A theoretical prediction of stability in hydrogen-bonded complexes formed between oxirane and oxetane rings with HX (X=F and Cl)

The optimised geometries of heterocyclic hydrogen-bonded complexes, C2H4O...HX and C3H6O...HX, where X=F or Cl, were determined at DFT/B3LYP/6-311++G(d,p) computational level. Structural, electronic and vibrational properties of these complexes are used in order to compare the strained ring, which confer the great reactivity of these heterocyclic rings with monoprotic acids, forming a primary hydrogen bond. A secondary hydrogen bond between the hydrogen atoms of the CH2 groups and the halide species also takes place, thus causing a nonlinearity (characterized by the theta angle), in the primary hydrogen bond.     

Infrared spectrum, DFT: pBP86/DN** and NCA vibrational calculations of 2-methylthiosemicarbazide copper(II) nitrate [Cu(2MeTSC)2(NO3)2

To elucidate tentative assignments of metal-ligand modes of thiosemicarbazide complexes, a structural study and a assignment of the normal vibrations of 2-methylthiosemicarbazide copper(II) nitrate, [Cu(2MeTSC)(2)(NO(3))(2)] have been done through the ab initio DFT: pBP86/DN** procedure, and through the normal coordinate analysis (NCA). In the vibrational calculations, the elongated CuONO(2) bonds of the nitrate groups were considered in the CS and CN tautomers of the complex. DFT calculations had revealed that the infrared spectra can be well interpreted through the CN tautomer, failing in the prediction of the -NO(2) group wavenumbers. A little difference stabilization energy for the tautomers were found: for the CN tautomer was E=-3487,36376a.u., and for the CS tautomer, E=-3473,93598a.u. The observed combination bands at 1763.0 and at 1754.0 cm(-1) are an indicative that the -NO(3)(-) groups acts as monodentate ligands. Calculations had confirmed the experimental assignment of the infrared spectrum.     

Unraveling the importance of protein-protein interaction: application of a computational alanine-scanning mutagenesis to the study of the IgG1 streptococcal protein G (C2 fragment) complex

Alanine-scanning mutagenesis of protein-protein interfacial residues is a very important process for rational drug design. In this study, we have used the improved MM-PBSA approach that combining molecular mechanics and continuum solvent permits one to calculate the free energy differences through alanine mutation. To identify the binding determinants of the complex formed between the IgG1 (immunoglobulin-binding protein G) and protein G, we have extended the experimental alanine scanning mutagenesis study to both proteins of this complex and, therefore, to all interfacial residues of this binding complex. As a result, we present new residues that can be characterized as warm spots and, therefore, are important for complex formation. We have further increased the understanding of the functionality of this improved computational alanine-scanning mutagenesis approach testing its sensitivity to a protein-protein complex with an interface made up of residues mainly polar. In this study, we also have improved the method for the detection of an important amino acid residue that frequently constitutes a hot spot--tryptophan.     

The embedded singly periodic Scherk-Costa surfaces

We give a positive answer to M. Traizet's open question about the existence of complete embedded minimal surfaces with Scherk-ends without planar geodesics. In the singly periodic case, these examples get close to an extension of Traizet's result concerning asymmetric complete minimal submanifolds of with finite total curvature. Dedicated to Hermann Karcher on the Occasion of his 65th Birthday Martín's research is partially supported by MCYT-FEDER grant number BMF2001-3489.     

Comparison of gas chromatography-based approaches after fast miniaturised sample preparation for the monitoring of selected pesticide classes in fruits

The feasibility of a miniaturised generic sample preparation method based on matrix solid-phase dispersion for the determination of three relevant classes of pesticides (organophosphorus pesticides, triazines and pyrethroids) in selected fruits, i.e. orange, apple, pear and grape, have been demonstrated. Satisfactory results were obtained with gas chromatography coupled to mass spectrometry with recoveries of 78–113% in orange, 62–102% in grape, 71–116% in apple and 91–110% in pear, and reproducibilities in general below 20%. The feasibility of simultaneous separation of the three families of pesticides by comprehensive two-dimensional gas chromatography with micro-electro-capture detector was also evaluated. Columns with different polarity and selectivity, including ZB-5, HT-8 and DB-17, were assayed as first dimension and combined with columns of increasing polarity in the second dimension, i.e. HT-8, BPX-50 and Supelcowax-10. The best results for real-life samples after treatment by the proposed miniaturised method were achieved with ZB-5 × BPX-50 column combination. The low limits of detection achieved with this technique (in general, below 0.56 μg/kg) proved its suitability for accurate monitoring of the pesticides classes included in the study at the maximum residue levels set in the European Union.     

Erratum to: “Multiple critical points of perturbed symmetric strongly indefinite functionals” [http://dx.doi.org/10.1016/j.anihpc.2008.06.002]

We correct the statement and the proof of Proposition 9 in [D. Bonheure, M. Ramos, Multiple critical points of perturbed symmetric strongly indefinite functionals, http://dx.doi.org/10.1016/j.anihpc.2008.06.002].     

Gas‐phase fragmentation of protonated C60‐pyrimidine derivatives

Electrospray ionization mass spectrometry/mass spectrometry (ESI/MS/MS) and multiple stage mass spectrometry (MSⁿ, n > 2) were used in the positive ion mode, with two different types of mass spectrometers, a quadrupole time‐of‐flight and an ion trap, to characterize two sets of different types of C₆₀‐aminopyrimidine exohedral derivatives. In one set, the pyrimidine moiety bears an amino acid methyl ester residue, and in the other the pyrimidine ring is part of a nucleoside‐type moiety, the latter existing as two separated diastereoisomers. We have found that retro‐cycloaddition processes occur for the closed shell protonated species formed by electrospraying C₆₀ derivatives synthesized by Diels–Alder reactions, whereas for the C₆₀ derivatives synthesized via 1,3‐dipolar cycloadditions, these processes did not occur. Formation of diagnostic ions allowed the differentiation between the two groups of fullerene derivatives, and between the diastereoisomers of C₆₀ derivatives with a nucleoside‐type moiety. In general, the fragmentation processes are strongly dependent on the protonation sites and on the structure of the exohedral moieties. Copyright © 2009 John Wiley & Sons, Ltd.     

Micro‐Raman spectroscopy of decorated pottery from the Iberian archaeological site of Puente Tablas (Jaén,Spain, 7th–4th century B.C.)

In this paper, Raman spectroscopy is used for the first time to identify the pigments on decorated antique Iberian pottery. Ceramic fragments of type Real and others from the archaeological excavation in the oppidum Puente Tablas were examined. Different types of iron oxide pigments (hematite and goethite) were identified, along with amorphous carbon. In some samples, the presence of chalk or gypsum could be demonstrated. Some unattributed Raman bands are believed to be associated either with post‐burial organic deposition or with silicate materials that are present in red ochre. It was possible to relate the findings with geological data from the region and to make assumptions on a local production. Copyright © 2009 John Wiley & Sons, Ltd.