Infrared photoluminescence from TlGaS2 layered single crystals

Photolimuniscence (PL) spectra of TlGaS₂ layered crystals were studied in the wavelength region 500‐1400 nm and in the temperature range 15‐115 K. We observed three broad bands centered at 568 nm (A‐band), 718 nm (B‐band) and 1102 nm (C‐band) in the PL spectrum. The observed bands have half‐widths of 0.221, 0.258 and 0.067 eV for A‐, B‐, and C‐bands, respectively. The increase of the emission band half‐width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm^‐2. The proposed energy‐level diagram allows us to interpret the recombination processes in TlGaS₂ crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of chromatographic dissociation constants of some carbapenem group antibiotics and quantification of these compounds in human urine

The dissociation constant values (_s^spK_a) of some carbapenem group drugs (ertapenem, meropenem, doripenem) in different percentages of methanol–water binary mixtures (18, 20 and 22%, v/v) were determined from the mobile phase pH dependence of their retention factor. Evaluation of these data was performed using the NLREG program. From calculated pK_a values, the aqueous pK_a values of these subtances were calculated by different approaches. Moreover, the correlation established between retention factor and the pH of the water–methanol mobile phase was used to determine the optimum separation conditions. In order to validate the optimized conditions, these drugs were studied in human urine. The chromatographic separation was realized using a Gemini NX C₁₈ column (250 × 4.6 mm i.d., 5 µm particles) and UV detector set at 220 and 295 nm. Copyright © 2013 John Wiley & Sons, Ltd.     

Conformational search of peptides and proteins: Monte Carlo minimization with an adaptive bias method applied to the heptapeptide deltorphin

The energy function of a protein consists of a tremendous number of minima. Locating the global energy minimum (GEM) structure, which corresponds approximately to the native structure, is a severe problem in global optimization. Recently we have proposed a conformational search technique based on the Monte Carlo minimization (MCM) method of Li and Scheraga, where trial dihedral angles are not selected at random within the range [-180 degrees,180 degrees ] (as with MCM) but with biased probabilities depending on the increased structure-energy correlations as the GEM is approached during the search. This method, called the Monte Carlo minimization with an adaptive bias (MCMAB), was applied initially to the pentapeptide Leu-enkephalin. Here we study its properties further by applying it to the larger peptide with bulky side chains, deltorphin (H-Tyr-D-Met-Phe-His-Leu-Met-Asp-NH(2)). We find that on average the number of energy minimizations required by MCMAB to locate the GEM for the first time is smaller by a factor of approximately three than the number required by MCM-in accord with results obtained for Leu-enkephalin.     

Investigation of Separation and Identification Possibilities of Some Metal-Dithizonate Complexes by Sequential TLC-IR System

The separation and identification possibilities of a number of metal–dithizonate complexes were investigated by means of a TLC-IR sequential system. Dithizonate complexes of some metal cations were pre-pared in a predetermined optimum pH or pH range. Optimum separation conditions of these complexes and the reproducibility of their R _f values were investigated on a series of precoated or laboratory-made TLC plates. R _f values were determined by using the one-dimensional ascending technique. The precision of the procedures was determined for replicates in terms of standard deviation. Detection limits were also determined for each metal complex. The IR spectra were scanned and interpreted for precise identification after preconcentration with the wick-stick procedure for complexes giving overlapped R _f values. The complexes were able to be identified with the aid of IR absorption bands. It has been determined that these IR absorption bands will also be able to be used as reference spectral bands in possible quantitative studies. It has been concluded that an effective and successful qualitative analysis will be executable for incompletely separated complex compounds using an IR spectrophotometer as a TLC detector.     

Shear flocculation of celestite with sodium oleate and tallow amine acetate: effects of cations

Sodium oleate and tallow amine acetate (TAA) were used as surfactants for the shear flocculation of celestite. The shear-flocculation power values obtained with sodium oleate were higher than those obtained with TAA in terms of the concentrations used in the shear-flocculation experiments. In addition, sodium oleate and TAA were more effective on the celestite suspension in the pH ranges of 7-11 and 6-10, respectively. For the shear-flocculation experiments with sodium oleate at pH 11, with preaddition of calcium or magnesium ions at 5 x 10(-5) M and lower concentrations into the suspension, the shear flocculation of the celestite suspension was promoted by the coagulation process due to the calcium and magnesium cations added. However, the shear-flocculation power values decreased due to the interaction between surfactant and cations at concentration values higher than 5 x 10(-5) M for magnesium ions and 10(-3) M for calcium ion. Particularly, magnesium ions significantly reduced the shear-flocculation power values by slime coating of Mg(OH)2 precipitates.     

Thermal stability of polydiphenylamine synthesized through oxidative polymerization of diphenylamine

The thermal stability of polydiphenylamine synthesized through the oxidative polymerization of diphenylamine has been studied. It has been established that the main processes of thermal and thermooxidative degradation of polydiphenylamine begin at 600–650 and 450°C, respectively. It has been shown that, in the course of thermal oxidation of the doped polydiphenylamine, the elimination of a dopant takes place first. With a further increase in temperature, the behavior of this material becomes similar to that of the neutral polymer.     

Pair-excitation MCSCF treatment of small molecules in an optimized Slater–Transform–Preuss basis set

Pair-excitation multiconfigurational self-consistent field (PEMCSCF ) treatment of 11 small molecules (LiH, BeH₂, BH₃, BF, CH₄, C₂H₄, C₂H₂, CH₂O, NH₃, H₂O, and HF) has been carried out in a minimum basis set of Slater Transform Preuss functions as fitted by six cartesian gaussians (STP -6G). The advantages of accuracy without using a split basis are shown by comparison to familiar 4-31G and 6-31G calculations using molecular geometries optimized with STO -6G basis sets. A benefit is shown for the use of minimum basis fitted to STP functions: they overemphasize long-tail radial dependence to achieve long range basis sensitivity without increasing the basis size at the AO -to-MO transformation step in the configuration interaction portion of the MCSCF algorithm. Fully optimized STP -6G parameters are given and appear to be transferable as shown for acrolein. A FORTRAN listing of the full least squares fitting algorithm is available* for in situ generation of STP -6G orbitals energetically superior to 4-31G, or a less accurate STP -6G 1S, 2S, and 2P basis may be scaled directly as if they were STO -6G functions, but with considerably lower energy that with an STO -6G basis.     

Synthesis of New Glyoxime Derivatives,Characterization and Investigation of Their Complexes with Co(II), Ni(II), and Cu(II) Metals and Thermal Studies

In this study, two new vic-dioxime ligands and their complexes with Co²⁺, Ni²⁺, and Cu²⁺ ions were synthesized. Secondary amines (morpholine and piperidine) reacted with anti-chloroglyoxime to give morpholineglyoxime (H₂L¹) and piperidineglyoxime (H₂L²) ligands. All the complexes have a metal to ligand ratio of 1 : 2. The structure of the ligands and their complexes was proposed from elemental analyses, IR, UV-VIS, ¹H and ¹³C NMR spectra, conductivity, magnetic susceptibility measurements, and thermogravimetric analyses.__________From Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 535–539.Original English Text Copyright © 2005 by Ozkan, Canpolat, Kaya.The text was submitted by the authors in English.     

Voltammetric investigation of Tamsulosin

The electrooxidative behavior and determination of Tamsulosin HCl (TAM), one of the alpha(1)-adrenoceptor antagonist, on a glassy carbon disc electrode were investigated for the first time by using cyclic, linear sweep, differential pulse (DPV) and square wave voltammetry (SWV). TAM showed an irreversible oxidation behavior at all pH values and buffers studied. From the electrochemical response, the main oxidation step was found to be related to the methoxy group on the phenyl ring. DPV and SWV were used to generate peak current versus concentration curves for TAM. A linear response was obtained in the range comprised between 2x10(-6) and 4x10(-4) M for both techniques with detection limit of 3.34x10(-7) M for DPV and 2.45x10(-7) M for SWV. The methods were proposed for the determination of TAM in dosage forms adopting both DPV and SWV modes. The methods were extended to the in vitro determination of TAM in spiked serum samples.