Association constants for the NaSO(4)(-) ion pair in concentrated cesium chloride solutions

Values of the association constant, beta(NaSO(4)(-)), for the weak ion-pair formed by sodium and sulfate ions in aqueous solution have been determined at 25 degrees C by high precision sodium ion-selective electrode potentiometry in solutions of ionic strength ranging from 0.50 to 7.00 M in CsCl media and in 1.00 M Me(4)NCl. The data in CsCl media were fitted to an extended form of the Debye-Hückel equation which yielded log beta(NaSO(4)(-))(0)=0.834+/-0.005 at infinite dilution. Evidence is also presented for the formation of very weak ion-pairs between Cs(+) and SO(4)(2-).     

Pivotal steps towards quantification of molecular diffusion coefficients by NMR.

Using nuclear magnetic resonance (NMR) spectroscopy with a pair of pulsed field gradients (PFGs), Stajeskal and Tanner successfully measured molecular diffusion coefficients in solution in 1965. This method has since been used extensively in various applications, especially after the PFG was implemented in commercial NMR probes. Due to the nonuniformity of the PFG and radio frequency (RF) fields, molecules distributed throughout the sample experience different PFG and RF fields and contribute unevenly to the measured diffusion coefficients, resulting in considerable errors in conventional NMR diffusion experiments. By selective excitation of a central sample region with an offset-independent adiabatic inversion pulse and a PFG, a uniform RF field can be assumed, and the PFG can be represented as a linear approximation. Under these conditions, the molecules diffuse as if they were all experiencing the same effective gradient g(e), leading to a Gaussian signal decay as a function of the PFG strength. Quantitative measurement of molecular diffusion coefficients is therefore made possible. From the diffusion coefficient of a 90 % H(2)O/10 % D(2)O sample, it is convenient to calibrate g(e) with a Java program. In a similar way the nonlinearity of the PFG can be corrected.     

Determination of the association constant of NaSO 4 − with the sodium-selective electrode

The association constant of the NaSO ₄ ^? complex has been determined using a sodium-selective electrode in an aqueous medium of 0.5 M ionic strength at 25°C. The constant calculated was 2.5±0.2, and no evidence was found under the present conditions for the existence of higher complexes.     

Initial steps of dissolution of monoclinic and rhombic crystals of paracetamol

The initial steps of dissolution of Paracetamol (monoclinic and rhombic modifications) in a series of solvents (10% solutions of acetic anhydride, pyridine, 1,4-dioxane, morpholine, and N-methylmorpholine in CCl₄) were studied. The etching patterns on planes parallel and perpendicular to Paracetamol molecular layers were compared.     

12-4-12/tCA沉淀相的光响应溶解及聚集体结构转变

双子表面活性剂12-4-12与反式肉桂酸(tCA)由于强烈的静电吸引作用而生成12-4-12/tCA沉淀相.通过偏光显微镜和X射线衍射分析发现,12-4-12/tCA沉淀相具有六角和层状的复合晶体结构.在365nm紫外光照射下,12-4-12/tCA沉淀相会逐渐溶解,依次经历晶体-囊泡-蠕虫状胶束的转变,对12-4-1...     

Determination of 4- n -nonylphenol in water by enzyme immunoassay

A range of monoclonal antibody-based competitive immunoassays in the format of microtitre plate ELISA and dipstick tests for quantitative and semi-quantitative detection of 4- n -nonylphenol in water was developed. A simple visual dipstick test was based on changing of spot colour from green to brown in the presence of 4- n -nonylphenol at concentrations within the range 10-100 ng mL(-1). Two different detection systems were used for quantitative immunoassay. Application of enhanced chemiluminescence (ECL) resulted in an increase of the sensitivity of ELISA when compared to conventional colorimetric detection. Thus a detection limit of 0.06 ng mL(-1 )of 4- n -nonylphenol was achieved with IC(50) 2.0 ng mL(-1). The tests developed were applied to natural and spiked water samples.     

First synthetic approach towards K-259-2, a unique calmodulin antagonist

K-259-2, a unique calmodulin antagonist, is an allyl chain containing anthraquinone natural product. A regiospecific synthetic approach towards K-259-2 is herein represented. The study also showcases a protocol for synthesizing heavily substituted bromo naphthoate which was found to be suitable for fabricating the K-259-2 motif.     

Synthesis of highly substituted 2,6-anti-configured tetrahydropyrans. First steps towards an efficient access to amphidinol 3 ring system

Highly functionalised and polysubstituted tetrahydropyrans, akin to the middle core of the amphidinols, can be efficiently synthesised, with full stereocontrol and in good yields, using as key steps an anti-allylation reaction coupled with an intramolecular Sakurai cyclisation. Three approaches were devised in order to reach a broad range of substitution patterns.     

Tailoring the electroactive area of carbon screen-printed electrodes by simple activation steps towards rutin determination

Journal of Solid State Electrochemistry - Screen-printed electrodes (SPEs) have the advantage of being considered electrochemical cells that can be implemented in portable sensor applications. With...     

Primary reaction steps of Al13- clusters in an HCl atmosphere: snapshots of the dissolution of a base metal

Recently, the icosahedral Al13- cluster has been shown to possess some unusual characteristics due to its special stability (Bergeron, D. E.; et al. Science 2004, 304, 84-87; 2005, 307, 231-235). Here we present reactions of isolated Al13- clusters with hydrogen chloride, following their oxidation through the application of Fourier transform ion cyclotron resonance mass spectrometry. Due to the ultra-low-pressure conditions, the reaction time can be expanded to make one intermediate after another come into view. The following intermediates are generated sequentially, releasing AlCl and H2: Al13HCl-, Al12H-, Al12H2Cl-, Al11H2-, Al12Cl-, and Al11-. The resulting reaction scheme proves to be a molecular model for the dissolution of a metal in an acid, revealing the initial steps of a heretofore unknown fundamental heterogeneous reaction.     

Biogenetic hypothesis and first steps towards a biomimetic synthesis of haouamines

A detailed hypothesis for the biogenesis of haouamines is reported herein, supported by experiments headed towards biomimetic synthesis of these compounds.     

Activation of the dissolution of carbonate materials in water by electric impulse discharges

Effect of electric impulse discharges on the equilibrium in the systems calcium carbonate-water and calcium carbonate-water-carbon dioxide was studied.     

Solute-induced dissolution of hydrophobic ionic liquids in water

Significant solubilization of ostensibly water-immiscible ionic liquids (ILs) in acidic aqueous phases is induced by the presence of any of a variety of neutral extractants, the apparent result of the formation of the protonated form of the extractant and its subsequent exchange for the cationic component of the IL. The extent of this solubilization is shown to diminish with increasing hydrophobicity of the IL cation and decreasing extractant basicity. These observations raise concerns as to the viability of ILs as “drop in replacements” for traditional organic solvents in the solvent extraction of metal ions.     

Oleic acid-enhanced dissolution of cellulose in high-temperature water

This paper reports, for the first time, the enhanced dissolution of cellulose in subcritical water by addition of a fatty acid. Simply adding oleic acid dramatically promoted the dissolution of cellulose. High-pressure in-situ observation showed that cellulose dissolved in high-temperature water at approximately 500 K, which is 70 K lower than without oleic acid. The yield of oligo and monosaccharides with oleic acid at 473 K was seven times higher than without oleic acid.     

Permeability of poly(1-4-piperazinediylterephthaloyl) microcapsules towards sodium chloride

Water-loaded poly(1,4-piperazinediylterephthaloyl) (PPiP) microcapsules were prepared by an interfacial polycondensation technique using piperazine and terephthaloyl dichloride as water-soluble and water-insoluble monomers, respectively. The organic solvents used were mixtures of cyclohexane and chloroform and n-hexane and chloroform in various volume ratios. The microcapsules obtained were washed successively with n-hexane, acetone, and water and fractionated into several fractions of different sizes. A suspension of each fraction and a solution of sodium chloride were mixed and the change with time in electroconductivity of the mixture was measured to estimate the rate of salt entry into the microcapsules. The permeability coefficient for the salt was calculated from the rate of salt entry. It was found that the permeability increased as the capsule size increased and was higher for the capsules prepared with n-hexane—chloroform mixtures than for those prepared with cyclohexane—chloroform mixtures. These findings were explained in terms of the density and thickness of the capsule membrane.     

Inhibition of copper dissolution in water solutions of triazoles

The influence of the chemical structure of certain triazoles on the inhibition of copper dissolution in water solutions at pH 7.40 is studied by electrochemical and ellispometric means. It is established that adsorption of the studied triazoles on copper at potential E = 0.0 V relative to a normal hydrogen electrode is polymolecular, the first layer is described by the Frumkin equation with values of the free adsorption of energy values (?ΔG _a ⁰ ) = 50.5–70.1 kJ/mol. In addition, possible orientations of triazole molecules with respect to a surface of oxidized copper are revealed.     

Thermodynamics of the dissolution of crystalline L-methionine in water

The enthalpies of dissolution of crystalline L-methionine in water and aqueous solutions of potasium hydroxide at 298.15 K are measured by means of direct calorimetry. The standard enthalpies of formation are calculated for L-methionine and products of its dissociation in aqueous solution.     

An approach towards the synthesis of 4-phenyl-5-arylimino-δ2-1,2,3,4-thiatriazolines

4-Phenyl-5-arylimino-δ²-1,2,3,4-thiatriazolines are presumably formed by reacting 5-arylaminothiatriazoles with benzyne at 50°, but decompose in situ to benzothiazole derivatives by way of the two pathways (a) and (b) shown in Scheme 4.