Adsorption and microcalorimetric investigations ofn-butylamine intercalation in α- and γ-zirconium phosphates

The intercalation process ofn-butylamine was investigated. The adsorption ofn-butylamine in interlamellar space had stepwise character in case of both crystalline forms of zirconium phosphate. The intercalatedn-butylamine existed at low concentration as bilayered complex. The reaction heat was determined by a microcalorimetric method. It was found that about 90% of it refers to the neutralization ofn-butylamine and only about 10% is related with surface adsorption (ion exchange). The steps of adsorption are 6.0 J/g and 1.0 J/g reaction heat values, respectively. The enthalpy balance of total process in dilute solution system (c ₀=3.0 vol%) is 14.67 kJ/mol. The calculated value for ion adsorption (exchange) was 1.37 kJ/mol.     

On-line preconcentration of inorganic mercury and methylmercury in sea-water by sorbent-extraction and total mercury determination by cold vapour atomic absorption spectrometry

A comparative study of three mercury chelate forming reagents [diethyldithiocarbamate, pyrrolidin-1-yldithioformate and diphenylthiocarbazone (dithizone)] has been carried out for the preconcentration of ultratrace amounts of inorganic mercury and methylmercury in silica C(18) minicolumns as the solid sorbent. Sample flow injection in-line sorbent extraction was coupled with continuous cold vapour atomic absorption spectrometry (CVAAS) for detection. Results showed the superiority of the carbamate type reagents over the dithizone for the on-line formation and preconcentration of the corresponding mercury chelates. Using diethyldithiocarbamate (DDC) as reagent, aqueous sample volumes of 100 ml can be preconcentrated with 100% efficiency for both inorganic mercury and methylmercury. Quantitative release of the retained DDC chelates was obtained for volumes of eluent (ethanol) of 50 microl. Following the proposed procedure, detection limits of 16 ng/l. of mercury were achieved for sample volumes of 25 ml. The relative standard deviation was +/- 3.4% at 0.5 microg/l. Hg(II) levels. The method has been successfully applied to the determination of low levels of mercury in sea-water.     

Synthese von 4H-Pyrano[2,3-d]pyrimidinen

Summary Good yields of substituted 5-(5R-2-furyl)-4H-pyrano[2,3-d]pyrimidines4 were obtained in the reaction of 2-ethoxymethyleneamino-3-cyano-4H-pyranes2 with ammonia. Compounds2 were prepared by the condensation of the starting 2-amino-5-acetyl-3-cyano-6-methyl-4H-pyranes1 with ethyl orthoformate. Spectral properties of the bicyclic system4 in relation to compounds3 are discussed.

     

Comprehensive kinetic studies on isothermal and non-isothermal reactions of some aluminium compounds

Residual differences after model fitting were investigated in both isothermal and non-isothermal kinetics in order to make numerical comparisons between several models and various parameter-estimating methods. Data from two independent experimental series were evaluated. A large data set, collected earlier under isothermal conditions from decompositions and hydrothermal reactions of aluminium hydroxides and oxides, was processed first. It showed that mechanical activation of the starting gibbsite affected reactivity of samples in several subsequent reactions for all model equations tried. The relative residual deviation concept is introduced, and statistics were applied to find a model that fits a certain reaction in most of the cases. In the second study, the sulphate decomposition step of aluminium sulphate octadecahydrate was investigated. TG curves were measured using a constant heating rate. Dynamic models were fitted by three mathematical methods, including a new general purpose one. Fitting ability of the methods with various complexity were compared on the basis of residual deviations obtained after integration of the model equations. As well as evaluating the best fit, this new parameter-estimating method provides a statistical analysis of the reliability of the whole model fitting process.     

Structure of the acetone liquid-vapor interface as seen from Monte Carlo simulations

The orientational order of the molecules at the liquid-vapor interface of acetone has been investigated by computer simulation. To fully describe the orientational preferences of the acetone molecules, the bivariate joint distribution of two independent orientational parameters has been determined at different layers of the interface. The strength of the orientational ordering of the interfacial molecules has been found to be liquid-like rather than crystal-like. The obtained results have revealed that the interfacial acetone molecules have dual orientational preferences. The main symmetry axis of the molecules declines by about 50-70 degrees from the interface normal axis, pointing toward the liquid phase in both of the preferred orientations. However, the plane of the molecules in the orientation preferred on the liquid side of the interface is perpendicular to the interfacial plane, whereas the other preferred orientation, which is present on the vapor side of the interface, corresponds to the alignment obtained from this orientation by an almost 90 degrees rotation around the main symmetry axis. Because the population of the liquid side is higher than that of the vapor side of the interface, the first of the two preferred orientations is the dominant alignment over the entire interface, in good agreement with recent experimental findings (Chen, H.; Gan, W.; Wu, B. H.; Wu, D.; Zhang, Z.; Wang, H. F. Chem. Phys. Lett. 2005, 408, 284).     

Action spectroscopy and temperature diagnostics of H+ 3 by chemical probing

Infrared absorption spectroscopy of few hundred H+(3) ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v(1)=0,v(2) (l)=3(1))<--(0,0(0)) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H+(3) ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR).     

Determination of nonsteroidal anti-inflammatory drugs in biological fluids by automatic on-line integration of solid-phase extraction and capillary electrophoresis

A new, automatic method for the clean-up, preconcentration, separation, and quantitation of nonsteroidal anti-inflammatory drugs (NSAIDs) in biological samples (human urine and serum) using solid-phase extraction coupled on-line to capillary electrophoresis is proposed. Automatic pretreatment is carried out by using a continuous flow system operating simultaneously with the capillary electrophoresis equipment, to which it is linked via a laboratory-made mechanical arm. This integrated system is controlled by an electronic interface governed via a program developed in GWBasic. Capillary electrophoresis is conducted by using a separation buffer consisting of 20 mM NaHPO4, 20 mM beta-cyclodextrin and 50 mM SDS at pH 9.0, an applied potential of 20 kV and a temperature of 20 degrees C. The analysis time is 10 min and the detection limits were between 0.88 and 1.71 microg mL(-1). Automatic clean-up and preconcentration is accomplished by using a C-18 minicolumn and 75% methanol as eluent. The limit of detection of NSAIDs can be up to 400-fold improved when using sample clean-up. The extraction efficiency for these compounds is between 71.1 and 109.7 microg mL(-1) (RSD 2.0-7.7%) for urine samples and from 77.2 to 107.1 microg mL(-1) (RSD 3.5-7.1%) for serum samples.     

On-line preconcentration and determination of mercury in biological samples by flow injection vapour generation inductively coupled plasma atomic emission spectrometry

An FI-ICP-AES method for the determination of trace levels of mercury in biological samples has been described, which is based on the extraction of the mercury complex with 1,5-bis (di-2-pyridyl)methylene thiocarbonohydrazide (DPTH) on-line into isobuthyl-methyl ketone (IBMK). The organic phase (containing the complex) has been mixed on-line with SnCl₂ in N,N-dimethylformamide. Thus, mercury vapour can be generated directly from the organic phase and separated in a gas-liquid separation device. The detection limit for mercury is 4 ng/ml and the calibration curve is linear at least from 10 to 2500 ng/ml. The relative standard deviation for 10 replicate measurements is ±1% for 100 ng/ml of Hg(II). Results from the analysis of some certified biological reference materials are given.     

Quasi‐random integration in quantum chemistry: Efficiency,stability, and application to the study of small atoms and molecules constrained in spherical boxes

This project consists of two parts. In the first part, a series of test calculations is performed to verify that the integrals involved in the determination of atomic and molecular properties by standard self‐consistent field (SCF) methods can be obtained through Halton, Korobov, or Hammersley quasi‐random integration procedures. Through these calculations, we confirm that all three methods lead to results that meet the levels of precision required for their use in the calculation of properties of small atoms or molecules at least at a Hartree–Fock level. Moreover, we have ensured that the efficiency of quasi‐random integration methods that we have tested is Halton=Korobov>Hammersley?pseudo‐random. We also find that these results are comparable to those yielded by ordinary Monte Carlo (pseudo‐random) integration, with a calculation effort of two orders of smaller magnitude. The second part, which would not have been possible without the integration method previously analyzed, contains a first study of atoms constrained in spherical boxes through SCF calculations with basis functions adapted to the features of the problem: Slater‐type orbitals (STOs) trimmed by multiplying them by a function that yields 1 for 0 < r < (R‐δ), polynomial values for (R‐δ) < r < R and null for r > R, R being the radius of the box and δ a variationally determined interval. As a result, we obtain a equation of state for electrons of small systems, valid just in the limit of low temperatures, but fairly simple. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The structural phase transitions of aminoguanidinium(1+) dihydrogen phosphate—study of crystal structures, vibrational spectra and thermal behavior

Aminoguanidinium(1+) dihydrogen phosphate was prepared by crystallization from aqueous solution. On the basis of the results of DSC measurements, X-ray structural analysis was carried out at temperatures of 160, 215 and 293 K for three aminoguanidinium(1+) dihydrogen phosphate phases ( |Z=2|non-ferroic |melting point 408 K; II |201-222 K|(2) |Z=2|non-ferroic|-; III |<201 K|(2)|Z=4|non-ferroic|-). The triclinic unit cell dimensions (a=6.8220(2), b=7.1000(2), c=7.4500(2) Å, α=86.925(2)°, β=80.731(2)°, γ=79.630(2)°, V=350.21(2) Å³—phase I) are similar for all three structural phases with the exception of phase III, where doubling of the c-axis length leads to an increase in the volume to 692.34(3) Å³. The crystal structure of all three modifications consists of parallel layers of dihydrogen phosphate anions that are interconnected by aminoguanidinium(1+) cations through hydrogen bonds of the N-H…O type. The planar aminoguanidinium(1+) cations are oriented almost parallel to each other and are perpendicular to the anion layers. The primary differences amongst phases I, II and III lie in the location of the H atom in the short O-H…O bonds connecting the dihydrogen phosphate anions in layers. The FTIR and FT Raman spectra of natural and deuterated compounds were recorded and interpreted. The FTIR spectra were studied down to a temperature of 90 K.