Effect Of Aprotic Solvents Research Articles

Effect of Aprotic Solvents on the Microtensile Bond Strength of Composite Core and Fiber-Reinforced Composite Posts.

This investigation evaluated the effects of aprotic solvents, i.e., tetrahydrofuran, pyridine, and morpholine, compared with hydrogen peroxide, on the surfaces of fiber-reinforced composite posts with a composite core based on the microtensile bond strength. In total, 150 FRC Postec Plus posts and 150 D.T. Light-Posts were randomly divided into three groups (non-thermocycling, 5000-cycle, and 10,000-cycle thermocycling groups). Each group was divided into five subgroups according to the post-surface treatment: C, non-treatment group; H2O2, immersed in 35% hydrogen peroxide; THF, immersed in tetrahydrofuran; PY, immersed in pyridine; and MP, immersed in morpholine. The treated specimens were placed in the bottom of a plastic cap and filled with a composite core material in preparation for the microtensile bond test. The data were evaluated using one-way ANOVA and Tukey's test (p < 0.05) as well as an independent t-test (p < 0.05). For the surface roughness, white light interferometry was used for measurement, and the mean surface roughness was analyzed via one-way ANOVA and Tukey's test (p < 0.05). The results showed that, under non-thermocycling conditions, the PY subgroup with D.T. Light-Post had the highest microtensile bond strength, followed by THF, MP, H2O2, and the control groups. For FRC Postec Plus, the PY group had the highest microtensile bond strength, followed by MP, THF, H2O2, and the control groups. Although the thermocycling conditions decreased the microtensile bond strength in all groups, the PY subgroup still had the highest value. An independent t-test revealed that even under all non-thermocycling and 5000- and 10,000-cycle thermocycling conditions, D.T. Light-Post in the PY subgroup displayed significantly higher microtensile bond strengths than FRC Postec Plus in the PY subgroup. While the surface roughness of the fiber-reinforced composite posts showed that the posts treated with pyridine possessed the highest surface roughness for each material type, In conclusion, as an aprotic solvent, pyridine generates the highest microtensile bond strength between the interfaces of composite cores and fiber-reinforced composite posts.

Effects of aprotic solvents on the physicochemical properties and ferric ion oxidation activity of iron-based ionic liquids.

In recent years, iron-based ionic liquids (e.g. BmimFeCl4, Fe-IL) have been widely used in the catalytic oxidation removal of hydrogen sulfide owing to their excellent redox reversibility and stability. Nevertheless, the high viscosity and poor Fe3+ activity of BmimFeCl4 limit its large-scale industrial application. The addition of aprotic organic solvents to BmimFeCl4 is an effective strategy to enhance its mass transfer efficiency and catalytic oxidation desulfurization performance. In this work, the effects of two kinds of aprotic organic solvents, weak polar polyether alcohols (NHD, PEG200) and strong polar amides (DMAC, DMF, and NMP), on the density, viscosity, conductivity and ferric activity of Fe-IL were investigated. The Eyring equation fitted well for the relationship between the viscosity and the temperature of the composites. When the mass ratio of BmimFeCl4 to solvent was 7 : 3 at 298.2 K, the viscosity of BmimFeCl4/DMAC and BmimFeCl4/NHD was 8.67 mPa s and 27.19 mPa s, respectively. The excess molar volume (VE) and viscosity deviation (Δη) of the two composite systems were calculated and fitted using the Redlich-Kister equation. The study of VE implies that DMAC has stronger solvation to the BmimFeCl4 ion pairs, and NHD could cause a more obvious volume shrinkage. For the composites investigated, Δη of BmimFeCl4/DMAC is negative while that of BmimFeCl4/NHD is positive, showing that DMAC could significantly weaken the combination ability of [Bmim]+ and [FeCl4]-, and NHD may form a stronger interaction with [Bmim]+. The FT-IR spectra and DFT calculations demonstrated that both polyether alcohol and amide could interact with C2-H on [Bmim]+. The CV curves and the MK charges show that the addition of aprotic polar solvents could effectively improve the activity of Fe3+ under the action of a hydrogen bond, and the effect of amide solvents on the activation of Fe3+ is stronger than that of polyether alcohol solvents. In conclusion, it is found that the composites with stronger ferric activity have much better catalytic oxidation ability for the conversion performance of hydrogen sulfide, and the the interactions induced by the molecular weight and the polarity of the solvent have a significant effect on the configuration of the Fe-IL ion pairs.

Effect of aprotic solvent on characteristics of Al2O3 ceramic hollow fiber substrates prepared by phase inversion for hydrogen permeation applications

ABSTRACT The phase inversion procedure was used to prepare Al2O3 ceramic hollow fiber substrates (AlCHFS) utilizing the dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), and 1-methyl-2-pyrrolidone (NMP) aprotic solvents. Different aprotic solvent and non-solvent (water) interactions were used to calibrate different ceramic oxide substrates. AlCHFS with an asymmetrical structure consisting of a finger-like structure on the lumen side and a pore structure on the shell side was obtained using an aprotic solvent/non-solvent pair with a high total Hildebrand solubility (δt). As the aprotic strength was reduced, the finger-like structure on the shell sides became more prominent. Hydrogen permeation studies conducted between 350°C and 450°C reveal that the Pd-coated AlCHFS produced from DMAC aprotic solvent has the maximum hydrogen flux (~0.24 mol m−2 s−1). The activation energy for the thermally activated hydrogen transport process through the Pd-coated AlCHFSs is determined to be around 11.06–14.61 kJ mol−1 in the temperature range of 350°C to 450°C, and it increases linearly with increasing surface porosity of ceramic oxide substrate.

Solvent effect on the absorption and emission spectra of carbon dots: evaluation of ground and excited state dipole moment

BackgroundCarbon dots (C-dots) are photoluminescent nanoparticles with less than 10 nm in size. Today, many studies are performed to exploit the photoluminescence (PL) property of carbon dots, and our focus in this study is to estimate the dipole moment of carbon dots. For reaching our aims, C-dots were synthesized and dissolved in the different solvents.ResultsCarbon dots with intense photoluminescence properties have been synthesized by a one-step hydrothermal method from a carbon bio-source. In this research, we report on the effect of aprotic solvents on absorption and fluorescence spectra and dipole moments of C-dots dispersed in a range of many aprotic solvents with various polarity and dielectric constant at room temperature. The change in the value of dipole moment was estimated by using the Stokes shifts. The difference between the dipole moment of the excited state and the ground state was shown using an extended form of Lippert equations by Kawski and co-workers.ConclusionsThe values found for μg = 1.077 D, and μe = 3.157 D, as well as the change in the dipole moments. The results showed that the dipole moment of the excited state is more than the ground state, indicating a high density and redistribution of electrons in the excited state. Finally, the quantum yield of C-dots in the eclectic aprotic solvents was communicated and discussed.

Synthesis, biological activity and molecular modeling of a new series of condensed 1,2,4-triazoles

A ring transformation of 6-methyl-7H[1,2,4]triazolo [4,3-b][1,2,4] triazepine-8(9H)-ones (thiones) in the presence of acetic anhydride give rise to a new series of 17 condensed 1,2,4-triazole derivatives (1–17). Plausible mechanisms are proposed and show the formation of a beta fused β-lactam moiety. The compounds were tested for their (i) inhibitory potential on digestive enzymes (α-amylase and α-glucosidase), and (ii) antioxidant activity using radical scavenging (DPPH and ABTS radicals) and ferric reducing power assays. The compounds showed interesting and promising antidiabetic activities compared to the reference drug Acarbose. Molecular docking study has been carried out to determine the binding mode interactions between these derivatives and the targeted enzymes. The results showed the strength of intermolecular hydrogen bonding in ligand-receptor complexes as an important descriptor in rationalizing the observed inhibition results. Moreover, molecular dynamics simulations are also performed for the best protein-ligand complex to understand the stability of small molecule in a protein environment. To shed light on the antioxidant activity of the synthesized compounds and the mechanism involved in DPPH free radical, DFT calculations were performed at the B3P86/6-311++G(d,p) level using the polarizable continuum model. The effect of aprotic solvent on bond dissociation enthalpies (BDEs) is investigated by calculating and comparing BDEs of 1 in methanol and dimethylsulfoxide as solvents using PCM. The obtained results show that the mechanism of action depends on the basic skeleton and the presence of substituted functional groups in these derivatives. BDEs are found to be slightly influenced by the aprotic solvent of less than 0.01 kcal/mol compared with those obtained in methanol.

Effects of aprotic solvents on the stability of metal-free superoxide dismutase probed by native electrospray ionization-ion mobility-mass spectrometry.

Considering that aprotic solvents are often used as cosolvents in investigating the interactions between small molecules and proteins, we assessed the effects of five aprotic solvents represented by dimethylformamide (DMF) on the structure stabilities of metal-free SOD1 (apo-SOD1) by native electrospray ionization-ion mobility-mass spectrometry (ESI-IM-MS). These aprotic solvents include DMF, 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), acetonitrile (ACN), and tetrahydrofuran (THF). Results indicated that DMI, DMSO, and DMF at low percentage concentration could reduce the average charge and the dimer dissociation of apo-SOD1. By contrast, ACN and THF at low concentration have no similar effect. DMF was selected as a representative solvent to further investigate the detailed effects on the structure stability of apo-SOD1 by using collision-induced dissociation and unfolding. The results reveal that the addition of minimal DMF to an aqueous protein solution can protect against the unfolding and dissociation of dimer, even under destabilizing conditions (such as low pH or high cone voltage). When the different percentage concentrations of DMF were added, the average collision cross section of apo-SOD1 showed that apo-SOD1 became compacted when the DMF concentration increased from 0% to 1% and eventually started extending when increased from 1% to 20%. The results indicated that DMF has similar effects to DMSO in native mass spectrometry (MS) and it can also be used as a cosolvent besides DMSO in investigating the stabilities of proteins and the interactions between small molecules and proteins.

Electron injection from a carboxylic anchoring dye to TiO2 nanoparticles in aprotic solvents

Injection of photoexcited electrons in the para-Ethyl Red dye to TiO2 nanoparticles (Anatase, 40 nm diameter) is characterized by transient absorption on ultrafast time scales. This study focuses on understanding the effect of aprotic solvents on the injection rate. Transient absorption at 1900 cm−1 is probed following a 400 nm pulse which excites the electronic transition of p-ER adsorbed on TiO2 through its carboxylic group. Measurements conducted in three different solvents show that electron injection lifetimes are in the 250–300 fs range but display a trend in correlation with solvent polarity: the electron injection lifetime is the shortest (257 fs) in acetonitrile followed by dichloromethane (271 fs) and chloroform (296 fs). This trend can be understood by using the Marcus theory in which the reorganization energy varies correspondingly in the three different solvents. This study shows that for aprotic solvents the one with the highest polarity facilitates the fastest electron injection.

Aprotic solvents effect on the UV–visible absorption spectra of bixin

We describe here the effects of aprotic solvents on the spectroscopic characteristics of bixin. Bixin was dissolved in dimethyl sulfoxide, acetone, dichloromethane, ethyl acetate, chloroform, dimethyl carbonate, cyclohexane and hexane, separately, and its spectra in the resulting solutions were determined by UV–visible spectrophotometry at normal pressure and room temperature. We analyzed the effect of aprotic solvents on λmax according to Onsager cavity model and Hansen theory, and determined the approximate absorption coefficient with the Beer–Lambert law. We found that the UV–visible absorption spectra of bixin were found to be solvent dependent. The S0→S2 transition energy of bixin in solution was dependent principally on the refractive index of the solvents and the bixin–solvent dispersion interaction. There was a small influence of the solvents dielectric constant, permanent dipole interaction and hydrogen bonding occurred between bixin and solvents. The absorbance of bixin in various solvents, with the exception of hexane, increased linearly with concentration.

The comparative study of linear solvatation energy relationship for the reactivity of pyridine carboxylic acids with diazodiphenylmethane in protic and aprotic solvents

Protic and aprotic solvent effects on the reactivity of picolinic, nicotinic and isonicotinic acid, as well as of some substituted nicotinic acids with diazodiphenylmethane (DDM) were investigated. In order to explain the kinetic results through solvent effects, the second-order rate constants for the reaction of the examined acids with DDM were correlated using the Kamlet-Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of the multiple linear regression analysis and the solvent effects on the reaction rates were analyzed in terms of the contributions of the initial and the transition state. The signs of the equation coefficients support the already known reaction mechanism. The solvatation models for all the investigated acids are suggested and related to their specific structure.

The effect of protic solvents on luminescent properties of dye molecules

The effect of a protic solvent on the spectral-luminescent properties (associated with relative energies of ππ⁎ and nπ⁎ states) of a dye molecule is considered. It is shown that generally this effect cannot be reduced to changes caused by H-bond formation, since changes caused by universal (non-specific) interactions with medium are comparable to them. It is shown that the common interpretation of the effect of protic-solvents on luminescent properties of luminophores (based on the consideration only of specific interactions) is reasonable only in case of bimolecular complexes in a non-polar solvent or in a gas phase. Neglecting the effect of non-specific (dipole–dipole) interactions is generally not reasonable.

The effect of aprotic solvent on the selectivity of ion-exchange membranes

The effect of N,N-dimethylacetamide on the selectivity of heterogeneous (MK-40, MA-40, and MA-41) and homogeneous (MF-4SK) ion-exchange membranes is studied for the first time. Concentration dependences of electrical conductivity and diffusion permeability of the membranes were measured experimentally over wide lithium chloride concentrations; on their basis, electrodiffusion coefficients of the co- and counterions were calculated. The interrelation between the electrodiffusion coefficients and the specific moisture capacity of the heterogeneous and homogeneous membranes (which affect their selectivity) is revealed. The calculated electrodiffusion coefficients were used in the calculations of the electromigration transport numbers of counterions in the initial membranes and those processed in mixed solvent. It is shown that the heterogeneous membrane selectivity either increased under the action of the aprotic solvent to polymer material (MA-40, MA-41) or remained practically unchanged (MK-40); the selectivity of homogeneous perfluorinated membranes (e.g., MF-4SK) decreased, thus approaching that of the studied heterogeneous anion-exchange membranes.

The effect of aprotic solvents on the adsorption of phenol by alumina.

Abstract The isotherms for the adsorption of phenol onto alumina from cyclohexane, benzene, nitrobenzene, ethyl acetate and 1,4-dioxan solutions have been determined at 25°. The change in solvent in the above order causes a successive decrease in the amount of phenol adsorbed at the ‘saturation level’ and possible explanations of the solvent effects are discussed.

Copolymerization of vinyl chloride with 1-(vinyloxyalkoxy)propylene oxides-2,3: Solvophobic effects of solvents

The influence of solvophobic effects of aprotic solvents on the reactivity of 1-(vinyloxyalkoxy)propylene oxides-2,3 in free-radical copolymerization with vinyl chloride has been studied by dynamic light scattering. It has been shown that the association of copolymer macromolecules in aprotic solvents results in the reduced reactivity of 1-(vinyloxyalcoxy)propylene oxides-2,3. This effect can be explained by a decrease in their local concentration in the vicinity of the reaction center.

Iron(III)-Mediated Atom Transfer Radical Polymerization in the Absence of Any Additives

The pyridylphosphine ligand, 2-(diphenylphosphino)pyridine (DPPP), was employed in the iron(III)-catalyzed atom transfer radical polymerizations (ATRPs) of methyl methacrylate (MMA) with various initiators and solvents in the absence of any radical initiators or reducing agents. In studies of their ATRP behavior, most of these systems were well controlled with a linear increase in the molecular weight (Mn) versus conversion in agreement with the theoretical Mn, and low-molecular-weight distributions (Mw/Mn = 1.10 to 1.25) were observed throughout the reactions. The effect of a protic solvent (methanol) was also investigated, and it was shown that living radical polymerization occurred, even in the presence of relatively high concentrations of methanol. The controlled nature of the polymerization was confirmed by the monomer addition experiment and the block copolymerization.

Effect of aprotic solvents on the enzymatic activity of lipase in AOT reverse micelles

The modification of reverse micellar systems composed of AOT, isooctane, water by the addition of aprotic solvents has been performed. The impact of this change on the activity, stability and kinetics of solubilized Chromobacterium viscosum lipase (glycerol-ester hydrolase, EC 3.1.1.3) was investigated. Of seven aprotic solvents tested, dimethyl sulfoxide (DMSO) was found to be most effective. It was found that lipase activity was enhanced by optimizing some relevant parameters, such as water–AOT molar ratio ( W 0), buffer pH and surfactant concentration. A kinetic model that considers the free substrate in equilibrium with the substrate adsorbed on the micellar surface was successfully used to deduce some kinetic parameters ( V max, K m and K ad), and the values of K m and K ad were significantly reduced by the presence of DMSO. Higher lipase stability was found in AOT reverse micelles with DMSO compared with that in simple AOT systems with half-life of 125 and 33 days, respectively. Fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR) were used to elucidate the effects of DMSO on the properties of AOT reverse micelles.

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XLII. Effect of Aprotic Solvent on the Rate of 3-Methyl-3-chloro-1-butene Dehydrochlorination. Correlation Analysis of Solvation Effects

The kinetics of 3-methyl-3-chloro-1-butene dehydrochlorination in propylene carbonate, γ-butyrolactone, sulfolane, acetone, MeCN, PhNO2, PhCN, PhCOMe, MeCOEt, cyclohexanone, o-dichlorobenzene, PhCl, PhBr, 1,2-dichloroethane, dioxane, and AcOEt were studied; v = k[C5H9Cl], E1 mechanism. The reaction rate is satisfactorily described by the parameters of the polarity, electrophilicity, and cohesion of the solvent; the solvent nucleophilicity and polarizability exert no effect on the reaction rate.

Effect of Aprotic Solvents on the Macromolecular Reaction of Hydrazidation of the Graft Copolymer of Polycaproamide and Polyglycidyl Methacrylate

The kinetic parameters of the initial stage of the heterophase reaction of α-oxide groups in the graft copolymer of polycaproamide and polyglycidyl methacrylate in different solvents are determined. The significant effect of substitution of a polar hydroxyl-containing solvent by bipolar aprotic solvents on the reaction rate of hydrazidation of PCA-PGMA copolymer is demonstrated and is primarily caused by an increase in the nucleophilicity of hydrazine hydrate due to a change in its solvation and an increase in the diffusion coefficient.

Reactivity of cyclohex-1-enylcarboxylic and 2-methylcyclohex-1-enylcarboxylic acids with diazodiphenylmethane in aprotic solvents

Rate constants for the reaction of diazodiphenylmethane with cyclohex-1-enylcarboxylic acid and 2-methylcyclohex-1-enylcarboxylic acid were determined in nine aprotic solvents, as well as in seven protic solvents, at 30?C using the appropriate UV-spectroscopic method. In protic solvents the unsubsituted acid displayed higher reaction rates than the methyl-substituted one. The results in aprotic solvents showed quite the opposite, and the reaction rates were considerably lower. In order to explain the obtained results through solvent effects, reaction rate constants (k) of the examined acids were correlated using the total solvatochromic equation of the form: log k=logk0+s?*+a?+b?, where ?* is the measure of the solvent polarity, a represents the scale of the solvent hydrogen bond donor acidities (HBD) and b represents the scale of the solvent hydrogen bond acceptor basicities (HBA). The correlation of the kinetic data were carried out by means of multiple linear regression analysis and the opposite effects of aprotic solvents, as well as the difference in the influence of protic and aprotic solvents on the reaction of the two examined acids with DDM were discussed. The results presented in this paper for cyclohex-1-enylcarboxylic and 2-methylcyclohex-1-enylcarboxylic acids were compared with the kinetic data for benzoic acid obtained in the same chemical reaction, under the same experimental conditions.

Re-Examination of the Effect of Aprotic Solvents upon the Fundamental Vibrational Peak of the Carbonyl Group in 1,1,3,3-Tetramethylurea

The 1650 cm−1 IR absorption band for the fundamental vibration of the C=O group in tetramethylurea (TMU) exhibits a substantial solvent-induced shift in polar and nonpolar aprotic solvents at 298 K. Earlier studies have rationalized the max(C=O) shifts in terms of the empirical Gutmann acceptor numbers (ANs) for the solvents or the Kirkwood parameter in dielectric permittivity. With a larger set of test data, other reaction field models are now compared which incorporate alternative continuum functions as elements in the formulation of an SCRF-MO perturbation description for the aprotic solvent effect upon the max(C=O) of TMU. The magnitude of the band shift appears to depend on both the solvent dipolarity and solvent polarizability, with the first being the dominant factor in the more reliable model.

Spectroscopic Studies of some Organic Compounds. Part-I. Aprotic Solvent Effects on Electronic Absorption Spectra of 2-[p-( 4-Methylpiperidino )phenyl]cinchoninic Acid

Spectroscopic Studies of some Organic Compounds. Part-I. Aprotic Solvent Effects on Electronic Absorption Spectra of 2-[p-( 4-Methylpiperidino )phenyl]cinchoninic Acid