New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Synthesis and Investigation of Phthalazinones as Antitubercular Agents

A series of 2‐ and 7‐substituted phthalazinones was synthesised and their potential as anti‐tubercular drugs assessed via Mycobacterium tuberculosis (mc²6230) growth inhibition assays. All phthalazinones tested showed growth inhibitory activity (MIC <100 μm ), and those compounds containing lipophilic and electron‐withdrawing groups generally exhibited better anti‐tubercular activity. Several lead compounds were identified, including 7‐((2‐amino‐6‐(4‐fluorophenyl)pyrimidin‐4‐yl)amino)‐2‐heptylphthalazin‐1(2H)‐one (MIC=1.6 μm ), 4‐tertbutylphthalazin‐2(1H)‐one (MIC=3 μm ), and 7‐nitro‐phthalazin‐1(2H)‐one (MIC=3 μm ). Mode of action studies indicated that selected pyrimidinyl‐phthalazinones may interfere with NADH oxidation, however, the mode of action of the lead compound is independent of this enzyme. MIC=minimum inhibitory concentration.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

Über Chalkogenolate. 98 [1]. Kristall- und Molekülstruktur von Wolfram(IV)-äthylthioxanthat

On Chalcogenolates. 98. Crystal and Molecular Structure of Tungsten(IV) Ethylthioxanthate W[S₂C? SC₂H₅]₄ crystallizes with Z = 2 in the tetragonal space group P4₂/n with cell dimensions a = 11.108(5) Å and c = 9.489(5) Å. The crystal and molecular structure has been determined from single crystal X-ray data at ?160°C and refined to a conventional R of 0.058. The structure consists of isolated molecules. The tungsten atom is bonded to eight sulfur atoms from four chelating thioxanthate ligands. The coordination geometry approximates very closely to triangularly dodecahedral.     

Effects of amine modifiers on retention and peak shape in reversed-phase high-performance liquid chromatography

A systematic evaluation of the effects of 15 different amine modifiers on the retention and peak symmetry of three solutes, a primary, a secondary, and a tertiary amine, is presented. Using automated experimentation, mobile phase combinations for each modifier over a pH range of 2.5 to 8 were investigated. The effect of changing the sodium ion concentration of the mobile phase was also examined. The importance of hydrophobic, ion exchange, and hydrogen bonding interactions as mechanisms for retention and peak symmetry of positively charged solutes is discussed.     

Reaktion von Acetamidin mit Kohlenstoffdisulfid 5. Kristall- und Molekülstruktur der N-Acetimidoyldithiocarbamidsäure

On Chalcogenolates. 176. Reaction of Acetamidine with Carbon Disulfide. 5. Crystal and Molecular Structure of N-Acetimidoyl Dithiocarbamic Acid N-Acetimidoyl dithiocarbamic acid crystallizes with Z = 8 in the monoclinic space group P2₁/c (No. 14) with cell dimensions a = 9.502(3) Å, b = 11.585(1) Å, c = 10.765(3) Å, β = 92.19(4)°. The crystal structure has been determined from single crystal X-ray data measured at 21°C and refined to a conventional R of 0,043 for 3450 independent reflections (R_w = 0,050). The acid exists in the dipolar form in two different conformations. The molecules are roughly plane. They are linked together by different S…?H? N hydrogen bridges.