Rosa Méndez

Biodesulphurisation of coal by microorganisms isolated from the coal itself

Abstract An attempt was made to desulphurise various types of coal, using as inocula enriched cultures from the bacteria adhering to each of the coal types, while the desulphurisation of the same coal types, inoculated with an indigenous culture derived from the drainage of a mine, was simultaneously monitored. The results demonstrate the convenience of using coal-derived inocula, with 70–90% of pyritic sulphur being removed, while chemical desulphurisation is of little significance with the majority of coal types. In reference to the Immediate Analysis of the coal, it should be stressed that this scarcely changed apart from the variations caused by acid attack; owing to that the ashes were partially eliminated and the treatment reduces the sulphur emission value.

Studies on clavulanic acid. Part 1. Stability of clavulanic acid in aqueous solutions of amines containing hydroxy groups

The kinetics of the decomposition of clavulanate ion, (Z)-(2R,5R)-3-(2-hydroxyethylidene)-7-oxo4-oxa-1-azabicyclo[3.2.0]heptane-2-carboxylate, in aqueous solutions of 2-amino-2-methylpropane1,3-diol, 2-amino-2-methylpropan-1-ol, 2-methoxyethylamine, 2,2,2-trifluorethylamine, and aminoacetonitrile have been studied. All reactions were conducted at 35.0 °C and 0.5M-ionic strength. In the pH range 8.05–9.80 the reaction is pseudo-first-order with respect to the concentration of clavulanate ion. The, aminolysis rate constants can be expressed as a sum of the terms representing the uncatalysed or water-catalysed amine reaction, the self-assisted nucleophilic reaction, and the hydroxide-ion-catalysed nucleophilic attack of amine on the β-lactam moiety.

Zn2+ catalysed hydrolysis of β-lactams: experimental and theoretical studies on the influence of the β-lactam structure

We present both experimental and theoretical results on simple model systems of zinc-β-lactamases. Kinetic studies show that the rate of degradation of β-lactam antibiotics in the presence of zinc ions and tris(hydroxymethyl)aminomethane buffers depends markedly on the structure of the β-lactam. Carbapenems are highly reactive whereas monobactam antibiotics like aztreonam, which are known to be non-susceptible to the catalytic action of the metallo-β-lactamases, are less reactive by three orders of magnitude. To complement the experimental studies, density functional calculations were carried out on model systems. These calculations allowed us to characterise the reactive mode of binding between the β-lactam nucleus and Zn2+ ions as well as to rationalise the kinetic trends observed experimentally. Docking analyses are reported for the complex formed between aztreonam and the mononuclear metallo-β-lactamase from Bacillus cereus. On the basis of all the results, we hypothesise that the aztreonam–metallo-β-lactamase complex might be poorly reactive due to a potential interaction of the N-sulfonate group of aztreonam with the essential Zn ion at the active site.

Reversed-phase ion-pair high-performance liquid chromatographic determination of triclabendazole metabolites in serum and urine

An ion-pair high-performance liquid chromatographic method was developed for measuring the concentrations of triclabendazole metabolites (sulphoxide and sulphone) in plasma and urine samples. The diluted biological fluids are ultrafiltered before chromatography through a 30,000 relative molecular mass cut-off filter and then injected into a C18 column. They are then isocratically eluted with a mobile phase consisting of 0.05 M phosphate buffer (pH 7.0)-acetonitrile (55:45, v/v) with addition of 1.0 mmol/l sodium decanesulphonate and monitored by ultraviolet-visible spectrophotometry at 312 nm. Recoveries over the range 0.01-9.0 micrograms/ml for triclabendazole sulphoxide and sulphone are, respectively, 91.7% and 91.6% in serum and 90.3% and 90.2% in urine. For both metabolites, the limit of detection is 10 ng/ml in both urine and serum.

Studies on clavulanic acid part 3. Catalysis of hydrolysis and aminolysis of clavulanic acid by metal chelates

The ZnII–tris(hydroxymethyl)aminomethane (Tris) system has a large catalytic effect on the hydrolysis and aminolysis of the clavulanate ion, (Z)-(2R,5R)-3-(2-hydroxyethylidene)-7-oxo-4-oxa-1-azabicyclo[3.2.0]heptane-2-carboxylate. In order to ascertain the mechanism of this catalysis we have analysed the effects of other metal ions (CdII, CoII, CuII, NiII, and MnII), of amines structurally related to Tris, and of blocking the carboxylate group of the clavulanate ion. From these studies, we conclude that only the CdII-Tris and CoII-Tris systems have any substantial catalytic effect, although this is not as important as that of ZnII-Tris. Studies with methyl clavulanate indicate that co-ordination of the metal ion by the carboxylate group is necessary. We suggest that catalysis takes place via a ternary complex in which the metal ion plays a double role by (a) placing the clavulanate ion and the amino alcohol in the right position for the reaction and (b) lowering the pKa of the hydroxide group of Tris, which is co-ordinated with the metal ion generating a strong nucleophile.

Removal of tetracyclines from swine manure at full-scale activated sludge treatment plants

The purpose of this study was to investigate the fate of three tetracyclines (TCs), namely oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC) at two different full-scale swine manure-activated sludge treatment plants. Throughout treatment, OTC, CTC and DC were removed by 71–76%, 75–80% and 95%, respectively. Removal of these TCs under physical treatment was deniable. On the contrary, the flocculation–coagulation and the secondary clarification resulted in a relevant reduction of the concentration of these TCs.

High-performance liquid chromatographic methods for the determination of the penems SCH 29482 and FCE 22101 in human serum and urine

High-performance liquid chromatographic methods have been developed for the determination of two 6-(1-hydroxyethyl)penems, SCH 29482 (I) and FCE 22101 (II), in serum and urine. Serum samples were combined with an equal volume of methanol to remove proteins and, after centrifugation, an aliquot of the supernatant was analysed by ion-pair chromatography on a reversed-phase C18 column with hexadecyltrimethylammonium bromide as the ion-pairing agent. The compounds were detected by their ultraviolet absorbance at 305 nm for II and 322 nm for I. Urine samples were diluted, filtered and analysed by the same chromatographic procedure. At concentrations of 1-500 micrograms/ml of each compound, the within- and between-day precisions were 1.8-3.6 and 2.6-5.1%, respectively. The detection limit was 0.2 micrograms/ml for I and 0.3 micrograms/ml for II.

Spectrophotometric Assay of Penem (SCH 29482) by Reaction with Imidazole

Abstract A rapid method is described for the determination of SCH 29482. This is based on the spectrophotometric measurement at 386 nm of the product of reaction with imidazole formed at 35°Cin a 1.5 M imidazole and 2×10−3M mercuric chloride solution at pH 7.50. The method, which permits detection of concentrations of SCH 29482 as low as to 2.8, μg/ml, is reproducible and specific for intact SCH 29482 in the presence of degradation products. The molar absorptivity for the chromophore formed is 2.54×l04 I mol−1cm−1.