Synthesis of anticonvulsant sulfamides. Theoretical study of the related mechanism

A theoretical study of the mechanisms associated with the synthesis of anticonvulsant symmetric N,N-substituted sulfamides is presented. Two possible synthetic routes are compared, which mainly differ in the use of pyridine as a nucleophilic agent in the reaction mechanism. Geometry optimization techniques and transition-state detection at the B3LYP/6-31G** level, modeling the solvent by means of an isodensity polarizable continuum approach, allow the most suitable method for the experimental process to be discerned.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

The electrophilic reactions of pentacyanonitrosylferrate(II) with hydrazine and substituted derivatives. Catalytic reduction of nitrite and theoretical prediction of eta(1)-, eta(2)-N(2)O bound intermediates

The electrophilic reactivity of the pentacyanonitrosylferrate(II) ion, [Fe(CN)(5)NO](2)(-), toward hydrazine (Hz) and substituted hydrazines (MeHz, 1,1-Me(2)Hz, and 1,2-Me(2)Hz) has been studied by means of stoichiometric and kinetic experiments (pH 6-10). The reaction of Hz led to N(2)O and NH(3), with similar paths for MeHz and 1,1-Me(2)Hz, which form the corresponding amines. A parallel path has been found for MeHz, leading to N(2)O, N(2), and MeOH. The reaction of 1,2-Me(2)Hz follows a different route, characterized by azomethane formation (MeNNMe), full reduction of nitrosyl to NH(3), and intermediate detection of [Fe(CN)(5)NO](3)(-). In the above reactions, [Fe(CN)(5)H(2)O](3)(-) was always a product, allowing the system to proceed catalytically for nitrite reduction, an issue relevant in relation to the behavior of the nitrite and nitric oxide reductase enzymes. The mechanism comprises initial reversible adduct formation through the binding of the nucleophile to the N-atom of nitrosyl. The adducts decompose through OH(-) attack giving the final products, without intermediate detection. Rate constants for the adduct-formation steps (k = 0.43 M(-)(1) s(-)(1), 25 degrees C for Hz) decrease with methylation by about an order of magnitude. Among the different systems studied, one-, two-, and multielectron reductions of bound NO(+) are analyzed comparatively, with consideration of the role of NO, HNO (nitroxyl), and hydroxylamine as bound intermediates. A DFT study (B3LYP) of the reaction profile allows one to characterize intermediates in the potential hypersurface. These are the initial adducts, as well as their decomposition products, the eta(1)- and eta(2)-linkage isomers of N(2)O.     

Bioelectrochemical determination of lactic and malic acids in wine

Electroanalytical methods based on biosensor technology and differential pH measurement for the determination of l-lactic and l-malic acids in wine were developed. Lactic acid was determined according to two procedures consisting of the use of two lactate electrochemical biosensors, one based on a Clark O(2) probe and the other based on the H(2)O(2) probe. The two probes were assembled employing a polymeric membrane where the enzyme lactate oxidase was previously immobilized. Both sensors exhibited high storage and operational stabilities, and good reproducibility when used in wine matrix. Measurement of lactate was carried out using two different flow-through cells assembled with the lactate probes. The low detection limit of these probes and the relatively high concentration of lactate in wine samples required a serial dilution in the range 1:100 to 1:200, thus eliminating all potential electrochemical or enzyme interferences present in the sample. Malic acid was determined using a differential commercially available pH-meter and an enzymatic procedure. For this analysis, we employed the malic enzyme (EC 1.1.1.40) and the NADP(+) cofactor. The pH variation due to the action of this enzyme on malic acid was found to be proportional to the malic acid present in the sample. Experimental parameters such as pH, temperature, and co-factor concentration were optimized, resulting in malate determination in less than 1 min with good reproducibility. Various samples of wine and wine musts were assayed for lactate with the two biosensor procedures, and for malate with differential pH-metry. The results when compared with those obtained with the commonly used spectrophotometric procedure correlated well.     

New dinuclear catalysts Rh(2)(N-O)(2)[(C6H4)P(C6H5)2]2 with imidate ligands: synthesis and isomerization from head-to-tail to head-to-head configuration of the imidate ligands

Two new dirhodium(II) catalysts of general formula Rh(2)(N-O)(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (N-O = C(4)H(4)NO(2)) are prepared, starting from Rh(2)(O(2)CCH(3))(2)(PC)(2)L(2) [PC = (C(6)H(4))P(C(6)H(5))(2) (head-to-tail arrangement); L = HO(2)CCH(3)]. The thermal reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with the neutral succinimide stereoselectively gives one compound that according to the X-ray structure determination has the formula Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (1). It corresponds to the polar isomer with two bridging imidate ligands in a head-to-head configuration. However, stepwise reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with (CH(3))(3)SiCl and potassium succinimidate yields a mixture of 1 and one of the two possible isomers (structure B) with a head-to-tail configuration of the imidate ligands, Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (2), also characterized by X-ray methods. In solution, compound 2 undergoes slow isomerization to 1; the rate of this process is enhanced by the presence of acetonitrile. Compounds 1 and 2 are obtained as pure enantiomers starting from (M)- and (P)-Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) rather than from the racemic mixture. Their enantioselectivities in cyclopropanation of 1-diazo-5-penten-2-one are similar to those reported for the dirhodium amidate catalysts.     

Odour-causing organic compounds in wastewater treatment plants: evaluation of headspace solid-phase microextraction as a concentration technique

Odorous emissions from wastewater collection systems and treatment facilities affecting quality of life have given local populations reasons to complain for decades. In order to characterise the composition of such malodorous emissions, a method based on headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry (GC-MS) has been developed to determine a list of compounds belonging to different chemical families, which have been previously described as potentially responsible for odour complaints, in wastewater matrices. Some parameters affecting the chromatographic behaviour of the target compounds were studied (e.g. splitless time). Experimental conditions affecting the extraction process (temperature, time and salt content) were evaluated by applying a factorial design at two levels. Using a DVB/CAR/PDMS fibre and the optimised HS-SPME conditions, calibration curves were constructed with detection limits in the range of 0.003-0.6 μg L(-1). Recovery values higher than 70% and relative standard deviation values between 5 and 16% (n=5) were obtained for all compounds and found to be satisfactory. In wastewater samples, a decrease in the concentration of the analysed compounds through the different treatments was observed. Most of the target analytes were found in influent samples while only octanal and carvone were detected in samples from the plant effluent.     

Angular dispersion of femtosecond pulses in a Gaussian beam

The angular dispersion of spatially Gaussian laser pulses, unlike for plane waves, changes with the distance between the disperser and the observer and between the beam waist and the disperser. The formula that is derived is experimentally verified by use of a high-precision measurement technique. Because the angular dispersion of a Gaussian beam is substantially different from that of a plane wave after the same disperser, the phenomenon may be of special interest for short-pulsed laser systems, for which alignment of the stretcher-compressor system for zero residual angular dispersion is essential.     

Claisen-type addition of glycine to pyridoxal in water

The reaction between 5'-deoxypyridoxal and glycine in D2O buffered at pD 7.0 does not result in significant formation of the expected products of pyridoxal-catalyzed transamination or deuterium exchange of the alpha-amino protons of glycine, but rather gives a quantitative yield of the two diastereomeric products of the formal Claisen-type addition of glycine to 5'-deoxypyridoxal. The unexpected extensive formation of these products reflects the extraordinary selectivity of the 5'-deoxypyridoxal-stabilized glycine enolate toward addition to the carbonyl group of 5'-deoxypyridoxal in the protic solvent water.     

Coordination versatility of pyridine-functionalized N-heterocyclic carbenes: a detailed study of the different activation procedures. Characterization of new Rh and Ir compounds and study of their catalytic activity

Three different reaction procedures for the coordination of N-n-butyl-N'-(2-pyridylmethyl)imidazolium salt have produced new N-heterocyclic complexes of Rh and Ir. The direct reaction of the imidazolium salt with [IrCl(cod)](2) provides a NHC-Ir(III)-H complex, while transmetalation from a silver-NHC complex and deprotonation with NEt(3) give new NHC complexes of M(I) and M(III) when reacting with [MCl(cod)](2) or [MCl(coe)(2)](2) (M = Rh, Ir). The crystal structures of the biscarbene Rh(III) and Ir(III) complexes are described. The catalytic properties of the compounds obtained have been tested in the hydrosilylation of acetylenes, the cyclization of acetylenic carboxylic acids, and hydrogen transfer to ketones.