Transition moment directions of some important in-plane vibrations of uracil,thymine and cytosine. A fixed partial charge model calculation

Transition moment directions for the double-bond region vibrations of uracil, thymine and cytosine are calculated using the fixed partial charge model approximation. The coupling between the two carbonyl bonds and the carbon—carbon double bond in uracil and thymine is sensitive to the choice of the corresponding stretching force constants. The transition moment directions are correspondingly changed, thus, in principle, enabling the quantitative determination of coupling between the vibrations from linear dichroism measurements.     

Die Anzahl von Lösungen gewisser diophantischer Gleichungen

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Zur Axiomatik endlicher Gruppen

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Miniatyrisering av elektronikkomponenter

The paper describes the main features of the miniaturization technique used for production of circuit elements. Integrated circuits (microblocks) are believed to dominate in the near future, while micro-circuits produced by thin-film-technique, and discrete active and passive components should be much less frequent. The influence of the miniaturization on the size and the speed of computers is particularly stressed.     

Nucleic acid-metal interactions. III. Complexes of Ag(I) with adenine and 1-methyladenine from studies of UV and IR dichroic spectra

Attempts to characterize nucleic acid-silver interactions raise questions about how the free nucleic acid bases interact with silver ions in dilute aqueous solution. Studies of ultraviolet and infrared dichroism lead to the conclusion that with silver(I) ions in dilute solution adenine forms linear polymers, whereas 1-methyladenine forms dimers. The composition and structure of the complexes are further discussed against the background of the spectroscopic results.     

NMR studies of conformations and dynamic processes—II : [26]Bicyclophanes with ethylene bridges

The conformations and dynamic processes in two bicyclophanes have been analysed on the basis of temperature-dependent ¹H NMR spectra. Both bicyclophanes are suggested to have a lowest-energy conformation of D₃ symmetry in which the substituents at all ethylene bridges are gauche⁺ (or gauche^?) oriented. The interconversion of the mirror image conformers of each bicyclophane equilibrates the two hydrogens in each methylene group, the barriers being ca 36 and 37 kJ mol^?1, respectively, as determined by line-shape analysis.     

Glutathione transferase: new model for glutathione activation

Glutathione transferases are enzymes of the cellular detoxification system that metabolize a vast spectrum of xenobiotic and endobiotic toxic compounds. They are homodimers or heterodimers and each monomer has an active center composed of a G-site in which glutathione (GSH) binds and an H-site for the electrophilic substrate. When GSH binds to the G-site, the pKa value of its thiol group drops by 2.5 units; this promotes its deprotonation and, therefore, produces a strong nucleophilic thiolate that is able to react with the electrophilic substrate. The mechanism behind the deprotonation of the thiol group is still unknown. Some studies point to the fact that the GSH glutamyl alpha-carboxylate group is essential for GSH activation, whereas others indicate the importance of the active-center water molecules. On the basis of QM/MM calculations, we propose a mechanism of GSH activation in which a water molecule, acting as a bridge, is able to assist in the transfer of the proton from the GSH thiol group to the GSH glutamyl alpha-carboxylate group, after an initial GSH conformational rearrangement. We calculated the potential of mean force of this GSH structural rearrangement that would be necessary for the approach of both groups and we then performed a QM/MM ONIOM scan of water-assisted proton transfer. The overall free-energy barrier for the process is consistent with experimental studies of the enzyme kinetics.