Aroylhydrazones as chelating agents: d10-metal complexes of pyridine-2-carbaldehyde salicyloylhydrazone and x-ray structure of the zinc derivative

The title organic ligands (Hsip) gave, by reaction with d¹⁰-metal acetates, complexes of the type M(sip)₂ (M = Zn, Cd, Hg), in which the ligand behaved as terdentate, producing a distorted octahedral environment around the metal. The ¹H and ¹³C chemical shifts found for these complexes in DMSO are compared with the corresponding ones of the free ligand. The crystal structure of the zinc derivative has been determined from diffractometer data to R = 0.072 for 1086 independent reflections. Crystals are monoclinic, space group C2/c, with unit-cell dimensions a = 18.193(2), b = 24.532(6), c = 11.535(2) Å,β = 103.71(1)° and Z = 8. Coordination occurs through the carbonyl oxygens (Zn?O = 2.10, 2.16(1) Å), the azomethine nitrogens (Zn?N = 2.04, 2.07(1) Å) and the pyridine nitrogen s(Zn?N = 2.24, 2.26(1) Å).     

Spontaneous compactification to non-symmetric spaces

We investigate the spontaneous compactification of 4+d dimensions toM ₄ ×K/H whereK/H is ad-dimensional non-symmetric space. We present a formula giving the complete massless spinor spectrum for allK/H spaces. We discuss in detail all six-dimensional non-symmetric spacesK/H withK being simple.     

Fate of the benzene hydrogens in ergot alkaloids biosynthesis

Feeding experiments with specifically labelled precursors showed that in ergot alkaloids biosynthesis, the isoprenylation of tryptophan occurs without intermediate hydroxylation.     

Enhancing the hydrophobic effect in confined water nanodrops

The distribution of hydrophobic solutes, such as methane, enclosed in a nanosized water droplet contained in a reverse micelle of diameter 2.82 nm is investigated using Monte Carlo simulations. The effect of the hydrophobic solute's atomic diameter on the solute-solute potential of mean force is also studied. The study reveals that confinement has a strong influence on the solute's tendency to associate. The potential of mean force exhibits only a single minimum, indicating that the contact pair is the only stable configuration between solutes. The solvent-separated pair that is universally observed for small solutes in bulk water is conspicuously absent. This enhanced hydrophobic effect is attributed to the lack of sufficient water to completely hydrate and stabilize the solvent-separated configurations. The study is expected to be important in understanding the role of hydrophobic forces during protein folding and nucleation under confinement.     

Classification of ancient proteinaceous painting media by the joint use of pattern recognition and factor analysis on GC/MS data

Reference proteinaceous binding media of the kinds historically used in painting (specially prepared for this study) and samples collected from ancient polychrome works of art were analysed by gas chromatography – mass spectrometry. The data have been processed by several multivariate chemometric techniques, such as cluster analysis, principal component analysis, factor analysis and SIMCA technique in order to classify the binding media of the ancient works of art on the basis of the proteinaceous material used. The characterisation of ancient samples was possible by the joint use of SIMCA technique and factor analysis. The latter, in particular, has made it possible to point into evidence the presence of at least two latent factors. The first factor seems to be connected with the chemical composition of the painting media, while the second factor is likely to be connected with ageing processes. Received: 14 October 1998 / Revised: 23 April 1999 / Accepted: 20 May 1999     

Solvent effect in free radical reactions on protonated heteroaromatic bases

The influence of reaction medium on the relative reactivity of various carbon radicals towards 4-CH₃-and 4-CN- quinolines has been investigated. A relevant solvent effect for α-amidoalkyl and α-oxyalkyl radicals has been demonstrated and a solvent-radical interaction is proposed to explain the phenomenon.     

NLIE of Dirichlet sine-Gordon model for boundary bound states

We investigate boundary bound states of sine-Gordon model on the finite-size strip with Dirichlet boundary conditions. For the purpose we derive the nonlinear integral equation (NLIE) for the boundary excited states from the Bethe ansatz equation of the inhomogeneous XXZ spin 1/2 chain with boundary imaginary roots discovered by Saleur and Skorik. Taking a large volume (IR) limit we calculate boundary energies, boundary reflection factors and boundary Lüscher corrections and compare with the excited boundary states of the Dirichlet sine-Gordon model first considered by Dorey and Mattsson. We also consider the short distance limit and relate the IR scattering data with that of the UV conformal field theory.     

Synthesis and spectroscopic characteristics of 2,3,-biindolyl and 2,2-indolylpyrroles

A general and selective method has been achieved to synthesize 2,3'- biindolyls and 2,2'-indolylpyrroles through an acid catalysed reaction of 3-bromoindoles with indoles or pyroles. I.R., ¹H-NMR, ¹³C-NMR and MS data of the dimers are also reported.     

Comparing the hierarchy of author given tags and repository given tags in a large document archive

Folksonomies – large databases arising from collaborative tagging of items by independent users - are becoming an increasingly important way of categorizing information. In these systems users can tag items with free words, resulting in a tripartite item-tag-user network. Although there are no prescribed relations between tags, the way users think about the different categories presumably has some built in hierarchy, in which more special concepts are descendants of some more general categories. Several applications would benefit from the knowledge of this hierarchy. Here we apply a recent method to check the differences and similarities of hierarchies resulting from tags given by independent individuals and from tags given by a centrally managed repository system. The results from our method showed substantial differences between the lower part of the hierarchies, and in contrast, a relatively high similarity at the top of the hierarchies.