Cis‐trans Isomerism in Copper(II) Complexes with N‐acyl Thiourea Ligands

The N‐acyl thiourea complexes bis[N,N‐diethyl‐N′‐(p‐nitrobenzoyl)‐thioureato]copper(II) ( 1a,1b ) and bis(N,N‐diphenyl‐N′‐benzoylthioureato)copper(II) ( 2a,2b ) crystallize in each case in two modifications. X‐ray structural analysis shows that 1a and 1b are cis‐trans isomers. This is very unusual for N‐acyl thioureato complexes because with exception of one platinum(II) complex up to now only cis complexes have been found. In contrast X‐ray structural analysis of both forms 2a and 2b of the other complex shows no cis‐trans pair. Both modifications are cis complexes. In solution both isomers of the copper(II) complexes are observable by EPR spectroscopy.     

Fast multidimensional localized parallel NMR spectroscopy for the analysis of samples

A parallel localized spectroscopy (PALSY) method is presented to speed up the acquisition of multidimensional NMR (nD) spectra. The sample is virtually divided into a discrete number of nonoverlapping slices that relax independently during consecutive scans of the experiment, affording a substantial reduction in the interscan relaxation delay and the total experiment time. PALSY was tested for the acquisition of three experiments 2D COSY, 2D DQF‐COSY and 2D TQF‐COSY in parallel, affording a time‐saving factor of 3–4. Some unique advantages are that the achievable resolution in any dimension is not compromised in any way: it uses conventional NMR data processing, it is not prone to generate spectral artifacts, and once calibrated, it can be used routinely with these and other combinations of NMR spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Oscillator strengths and photoionisation cross sections for Rydberg transitions in acetaldehyde

Oscillator strengths for electronic transitions involving Rydberg states of acetaldehyde, as well as cross sections for all the dipole allowed photoionisation channels, all ending in the ground state of the molecular cation, are reported. The molecular quantum defect orbital method, which has proved to be reliable in previous applications to molecular Rydberg states, has been used. Despite its relevance for atmospheric chemistry and astrophysics, only a few data seem to be available in the literature. The continuity of the calculated differential oscillator strength across the ionisation threshold has been adopted as a quality criterion. To our knowledge, predictions of oscillator strengths for transitions to high-lying Rydberg states, as well as of photoionisation profiles on acetaldehyde are made here for the first time and we are not aware of any reported experimental data. We, thus, hope the present results may be useful in the interpretation of the spectrum of acetaldehyde and might be of help in future experimental measurements.     

Quantitative determination of L-DOPA in tablets by high performance thin layer chromatography

A densitometric high performance thin-layer chromatographic (HPTLC) method was developed and validated for quantitative analysis of L-DOPA in tablets. Chromatographic separation was achieved on precoated silica gel F 254 HPTLC plates using a mixture of acetone-chloroform-n-butanol-acetic acid glacial-water (60:40:40:40:35 v/v/v/v/v) as mobile phase. Quantitative analysis was carried out at a wavelength of 497 nm. The method was linear between 100 and 500 ng/microL, with a correlation coefficient of 0.999. The intra-assay variation was between 0.26 and 0.65% and the interassay was between 0.52 and 2.04%. The detection limit was 1.12 ng/microL, and the quantification limit was 3.29 ng/microL. The accuracy ranged from 100.40 to 101.09%, with a CV not higher than 1.40%. The method was successfully applied to quantify L-DOPA in real pharmaceutical samples, including the comparison with HPLC measurements. The method was fast, specific, with a good precision, and accurate for the quantitative determination of L-DOPA in tablets.     

A potential model for the study of ices and amorphous water: TIP4P/Ice

The ability of several water models to predict the properties of ices is discussed. The emphasis is put on the results for the densities and the coexistence curves between the different ice forms. It is concluded that none of the most commonly used rigid models is satisfactory. A new model specifically designed to cope with solid-phase properties is proposed. The parameters have been obtained by fitting the equation of state and selected points of the melting lines and of the coexistence lines involving different ice forms. The phase diagram is then calculated for the new potential. The predicted melting temperature of hexagonal ice (Ih) at 1 bar is 272.2 K. This excellent value does not imply a deterioration of the rest of the properties. In fact, the predictions for both the densities and the coexistence curves are better than for TIP4P, which previously yielded the best estimations of the ice properties.     

A minimal multiconfigurational technique

A direct minimization method previously presented by the authors is applied here to biconfigurational wave functions. A very moderate increasing in the time by iteration with respect to the one-determinant calculation and good convergence properties have been found. So qualitatively correct studies on singlet systems with strong biradical character can be performed with a cost similar to that required by Hartree-Fock calculations.     

Production of exocellular polysaccharide by azotobacter chroococcwn

Environmental conditions affect the production of extracellular polysaccharide by Azotobacter chroococcum ATCC 4412. Production of exocellular polymer from a variety of carbon sources depended on the air flow rate. A high sucrose concentration in medium (8%) markedly favored expopolysaccharide production, which reached 14 g/L in about 72 h. In cell suspensions incubated in the presence of 8% sucrose in a nitrogen-free medium, biopolymer final concentration of 9 g/L corresponds to 68 g/g biomass. Maximum efficiency of sucrose conversion into exopolysaccharide peaked at 70% for initial disaccharide concentration of 6%. High performance liquid chromatography and gas liquid chromatography of acid hydrolysates of the exopolymer revealed the presence of mannuronosyl, guluronosyl, and acetyl residues, but not neutral sugars. The infrared spectrum corroborated the presence of carboxylate anions and O-acetyl groups in the exopolymer. Though the presence of more than one kind of polysaccharide cannot be ruled out, these data suggest that, under the experimental conditions used in this work, only a type of alginate-like exopolysaccharide is produced by A. chroococcum ATCC 4412.     

New classes of 2-weight cyclic codes

We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes