Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SOLVENTS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1980

A kinetic method for the study of solvent environments of thiol groups in proteins involving the use of a pair of isomeric reactivity probes and a differential solvent effect. Investigation of the active centre of ficin by using 2,2'- and 4,4'- dipyridyl disulphides as reactivity probes.

1. Whereas the second-order rate constants for the reaction of the thiolate ion of 2-mercaptoethanol with 4,4'-dipyridyl disulphide (k4PDS) and with 5,5'-dithiobis-2-nitrobenzoate dianion increase with decreasing dielectric constant of the solvent, or remain unchanged, the rate constant for the analogous reaction with 2,2'-dipyridyl disulphide (k2PDS) decreases. This anomalous solvent effect and other unusual physicochemical properties of 2,2'-dipyridyl disulphide are discussed. 2. The differential effect of solvent on the reactions of thiolate ion with the 2,2'- and 4,4'-dipyridyl disulphides is shown to provide a method of characterizing solvent environments of thiol groups in proteins by a reactivity-probe method that should not suffer from the usual drawback associated with the existence of steric or binding effects of unknown magnitude. Application of the method to ficin (EC 3.4.22.3) suggests that its active-centre thiol group resides in a relatively hydrophobic environment. 3. The pH-k profile for the reaction of ficin with 4,4'-dipyridyl disulphide is reported.

2,2'-Dipyridyl↗
PubMed2002

Tailoring fatty food simulants made from solvent mixtures (2): determining the equivalent migration behaviour of olive oil and of solvents in the case of polyolefins.

It is suggested that solvent mixtures consisting of an ester and of an inert solvent can be used as fatty food simulants capable of having the same migration behaviour as olive oil with plastics. Migration tests carried out with low-density polyethylene for 20 and 48 h in an 8 and 5% mixture of tert-butyl acetate in ethanol respectively gave results equivalent to those obtained with olive oil after 10 days at 40 degrees C. The use of solvent mixtures facilitated the analysis and improved detection limits, giving good repeatability. Furthermore, the more rapid migration in solvent mixtures can be particularly useful for industrial controls as alternative test methods.

Diffusion↗
PubMedDate not supplied

Effects of solvent evaporation rate on the properties of protein-loaded PLLA and PDLLA microspheres fabricated by emulsion-solvent evaporation process.

This paper investigated the effects of the rate of solvent removal by varying the ambient pressure at a fixed temperature on the morphology, particle size, encapsulation efficiency and release pattern of albumin-loaded PLLA and PDLLA microspheres, prepared by the W/O/W emulsion-solvent evaporation process. For PLLA microspheres prepared either with a fast rate of solvent evaporation (FRSE) or a normal rate of solvent evaporation (NRSE) process, the difference in morphology was minor. In contrast, the different processes did affect the morphology of PDLLA microspheres. Large (surface) pores were observed for PDLLA microspheres fabricated with a FRSE process, while a smooth surface was seen in those with a NRSE process. With the FRSE process, both PLLA and PDLLA microspheres showed smaller particle sizes and lower albumin encapsulation efficiencies than those prepared in the NRSE process. PLLA microspheres prepared with the NRSE process had higher drug encapsulation efficiencies than PDLLA ones, but this was not the case for the FRSE process. An initial burst release of albumin was observed for both PLLA and PDLLA microspheres prepared with the NRSE process, while a lesser burst release was seen for those prepared with the FRSE process. In subsequent stages of drug release, PLLA microspheres prepared with the two different processes showed differences, but this was not the case for PDLLA ones.

Albumins↗
PubMed1991

Derivatives of CAP having no solvent-accessible cysteine residues, or having a unique solvent-accessible cysteine residue at amino acid 2 of the helix-turn-helix motif.

The Escherichia coli catabolite gene activator protein (CAP) is a helix-turn-helix motif sequence-specific DNA binding protein. CAP contains a unique solvent-accessible cysteine residue at amino acid 10 of the helix-turn-helix motif. In published work, we have constructed a prototype semi-synthetic site-specific DNA cleavage agent from CAP by use of cysteine-specific chemical modification to incorporate a nucleolytic chelator-metal complex at amino acid 10 of the helix-turn-helix motif [Ebright, R., Ebright, Y., Pendergrast, P.S. and Gunasekera, A., Proc. Natl. Acad. Sci. USA 87, 2882-2886 (1990)]. Construction of second-generation semi-synthetic site-specific DNA cleavage agents from CAP requires the construction of derivatives of CAP having unique solvent-accessible cysteine residues at sites within CAP other than amino acid 10 of the helix-turn-helix motif. In the present work, we have constructed and characterized two derivatives of CAP having no solvent-accessible cysteine residues: [Ser178]CAP and [Leu178]CAP. In addition, in the present work, we have constructed and characterized one derivative of CAP having a unique solvent-accessible cysteine residue at amino acid 2 of the helix-turn-helix motif: [Cys170;Ser178]CAP.

Base Sequence↗
PubMed1996

Relationship between solvent inhalation and antisocial behavior: special emphasis on two types of violence seen in solvent abusers.

Organic solvent inhalation is a serious problem among youths in Japan. It induces physical and mental disorders, and is related closely to crime and delinquency. The relationship between solvent inhalation and antisocial behavior was investigated in 75 youths. The subjects were divided into three groups according to the level of violent behavior and the time of appearance: a non-violent group, a late-onset group (violence occurred after the start of inhalation) and an early-onset group (violence had occurred before the start of inhalation). Various parameters were compared among the groups. The late-onset group showed the following characteristics; (i) the frequency of inhalation was high, and many subjects experienced hallucinations and mood changes caused by inhalation; (ii) the family environment was characterized by conflict; and (iii) the subjects had strong psychological conflicts and showed dissociative coping with frustration. The violence, psychological conflict and dissociation in this group were found to be related to the inhalation, with familial conflict as a background. The violence in the early-onset group was considered to be the manifestation of a violent personality as the frequency of inhalation and the incidence of mental symptoms were both low. The subjects in this group showed weak psychological conflict and tended to be demanding of others when attempting to cope with frustration. Two types of violent behaviors in the teenagers who inhaled solvents were identified. The violence of solvent inhalers should be managed according to the type.

Administration, Inhalation↗
PubMed2001

Transposon mutations in the flagella biosynthetic pathway of the solvent-tolerant Pseudomonas putida S12 result in a decreased expression of solvent efflux genes.

Fourteen solvent-sensitive transposon mutants were generated from the solvent-tolerant Pseudomonas putida strain S12 by applying the TnMod-KmO mutagenesis system. These mutants were unable to grow in the presence of octanol and toluene. By cloning the region flanking the transposon insertion point a partial sequence of the interrupted genes was determined. Comparison of the deduced amino acid sequences with a protein database revealed the following interrupted putative gene products: organic solvent efflux proteins SrpA and SrpB, the flagellar structural proteins FlgK, FlaG, FliI, FliC, and FliH, the transcriptional activator FleQ, the alternative RNA polymerase sigma factor RpoN, and the flagellum-specific RNA polymerase sigma factor FliA (RpoF). The transposon mutants, except for the organic solvent efflux mutants, were nonmotile as determined by a swarm assay and the formation of the flagellum was totally impaired. Expression studies with a srp promoter probe showed a decreased expression of the SrpABC efflux pump in the nonmotile mutants.

Bacterial Proteins↗
PubMed2005

Enhanced reactivity of Rhizopus oryzae lipase displayed on yeast cell surfaces in organic solvents: potential as a whole-cell biocatalyst in organic solvents.

Immobilization of enzymes on some solid supports has been used to stabilize enzymes in organic solvents. In this study, we evaluated applications of genetically immobilized Rhizopus oryzae lipase displayed on the cell surface of Saccharomyces cerevisiae in organic solvents and measured the catalytic activity of the displayed enzyme as a fusion protein with alpha-agglutinin. Compared to the activity of a commercial preparation of this lipase, the activity of the new preparation was 4.4 x 10(4)-fold higher in a hydrolysis reaction using p-nitrophenyl palmitate and 3.8 x 10(4)-fold higher in an esterification reaction with palmitic acid and n-pentanol (0.2% H2O). Increased enzyme activity may occur because the lipase displayed on the yeast cell surface is stabilized by the cell wall. We used a combination of error-prone PCR and cell surface display to increase lipase activity. Of 7,000 colonies in a library of mutated lipases, 13 formed a clear halo on plates containing 0.2% methyl palmitate. In organic solvents, the catalytic activity of 5/13 mutants was three- to sixfold higher than that of the original construct. Thus, yeast cells displaying the lipase can be used in organic solvents, and the lipase activity may be increased by a combination of protein engineering and display techniques. Thus, this immobilized lipase, which is more easily prepared and has higher activity than commercially available free and immobilized lipases, may be a practical alternative for the production of esters derived from fatty acids.

Agglutinins↗
PubMedDate not supplied

Phosphorylation of Ca2+-ATPase by inorganic phosphate in water-organic solvent media: dielectric constant and solvent hydrophobicity contribution.

The effect of organic solvents on the phosphorylation of the Ca2+-dependent ATPase of sarcoplasmic reticulum by inorganic phosphate in the absence of a calcium gradient was investigated. Kinetic analysis of the reaction in water and water-organic solvent media according to a bireactant scheme shows no correlation between changes in kinetic parameters and the dielectric constant of the mixed solvents. The pronounced increase in equilibrium levels of phosphoenzyme in water-solvent mixtures is attributed to changes in the water activity of the medium.

Animals↗
PubMed1981

[Retention of organic solvent vapors in plastic bags. Part 5. A basic study about correction methods of concentration of organic solvent vapors in plastic bags (author's transl)].

The concentration of organic solvents in plastic bags is decreased with time elapsed. It was supposed to permeate in plastic films. Therefore, we assumed that this phenomenon will be approximately regulated by the first order order reaction (C = C0e-kt). We got the permeation coefficient (k) by experiments and used it to correct organic solvent concentrations in the plastic bags. In the present experiment, we used Tedlar bags, toluene and ethyl methyl ketone (MEK) as organic solvents and determined the values by gas chromatography. Initial organic solvents concentration and that after t hr standing being taken as C0 and C. k Values are obtained by the formula C = C0e-kt. Mean values of k about toluene and MEK were found: k = 6.00 X 10(-3) and k = 4.86 X 10(-3). The results by this correction were as follows: Retention of toluene concentration in 24 hr standing bags showed to increase from 81% to 93%, or, in the case of 96 hr standing bags, it was shown to increase from 56% to 100%. Retention of MEK concentration in 24 hr standing bags showed to increase from 86% to 97%, or, in the case of 96 hr standing bags, it was shown to increase from 68% to 109%.

Butanones↗
PubMedDate not supplied

Role of the solvent-diffusion-rate modifier in a new emulsion solvent diffusion method for preparation of ketoprofen microspheres.

A new emulsion solvent diffusion method to prepare the microspheres of ketoprofen with an acrylic polymer was developed by utilizing sugar esters as solvent diffusion modifiers. The microspheres were produced via transient o/w emulsion droplets of the polymer, which was formed by the interaction of drug and water-miscible organic solvent, e.g. ethanol. The solvent consisting in oil droplets diffused into the outer aqueous medium. In the droplets, ethanol interacted with ketoprofen via hydrogen bonding between -OH group of ethanol and both -COOH and = CO groups of ketoprofen. These hydrogen bonds made ethanol solution strongly hydrophobic. The sugar ester added in the ethanol could inhibit such intermolecular interaction between ethanol and the = CO group of ketoprofen. Modulation in the binding force of ketoprofen-ethanol by the sugar ester contributed to achieving a desirable initial ethanol diffusion rate from the oil droplets for the formation of ketoprofen microspheres with high yield (> 85 per cent) and drug entrapment ratio (> 90 per cent).

Acrylates↗
PubMed1999

Mechanisms of solvent evaporation encapsulation processes: prediction of solvent evaporation rate.

The mechanism of organic solvent evaporation during microencapsulation and its role during microsphere hardening has been investigated. Evaporation and encapsulation studies were carried out in a jacketed beaker, filled with aqueous hardening solution, which was maintained at constant temperature and constant stirring rate in the turbulent regime. Evaporation of dissolved methylene chloride (MC), ethyl acetate (EA), and acetonitrile (ACN) was examined by the decline in organic solvent concentration in the hardening bath, which was monitored by gas chromatography. The evaporation from the bath followed first-order kinetics under dilute conditions (e.g., MC < 3 mg/mL), yielding an overall permeability coefficient, P. The value of P was theoretically related to the Kolmogorov length-scale of turbulence under conditions that favor liquid-side transport control. According to theory, factors that favored liquid-phase control (as opposed to gas-phase control) were those that favored a high Henry's law constant [i.e., elevated temperature near the normal boiling point (bp) of the organic solvent] and properties of the dissolved organic solvent (i.e., low normal bp and low aqueous solubility). These theoretical hypotheses were confirmed by (1) correlating the experimentally determined P with process variables raised to the appropriate power according to theory, r(2) = 0.95 (i.e., P approximately rotational speed, omega(3/4), impeller diameter, d (5/4), volume of hardening bath, V(-1/4), and the product of kinematic viscosity and diffusion coefficient, nu(-5/12)D (2/3)), and (2) illustrating that at constant temperature, the tendency of the evaporation system to obey liquid-side transport control follows the same order of increasing Henry's law constant (i.e., MC > EA > ACN). To establish the relationship of evaporation with microsphere hardening, the decline in MC concentration was determined in both the continuous and dispersed polymer phases during microencapsulation. By applying a mass balance with respect to MC in the hardening bath, the cumulative hardening profile of the microspheres was accurately predicted from the interpolating functions of the kinetics of MC loss from the bath with and without polymer added. These results have potential use for microsphere formulation, design of encapsulation apparatus, and scale up of microsphere production.

Algorithms↗
PubMed1987

The urinary concentration of solvents as a biological indicator of exposure: proposal for the biological equivalent exposure limit for nine solvents.

Organic solvents are generally volatile substances that are absorbed mainly through the lungs; they are eliminated chiefly through the lungs and kidneys. In urine they are present as metabolites and, in very little part, as parent compound. The urinary concentration of solvent (Cu) can be used for the biological monitoring of exposed subjects to evaluate their exposure and correlate with the Threshold Limit Value (TLV) during the working day. The authors report some results obtained with workers occupationally exposed to solvents. The results concern the correlation between urinary concentration (Cu, micrograms/L) vs. average environmental concentration (Ci, mg/m3) measured in the breathing zone. For each solvent studied (acetone, 2-cyclohexane, 1,2-dichloropropane, n-hexane, methyl ethyl ketone, perchloroethylene, styrene, toluene, 1,1,1-trichloroethane) the authors propose a Biological Equivalent Exposure Limit (BEEL) corresponding to the environmental TLV.

Air Pollutants, Occupational↗
PubMed2000

Purification and characterization of organic solvent-stable lipase from organic solvent-tolerant Pseudomonas aeruginosa LST-03.

An organic solvent-stable lipase (LST-03 lipase) secreted into the culture broth of the organic solvent-tolerant Pseudomonas aeruginosa LST-03 was purified by ion-exchange and hydrophobic interaction chromatography in the presence of 2-propanol. The purified enzyme was homogeneous as determined by SDS-PAGE. The molecular mass of the lipase was estimated to be 27.1 kDa by SDS-PAGE and 36 kDa by gel filtration. The optimum pH and temperature were 6.0 and 37 degrees C. LST-03 lipase was stable at pH 5-8 and below 40 degrees C. Its hydrolytic activity was highest against tricaproin (C6), methyl octanoate (C8), and coconut oil respectively among the triacylglycerols, fatty acid methyl esters, and natural oils investigated. The enzyme cleaved not only the 1,3-positioned ester bonds, but also the 2-positioned ester bond of triolein. It exhibited high levels of activity in the presence of n-decane, n-octane, DMSO, and DMF as well as in the absence of an organic solvent. In addition, LST-03 lipase was stabler in the presence of n-decane, ethyleneglycol, DMSO, n-octane, n-heptane, isooctane, and cyclohexane than in the absence of an organic solvent.

Journal Article↗
PubMed2006

Solvent reorganization entropy of electron transfer in polar solvents.

We report the results of molecular dynamics simulations of the solvent reorganization energy of intramolecular electron transfer in a charge-transfer molecule dissolved in water and acetonitrile at varying temperatures. The simulations confirm the prediction of microscopic solvation theories of a positive reorganization entropy in polar solvents. The results of simulations are analyzed in terms of the splitting of the reorganization entropy into the contributions from the solute-solvent interaction and from the alteration of the solvent structure induced by the solute. These two contributions mutually cancel each other, resulting in the reorganization entropy amounting to only a fraction of each component.

Journal Article↗
PubMed2006

Solvent reorganization of electron transitions in viscous solvents.

We develop a model of electron transfer reactions at conditions of nonergodicity when the time of solvent relaxation crosses the observation time window set up by the reaction rate. Solvent reorganization energy of intramolecular electron transfer in a charge-transfer molecule dissolved in water and acetonitrile is studied by molecular dynamics simulations at varying temperatures. We observe a sharp decrease of the reorganization energy at a temperature identified as the temperature of structural arrest due to cage effect, as discussed by the mode-coupling theory. This temperature also marks the onset of the enhancement of translational diffusion relative to rotational relaxation signaling the breakdown of the Stokes-Einstein relation. The change in the reorganization energy at the transition temperature reflects the dynamical arrest of the slow, collective relaxation of the solvent related to the relaxation of the solvent dipolar polarization. An analytical theory proposed to describe this effect agrees well with both the simulations and experimental Stokes shift data. The theory is applied to the analysis of charge-transfer kinetics in a low-temperature glass former. We show that the reorganization energy is substantially lower than its equilibrium value for the low-temperature portion of the data. The theory predicts the possibility of discontinuous changes in the dependence of the electron transfer rate on the free energy gap when the reaction switches between ergodic and nonergodic regimes.

Journal Article↗
PubMed2006

Reliable molecular simulations of solute-solvent systems with a minimum number of solvent shells.

In this work, the mean field (MF) method, a continuum-based model designed for treating complex molecular systems, such as liquids and solutions, recently presented by Brancato et al. [J. Chem. Phys. 122, 154109 (2005)], has been further developed and improved especially in the treatment of the electrostatics. The revised model has been used to investigate the size effects on several physical properties of various solute-solvent systems by increasing the number of explicitly included solvent molecules from few tens up to thousands. Results on simple ions, such as sodium and chloride ions, and on a small peptide, such as alanine dipeptide analog (AcAlaNHMe), have shown that solvation structures and dynamics, as well as solvent-induced changes in the solute conformation, can be correctly reproduced by the MF model, providing that only two or three solvent layers are treated explicitly.

Journal Article↗
PubMed2005

Solvent-induced symmetry breaking: varying solvent strength.

The triiodide ion is an example of a system where symmetry breaking may be induced by a solvent. The Landau free energy is expected to have a similar form to that for the mean field Ising model, but with solvent strength rather than temperature as the control parameter determining whether there is symmetry breaking. In order to examine the extent of anomalous behavior near the critical point we have studied the properties of the ion in a solvent based on a model for water with charges scaled by a factor lambda . As lambda is increased from zero the solvent strength increases and the system changes from one with no symmetry breaking to one with strong symmetry breaking. The Shannon entropy as a function of lambda shows only a weak maximum near the critical value of lambda= lambda(c) , while the susceptibility has no anomalous behavior. We examine a simple model and show that anomalies near the critical point would increase as the temperature decreases, but divergences associated with a second order phase transition would only be seen in the limit of zero temperature.

Journal Article↗
PubMed2001

Solvent effect on ion-pair extraction of 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with solvated hydroxonium ion using alcohols and 1-octanol/octane mixed solvents.

Extraction of 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with solvated hydroxonium ion was carried out using 14 kinds of alcohols and 1-octanol/octane mixed solvents as a solvent at 25 degrees C. Alcohols are 1-pentanol, 1-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol, 3-octanol, 1-nonanol, 2-nonanol, 3-nonanol, 5-nonanol and 1-decanol. Among them, 1-octanol was found to be extremely high in extractability for 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with hydroxonium cation. The extraction equilibrium for the systems using 1-octanol/octane mixed solvents was analyzed in detail in order to examine the extraction mechanism for these extraction systems. 2-(2-Pyridylazo)-1-naphthol-4-sulfonate anion was found to be extracted with the hydroxonium ion solvated by three 1-octanol molecules as an ion-pair. The extraction and partition constants of the ion-pair of 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with solvated hydroxonium ion were estimated in the 1-octanol/octane mixed solvent systems.

Journal Article↗