David Hull

Journal of Optimization Theory and Applications -     

Dampfdruck- und Leitfähigkeitsuntersuchungen der Ionensolvatation in Amiden

The solvating properties of formamide, N-methylformamide, dimethylformamide, N-ethylformamide and diethylformamide have been investigated by means of vapour pressure and conductivity measurements. For the salts and ions, resp. average solvation numbers have been calculated from vapour pressure data and limiting ionic conductances. The solvation numbers are used for a discussion of the influence of N-substituents on the solvating properties of the amides.

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Mit 2 Abbildungen     

Periodic Image Trajectories in Earth–Moon Space

The problem of identifying orbits that enclose both the Earth and the Moon in a predictable way has theoretical relevance as well as practical implications. In the context of the restricted three-body problem with primaries in circular orbits, periodic trajectories exist and have the property that a third body (e.g. a spacecraft) can describe them indefinitely. Several approaches have been employed in the past for the purpose of identifying similar orbits. In this work the theorem of image trajectories, proven five decades ago, is employed for determining periodic image trajectories in Earth–Moon space. These trajectories exhibit two fundamental features: (i) counterclockwise departure from a perigee on the far side of the Earth, and (ii) counterclockwise arrival to a periselenum on the far side of the Moon. An extensive, systematic numerical search is performed, with the use of a modified Poincaré map, in conjunction with a numerical refinement process, and leads to a variety of periodic orbits, with various interesting features for possible future lunar missions.     

George Leitmann

Journal of Optimization Theory and Applications -     

Dedication

Journal of Optimization Theory and Applications -     

The effect of N-substitution on the metal binding properties of peptide binding sites

The influence of methyl- and ethylsubstitution at the nitrogen atom of peptide groups on their interaction with alkali and alkaline earth metal ions has been studied by means of quantum chemical calculations on the complexes of lithium, sodium and beryllium with the different substituted amides, and by means of difference energy surfaces obtained fromab initio calculations employing minimalGaussian basis sets. Characteristic ion specific differences are found to occur in the interaction according to the respective substitutions, which will influence the potential for the metal ion in the field of the peptide groups quite strongly. Binding energies and electron density distribution in the complexes are discussed with respect to recent experimental data obtained by metal nmr spectroscopy. The results of the calculations give some indications to possible ways of influencing the ion specifity and reactivity of peptide and protein metal binding sites in biological systems.

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Der Effekt der N-Substitution auf die metallbindenden Eigenschaften von Peptiden

Zusammenfassung Der Einfluß von Methyl- und Ethyl-Substitution am Stickstoff der Peptidbindung auf die Wechselwirkung mit Alkali- und Erdalkali-Metallionen wurde mittels quantenchemischer Berechnungen an Komplexen mit Lithium, Natrium und Beryllium mit verschieden substituierten Amiden, und mittels der Differenz-Energie-Flächen vonab initio Berechnungen mit minimalemGauß-Basis-Set, studiert. Es wurden charakteristische ionenspezifische Differenzen in den Wechselwirkungen-entsprechend den verschiedenen Substituenten gefunden, die das Potential der Metallionen im Feld der Peptidbindungsgruppe sehr stark beeinflussen. Es werden Bindungsenergien und Elektronendichten in den Komplexen, bezogen auf neuere experimentelle Daten der Metall-NMR-Spektroskopie, diskutiert. Die Ergebnisse der Berechnungen zeigen mögliche Wege auf, die Ionenspezifität und die Reaktivität von Peptid- und Protein-Metall-Bindungszentren in biologischen Systemen zu beeinflussen.