Anhydrous Organic Solvents Research Articles

Highly Active Catalyst for the Heterogeneous Suzuki—Miyaura Reaction: Assembled Complex of Palladium and Non‐Cross‐Linked Amphiphilic Polymer.

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Structural Effects of Amphiphiles on Candida rugosa Lipase Activation by Freeze-Drying of Aqueous Solution of Enzyme and Amphiphile

Lipases co-lyophilized with water-soluble gemini-type amphiphiles were found to have high enzyme activity in nonaqueous media without washing out of the amphiphile with anhydrous organic solvent. In this study, we obtained freeze-dried complexes of Candida rugosa lipase (CRL) with six water-soluble twin glusitol-headed amphiphiles bearing different types of hydrophobic tails, including newly synthesized ones, and their transesterification activity in organic solvent was evaluated. The results indicate that the increased enzyme activity upon CRL modification at 200 molar ratio of amphiphile/CRL, which are restricted to the ester-containing amphiphiles, is probably due to the surface activation by the interaction between ester-carbonyl of the amphiphile and phenyl group of the tyrosine residue situated on the surface of the lid in the CRL.

Highly active catalyst for the heterogeneous Suzuki-Miyaura reaction: assembled complex of palladium and non-cross-linked amphiphilic polymer.

An assembled insoluble catalyst, PdAS, prepared from palladium ((NH4)2PdCl4 (1)) and non-cross-linked amphiphilic copolymer poly(N-isopropylacrylamide-co-4-diphenylstyrylphosphine) (2) was developed. It was found that PdAS is an excellent catalyst for the Suzuki-Miyaura reaction on three points: (1) The use of 8 x 10(-7) to 5 x 10(-4) mol equiv of PdAS afforded the coupling products efficiently after easy workup, with the turnover number reaching up to 1,250,000. (2) The catalyst was reusable many times without loss of catalytic activity. (3) PdAS showed good stability in any reaction medium (i.e., water or aqueous or anhydrous organic solvents). Analytical study of PdAS indicates that the phosphines in 2 coordinate to palladium to form PdCl2(PPh2Ar)2 species.

Lipase-Catalyzed Synthesis of Precursor Dipeptides of RGD in Aqueous Water-Miscible Organic Solvents

PPL-catalyzed synthesis of the precursor dipeptides of RGD as a cellular adhesion factor, Benzyl-Arg-Gly-NH2 and CBZ-Gly-Asp-NH2, was conducted in water-organic cosolvents systems. Five water-miscible organic solvents, which have some advantage over the water-immiscible organic solvent systems or the anhydrous organic solvent systems used often in protease-catalyzed synthesis of a peptide bond, were tested. The reaction condition of PPL-catalyzed synthesis of the dipeptides was optimized by examining the main factors affecting the product yield. The optimal reaction condition for the synthesis of Benzyl-Arg-Gly-NH2 was set up as pH 8.0, 15°C in 40% MeOH for 10 h with the maximum yield of 73.6%. The optimum condition for the synthesis of CBZ-Gly-Asp-NH2 was pH 7.0, 15°C in 50% MeOH for 10 h with the maximum yield of 67.0%.

Removal of dibenzothiophene and its oxidized product in anhydrous water-immiscible organic solvents by immobilized cytochrome c

In various anhydrous water-immiscible organic solvents, dibenzothiophene (DBT) was removed by more than 80% by cumene hydroperoxide (α,α-dimethylbenzyl hydroperoxide) catalyzed by the immobilized cytochrome c on Celite. DBT-sulfone, the oxidation product of DBT, strongly adsorbed on Celite in highly hydrophobic organic solvents such as hexadecane, decane and n-octane. The adsorbed DBT-sulfone was desorbed from Celite by a simple washing of the Celite with a less hydrophobic solvent such as octanol.

Anodic dissolution of silicon monocrystals in anhydrous organic solutions of chlorides

The electrochemical investigations of p- and n-silicon monocrystals were performed in anhydrous organic solutions of LiClO 4, LiCl and HCl to examine the possibility of etching and passivation of silicon semiconductors. The results obtained by means of linear sweep voltammetry (LSV), potentiostatic and galvanostatic transient technique, as well as XPS surface analysis allow us to give an explanation of the mechanism of silicon dissolution in these media. Silicon dissolves in anhydrous organic solvents (methanol, N, N-dimethyloformamide, formamide) which contain chloride ions according to the consecutive two-step mechanism. The Si(II) ad intermediate inhibits the anodic dissolution at low overpotentials. The presence of this intermediate was confirmed by means of XPS measurements on potentiostatically etched surface. The increase in chloride concentration in organic solvents stimulates desorption of the intermediate and therefore increases the rate of surface etching. The best results in anodic etching of silicon monocrystals have been obtained in anhydrous HCl solutions. Microscopic observations of surface morphology of Si monocrystals after etching show anisotropy of anodic dissolution.

Small water amounts increase the catalytic behaviour of polar organic solvents pre-treated Candida rugosa lipase

Following a simple and quick treatment based on dissolving the crude lipase of Candida rugosa in different percentages (v/v) of several polar organic solvents (methanol, ethanol, acetone, 1-propanol, 2-propanol, 1-butanol and 2-butanol), and a further dialysis, different preparations with enhanced activity and thermal stability were obtained. This improved catalytic behaviour was observed in aqueous media (more efficient triglyceride hydrolysis) as well as in anhydrous organic solvents (better enantioselectivity and/or yield in the esterification of R- and S-ketoprofen).Combination of this treatment with organic solvents with a correct control of water activity in the reaction media allowed a much better catalytic behaviour, dramatically increasing the reaction yield and the enantiodiscrimination ability in the esterification of S-ketoprofen vs. the R counterpart.

Multiselective enzymatic reactions for the synthesis of protected homochiral cis- and trans-1,3,5-cyclohexanetriols

For the synthesis of the potentially antipsoriatic vitamin D derivative 3 (Ro 65-2299) an efficient and multiselective enzymatic step had been developed in which the easily accessible trans-1,3,5-triacetoxy-cyclohexane 5 was selectively monohydrolyzed in the presence of the cis-isomer 8 to give (1 R,3 R)-1,3-diacetoxy-5-hydroxy-cyclohexane 6 in high enantiomeric excess (>99%) and yield (84%). Furthermore, for the synthesis of the enantiomer of 3, a simple and efficient enzymatic procedure for the asymmetric acetylation of cis-1,5-dihydroxy-3-( tert-butyldimethylsilanoxy)-cyclohexane 10 in an anhydrous organic solvent providing (1 R,3 S,5 S)-1-acetoxy-3-hydroxy-5-( tert-butyldimethylsilanoxy)-cyclohexane 11 in >99% ee and quantitative yield is described.

N- and p-Doped Poly(3,4-ethylenedioxythiophene): Two Electronically Conducting States of the Polymer

Neutral poly(3,4-ethylenedioxythiophene) (PEDOT) thin films can be switched to an electronically conducting form either by oxidation (p-doping) or reduction (n-doping) in anhydrous organic solvents. The maximum attainable n-conductivity is ca. 1% of the maximum p-conductivity. However, based on spectroelectrochemical and in-situ conductance measurements, the p-conductivity regime can be divided into two domains, in which either positive polarons or bipolarons and free carriers are the major charge carriers. In the n-conductivity regime, voltammetric, spectral, and conductance data suggest only the generation of negative polaron-type carriers. These results imply that the conductivity due to positive or negative polarons is of the same order of magnitude and that the higher maximum p-conductivity may be attributed to the generation of other charge carriers in the highly stable oxidized PEDOT films. The reduced form is not stable even in an extremely dry oxygen-free environment, which severely hampers the u...

Regioselective lipase-catalysed γ-monoamidation of d-glutamic acid diesters: effect of the N-protecting group

N-Blocked- d-glutamic acid diethylesters are γ-regioselectively amidated in a reaction catalysed by Candida antarctica lipase B, carried out in an anhydrous organic solvent. The ratio of γ:α-monoamides, as a measure of regioselectivity, depends on the N-protecting group present in the substrate. In the examples reported in this work, we have found that γ:α ranges from about four ( N-group=Cbz) to 35 ( N-group=isobutyryl). No diamides were detected.

Surfactant–protease complex as a novel biocatalyst for peptide synthesis in hydrophilic organic solvents☆

The peptide synthesis from N-acetyl- l-phenylalanine ethyl ester with alaninamide catalyzed by a surfactant-protease complex has been performed in anhydrous hydrophilic organic solvents. Proteases derived from various sources were converted to surfactant-coated complexes with a nonionic surfactant. The surfactant-subtilisin Carlsberg (STC) complex had a higher enzymatic activity than the other protease complexes and the initial reaction rate in tert-amyl alcohol was 26-fold that of STC lyophilized from an optimum aqueous buffer solution. Native STC hardly catalyzed the same reaction. The addition of water to the reaction medium activated the lyophilized STC, however, the reaction rate was much lower than that of the STC complex, and a hydrolysis reaction preferentially proceeded. The STC complex exhibited a high catalytic activity in hydrophilic organic solvents (e.g. tertiary alcohol). The addition of dimethylformamide as a cosolvent improved the solubility of amino acid amides and further activated the STC complex due to the water mimicking effect. When hydrophilic amino acid amides were employed as an acyl acceptor, the peptide formation proceeded efficiently compared to that using hydrophobic substrates. The surfactant-STC complex is a powerful biocatalyst for peptide synthesis because the STC complexes display a high catalytic activity in anhydrous hydrophilic organic solvents and did not require the excess amount of water. Thus the side (hydrolysis) reaction is effectively suppressed and the yield in the dipeptide formation is considerably high.

Phospholipase D-catalyzed transphosphatidylation in anhydrous organic solvents.

A new reaction system suitable for phospholipase D (PLD)-catalyzed transphosphatidylation of alcohols with phosphatidylcholine under anhydrous conditions is reported. The key innovation of the reaction system is a cation-exchange resin serving as a scavenger for choline that forms as a byproduct in the transphosphatidylation reaction. Due to the absence of water in this system, the reaction path dramatically shifts in favor of the target transphosphatidylated product, whereas the undesirable side hydrolysis of phosphatidylcholine is completely suppressed, in contrast to commonly used biphasic water-organic systems. In addition, a salt activation technique is successfully applied to increase the catalytic activity of PLD in this anhydrous system. The new reaction system is successfully used for transphosphatidylation of a wide range of primary, secondary, and aromatic alcohols catalyzed by PLD from Streptomyces sp.

Candida antarctica lipase B catalysed amidation of pyroglutamic acid derivatives. A reaction survey

Pyroglutamic acid esters, both ( S)- and ( R)-enantiomers, have been studied as substrates of the Candida antarctica lipase B catalyzed amidation in anhydrous organic solvents. They behaved as very good substrates when primary amines or ammonia were used as nucleophiles, affording the corresponding secondary and primary amides, respectively, but did not react with secondary amines. The reaction was enantioselective for the ( R)-enantiomer of chiral amines although little kinetic difference was observed between ( S)- and ( R)-pyroglutamates as acyl donors. As an example of an infrequent reaction, free ( S)-pyroglutamic acid may also act as a substrate of the reaction, but is much less reactive than its esters.

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

Solutions of sodium salicylate in anhydrous polar solvents exhibit a weak, temperature-dependent absorption band (λmax ≈ 325 nm) lying in the Stokes gap between the main absorption (296 nm) and the fluorescence band (396 nm, acetonitrile). This weak, longer wavelength absorption band is hardly observable in aqueous solution, but its intensity increases with temperature and increases with polarity in anhydrous organic solvents in the order of ethanol < acetonitrile < dimethyl sulfoxide at room temperature. After correction for solvent thermal contraction, the temperature-dependent absorption spectrum of salicylate in acetonitrile solutions reveals a clear isosbestic point (e310 = 2000 M-1 cm-1) characteristic of an equilibrium between two salicylate species with band-maximum extinction coefficients of e325 = 3400 M-1 cm-1 and e296 = 3586 M-1 cm-1. In acetonitrile at room temperature (298 K) the concentration equilibrium constant (minor/major) for the interconversion reaction between the two species is K298...

Studies on synthesis of short chain alkyl esters catalyzed by goat pregastric lipase

Goat pregastric lipase, in the form of a suspended enzyme powder, was found to be active in catalyzing the synthesis of alkyl esters in anhydrous organic solvents. The rate of catalyzed synthesis of esters was very dependent on the solvent medium, and maximum activity was found when a hydrocarbon was used as the solvent. The optimal temperature for the catalyzed synthesis ranged from 30 to 40°C and the maximal temperature was 35°C for the synthesis of butyl caproate in isooctane. The selectivity for the carbon-chain length of the fatty acid by the lipase was similar to that seen in hydrolysis reactions in aqueous solution, and the optimal rate of synthesis of alkyl esters was found for synthesis of the esters which had 8 or 10 carbons in the alkyl moieties from the two individual substrates. The rate of synthesis was also dependent on the water content in the system, with maximum activity occurring at 1% w/w water in isooctane.

Phototransformations of non‐toxic antioxidants, the derivatives of 1,2‐dihydroquinolines, in homogeneous and micellar solutions

Reactions of transient species photogenerated from 6‐R‐2,2,4‐trimethyl‐1,2‐dihydroquinolines (TMDQ) are very sensitive to medium variation. In anhydrous organic solvents, aminyl radicals were generated. They decay in the reaction of dimerization with the second‐order rate constant decreasing in a row heptane&gt;benzene&gt;2‐propanol. When passing from organic solvents to water, methanol, and water‐alcohol solutions, the kinetics and the direction of the reaction crucially change. As a result of the photolysis, the product of the addition of a solvent to the double bond of heterocycle, 4‐hydroxy‐ or 4‐methoxy‐6‐R‐2,2,4‐ tetramethyl‐1,2,3,4‐tetrahydroquinoline is formed in water and methanol, respectively. The transformation is a complex reaction, and the formation of excited transient species is followed by a sequence of first‐order and pseudo‐first‐order reactions. Unlike the photolysis in anhydrous organic solvents, the reaction in water and methanol does not involve aminyl radicals. In aqueous solutions, the first‐order rate constants for the decay of transient species are higher in acidic and neutral solutions. At the pH close to pKa of the transient species, it drops, indicating that the neutral form is less reactive. The same product is formed over the whole range of pH. For the anionic surfactant (SDS) in acidic and alkaline solutions, the apparent rate constant in the micellar solutions is lower than that in the aqueous (negative micellar catalysis). At the medium pH, a positive micellar catalysis is observed, and the rate constant of the decay depends linearly on the concentration of TMDQ in the micelles, indicative of the direct reaction between TMDQ and the cationic transient species.

A novel lipolytic activity of Rhodotorula glutinis cells: Production, partial characterization and application in the synthesis of esters

Cell-bound lipase activity (10 pNPL units/g dry cell weight) was released when the yeast Rhodotorula glutinis was cultured in a 7- l stirred tank fermentor using palm-oil as the sole carbon source. The enzyme showed relative specificity towards medium chain organic acids since the apparent K m values for pNPB ( p-NitroPhenyl-Butyrate) and pNPL ( p-NitroPhenyl-Laurate) were equal to 2.7 and 0.7 mM, respectively. In addition, 80% of this activity could be detected on the surface of the cells. The cell-bound nature of the enzyme increased its thermal stability showing half-life times of 200 and 60 min at 50 and 60°C, respectively, as well as good stability in organic solvents. Freeze-dried cell preparations were successfully used to catalyze the synthesis of fatty acid esters of butanol and heptanol in nearly anhydrous organic solvents. A conversion of 60–62% was obtained upon esterification of palmitic or oleic acid with butanol, within 96 h. The enzyme preparation was used in four consecutive batch reactions with only 10% loss of activity.

電解質を添加した無水有機溶媒中における鉄の腐食と抑制

電解質を添加した無水有機溶媒中における鉄の腐食と抑制

Layered Zincophosphate Materials Prepared from a Molecular Zinc Di(tert-butyl)phosphate Complex in Organic Solvents

Layered zincophosphate materials were prepared from the molecular precursor Zn4(μ4-O)[O2P(OtBu)2]6 (1) via thermolysis (180−215 °C) in anhydrous organic solvents in the presence of long-chain primary amines. Through variation of the amine concentration, two series of materials were obtained with the stoichiometries Zn2(HPO4)3(H3NCnH2n+1)2 and Zn2(HPO4)3(H3NCnH2n+1)2(H2NCnH2n+1) (n = 8−16). These materials possess an unusual Zn/P ratio of 2:3 which is uncommon for layered zincophosphate materials prepared in aqueous media.

Thermokinetic Studies of Porphyrin Complexation in Non-Aqueous Solutions by Heat Conduction Microcalorimetry

Abstract Porphyrins are known as unique ligands forming some of the most stable complexes with various metal ions. In this work the thermokinetic investigations of complex formation of tetraphenylporphyrins with copper(II) acetate were carried out in two anhydrous organic solvents: acetic acid and DMF at 25C. Measurements were performed in a heat conduction microcalorimeter [7] adapted for non-aqueous solvents. Total heat effects and thermokinetics were determined. The results were discussed together with spectrophotometric data. Taking into account the high stability of metalloporphyrin complexes, the heat of their formation is rather small (in the case of acetic acid ΔQ=32.71.2 kJ mol−1, for DMF ΔQ=26.21.3 kJ mol−1). Such result can suggest that: 1) the stability of complexes is influenced strongly by an entropy factor, 2) the complexation involves breaking of the NH-bond in the porphyrin coordination centre, accompanied by high consumption of energy.