Inversion of the Kirkwood–Buff theory of solutions: application to binary systems

Kirkwood–Buff (K–B) integrals play an important role in characterizing the properties and interactions of various liquid mixtures. However, there exists no method to calculate directly the K–B integrals from the easily available experimental data of ultrasonic velocity and density. An attempt has been made to evaluate the same using these initial parameters. A statistical mechanical theory advanced by Arakawa et al. has been used here, in combination with a semi-empirical formula to compute K–B parameters in the whole concentration range for six binary systems at atmospheric pressure and at 298.15 K.     

Local composition in the vicinity of a protein molecule in an aqueous mixed solvent

This paper is focused on the composition of a cosolvent in the vicinity of a protein surface (local composition) and its dependence on various factors. First, the Kirkwood-Buff theory of solution is used to obtain analytical expressions that connect the excess or deficit number of cosolvent and water molecules in the vicinity of a protein surface with experimentally measurable quantities such as the bulk concentration of the mixed solvent, the preferential binding parameter, and the molar volumes of water and cosolvent. Using these expressions, relations between the preferential binding parameter (at a molal concentration scale) and the above excesses (or deficits) are established. In addition, the obtained expressions are used to examine the effect of the nonideality of the water + cosolvent mixtures and of the molar volume of the cosolvent on the excess (or deficit) number of cosolvent molecules in the vicinity of the protein surface. It is shown that at least for the mixed solvents considered (water + urea and water + glucose) the nonideality of the mixed solvent is not an important factor in the local compositions around a protein molecule and that the main contribution is provided by the nonidealities of the protein-water and protein-cosolvent mixtures. Special attention is paid to urea as cosolvent, because urea is one of only a few compounds with a concentration at the protein surface larger than its concentration in the bulk. The composition dependence of the excess of urea around a protein molecule is calculated for the water + lysozyme + urea mixture at pH = 7.0 and 2.0. At pH = 7.0, the excess of urea becomes almost composition independent at high urea concentrations. Such independence could be explained by assuming that urea totally replaces water in some areas of the protein surface, whereas on the remaining areas of the protein surface both water and urea are present with concentration comparable to those in the bulk. The Schellman exchange model was used to relate the preferential binding parameter in water + lysozyme + urea mixtures to the urea concentration.     

Reaction of alkynylsilanes with CuCl in polar solvents leading to alkynyl group transfer from Si to Cu

The reaction of 1-phenyl-2-trimethylsilylethyne with CuCl at 80–100°C in N,N-dimethylformamide (DMF) or N,N-dimethylimidazolidinone (DMI) yielded the alkynylcopper species [Cu₂Cl(CCPh)]_n (1) in 56–63% yields. Heating 1 at 80°C under aerobic conditions gave 1,4-diphenyl-1,3-butadiyne in 82% yield via an oxidative coupling of the phenylethynyl ligands.     

Studies on acid–base equilibria of 4-R-2,6-dimethylpyridine N-oxide systems in non-aqueous solvents

Acid–base equilibrium constants, i.e. acid dissociation, cationic homoconjugation and cationic heteroconjugation constants in 4-R-2,6-dimethylpyridine N-oxide systems (where R denotes methoxy-, methyl-, chloro- or nitro-group) in polar non-aqueous solvents: protophobic aprotic nitromethane, acetonitrile and acetone, protophilic aprotic N,N-dimethylformamide and amphiprotic methanol have been determined. The acidity constant values of protonated N-oxides in solvents studied have been found to change according to the substituent effect and to the sequence of acidity changes in water. This finding allowed to correlate the pK_a values determined in water with those determined in the solvents studied. Further, it was found that the cationic homo- and heteroconjugation constant values increased with decreasing solvent basicity and with increasing basicity of the N-oxide, and in the case of heteroconjugating systems, with increasing basicity of the the proton acceptor.     

Spectrophotometric determination of tetracyclines in pharmaceutical preparations, with uranyl acetate

Uranyl acetate is proposed as a reagent for the spectrophotometric determination of the tetracycline group of antibiotics. The reagent forms orange-red 1:1 complexes with the drugs in N,N-dimethylformamide medium. The complexes show absorption maxima at 414, 406, 419, 405 and 402 nm for tetracycline hydrochloride (TCH), oxytetracycline hydrochloride (OTCH), chlortetracycline hydrochloride (CTCH), doxycycline hydrochloride (DCH) and methacycline hydrochloride (MCH), respectively. Beer's law is valid over the concentration ranges 0–115, 0–120, 0–125, 0–135 and 0–110 μg/ml for TCH, OTCH, CTCH, DCH and MCH, respectively.     

Density functional and multiphoton ionization studies of N,N-dimethylformamide–(methanol)n clusters

The multiphoton ionization of the hydrogen-bonded clusters N,N-dimethylformamide–(methanol)_n (DMF–(CH₃OH)_n) was studied using a time-of-flight mass spectrometer at the wavelengths of 355 and 532 nm. At both wavelengths, a series of protonated DMF–(CH₃OH)_nH⁺ ions was obtained. The clusters were also investigated by density functional theory B3LYP method in conjunction with basis sets 6-31+G(d,p) and 6-311+G(2d,p). Equilibrium geometries of both neutral and ionic DMF–CH₃OH clusters, and dissociation channels and dissociation energies of the ionic clusters are presented. The results show that when DMF–CH₃OH is vertically ionized and dissociated, DMFH⁺ and CH₃O are the dominant products via proton transfer reaction. A high energy barrier makes another channel corresponding to the production of DMFH⁺ and CH₂OH disfavored. In the DMF–(CH₃OH)H⁺ ion, the proton prefers to link with the O atom of DMF molecule. Variation of atomic charges during proton transfer in hydrogen bond of the protonated cluster DMF–(CH₃OH)H⁺ ion is also discussed.     

Asymmetric alcoholysis of 2-phenyl-5(4H)-oxazolones by the catalytic mixture of cyclo[(S)-His-(S)-Phe] with chiral auxiliaries

Some derivatives of dipeptides containing a His residue catalyzed the ring opening of 2-phenyl-4-benzyl-5(4H)-oxazolone by methanol. The mixture of cyclo[(S)-His-(S)-Phe] (CHP) with chiral auxiliaries which possess both a hydrogen-bond donor and a hydrogen-bond acceptor was a more effective and enantioselective catalyst than the CHP alone. The influence of racemic and the two enantiomerically pure auxiliaries on the cyclo[(S)-His-(S)-Phe]-catalyzed alcoholysis of the 5(4H)-oxazolone was different. A mixture of CHP with -diisopropyl tartrate catalyzed the enantioselective ring opening of 2-phenyl-4-benzyl-5(4H)-oxazolone by methanol, ethanol and n-butanol, preferentially affording the N-benzoyl- -phenylalaninates (20–39% e.e.).     

Chiral C2-symmetric 2,3-disubstituted aziridine and 2,6-disubstituted piperidine as chiral ligands in the addition reaction of diethylzinc with arylaldehydes

Chiral C₂-symmetric 2,3-disubstituted aziridines and 2,6-disubstituted piperidines having a β-amino alcohol moiety have been successfully synthesized and their catalytic chiral induction properties have been examined in the asymmetric addition reactions of diethylzinc with arylaldehydes in hexane. When N-(2,2-diphenyl-2-hydroxyethyl)-(S,S)-2,3-bis(methoxymethyl)aziridine 11 was used as a catalytic chiral ligand, sec-alcohols having (S)-configuration formed in high yields of 86–92% but low enantiomeric excesses (ee's) of 11–13%. However, when N-(2,2-diphenyl-2-hydroxyethyl)-(R,R)-2,6-disubstituted piperidine derivatives 16 and 20 were used as the chiral ligands under the same reaction conditions, the ee's of the corresponding sec-alcohols were 20–30 and 5–6%, respectively, along with the inversion of absolute configuration. A plausible mechanism for this inversion is proposed.     

A protein molecule in an aqueous mixed solvent: fluctuation theory outlook

In the present paper a procedure to calculate the properties of proteins in aqueous mixed solvents, particularly the excesses of the constituents of the mixed solvent near the protein molecule and the preferential binding parameters, is suggested. Expressions for the Kirkwood-Buff integrals in ternary mixtures and for the preferential binding parameter were derived and used to calculate various properties of infinitely dilute proteins in aqueous mixed solvents. The derived expressions and experimental information regarding the partial molar volumes and the preferential binding parameters were used to calculate the excesses (deficits) of water and cosolvent (in comparison with the bulk concentrations of protein-free mixed solvent) in the vicinity of ribonuclease A, ribonuclease T1, and lysozyme molecules. The calculations showed that water was in excess in the vicinity of ribonuclease A for water/glycerol and water/trehalose mixtures, and the cosolvent urea was in excess in the vicinity of ribonuclease T1 and lysozyme. The derivative of the activity coefficient of the protein with respect to the mole fraction of water was also calculated. This derivative was negative for the water/glycerol and water/trehalose mixed solvents and positive for the water/urea mixture. The mixture of lysozyme in the water/urea solvent is of particular interest, because the lysozyme at pH 7.0 is in its native state up to 9.3M urea, while at pH 2.0 it is denaturated between 2.5 and 5M and higher concentrations of urea. Our results demonstrated a striking similarity in the hydration of lysozyme at both pHs. It is worthwhile to note that the excesses of urea were only weakly composition dependent on both cases.     

Stereoselective synthesis of (1R,2S)-2-amino-1,3-diols from (R)-cyanohydrins

Vinyl substituted (1R,2S)-amino alcohols 5 were obtained by addition of vinyl magnesium bromide to the corresponding cyanohydrin O-trimethylsilyl ethers (R)-2. The O- and N-protected vinyl amino alcohols 6 were ozonized at −78°C in methanol yielding (1R,2S)-2-amino-1,3-diols7 in high enantiomeric and diastereomeric excesses. For purification, compounds 7 in some cases were acetylated to give the derivatives (1R,2S)-8. Racemic 6a was converted by oxidative ozonolysis at −78°C in methanolic NaOH solution to the corresponding methyl N-acetyl-β-hydroxy propanoate 9a. The configuration of (1R,2S)-8a was confirmed by x-ray crystallographic analysis.     

Homogeneous blend membrane made from poly(ether sulphone) and poly(vinylpyrrolidone) and its application to water electrolysis

A homogeneous blend membrane has been successfully prepared from poly(ether sulphone) (PES) and poly(vinylpyrrolidone) (PVP), which have been usually thought to be immiscible to each other. The PES–PVP membrane possesses combined advantages of the hydrophobic and hydrophilic components; specifically, both good mechanical strength and excellent hydrophilicity have been achieved simultaneously. The success of achieving such special properties can be ascribed to the appropriate choice of solvent for membrane casting, N,N-dimethylformamide (DMF) in this case, and the post-treatment of the membrane in alkaline ethanol solution for obtaining hydrophilicity. Membranes with different blending ratios were characterized with tensile test, scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and electrochemical measurements. The membrane was found to function well as a diaphragm in water electrolysis. In comparison with the traditional asbestos diaphragm, an energy saving of ca. 10% can be reached upon employing PES–PVP membranes in water electrolysis.     

Preparation of P(AN–MMA) microporous membrane for Li-ion batteries by phase inversion

A novel process was proposed for preparation of microporous poly(acrylonitrile–methyl methacrylate) (P(AN–MMA)) membranes by phase inversion techniques using ultrasonic humidifier. Being prepared by dissolving the polymer (PAN–MMA) in the N,N-dimethylformamide (DMF) solution with mechanical stirring, the homogenous casting solution was cast onto a clean glass plate. Successively, the glass plate was exposed to the water vapor produced by ultrasonic humidifier, inducing the phase inversion. It is found the pore size is much more uniform across the cross-section of the membrane than that of the porous membrane prepared by conventional water bath coagulation technique. The microporous membranes were directly obtained after the washing and drying. It had about 1–5 μm of pores and presented an ionic conductivity of 2.52 × 10⁻³ S/cm at room temperature when gelled with 1 M LiPF₆/EC-DMC (1:1 vol.%) electrolyte solution. The test cells with the gel electrolytes prepared from as-prepared microporous membranes showed stable cycling capacities, indicating that the microporous membrane, which was prepared from cheap starting materials acrylonitrile and methyl methacrylate, can be used for the gel electrolyte of lithium batteries.     

Excess volumes of ternary mixtures of N,N-dimethylformamide-diethyl ketone-1-alkanols at 303.15K

Volume changes on mixing of ternary liquid mixtures of N,N-dimethylformamide and diethyl ketone with 1-alkanols have been measured as a function of composition at 303.15 K. The alkanols include 1-propanol, 1-butanol, 1-pentanol and 1-hexanol. The measured V^E values are negative in the mixtures of N,N-dimethylformamide, diethyl ketone and 1-propanol, or 1-butanol. The V^E data exhibits an inversion in sign in the mixture containing 1-pentanol and positive excess volumes are observed in the mixture containing 1-hexanol. The measured data are compared with predicted values based upon empirical relations. The excess volume for the binary mixture of N,N-dimethylformamide with diethyl ketone has been measured over the entire range of composition at 303.15 K. The V^E values are negative for the binary mixture.     

Revision of the volumetric method for measurements of liquid–liquid equilibria in binary systems

A theoretical analysis of the accuracy of the volumetric method for the determination of liquid–liquid equilibrium was carried out. The results show that, under certain conditions, this method can be used to investigate systems showing relatively small mutual solubilities. Relations were derived to estimate standard deviations of the equilibrium compositions determined by the volumetric method.

In the experimental part of the work, an apparatus for measurements of mutual solubilities of liquids was constructed. A procedure that enabled us to determine precisely volumes of liquid phases was developed. This procedure and apparatus present the advantage that relatively small amounts of samples are required (approximately 2 × 20 ml). Theoretical conclusions concerning the applicability of the volumetric method were checked by measuring mutual solubilities at 303.15 K in systems methylcyclohexane + N,N-dimethylformamide, 1-butanol + water and dimethyl phthalate + water. Further, the method was used to measure systematically the liquid–liquid equilibrium in systems ethyl acetate + ethylene glycol and phenyl acetate + ethylene glycol at temperatures from 293 to 323 K. Data for these systems were acquired by means of other methods as well and a good agreement was observed on comparison.     

Cyano-bridged bimetallic complexes of copper(II) with tetracyanonickelate(II). Crystal structure of [Cu(dpt)Ni(CN)4]

Five new complexes of composition [Cu(dpt)Ni(CN)₄] (1) (dpt=dipropylenetriamine), [Cu(dien)Ni(CN)₄]·2H₂O (2) (dien=diethylenetriamine), [Cu(N,N′-dimeen)Ni(CN)₄]·H₂O (3) (N,N′-dimeen=N,N′-dimethylethylenediamine), [Cu(N,N-dimeen)Ni(CN)₄]·H₂O (4) (N,N-dimeen=N,N-dimethylethylenediamine) and [Cu(trimeen)Ni(CN)₄] (5) (trimeen=N,N,N′-trimethylethylenediamine) have been obtained by the reactions of the mixture of Cu(ClO₄)₂·6H₂O, appropriate amine and K₂[Ni(CN)₄] in water and have been characterized by IR and UV–Vis spectroscopies and magnetic measurements. The crystal structure of [Cu(dpt)Ni(CN)₄] (1) has been determined by single-crystal X-ray analysis. The structure of 1 consists of a one-dimensional polymeric chain ---Cu(dpt)---NC---Ni(CN)₂---CN---Cu(dpt)--- in which the Cu(II) and Ni(II) atoms are linked by CN groups. The nickel atom is four coordinate with four cyanide-carbon atoms (two cyano groups are terminal and two cyano groups (in cis fashion) are bridged) in a square-planar arrangement and the copper atom is five coordinate with two cyanide-nitrogen and three dpt-nitrogen atoms, in a distorted square-pyramidal arrangement. The temperature dependence of magnetic susceptibility (2–300 K) was measured for compound 1. The magnetic investigation showed the presence of a very weak antiferromagnetic interaction (J=−0.16 cm⁻¹) between the copper atoms within each chain through the diamagnetic Ni(CN)₄ ²⁻ ions.     

Self-assembled four-membered networks of trimesic acid forming organic channel structures

By the co-crystallization of trimesic acid, TMA, with molecules such as dimethylamine, N,N,N′,N′-tetramethylethylenediamine and methanol, it has been possible to generate hydrogen-bonded four-membered networks of TMA. The three-dimensional arrangement of the four-membered networks gives rise to channels occupied by the guest molecules. It has also been possible to generate a four-membered network by co-ordination of TMA with Co(II).     

Preparation of photoinitiator-bound celluloses and their reactivity

Photoinitiator-bound celluloses (Cell-AQ and Cell-BP) were prepared by reaction of epoxy-activated cellulose with, respectively, 1-aminoanthraquinone (AQNH₂) and 4-aminobenzophenone (BPNH₂) in N,N-dimethylformamide at 70°C. About 60% of the initial epoxy groups (1·90–2·10 mmol/(g cellulose)) was found to participate in the reaction under alkaline conditions. The photoinitiator-bound celluloses exhibited an activity towards photoinduced formation of hydrogen peroxide in aqueous solutions of -glucose, and isopropyl alcohol. The amount of hydrogen peroxide formed was higher for the Cell-BP than the Cell-AQ. Moreover, the photoinitiator-bound celluloses showed an ability to initiate photografting of methyl methacrylate at 60°C in a water medium, indicating a higher percentage of grafting and a lower percentage of homopolymer compared to photoinitiator-sensitized celluloses, which were prepared by immersing a cellulose sample in acetone solutions of AQNH₂ and BPNH₂ and drying under vacuum to remove the solvent. It was found that the photoinitiator residues introduced into the cellulose substrate are capable of abstracting hydrogen atoms from the substrate.     

Estimation of type I error probability from experimental Dixon's "Q" parameter on testing for outliers within small size data sets

Common significance tests carried out using statistical software packages usually return to the user the probability p of type I error as the result. Based on p and the preset confidence level the user will decide on the acceptance or the rejection of the associated null hypothesis. Dixon's test (Q-test) is commonly used for the detection of an outlier within a set of N observations (typically: N = 3–12). Q-test can only be applied by comparing the experimental value of the statistic Q with tabulated critical Q-values corresponding to some standard values of p. Hence, for a given value of Q and a number of observations, N, the user knows only the range and not the value of the associated probability p of type I error (erroneous rejection). This is due to the lack of explicit expressions of the form p = F(Q,N). In this work, a simple stochastic (Monte Carlo) approach is presented for the estimation of p corresponding to a given experimental value of Q and size N of the data set. In addition, based on Dixon's equations, explicit expressions of p are given for N = 3 and 4.     

Excess around a central molecule with application to binary mixtures

It was shown by us (J. Phys. Chem. B, 2006, 110, 12707) that the excess (deficit) of any species i around a central molecule j in a binary mixture is not provided by c(i)G(ij) (where c(i) is the molar concentration of species i in the mixture and G(ij) are the Kirkwood-Buff integrals) as usually considered and that an additional term, involving a volume V(j) which is inaccessible to molecules of species i because of the presence of the central molecule j, must be included. In this paper, the new expression is applied to various binary mixtures and used to establish a simple criterion for preferential solvation in a binary system. First, it is applied to binary Lennard-Jones fluids. The conventional expression for the excess (deficit) in binary mixtures, c(i)G(ij), provides always deficits around any central molecule in such fluids. In contrast, the new expression provides excess for one species and deficit for the other one. In addition, two kinds of binary mixtures involving weak (argon/krypton) and strong (alcohols/water) intermolecular interactions were considered. Again, the conventional expression for the excess (deficit) in a binary mixture, c(i)G(ij), provides always deficits for any central molecule in the argon/krypton mixture, whereas the new expression provides excess for argon (a somewhat smaller molecule) and deficit for krypton. Three alcohol/water binary mixtures (1-propanol/water, tert-butanol/water and methanol/water) with strong intermolecular interactions were considered and compared with the available experimental information regarding the molecular clustering in solutions. We found (for 1-propanol/water and tert-butanol/water) a large excess of alcohols around a central alcohol molecule and a large excess of water around a central water molecule. For both mixtures the maximum of the calculated excess with respect to the concentration corresponds to the maximum in the cluster size found experimentally, and the range of alcohol concentrations in which the calculated excess becomes very small corresponds to the composition range in which no clusters could be identified experimentally.     

Critical validation of a new simpler approach to estimate aqueous pKa of drugs sparingly soluble in water

A simple linear approach to estimate the aqueous pK_a of compounds sparingly soluble in water, mainly drugs, from solely one pK_a value determined in any methanol/water mixture is evaluated. The parameters (slope and intercept) of the linear relationships are related to the solvent composition and can be easily calculated according to the acidic or basic functional group of the compound. The method has been tested using the available literature data for phenols, aliphatic carboxylic acids, benzoic acid derivatives, both ortho and non-ortho substituted, amines and imidazole derivatives. The study involves the whole range of solvent composition and about one hundred compounds which show a wide variety of aqueous pK_a, from 1.3 to 12.4. The differences between calculated and previously published aqueous pK_a values are less of 0.2 pK units. Consistent values are obtained whatever the composition of methanol/water mixture employed in the experimental measurements. The results support the usefulness of the tested method as a very simple approach to get reliable aqueous pK_a values for sparingly soluble drugs.