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     

Quantitative 2H NMR spectroscopy with 1H lock extender

An inexpensive external unit that allows the use of the commercial high-resolution NMR spectrometer for (2)H observation with an (1)H lock system is described. The external unit does not require any tuning, is extremely easy to use, and could be a cheaper and more straightforward alternative to the more expensive (19)F lock configuration. An application for the quantitative determination of the natural isotopic ratio (2)H/(1)H of ethanol and acetic acid is reported.     

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.     

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.     

Properties of L-phenylalanine tetraamides as chiral selectors for D,L-amino acids by capillary gas chromatography

Summary A wide series of L-phenylalanine tetraamide selectors (Phe-n-O-TA) have been synthesized and used as stationary phases for chiral resolution of D,L-amino acids by capillary gas chromatography. The influence of length and polarity of the oxaalkanoyl bridge spacing the diamide chains of the selectors and the effects of steric hindrance on separating power were investigated. The characteristics of the chiral columns and the separation factors of D,L-n-butyl-N-trifluoroacetyl amino esters are reported.