Solvent effect on the conformational behaviour of amino acid and oligopeptide derivatives

The solvent effect on acetyl amino acid methyl esters and C- and N-protected di- and tripeptide derivatives has been studied in deuterium oxide (D₂O), 1.1.1.3.3.3-hexafluoroisopropanol (HFiP), dimethyl sulfoxide (DMSO) and methylene chloride (CH₂Cl₂). The interpretation is based on the amide I region. For the amino acid derivatives the relative shift of the amide I signal clearly indicates the strength of the interaction with the solvent molecules. However, in HFiP and DMSO solutions the occurrence of two overlapping signals for the amide I and the ester carbonyl signal, respectively, indicates the existence of two major conformers. Knowing the solvent effects on the small amino acid esters allows the assignment of the signals in di- and tripeptide derivatives. Although the identification of turn structures in these flexible molecules is not possible, the band positions and intensity of the deconvoluted amide I region clearly shows that certain conformers can be stabilised. It can be concluded that the band profile in the amide I region is determined by the number of amino acid residues linked in the molecule, the bulkiness of the side chains and their sequence and to a major extend by the solvent properties.     

Minimum Weight Design for Structural Eigenvalue Problems by Optimal Control Theory*, †

The application of optimal control theory to minimum weight design of continuous one-dimensional structural elements subject to eigenvalue constraints is discussed. If not only the value of an eigenvalue is prescribed but also its position in the sequence of the ordered eigenvalues—for example, the critical buckling load of a column—the corresponding optimal control problem is shown to include necessarily all eigenvalues. Considering the unspecified eigenvalues as free parameters, necessary conditions for minimum weight design are derived. These conditions are compared with those obtained by use of variational methods. Attention is focused on the special case of multimodal solutions.     

KRS and Powers of determinantal ideas

The goal of this paper is to determine Göbner bases of powers of determinantal ideals and to show that the Rees algebras of (products of) determinantal ideals are normal and Cohen–Macaulay if the characteristic of the base field is non-exceptional. Our main combinatorial result is a generalization of Schensted's Theorem on the Knuth–Robinson–Schensted correspondence.     

Submonolayer Au on Si(111) phase diagram

Based on a review of the current literature, a surface phase diagram is proposed for the submonolayer Au on Si(111) system. Kinetic considerations are reviewed and key surface phase diagram features such as the Θ < 0.4 ML metastable structure and the high temperature to Si(111)-(1 × 1)Au second order phase transition are discussed. Experiments to verify certain portions of the phase diagram are proposed.     

A Collocation Code for Singular Boundary Value Problems in Ordinary Differential Equations

We present a MATLAB package for boundary value problems in ordinary differential equations. Our aim is the efficient numerical solution of systems of ODEs with a singularity of the first kind, but the solver can also be used for regular problems. The basic solution is computed using collocation methods and a new, efficient estimate of the global error is used for adaptive mesh selection. Here, we analyze some of the numerical aspects relevant for the implementation, describe measures to increase the efficiency of the code and compare its performance with the performance of established standard codes for boundary value problems.     

Investigation of copolymers of styrene and ethyl methacrylate by size exclusion chromatography and gradient HPLC

Summary Copolymers of styrene and ethyl methacrylate have been separated according to composition by gradient HPLC on silica columns or CN bonded phase columns. This mode of separation according to composition was applied to fractions obtained by size exclusion chromatography (SEC). From viscosity and molecular mass data of copolymers with a styrene content ranging from 7.5 to 95.3 mass-% it can be concluded that SEC separates mainly by molecular mass even in this copolymer system. Thus, chromatographic cross-fractionation is possible by prefractionation by SEC and subsequent separation according to composition by gradient HPLC.

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Untersuchung von Copolymeren von Styrol und Ethylmethacrylat durch Ausschluß-Chromatographie und Gradienten-HPLC

     

Efficient electron transfer through a triazole link in ruthenium(II) polypyridine type complexes

Spectroscopic, electrochemical and theoretical characterisations of photoactive systems readily assembled via click-chemistry show an efficient bi-directional charge shift through the triazole link.     

Some remarks on the <Emphasis Type="Italic">q</Emphasis>-exponents of generalized modular functions

We discuss some properties of exponents of q-product expansions of specific generalized modular functions on the congruence subgroup Γ₀(N).