High Solvent Concentrations Research Articles

Effects of organic cosolvents on enzyme stereospecificity. The enantiomeric specificity of α-chymotrypsin is reduced by high organic solvent concentrations

The influence of a range of protic and aprotic solvents of varying polarities on the enantiomeric specificity of α-chymotrypsin has been examined using methyl (2S)- and (2R)-2-acetamido-2-phenylacetate (1) as representative L- and D-substrates. The rates of hydrolysis were determined in solutions containing up to 30% organic solvent. The addition of organic solvent reduced the overall rates of hydrolysis of (2S)- and (2R)-1 in each case, with those of the L-enantiomer (2S)-1 being affected more than those of the D-stereoisomer (2R)-1. However, the enzyme overwhelmingly retains its normal L-enantiomeric preference under all conditions surveyed. It is concluded that α-chymotrypsin, and possibly other strongly stereospecific enzymes, can be used with confidence for asymmetric synthesis or resolution purposes in aqueous solutions to which moderate (up to 40%) proportions of organic cosolvents have been added to increase solubility of hydrophobic organic substrates.

Function of peripheral nerves and signs of polyneuropathy in solvent-exposed workers at a Swedish steelworks.

A field study was performed at a Swedish steelworks concerning symptoms and signs of polyneuropathy in 42 workers exposed to organic solvents at the plastic coating line of the plant. Examination was done clinically and by simple electrophysiological methods. The workers were exposed to a mixture of solvents, including methyl ethyl ketone (MEK) and trichloroethyelen. Nosed to a mixture of solvents, including methyl ethyl ketone (MEK) and trichloroethylene. None of the solvents used are known to cause peripheral neuropathy. At times very high vapour concentrations of solvents in the air were attained. The exposed workers were compared with at group of reference subjects sampled from other sections of the steelworks, matched for sex, age and duration of employment. Among the exposed workers one plausible and two suspected cases of polyneuropathy were found. None of the reference subjects showed signs of polyneuropathy. Statistical assessment provided some evidence, though weak, of a connection between the exposure to organic solvents and the observed abnormalities. A brief review is made of the present state of knowledge about hazards to the peripheral nervous system from the solvents in question.

Novel solvent effects in the photopolymerization of methyl methacrylate by use of quinoline–bromine charge‐transfer complex as photoinitiator

AbstractPhotopolymerization of MMA was carried out at 40°C in diluted systems by use of quinolinebromine (Q–Br2) charge‐transfer complex as the initiator and chloroform, carbon tetrachloride, chlorobenzene, dioxane, THF, acetone, benzene, toluene, quinoline, and pyridine as solvents. The results showed variable monomer exponents ranging from 1 to 3. For chloroform, carbon tetrachloride, and chlorobenzene, the monomer exponent observed was unity; for other solvents used, the value of the same exponent was much higher (between 2 and 3). Initiation of polymerization is considered to take place through radicals generated in the polymerization systems by the photodecomposition of (Q–Br2)–monomer complex (C) formed instantaneously in situ on addition of the Q–Br2 complex in monomer. The kinetic feature of high monomer exponent is considered to be due to higher order of stabilization of the initiating complex (C) in presence of the respective solvents. In the presence of the retarding solvents, very low or zero initiator exponents were also observed, depending on the nature and concentration of the solvents used. The deviation from the square‐root dependence of rate on initiator concentration becomes higher at high solvent and initiator concentrations in general. This novel deviation is explained on the basis of initiator termination, probably via degradative chain transfer involving the solvent‐modified initiating complexes and the propagating radicals.

Photopolymerization of methyl methacrylate with the use of tetrahydrofuran–bromine charge‐transfer complex as the photoinitiator

AbstractThe polymerization of MMA was kinetically studied in the presence of visible light (using a 125‐W high‐pressure mercury vapor lamp with fluorescent coating, without a filter), a THF—bromine charge‐transfer complex being used as the photoinitiator. The initiator exponent was 0.5 in bulk polymerization. The monomer exponent varied from about 1.2 to about 2.5, depending on the nature of the solvent used; the initiator exponent also varied in diluted systems, depending on the nature and proportion of the solvent, the variation being from a value of 0.5 in bulk system to zero or almost zero at about 25% (v/v) solvent concentration. Other kinetic parameters, viz., kp2/kt and the activation energy for polymerization, were determined and are reported. Kinetic and other evidence indicates that the photopolymerization takes place by a radical mechanism and termination is bimolecular in nature in bulk systems; in dilute systems, termination by initiator complex assumes predominance, particularly at high solvent concentrations (≥25% v/v).

Random peptide synthesis using immobilized enzymes in high concentrations of organic solvents

Trypsin, leucine aminopeptidase, and carboxypeptidase B were separately immobilized on controlled pore glass and reacted with a dipeptide substrate in high concentrations of either acetone or 1-propanol. Hydrolytic activity was demonstrated and evidence for the possible synthesis of peptide polymer is presented. Directed synthesis using amino acids and blocked amino acids as substrates was not successful.

Three Component raoultian behavior in relation to metal refining by crystallization and reflux

A form of ternary solution behavior is derived, and used to predict the movement of elements between solid and liquid phases during metal refining by crystallization and reflux. This behavior is termed “Raoultian ternary behavior” because it refers to composition regions in which the solvent metal predominates,i.e. the impurities are present at dilute concentrations. Raoultian ternary solution behavior is limited to the solvent side of eutectic systems, for sufficiently high solvent concentrations; it is independent of the behavior of the system in the hypereutectic regions. It is shown, firstly, that the extent of solid solubility of an impurity in a dilute binary system may be predicted from latent heat of fusion and melting point data and the location of the liquidus line and, secondly, that by combining such data for two impurity-solvent binary systems it is possible to calculate the behavior of the corresponding dilute ternary system. It is also shown that Raoultian ternary behavior requires that the solidus and liquidus curves, on an isothermal composition diagram, be straight lines. The application of Raoultian solution behavior is discussed in relation to the prediction of the number of theoretical steps obtained during the operation of a crystallization and reflux column, and the practical results obtained.

Studies on immobilized trypsin in high concentrations of organic solvents.

Trypsin was covalently immobilized on porous glass in the presence and absence of a specific substrate and reacted in various organic solvents of different dielectric constants. Optimum solvent concentration, pH profile, Km(app), Vmax(app), productivity versus temperature, activity, and reaction rates were determined. Reaction rates of six lysyl dipeptides were compared. Crystalline trypsin was dansylated for studies by nanosecond fluorescence techniques to determine the effects of introducing high concentrations of organic solvents on the molecule. The results indicated that greater reaction rates were observed with dipeptides having more acidic carboxyl terminal groups. The data also indicated that greater reaction rates were observed in higher concentrations of solvents of lower dielectric constants. Nanosecond fluorescence spectroscopy of trypsin in high concentrations of a low dielectric constant solvent indicated major dehydration even though maximal enzyme activity was achieved under these conditions.

Behavior of soluble and immobilized acid phosphatase in hydro-organic media

The hydrolysis of p-nitrophenyl phosphate by wheat germ acid phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2) has been investigated in mixtures of aqueous buffers with acetone, dioxane and acetonitrile. The enzyme was either in free solution or immobilized on a pellicular support which consisted of a porous carbonaceous layer on solid glass beads. The highest enzyme activity was obtained in acetone and acetonitrile mixed with citrate buffer over a wide range of organic solvent concentration. In 50% (v/v) aceton both V and K m of the immobilized enzyme were about half of the values in the neat aqueous buffer, but the K i for inorganic phosphate was unchanged. In 50% (v/v) mixtures of various solvents and citrate buffers of different pH, the enzymic activity was found to depend on the pH of the aqueous buffer component rather than the pH of the hydro-organic mixture as measured with the glass-calomel electrode. The relatively high rates of p-nitrophenol liberation in the presence of glucose even at high organic solvent concentrations suggest that transphosphorylation is facilitated at low water activity.

Halogenated substituted benzenes as photosensitizers for vinyl polymerization—I: Polymerization of methyl methacrylate, styrene, vinyl chloride and vinyl acetate, initiated by bromobenzene

Bromobenzene has been shown to be a photosensitizer for the polymerizations of methyl methacrylate, styrene, vinyl acetate, and vinyl chloride. Light of wavelength 365 nm has been used to initiate the polymerizations. The reactions proceed by a free radical mechanism, termination occurring by the mutual interaction of growing polymer radicals. For the polymerization of methyl methacrylate, bromobenzene shows the usual solvent effect giving rise to an increased fractional rate at high solvent concentrations. For vinyl acetate, however, it acts as a degradative chain transfer agent in common with other aromatic compounds. Preliminary results with disubstituted bromo and chloro benzenes show that these are also photosensitizers for vinyl polymerization.

Ion-exchange resins in non-aqueous solvents—II: Sorption of P-nitroaniline and other weak bases in water-organic solvent mixtures

Sorption of p-nitroaniline and several weak organic bases on macro- and microreticular hydrogen-form resins is reported. The solvents used in the study are mixtures of water and fourteen watermiscible organic solvents. The distribution coefficients change from a large value at pure organic solvent to a minimum value at 80% organic solvent-20% water, then increase again except for the basic solvents where no sorption takes place at high organic solvent concentration. It is suggested that in the vicinity of the minimum D a transition in sorption mechanism takes place. A similar behaviour is observed for several other weak organic bases. The sorption of p-nitroaniline in 80% organic solvent-20% water as a function of time is reported. Mesh size and percentage cross-linking are other variables considered.

Activity of Bovine Pancreatic Ribonuclease A in Mixed Solvent Systems

IT has been shown that bovine pancreatic ribonuclease may be dissolved in organic solvents with full recovery of the activity after removal of the solvent1. We have found that ribonuclease A retains its activity in the presence of high concentrations of many organic solvents and have utilized this property for investigating its mode of action. If the solvent used is methanol then the products of the action of ribonuclease on cytidine-2′,3′-phosphate are cytidine-3′-phosphate and cytidine-3′-phosphate methyl ester as previously observed by Heppel and Whitfeld2. As the mole fraction of methanol is raised, methanolysis increases and hydrolysis decreases as shown in Fig. 1. This behaviour is consistent with competition between methanol and water for a site on the enzyme.

Vapor pressure of hexane‐soybean oil solutions at high solvent concentrations

Journal of the American Oil Chemists' SocietyVolume 28, Issue 8 p. 360-361 Article Vapor pressure of hexane-soybean oil solutions at high solvent concentrations Allen S. Smith, Allen S. Smith University of Notre Dame, Notre Dame, IndianaSearch for more papers by this authorBernard Florence, Bernard Florence University of Notre Dame, Notre Dame, Indiana Standard Oil Company of Indiana, Whiting, Ind.Search for more papers by this author Allen S. Smith, Allen S. Smith University of Notre Dame, Notre Dame, IndianaSearch for more papers by this authorBernard Florence, Bernard Florence University of Notre Dame, Notre Dame, Indiana Standard Oil Company of Indiana, Whiting, Ind.Search for more papers by this author First published: 01 August 1951 https://doi.org/10.1007/BF02589715Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume28, Issue8August 1951Pages 360-361 RelatedInformation

Acute Response of Guinea Pigs to the Inhalation of Ketone Vapors

This small publication is one of a long series that has continued over several years concerned with the dangers of industrially used volatile solvents. This particular study is concerned with eleven ketones, of which acetone (dimethyl ketone) is the best known representative. To the vapors of these several substances, in varying concentrations, guinea pigs were exposed under well controlled conditions. Injurious actions were regularly encountered in direct proportion to the concentration of the inhaled vapor, in relation to exposure time and, in the case of homologous straight chain methyl ketone, the probability of injury with relation to the number of carbon atoms present. Irritation of the nasal mucosa, which precedes more damaging effects, is regarded as providing some warning properties during the inhalation of these ketones. In this entire series of publications, observations have been made only to acute responses to comparatively high concentrations of the volatile solvents. Commonly the

FACTORS INVOLVED IN THE USE OF ORGANIC SOLVENTS AS PRECIPITATING AND DRYING AGENTS OF IMMUNE SERA

1. In concentrations of 70 to 75 per cent the organic solvents methyl, ethyl, and propyl alcohols, and acetone cause complete precipitation of serum proteins and produce maximum loss in solubility. We have referred to this concentration range as the critical concentration. 2. As the concentration of the solvents is increased from about 75 per cent precipitation continues complete but loss in solubility progressively decreases until at all concentrations above about 87 per cent the precipitates formed at room temperature are completely soluble. 3. The degree of resolubility of the precipitates formed even in these high concentrations of the organic solvent decreases as the temperature is raised and as the duration of exposure is increased. 4. At 5 degrees C. the precipitates formed in all concentrations of these organic solvents are completely resoluble. Also these solvents exert maximum precipitating effect at lower temperature. 5. Maximum precipitating effect by these organic solvents occurs at about pH 6.0 precipitation becoming progressively less as the pH value is altered either way from this point. 6. The more concentrated the serum, the greater the proportion of protein present that will be precipitated by any given concentrations of organic solvent. 7. A method for preparing dry immune sera has been given. Such dried sera have been extracted with a number of organic compounds without loss in solubility or antibody activity.