Medium effects on the ligand field bands of hexathiocyanato- chromate(III)

Transition Metal Chemistry - The wavelengths of absorption maxima are reported for two ligand field bands of hexathiocyanatochromate(III), $ {? Cr(NCS)_{6}^{3-}} $, over a range of...     

Intercalation ofn-alkylamines into α-titanium phosphate from aqueous solutions

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with...     

Porous glass electroosmotic pumps: theory

This paper presents an analytical study of electroosmotic (EO) pumps with porous pumping structures. We have developed an analytical model to solve for electroosmotic flow rate, pump current, and thermodynamic efficiency as a function of pump pressure load for porous-structure EO pumps. The model uses a symmetric electrolyte approximation valid for the high-zeta-potential regime and numerically solves the Poisson-Boltzmann equation for charge distribution in the idealized pore geometry. Generalized scaling of pumping performance is discussed in the context of a parameterization that includes porosity, tortuosity, pore size, bulk ionic density, and the nonuniform conductivity distribution over charge layers. The model also incorporates an approximate ionic-strength-dependent zeta potential formulation.     

Fragmentation of carbohydrate anomeric alkoxyl radicals. A new synthesis of chiral beta-iodo azides, vinyl azides, and 2H-azirines

[reaction: see text] The reaction of 3-azido-2,3-dideoxy-hexopyranose compounds from the d-gluco, d-galacto, d-lacto, and l-arabino carbohydrate series, with (diacetoxyiodo)benzene and iodine, generated 2-azido-1,2-dideoxy-1-iodo-alditols with one carbon less than the starting carbohydrate. These beta-iodo azides could be transformed by dehydroiodination into vinyl azides, which in turn afforded 3-monosubstituted 2H-azirines under thermal conditions. These beta-iodo azides and 2H-azirines may be interesting chiral synthons for the preparation of more complex heterocyclic systems.     

Changes in the Transfer Function of a flow microcalorimeter

Flow microcalorimeters are used to determine thermodynamic properties of liquid mixtures, the accuracy of these measures depends on the right calibration of the instrument. In this work the system is identified by means of the transfer functions of the two poles, it is proven that the first time constant and the sensitivity change with the value of rc _p f of the injected liquids (r - density, c _p - heat capacity, f - injection flow), and that the sensitivities obtained in the electrical and chemical calibrations are different for the same value of rc _p f because the dissipation in each case does not occur in the same place. As a summary of the calibration carried out, it is proposed a sensitivity value of 313±4 mV W^-1 for rc _p f<15 mW K^-1 that permits to make thermal measures with an uncertainty of 3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transition probabilities and average cross sections for the Na2 B1pi(u) --> X1sigma(g)+ system using as excitation the 4880 A Ar+ laser line

The fluorescence spectrum of Na2 induced by the 4879.86 A line of an Argon ion laser has been analyzed with special emphasis on determination of accurate relative intensities. We have observed nineteen fluorescence series for the B1pi(u) --> X1sigma(g)+ band system. Some series are reported for the first time. The radiative transition probabilities for the observed fluorescence series were calculated using hybrid potential energy curves for the B1pi(u) and X1sigma(g)+ states constructed up to dissociation and a B-X transition dipole moment function. Radiative lifetimes for the rovibrational levels of the upper states pumped by the laser line have also been calculated. The transition probabilities and lifetimes agree with the corresponding observed measurements usually within the experimental uncertainty. From the rotational satellite structure with deltaJ' = +/- 1, +/- 2...+/- 20, for some nu'-bands of the most intense fluorescence series induced by emission from the vibrational-rotational levels: nu' = 6, J' = 43 and v' = 9, J' = 56, collision-induced transition rates and average cross sections have been obtained.     

Potentiometric stripping analysis (PSA) for monitoring of antimony in samples of vegetation from a mining area

A potentiometric stripping analysis (PSA) method has been developed and checked for the fast and reliable determination of antimony in vegetation samples of Cistus ladanifer from a mining area in Badajoz, Southwest Spain. The method, modified from previous PSA methods for Sb in environmental samples, is based on dry ashing of the homogenized leaves, dissolution in hydrochloric acid, and PSA analysis on a mercury film plated on to a glassy carbon disk electrode. The influence of experimental variables such as the deposition potential, the deposition time, the signal stability and the calibration parameters, has been investigated. The method has been compared with an independent technique (instrumental neutron activation analysis) by analysis of standards and reference materials and comparison of the results. As a result of automation of the PSA equipment, the proposed method enables unattended analysis of 20 digested samples in a total time of 2 h, thus providing a useful tool for Sb monitoring of a large number of samples.