The Near-Infrared YΣ-XΠ Transition of CuSe

The near-infrared Y²Σ⁺-X²Π transition of the diatomic molecule CuSe was observed for the first time. A King-type carbon tube furnace was used to produce the gas phase of the CuSe molecules. The Fourier transform spectrometer associated with the National Solar Observatory, Kitt Peak, Arizona was used to record the molecular emission spectrum in the region 9850-12 400 cm⁻¹. A vibronic analysis and comparisons of the spin-orbit constant and the ²Σ⁺ transition energy to those for related isovalent molecules are presented.     

PHOSPHORANES PAR FERMETURE TRANS ANNULAIRE IV. Quelques Exemples de Phosphoranes Bicycliques Chiraux

Abstract

Nous avons synthétisé sept phosphoranes bicycliques nouveaux 1–7 comportant un atome de phosphore pentacoordiné chiral. 5 et 6 possèdent en outre un atome de carbone chiral et 7 deux atomes de carbone chiraux. Une étude comparative des paramètres RMN du groupement P–H nous a permis de proposer une configuration de l'atome de phosphore de ces trois composés.

Seven new bicyclic phosphoranes 1–7 bearing a chiral pentaco-ordinated phosphorus atom are described. 5 and 6 possess a chiral carbon atom and 7 two chiral carbon atoms. A configuration of phosphorus atom of these three compounds is proposed based on a comparative study of the P–H NMR parameters.     

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

Structural Studies Reveal Enantiospecific Recognition of a DNA G‐Quadruplex by a Ruthenium Polypyridyl Complex

By using X‐ray crystallography, we show that the complexes Λ/Δ‐[Ru(TAP)₂(11‐CN‐dppz)]²⁺ (TAP=1,4,5,8‐tetraazaphenanthrene, dppz=dipyridophenazine) bind DNA G‐quadruplex in an enantiospecific manner that parallels the specificity of these complexes with duplex DNA. The Λ complex crystallises with the normally parallel stranded d(TAGGGTTA) tetraplex to give the first such antiparallel strand assembly in which syn‐guanosine is adjacent to the complex at the 5′ end of the quadruplex core. SRCD measurements confirm that the same conformational switch occurs in solution. The Δ enantiomer, by contrast, is present in the structure but stacked at the ends of the assembly. In addition, we report the structure of Λ‐[Ru(phen)₂(11‐CN‐dppz)]²⁺ bound to d(TCGGCGCCGA), a duplex‐forming sequence, and use both structural models to provide insight into the motif‐specific luminescence response of the isostructural phen analogue enantiomers.     

The cure of elastomers by dicumyl peroxide as observed in differential scanning calorimetry

Differential scanning calorimetry (DSC) has been used to determine the enthalpy changes accompanying the thermal homolysis and subsequent radical reactions occuring in the dicumyl peroxide (DCP) cure of elastomers (NR, EPDM, SBR, BR, NBR, and EPM). The thermal degradation of DCP alone, dispersed on kaolin clay in a hydrocarbon solvent, was also studied.The degradation of DCP alone results in an exothermic enthalpy change of ～ 215 kJ mole^?1. In elastomer systems, the observed enthalpy exchange can be ordered BR >; SBR ; NBR (34% ACN) > NBR (27% ACN) > NR > EPDM ～ EPM.Low enthalpy values are associated with systems containing predominantly secondary hydrogen atoms (EPDM, EPM). The high enthalpy of cure for BR appears associated with the known ability of the polybutadienyl radicals to propagate a limited chain reaction. The relative extent of cumyloxy radical disproportionation to hydrogen abstraction was determined in each system and this has no apparent effect on the observed enthalpy change.The method of Borchardt and Daniels was used for data reduction and calculation of apparent activation energies. For DCP degradation alone the calculated activation energy is in good agreement with literature values. In elastomer systems, the calculated activation energies must be treated with caution because, as pointed out by Borchardt and Daniels, their method does not apply to solid state reactions.     

Nuclear hyperfine splittings for copper monofluoride in the a3Σ+ state

Lines in the (0, 0) band of the a³Σ⁺-X¹Σ⁺ system of CuF have been recorded at Doppler-limited resolution by laser-induced fluorescence. Nuclear hyperfine structure associated with the Cu nucleus is clearly resolved in many rotational lines. The features have been measured and used to determine molecular parameters for ⁶³CuF in the a³Σ⁺ state. The implications of the hyperfine parameters for the electronic wavefunction are discussed and are shown to be consistent with recent theoretical calculations.     

Glycosides of Nadifloxacin—Synthesis and Antibacterial Activities against Methicillin-Resistant Staphylococcus aureus

The increase in the number of bacteria that are resistant to multiple antibiotics poses a serious clinical problem that threatens the health of humans worldwide. Nadifloxacin (1) is a highly potent antibacterial agent with broad-spectrum activity. However, its poor aqueous solubility has limited its use to topical applications. To increase its solubility, it was glycosylated herein to form a range of trans-linked (3a-e) and cis-linked (7a,b) glycosides, each of which was prepared and purified to afford single anomers. The seven glycoside derivatives (3a-e, 7a,b) were examined for potency against eight strains of S. aureus, four of which were methicillin-resistant. Although less potent than free nadifloxacin (1), the α-L-arabinofuransoside (3a) was effective against all strains that were tested (minimum inhibitory concentrations of 1–8 μg/mL compared to 0.1–0.25 μg/mL for nadifloxacin), demonstrating the potential of this glycoside as an antibacterial agent. Estimation of Log P as well as observations made during preparation of these compounds reveal that the solubilities of the glycosides were greatly improved compared with nadifloxacin (1), raising the prospect of its use in oral applications.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.