Effect Of Organic Cosolvents Research Articles

Controlling Interfacial Hydrogen Bonding at a Gold Surface: The Effect of Organic Cosolvents.

Water often serves as both a reactant and solvent in electrocatalytic reactions. Interfacial water networks can affect the transport and kinetics of these reactions, e.g., hydrogen evolution reaction and CO2 reduction reaction. Adding cosolvents that influence the hydrogen-bonding (H-bonding) environment, such as dimethyl sulfoxide (DMSO), has the potential to tune the reactivity of these important electrocatalytic reactions by regulating the interfacial local environment and water network. We investigate interfacial H-bonding networks in water-DMSO cosolvent mixtures on gold surfaces by using surface-enhanced infrared absorption spectroscopy and molecular dynamics simulations. Experiments and simulations show that the gold surface is enriched with dehydrated DMSO molecules and the mixture phase-separates to form water clusters. Simulations show a "buckled" water conformation at the surface, further constraining interfacial H-bonding. The small size of these water clusters and the energetically unfavorable H-bond conformations might inhibit H-bonding with bulk water, suppressing the proton diffusion required for efficient hydrogen evolution reaction processes.

Asymmetric synthesis of sulfoxides by novel Baeyer-Villiger monooxygenase from Fusarium

In the chemical industry, the oxidation reaction is one of the essential reactions, although some oxidizing reagents are potentially explosive. Hence, the safe reaction catalyzed by monooxygenases, enzymes that can catalyze oxidation reactions using molecular oxygen in the air, becomes an attractive alternative as it promotes green and sustainable chemistry. Herein, sulfoxidation of alkyl aryl sulfides by a novel Baeyer-Villiger monooxygenase from a fungus, Fusarium sp. NBRC 109816 (FBVMO), was investigated. The effect of organic cosolvents was also examined using purified FBVMO, improving the activity by up to 247%. E. coli whole cell expressing FBVMO was used for the synthetic purpose, and various chiral sulfoxides were obtained successfully in up to 92% isolated yield and up to 99% ee (R).

Comparing the effects of organic cosolvents on acetylcholinesterase and butyrylcholinesterase activity

The use of cosolvents to solubilize compounds under investigation while having minimal effects on enzyme activity is an important component in many biochemical studies. Predicting the effects of cosolvents on enzyme activity can be complicated, as enzymes with similar overall structures might exhibit different behaviors in different cosolvents. In this study, the effects of several commonly used cosolvents: Methanol, acetonitrile, acetone, and dimethyl sulfoxide (DMSO), on two cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), were evaluated. Although the overall structures are highly similar, AChE activity was more sensitive to the organic cosolvents tested compared to BChE. Effects of the cosolvents on activity did not vary over time and activity was restored upon dilution of the cosolvent. Michaelis-Menten kinetics experiments showed that Vmax values were not substantially affected, while KM values increased up to ∼20-fold for AChE and ∼4-fold for BChE in the presence of 5% DMSO or acetone. The results suggest that BChE demonstrates more robustness to its cosolvent environment compared to AChE, and that cosolvents effects may arise from the molecules acting as inhibitors. The results may aid decisions of cosolvents used in enzyme assays and may help guide experimental conditions and design when conducting experiments comparing different enzymes.

The effect of organic cosolvent and solute–solvent interaction on the solubility of oil residue in Niger Delta soil

The solubility of crude oil residue in contaminated soil ( $$ \log S_{\text{s}} $$ ) from six locations in the Niger Delta region of Nigeria in solvent has been determined by batch desorption technique using various fractions of water:methanol cosolvent mixtures (0, 0.2, 0.4, 0.6, and 1.0) and 100% (v/v) of four organic solvents (ethanol, dichloromethane, chloroform, and hexane). Data obtained from the experiment were applied to the solvophobic theory to evaluate the relationship between the solubility of the crude oil residue, solvent polarity, and the age of oil residue in the spilled site. Differences were observed between calculated and experimental values of solubility of oil residue in water ( $$ \log S_{\text{w}} $$ ) obtained for both old and younger oil residue, with higher values obtained for oil residue older than 5 years. Linear solvation energy relationship (LSER) using multiple-linear regression showed that the polarizability of the solvent (SP) was responsible for solute–solvent interaction. This ultimately leads to increased solubility of oil residue in the cosolvent ( $$ \log S_{\text{s}} $$ ) and dissolution of hydrophobic solute in water. Differences in Alip/Pol ratio between samples were attributed to the effect of aging on the oil residues. The correlated parameters allow an explanation of the main factors to consider when implementing the best technical option for crude oil-contaminated soil remediation by soil washing.

A Study of the Viscosity Characteristics of Chitosan Solutions in the Presence of Organic Cosolvents

The effect of organic cosolvents (ethanol and isopropanol) on the viscosity characteristics of acetic acid aqueous solutions of chitosan is studied. Sorption and deformation–strength properties, as well as resistance to the process of enzymatic degradation of materials obtained from solutions, are determined. It is shown that the introduction of cosolvents into the chitosan–1% acetic acid system is accompanied by a consistent decrease in the intrinsic viscosity of polymers. It is found that, in the presence of cosolvents, at concentrations below the crossover concentration, chitosan molecules exist as systems of interacting (aggregated) macromolecules rather than isolated macromolecular coils. A change in the conformation of chitosan and the type of macromolecular aggregates in acetic acid solutions in the presence of cosolvents leads to a number of consequences: polymer units become less accessible to an enzyme preparation, the rate of enzymatic degradation decreases, and mechanical characteristics of film materials change.

Improved Efficacy of Synthesizing *MIII-Labeled DOTA Complexes in Binary Mixtures of Water and Organic Solvents. A Combined Radio- and Physicochemical Study.

Typically, the synthesis of radiometal-based radiopharmaceuticals is performed in buffered aqueous solutions. We found that the presence of organic solvents like ethanol increased the radiolabeling yields of [68Ga]Ga-DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacatic acid). In the present study, the effect of organic cosolvents [ethanol (EtOH), isopropyl alcohol, and acetonitrile] on the radiolabeling yields of the macrocyclic chelator DOTA with several trivalent radiometals (gallium-68, scandium-44, and lutetium-177) was systematically investigated. Various binary water (H2O)/organic solvent mixtures allowed the radiolabeling of DOTA at a significantly lower temperature than 95 °C, which is relevant for the labeling of sensitive biological molecules. Simultaneously, much lower amounts of the chelators were required. This strategy may have a fundamental impact on the formulation of trivalent radiometal-based radiopharmaceuticals. The equilibrium properties and formation kinetics of [M(DOTA)]- (MIII= GaIII, CeIII, EuIII, YIII, and LuIII) complexes were investigated in H2O/EtOH mixtures (up to 70 vol % EtOH). The protonation constants of DOTA were determined by pH potentiometry in H2O/EtOH mixtures (0-70 vol % EtOH, 0.15 M NaCl, 25 °C). The log K1H and log K2H values associated with protonation of the ring N atoms decreased with an increase of the EtOH content. The formation rates of [M(DOTA)]- complexes increase with an increase of the pH and [EtOH]. Complexation occurs through rapid formation of the diprotonated [M(H2DOTA)]+ intermediates, which are in equilibrium with the kinetically active monoprotonated [M(HDOTA)] intermediates. The rate-controlling step is deprotonation (and rearrangement) of the monoprotonated intermediate, which occurs through H2O (*M(HL) kH2O) and OH- (*M(HL) kOH) assisted reaction pathways. The rate constants are essentially independent of the EtOH concentration, but the M(HL) kH2O values increase from CeIII to LuIII. However, the log KM(HL)H protonation constants, analogous to the log KH2 value, decrease with increasing [EtOH], which increases the concentration of the monoprotonated M(HDOTA) intermediate and accelerates formation of the final complexes. The overall rates of complex formation calculated by the obtained rate constants at different EtOH concentrations show a trend similar to that of the complexation rates determined with the use of radioactive isotopes.

Effect of organic co-solvents in the evaluation of the hydroxyl radical scavenging activity by the 2-deoxyribose degradation assay: The paradigmatic case of α-lipoic acid

The 2-deoxyribose degradation assay (2-DR assay) is an in vitro method broadly used for evaluating the scavenging activity against the hydroxyl radical (HO). One of the major drawbacks of the assay, however, is that only water soluble compounds can be tested for their radical-scavenging activity. Lipoic acid (LA) is an excellent scavenger of HO but it exhibits a low solubility in the aqueous milieu of the 2-DR assay and a high tendency to polymerize under a variety of conditions. We used LA as a paradigmatic substrate to evaluate the effect of several organic co-solvents in increasing its solubility. Most of these solvents, however, demonstrated to be potent scavengers of HO making their use in the 2-DR assay improper. On the other hand, acetonitrile showed a remarkably low reactivity toward HO (rate constant ~8.7×106M−1s−1) which allowed us to use it as a co-solvent in the preparation of stock solutions of LA ~5mM. We therefore evaluated the radical-scavenging activity of LA by the 2-DR assay in a relatively large range of concentrations, 1–200μM. We found that the rate constant for LA+HO is diffusion-controlled (~1×1010M−1s−1 in water at 25°C) and uninfluenced by the presence of small quantities of acetonitrile. Therefore, the use of acetonitrile in the 2-DR assay does not interfere with the test and may increase the solubility of the radical scavengers.

Organic co‐solvents affect activity, stability and enantioselectivity of haloalkane dehalogenases

Haloalkane dehalogenases are microbial enzymes with a wide range of biotechnological applications, including biocatalysis. The use of organic co-solvents to solubilize their hydrophobic substrates is often necessary. In order to choose the most compatible co-solvent, the effects of 14 co-solvents on activity, stability and enantioselectivity of three model enzymes, DbjA, DhaA, and LinB, were evaluated. All co-solvents caused at high concentration loss of activity and conformational changes. The highest inactivation was induced by tetrahydrofuran, while more hydrophilic co-solvents, such as ethylene glycol and dimethyl sulfoxide, were better tolerated. The effects of co-solvents at low concentration were different for each enzyme-solvent pair. An increase in DbjA activity was induced by the majority of organic co-solvents tested, while activities of DhaA and LinB decreased at comparable concentrations of the same co-solvent. Moreover, a high increase of DbjA enantioselectivity was observed. Ethylene glycol and 1,4-dioxane were shown to have the most positive impact on the enantioselectivity. The favorable influence of these co-solvents on both activity and enantioselectivity makes DbjA suitable for biocatalytic applications. This study represents the first investigation of the effects of organic co-solvents on the biocatalytic performance of haloalkane dehalogenases and will pave the way for their broader use in industrial processes.

The role of active-site Phe87 in modulating the organic co-solvent tolerance of cytochrome P450 BM3 monooxygenase.

Understanding the effects of organic co-solvents on protein structure and function is pivotal to engineering enzymes for biotransformation in non-aqueous solvents. The effects of DMSO on the catalytic activity of cytochrome P450 BM3 have previously been investigated and the importance of Phe87 in its organic co-solvent tolerance was identified. To probe the DMSO inactivation mechanism and the functional role of Phe87 in modulating the organic co-solvent tolerance of P450 BM3, the haem domain (Thr1-Leu455) of the F87A variant was cocrystallized in the presence of 14%(v/v) and 28%(v/v) DMSO. At both DMSO concentrations the protein retained the canonical structure of the P450 haem domain without any sign of partial or global unfolding. Interestingly, a DMSO molecule was found in the active site of both structures, with its O atom pointing towards the haem iron. The orientation of the DMSO molecule indicated a dynamic coordination process that was in competition with the active-site water molecule. The ability of the DMSO molecule to coordinate the haem iron is plausibly the main reason why P450 BM3 is inactivated at elevated DMSO concentrations. The data allowed an interesting comparison with the wild-type structures reported previously. A DMSO molecule was found when the wild-type protein was placed in 28%(v/v) DMSO, in which the DMSO molecule coordinated the haem iron directly via its S atom. Intriguingly, no DMSO molecule was observed at 14%(v/v) DMSO for the wild-type structure. These results suggested that the bulky phenyl side chain of Phe87 protects the haem from being accessed by the DMSO molecule and explains the higher tolerance of the wild-type enzyme towards organic co-solvents compared with its F87A variant.

Effect of organic co-solvents on the solvation enthalpies of amino acids and dipeptides in mixed aqueous solutions

Transition enthalpies (ΔtrHo) of substances from water to binary solutions were calculated at 298.15 K on the basis of standard dissolution enthalpies (ΔsolHo) for six amino acids and five dipeptides in the mixtures of water with organic solvents of various chemical natures. The enthalpy pair coefficients of interaction hxy for biomolecules with organic component of mixture were estimated within the formalism of the McMillan-Mayer theory. The change in the character of the interaction of the components of solution was demonstrated in dependence on the physicochemical properties of the solvent and nature of the side radical of the dissolved bioorganic substance. Quantitative estimation of the type of interaction of the substance with the solvent was performed on the basis of correlation ratios relating the enthalpy characteristics of bioorganic substances to properties of organic cosolvents. It was shown that in the solutions under study, the effects of both the specific (mainly electron donor) and non-specific solvation of amino acids and peptides are observed.

The role of the medium on the acid dissociation constants of some azo dyes in view of experimental and theoretical data

In this study, the p K a values of some azo dyes derived from cyclohexane-1,3-dione in different organic solvent + water mixtures have been determined spectrophotometrically. The organic solvents used are ethanol, acetone and N, N-dimethylformamide (DMF). Thus, the nature and the proportion of the organic cosolvent effects as well as the molecular structure on acidity constants were evaluated. Furthermore, the proton-donating ability of N 10H reflected by thermodynamic parameters – Δ f ,298 H o, Δ 298 S o and Δ f ,298 G o – for compounds 1– 4 has been estimated using AM1and PM6 methods in the gas and aqueous phases. The data obtained provides a complete and accurate picture of the acid–base properties of the compounds under study. The p K a values predicted in aqueous phase by the previous methods were compared with the experimental values and the best agreement with the experimental data was obtained by AM1.

Solvatochromic Studies of Ionic Liquid/Organic Mixtures

Room-temperature ionic liquids (ILs) have potential for many different applications, including catalysis and synthesis. Organics are often present during IL applications; therefore, a more fundamental understanding of the interactions between IL and organics is necessary. A systematic study of the effects of organic cosolvents, cations, and anions on the solvent strength of IL/organic mixtures will allow for a greater understanding and potential for tuning of ILs for specific purposes. Solvent strength is commonly quantified using spectroscopic probes. We report the solvent strength of IL/organic mixtures using Reichardt's dyes 30 and 33, Kamlet-Taft parameters, and phenol blue. The results show that the polarity of ILs is largely unaffected by the organic cosolvent; that is, the probes are preferentially solvated by the ILs. However, more specific solvation forces, such as hydrogen bonding, can be influenced indirectly by the strength of the anion/cation interaction, giving counterintuitive results.

Effect of organic cosolvents on the free solution mobility of curved and normal DNA molecules

The free solution mobilities of curved and normal 199-bp DNA fragments have been measured in buffer solutions containing various quantities of the organic cosolvents methanol, ethanol, 2-propanol, 2-methyl-2,4-pentanediol (MPD), ethylene glycol, and ACN, using CE. The curved fragment, taken from the VP1 gene of SV40, contains five unevenly spaced A- and T-tracts in a centrally located "curvature module"; the A- and T-tracts have been mutated to other sequences in the normal 199-bp fragment. The free solution mobility of the curved 199-bp fragment is significantly lower than that of its normal counterpart in aqueous solutions [Stellwagen, E., Lu, Y. J., Stellwagen, N. C., Nucleic Acids Res. 2005, 33, 4425-4432]. The mobilities of both the curved and normal fragments decrease with increasing cosolvent concentration, due to the effect of the cosolvent on the viscosity and dielectric constant of the solution. The mobility differences between the curved and normal 199-bp fragments and the mobility ratios decrease approximately linearly with the increasing mole fraction of cosolvent in the solution. Hence, MPD and other organic cosolvents affect DNA electrophoretic mobility by a common mechanism, most likely the preferential hydration of the DNA surface that occurs in aqueous cosolvents. The gradual loss of the anomalously slow mobility of the curved 199-bp fragment with increasing cosolvent concentration, combined with other data in the literature, suggests that preferential hydration gradually widens the narrow A-tract minor groove, releasing site-bound counterions in the minor groove and shifting the conformation toward that of normal DNA.

Effect of organic cosolvent on kinetic resolution of tert-leucine by penicillin G acylase from Kluyvera citrophila

Penicillin G acylase (PGA) from Kluyvera citrophila immobilized on Amberzyml was used for enantioselective hydrolysis of N-phenylacetylated-DL-tert-leucine (N-Phac-DL-Tle) to produce L-tert-leucine (L-Tle). The effects of various organic cosolvents on hydrolysis of N-Phac-DL-Tle have been investigated in aqueous-cosolvent medium. It was founded that the rate of PGA-catalyzed reaction was significantly affected by the presence of 2% (v/v) organic cosolvent concentration. The initial rate fell with increasing logP of the cosolvent, but for logP values less than -0.24 the rate was faster than in purely aqueous medium. Additionally, the relative rate increases with the increase of dielectric constant (epsilon) of organic cosolvents. The yields of L-Tle in all aqueous-cosolvent systems were above 95% with the enantiomeric excess (ee) of >99%.

Combined Effects of Aging and Cosolvents on Sequestration of Phenanthrene in Soils

The objective of this study is to investigate the effect of organic cosolvents on the extractability of hydrophobic organic compounds (HOCs) from soils after defined aging periods following HOC contamination. Phenanthrene was used as the representative HOC. Two soils with organic matter contents 2.9 and 6.5%, respectively, were investigated. The soils were spiked with phenanthrene, then saturated in water or mixtures of water and methanol, and aged for up to 422 days. After freeze drying, the extent of phenanthrene release was measured using a mild extraction process. The results show that as aging period increases, phenanthrene removal from the soils becomes more difficult. The amount of easily extractable phenanthrene tended to increase when more methanol existed in the pore fluid during aging, but the difference largely diminished after about 400 days. At the early stage of aging, extraction of phenanthrene from the soil with lower organic matter content tended to be less difficult compared with that from the soil containing more organic matter. The opposite appeared to be true when the aging time was longer than 200 days. From the results, we propose that a shift in the predominant sequestration mechanisms occurred after a certain period of time, in which hydrophobic interactions between HOCs and organic matter gradually yield to physical trapping of the sorbate molecule in the meso- and micropores of the soil particles.

Peroxidase-catalyzed synthesis of neolignan and its anti-inflammatory activity

Different peroxidases were used to catalyze the synthesis of neolignan. Horseradish peroxidase (type I, Sigma) was employed successfully to catalyze the formation of magnolol by the phenolic oxidative coupling of allyphenol. The effects of organic co-solvents, pH, addition rate of H 2O 2, and the ratio of enzyme/substrate on the yields of dimer were studied. After the peroxidase-catalyzed reaction was performed, different neolignans were isolated and identified as magnolol ( 3), the trimeric ortho– ortho-coupled product dunnianol ( 4), the ortho- O-coupled product isomagnolol ( 5), and the Pummerer's ketone derivative ( 6). The inhibitory activities of magnolol against cyclo-oxygenase and lipoxygenase were also reported.

Effect of Organic Cosolvents on the Solubility of Ionic Liquids in Supercritical CO2

The solubilities of ionic liquids (ILs) 1-butyl-3- methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]) in supercritical (sc) CO2 with and without organic cosolvents were determined at 40.0 °C and 15.0 MPa. The mole fraction of a cosolvent was up to 0.3. The solubilities of the ILs in sc CO2 + polar cosolvent mixtures increased dramatically as the cosolvent concentration exceeded 10 mol %, but the solubility was extremely low when the concentration of the cosolvent was lower than 10 mol %. The effect of a cosolvent on the solubility of the ILs in sc CO2 depends mainly on its polarity. The stronger the polarity of a cosolvent, the larger the effect. The ability of the mixed cosolvent to enhance the solubility is intermediate between the two pure cosolvents.

Medium Effect on the Apparent Dissociation Constants of Guanine, Thymine, Uracil, Hypoxanthine, and Cytosine in Various Hydroorganic Media

The apparent dissociation constants of the nucleobases guanine, thymine, uracil, hypoxanthine, and cytosine were determined at (25.0 ± 0.1) °C and I = 0.1 mol·dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol and ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide (DMF), dimethyl sulfoxide, acetone, and dioxane as hydrogen bond acceptor solvents. A computer program was used to refine the initial estimates of the apparent dissociation constants of the five purine and pyrimidine nucleobases. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents. The effects of organic cosolvents on the acid dissociation equilibria have been interpreted using the solvatochromic quantitative values of Kamlet−Taft hydrogen bond acidity and basicity (α, β) and dipolarity polarizability π* of the solvent. The free energy of transfer of the protons from wate...

Effects of ethylene glycol on the synthesis of ampicillin using immobilized penicillin G acylase

AbstractThe effects of organic cosolvents on the synthesis of ampicillin from phenylglycine methyl ester (PGME) and 6‐amino penicillanic acid (6‐APA) using immobilized Bacillus megaterium penicillin G acylase have been examined. Several cosolvents were tested for their influence on the enzyme in terms of enzyme stability and hydrophobicity. Among the cosolvents tested, ethylene glycol was found to increase the yield of ampicillin by 39–50%. The effects of ethylene glycol on the pKa of PGME, the hydrolysis of ampicillin and PGME, and synthetase/amidase and esterase/amidase ratios were also studied. Experimental data indicated that ethylene glycol inhibited more the hydrolysis of the ampicillin than the hydrolysis of the PGME and the synthetase/amidase ratio varied from 0.2 to 0.88 when the concentration (v/v) of the cosolvent increased from 0 to 40%. The enhancement of the synthesis yield was mainly caused by the reduction in the hydrolysis of acyl donor (PGME) and product (ampicillin) in the water–cosolvent system.© 2003 Society of Chemical Industry

Organic co-solvent effects on the bioconversion of (R)-(+)-limonene to (R)-(+)-α-terpineol

The effects of 22 organic solvents were tested on the bioconversion of (R)-(+)-limonene to (R)-(+)-α-terpineol by free and immobilized P. digitatum mycelia. Free cells showed the highest bioconversion activity in water-organic co-solvent single-phase systems. The relative activity increased 2·4 fold with dioctylphthalate (1·5%, v/v) and 2·2 fold with ethyl decanoate (1·5%, v/v). Immobilized cells showed the greatest bioconversion in detergent reversed micelle systems. When Tween 80 (0·1%) or Triton 100-X (0·1%) was added into an immobilized P. digitatum bioconversion system, the relative bioconversion activity increased 2 fold. Immobilization protected the fungal cells from the cytotoxic effects of organic solvents. Dioctylphthalate 1·5% to 2% (v/v) was the optimum concentration range for free cell bioconversion, and Tween 80 0·5% to 1% (v/v) was the optimum concentration range for immobilized cell bioconversion.