A potentiometric microbial sensor based on immobilized escherichia coli for glutamic acid

The sensor consists of immobilized E. coli (which contains glutamate decarboxylase) and a carbon dioxide gas-sensor. Continuous introduction of sample solution into a flow system incorporating the sensor gives a potential which increases until a steady state is reached after 5 min. Measurements can also be made with only a 1- or 3-min introduction period with little loss of sensitivity. Calibration plots of mV measurements vs. logarithmic glutamic acid concentration are linear in the range 100–800 mg l^-1. The sensor is highly selective, stable and reproducible. It has been applied to the determination of glutamic acid in fermentation broths.     

Enzymatic Synthesis and Polymerization of Cyclic Trimethylene Carbonate Monomer with/without Methyl Substituent

The direct enzymatic synthesis of a cyclic trimethylene carbonate (1,3‐dioxane‐2‐one) monomer with/without a methyl substituent was carried out using dimethyl or diethyl carbonate and 1,3‐diol with the objective of producing aliphatic poly(trimethylene carbonate), a typical biodegradable synthetic plastic. The lipase‐catalyzed condensation of dimethyl or diethyl carbonate with aliphatic 1,3‐diols using immobilized Candida antarctica lipase (lipase CA) in an organic solvent at 70 °C afforded the corresponding methyl‐substituted and unsubstituted cyclic trimethylene carbonates. The cyclic trimethylene carbonates obtained by the reaction of dimethyl or diethyl carbonates with 1,3‐propanediol and 2‐methyl‐1,3‐propanediol were polymerized by lipase to produce the corresponding polycarbonates.

Total TMC yield as a function of the reaction time.     

Structural and spectroscopic characterization of (mu-hydroxo or mu-oxo)(mu-peroxo)diiron(III) complexes: models for peroxo intermediates of non-heme diiron proteins

(mu-Hydroxo or oxo)(mu-1,2-peroxo)diiron(III) complexes having a tetradentate tripodal ligand (L) containing a carboxylate sidearm [Fe2(mu-OH or mu-O)(mu-O2)(L)2]n+ were synthesized as models for peroxo-intermediates of non-heme diiron proteins and characterized by various physicochemical measurements including X-ray analysis, which provide fundamental structural and spectroscopic insights into the peroxodiiron(III) complexes.     

Improvement of chemical analysis of antibiotics. X. Determination of eight tetracyclines using thin-layer and high-performance liquid chromatography

Analytical methods for eight tetracyclines (TCs) were established using silica gel high-performance thin-layer chromatography (HPTLC), reversed-phase thin-layer chromatography (RP-TLC) and high-performance liquid chromatography (HPLC). Good separations of eight TCs were obtained using chloroform-methanol-5% disodium ethylenediaminetetraacetate solution (65:20:5) (lower layer) and methanol acetonitrile 0.5 M oxalic acid solution (1:1:4) (pH 3.0) on silica gel HPTLC and C8 TLC plates, respectively. A combination of HPTLC and RP-TLC made possible the identification of the eight TCs. Each calibration graph was linear between 0.1 and 1.0 microgram using UV densitometry except for rolitetracycline. For detection reagents, the diazonium salts including Fast Violet B gave variously coloured spots with the eight TCs and good sensitivities were obtained except with minocycline. In HPLC, the simultaneous analysis of the eight TCs on a C8 column was possible using methanol-acetonitrile-0.01 M oxalic acid solution (1:1.5:7) adjusted to pH 3.0 as the mobile phase. A linear relationship was obtained between 1.0 and 10 ng using the usual sample preparation except for rolitetracycline. The direct determination of rolitetracycline was possible using tetrahydrofuran, dimethyl sulphoxide and the mobile phase as solvents for preparation of the sample. For the determination of residual rolitetracycline, it was effective to measure the amount of rolitetracycline as tetracycline by HPLC, HPTLC and RP-TLC after conversion of rolitetracycline to tetracycline by incubating for 5 min in methanol at 50 degrees C.     

First example of chiral N-heterocyclic carbenes as catalysts for kinetic resolution

Chiral N-heterocyclic carbenes, which are derived from C2-symmetric 1,3-bis(1-arylethyl)imidazolium salts, catalyze enantioselective acylation of racemic secondary alcohols.     

Vesicle formation in oleyldimethylamine oxide/sodium oleate mixtures

Vesicle formation in a mixture of oleyldimethylamine oxide (OleylDMAO) and sodium oleate (NaOl) was investigated by viscoelastic measurements and cryoscopic transmission electron micrograph (cryo-TEM) observations. The viscoelastic properties changed with increasing mole fraction of NaOl (X _NaOl) from the Maxwell behavior of OleylDMAO solutions (X _NaOl=0) suggesting a transient network of long flexible chains. For X _NaOl=0.2 and 0.4 mixtures, both the shear storage modulus G and the shear loss modulus G showed weak dependences on angular frequency with a relation G>G. From cryo-TEM observations, vesicles coexisted with threadlike micelles in mixtures of X _NaOl=0.2 and 0.3. As X _NaOl increased further (X _NaOl=0.5 and 0.6), threadlike micelles disappeared and the coexistence of vesicles and globular micelles was observed. At X _NaOl=0.5, the viscosity decreased remarkably, which was consistent with the disappearance of threadlike micelles. The results indicated that vesicles were formed by the addition of NaOl to OleylDMAO solutions, contrary to the expectation of a decrease of the packing parameter with the introduction of electric charges.     

Synthesis of thromboxane A2 analog DL-(9,11), (11,12)-dideoxa-(9,11)-epithio-(11,12)-methylene-thromboxane A2

A synthesis of the thromboxane A₂ analog, $\text{dl}$-(9,11), (11,12)-dideoxa-(9,11)-epithio-(11,12)-methylene-thromboxane A₂ is described.     

Multipoint recognition of catecholamines by hydrindacene-based receptors accompanied by the complexation-induced conformational switching

The molecular recognition of catecholamines by hydrindacene-based receptors 1 and 2, as well as the durene-based receptor 3, and the guest-induced conformational changes are reported. These receptors selectively bind adrenaline and dopamine salts through the guests' ammonium group and 3-hydroxyl group on the aromatic ring. In the case of adrenaline, an additional hydrogen bond with a benzylic hydroxyl group is formed. In 2 % CD3CN/CDCl3, the association constants are of the order of 10(4) M(-1), which is much larger than with guests without the 3-hydroxyl groups (10(3) M(-1)). The two amide groups of receptor 1 can rotate freely around the C(aromatic)--C(amide) bond, whereas the tert-amide in 2 changes between two stable conformations at a slow enough rate to allow detection by (1)H NMR spectroscopy. In the absence of a guest molecule, the syn-conformer is less stable than the anti-conformer. On complex formation with adrenaline, the syn-conformer becomes dominant due to an intramolecular dipole-reversal effect in addition to multipoint hydrogen bonding.     

A catalytic immuno-reactor for the amperometric determination of human serum albumin

A catalytic immuno-reactor for the determination of human serum albumin (HSA) was constructed by using immobilized antibody and an amperometric detector. A sandwich assay with hemin-labeled antibody to catalyze the decomposition of hydrogen peroxide was used, the catalytic activity of the hemin-antibody conjugate being determined by measuring the decrease in hydrogen peroxide concentration. The reaction of hemin-labeled antibody with antigen was complete within 30 min and the current decrease was correlated with the HSA concentration. The relative standard deviation was about 9% at an HSA concentration of 1 mg ml^?1.