Self-limited growth of a thin oxide layer on Rh(111)

The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.     

Isospin breaking in $K \to 3 \pi$ decays III : Bremsstrahlung and fit to experiment

We complete here our work on isospin violation in the system. We first calculate to the same order as we did in papers I and II of this series. This adds the effects of order G ₂₇ p ² (m _u -m _d ) and G ₂₇ p ² e ² to earlier work. We calculate also the lowest order bremsstrahlung contributions, . With these and our earlier results we perform a full fit to all available CP-conserving data in the system including isospin violation effects. We perform these fits under various input assumptions as well as test the factorization and the vector dominance model for the weak NLO low energy constants.Received: 18 January 2005, Published online: 3 March 2005PACS: 13.20.Eb, 12.39.Fe, 14.40.Aq, 11.30.Rd     

Hydrogen bonds in polymer folding

We studied the thermodynamics of a homopolymeric chain with both van der Waals and directed hydrogen bond interaction. The effect of hydrogen bonds is to reduce dramatically the entropy of low-lying states and to give rise to long-range order and to conformations displaying secondary structures. For compact polymers a transition is found between helix-rich states and low-entropy sheet-dominated states. The consequences of this transition for protein folding and, in particular, for the problem of prions are discussed.     

Unusual Multilayer Surface Alloy: Al(100)-c(2 x 2)-2Li

An unusual multilayer surface alloy is formed by adsorption of one monolayer Li on Al(100). It is shown by low energy electron diffraction that the first three layers consist of a mixed Al-Li layer, a pure Al layer, and a second Al-Li layer. Thus the alloy has the same layer stoichiometry as the (100) surface of the metastable Al(3)Li bulk alloy. However, the relative orientation of the two mixed layers is the same as that in the Al(3)Ti-type structure. These findings are confirmed by total-energy calculations, which lead further to the prediction that the bulk Al(3)Li alloy has a faulted, Al(3)Ti-type surface.     

A structure-activity relationship study of catechol-O-methyltransferase inhibitors combining molecular docking and 3D QSAR methods

A panel of 92 catechol-O-methyltransferase (COMT) inhibitors was used to examine the molecular interactions affecting their biological activity. COMT inhibitors are used as therapeutic agents in the treatment of Parkinson's disease, but there are limitations in the currently marketed compounds due to adverse side effects. This study combined molecular docking methods with three-dimensional structure-activity relationships (3D QSAR) to analyse possible interactions between COMT and its inhibitors, and to incite the design of new inhibitors. Comparative molecular field analysis (CoMFA) and GRID/GOLPE models were made by using bioactive conformations from docking experiments, which yielded q2 values of 0.594 and 0.636, respectively. The docking results, the COMT X-ray structure, and the 3D QSAR models are in agreement with each other. The models suggest that an interaction between the inhibitor's catechol oxygens and the Mg2+ ion in the COMT active site is important. Both hydrogen bonding with Lys144, Asn170 and Glu199, and hydrophobic contacts with Trp38, Pro174 and Leu198 influence inhibitor binding. Docking suggests that a large R1 substituent of the catechol ring can form hydrophobic contacts with side chains of Val173, Leu198, Met201 and Val203 on the COMT surface. Our models propose that increasing steric volume of e.g. the diethylamine tail of entacapone is favourable for COMT inhibitory activity.     

High-Resolution Fourier Transform Infrared Spectrum of the ν1+ν3 Band System of HCCH

A high-resolution vibration-rotation overtone spectrum of H¹³C¹²CH has been recorded with a Fourier transform infrared spectrometer in the wavenumber region 6400 to 6700 cm⁻¹. The main band, assigned as the C-H stretching combination band ν₁+ν₃, and some overtone and hot bands have been rotationally analyzed. Altogether eight parallel bands have been observed. The vibrational labels have been deduced on the basis of the assignments of the fundamental ν₃ antisymmetric C-H stretching band system.     

Study of the continuum generated by in-line filtering of solitons

The continuum generated by the filtering of solitons is studied analytically by use of a perturbation theory and numerically verified. The method applies to any filter transfer function and to sliding-frequency filtering as well. A general method for finding the input pulse adapted to a transmission line is presented and applied to the case of filtering.     

Active-site modifications of adenylation domains lead to hydrolysis of upstream nonribosomal peptidyl thioester intermediates

Site-directed mutagenesis of nonribosomal peptide synthetase (NRPS) adenylation (A) domains was investigated as a means to engineer new calcium-dependent antibiotics (CDA) in Streptomyces coelicolor. Single- and double-point mutants of the CDA NRPS module 7, A-domain were generated, which were predicted to alter the specificity of this domain from Asp to Asn. The double-point mutant produced a new peptide CDA2a-7N containing Asn at position 7 as expected. However, in both the single- and the double-point mutants, significant hydrolysis of the CDA-6mer intermediate was evident. One explanation for this is that the mutant module 7 A-domain activates Asn instead of Asp; however, the Asn-thioester intermediate is only weakly recognized by the upstream C-domain acceptor site (a), allowing a water molecule to intercept the hexapeptidyl intermediate in the donor site (d).     

Fluorimetric determinations by ion-pair extraction : Part V. Studies on ion-pair extraction with the fluorescent anion 9,10-dimethoxyanthracene-2-sulphonate

The fluorescent anion 9,10-dimethoxyanthracene-2-sulphonate has been studied in ion-pair extractions. Its ability to extract amines and quaternary ammonium compounds was investigated by fluorimetric determination of extraction and dissociation constants with methylene chloride as organic phase for two amines (amitriptyline and protriptyline) and two quaternary ammonium ions (tetrabutyl-and tetrapropylammonium). The optical properties of the anion and its ion pairs were characterized by quantum yield of fluorescence and a fluorescence sensitivity index. The determination of two of the ion pairs was studied, both after extraction to an organic phase and after a subsequent back-extraction of the anion component to an aqueous phase. Recoveries and standard deviations are given.