectivity (α-selectivity) is caused by the preferential coordination of a solvent molecule to the reactive cation on the α-side (β-side) of the anomeric carbon. Instead, explicit-solvent MD simulations of the oxacarbenium-counterion (triflate ion) complex (along with corresponding QM calculations) are compatible with an alternative mechanism, termed here the conformer and counterion distribution hypothesis. This new hypothesis suggests that the stereoselectivity is dictated by two interrelated conformational properties of the reactive complex, namely, (1) the conformational preferences of the oxacarbenium pyranose ring, modulating the steric crowding and exposure of the anomeric carbon toward the α or β face, and (2) the preferential coordination of the counterion to the oxacarbenium cation on one side of the anomeric carbon, hindering a nucleophilic attack from this side. For example, in acetonitrile, the calculations suggest a dominant B2,5 ring conformation of the cation with preferential coordination of the counterion on the α side, both factors leading to the experimentally observed β selectivity. Conversely, in dioxane, they suggest a dominant (4)H3 ring conformation with preferential counterion coordination on the β side, both factors leading to the experimentally observed α selectivity.

ChemInform Abstract: Asymmetric Aldol Reactions. Mechanism of Solvent Effect on Stereoselectivity is Specific, Stoichiometric Binding of Tetrahydrofuran to a Chiral Titanium Enolate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric aldol reactions. Mechanism of solvent effect on stereoselectivity is specific, stoichiometric binding of tetrahydrofuran to a chiral titanium enolate

Solvent plays an important role in aldol reactions of an acyloxazolidinone-derived titanium enolate. Diethyl ether produces nearly fivefold higher diastereofacial selectivity than THF. We now show that this strong solvent effect arises from stoichiometric binding, most probably to the titanium, of THF in the transition structure, whereas ether is not bound. These mechanistic results indicate that THF lowers the selectivity by interfering with chelation control, which is highly preferred in ether. Implications include the possibility of using other ethers to improve chelation/nonchelation control still more, or even use of chiral ethers as chiral controller groups or adjuncts.

Absorption and fluorescence spectra of europium(III) compounds in non-aqueous solution

The absorption and fluorescence spectra of Eu(III) were investigated at room temperature in non-aqueous solutions. It was found that the intensity of hypersensitive bands is closely related to the molar refractivity of the solvent. A possible mechanism of solvent effect on intensities of f-f transitions is discussed within the framework of Mason's polarizability mechanism Effect of solvent on fluorescence properties of Eu(III) was investigated and the mechanism of fluorescence quenching is also discussed.

Absorption and fluorescence spectra of europium(III) compounds in non-aqueous solutions

The absorption and fluorescence spectra of Eu(III) compounds were investigated at room temperature in different non-aqueous solutions. It was found that the intensity of hypersensitive bands is closely related to the refractivity of solvent. A possible mechanism of solvent effect on intensities of f-f transition is discussed within the framework of the Mason's polarizability mechanism. Effect of solvent on fluorescence properties of Eu(III) was investigated and mechanism of fluorescence quenching is proposed.

The Solvent effect on the Oxidation of N, N-Diethylnerylamine by Hydrogen Peroxide

The solvent effect on the oxidation of N, N-diethylnerylamine (NA) by 60% H2O2 aq.solution was examined. In alcohols, unreacted NA was little and N, N-diethylnerylamineoxide (NAO) was obtained in high yield. In aprotic solvents, a large amount of O-linalyl-N, N-diethylhydroxylamine (LHA) was formed by the Meisenheimer rearrangement of NAO and much unreacted NA remained. The yield of (NAO+LHA) was low, therefore aprotic solvents were unsuitable for the practical use. Further, the behavior of LHA in alcohols was studied and it was found that LHA rearranged to NAO in alcohols and this was a reversible reaction.From these results, the mechanism of solvent effect was discussed in connection with the function of the hydroxy group of solvents stabilizing NAO.

Solvent effect on optical activity in dilute solutions

The theory of optical activity is generalized to include the effects of molecular interactions arising from the moments induced by the electromagnetic field. It is shown that in the presence of these interactions the electric quadrupole terms do not vanish upon statistical averaging, thus giving rise to a new mechanism of solvent effect on optical activity. The theory is specialized to a dilute solution of optically active molecules in optically inactive solvents. It is predicted that for a 0.1 molar solution of optically active molecules having quadrupole polarizability of ≈10 −40 (in SI units), the change in rotation is ≈6° m −1.