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material as they share the properties of both organic and inorganic materials. Marcy et al. [ 7 ] reported that the nonlinearity of l -histidine tetrafluoroborate was at least five times higher than that of KDP. In the light of this, a series of l

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]. The basic amino acid l -histidine has been widely studied with the discovery of promising nonlinear optical NLO material l -histidine tetrafluoroborate [ 12 ]. Recently, several new salts of l -histidine have been reported with excellent NLO

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], herein, we report the effect of immobilized tridentate N -salicylidene- l -histidine Schiff base vanadium complex within the nanoreactors of Al-MCM-41 as catalysts for the epoxidation of geraniol, cinnamyl alcohol and trans -2-hexene-1-ol

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Abstract  

Due to physical decay properties commonly associated with therapeutic radionuclides, 188Re (t 1/2 = 16.98 h, E max = 2.12 MeV) is of high interest for endovascular brachytherapy and endoradiotherapy in general. Rhenium precursors in the low oxidation state +I, such as the organometallic fac-[Re(H2O)3(CO)3]+ are promising lead compounds compared to those with oxidation states +III and +V since they can be prepared under mild conditions and do not tend to reoxidize to oxidation state +VII while multidentate ligands can be attached under substitution of coordinated water molecules. This study comprises the application of the Free-Ion Selective Radiotracer Extraction (FISRE) technique in order to determine dissociation rate constants of complexes bearing the [188Re(CO)3]+-core at tracer levels in vitro with regards to their time-dependent kinetic speciation. As ligands, the tridentate l-histidine as well as the dipeptides l-carnosine (β-alanyl-l-histidine) and glycyl-l-histidine were chosen in order to study the effects of different moieties attached to the primary amine of l-histidine.

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Summary

Direct resolution of enantiomers of (RS)-ketorolac was achieved by thin-layer chromatography on silica gel plates using enantiomerically pure L-tryptophan, L-valine, L-methionine, and L-histidine as chiral additive in the stationary phase. The solvent system (acetonitrile, methanol water, and chloroform) with different ratios was successful in resolving the enantiomers. Spots were detected by use of iodine vapor. The detection limit was 0.4 µg mL−1 for each enantiomer of (RS)-ketorolac. The native enantiomers were isolated and characterized.

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Chromatography of some metal cations has been performed on silica gel layers with micellar mobile phases containing sodium dodecyl sulfate (SDS), an anionic surfactant. The effects on the mobility of metal ions of SDS concentration, mobile phase pH, and the presence of amino acids (l-arginine, dl-phenylalanine, l-tryptophan, and l-histidine) in the mobile phase were examined. Although amino acids caused diffusion (or tailing) of the metal ion spots, use of l-histidine or l-tryptophan facilitates the analytically important separation of a mixture of Au 3+ , Cu 2+ , and Ag + ions. The TLC system comprising silica gel G as stationary phase and 0.01 m SDS (pH 2.3)-0.01 m l-tryptophan or l-histidine, 1 + 9, as mobile phase was identified as the most suitable for the separation of mixtures of Au 3+ , Cu 2+ , and Ag + . The interference of impurities such as amines, phenols, and inorganic anions on the mobility and separation of a mixture of Au 3+ , Cu 2+ , and Ag + ions was also examined. The lower limit of detection of some metal ions, viz. Fe 3+ , Cu 2+ , Zn 2+ , Cd 2+ , and Hg 2+ was determined. The proposed method has been used for identification and separation of Au 3+ , Cu 2+ , and Ag + in a variety of spiked samples.

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Direct enantioresolution of (±)-etodolac has been achieved by adopting a new conceptual approach involving both achiral phases in thin-layer chromatography (TLC). Enantiomerically pure l-tryptophan, l-phenyl alanine, l-histidine, and l-arginine were used as chiral inducing reagents (CIR); none of these was impregnated with silica gel (while making TLC plates) or mixed with the mobile phase. The solvent system MeCN—CH2Cl2—MeOH, in different proportions, was found to be successful for enantioresolution. Spots were located in iodine chamber. Effect of concentration of chiral inducing reagent and temperature on enantioresolution was studied.

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Direct enantioseparation of (±)-terbutaline has been achieved by ligand-exchange thin-layer chromatography. Enantiomerically pure L-amino acids (namely, L-tryptophan, L-phenyl alanine, and L-histidine) and Cu(II) acetate were used for the preparation of ligand- exchange reagents. Three different approaches were adopted for impregnating the plate with ligand-exchange reagents. The solvent system MeCN–CH2Cl2–MeOH–H2O, in different proportions, was found to be successful for enantioseparation. The results obtained with all the approaches have been compared. The effect of the concentration of Cu(II) acetate and a chiral selector has also been investigated. The spots were located in an iodine chamber.

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A rapid, inexpensive, and stereoselective densitometric—thin-layer chromatographic (TLC) method using l-(+)-tartaric acid and l-histidine—Cu complex as chiral mobile phase additive for the enantioseparation of atracurium besylate and atropine sulfate, respectively, and quantitative determination of their chiral switching (eutomer) isomers, cisatracurium besylate and hyoscyamine sulfate, were used in this study. The effect on resolution of different chiral selector concentrations, temperatures, and pH values was investigated. The spots were detected with ultraviolet (UV) lamp followed by densitometric measurements at 280 nm and 215 nm for cisatracurium besylate and hyoscyamine sulfate, respectively. The mobile phases enabling successful resolution were acetonitrile—methanol—dichloromethane—glacial acetic acid—H2O containing 70 mg l-(+)-tartaric acid (7:1:0.5:0.7:1, by volume), pH 5 for atracurium besylate, and methanol—H2O containing 40 mmol l-histidine and 20 mmol copper(II) acetate (8.8:1.2, by volume), pH 6.5 for atropine sulfate. Thermodynamic parameters, enthalpy ΔH and entropy ΔS were investigated to study the effect of temperature on the enantioseparation using the Van’t Hoff plot.

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