Direct assignment of the relative configuration in acyclic 1,3-diols by 1H NMR spectroscopy

[chemical reaction: see text]. Using an operationally simple deuterium isotopic perturbation method, the relative configuration of 1,3-diols can be determined directly using 1H NMR spectroscopy. A comparison of the OH chemical shifts for OH/OH and OH/OD isotopomers provides a reliable assessment of the relative configuration of the diol; anti-1,3-diols within polyacetate and polypropionate frameworks have upfield isotope shifts of 2-16 ppb, whereas syn-1,3-diols show upfield isotope shifts of 20-33 ppb.     

Electroviscous effects on pressure-driven flow of dilute electrolyte solutions in small microchannels

A fundamental understanding of the flow characteristics of electrolyte solutions in microchannels is critical to the design and control of microfluidic devices. Experimental studies have shown that the electroviscous effect is appreciable for a dilute solution in a small microchannel. However, the experimentally observed electroviscous effects cannot be predicted by the traditional theoretical model, which involves the use of the Boltzmann distribution for the ionic concentration field. It has been found that the Boltzmann distribution is not applicable to systems with dilute electrolyte solutions in small microchannels because it violates the ion number conservation condition. A new theoretical model is developed in this paper using the Nernst equation and the ion number conservation, instead of the Boltzmann distribution, to obtain the ionic concentration field. The ionic concentration field, electrical potential field, and flow field in small microchannels are studied using the model developed here. In order to verify this model, the model-predicted dP/dx (applied pressure gradient) Re (Reynolds number) relationship is compared with the experimentally determined dP/dx approximately Re relationship. Strong agreement between the model predictions and the experimental results supports this model.     

N,N'-Ethylenedi-L-cysteine (EC) and Its Metal Complexes: Synthesis, Characterization, Crystal Structures, and Equilibrium Constants

N,N'-ethylenedi-L-cysteine (EC) and its indium(III) and gallium(III) complexes have been synthesized and characterized. The crystal structures of the ligand and the complexes have been determined by single-crystal X-ray diffraction. EC.2HBr.2H(2)O (C(8)H(22)Br(2)N(2)O(6)S(2)) crystallizes in the orthorhombic space group P2(1)2(1)2 with a = 12.776(3) ?, b = 13.735(2) ?, c = 5.1340 (10) ?, Z = 2, and V = 900.9(3) ?(3). The complexes Na[M(III)EC].2H(2)O (C(8)H(16)MN(2)O(6)S(2)Na) are isostructural for M = In and Ga, crystallizing in the tetragonal space group P4(2)2(1)2 with the following lattice constants for In, (Ga): a = 10.068(2) ?, (9.802(2) ?), b = 10.068(2) ?, (9.802(2) ?), c = 14.932(2) ?, (15.170(11) ?), Z = 4 (4), and V = 1513.6(5) ?(3), (1457.5(11) ?(3)). In both metal complexes, the metal atoms (In and Ga) are coordinated by six donor atoms (N(2)S(2)O(2)) in distorted octahedral coordination geometries in which two sulfur atoms and two nitrogen atoms occupy the equatorial positions, and the axial positions are occupied by two oxygen atoms of two carboxylate groups. The structures of the complexes previously predicted by molecular mechanics are compared with the crystal structures of the Ga(III) and In(III) complexes obtained experimentally. In contrast to the oxygen donors in phenolate-containing ligands, such as 1,2-ethylenebis((o-hydroxyphenyl)glycine) (EHPG) and N,N'-bis(o-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED), the thiolate donors of EC enhances affinity for In(III) relative to Ga(III). The following stability sequence has been obtained: In(III) > Ga(III) > Ni(II) > Zn(II) > Cd(II) > Pb(II) > Co(II). Evidence was also obtained for several protonated and hydroxo species of the complexes of both divalent and trivalent metals, where the corresponding protonation constants (K(MHL)) decrease with increasing stability of the chelate, ML(n)(-)(4), where M(n)()(+) represent the metal ion.     

Cd(II) binding by particulate low-rank coals in aqueous media: sorption characteristics and NICA-Donnan models

An experimental investigation of Cd(II) sorption onto two Australian coals was carried out in 0.1 M NaNO3 at 298.2 K. The initial concentration of Cd(II) was varied from 0.133 to 2.000 mmol/g in a series of batch adsorption experiments with an initial coal concentration of 3.75 g/L of Loy Yang (brown) or of Collie (sub-bituminous) coals in the p[H+] range 2-8. Adsorption edges were typical of metal ion adsorption onto negatively charged organic substrates, starting at p[H+] approximately 3 and increasing with increasing pH. The largest measured Cd(II) uptake capacities from these experiments were of 1.2 mmol/g for Loy Yang and 0.7 mmol/g for Collie coals. This difference is ascribed to the larger concentrations of carboxyl groups in Loy Yang coal (2.78 mmol/g) compared to Collie coal (1.34 mmol/g). An adsorption isotherm for Loy Yang coal at p[H+] 6 was collected up to a surface loading of 1.7 mmol/g of adsorbed Cd(II). These experiments also revealed a release of about 1.5-1.6 protons per adsorbed Cd(II). Zeta potentials of Loy Yang coal suspensions were not affected by Cd(II) adsorption, suggesting that the coal particles efficiently neutralize the charge of Cd(II). Collie coal, on the other hand, exhibited a zeta potential increase that may indicate a modification of the surface potentials of the coal particles. Cd(II) uptake data obtained from both batch experiments and proton balance data have been combined with p[H+] stat data for the same experimentally covered Cd(II)/coal ratios to model adsorption using the NICA-Donnan model. The modeling results suggest that both coals possess identical affinities and reaction stoichiometries. Loy Yang coal, however, possessed a narrower distribution of affinities.     

Biscavitands II: Self-Inclusion in a Back-to-Back Connected Biscavitand

A foot-to-foot or `back-to-back' connected biscavitand is prepared directly from a hexadecol resorcinarene precursor. The axial orientation of the biphenyl linker and hence the crown conformation of the hexadecol was established by an X-ray crystal study of the biscavitand. Each cavitand bowl is filled in the crystal by an alkyl `foot' from the next molecule, a self-inclusion which results in polymeric host–guest chains. The new biscavitand differs from previously prepared Z and C isomers of a bowl-to-bowl or `front-to-front' connected host, which crystallize as chains of carcerand-like, solvent-filled cages or as distinct molecules of hemicarceplex, respectively.     

Voltammaetric characterization of small platinum-iridium-based mercury film electrodes

A 25-μm diameter microelectrode is constructed from 80% platinum-20% iridium alloy. Mercury films and hemispheres are readily deposited by cathodic reduction of mercury(I) onto the electrode surface and are completely removed by anodic oxidation. The platinum-iridium surface, in contrast with a platinum surface, is not scarred by interaction with mercury. Steady-state reduction currents and sharp oxidation peaks are obtained for the determination of cadmium at the PtIr-based mercury film electrode. The voltammetric signals depend on the age of the film, and hence routine analytical applications will require further development.