Fatty-acid-modified enzymes as enantioselective catalysts in microaqueous organic media

Highly active lipase and protease complexes were prepared by non-covalent modification with stearic acid. The protein content and yield of the modified enzyme complexes depended on the enzymes' source. The increase in the transesterification activity of the modified enzymes was 15 fold for Candida rugosa lipase and porcine pancreatic lipase, with preservation of the enantioselectivity. Pseudomonas sp. lipase which showed no activity in its crude form, exhibited an activity of 38 mol/h·mg protein in the modified form. © Rapid Science Ltd. 1998     

Stability of bilirubin oxidase in organic solvent media: a comparative study on two low-water systems

The storage stability of bilirubin oxidase was studied in water-in-oil CTAB microemulsions with a chloroformrich continuous organic phase. The kinetics of the inactivation process were best described by a double exponential equation. Approximately half of enzymatic activity was lost during a "fast" phase with a half life of ca. 50 min, whereas the remaining activity was lost much more slowly (half life ca. 1000 min). Rates of inactivation were not affected significantly by variation of either solvent composition or concentration of water droplets, but inactivation was more rapid when droplet size was very small. Steady-state enzyme kinetics were studied at various stages in the inactivation process, and it was shown that inactivation occurred without change in the K(m) of the enzyme for bilirubin. Stability was also studied in a liquid/solid two-phase system; it was found that the inactivation process in this system; it was found that the inactivation process in this system was best described by a single exponential term. The rate was similar to the "fast" phase rate observed in the water-in-oil microemulsion system. Inactivation of the enzyme slow. Addition of the surfactant CTAB to the aqueous environment increased the rate of inactivation to levels comparable to those of the "slow" phase observed in water-in-oil microemulsions. (c) 1993 Wiley & Sons, Inc.     

Enzyme-polyelectrolyte noncovalent complexes as catalysts for reactions in binary mixtures of polar organic solvents with water

Summary The formation of non-covalent complexes with polyelectrolytes has been suggested to enhance the resistance of enzymes towards inactivation by organic solvents in their homogeneous mixtures with water. Existence of such complexes in water-cosolvent media was proved by experiments with a fluorescence dye, eosin. In the case of catalysis by -chymotrypsin, formation of the complex with polyelectrolytes produced two major eflects: i) considerable increase in enzyme activity at concentrations of ethanol and N,N-dimethylformamide of 10–30 % v/v; ii) conservation of the enzymatic activity at cosolvent concentrations of more than 40% v/v, where the native enzyme is completely inactive. General character of the observed activation and stabilization phenomena was shown by example of several experimental systems.     

Peptide synthesis by surfactant-chymotrypsin complexes in organic media

Peptide synthesis by surfactant-chymotrypsin (CT) complexes was performed in organic media containing 1%–8% (v/v) water. The CT complex exhibited a higher enzymatic activity than native CT. The control of the water content in the reaction media has a crucial effect on the enzymatic activity. The maximum conversion (57%) for the peptide synthesis by the surfactant-CT complex was obtained at 4% water content.     

Activity of immobilized papain dehydrated by n-propanol in low-water media

A propanol-rinsed enzyme preparations (PREP) of papain showed an activity of 59 nmol min(-1) (mg powder)(-1) in tert-butanol at the optimal water activity of 0.2. The immobilized papain was stable in aqueous media for 3 d at 4 degrees C. Solid-state buffers (bases and their HCl salts) suspended in the organic medium decreased the initial rate in all cases tested. The operational stability during Z-Gly-Phe-NH2 synthesis was improved when solid cysteine was added, doubling the yield after 24 h.     

Biocatalysis in low-water media: understanding effects of reaction conditions

The key role played by counter-ions with enzymes in low-water systems has become better appreciated with, for example, large effects on enantioselectivity. In low-dielectric media, counter-ions will associate strongly with charges in the protein or its substrates. Studies of temperature dependence have shown that hard-to-model entropies have a significant effect on behaviour, including enantioselectivity. Evidence has been presented that the supramolecular organisation of enzyme molecules can have important effects on behaviour, for example collapse of microstructure in cross-linked crystals.     

Non-cyclopentadienyl zirconium complexes as catalysts for 1-hexene polymerization

The new β-diketonate complexes (hfac)₂ZrCl₂, (hfac)₃ZrCl, hfac = hexafluoroacetylacetonate, and (thd)₂ZrCl₂, thd = 2,2,6,6-tetramethyl-3,5-heptanedionate, have been prepared in good yield by reacting the corresponding β-diketonate thallium complexes with ZrCl₄ in stoichiometric amounts and they have been characterized by elemental analyses and NMR spectra.These complexes and the β-diketonate complexes (acac)₂ZrCl₂, (acac)₃ZrCl and (thd)₃ZrCl have been tested as catalysts in the polymerization of 1-hexene in the presence of N,N′-(dimethylanilinium)-tetrakis(pentafluorophenylborate) or ethyltrichloroacetate as co-catalysts at room temperature using ethyl aluminum sesquichloride as scavenger.     

Native subtilisin Karlsberg and modified subtilisin 72 as effective catalysts of peptide bond formation in organic media

The activity and stability of native subtilisin Karlsberg and subtilisin 72 and their complexes with sodium dodecyl sulfate (SDS) in organic solvents were studied. The kinetic constants of the hydrolysis of specific chromogenic peptide substrates Z-Ala-Ala-Leu-pNA and Glp-Ala-Ala-Leu-pNA by the subtilisins were determined. It was found that the subtilisin Karlsberg complex with SDS in anhydrous organic solvents is an effective catalyst of peptide synthesis with multifunctional amino acids in positions P ₁ and P ₁ ^′ (Glu, Arg, and Asp) containing unprotected side ionogenic groups.     

Enantioselective esterification of glycidol by surfactant-lipase complexes in organic media

Enantioselective esterification of glycidol has been performed with lauric acid in organic media dosed with surfactant-lipase complexes as catalysts. Lipase derived from various biomaterial sources was complexed with nonionic surfactant, dioleyl-N-D-glucono-L-glutamate, prior to use. Surfactant-lipase D (from Rhizopus delemar) complex had a higher enantioselectivity (v R /v S = 7.6) than the other lipases and the corresponding initial reaction rate was averaging 100-fold better than that of native powder lipase D in cyclohexane at 35°C.     

Platinum (II) and palladium (II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes as intramolecular hydroamination catalysts in aqueous and organic media

Complexes of the general formula cis-[MX₂(PTA)₂] (M = Pd, Pt; X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were used to study the catalytic intramolecular hydroamination/cyclization of 4-pentyn-1-amine into 2-methyl-pyrroline in water, methanol, and dimethyl sulfoxide (DMSO). Kinetic data were measured via ¹H NMR under homogeneous conditions at 50 °C and showed the following trends in rate: (i) Fastest rates were observed in D₂O. (ii) The Pd complexes of this study produced faster rates than the Pt complexes. (iii) The identity of the halide had no effect on the catalytic rate. Cyclization by the catalytic precursor cis-[PdCl₂(PTA)₂] (4) in D₂O was zero-order in substrate and first-order in metal complex with ΔH^‡ = 20.0 ± 2.1 kcal/mol, ΔS^‡ = −7.4 ± 6.3 cal/mol K, and E_a = 20.6 ± 2.1 kcal/mol. The acetylide complex, trans-[Pt(CC(CH₂)₃NH₂)₂(PTA)₂] (6) precipitated from a catalytic mixture involving cis-[PtBr₂(PTA)₂] (2). Spectroscopic and kinetic studies indicated that 6 and its cis analog, 7, were the predominant species in solution and that they were both active catalysts for the cyclization reaction. These data, in conjunction with the rate trends, indicated that the mechanism of the Pd(II) and Pt(II) catalyzed hydroamination of terminal alkynylamines in aqueous solution followed a unique mechanism with cyclization of an acetylenic-amine ligand being rate determining.     

Synthesis and characterisation of new Schiff base metal complexes and their use as catalysts for olefin cyclopropanation

New transition metal complexes of Co^II, Cu^II, Ni^II and V^IVO with the Schiff base, HL, 3-acetylcoumarin-N(4)-phenylthiosemicarbazone have been prepared. Characterisation of the HL ligand and its complexes is also reported. Mass spectra and NMR assignments for the ligand, using COSY, NOESY homonuclear and HMQC and HMBC heteronuclear correlation techniques were carried out. Electronic and magnetic moments of the complexes indicate that the geometries of the metal centres are either distorted octahedral, square pyramidal, square planar or tetrahedral. The structures are consistent with the IR, UV-Vis, ESR, as well as conductivity and magnetic moments measurements. Cyclopropanation reactions of unactivated olefins by ethyldiazoacetate (EDA) in the presence of LCu^IICl as catalyst proceed with excellent TON (up to 9625).     

Novel rhodium complexes containing a bulky iminophosphine ligand and their use as catalysts for the hydroboration of vinylarenes

Addition of o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃ (1) to [RhCl(coe)₂]₂ (coe = cis-cycloctene) gave several new iminophosphino rhodium(I) complexes including [Rh(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)(μ-Cl)]₂ (2). Addition of 1 to Rh(acac)(coe)₂ (acac = acetylacetonato) gave [Rh(acac)(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)] (3) in yields of up to 75%. Complex 3 has been examined for its ability to catalyze the hydroboration of a series of vinyl arenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

National inventory of organic wastes for use as growing media for ornamental potted plant production: case study in Spain

An inventory of materials suitable for use as growing media for ornamental potted plant production in Spain has been prepared. Special attention has been paid to solid organic wastes generated by production, industrial and consumer activities. Information obtained from this study has been organised into two data bases. Data base 1 contains the "General Characteristics" file of more than 105 materials. In this file, data are available regarding generation points, material availability, uses, cost, disposal expenses, etc. Data base 2 is comprised of the "Specific Properties" file of 63 materials selected from data base 1. The main physical, chemical and biological properties of these materials as container media have been characterised, and the results obtained have been compiled. Finally, a computerised data bank has been created which can be found in the home page of the Spanish Ministry of Agriculture, Fisheries and Food (http://agritel2.mapya.es/sustratos/).     

Taylor-made palladium-pincer complexes: A new source of more efficient catalysts for sustainable organic synthesis

The synthesis and catalytic activity of different pincer type palladium complexes synthesized in our laboratory are compiled in this report. The specific design of these palladacycles allows the employment of sustainable protocols and the recycle of the catalytic systems.The results obtained by our group in this context will be compared with other previously reported and new advances in this field.     

Increasing the catalytic efficiency of Candida rugosa lipase for the synthesis of tert-alkyl butyrates in low-water media

Abstract

Reactions involving tert-alcohols and their esters are generally not catalyzed by lipases. Candida rugosa lipase is one of the few lipases which shows at least limited catalytic activity towards tert-alcohols and their esters. Using transesterification of tributyrin with tertiary butyl and amyl alcohols as a model reaction, it is shown that precipitation of lipase by a tertiary alcohol in the presence of a buffer with optimum concentration enhances the catalytic activity 7 fold as compared to rates obtained with lyophilized powders. Optimization of the ratio of triglyceride to tert-alcohols and medium engineering gave an initial rate which was 41 times higher than that obtained with lyophilized powders. Hence, use of a simple enzyme formulation, coupled with optimization of reaction conditions led to Candida rugosa lipase becoming a useful catalyst for catalyzing transesterification involving tertiary alcohols.     

Metal complexes of modified cyclen as catalysts for hydrolytic restriction of plasmid DNA

Simple and novel nuclease models have been synthesized. These involve metal-binding ligand 1,4,7,10-tetraazlcyclododecane (cyclen) tethered to an acridine ring (a DNA-binding group) by amide linkers of various lengths. Binding of these probes to DNA was studied by monitoring changes in their UV-visible spectra affected by the presence of DNA. Titration of these compounds with increasing amounts of pBR322 DNA caused hypochromic effects and shifted the acridine absorption at 360 nm to a longer wavelength. Under biologically relevant conditions (37 °C and pH 7.4), specific transition metal complexes of these compounds are found to be highly effective catalysts toward the hydrolysis of plasmid DNA. This is demonstrated by their ability to convert the super-coiled DNA (form I) to open-circular DNA (form II). Structure-activity correlation studies show that hydrolytic activity depends on both the structure of ligand (L₁ > L₂ > L₃) and the nature of metal ion cofactor (Co³⁺ > Zn²⁺ > Cr²⁺ > Ni²⁺ > Cu²⁺ > Fe³⁺).     

Polyvinyl alcohol--trypsin as a catalyst for amino acid ester synthesis in organic media

The bovine trypsin-catalyzed synthesis of N-alpha-benzoyl-DL-arginine esters from N-benzoyl-DL-arginine were studied in various organic solvents. Trypsin was immobilized to polyvinyl alcohol (PVA) by adsorption from its aqueous solutions. Immobilized enzyme showed higher catalytic activities than free enzyme for amino acid esterification in ethanol. The yield of ester is strongly dependent upon the PVA/trypsin ratio and water content in the reaction medium. The rate and equilibrium constant of the ester formation reaction are also dependent on water content.