Aqueous-organic Systems Research Articles

Enzyme-catalyzed peptide synthesis in biphasic aqueous-organic systems

A preparative protease-catalyzed peptide synthesis in biphasic aqueous-organic systems is described. This approach using both free as well as immobilized proteases as catalysts provides high yields and includes the possibility to re-utilize the enzymes.

Surface-active materials from Athabasca oil sands

Surface-active derivatives can be separated, or chemically-derived, from Athabasca bitumen. These materials have the ability to lower the surface tensions of aqueous solutions as well as substantially reduce the interfacial tensions of aqueous-organic systems. As such, they do appear to have a beneficial effect on bitumen recovery processes.

Retention behaviour of benzene derivatives on bonded reversed-phase columns

The retention behaviour of fourteen benzene derivatives has been studied in reversed-phase chromatography, eluting them with various aqueous organic solvent systems from the hydrocarbon chemically bonded reversed phase using a micro-chromatograph. The effects of eluent composition and of packings are discussed using the capacity factor, k. A linear relationship ws observed between log k and the logarithm of the molarity of the organic moiety, log [C], in the mobile phase. A p value for each solute was obtained from the slope of the linear relationship of log k vs. log [C]. This value was recognized as the number of the released solvent molecules after the formation of the bristle—solvent—solute complex when the solvated solute molecules were adsorbed on the solvated bristles of the bonded materials. Consideration of p offered a key to the explanation of the role of the eluent on chemically bonded reversed-phase chromatography.

Solvent extraction behaviour of iodine and bromine in aqueous-organic systems, analogy with radioactive decay

The extraction of iodine and bromine under various conditions from their saturated aqueous solutions by CCl4, C6H6 and o-xylene has been studied. The data obtained from the experiments carried out at various temperatures, for H2O(I2)−CCl4 and H2O(I2)−C6H6 systems, exhibit an Arrhenius behaviour. The overall activation energy calculated for the extraction in the H2O(I2)−CCl4 system, 650±50 cal·mol−1 is lower than that of H2O(I2)−C6H6, 3600±300 cal·mol−1. The use of the solubility parameter for the interpretation of the data in the extraction of iodine is investigated. The data obtained in multiple extractions are treated by using the analogy between extraction and radioactive decay. The half number of extraction for each system is determined. The complex curves obtained in the H2O(I2)−CCl4 and H2O(I2) −Br2)−CCl4 systems are resolved into two components.

Lipophilic [2.2.2] cryptands as phase-transfer catalysts. Activation and nucleophilicity of anions in aqueous-organic two-phase systems and in organic solvents of low polarity

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLipophilic [2.2.2] cryptands as phase-transfer catalysts. Activation and nucleophilicity of anions in aqueous-organic two-phase systems and in organic solvents of low polarityDario Landini, Angelamaria Maia, Fernando Montanari, and Pietro TundoCite this: J. Am. Chem. Soc. 1979, 101, 10, 2526–2530Publication Date (Print):May 1, 1979Publication History Published online1 May 2002Published inissue 1 May 1979https://doi.org/10.1021/ja00504a004RIGHTS & PERMISSIONSArticle Views582Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (637 KB) Get e-Alerts Get e-Alerts

The effect of specific solvation on the absorption of millimeter-range radiation in aqueous organic systems

1. Measurement has been made of the absorption of electromagnetic radiation of wavelengths in the 0.8–2 mm range, working with aqueous solutions of DMSO, DMPhA, acetonitrile, dioxane, and acetone, and covering the entire range of relative concentrations. 2. Departures from absorption additivity increase in the order: dioxane, acetonitrile, acetone, DMSO, DMPhA. 3. Hydration numbers have been calculated for the various solvents

Heat capacity evidence for pseudophase transitions in aqueous organic binary systems

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHeat capacity evidence for pseudophase transitions in aqueous organic binary systemsGenevieve Roux, Gerald Perron, and Jacques E. DesnoyersCite this: J. Phys. Chem. 1978, 82, 8, 966Publication Date (Print):April 1, 1978Publication History Published online1 May 2002Published inissue 1 April 1978https://doi.org/10.1021/j100497a024RIGHTS & PERMISSIONSArticle Views69Altmetric-Citations37LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (154 KB) Get e-Alerts

A new approach to preparative enzymatic synthesis.

AbstractA new approach to preparative organic synthesis in aqueous–organic systems is suggested. It is based on the idea that the enzymatic process is carried out in a biphasic system “water–water‐immiscible organic solvent.” Thereby the enzyme is localized in the aqueous phase—this eliminates the traditional problem of stabilizing the enzyme against inactivation by a nonaqueous solvent. Hence, in contrast to the commonly used combinations “water–water‐miscible organic solvent,” in the suggested system the content of water may be infinitely low. This allows one to dramatically shift the equilibrium of the reactions forming water as a reaction product (synthesis of esters and amides, polymerization of amino acids, sugars and nucleotides, dehydration reactions, etc.) toward the products. The fact that the system consists of two phases provides another very important source for an equilibrium shift, i.e., free energies of the transfer of a reagent from one phase to the other. Equations are derived describing the dependence of the equilibrium constant in a biphasic system on the ratio of the volumes of the aqueous and nonaqueous phases and the partition coefficients of the reagents between the phases. The approach has been experimentally verified with the synthesis of N‐acetyl‐L‐tryptophan ethyl ester from the respective alcohol and acid. Porous glass was impregnated with aqueous buffer solution of chymotrypsin and suspended in chloroform containing N‐acetyl‐L‐tryptophan and ethanol. In water (no organic phase) the yield of the ester is about 0.01%, whereas in this biphasic system it is practically 100%. The idea is applicable to a great number of preparative enzymatic reactions.

Enthalpies of solution of tetramethyl-ammonium chloride in aqueous-organic binary solvent systems

Enthalpies of solution of tetramethylammonium chloride in H2O+acetone, H2O+DMSO, and H2O+2,2,2-trifluoroethanol (TFE) are reported. The enthalpies of solution for the frist two solvent systems are positive for all compositions investigated, whereas for the H2O+TFE systemsΔHs becomes large and negative as the mole fraction of TFE is increased past 0.2. The enthalpy-of-solution data are rationalized on the basis of solvent structural effects and solvation.

EFFECT OF WAVELENGTH, CARBONYL GROUP AND SOLVENT ON PHOTO-INDUCED GRAFT POLYMERIZATION ONTO DIALDEHYDE CELLULOSE

Graft polymerization of various vinyl monomers onto dialdehyde cellulose (H-sample) by a photo-induced method was carried out in aqueous systems using qualz and pyrex tube, and the results were compared with those for the photo-induced graft polymerization onto purified cotton linter (C-sample).The degree of grafting of methyl methacrylate (MMA) onto H-sample contained a small amounts of carbonyl group is greater than that onto C-sample. H-sample was easily grafted by the light with the wavelength above 300nm. The chain scission in H-sample occurred with the light of 253nm wavelength. From these results, it is indicated that the graft polymerization proceeds mainly via the photolysis of carbonyl groups in cellulose, and the difference in the wavelength of absorbed light has an effect on the grafting site.In the graft polymerization of various vinyl monomers onto H-sample, the total conversion and the degree of grafting increased with increasing carbonyl group content in cellulose. The grafting activity decreased in the order of MMA, acrylamide, vinyl acetate, acrylonitrile and styrene.In the graft polymerization of MMA in aqueous organic solvent systems, the degree of grafting decreased with increase of the organic solvent concentration, but the grafting efficiency yield 85-95%. The chain transfer constants of CCl4, i-BuOH, (Me)2CO and dimethylformamide were 10.3, 3.8, 1.3 and 0.7×10-5, respectively.

Cryoenzymology: The use of sub-zero temperatures and fluid solutions in the study of enzyme mechanisms

Theoretical and experimental support for the use of sub-zero temperatures and fluid aqueous organic solvent systems in the study of enzyme mechanisms is presented. If the reaction between enzyme and substrate is initiated by mixing them at a suitably low temperature non-steady state, non-turnover conditions will result. Under such circumstances, the overall catalytic reaction will potentially appear as a series of reactions as the temperature is raised, each one corresponding to the transformation of one intermediate into a subsequent one. The technique is especially suited for the accumulation of high concentrations of intermediates which makes physical and chemical studies on their structure quite feasible. Recent investigations have shown that enzyme-substrate intermediates can be trapped in the crystalline state and that X-ray crystallographic studies can be carried out on them at sub-zero temperatures. Rate reductions of the order of 10 10 are possible using the combined effects of pH and temperature. Kinetic and thermodynamic information concerning intermediate transformations may also be obtained. Kinetic expressions for such systems are derived in the Appendix. The advantages and limitations of the method, including possible problems relating to the effects of solvent and temperature on the enzyme structure, experimental procedures, and interpretation of results are considered.

Synthesis of N‐protected peptides by the o‐nitrophenylsulfenyl group using o‐nitrophenylsulfenyl N‐carboxy α‐amino acid anhydrides

AbstractN‐protected peptides, which are important intermediates as a carboxyl component in the fragment condensation method, have been prepared in high yields by the reaction of o‐nitrophenylsulfenyl (Nps) N‐carboxy α‐amino acid anhydrides with unprotected peptides and amino acids in aqueous organic systems. An Nps hexapeptide ester was prepared by the fragment condensation of an Nps tripeptide with a tripeptide ester. It was demonstrated that the synthesis of unprotected peptides by the NCA method, followed by N‐protection by the Nps‐NCA, is a rapid and very useful method for preparing Nps peptides.

PIGMENTATION IN THE ORANGE TUNICATE, ECTEINASCIDIA TURBINATA.

Some chemical properties of the orange pigment from eggs and embryos and the mantle tissue of adult Ecteinascidia turbinata, as well as ultrastructural characteristics of pigment masses in the mantle, have been examined. The diffuse egg and embryo pigment has solubility and absorbence characteristics of carotenoids, which are solubilized within yolk platelets. The granular mantle pigment, however, is not carotenoid. It is soluble only in organic-aqueous systems, stable to boiling and gross changes in pH, and absorbs strongly in the UV region with a single major peak at 360 nm. Mantle pigment is found in pigment bodies which ultrastructurally are composed of apparently straight and continuous tubular subunits, approximately 500 to 600 Å in diameter, and oriented parallel to the long axis of the body. The pigment bodies are not localized in obvious cells but found within large areas of fibrillar material that are bound by cytoplasmic membranes and occasionally contain an apparently degenerate nucleus. It may be that mantle pigment is derived from pigment cells of the blood which lose their typical cellular appearance as they become permanent features of the mantle tissue.

An electrocapillary study to test the applicability of the Flory-Huggins isotherm

The Flory-Huggins isotherm with interaction parameter has been tested using accurate electrocapillary data for four aliphatic compounds at the mercury-electrolytic solution interface. When surface coverages derived by differentiation of surface pressure-activity data were tested in the Flory-Huggins isotherm and when all parameters were freely optimized, the equation fit the data very well in all cases, but the size ratio parameter thus obtained was about 0.5. When parameters of the Flory-Huggins isotherm were fixed by limiting properties of surface pressure-activity data directly (with no differentiations performed), the size parameter was about 1.0. The size parameter expected physically is about 3.0. The Flory-Huggins isotherm with realistic size parameters did not fit the data as well as the simpler Frumkin equation in any of the cases considered. The physical basis underlying both models is weak for interaction parameters as large as encountered in aqueous-organic solute systems.

Liquid-vapor critical temperatures of several aqueous-organic and organic-organic solution systems

Liquid-vapor critical temperature curves have been determined for the two-component systems, methanol-water, ethanol-water, acetone-water, tetrahydrofuran-water, dioxane-water, benzene-toluene and acetone-ethanol. Variations in the critical temperatures ( t c) are described by plots of t c against both composition (mole fraction) and concentration (molarity). Some interpretations of differences in behavior for several of the systems are proposed but they depend upon whether composition or concentration is used as the variable. For example, values of t c for the several systems formed separate curves when plotted against mole fraction. However, when the molarity of water was used, some values of t c, notably for the alcohol-water and acetone-water systems, fell predominantly on the same curve. This latter behavior suggested that concentration might be more appropriate to use than composition in attempts to understand multicomponent critical temperature behavior.

Gas hydrates in aqueous-organic systems: IV. Formation and detection of ethylene oxide hydrate in tissue

Formation of gas hydrate (aqueous clathrate or clathrate hydrate) crystals in intact tissue was studied using water-soluble ethylene oxide as a hydrate former. The presence of internal hydrate crystals was assessed by the characteristics of time-temperature plots obtained during warming of treated samples, by microscopic examination of treated samples, and by visual observation of hydrate formation in a device containing treated tissue embedded in three layers of polyacrylamide gel. On the basis of these tests, it was concluded that ethylene oxide hydrate can be formed in either plant or animal tissue if a sufficient quantity of ethylene oxide is allowed to diffuse into the tissue prior to initiation of crystallization.

Gas hydrates in aqueous-organic systems: V. Effects of ethylene oxide and ethylene oxide hydrate in animal tissue

Ethylene oxide (EO) and EO hydrate were studied to determine their effects in beef muscle and rat liver tissue. It was found that: 1) EO (no detectable hydrate crystals) causes muscle and liver cells to shrink and separate, 2) slowly crystallized EO hydrate appears to form only in extracellular areas and its presence results in shrinkage of tissue cells that is much more pronounced than that caused by EO alone (no hydrate), and 3) cell shrinkage tends to increase with increasing time (1 to 72 hrs) and temperature (0 to 5 °C) of EO hydrate formation. The behavior in 2) and 3) is similar to that observed during conventional slow freezing of animal tissue.

Gas hydrates in aqueous-organic systems: VII. Linear crystallization velocities of the hydrates of ethylene oxide and tetrahydrofuran

Linear crystallization velocities of hydrates (aqueous clathrates) of type I ethylene oxide and type II tetrahydrofuran were determined in simple solutions and polyacrylamide gels supercooled from 3.1 to 24 °C. At any given degree of supercooling, all hydrate-forming solutions crystallized much more slowly than pure water, and the hydrate of tetrahydrofuran crystallized more slowly than the hydrate of ethylene oxide. Ethylene oxide hydrate formed at a velocity greater than tetrahydrofuran hydrate even when the solutions were designed to bind approximately equal numbers of water molecules during hydrate formation. In all instances, the presence of polyacrylamide gel decreased the velocity of hydrate formation.

Gas hydrates in aqueous-organic systems: VI. Effects of hydrate formers and hydrate crystals in carrot tissue

Carrot samples containing ethylene oxide (EO), tetrahydrofuran (THF), and their hydrates were studied. It was found that: (1) the microscopic appearance of carrot tissue was not altered appreciably by EO or THF (no detectable hydrate crystals), (2) slow formation of EO hydrate (Type I) and THF hydrate (Type II) resulted in extracellular crystalline areas which were large and few in number, and their presence was associated with severe shrinkage and distortion of adjacent tissue (this behavior is similar to that observed during conventional slow freezing of carrot tissue), and (3) crystalline masses of EO hydrate in carrot tissue tended to increase in size and become less numerous as the rate of formation was decreased and the growth period was increased. These results differed from those obtained previously with animal tissue. EO (no detectable hydrate crystals) was much less detrimental to the microscopic appearance of carrot tissue than it was to the microscopic appearance of beef muscle (BM) or rat liver (RL). Furthermore, slow formation of EO hydrate resulted in extracellular crystalline areas which were larger and less numerous in carrot tissue than in BM, or RL, and this in turn resulted in cell shrinkage which was less uniform and more severe (adjacent to crystalline areas) in carrot tissue than in BM or RL.

Solvent effects on solubilities and partition coefficients of some copper(II)-beta-diketone complexes

The solubilities of three members of a homologous series of copper(II)-beta-diketone complexes have been measured in a number of common organic solvents at 25 ± 0·02 deg centigrade. Using these data and respective molar volumes of the solid chelates, solubility parameter values (δ) were calculated. The constancy of the calculated values was taken as evidence of the adequacy of the regular solution concept for explaining the observed solubility trends in the solvents studied. Distribution coefficients for the first member of the series were measured in a number of aqueous-organic solvent systems. The extraction data were examined by the regular solution treatment and good agreement of solubility parameter values (δ) calculated from solubility and distribution data was obtained. A comparison of results obtained by the various proposed methods is given. A verification of the validity of estimating δ values for chelate compounds from structural information was attempted.