Two-particle dynamics on an electrode in ac electric fields

The relative motion between pairs of negatively charged latex particles 9.7 microm in diameter and deposited on an electrode was measured by optical microscopy and image analysis. At an rms field of approximately 30 V cm(-1), the two particles moved toward each other at frequencies below 500 Hz, but they separated at 1000 Hz. In the cases of aggregation, there are several interesting characteristics. First, when the center-to-center separation of a pair was initially 6 particle radii or more apart, a transient 'incubation' period of tens of seconds was observed before the particles began to move toward each other. Second, the two particles never came into contact, rather at long times the pair maintained a stationary gap between them equal to approximately one-half the particle radius. This stationary gap between particles was also observed for the aggregation of clusters of three or more particles. Finally, the rate of approach for a pair of particles decreased as the frequency increased. Larger fields are required to move particles together in ac compared to dc fields; at 30 Hz the ac field must be 130 times greater than the dc field to achieve the same rate of approach. Taking advantage of the qualitative and quantitative differences of the cooperative motion of particles in dc vs. ac fields, one should be able to re-position particles by alternating between these two modes. We demonstrated that the same pair of particles can be brought together at low frequency (100 or 200 Hz) and then separated at high frequency (1000 Hz).     

A crystallite packing model for pseudoboehmite formed during the hydrolysis of trisecbutoxyaluminium to explain the peptizability

A model for pseudoboehmite crystallite packing formed during the hydrolysis of trisecbutoxyaluminium is postulated. The model describes platelike crystallites of pseudoboehmite stacked in a sharing edges only configuration. With this type of stacking, the pore sizes detected are approximately equal to the crystallite sizes of the hydrolysates. The hydrolysates age via a dissolution re-precipitation reaction. This increases the size of the crystallite size of the pseudoboehmite formed, speeding peptization by allowing nitrate ions to enter pores and access the surfaces of the crystallites. This type of model also allows an explanation for the peptization kinetics of systems containing sec-butanol formed during the hydrolysis of trisecbutoxyaluminium.     

Two-dimensional metallic chain compounds Y5M2Te2 (M = Fe, Co, Ni) that are related to Gd3MnI3. The hydride derivative Y5Ni2Te2D0.4

Y(5)M(2)Te(2) (M = Fe, Co, Ni) have been prepared by high-temperature solid-state techniques and shown to be isostructural and orthorhombic Cmcm (No. 63), Z = 4. The structure was established by single crystal X-ray methods at 23 degrees C for M = Fe, with a = 3.9594(3) A, b = 15.057(1) A, and c = 15.216(1) A. The new structure contains zigzag chains of the late transition metal sheathed by a column of yttrium atoms that are in turn condensed through trans vertices on the latter to yield 2D bimetallic layers separated by single layers of tellurium atoms. Reaction of hydrogen with Y(5)Ni(2)Te(2) causes a rumpling of the Y-Ni layers as determined by both single X-ray crystal means at 23 degrees C and neutron powder diffraction at -259 degrees C for Y(5)Ni(2)Te(2)D(0.41(1)), Pnma (No. 62), Z = 4. Lattice constants from the former study are a = 14.3678(7) A, b = 4.0173(2) A, and c = 15.8787(7) A. The hydrogen is accommodated in tetrahedral yttrium cavities generated by bending the formerly flat sheets at the trans Y vertices. A higher hydride version also exists. Band structure calculations confirm the 2D metal-bonded character of the compounds and also help illustrate the bonding/matrix changes that accompany the bonding of hydrogen. The ternary structures for both Y(5)M(2)Te(2) and Sc(5)Ni(2)Te(2) can be derived from that of Gd(3)MnI(3), the group illustrating three different kinds of metal chain condensation.     

Coordination complexes of l-azetidine-2-carboxylic acid with platinum(II) and palladium(II)

Summary The complexes K[Pt(l-aze)Cl₂, [Pt(l-aze)₂] and [Pd(l-aze)₂] (l-aze = l-azetidine-2-carboxylate) were prepared. X-ray structures show that [Pt(l-aze)₂] and [Pd(l-aze)₂] are isomorphous, having a planar tetragonal geometry with a trans configuration around the Pt and Pd atoms. Slight puckerings of the MN(1)N(11)O(11) chelate ring (M = Pt or Pd) and the azetidine ring were observed. The circular dichroism (c.d.) spectra of the complexes in aqueous solution agree with the structures found in the solid state as far as the hexadecant rule is concerned, giving, for the trans configuration of [M(l-ia)₂] (where ia = imino acid), the profile of the c.d. signs for the three predominant d-d transitions as: +,-,-. I.r., conductivity and n.m.r. measurements are also reported and are in accord with the proposed structures.     

ICP-MS for elemental speciation studies

The use of inductively coupled plasma mass spectrometry (ICP-MS) coupled with separation techniques for the purpose of elemental speciation has recently gained a lot of attention. Much of this is due to ever improving separation capabilities of Chromatographic techniques, the high sensitivity of ICP-MS, and the continuing development of better interface techniques. Additionally, there is a growing awareness of the need to monitor various species of an analyte, rather than just total analyte concentrations, due to their often varying natures. For the sake of learning from different elemental speciation approaches, this review brings together some selected types of elemental speciation which have been recently seen in literature. These include separations using various forms of liquid chromatography, such as reversed phase, reversed phase ion pairing, micelle, ion exchange, and size exclusion. Elemental speciation employing gas Chromatographie separations and supercritical fluid separations are discussed as well as elemental speciation using capillary electrophoresis.     

Ozonolysis of tetramethylethylene: characterization of cyclic and open-chain oligoperoxidic products

The ozonolysis of tetramethylethylene (TME) in solution to high conversion in nonparticipating solvents at -60 degrees C yields predominantly oligoperoxides. For the first time, these products have been characterized using electrospray ionization mass spectrometry (ESI-MS) under soft ionization conditions. The predominant structure formed in reactions carried out in pentane (up to 2.0 M TME) is shown to be the cyclic hexamer of acetone carbonyl oxide (oligocarbonyl oxide with degree of polymerization, n = 6), but cyclic structures with n up to 19 are observed. A small proportion of the oligoperoxides formed are open-chain compounds with end groups that suggest that chain termination of oligocarbonyl oxides can occur through reaction with either water or hydrogen peroxide. Ozonolysis in dried butyl acetate similarly produces mainly cyclic oligoperoxides. However, ozonolyses carried out in undried butyl acetate yield mainly open-chain oligoperoxides, confirming that propagating carbonyl oxide chains are readily terminated by water. Relative amounts of the open-chain oligomers so-formed suggest that undried butyl acetate contains ca. 0.1% w/w water. The ozonolysis of TME in the participating solvent, methanol, at -60 degrees C yields 2-methoxyprop-2-yl hydroperoxide via reaction of acetone carbonyl oxide with methanol; no oligoperoxidic products are formed in this case.     

Application of flow-injection analysis in the on-line monitoring of sugars,lactic acid,protein and biomass during lactic acid fermentations

A laboratory system for the on-line monitoring of important lactic acid fermentation variables is described. The system contains flow-injection analysers for glucose, lactose, galactose, lactate and protein and a continuous-flow analyser for the biomass concentration. The sugar and lactate analysers are based on enzymatic reactions involving oxidases followed by chemiluminescence detection of the hydrogen peroxide formed. The protein analyser is based on the biuret reaction. The system has been used to monitor many fermentation experiments, and some results are presented as examples.     

A re‐examination of supra­molecular aggregation in two polymorphs of acetone 2,4‐dinitro­phenyl­hydrazone

The structure of the triclinic polymorph of acetone 2,4‐dinitrophenylhydrazone, C₉H₁₀N₄O₄, has been redetermined from diffraction data collected at 120 (2) K; the mol­ecules are linked by C—H⋯O hydrogen bonds into centrosymmetric R₂²(10) dimers which are themselves linked into a chain by an aromatic π–π stacking inter­action. In the monoclinic polymorph, which crystallizes with Z′ = 2 in the space group P2₁/n, one type of mol­ecule forms dimers exactly as in the triclinic polymorph, while the other forms C(6) chains.     

Heterometallic Ln/Hg compounds with fluorinated thiolate ligands

The early lanthanide benzenefluorothiolates (Ln(SC(6)F(5))(3); Ln = La, Ce, Pr, Nd, Sm, Gd) react with Hg(SC(6)F(5))(2) in DME to form ionic heterometallic compounds with Ln cations and Hg anions. X-ray diffraction analyses of all compounds reveal an isostructural series with the general formula [(DME)(3)Ln(SC(6)F(5))(2)](2)[Hg(2)(SC(6)F(5))(6)]. In the structures, a fluorothiolate ligand has been extracted from the Ln coordination sphere that is saturated with three neutral DME donor ligands and a dative interaction between one ortho fluorine and the Ln. Distances between Ln and F do not vary simply with Ln ionic radius. There are two Ln cations with charge balanced by a Hg(2)(SC(6)F(5))(6) dianion composed of two distinctly nonideal Hg(II) tetrahedra, all connected through a series of pi-pi interactions that link cations with anions in a one-dimensional array and anions to anions in a more complex 2D network.     

Spontaneously formed unilamellar vesicles with path-dependent size distribution

We observe the spontaneous formation of path-dependent monodisperse and polydisperse phospholipid unilamellar vesicles (ULV) from two different equilibrium morphologies specifically, disklike micelles and extended lamellae, respectively. On heating beyond a temperature Tc, low temperature disklike micelles, or so-called bicelles, transform into lamellae. Dilution of the lamellar phase, at a fixed temperature, results in a complete unbinding transition and the formation of polydisperse ULV, demonstrating the instability of the lamellar phase. On the other hand, heating of a dilute bicellar phase above Tc results in monodisperse ULV, which on cooling revert back to bicelles for lipid concentrations phi > or = 0.5 wt % and transform into oblate ellipsoids for phi = 0.1 wt %, a morphology not previously seen in "bicellar" lipid mixtures. Monodisperse ULV reform on heating of the oblate ellipsoids.