Enzyme catalysis in organic solvents: a promising field for optical biosensing

The ability of enzymes to work in non-aqueous media offers new and almost unexploited possibilities for the development of new optical biosensors. The advantages of performing biocatalytic reactions in non-aqueous media are discussed in relation to their possible application in optical biosensor design. Attention is focused on the factors that influence enzymatic catalysis in organic solvents, including the role of enzyme-associated water, criteria for solvent selection and the alteration of enzyme specificity. Recent examples of relevant applications and future prospects of organic-phase optical biosensing are discussed.     

Using molecular simulation to predict solute solvation and partition coefficients in solvents of different polarity

A methodology is proposed for the prediction of the Gibbs energy of solvation (Δ(Solv)G) based on MD simulations. The methodology is then used to predict Δ(Solv)G of four solutes (namely propane, benzene, ethanol and acetone) in several solvents of different polarities (including n-hexane, n-hexadecane, ethylbenzene, 1-octanol, acetone and water) while testing the validity of the TraPPE force field parameters. Excellent agreement with experimental data is obtained, with average deviations of 0.2, 1.1, 0.8 and 1.2 kJ mol(-1), for the four solutes respectively. Subsequently, partition coefficients (log P) for forty different solute/solvent systems are predicted. The a priori knowledge of partition coefficient values is of high importance in chemical and pharmaceutical separation process design or as a measure of the increasingly important environmental fate. Here again, the agreement between experimental data and simulation predictions is excellent, with an absolute average deviation of 0.28 log P units. However, this deviation can be decreased down to 0.14 log P units, just by optimizing partial atomic charges of acetone in the water phase. Consequently, molecular simulation is proven to be a tool with strong physical basis able to predict log P with competitive accuracy when compared to the popular statistical methods with weak physical basis.     

Photochemistry of benzimidazolocyanine dyes in solvents of different polarity

The effect of ion pair formation on the kinetics of the decay of the photoisomers and triplet states of cationic benzimidazolocyanine dyes is studied by flash photolysis. An increase in the rate constant of the reversecis-trans isomerization of the photoisomers is observed when ion pairs are formed (in nonpolar solvents). In the case of benzimidazolocyanine dyes with the I^– anion, ion-pair formation causes an increase in the rate constant of decay of the triplet state. Acceleration of S₁ S₀ internal conversion is discovered for the dyes with I^–1 Translated fromIvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 507–512, March, 1993.     

Naphthalene adsorption on activated carbons using solvents of different polarity

The hydrophobic-hydrophilic character of a series of microporous activated carbons was explored as a key factor in competitive adsorption of a non-polar compound from liquid phase. The selectivity of the carbon surface towards naphthalene was explored by performing the adsorption isotherms in water, cyclohexane and heptane. Solvent polarity and adsorbent hydrophobic character were found to strongly influence the adsorption capacity of naphthalene. In aqueous media, despite the non-polar character of the adsorbate, surface acidity lowered adsorption capacity. This is attributed to the competition of water from the adsorption sites, via H-bonding with surface functionalities and the formation of hydration clusters that reduce the accessibility and affinity of naphthalene to the inner pore structure. In organic media the uptake decreased due to competition of the hydrophobic solvent for the active sites of the carbon and to solvation effects. This competitive effect of the solvent is minimized in oxidized carbons as opposed to the trend obtained in aqueous solutions. The results confirmed that although adsorption of naphthalene strongly depends on the narrow microporosity of the adsorbent, competitive adsorption of the solvent for the active sites becomes important.     

Chiral aldehyde catalysis: a highly promising concept in asymmetric catalysis

<正>Asymmetric organocatalysis has been a robust tool for manufacturing optically active molecules, in addition to asymmetric metal and biocatalysis [1]. The development of new concepts and catalysts to enable the creation of efficient synthetic methods has been a longstanding activity in this field. During the last decades, a diverse spectrum of chiral organocatalysts, including ketones, amine, Br?nsted acids     

Anion nucleophilicity in ionic liquids: a comparison with traditional molecular solvents of different polarity

The nucleophilic reactivity of a homogeneous series of anions (halides, pseudohalides and organic anions) in the ionic liquids [hexmim] [ClO₄] and [hexmim] [PF₆] has been measured in their reaction with n-alkyl methanesulfonates, and compared with that found in traditional molecular solvents of different polarity, that is, chlorobenzene, DMSO, and MeOH.     

Conformation equilibrium of 3-(hydroxymethyl)piperidine in solvents with different polarity

Quantum-chemical calculations of the 3-(hydroxymethyl)piperidine molecule conformers were performed at the B3LYP/6-31+G** level of theory, and four most stable conformations with different relative orientation of CH₂OH and N–H groups were determined. The optimized structures, vibration frequencies, and band intensities in the spectra of the conformers were obtained. The conformational equilibria of the most stable rotational isomers in solvents of different polarity was studied within the polarizable continuum model. According to the results of calculations, the conformational equilibrium in solution is substantially changed on varying the solvent polarity. This conclusion was confirmed by comparison with IR absorption spectra of 3-(hydroxymethyl)piperidine solutions in carbon tetrachloride in the region of ОН-stretchings.

     

A unified cosolvency model for calculating solute solubility in mixed solvents

Organic solvents are amongst the most powerful solubilization agents for a large number of water-insoluble drugs. A number of equations has been reported for mathematical representation of solute solubility in mixed solvents. The question is then posed--is there a mathematical difference between these models? To address this point, it has been demonstrated that all cosolvency models could be made equivalent by using algebraic manipulations. In order to familiarize the readers with the available cosolvency models, they are briefly reviewed. The models can be divided into two mathematical categories, i.e. linear and non-linear models. The linear models include: the log-linear, extended Hildebrand solubility approach, excess free energy equations, combined nearly ideal binary solvent/Redlich-Kister equation and Margule equations which can be converted to a general single model which expresses the logarithm of mole fraction solubility of a solute as a power series of volume fraction of the cosolvent. The non-linear models include the mixture response surface methods, two step solvation model and modified Wilson model which can be converted to a non-linear general form. Also, it has been shown that both the general single model and a non-linear general model are mathematically identical. To show the applicability of the models on real experimental data, 35 data sets have been collected from the literature. Both linear and nonlinear models produced comparable accuracies when an equal number of constant terms was employed in numerical analyses.     

Enthalpies of solvation of macrocyclic ether of dibenzo-24-crown-8 in solvents of different polarity

Enthalpies of solution of dibenzo-24-crown-8 in tetrachlormethane, benzene, chloroform, pyridine, acetone, acetonitrile, DMF, DMSO and propylene carbonate have been determined by calorimetric method at 298.15 K. The changes in enthalpy of solute-solvent interaction for the transfer the ether from inert tetrachlormethane into various solvents have been calculated from the obtained data. The thermochemical characteristics obtained for dibenzo-24-crown-8 have been compared with similar ones for dibenzo-18-crown-6 having a smaller cycle size. It has been found that an exothermicity of solute-solvent interaction changes to a lesser extent for transfer of the larger cyclic ether into polar solvents. But the effect increases more sharply for the transfer to chloroform. It has been concluded that the contribution from electrostatic interaction with solvent decreases with an increase of the cycle size as result of the increasing structural flexibility and decreasing polarity of cycle. But the contribution from hydrogen bonding with chloroform becomes larger due to an increase in the number of donor atoms of the ether molecules. It was ascertained that the ability to bind specifically acetonitrile molecules disappears in going from 18-merous to 24-merous cycle.     

On the theory of solute solubility in mixed solvents

A series of equations are developed for the study of the effects of cosolvents on the solubility of a solute in mixed solutions where the solute displays a finite solubility. The equations differ depending on the scale used for the solute (and cosolvent) concentrations. The expressions use Kirkwood-Buff integrals to relate the changes in solubility to changes in the local solution composition around the solute and can be applied to study any type of ternary system including electrolyte cosolvents. The expressions provided here differ from previous approaches because of the use of a semi-open ensemble and the extension to finite solute solubilities.     

Optical properties of CdSe and CdSe/ZnS quantum dots dispersed in solvents of different polarity

Original organic capping TOPO/TOP groups of CdSe and CdSe/ZnS quantum dots (QDs), from mother solution were replaced with 2_mercaptoethanol, which was chosen as model compound, in order to achieve water solubility. Obtained water dispersions of CdSe and CdSe/ZnS QDs were characterized by UV/VIS absorption and luminescence techniques. Luminescence measurements revealed that bare cores are very sensitive to surface capping, transfer into water diminished emission intensity. Core/shell, CdSe/ZnS, QDs are much more resistant to changes of the capping and solvent, and significant part of emission intensity was preserved in water. The article is published in the original.     

Methods for evaluating the association of some extractants in low polarity solvents

On the basis of vapor phase osmometry data the activity coefficients of TBP, D2EHPA and some tertiary amines have been calculated. The applicability of various methods for the evaluation of association constantsK _i in the extraction systems is presented.     

The full evaporation technique: a promising alternative for residual solvents analysis in solid samples

The static headspace technique is the most common approach to residual solvent analysis in pharmaceutical and environmental matrices. This paper presents an alternative tool where the volatile impurities are released from the matrix by working directly on a small amount of sample at a high equilibration temperature: the so-called Full Evaporation Technique (FET). The capability of this method was evaluated on a mixture of nine solvents, which belong to Class 3 in the classification of the European Pharmacopoeia Agency for residual solvents, at various levels of concentration: ethanol, acetone, 2-propanol, methyl acetate, 2-butanone, ethyl acetate, tetrahydrofuran, 2-methyl-1-propanol, 1-butanol. Data on linearity, accuracy, precision and sensitivity are reported. Use of an internal standard proved to be necessary when using such a method. The method is then successfully applied to the analysis of solvent traces in permethylated beta-cyclodextrin.     

Development of new acid-functionalized resins for combinatorial synthesis on solid supports

New methods for the synthesis of acid-functionalized polystyrene and TentaGel resins are described; these methods serve to overcome problems with currently available resins and will be instrumental in spurring the use of carboxylic acid resins in solid phase chemistry.     

Solute dependence of mobility of solvent molecules in solvophobic solute solutions: Dielectric relaxation of nonpolar solute/alcohol mixtures

The dielectric relaxation spectra of alcohol/nonpolar solute mixtures are measured at several temperatures (-15 degrees C < or = T < or = 25 degrees C) and for several molar fractions of solute (0 < or = X(s) < or = 0.114) in the frequency range of 200 MHz < or = nu < or = 20 GHz. The double-Debye-type function is used for fitting of the spectra of mixtures, and the mean dielectric relaxation times (tau(mean)) of alcohol molecules are determined. In the systems having strong interaction between alcohol and nonpolar solutes, tau(mean) becomes shorter with an increase in the concentration of the solutes. On the other hand, tau(mean) becomes longer in the system having weak interaction between alcohol and nonpolar solutes. These results contradict with our intuitive predictions, do not correspond to mixing enthalpy, and are not explained by the hydrodynamic theory. They are attributed to the mechanism of the coupling between long-range electrostatic interactions and concentration fluctuation caused by the addition of solutes, which is suggested by Yamaguchi et al. based on the mode-coupling theory (Yamaguchi, T.; Matsuoka, T.; Koda, S. J. Chem. Phys. 2004, 120, 7590).     

反相HPLC中溶剂极性对容量因子的影响

考查了反相HPLC中,溶剂极性改变对容量因子的影响及其相关规律。结果发现:其影响是复杂的,不同溶质对不同溶剂极性改变的敏感程度差异较大。反映在容量因子的变化上就是:有时极性改变较大,但某些溶质的容量因子变化却较小;反之有时极性改变较小,但某些溶质的容量因子变化却较大。随着溶剂极性的改变,原来容量因子小的溶质变化幅度小,原来容量因子大的溶质变化幅度大。最后探讨了产生这种复杂变化的机理。