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PubMedDate not supplied

Solvent selection strategies for extractive biocatalysis.

This report follows the development of systematic solvent screening strategies for the identification of superior pure solvents and introduces techniques for the identification of effective coextractants. Specifically, methods to predict the biocompatibility and extractant capability of solvents are discussed. Biocompatibility is predicted by using heuristic data or the correlations between bioactivity and the logarithm of the partition coefficient of the solvent or the concentration of solvent in the cell membrane. A computer program, known as the extractant screening program or ESP, has been developed to effectively predict the behavior of virtually any product in any solvent/aqueous system. It is demonstrated that a biocompatible yet poor solvent can be mixed with a toxic solvent that has better extractant properties to yield a mixture with improved solvent characteristics that is still biocompatible. The fact that solvents do not mix in an ideal manner is exploited by using ESP to identify solvent mixtures that are still biocompatible at relatively high concentrations of toxic solvent.

Animals↗
PubMedDate not supplied

Combination of extractive solvent addition and immobilization culture for continuous production of scopoletin by tobacco cells.

Extractive solvent addition was combined with immobilization cultures of Nicotiana tabacum cells to produce scopoletin. Using various solvents, the partition coefficients of scopoletin between the solvent and water phases and the solvent toxicity to the cell viability were investigated. The effect of the solvent addition on cell growth and scopoletin production was elucidated in the suspension cultures. Coconut oil, one of the natural vegetable oils, was selected as the most suitable extractive solvent. The cells were immobilized in the calcium alginate gel bead coated with a cell-free gel film and then the batch cultures with the addition of various volumes of the coconut oil were performed. The total scopoletin production increased with the solvent volume according to the amount of scopoletin transferred from the medium to the solvent. The maximum productivity obtained in the batch immobilization cultures was about 16 times larger than that in the suspension culture without solvent. A continuous production system, in which the fresh solvent was supplied to the culture system and the solvent containing scopoletin was recovered from it, was constructed. The integrated scopoletin production in the effluent oil attained 2.21 mg/gDCW for 30 days at 100 cm(3)/day without cell leakage.

Scopoletin↗
PubMed2005

Enhancing the rate of the Diels-Alder reaction using CO2 + ethanol and CO2 + n-hexane mixed solvents of different phase regions.

The reaction rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthrance in CO2 + ethanol and CO2 + hexane mixed solvents of different compositions were determined by in situ UV/vis spectroscopy at 318.15 K and different pressures. The density of the mixed solvents at different pressures was also determined and the isothermal compressibility was calculated using the density data. The activation volume of the reaction was calculated based on the dependence of rate constant (kc) on pressure. It was demonstrated that the kc was very sensitive to the pressure in the mixed solvents near the critical region and the kc increased dramatically as pressure approached dew points, critical point, and bubble points of the mixed solvents. However, the kc in the mixed solvents outside the critical region or in pure CO2 was not sensitive to pressure. At suitable conditions, kc could be 40 times larger than that in acetonitrile. The activation volume of the reaction was nearly independent of pressure as the pressure was much higher than the phase separation pressure of the mixed solvents, while it increased considerably as pressure approached the bubble points, critical point, and dew points from high pressure. The clustering of the solvent molecules with the reactants and the activated complex in the reaction systems near the phase boundary in the critical region may be the main reason for the interesting phenomena observed. This work also shows that, using pure CO2 as the solvent, the reaction cannot be carried out in the critical region of the solvent due to the limitations of the reactants, while it can be conducted in the critical region of mixed solvents of suitable compositions, where the solvents are highly compressible and the reaction rate can be tuned effectively by pressure.

Anthracenes↗
PubMed2002

Helicogenicity of solvents in the conformational equilibrium of oligo(m-phenylene ethynylene)s: implications for foldamer research.

A (R)-binaphthol tethered bis-hexameric oligo(m-phenylene ethynylene) foldamer was examined in 30 solvents to correlate the unfolded-folded conformational equilibrium to bulk solvent properties and specific solvent-chain interactions. The oligomer is soluble in a variety of solvents of intermediate polarity, with the majority of these solvents being helicogenic. The amphiphilic nature of the chain allows the solvophobic backbone to be solubilized in a wide range of solvents through the polar triethylene glycol side chains. As demonstrated through UV and CD spectroscopic experiments, the helical conformation is increasingly stabilized with increasing solvent polarity in the absence of specific solvent-chain interactions. Surprisingly, very few solvents are capable of fully denaturing the helix, indicating the strength of the solvophobic driving forces in this cooperative system. The folding reaction for this amphiphilic oligomer can be described as a compromise in solubility properties, where chains collapse intramolecularly into helical conformations to minimize solvent-backbone contacts while maintaining favorable solvent-side chain interactions for solvation. In terms of mimicking the properties of biomacromolecules, foldamers using solvophobic driving forces must be tempered with functionalities that promote solubility of the folded state while at the same time allowing access to the unfolded state through the use of denaturants.

Alkynes↗
PubMed1982

The constitution of adhesives, and its relationship to solvent abuse.

1 An adhesive, in general, must be a liquid at the time of application, so that the adherends are wetted out, but must then solidify to enable development of adequate bond strength. The use of volatile solvent is only one way in which the solid ingredients can be converted to a liquid for application. 2 Only those adhesives containing solvents are capable of providing the narcotic effect desired by the 'sniffer'. 3 Solvents used in adhesives include highly volatile hydrocarbons, esters, ketones and chlorinated hydrocarbons. 4 Commonly available domestic materials other than solvent-borne adhesives contain such solvents, and are hence capable of misuse by 'sniffers'. Often such materials are of greater potential harm to the mis-user. 5 Aversive additives in solvent-borne adhesives have been found ineffective and also deter the bona fide user. 6 Aqueous substitutes for existing popular and safely-used solvent-borne adhesives have not found sufficient favour with the domestic adhesive user as to enable the manufacturers to replace the solvent-borne type in the market place. 7 Removal of solvent-borne adhesives from the market would not of itself solve the problem of solvent abuse because of the other solvent sources available. The remedy lies in the removal of the causes of such social misbehaviour, rather than in treatment of the symptoms.

Adhesives↗
PubMed1978

Effective use of organic solvents to remove drugs from biologic specimens.

While studies on the extraction of drugs by various organic solvents are numerous, very few direct comparisons of all the commonly used extraction solvents have been made. Review of the literature and some specific studies undertaken by the author show that the solvents more frequently used in toxicology are not all alike but vary with respect to type of drug being extracted. Hexane, 1-chlorobutane, dichloromethane, chloroform, isopropyl ether, ethyl ether, ethyl acetate, and 1-butanol all extract nonpolar drugs quite efficiently; drugs which have polar functional groups such as alcohols, phenols, carboxylic acids, imides, amides, esters, and sulfonamides require more polar solvents for their removal from aqueous solution in high yield. Ethyl ether and other ethers, ethyl acetate, and ketones are hydrogen bond acceptor molecules and therefore extract electron donor solutes more readily than chloroform, the most commonly used electron donor solvent. Alcohols such as 1-butanol are excellent general drug extractors but pose other problems such as odor and emulsion formation. Hexane, on the other end of the polarity scale, extracts polar solutes very poorly. Thus, chloroform and ethyl ether are the most versatile solvents, although dichloromethane and 1-chlorobutane are finding more use. Solvent costs and health hazards vary within the group of solvents discussed. 1-Chlorobutane and chloroform are relatively expensive, while ethyl ether, hexanes, and dichloromethane are less expensive. No solvent is 100% safe with respect to fire, explosion, and health hazard. While chloroform has the lowest TLV, a safety limit, some of the other solvents have higher vapor pressures. The most useful solvent for small volume extractions is chloroform or chloroform with a small percentage of an alcohol. Although poor recoveries are obtained for many drugs by the small volume extraction technique, more and more use of this approach is expected in the future.

Animals↗
PubMed1984

Etoposide-induced blood-brain barrier disruption. Effect of drug compared with that of solvents.

The intracarotid infusion of the anti-neoplastic compound, etoposide, has been shown to exert a dose-dependent effect on blood-brain barrier (BBB) permeability. Etoposide, however, is formulated in a complex solvent solution containing alcohol, Tween 80, polyethylene glycol 300, and citric acid. To investigate the contribution of the solvent solution to BBB disruption, the authors studied Sprague-Dawley rats after the internal carotid artery infusion of the solvent solution with and without the addition of etoposide. Experiments were performed at four doses of drug and/or solvent. Disruption of the BBB was evaluated qualitatively by the appearance of the systemically administered dye, Evans blue, in the cerebral hemispheres and quantitatively by the ratio of gamma counts of the technetium-labeled chelate of diethylenetriaminepentaacetic acid (99mTc-DTPA) in the ipsilateral:contralateral hemisphere. Significant barrier opening was obtained in all four groups of animals infused with solvent plus etoposide. In the corresponding groups of rats infused with the solvent solution alone, BBB disruption was markedly lower. Only in the group infused with the largest dose of solvent was the hemispheric ratio of 99mTc-DTPA significantly different from saline-infused animals. Each of the groups with solvent plus etoposide had 99mTc-DTPA ratios significantly different from the control group. Intracarotid infusion and subsequent BBB disruption were well tolerated by the animals receiving either solvent alone or solvent and etoposide. Disruption of the BBB secondary to the intracarotid infusion of etoposide is primarily caused by the drug itself and not by the solvent solution.

Animals↗
PubMedDate not supplied

Organic solvents for pharmaceutical parenterals and embolic liquids: a review of toxicity data.

Non-aqueous solvents have long been used in subcutaneous or intramuscular pharmaceutical formulations to dissolve water-insoluble drugs. In recent years, the need for these vehicles was increased since the drug discovery process has yielded many poorly water-soluble drugs. Besides, preparations containing embolic materials dissolved in undiluted non-aqueous water-miscible solvents have been proposed for the intravascular treatment of aneurysms, arteriovenous malformations, or tumors. These organic solvents, regarded as chemically and biologically inert, may show pharmacological and toxicological effects. Therefore, knowledge of tolerance and activity of non-aqueous solvents is essential before they can be administered, especially when given undiluted. This paper focuses on thirteen organic solvents reported as possible vehicles for injectable products and details toxicological data when they have been administered intravascularly. These solvents can be subdivided into three groups according to their description in the literature either for intravenous pharmaceutical parenterals or for intravascular embolic liquids: well-documented organic solvents (propylene glycol, polyethylene glycols, ethanol), solvents described in specific applications (dimethyl sulfoxide, N-methyl-2-pyrrolidone, glycofurol, Solketal, glycerol formal, acetone), and solvents not reported in intravascular applications but potentially useful (tetrahydrofurfuryl alcohol, diglyme, dimethyl isosorbide, ethyl lactate). This review of the literature shows that toxicity data on intravascular organic solvents are insufficient because they concern solvents diluted with water and because of the lack of comparative evaluation using the same methodologies.

Animals↗
PubMedDate not supplied

Effect of the solvent system on the in vitro permeability of nicardipine hydrochloride through excised rat epidermis.

PURPOSE: The present investigation was carried out to study the effect of the solvent system on the permeation of nicardipine hydrochloride across excised rat epidermis in order to select a suitable solvent system for use in the development of a transdermal therapeutic system. METHODS: The solubility of nicardipine hydrochloride in pure and mixed solvent systems was determined. The solvents used were water, propylene glycol, ethanol or various proportions of ethanol and water. The effect of these pure or mixed solvent systems on the skin permeation of nicardipine hydrochloride was also studied using in vitro permeation studies through excised rat epidermis mounted in modified Keshary-Chien diffusion cells. Fourier Transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC) studies were carried out to study the effect of these solvents on the biophysical properties of rat' stratum corneum. RESULTS: Although the solubility of nicardipine hydrochloride in propylene glycol (51.23 mg/mL) was higher than that in water (7.90 mg/mL) and ethanol (20.01 mg/mL), the flux of the drug from propylene glycol was as low (7.25+/-0.13 microg/cm(2)/h) as that from water (7.05+/-0.15 microg/cm(2)/h) and lower than that from ethanol (21.51+/-0.81 microg/cm(2)/h). The solubility of nicardipine hydrochloride in binary ethanol-water solvent systems in various proportions was higher than in pure solvents. The highest permeability was observed from an ethanol-water (70:30 v/v) solvent system (56.10+/-1.23 micro g/cm(2)/h) which showed the highest solubility (224.21 mg/mL). The DSC and FT-IR data indicated that the binary solvent system containing ethanol-water in the ratio of 70:30 v/v increased the drug permeability through the skin by disrupting the highly ordered intercellular lipid structure of the stratum corneum in comparison with the untreated stratum corneum. CONCLUSIONS: The results of the study indicate that the use of a binary solvent system, ethanol and water in the ratio of 70:30 v/v, is an effective vehicle for the development of a transdermal therapeutic system for nicardipine hydrochloride.

Administration, Cutaneous↗
PubMed1992

[A study on the relationship between solvent abusers and alcoholism in the parental generation].

In recent years, attention has been paid to the fact that alcoholism and/or drug addiction runs in families. Few studies have investigated the relationship between solvent abuse in adolescents and alcoholism in their parents. Two hundred and ten solvent abusers who came to Serigaya-en, alcoholism and drug addiction treatment hospital, during from 1983 to 1989, were examined from the following two standpoints. The proportion of solvent abusers with alcoholic parents (A group), what characteristics the solvent abusers in A group had as compared with those whose parents were not alcoholic (NA group). The findings were summarized as follows; 21.4% of the subjects had an alcoholic (FH-RDC) parent. They were approximately two years older than those in the NA group at the first examination. The solvent abusers of the A group presented with: 1) more experiences of parental death and/or separation prior to the age of 15; 2) a higher frequency of school refusal in elementary or junior high school; 3) poorer socioeconomic status; 4) a longer duration of solvent abuse; 5) more abuse of addictive drugs other than solvent; 6) a more severe psychopathology; 7) a higher incidence of chronic organic diseases among their parents; 8) a higher incidence of solvent abuse among their siblings. The present study indicates that: 1) many a solvent abuser come from alcoholic families; 2) parental alcoholism is responsible not only for solvent abuse, but also for the development of addictions, (e.g., prolonged solvent abuse, developing into alcoholism or poly-substance abuse); 3) clinical and socioeconomic deterioration occurs not merely in the individual abusers but also in other family members, especially in the A group. The results lead the author to stress the importance of focusing the therapy upon the family itself.

Adolescent↗
PubMed2005

Photoreactivity of biologically active compounds. XVII. Influence of solvent interactions on spectroscopic properties and photostability of primaquine.

The influence of solvent interactions on absorption properties, fluorescence properties (emission spectra and quantum yields) and relative photochemical degradation rates of primaquine has been investigated, in order to evaluate photochemical reaction mechanisms and chemical properties of the compound. The first absorption band (n - pi*) of primaquine is only slightly dependent on properties of the solvent, which can be ascribed to a strong, intramolecular hydrogen bond between the quinoline N and amine group in the ground state (S0). Amphiprotic solvents with predominant acidic properties (water and methanol) will to some extent stabilize the molecule and initiate hypsochromic shifts of the absorption band by protic interactions, while the other solvents (amphiprotic, basic and neutral) influence the absorption spectrum by general solvent effects only. The excited singlet (S1*) state of primaquine interacts more efficiently with the surrounding solvents than the S0 state, as evaluated by the Stokes shifts. The pKa value of the quinoline N is likely to increase in the S1* state, which is important for the observed protic interactions with amphiprotic solvents of predominant acidity. Specific solvent effects are highly important for the efficiency of the fluorescence (fluorescence quantum yields; phi f). The fluorescence is quenched by amphiprotic solvents, likely due to a rupture of the intramolecular bond and protonation of the quinolone N, and enhanced by polar, non-protic (basic) solvents, probably by stabilization of the delta intramolecular hydrogen bond. The observed photochemical degradation rates of primaquine in amphiprotic media are positively correlated with phi f, indicating that the photochemical degradation of primaquine is dependent on intramolecular hydrogen bonding and non protonated lone-pair electrons at the quinoline N. The intramolecular ring-formation with a subsequent increased lipophilic character and (lack of) interactions with the surroundings, are important factors for biological behavior as well as pharmaceutical properties of primaquine. Knowledge about solvent interactions with primaquine in the S0 and S1* states is essential for the proceeding evaluation of photostability and phototoxicity of the drug.

Antimalarials↗
PubMed1988

Enzymatic catalysis in nonaqueous solvents.

Subtilisin and alpha-chymotrypsin vigorously act as catalysts in a variety of dry organic solvents. Enzymatic transesterifications in organic solvents follow Michaelis-Menten kinetics, and the values of V/Km roughly correlate with solvent's hydrophobicity. The amount of water required by chymotrypsin and subtilisin for catalysis in organic solvents is much less than needed to form a monolayer on its surface. The vastly different catalytic activities of chymotrypsin in various organic solvents are partly due to stripping of the essential water from the enzyme by more hydrophilic solvents and partly due to the solvent directly affecting the enzymatic process. The rate enhancements afforded by chymotrypsin and subtilisin in the transesterification reaction in octane are of the order of 100 billion-fold; covalent modification of the active center of the enzymes by a site-specific reagent renders them catalytically inactive in organic solvents. Upon replacement of water with octane as the reaction medium, the specificity of chymotrypsin toward competitive inhibitors reverses. Both thermal and storage stabilities of chymotrypsin are greatly enhanced in nonaqueous solvents compared to water. The phenomenon of enzymatic catalysis in organic solvents appears to be due to the structural rigidity of proteins in organic solvents resulting in high kinetic barriers that prevent the native-like conformation from unfolding.

Catalysis↗
PubMed1979

Whole-body autoradiography and allied tracer techniques in distribution and elimination studies of some organic solvents: benzene, toluene, xylene, styrene, methylene chloride, chloroform, carbon tetrachloride and trichloroethylene.

Whole-body autoradiography has been used to study the distribution and fate of 14C-labeled benzene, toluene, xylene, styrene, methylene chloride, chloroform, carbon tetrachloride and trichloroethylene in mice after inhalational exposure. Total radioactivity, including the volatile part of the solvents were registered by autoradiography of dried, evaporated tape-fastened sections. In addition, dried, evaporated tape-fastened sections were extracted with water, trichloroacetic acid and a series of organic solvents and autoradiographed to register organs where metabolites were firmly bound. In another facet of the study, the quantitative elimination of the solvents and their metabolites via various routes was investigated. The expiration of unchanged solvents was subject to mathematical and computerized compartmental pharmacokinetic analysis. All solvents were rapidly taken up in fatty and nervous tissues where they were retained for different periods of time largely dependent on their fat solubility. Unexpectedly long retention times were noted for the chlorinated solvents, particularly for chloroforn, which showed a specific long-term retention in the cerebellum, meninges and spinal nerves, indicating interactions with specific nervous tissue receptors. Solvent metabolites appeared rapidly in several organs, mainly the liver and kidney, and were excreted both via urine and bile. Toluene and xylene metabolites were completely extractable whereas firmly bound metabolites were registered after inhalation of benzene, styrene and all chlorinated solvents, notably in the liver and kidney but also in the bronchi of the lung. Three-compartment pharmacokinetics were observed for the majority of the solvents selected for study although a two-compartment model was found to fit the elimination rate curves for styrene, methylene chloride and chloroform in the exhaled air. The fat solubility of the solvents was found to influence their pharmacokinetics since lower rate constants were generally obtained for the expiration of more fat soluble solvents.

Adipose Tissue↗
PubMed2005

Solvent dependence of the spectra and kinetics of excited-state charge transfer in three (alkylamino)benzonitriles.

Steady-state absorption and emission spectra and emission decay kinetics are reported for 4-aminobenzonitrile (ABN), 4-(1-azetidinyl)benzonitrile (P4C), 4-(1-pyrrolidinyl)benzonitrile (P5C), and 4-(1-piperidinyl)benzonitrile (P6C) in 24 room temperature solvents. In solvents of modest to high polarity, P4C, P5C, and P6C exhibit dual fluorescence and emission decays characteristic of the transformation from an initially prepared (LE) state to a more polar charge transfer (CT) state, whereas ABN does not undergo this reaction. The frequencies of the steady-state absorption and emission spectra of all of these solutes can be rationalized using a dielectric continuum description of the solvent and considering only the minima on the reactive surfaces, which are assumed to involve both an intramolecular (twisting) and a solvation coordinate. Characteristics of the gas-phase solutes deduced from this analysis are in good agreement with electronic structure calculations and indicate that differences in their spectra mainly reflect differences in the relative energies of the gas-phase LE and CT states. The relative yields of LE and CT emission are not described as satisfactorily by this model, and reasons for this failure are discussed. The kinetics of the LE --> CT reaction vary considerably with solute and solvent. In many solvents, the emission decays of P4C are reasonably described by a simple two-state kinetic scheme with time-independent rate constants. In P5C and P6C multiexponential decays are observed that reflect time-dependent shifts of the component spectra as well as time-dependent reaction rates. A simplified analysis of these complex dynamics provides estimates for both the free energy change Delta(r)G and (average) LE --> CT rate constant k(f) for a wide range of solute and solvent combinations. The driving force for reaction (-Delta(r)G) follows the order P6C > P5C > P4C and increases with increasing solvent polarity. The reaction rates are correlated to Delta(r)G and follow the opposite trend. The relationships observed between k(f) and Delta(r)G suggest that static solvent effects, i.e., barrier height changes, are the primary determinants of the solvent dependence in P4C. Correlations between barrier-corrected rates and solvation times suggest that dynamical solvent effects contribute substantially to the solvent dependence of the rates in P5C, and especially P6C.

Journal Article↗
PubMed2005

Tunable solvation effects on the size-selective fractionation of metal nanoparticles in CO2 gas-expanded solvents.

This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.

Journal Article↗
PubMed2006

How does solvent molecular size affect the microscopic structure in polymer solutions?

Monte Carlo simulation has been used to investigate the effects of linear solvent molecular size on polymer chain conformation in solutions. Increasing the solvent molecular size leads to shrinkage of the polymer chains and increase of the critical overlap concentrations. The root-mean-square radius of gyration of polymer chains (R(g)) is less sensitive to the variation of polymer concentration in solutions of larger solvent molecules. In addition, the dependency of R(g) on polymer concentration under normal solvent conditions and solvent molecular size is in good agreement with scaling laws. When the solvent molecular size approaches the ideal end-to-end distance of the polymer chain, an extra aggregation of polymer chains occurs, and the solvent becomes the so-called medium-sized solvent. When the size of solvent molecules is smaller than the medium size, the polymer chains are swollen or partially swollen. However, when the size of solvent molecules is larger than the medium size, the polymer coils shrink and segregate, enwrapped by the large solvent molecules.

Journal Article↗
PubMed2000

Importance of gas-phase proton affinities in determining the electrospray ionization response for analytes and solvents.

The effect of gas-phase proton transfer reactions on the mass spectral response of solvents and analytes with known gas-phase proton affinities was evaluated. Methanol, ethanol, propanol and water mixtures were employed to probe the effect of gas-phase proton transfer reactions on the abundance of protonated solvent ions. Ion-molecule reactions were carried out either in an atmospheric pressure electrospray ionization source or in the central quadrupole of a triple-quadrupole mass spectrometer. The introduction of solvent vapor with higher gas-phase proton affinity than the solvent being electrosprayed caused protons to transfer to the gas-phase solvent molecules. In mixed solvents, protonated solvent clusters of the solvent with higher gas-phase proton affinity dominated the resulting mass spectra. The effect of solvent gas-phase proton affinity on analyte response was also investigated, and the analyte response was suppressed or eliminated in solvents with gas-phase proton affinities higher than that of the analyte.

Atmospheric Pressure↗
PubMed2000

Solvent effect on lipase enantioselectivity. Evidence for the presence of two thermodynamic states.

The enantioselectivity of lipase-catalyzed kinetic resolutions has been measured at various temperatures in binary mixtures of solvents. Varying the solvent composition and temperature had a profound effect on the enantiomeric ratio. The values for delta delta H(R-S)(#) and delta delta S(R-S)(#), calculated from the E values measured at various temperatures, were estimated as a function of the solvent composition. By plotting delta delta H(R-S)(#) versus delta delta S(R-S)(#) as a function of the solvent composition, an extreme was observed. The resulting "hairpin-type" enthalpy-entropy compensation plots can be described by assuming the presence of two thermodynamically distinct physical states, displaying different enantioselectivities, that are in equilibrium with one another. Changing the solvent composition results in a change in the equilibrium constant K(eq) for the two states. The intriguing bell-shaped curves of the enantioselectivity versus solvent composition observed for lipase-catalyzed kinetic resolutions can be described assuming a linear correlation for the logarithm of K(eq) and the solvent composition. Thus, a simulation of the two-state model adequately describes the solvent effects found for lipase-catalyzed kinetic resolutions in binary mixtures of solvents and possibly in series of homologous organic solvents.

Biotechnology↗