Structure and stability of (CuNO) isomers

Quantum-mechanical calculations have been performed on various isomers of the (CuNO)⁺ system. A ²Π ground state is found for the linear CuNO⁺ and CuON⁺ isomers and a ²A′ state for the bent CuNO⁺ and CuON⁺ isomers. Energy calculations indicate that the linear CuNO⁺ structure is the most stable, the bent CuNO⁺ and CuON⁺ and the linear CuON⁺ structures are at 0.86 eV, 0.99 eV and 1.04 eV above this respectively. In the CuNO⁺ → CuON⁺ interconversion between the linear isomers, three transition states are involved, whereas the bent CuNO⁺ isomer is found to be an intermediate species. The isomerization barriers, dissociation energies, equilibrium geometries and vibration frequencies are given for all isomers in their ground and first excited states.     

Alpha-nucleus elastic scattering at intermediate energies

Elastic scattering of 288,340,480 and 699 MeV Alpha-particles was measured on ²⁰⁸Pb, ¹¹⁶Sn and ⁵⁸Ni. The data were analysed in terms of a phenomenological optical model. The optical potentials obtained were found to vary consistently with the target nucleus and the incident energy. The radial zone where the potentials are well determined was studied in detail. The data for ²⁰⁸Pb were also analysed with a folding model. The energy dependence of the strong-absorption radius and of the reaction cross section shows that the nuclear surface becomes slightly transparent for incident energies above 150 MeV per nucleon.     

Characterization and event specific-detection by quantitative real-time PCR of T25 maize insert

T25 is one of the 4 maize transformation events from which commercial lines have so far been authorized in Europe. It was created by polyethylene glycol-mediated transformation using a construct bearing one copy of the synthetic pat gene associated with both promoter and terminator of the 35S ribosomal gene from cauliflower mosaic virus. In this article, we report the sequencing of the whole T25 insert and the characterization of its integration site by using a genome walking strategy. Our results confirmed that one intact copy of the initial construct had been integrated in the plant genome. They also revealed, at the 5' junction of the insert, the presence of a second truncated 35S promoter, probably resulting from rearrangements which may have occurred before or during integration of the plasmid DNA. The analysis of the junction fragments showed that the integration site of the insert presented high homologies with the Huck retrotransposon family. By using one primer annealing in the maize genome and the other in the 5' end of the integrated DNA, we developed a reliable event-specific detection system for T25 maize. To provide means to comply with the European regulation, a real-time PCR test was designed for specific quantitation of T25 event by using Taqman chemistry.     

π-electron approximation in pyridine and related compounds

A semi-empirical LCAO calculation including a- and -electrons has been performed for pyridine and related heterocyclics. The diagonal matrix elements of Hamiltonian are evaluated from atomic spectroscopic data through the use of a formula derived from the SCF equations. The non-diagonal matrix elements are estimated through the Wolfsberg-Helmholz formula. All overlap integrals have been included. The results disagree with what one can expect from a-electron treatment, mainly with respect to population analysis, but they seem strongly supported by the conclusions of ab initio calculations for other compounds and the trend of dipole moment in the sequence pyridine, quinoline, acridine.

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Resume Für Pyridin und verwandte Heterozyklen wurde eine LCAO-Rechnung mit und-Elektronen durchgeführt. Die Diagonalelemente des Hamiltonoperators wurden mittels atomspektroskopischer Daten berechnet unter Benutzung einer aus SCF Rechnungen abgeleiteten Formel, die Nicht-Diagonalelemente mit der Wolfsberg-Helmholz-Formel. Alle Überlappungsintegrale wurden berücksichtigt. Die Ergebnisse stimmen mit solchen aus-Elektronen-Behandlungen nicht überein (besonders die Dichteverteilung), scheinen aber stark durch ab initio-Rechnungen für andere Verbindungen und das Verhalten des Dipolmoments in der Folge Pyridin, Chinolin, Acridin gestützt zu werden.

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Zusammenfassung L'ensemble des systèmes électroniques et de la pyridine et de ses homoogues supérieurs a été étudiée par une méthode LCAO semi-empirique. Les élements de matrice diagonaux de l'hamiltonien sont évalués à partir de données de spectroscopie atomique, en faisant appel à une formule dérivée des équations du champ self-consistant. Les éléments de matrice non diagonaux sont calculés par la formule de Wolfsberg-Helmholz. Toutes les intégrales de recouvrement ont été introduites. Surtout en ce qui concerne l'analyse de population, les résultats sont en désaccord avec ce que l'on peut attendre d'un calcul limité au système d'électrons; par ailleurs, ils paraissent confirmés par les conclusions de calculs ab initio relatifs à d'autres composés et par l'évolution du moment dipolaire dans la série pyridine, quinoléine, acridine.

     

A single step synthesis of 6-aminophenanthridines from anilines and 2-chlorobenzonitriles

Biologically active 6-aminophenanthridines were prepared in a single step procedure: Metal amides in liquid ammonia promoted the condensation of anilines with 2-chloro-benzonitriles. 6-Aminophenanthridines were isolated in moderate yield.     

Total synthesis of cimiracemate B and analogs

The synthesis of the biologically active cimiracemate B and some analogs is described. The key step of the synthesis is a coupling between a bromoketone and a cinnamic acid derivative.     

Comments on the status of the chemical bond in methods of quantum chemistry

Chemists do not take the view that chemistry can be derived from quantum mechanics by computations too literally; the difficulties are illustrated by the double bond concept. Quantum mechanics is very useful, but recent calculations have been mainly concerned with physical properties rather than chemical processes. In general, the chemical formula plays a central role in all interpretation of quantum-chemical results, thus suggesting that the chemical bond is a preexistent notion. Moreover, the Born–Oppenheimer approximation seems to be necessary for deriving the existence of bonds between atoms previously assigned to suitable positions. Recent analyses by Claverie and Diner, Woolley, Primas, and others are briefly recalled, concluding with an expression of hope that use of more general Hamiltonians can lead to progress in obtaining a fully independent quantum theory of chemistry.     

Anhydrodihydroartemisinin and its 10-trifluoromethyl analogue: access to novel d-ring-contracted artemisinin trifluoromethyl ketones

The preparation of the 10-trifluoromethyl hydroartemisinin, followed by dehydration, afforded the trifluoromethyl analogue 2 of anhydrodihydroartemisinin 1. The reactivity of these two glycals of artemisinin were compared in epoxidation and halogenation reactions. Iodination of glycal 1 in water and the further rearrangement of the produced iodo hemiacetal provided the new D-ring-contracted aldehyde 8alpha, where the methyl at C-9 is beta. Epoxidation of 10-trifluoromethyl anhydrodihydroartemisinin 2 stereoselectively provided the beta-epoxy ether 11 in high yield. When treated with hexafluoro-2-propanol or trifluoroethanol, 11 readily underwent a rearrangement yielding to the D-ring-contracted trifluoromethyl ketone 9alpha with retention of configuration at C-9.