Twin comprehensive two-dimensional gas chromatographic system: concept and applications

A twin GC x GC system has been designed which enables the analysis of a sample by means of two different and independent column combinations simultaneously. Both combinations are incorporated in the same oven, using the same temperature programme, and are fed using a 50:50 column-entrance-split. It is demonstrated that, employing combinations of a conventional non-polar x polar and a reversed-type polar x non-polar column set, the information content is as high, and the analytical performance is as good as when using two separate GC x GC systems. That is, there is an appreciable gain of time and a reduction of costs without any loss of quality. The general usefulness of performing, and comparing two mutually different GC x GC runs is further illustrated with FAMEs in olive oil, and pollutants in a sediment sample.     

Strong solute-solute dispersive interactions in a protein-ligand complex

The contributions of solute-solute dispersion interactions to binding thermodynamics have generally been thought to be small, due to the surmised equality between solute-solvent dispersion interactions prior to the interaction versus solute-solute dispersion interactions following the interaction. The thermodynamics of binding of primary alcohols to the major urinary protein (MUP-I) indicate that this general assumption is not justified. The enthalpy of binding becomes more favorable with increasing chain length, whereas the entropy of binding becomes less favorable, both parameters showing a linear dependence. Despite the hydrophobicity of the interacting species, these data show that binding is not dominated by the classical hydrophobic effect, but can be attributed to favorable ligand-protein dispersion interactions.     

Even and odd diagonals in doubly stochastic matrices

The existence of even or odd diagonals in doubly stochastic matrices depends on the number of positive elements in the matrix. The optimal general lower bound in order to guarantee the existence of such diagonals is determined, as well as their minimal number for given number of positive elements. The results are related to the characterization of even doubly stochastic matrices in connection with Birkhoff's algorithm.     

4-Iodo-2-methyl-5-nitro­aniline exhibits neither strong hydrogen bonding nor intermolecular I⃛nitro interactions

In the title compound, C₇H₇IN₂O₂, the O atoms of the nitro group are disordered over two sets of sites and there is evidence that the intramolecular I⃛nitro interaction is repulsive. In the crystal structure, there are neither strong hydrogen bonds, nor intermolecular I⃛nitro interactions, nor aromatic π–π-stacking interactions.     

Modeling structural recovery in glasses: An analysis of the peak‐shift method

Amorphous polymers below their glass‐transition temperature are inherently not at equilibrium. As a result, their structures continuously relax in an attempt to reach the equilibrium state. The current models of structural recovery can quantitatively describe the process. One of the parameters needed for the models is the nonlinearity parameter x. It has been proposed that x can be obtained from experimental data with the so‐called peak‐shift method. In this work, we use the Tool–Narayanaswamy–Moynihan model to identify the factors that determine the accuracy of the peak‐shift method and to quantify the errors in the value of x obtained from the peak‐shift method. In addition, we determine the influence of the error in x on the evaluation of the nonexponential model parameter β. Finally, the peak‐shift method is compared with the traditional curve‐fitting method for model parameter determination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2027–2036, 2002     

Permanganate oxidation of unsaturated alcohols in alkaline media

A study was made on permanganate oxidation of olefinic and acetylenic alcohols in aqueous alkali media. Deprotonation constants of alcohols can be calculated from the kinetic data. The rate constant of alkoxide group oxidation exceeded that of the unsaturated bond. For oxidation of the alcoholic group a mechanism based on hydride ion transfer is proposed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 561–567, 2002     

Experimental results on neutrino-electron scattering

A determination of sin² θ _w based on measurements of elastic scattering of muon-neutrinos and muon-anti-neutrinos on atomic electrons is described. These purely leptonic processes were studied using the CHARM calorimeter exposed to neutrino and antineutrino wide-band beams at the CERN super proton synchrotron. A total of 83±16 neutrino-electron and 112±21 antineutrino-electron events have been detected. From the measurement of the ratio of muon-neutrino and muon-antineutrino cross-sections a value of sin² θ _w =0.211±0.037 was obtained.