Effect Of Organic Cosolvents Research Articles

Organic cosolvent effects on the sorption and transport of neutral organic chemicals

Soil column miscible displacement techniques were used to investigate the effects of an organic cosolvent (methanol) on the sorption and transport of three neutral organic chemicals, naphthalene, phenanthrene, and the herbicide diuron, through a sandy surface soil. A two-domain, or bicontinuum, first-order mass transfer model described the experimental data well. For the three solutes used in this study, the equilibrium sorption coefficient (K) decreased log-linearly as the volume fraction of methanol (f c) increased. The physical properties calculator of the SPARC computer model was used for generating solute solubility profiles to estimate the slope of the Log K-f c relationship.

Effect of organic cosolvents on the stability and activity of the β-1,4-galactosyltransferase from bovine colostrum

The influence of various organic cosolvents on the stability and activity of the β-1,4-galactosyltransferase from bovine colostrum (GalT) and of its ancillary enzyme UDP-galactose-4′-epimerase has been investigated using the glucosylated alkaloid colchicoside ( 1) as a model substrate. It has been found that some cosolvents, such as Me 2SO and MeOH, can be used up to 20% v/v without any influence on the performance of these enzymes, while others, such as tetrahydrofuran, rapidly inactivated GalT at concentrations as low as 5% v/v. These results have been exploited for the galactosylation of the poorly water soluble coumarinic glucoside fraxin ( 2).

Organic Cosolvent Effects on Sorption Kinetics of Hydrophobic Organic Chemicals by Organoclays

Data obtained from batch kinetics sorption experiments for naphthalene and diuron using two organoclays [trimethylphenylammonium (TMPA)-clay and benzyldimethyltetradecylammonium (BDTDA)-clay] in aqueous and methanol−water systems were analyzed with a first-order one-site mass transfer model (OSMTM) to obtain kinetic parameters. The mass transfer coefficient (e) exponentially decreased as the sorption coefficient (Kp) increased, and a log-linear increase in e was observed with an increase in the volume fraction of cosolvent (f c) in the system. Regression equations relating e to f c, measured in mixed solvents, could be extrapolated to f c = 0 to obtain the coefficients in aqueous systems. The organic cosolvent effects on the sorption kinetics behavior of naphthalene and diuron depended on the sorbate structure, the cosolvent fraction, and the arrange ment of the exchanged quaternary alkylammonium ions in montmorillonite-clay interlayers.

The effect of organic cosolvent on the aggregation stability of an aqueous polystyrene latex dispersion

The aggregation stability of polystyrene latex as a function of 1-propanol concentration in the presence of an electrolyte and a surfactant was assessed via the zeta potential and the critical coagulation concentration of the electrolyte. The zeta potential exhibited a maximum as a function of 1-propanol concentration in all cases, regardless of whether barium perchlorate or ammonium perchlorate was the background electrolyte, or in the presence or absence of sodium dodecyl sulfate or cetyl trimethyl ammonium bromide surfactant. The critical coagulation concentration (CCC) of the background electrolyte also showed a maximum in all cases for which it was measured. Several explanations for the observed stability behavior were considered. The counterion displacement mechanism suggested by Vincent [B Vincent, Adv. Colloid Interface Sci., 42 (1992) 279–302] may be operative, although experimental evidence regarding the occurrence of specific adsorption does not always support this mechanism. Changes in the conformation of the hairy layer were not responsible for the anomalous behavior, as demonstrated by hydrodynamic size measurements. A mechanism is suggested whereby the change in the double-layer dielectric constant as a function of 1-propanol concentration is responsible for the anomalous maximum observed in the zeta potential and the CCC.

Organic Cosolvent Effects on Sorption Equilibrium of Hydrophobic Organic Chemicals by Organoclays

Isotherms were measured for sorption of naphthalene and diuron by four organoclays in equilibrium with various mixtures of methanol and water. The organoclays were prepared from Wyoming montmorillonite by replacing the natural exchangeable cations of the clay by the quaternary ammonium ions TMA (tetramethylammonium), TMPA (trimethylphenylammonium), HDTMA (hexadecyltrimethylammonium), and BDTDA (benzyldimethyltetradecylammonium). TMPA-clay showed the greatest sorptive capacity for naphthalene, while BDTDA-clay was the most effective sorbent for diuron. The sorption mechanism for each sorbate−sorbent combination was related to the arrangement of the quaternary ammonium cations in the exchanged clay and the volume fraction of methanol in solution (fc). As expected from the solvophobic theory, the linear sorption coefficients decreased log-linearly with increasing fc in the binary solvent mixture, except for TMPA-clay at fc > 0.5. In addition to solute−solvent and solvent−sorbent interactions, an additional effect involving solute-organoclay interactions influenced the sorption of naphthalene and diuron by organoclays from aqueous and mixed solvents.

Evidence for the Importance of Weakly Bound Water for Matrix Metalloproteinase Activity

The effects of organic cosolvents on the kinetic characteristics of two matrix metalloproteinases, gelatinase A and stromelysin 1, were investigated. In each case, addition of the cosolvent resulted in a decrease in the apparent kcat/Km for the catalyzed hydrolysis of fluorogenic peptide substrates. Two factors were identified as being responsible for this decrease in catalytic activity: hydrophobic partitioning of the substrate in favor of the bulk solvent and decrease in the water content of the enzyme. The former reflects the hydrophobic nature of the enzyme-substrate interaction and the effect can be corrected for by using the solvent to water partition coefficient of the substrate in the mixed solvent systems. The catalyzed hydrolysis of substrate, corrected for the effect of hydrophobic partitioning, was demonstrated to be sixth order in water for gelatinase A and third order in water for stromelysin 1. Variation in water concentration did not produce saturation even at concentrations close to 55.5 M. The results indicate that weakly bound water molecules are essential to mediate the interaction between substrate and enzyme. The sensitivity of these enzymes to water concentration could be an important mechanism for regulating catalytic activity in vivo.

Effect of Organic Cosolvents on Enantio-Enrichments via Cyclodextrin-Based Precipitations: An Examination of Production Efficiency

Crystallization or precipitation of cyclodextrins in the presence of racemates has proven to be a useful method to enrich enantiomers. The technique is commonly performed in neat aqueous solutions which limits its utility in resolving many hydrophobic compounds with poor water solubility. In this work we demonstrate that it is possible to enhance the enantiomeric enrichment of (±)-3-dimethyl-aminopropiophenone using organic cosolvents via β-cyclodextrin precipitation. In addition, an equation that allows the calculation of the production efficiency of an enantiomeric enrichment is proposed and utilized. Water plus various organic solvents, including methanol, ethanol, isopropanol, 1-propanol, tert-butanol, and acetonitrile, are studied as cosolvents. Several factors are investigated in terms of their effect on the enantiomeric enrichment including a) molar ratio of β-cyclodextrin to analyte, b) solubility of the analyte, c) solubility of β-cyclodextrin, d) solution pH, and e) amount of analyte co...

Enzymatic resolution of racemic ibuprofen esters: Effects of organic cosolvents and temperature

The effects of organic additives on enzymatic hydrolysis of racemic ibuprofen methyl ester were investigated using Candida cylindracea lipase. Several polar solvents such as N,N-dimethylformamide, formaldehyde, and formamide were found to enhance the enantioselectivity of the enzyme. The effects of temperature on enzyme selectivity were also examined.

Effect of organic cosolvents on adsorption of organophosphorus pesticides by soils

A study was conducted to describe the adsorption and mobility of diazinon and acephate in soils from aqueous medium and mixtures of methanol-water and hexane-water. Pesticide adsorption from aqueous system was related to organic matter content ( viz. diazinon), and to content and composition of clay mineral fraction ( viz. acephate). In the methanol-water systems, the adsorption of diazinon and acephate by soils decreases. In the hexane-water mixtures the adsorption of diazinon decreases, whereas the adsorption of acephate increases.

The effect of organic cosolvents on the oxygen affinity of fetal hemoglobin

We have studied the effects of organic cosolvents (monohydric alcohols and formamide) on the oxygen affinity of human fetal hemoglobin stripped of phosphates and have compared them with the effects of the same cosolvents on the oxygen affinity of human adult hemoglobin under the same experimental conditions. Our results confirm that, in fetal hemoglobin, the T in equilibrium R conformational equilibrium is more displaced toward the T conformation than in the adult form and indicate that increased electrostatic and hydrophobic protein-solvent interactions contribute to this effect. The data reported are discussed in terms of the known amino acid substitutions between the beta- and gamma-chains and an attempt is made to rationalize the results with a molecular mechanism based on the crystallographic structure of fetal deoxyhemoglobin.

Medium effect in the base hydrolysis of pentaamminebromocobalt(III) ion

The effect of organic cosolvent on the rate constant of the base hydrolysis of pentaamminebromocobalt(III) ion was investigated in mixtures of H2O with MeOH, EtOH,i-PrOH,t-BuOH, and dioxane. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures, were evaluated from kinetic measurements and from solubilities of the complex salt. The experimental results are in good agreement with a dissociative mechanismvia the conjugate base.

Effect of organic cosolvent on adsorption and desorption of linuron and simazine in soil

The adsorption and desorption of two herbicides, Linuron and Simazine, on a clay soil have been studied in mixtures of methanol and water. Adsorption of the herbicides decreased with increasing methanol content of the solution. An inverse log-linear relationship between the Freundlich adsorption coefficients for the two herbicides and the concentration of methanol was found. Adsorption of the herbicides in the presence of methanol followed the solvophobic theory, which describes the adsorption of hydrophobic organic compounds in soils. Values of the Freundlich adsorption coefficient for aqueous solutions, of the two herbicides extrapolated from adsorption data for the methanol/water mixtures, showed close agreement with those obtained experimentally. Hence, adsorption in aqueous solutions for pesticides of low aqueous solubility can readily be predicted on this basis. Hysteresis, observed after desorption in CaCl2 solution, decreased with increasing methanol contents for both herbicides. The decrease in hysteresis was ascribed to the swelling of the organic matter and the accompanying increased accessibility to solutes. The study showed that the presence of an organic solvent significantly affected not only the adsorption but also the desorption of herbicides in soils.

Kinetics of oxidation ofcis-, andtrans-chlorobis(ethylenediamine)isothiocyanatocobalt(III)ion with peroxodisulphate in aqueous alcoholic mixtures

The effect of organic cosolvent on the rate constants and activation parameters of oxidation of coordinativelybound thiocyanate with peroxodisulphate was investigated in mixtures of water with methanol,i-propanol andt-butanol. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from the solubilities of corresponding salts. The experimental results are interpreted in terms of the solvation of both the initial state and the activated complex.

Effect of organic co-solvents on the dimer/tetramer equilibrium of human haemoglobin

We have studied the effect of organic co-solvents (monohydric alcohols and formamide) on the dimer-tetramer equilibrium of human haemoglobin by measuring the dependence of oxygen affinity upon haemoglobin concentration over a 100-fold concentration range and analysing the data with a modified Monod-Wyman-Changeux model in which the equilibrium (tetramer) ⇋ (dimer) + (dimer) was taken into account. This procedure enabled us to obtain the dimer-tetramer equilibrium constant and to find its dependence upon co-solvent concentration. Then by following the procedure already reported for the tense → relaxed state transition of haemoglobin, we separated the co-solvent effects into bulk electrostatic and non-bulk electrostatic (hydrophobic) contributions. We believe that our results demonstrate that during haemoglobin dissociation, just as we have already shown for the tense to relaxed state transition, both charged groups and hydrophobic surfaces become exposed to the solvent.

Effects of organic co-solvents on the oxygen equilibrium of N-ethylmaleimide-treated human haemoglobin

We have studied the effects of monohydric alcohols and formamide on the oxygen equilibrium of native and N-ethylmaleimide-treated human haemoglobin. Comparison of the results obtained for the two haemoglobins gives further and compelling evidence in favour of the model, proposed recently by our group, on the role played by the solvent in the conformational equilibria of haemoglobin; moreover the results provide direct functional evidence of the relevance of the electrostatic free energy of salt bridges to the T ⇋ R equilibrium of haemoglobin.

KINETICS OF SUBSTITUTION OF NICOTINAMIDE AT PENTACYANO(NICOTINAMIDE)IRON(II) BY DIMETHYL SULFOXIDE IN AQUEOUS AND NON-AQUEOUS SOLVENTS

Abstract The effect of organic cosolvent on the rate constant and activation parameters δH‡, δS‡ of substitution of nicotinamide at pentacyano(nicotinamide)iron(II) by dimethyl sulfoxide was investigated in mixtures containing up to 50% methanol, t-butanol, acetone, acetonitrile, glycerine and glycol. From correlations between the logarithm of the rate constant and Grunwald-Winstein Y values, and between δ m δG‡ and excess Gibbs free energy of mixing GE, the effect of the change in the solvation on the reaction rate was elucidated. The effects of pH on the reaction rate and activation parameters, and the effect of organic cosolvent on the shift of the charge-transfer band of the complex mentioned above are also reported.

Influence of organic cosolvents on sorption of hydrophobic organic chemicals by soils

Sorption of anthracene and two herbicides (diuron and atrazine) by soils from aqueous solutions and binary solvent mixtures consisting of methanol-water and acetone-water was measured. These data were used to evaluate recently proposed solvophobic theory for describing sorption of hydrophobic molecules from mixed solvents. As predicted by the theory, the sorption coefficient (K/sup m/) decreased exponentially with increasing fraction of the organic cosolvent (f/sup c/) in the binary solvent mixtures. The slope of the ln K/sup m/ vs. f/sup c/ plot, designated as sigma/sup c/, was unique to each sorbate-solvent combination and was independent of the soil (sorbent). Thus, the organic cosolvent effects on sorption could be specified by a single parameter that combines the coefficients characterizing solvent and sorbate properties. The sigma/sup c/ value was shown to be directly proportional to the solvent-sorbate interfacial free energy( ..delta gamma../sup c/) and the hydrocarbonaceous molecular surface area (HSA) of the sorbate.

Oxygen affinity of bovine haemoglobin: Relevance of electrostatic and hydrophobic interactions

We have studied the effects of organic cosolvents (monohydric alcohols and formamide) on the oxygen equilibrium of bovine haemoglobin and have compared them with the effects of the same cosolvents on the oxygen equilibrium of human haemoglobin. Our results indicate: (1) that in agreement with previous suggestions, the lower affinity of bovine haemoglobin for oxygen is not due to an increased number of salt bridges stabilizing the T structure; (2) that, following T → R transition, more hydrophobic surface is exposed to the solvent by bovine than by human haemoglobin. We suggest, therefore, that a relevant role in keeping the oxygen affinity of bovine haemoglobin lower than that of human haemoglobin is played by the higher free energy needed to expose this more hydrophobic surface to the solvent. We stress, however, that our analysis does not enable us to say which particular amino acid residues are concerned in these effects.

Enantioselective catalysis of deacylation of p-nitrophenyl N-acylphenyl-alanates by mixed micelles composed of Nα-hexadecanoyl-L-histidine and a cationic surfactant

The deacylation of p-nitrophenyl N-acyl-L- and -D-phenylalanates (acyl = acetyl, decanoyl, and hexadecanoyl) with the co-micellar system composed of Nα-hexadecanoyl-L-histidine and octadecyltrimethylammonium chloride was investigated for the 20–35 °C range in CH3CN–H2O (3 : 97 v/v). The enantioselective properties of the co-micellar system effective for the deacylation of such substrates were investigated in the light of substrate-binding properties, activation parameters, and kinetic salt and organic co-solvent effects. Kinetic enantioselectivity is exclusively favoured for the L-substrates, even though the binding constants for the D-isomers are greater than those for the corresponding L-isomers in most cases. The highest enantioselectivity in terms of the apparent second-orde rate ratio (ka, obsL/ka, obsD) is 4.7 as observed for the deacylation of p-nitrophenyl N-decanoyl-L- and -D-phenylalanate at 20 °C and pH 7.6.

Function of biomolecules as a probe for studying the effects of organic co-solvents on their conformations

Conformation changes associated with the function of biomolecules can bring out variations of the extent and specific structure of their hydrophobic areas exposed to solvent, with consequent local rearrangements of the solvent. This is one of the channels through which the solvent exerts its role in the functional equilibria of biomolecules. The function of biological macromolecules in perturbed aqueous solvent can therefore be a suitable probe for studying the response of macromolecule-solvent systems to perturbations caused by organic co-solvents. We shall discussed the effects that the presence of some monohydric alcohols and some amides in the aqueous medium have on some thermodynamic parameters related to the reaction of hemoglobin with oxygen. A comparison with other data concerning functional equilibria of bovine liver β-galactosidase and conformational equilibria of ribonuclease and DNA will follow.