A comparison of the AMBER*, OPLSAA and HF potential energy surfaces for a series of diastereomeric cyclic urea HIV-1 inhibitors

The LM:MC conformational search method was used to identify the low energy structures on the OPLS-AA/GBSA(water) and AMBER*/GBSA(water) surfaces for a diastereomeric series of cyclic urea molecules that have been shown to be potent inhibitors of the HIV-1 protease enzyme. The lowest energy structures from each search were then subjected to geometry optimization and frequency analysis using the HF/6-311G** method in conjunction with the self-consistent reaction field (SCRF) treatment for water. A comparison of the diastereomeric energies and structures indicates that the OPLSAA/GBSA(water) surface is in good agreement with the HF/6-311G**/SCRF(water) surface.     

Al2O3-TiO2 SOL-GEL MIXED OXIDES AS SUITABLE SUPPORTS FOR THE REDUCTION OF NO BY CO

Sol–Gel alumina-titania supports were prepared by the co-gelling aluminum tri-sec-butoxide and titanium isopropoxide (10 wt.% TiO₂) at pH 3 and pH 9. Supports showed specific surface areas higher than 250 m²/g, and Lewis acidity was observed by FTIR pyridine adsorption. Cu°, Cu¹⁺ and Cu²⁺species on impregnated Cu/Al₂O₃-TiO₂catalysts were identified by means of FTIR-CO adsorption. A correlation between Cu⁺/Cu²⁺ abundance and the activity for NO reduction by CO is reported.     

Application of the ligand vapour technique to the volatilization of unstable chelate compounds (particularly iron(III) trifluoroacetylacetonate) in AAS

Summary This paper describes a method for volatilizing chelate complexes in AAS using a carrier gas containing ligand vapour in order to prevent chelate decomposition on heating. The method is evaluated with iron(III) trifluoroacetylacetonate. The sample containing chelate is injected into an electrically heated system, and is carried by nitrogen gas containing trifluoroacetylacetone H(TFA) to a silica tube where atomization occurs. This system increases the reproducibility of atomic absorption signals and decreases the high blanks which occur with the conventional method as a result of chelate decomposition. The characteristic mass of the combined analytical procedure is 1.30 ng Fe, the detection limit 12.0 ng Fe, and the relative standard deviation is 4.7% ng Fe (n=10). Sensitivity is improved 16-fold with respect to the system involving conventional nebulization and atomization of aqueous solutions in air-acetylene flame.     

An unusual 3D coordination polymer based on bridging interactions of the nucleobase adenine

The first 3D coordination polymer containing a nucleobase as a bridging ligand, [[Cu2(mu-ade)4(H2O)2][Cu(ox)(H2O)]2 x approximately 14H2O]n (1), has been synthesized by reaction of adenine (Hade) with a basic solution of K2[Cu(ox)2] x 2H2O (ox = oxalato dianion). Compound 1 crystallizes in the trigonal space group R3 with a = b = 31.350(1) angstroms, c = 14.285(1) angstroms, V = 12158.7(10) angstroms3, and Z = 9. X-ray analysis shows a covalent 3D network in which the copper(II) centers are bridged by tridentate mu-N3,N7,N9 adeninate ligands. The compound has relatively large, nanometer-sized tubes associated with the self-assembly process directed solely by metal-ligand interactions. The covalent 3D framework remains intact upon removal of the guest water molecules trapped in the nanotubes. Magnetic measurements indicate an overall antiferromagnetic behavior of the compound.     

Flame atomic-absorption determination of beryllium after extraction from NH(4)SCN medium with trioctylamine in MIBK

A study has been made of the experimental conditions, errors, sensitivity, limits of detection and linear response range in the determination of beryllium by AAS in a nitrous oxide-acetylene flame, with aqueous or aqueous organic solutions or MIBK solutions containing the ion-pair [Be(SCN)(2-)(4)][(R(3)NH)(2+)(2)]. The interference of Al, Mg, Ti, V, Fe, Ca, Mn, Na, K, SiO(2-)(3), PO(3-)(4), Cl(-), SO(2-)(4), F(-), ClO(-)(4), H(2)BO(-)(3) and SCN(-) has been studied, and methods established for eliminating that of titanium, aluminium, fluoride and silicon.     

Sulphate determination after its reduction to hydrogen sulphide and volatile separation by molecular absorption spectrometry

A rapid spectrophotometric method for sulphate determination in a discontinuous mode is described. The method is based on sulphate reduction to hydrogen sulphide followed by its volatilization and absorption in an alkaline solution. The reduction is obtained when a sulphate sample is heated to 287 degrees C for 15 min, with a mixture of Fe(o)/KI and phosphoric acid. The resulting gas is swept by nitrogen flow into a 0.1 M sodium hydroxide solution and the absorbance of the sulphide ions is measured directly at 230 nm. The proposed method enabled us to determine 50-700 mug of total sulphate with a relative standard deviation of the order of 5%. The method has been applied for the determination of sulphates in liquid (mineral waters) and solid (gypsiferous soils) samples.     

Liquid chromatographic determination of the total available free and intrachain lysine in various foods

A method for the quantitative determination of the total available lysine in various foods is developed. The method is based on the reaction of the amino groups on the lysine molecule with fluorodinitrobenzene and is capable of furnishing simultaneous determination of the available intrachain lysine (known as N-epsilon-[2,4-dinitrophenyl]-L-lysine) or the available free and/or N-terminal lysine (known as N,N'-di-[2,4-dinitrophenyl]-L-lysine). Optimum conditions for separation and quantitation are studied. The results show the proposed method to be both accurate and precise and suitable for food samples containing hydrolyzed proteins.     

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 μl of 0.1%, w/v sodium fluoride solution into 100 μl of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min⁻¹ Ar carrier gas. The calibration curve was linear up to at least 100 μg ml⁻¹ of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 μl. The relative standard deviation for six measurements of 10 μg ml⁻¹ of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.     

Analysis of industrial effluents to determine endocrine-disrupting chemicals

Contaminated industrial effluents often contain a variety of organic pollutants that can disturb the development of the endocrine system and the organs that respond to endocrine signals in organisms. Total characterisation of the effluents to detect all these potential endocrine disruptors by standard GC-MS methods is difficult since this technique often misses the more polar or non-volatile fraction of these organic compounds. The wide spectrum of endocrine-toxic substances and their low concentrations require powerful analytical approaches like LC-MS for their identification. Furthermore, the methods for the detection of endocrine effects developed up to now do not show all the possible oestrogenic effects and results of the different tests are not comparable to one another. Therefore, further ecotoxicological research should be carried out so that new strategies can be proposed. In this article, an overview of the analytical methods for determining organic contaminants in industrial effluents and tests for the identification of endocrine disruptors and their effects is presented.     

Oxidation of bis(4-toluenesulphonyl-L-serinato)copper(II) to bis(formylglycine)copper(II)

Summary Oxidation of L-serine occurs on degradation of bis(L-serinato)copper(II) and at the same time copper is reduced.