Kinetic study of penicillin acylase from Alcaligenes faecalis

AbstractPenicillin acylase from Alcaligenes faecalis has a very high affinity for both natural (benzylpenicillin, Km=0.0042 mM) and colorimetric (6-nitro-3-phenylacetamidobenzoic acid, Km=0.0045 mM) substrates as well as the product of their hydrolysis, phenylacetic acid (Ki=0.016 mM). The enzyme is partially inhibited at high benzylpenicillin concentrations but the triple SES complex formed still retains 43% of the maximal catalytic activity; the affinity of benzylpenicillin for the second substrate molecule binding site is much lower (KS′=54 mM) than for the first one. Phenylmethylsulfonyl fluoride was shown to be a very effective irreversible inhibitor, completely inactivating the penicillin acylase from A. faecalis in a few minutes at micromolar concentrations; this compound was used for enzyme active site titration. The absolute values of the determined kinetic parameters for enzymatic hydrolysis of 6-nitro-3-phenylacetamidobenzoic acid (kcat=95 s−1 and kcat/Km=2.1×10−7 M−1 s−1) and benzylpenicillin (kcat=54 s−1 and kcat/Km=1.3×10−7 M−1 s−1) by penicillin acylase from A. faecalis were shown to be highest of all the enzymes of this family that have so far been studied

Effect of the ionic liquid [bmim]Cl and high pressure on the activity of cellulase

The effect of the ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl) and of high pressure on the activity of cellulase from Aspergillus niger were studied separately and in combination. The enzyme activity decreased with increasing concentrations of [bmim]Cl, reaching 50% the value in aqueous buffer with 20% [bmim]Cl. However, when the enzyme is held in 10% [bmim]Cl and is then assayed in 1% [bmim]Cl, it showed only 8% reduction of activity. These results can be explained by the fact that the activity of the enzyme in [bmim]Cl is linearly correlated with the decrease of the thermodynamic water activity (aw). Under pressure the enzyme activity varied from less 60% (at 200MPa) to equal (at 400 MPa), compared to atmospheric pressure. In 10% [bmim]Cl under pressure, cellulase activity is improved compared to atmospheric pressure, varying from equal (at 600 MPa) to 1.7-fold higher (at 100 MPa). This opens the possibility to improve cellulase activity in ionic liquids, and possibly of other enzymes, by carrying out the reaction under pressure

Biocatalytic N-acylation of amines in water using an acyltransferase from Mycobacterium smegmatis

A straightforward one-step biocatalyzed synthesis of different N-acyl amides in water was accomplished using the versatile and chemoselective acyltransferase from Mycobacterium smegmatis (MsAcT). Acetylation of primary arylalkyl amines was achieved with a range of acetyl donors in biphasic systems within 1 hour and at room temperature. Vinyl acetate was the best donor which could be employed in the N-acetylation of a large range of primary amines in excellent yields (85-99%) after just 20 minutes. Other acyl donors (including formyl-, propionyl-, and butyryl- donors) were also efficiently employed in the biocatalytic N-acylation. Finally, the biocatalyst was tested in transamidation reactions using acetamide as acetyl donor in aqueous medium, reaching yields of 60-70%. This work expands the toolbox of preparative methods for the formation of N-acyl amides, describing a biocatalytic approach easy to accomplish under mild conditions in water

The kinetics and mechanism of the organo-iridium catalysed racemisation of amines

The dimeric iodo-iridium complex [IrCp*I2 ]2 (Cp*=pentamethylcyclopentadiene) is an efficient catalyst for the racemisation of secondary and tertiary amines at ambient and higher temperatures with a low catalyst loading. The racemisation occurs with pseudo-first-order kinetics and the orresponding four rate constants were obtained by monitoring the time dependence of the concentrations of the (R) and (S) enantiomers starting with either pure (R) or (S) and show a first-order dependence on catalyst concentration. Low temperature 1H NMR data is consistent with the formation of a 1:1 complex with the amine coordinated to the iridium and with both iodide anions still bound to the metal-ion, but at the higher temperatures used for kinetic studies binding is weak and so no saturation zero-order kinetics are observed. A cross-over experiment with isotopically labelled amines demonstrates the intermediate formation of an imine which can dissociate from the iridium complex. Replacing the iodides in the catalyst by other ligands or having an amide substituent in Cp* results in a much less effective catalysts for the racemisation of amines. The rate constants for a deuterated amine yield a significant primary kinetic isotope effect kH/kD = 3.24 ndicating that hydride transfer is involved in the rate-limiting step

Application of Ionic Liquids in the Microwave-Assisted Extraction of Proanthocyanidins from Larix gmelini Bark

Ionic liquid based, microwave-assisted extraction (ILMAE) was successfully applied to the extraction of proanthocyanidins from Larix gmelini bark. In this work, in order to evaluate the performance of ionic liquids in the microwave-assisted extraction process, a series of 1-alkyl-3-methylimidazolium ionic liquids with different cations and anions were evaluated for extraction yield, and 1-butyl-3-methylimidazolium bromide was selected as the optimal solvent. In addition, the ILMAE procedure for the proanthocyanidins was optimized and compared with other conventional extraction techniques. Under the optimized conditions, satisfactory extraction yield of the proanthocyanidins was obtained. Relative to other methods, the proposed approach provided higher extraction yield and lower energy consumption. The Larix gmelini bark samples before and after extraction were analyzed by Thermal gravimetric analysis, Fourier-transform infrared spectroscopy and characterized by scanning electron microscopy. The results showed that the ILMAE method is a simple and efficient technique for sample preparation

Tuning the electronic environment of cations and anions using ionic liquid mixtures

Electrostatic interactions are ubiquitous in ionic liquids and therefore, the electronic environment (i.e. the distribution of electron density) of their constituent ions has a determining influence on their properties and applications. Moreover, the distribution of electron density on atoms is at the core of ionic liquid molecular dynamics simulations. In this work, we demonstrate that changing the composition of ionic liquid mixtures can tune the electronic environment of their constituent ions, both anions and cations. The electronic environment of these ions can be monitored by measuring the characteristic electron binding energies of their constituent atoms by X-ray photoelectron spectroscopy (XPS). The possibility to fine tune, in a controlled way, the electronic environment of specific ions provides an invaluable tool to understand ionic liquid properties and allows the design of ionic liquid mixtures towards specific applications. Here, we demonstrate the power of this tool by tuning the electronic environment of a catalytic centre, and consequently its catalytic activity, by the use of ionic liquid mixtures

Recent advances in the use of ionic liquids for electrochemical sensing

Ionic Liquids are salts that are liquid at (or just above) room temperature. They possess several advantageous properties (e.g. high intrinsic conductivity, wide electrochemical windows, low volatility, high thermal stability and good solvating ability), which make them ideal as non-volatile electrolytes in electrochemical sensors. This mini-review article describes the recent uses of ionic liquids in electrochemical sensing applications (covering the last 3 years) in the context of voltammetric sensing at solid/liquid, liquid/liquid interfaces and carbon paste electrodes, as well as their use in gas sensing, ion-selective electrodes, and for detecting biological molecules, explosives and chemical warfare agents. A comment on the future direction and challenges in this field is also presented