Enzymatic transesterification of steroid esters in organic solvents

A mild procedure for the conversion of steroid esters into the corresponding alcohols via lipase-catalyzed transesterification reaction in organic solvents is described. Aspects of stereoselectivity and regioselectivity of the reaction are noted.     

Modified enzymes for reactions in organic solvents

Recent studies on biocatalysis in water—organic solvent biphasic systems have shown that many enzymes retain their catalytic activities in the presence of high concentrations of organic solvents. However, not all enzymes are organic solvent tolerant, and most have limited and selective tolerance to particular organic solvents. Protein modification or protein tailoring is an approach to alter the characteristics of enzymes, including solubility in organic solvents. Particular amino acids may play pivotal roles in the catalytic ability of the protein. Attaching soluble modifiers to the protein molecule may alter its conformation and the overall polarity of the molecule. Enzymes, in particular lipases, have been chemically modified by attachment of aldehydes, polyethylene glycols, and imidoesters. These modifications alter the hydrophobicity and conformation of the enzymes, resulting in changes in the microenvironment of the enzymes. By these modifications, newly acquired properties such as enhancement of activity and stability and changes in specificity and solubility in organic solvents are obtained. Modified lipases were found to be more active and stable in organic solvents. The optimum water activity (a _w ) for reaction was also shifted by using modified enzymes. Changes in enantioselective behavior were also observed.     

Photochemical reactions of organomercury compounds in organic solvents

The quantum yields of photolysis of organomercury compounds in different organic solvents have been measured. It was shown that the quantum yields of photolysis of nitro derivatives of mercury compounds and the symmetric (methylnaphtyl)mercury compound are equal to unity. The photolysis of halo derivatives of benzylmercury proceeds with lower quantum yields as compared with photolysis of analogous dibenzylmercury derivatives. The quantum yields of photolysis of organomercury compounds are almost independent of the solvent.     

Flavone photoreactivity. UV-induced reactions in organic solvents and micellar systems

Flavonoid photochemistry is a subject of interest in studies dealing with the role of phenolic compounds as screening pigments in plants. In order to contribute to the understanding of the processes involved in the interaction between flavonoids and UV radiation, we have studied UV-induced flavone photodegradation in both organic solvents and micellar systems. The results obtained show that flavone photosensitivity depends on the characteristics of the reaction environment and is influenced by the medium polarity and the charges on the micellar surface. Qualitative and quantitative differences in the photodegradation products were demonstrated by high performance liquid chromatography (HPLC) analysis.     

Fluorometric assay protocol for protease-catalyzed transesterification reactions in organic solvents

A flourometric assay protocol for a subtilisin-catalyzed transesterification reaction in n-hexane has been developed. The method makes use of a Michael acceptor that forms a fluorescent adduct with thiophenol, one of the products generated in the transesterification reaction. The method may be employed for screening a biocatalyst useful for transesterification reactions in organic solvents and for optimizing the transesterification reaction conditions.     

Engineered phenylalanine dehydrogenase in organic solvents: homogeneous and biphasic enzymatic reactions

The use of engineered phenylalanine dehydrogenase N145A supported on Celite for the reductive amination of phenylpyruvic acid in homogeneous and biphasic aqueous-organic solvents is reported. The results indicate that the immobilised biocatalyst is remarkably robust, even in the presence of high concentrations of polar or non-polar organic solvents such as acetone, methanol, n-hexane, toluene and methylene chloride. Cofactor regeneration with alcohol dehydrogenase from Saccharomyces cerevisiae and ethanol was successfully explored. Application to the non-natural poorly water-soluble 2-oxo acid p-NO(2)-phenylpyruvic acid was successfully performed, resulting in the biocatalytic synthesis of p-NO(2)-phenylalanine. In all cases 100% stereoselectivity for the production of the amino acid was retained.     

DESs: Green solvents for transition metal catalyzed organic reactions

The recent development about using DESs as green solvents in transition metal catalyzed organic reactions was highlighted, and Au, Metal impregnated on magnetite, Pd, Ru catalyzed organic reactions proceeded smoothly in DESs and gave corresponding products in reasonable yields. And in some cases, the catalytic systems could be recycled up to several times.     

DESs: Green solvents for transition metal catalyzed organic reactions

In this review, the recent development about using DESs as green solvents in transition metal catalyzed organic reactions was highlighted. Firstly, the development of DESs was simply introduced. After presenting the advantages of DESs, transition metals catalyzed organic reactions using DESs as green solvents were classified and introduced in detail. Different transition metals such as Au, metal impregnated on magnetite, Pd and Ru catalyzed organic reactions proceeded smoothly in DESs and gave corresponding products in good yields. And in some cases, the catalytic systems could be recycled up to several times without any decrease in activity.     

Chain-growth polycondensation for well-defined condensation polymers and polymer architecture

The historical development of our research on polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth polycondensation") for well-defined condensation polymers is described. We first studied polycondensation in which change of the substituent effect induced by bond formation drove the reactivity of the polymer end group higher than that of the monomer. In this approach, well-defined aromatic polyamides, polyesters, polyethers, and poly(ether sulfone)s were obtained. The second approach was the study of the phase-transfer polymerization of a solid monomer dispersed in an organic solvent. In this type of polymerization, the solid monomer was physically unable to react with another monomer and was carried with the phase transfer catalyst into the solution phase where it reacted with an initiator and the polymer end group in the solvent in a chain polymerization manner. We also found catalyst-transfer polycondensation as a third approach to chain-growth polycondensation. In the Ni-catalyzed polycondensation of 2-bromo-5-chloromagnesiothiophenes, the Ni catalyst transferred to the polymer end group, and a coupling reaction occurred there to yield a well-defined polythiophene. This chain-growth polycondensation was applied to the synthesis of condensation polymer architectures such as block copolymers, star polymers, graft copolymers, and so on.     

Enzymatic methods for the preparation of enantiopure malic and aspartic acid derivatives in organic solvents

The kinetic resolution of malic and aspartic acid diesters as well as of its N-butanoyl dimethyl ester by highly regioselective lipases and acylase I enzymes were studied. Candida antarctica lipase A on Celite catalyzed the enantioselective acylation of the hydroxyl and amino groups. Acylase I from Aspergillus melleus and Candida antarctica lipase B catalyzed the enantioselective alcoholyses of the ester groups at the α- and β-positions, respectively.     

Metal ions dramatically enhance the enantioselectivity for lipase-catalysed reactions in organic solvents

We propose a simple and a powerful method to enhance the enantioselectivity for lipase-catalysed transformations in organic solvents by an addition of metal ion-containing water to the reaction mixture. In this paper, various metal ions such as LiCl or MgCl2 are tested to improve the enantioselectivity for the model reactions. The enantioselectivities obtained are dramatically enhanced, the E values of which are about 100-fold as compared with the ordinary conditions without a metal ion, for example, E = 200 by addition of LiCl. Furthermore, lowering the reaction temperature led to an almost perfect enantioselectivity of lipase in the presence of a metal ion, for example, E = 1,300 by addition of LiCl. Also, a mechanism for the drastic enhancement by metal ions is discussed briefly on the basis of the EPR spectroscopic study and the initial rate for each enantiomer of the substrate.     

Synthesis of methylated resveratrol and analogues by Heck reactions in organic and aqueous solvents

The Heck reaction under phosphane free conditions using oxime-derived palladacycles or Pd(OAc)₂ as catalysts is a general methodology for the synthesis of methoxylated (E)-stilbene derivatives. Couplings can be performed either with (dicyclohexyl)methylamine as base and TBAB in aqueous DMA or in neat water and with Et₃N as base in DMA in air and under thermal and microwave conditions. The arylation of different styrenes are performed with 3,5-dimethoxyiodobenzene to afford a series of important biologically active (E)-stilbene derivatives containing the 3,5-dimethoxyphenyl moiety, including resveratrol, piceatannol and pinosilvine, which are efficiently prepared with high regioselectivity and total stereoselectivity (TON up to 10⁴).     

Using geminal dicationic ionic liquids as solvents for high-temperature organic reactions

[reaction: see text] Several organic reactions conducted at high temperatures, including the isomerization reaction, the Claisen rearrangement, and the Diels-Alder reaction, were investigated in three geminal dicationic ionic liquids with high thermal stability. High to moderate yields of the products for most entries were obtained. Advantages of these approaches are discussed. These ionic liquids were shown to be recyclable. The utility of these ionic liquid solvents for high-temperature organic reactions was demonstrated.     

Enzymatic synthesis of butyryl-rutin ester in organic solvents and its cytogenetic effects in mammalian cells in culture

Enzymic acylation of a flavonoid, rutin, with trichloroethylbutyrate (TCEB) has been performed by subtilisin protease in anhydrous pyridine solution. The addition of a hydrophobic compound on rutin is expected to change the hydrophilic/hydrophobic balance of the molecule, giving new properties to this compound. This work aimed at investigating the various cytological properties of the rutin-ester and compared them with those of the native molecule. No difference in the levels of sister chromosomes exchange (SCE) between rutin and rutin-ester treated cells at doses varying from 25 to 200 μg/mL was found. On the contrary impressive difference in the induced frequency of micronuclei (MN) between rutin and rutin ester treated cells was observed, for example, at a dose of 100 μg/mL of rutin were 3.5% MN counted, whereas for a similar dose treatment with rutin-ester a frequency of 8% of MN was found. The fact that rutin-ester is causing significantly higher levels of MN than the rutin alone can be considered as a manifestation of a higher action of the agent on the chromosome owing to its easier penetration in to the cell after its esterification.     

Unexpected reactions of dichloro(ethyl)silane with DMSO in organic solvents

The effect of the solvent nature on the composition of the products formed upon the reaction between EtSi(H)Cl₂ and DMSO (molar ratio 1: 1, 0 °C) was revealed. This reaction in non-polar and low polar solvents (toluene, chloroform) gives oligoethyl(hydro)cyclo-siloxanes ((EtSi(H)O) _n , n = 3—8) as the major products in the yields up to 77%. In MeCN, oligoethyl(hydro)cyclosiloxanes are formed along with cyclic monochlorinated siloxanes ((EtSi(H)O) _n (EtSi(Cl)O), n = 2—7) in a ratio of ~7: 3 (68: 29 wt.%). In excess diethyl ether, the overall yield of oligoethyl(hydro)cyclosiloxanes does not exceed 25% and the major products are linear α,ω-diethoxyoligoethyl(hydro)siloxanes (EtO(EtSi(H)O) _n Et, n = 2—7) formed in 70—75% yields. A plausible reaction mechanism leading to the final products was suggested. Apparently, the reaction proceeds via ethyl(hydro)-and chloro(ethyl)silanones as intermediates.     

Demixing instability in coil-rod blends undergoing polycondensation reactions

The authors extend their earlier work on the stability of a reacting binary polymer blend with respect to demixing [D. J. Read, Macromolecules 31, 899 (1998); P. I. C. Teixeira et al., Macromolecules 33, 387 (2000)] to the case where one of the polymers is rod-like and may order nematically. As before, the authors combine the random phase approximation for the free energy with a Markov chain model for the chemistry to obtain the spinodal as a function of the relevant degrees of reaction. These are then calculated by assuming a simple second-order chemical kinetics. Results are presented, for linear systems, which illustrate the effects of varying the proportion of coils and rods, their relative sizes, and the strength of the nematic interaction between the rods.     

Recent progress on immobilization of enzymes on molecular sieves for reactions in organic solvents

Enzymes exhibit high selectivity and reactivity under normal conditions but are sensitive to denaturation or inactivation by pH and temperature extremes, organic solvents, and detergents. To extend the use of these biocatalysts for practical applications, the technology of immobilization of enzymes on suitable supports was developed. Recently, these immobilized biomolecules have been widely used and a variety of immobilization supports have been studied. The majority of these supports cover diverse kinds of materials such as natural or synthetic polyhydroxylic matrives, porous in organic carriers, and all kinds of functional polymers. Microporous molecular sieve, zeolite, has attracted extensive interest in research because of its distinctive physical properties and geochemistry. Recently, with the discovery of a new family of mesoporous molecular sieves, MCM-41, this series of materials shows great potential for various applications. Molecular sieves involve such a series of materials that can discriminate between molecules, particularly on the basis of size. As support materials, they offer interesting properties, such as high surface areas, hydrophobic or hydrophilic behavior, and electrostatic interaction, as well as mechanical and chemical resistance, making them attractive for enzyme immobilization. In this article, different types of molecular sieves used in different immobilization methods including physical adsorption on zeolite, entrapment in mesoporous and macroporous MCM series, as well as chemically covalent binding to functionalized molecular sieves are reviewed. Key factors affecting the application of this biotechnology are discussed systematically, and immobilization mechanisms combined with newly developed techniques to elucidate the interactions between matrixes and enzyme molecules are also introduced.     

Inorganic polarography in organic solvents

A review of inorganic polarography in organic solvents is presented.     

Asphaltene aggregation in organic solvents

Asphaltenic solids formed in the Rangely field in the course of a carbon dioxide flood and heptane insolubles in the oil from the same field were used in this study. Four different solvents were used to dissolve the asphaltenes. Near-infrared (NIR) spectroscopy was used to determine the onset of asphaltene precipitation by heptane titration. When the onset values were plotted versus asphaltene concentrations, distinct break points (called critical aggregation concentrations (CAC) in this paper) were observed. CACs for the field asphaltenes dissolved in toluene, trichloroethylene, tetrahydrofuran, and pyridine occurred at concentrations of 3.0, 3.7, 5.0, and 8.2 g/l, respectively. CACs are observed at similar concentrations as critical micelle concentrations (CMC) for the asphaltenes in the solvents employed and can be interpreted to be the points at which rates of asphaltene aggregations change. CMC values of asphaltenes determined from surface tension measurements (in pyridine and TCE) were slightly higher than the CAC values measured by NIR onset measurements. The CAC for heptane-insoluble asphaltenes in toluene was 3.1 g/l. Thermal gravimetric analysis (TGA) and elemental compositions of the two asphaltenes showed that the H/C ratio of the heptane-insoluble asphaltenes was higher and molecular weight (measured by vapor pressure osmometry) was lower.