Spectral properties of 1,3,4-oxadiazole derivatives in binary solvent mixtures

The influence of nonspecific intermolecular interactions on the fluorescence band shift of 1,3,4-oxadiazole derivatives has been investigated in the binary solvents hexane-ethanol, toluene-ethanol, toluene-acetonitrile, and carbontetrachloride-2-propanol. The dependences obtained have been analyzed in terms of preferential solvation. It has been shown that the maximum solvation energy for slightly polar compounds occurs in toluene-ethanol, toluene-acetonitrile, and carbontetrachloride-2-propanol. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 177–181, March–April, 2008.     

Solvatochromic dipolarity micro‐sensor behaviour in binary solvent systems of the (water + ionic liquid) type: application of preferential solvation model and linear solvation energy relationships

The type of specific intermolecular and interionic interactions that are established when an ionic liquid is dissolved in water was here analysed. The study of the solvatochromic response of dipolarity micro‐sensors based on Reichardt E_T(30) and Kamlet–Abboud–Taft solvent scales and the application of the solvent exchange model confirmed the formation of different intersolvent complexes in binary mixtures of (water + [C₄mim] [BF₄]/[Br]) type. These complexes provide H‐bond or electron pairs to the polar network, respectively. Moreover, for 4‐methoxybenzenesulfonyl chloride hydrolysis reaction in the (water + [C₄mim] [BF₄]) system, a higher inhibition (13 times) on the k_obs values was observed. Multiple linear regression analysis that allows confirming the solvent effect upon the reactive system is due to the hydrogen‐bond donor properties of intersolvent complex formed. Then, the correlation between two different solvent‐dependent processes proved to be successful. Copyright © 2014 John Wiley & Sons, Ltd.     

Selective nonspecific solvation under dielectric saturation and fluorescence spectra of dye solutions in binary solvents

The influence of selective nonspecific solvation on the fluorescence spectra of three substitutedN-methylphthalimides in a binary solvent system consisting of a nonpolar (n-heptane) and a polar (pyridine) component has been studied under conditions close to dielectric saturation. The substantially nonlinearity of the effect is confirmation that the spectral shifts of fluorescence bands depend on the number of polar solvent molecules involved in solvating the dye molecule. The measured fluorescence spectral shifts determined by substituting one nonpolar solvent molecula with a polar one in the proximity of the dye molecule agree quantitatively with the forecasts of the previously proposed semiempirical theory which describes this nonlinear solvation phenomenon.     

The origin of preferential attachment and the generalized preferential attachment for weighted networks

In this paper, we first discuss the origin of preferential attachment. Then we establish the generalized preferential attachment (GPA) which has two new properties; first, it encapsulates both the topological and weight aspects of a network, which makes it is neither entirely degree preferential nor entirely weight preferential. Second, it can tell us not only the chance that each already-existing vertex being connected but also how much weight each new edge has. The GPA can generate four power-law distributions, besides the three for vertex degrees, vertex strengths, and edge weights, it yields a new power-law distribution for the subgraph degrees.     

Comments concerning “Study of solute–solvent and solvent–solvent interactions in pure and mixed binary solvents”

A number of mathematical equations representing the solute solubility in monosolvent and binary solvent mixtures are discussed. This work is a commentary to the article of Maitra and Baghchi that appeared in this journal.     

Effect of solvation on polarization characteristics of fluorescence for 1,3,4-oxadiazole derivatives in binary solvents

We have studied the degree of fluorescence polarization for 1,3,4-oxadiazole derivatives in the binary solvents hexane-ethanol, toluene-ethanol, toluene-acetonitrile, 2-propanol-water, dioxane-water, 2-propanol-glycerol, glycerol-water vs. the composition of the solvent. We have shown that in systems with predominant universal interactions, the characteristic changes in the degree of polarization reflect the change in the viscosity of the mixture, while in systems with pronounced specific interactions they reflect the characteristic structural features of the fluorescent centers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 677–683, September–October, 2008.     

Reaction kinetics and solubility in water‐organic binary solutions are governed by similar solvation equilibria

The solvation effects observed in water‐organic solutions were studied by combining data for reaction kinetics and dissolution equilibria by means of a linear free‐energy (similarity) analysis. Kinetic data for the pH‐independent hydrolysis of (4‐methoxyphenyl)‐2,2‐dichloroacetate measured in this work and solubility data for naphthalene, and other substrates of low polarity, in aqueous binary mixtures of methanol, ethanol, acetonitrile, dimethyl sulfoxide (DMSO), and 1,4‐dioxane were used. Linear similarity relationships were discovered for these data over the full range of solvent compositions studied. To gain insight into the similarities observed between these different phenomena, molecular dynamics simulations were carried out for naphthalene and an ester in water–acetonitrile solutions. The results revealed considerable preferential solvation of these substrates by the co‐solvent. Linear relationships between the experimental data and the mole fractions of acetonitrile in the solvation shells of substrates were found. Surprisingly, a linear relationship was found between the mole fractions of acetonitrile in the solvation shells of the ester and naphthalene. This linearity indicated that a similar solvation mechanism governs even such different phenomena as dissolution and reaction kinetics. The relationships between the experimental data and the results of the molecular dynamics calculations found in this work explained the solvent effect observed in water‐organic solutions on the molecular level. Copyright © 2015 John Wiley & Sons, Ltd.     

On the surface tensions of binary mixtures

For binary mixtures with fixed concentrations of the species, various relationships between the surface tensions and the concentrations are briefly reviewed.     

Effect of the age of papers on the preferential attachment in citation networks

In this paper, we investigated the influences of the age of papers on the preferential attachment on the basis of three actual citation networks. We found that the time dependence of the attachment rate follows a uniform exponentially decreasing function, T(t)∼exp(−λt), in different citation networks. Younger papers are more likely to be cited by new ones than older papers. On the basis of the aging influences, we modified the expression for the preferential attachment, to . Our results show that the modified preferential attachment works well for citation networks.     

The influence of polarity in binary solvent mixtures on the conformation of bis-triazinyl-pyridine in solution

We report a combined computational and experimental study to investigate the influence of the solvent on the electronic and molecular structure of the bis-triazinyl-pyridine (BTP) ligand. Experimental measurements and quantum-chemical calculations using geometries from molecular dynamics simulations in different solvent methanol/water mixtures reveal a change in the UV/vis absorption spectra for the investigated BTP compound. This change is investigated further using nuclear magnetic resonance (NMR) techniques, both experimental and computational, to gain insight to ligand conformation. Comparison of experimental and computational results enables the analysis of relevant BTP conformers, which cannot be accessed using experimental measurements alone. Based on this approach, we conclude that the BTP ligands change conformation with decreasing solvent polarity to maximise the lipophilic accessible surface – a concept which is transferrable to various classes of compounds.     

Depletion interactions in binary mixtures of repulsive colloids

Acceptance ratio method, which has been used to calculate the depletion potential in binary hard-sphere mixtures, is extended to the computation of the depletion potential of non-rigid particle systems. The repulsive part of the Lennard-Jones pair potential is used as the direct pair potential between the non-rigid particles. The depletion potential between two big spheres immersed in a suspension of small spheres is determined with the acceptance ratio method through the application of Monte Carlo simulation. In order to check the validity of this method, our results are compared with those obtained by the Asakura-Oosawa approximation, and by Varial expansion approach, and by molecular dynamics simulation. The total effective potential and the depth of its potential well are computed for various softness parameters of the direct pair potential.     

On the solvation force of water-like fluid models with square-well attraction and site–site association in slit-like pores: density functional approach

The solvation force of the water-like fluid models with square-well attraction and site–site chemical association confined to slit-like pores has been explored. Theoretical procedure is based on the application of the density functional approach with mean-field approximation for the attractive interparticle interactions. The chemical association effects are treated by using the first-order thermodynamic perturbation theory of Wertheim. Trends of behaviour of the solvation force are put in correspondence with the distribution of molecules in the pores and with the average density of the adsorbate. Moreover, the distribution of non-bonded species on pore width is described. The influence of the width of the square-well and of the gas–solid attraction is discussed. A comparison of theoretical predictions with computer simulations results for water models in slit-like pores is performed.     

On the theory of spinodal decomposition in solid and liquid binary mixtures

The kinetics of phase separation is discussed with emphasis on the transition between spinodal decomposition and nucleation. A reanalysis of the theory of Langer, Baron and Miller shows that it exhibits a spinodal line somewhat closer to the coexistence curve than the meanfield spinodal. There the same (as we think unphysical) critical singularities occur as in Cahn-Hilliard theory. The precise location of this spinodal line depends on the cell size of the coarse graining. For concentrations less than the spinodal one the structure factorS(k, t) converges then towards the structure factor of the metastable onephase state, implying an infinite lifetime of the latter.In order to include the effects of nucleation and growth we hence present an alternative treatment, extending our previous work on cluster dynamics. From a simple approximation for the radial concentration distribution function of clustersS(k, t) is computed numerically. Even at rather low concentrations the time evolution ofS(k, t) is then similar to what Langer et al. find at high concentrations, implying a very gradual transition from nucleation and growth to spinodal decomposition, at least for parameter values appropriate to the Ising model. This treatment, which is consistent with Lifshitz-Slyozov's coarsening law at late times, is extended to the early stages of phase separation in liquid mixtures.     

Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

Solvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and C S stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li⁺, calculated by the changes in intensities of the C S asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the C H stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Fluorescence quenching of newly synthesized biologically active coumarin derivative by aniline in binary solvent mixtures

The fluorescence quenching of newly synthesized coumarin (chromen-2-one) derivative, 4-(5-methyl-3-furan-2-yl-benzofuran-2-yl)-7-methyl-chromen-2-one (MFBMC) by aniline in different solvent mixtures of benzene and acetonitrile was determined at room temperature (296 K) by steady-state fluorescence measurements. The quenching is found to be appreciable and positive deviation from linearity was observed in the Stern-Volmer (S-V) plots in all the solvent mixtures. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the fluorescence quenching process have been determined by using the modified Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. The dependence of Stern-Volmer constant K_SV, on dielectric constant ε of the solvent mixture suggests that the fluorescence quenching is diffusion-limited. Further with the use of finite sink approximation model, it is concluded that these bimolecular quenching reactions are diffusion-limited. Using lifetime (τ_o) data, the distance parameter R′ and mutual diffusion coefficient D are estimated independently.     

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part III. Hydrophobic hydration and preferential solvation of crown ethers in water-amide mixtures at 298.15 K

Enthalpies of solution of 15-crown-5 (15C5) and benzo-15-crown-5 ether (B15C5) in the mixture of water with formamide (F) and N-methylformamide (NMF) have been measured at 298.15 K. The values of standard enthalpies of solution of 15C5 are negative and those of B15C5 are positive in the mixtures. The results of calorimetric measurements of dissolution enthalpies of 15C5 and B15C5 in the mixture of water and organic solvents at 298.15 K are discussed with regard to the intermolecular interactions that occur in the solution. Considering the properties and molecular structure of the examined crown ethers, particular attention is given to the hydrophobic hydration and preferential solvation of solute in the mixed solvents. The preferential solvation in the examined systems was analysed using the Covington model developed by Balk and Somsen. The relative importance of the solvation mechanism appeared to depend on co-solvent properties.     

Effect of solvent on the quenching of fluorescence of safranine T(3,7-diamino-2,8-dimethyl-5-phenylphenazinium chloride) in binary solvent mixtures

Fluorescence quenching of 3,7-diamino-2, 8-dimethyl-5-phenylphenazinium chloride (safranine T (ST)) by halides and pseudo halides in binary solvent mixtures was investigated by steady-state fluorescence spectroscopy. Several parameters, such as dielectric constant, viscosity coefficient, and fluorescence quantum yield have been investigated as a function of solvent compositions. In mixed solvents ST has been used as a probe for studying the microheterogenity of the mixture. The preferential solvations around ST in the excited state were determined. The Stern-Volmer quenching constants at different compositions of solvent mixtures were determined and the rational analysis of the results was attempted.     

Detecting intermolecular NOEs by means of a novel DPFGSE pulse sequence. Application to the solvation of carbohydrates in binary mixtures

We present a pulse sequence based on solute-to-solvent NOE enhancement and aimed at the detection of intermolecular NOE's. Thus, a W3 pulse cluster is used to selectively filter the solvent signals in a DPFGSE sequence. The sequence has been tested on a sample of glucose dissolved in two binary aqueous mixtures (water-acetonitrile and water-DMSO). We show how the resulting enhancements may derive from intermolecular cross-relaxation or, in the water-DMSO sample, also from chemical exchange. In each case, a quantitative interpretation of the data is also supplied, both in terms of local enrichment in one specific solvent (preferential solvation), and by means of a kinetic model for a two-site chemical exchange.     

Effect of aqueous solvation on the structures of pyruvic acid isomers and their reactions in solution: a computational study

The pyruvic acid molecule and its various isomers have been studied in aqueous solution in order to understand the mechanism of decarboxylation. The tautomeric equilibrium remains in favor of the keto form in aqueous solution, but the energy difference between the two tautomers decreases. The anion also exists in the keto form in aqueous solution. Good agreement between the calculated and observed gas phase protonation and basicity values is obtained, and the calculated pK_a value is also in reasonable agreement with the literature value. The importance of the catalytic mechanism may be gauged from the fact that, in the absence of an enzymatic pathway, the reaction has high activation barrier and may not occur at all. Copyright © 2007 John Wiley & Sons, Ltd.