Rapid method for the isolation of the mature collagen cross-links, hydroxylysylpyridinoline and lysylpyridinoline

Hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are two non-reducible cross-links of mature collagen which are formed by a sequence of post-translational modifications. HP is a derivative of three residues of hydroxylysine and is present in almost all mature tissues (e.g., tendons, vessel walls, cartilage, teeth and bone). LP is a derivative of two residues of hydroxylysine and one residue of lysine and is present only in dentine and bone. Neither cross-link is found in normal human skin. HP and LP were purified from commercially available bone gelatine (“ossein hydrolysate”) by preparative reversed-phase HPLC and the degree of purity was verified by amino acid determination ( > 98% dry mass). Hydroxylysylpyridinoline and lysylpyridinoline are promising markers in urine of collagen resorption because their levels in urine should reflect only the breakdown of collagen fibres of skeletal tissues. The two components were used as external standards and the determination of HP and LP in urine provides a good means for the specific evaluation of pathological conditions associated with increased bone resorption, e.g., high turnover post-menopausal osteoporosis.     

Comparison of silanization/hydrosilation and organosilanization modification procedures on etched capillaries for electrokinetic chromatography

Etched capillaries for use in open tubular electrochromatography are modified by silanization/hydrosilation and organosilanization. The migration behavior of both types of capillaries is evaluated with small basic molecules, peptides and proteins. Comparisons of peak symmetry and efficiency are used to measure the effectiveness of the two methods for modifying the etched surface. From this information, the suitability of each method for use with etched capillaries can be determined.     

Theoretical Study of the Distortion from Regular Tetrahedral Structure of M(NH2)4 Complexes

Theoretical study on tetrakis-amido complexes (M(NR₂)₄, M = Ti, V, Cr, and Mo; R = H, Me) is presented. At first a rough investigation of the potential energy surface indicates that all stationary points are of S ₄ or D ₂ symmetry depending on the coupled rotations of the NR₂ groups. Qualitative correlation diagrams are calculated within S ₄ or D ₂ symmetry constraint between two limiting structures of D ₂ d symmetry. DFT (B3LYP) calculations on these two paths are presented for unsubstituted complexes (R = H) and the various minima are optimized and characterized. These results are discussed in the light of the correlation diagrams. Finally, optimization of the different minima has been performed on substituted species (R = Me) and the theoretical results are shown to be in good agreement with the experimental structural determination when available.     

Nuclear magnetic resonance studies of sulfur inversion in bis(cyclopentadienyl)-molybdenum and -tungsten complexes with dithioethers

The metallocene thioether derivatives [Cp₂M(MeSCH₂CH₂SMe)][PF₆]₂ (1, M = MO; 2, M = W), [Cp₂Mo(SCH₂CH₂SMe)][PF₆] (3) and [Cp₂M(SCH₂CH₂S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 ± 2 kJ mol⁻¹), 2 (51.2 ± 4.6 kJ mol⁻¹) and 3 (30.0 ± 3.1 kJ mol⁻¹). Extended Hückel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S---C---C---S chain, is responsible for the observed fluxional behaviour.     

Anion-pi interactions in cyanuric acids: a combined crystallographic and computational study

Several structures of pi complexes of isocyanuric acid and of several thio derivatives with anions have been computed by using high level ab initio calculations. The nature of the complexes has been studied by means of the method of molecular interaction potential with polarization (MIPp) and Bader's theory of atoms-in-molecules. These molecules form favorable complexes with anions and can be used as binding units for building receptors for the molecular recognition of anions. In several cases, the anion-pi interaction has been demonstrated experimentally by means of X-ray crystallography.     

X-ray crystal structures of three nonbenzodiazepinic ligands for the benzodiazepine receptor sites: SR95926, CMW1842, and L16317:nab initio MO study of the electronic properties

The crystal structures ofp-methoxyphenyl-3-triazolo [4,3-a] isoquinoline (SR95926),p-methoxyphenyl-3-triazolophtalazine (CMW1842), andp-methoxyphenyl-3-N-dimethoxyethylamino-6-triazolophtalazine (L16317) have been solved by direct methods from single-crystal X-ray diffraction data, and refined by full-matrix least squares. SR95926: monoclinic,P2₁/n,a=20.950(3),b=6.769(1),c=9.465(2) Å,=100.90(1)°. CMW1842: triclinic,P¯1,a=8.784(1),b=9.160(4),c=8.555(1) Å,=99.10(2),=93.90(1), =106.77(1)°. L16317: monoclinic,P2₁/_n,a=20.124(3),b=9.586(1),c=10.788(1) Å,=91.91(1)°. FinalR factors are 0.034, 0.037, and 0.053, respectively. Experimental geometries were used to perform STO-3Gab initio molecular-orbital calculations. A relationship between the electronic pattern within the molecules and the affinity of the benzodiazepine receptor sites is pointed out.     

Topological excitations vs intergranular phase — coherence in a HTSC Y0.5Sm0.5Ba2Cu3O7 ceramics

This paper reports a detailed study of the electrical transport properties of good quality superconducting Y_0.5Sm_0.5Ba₂Cu₃O₇ ceramic samples. Analyses of the dependence of resistance on temperature, the relations current-voltage and the magnetoresistance allows to identify:a) the mean field critical temperature (T _CO =93.73±0.01 K);b) a power law behaviorVI atT _CO . The exponent jumps abruptly from 1 to 3, at a certain temperatureT _C =93.276±0.005 K;c) an exponential inverse root-square temperature dependence of the resistivity in theT _{C–T CO} temperature range. These features, typically observed when topological excitations sets in two dimensional systems, can also be interpreted as a signature of a percolation process and a transition towards intergranular phase coherence. We analyze and discuss the relevance of both models to account for the experimental data.