Necessity of aromatic carboxylate anions to be planar to induce growth of cationic micelles

It is well-known that some aromatic anions have the ability to induce viscoelastic transformation in aqueous solutions of cationic surfactants even at added salt concentrations as low as 10-20 mM. This behavior is associated with the formation of an entangled network of elongated micelles. However, the effect of aromatic ring substituents on the anion's ability to promote rapid micelle growth is not well-understood. We have performed ab initio calculations of the carbonyl group rotation barriers in a series of substituted benzoate and naphthoate anions at the MP2/STO-3G level of theory. It was found that aromatic carboxylates, known to be particularly effective in causing sphere-rod transition in cationic micelles, preferably adopt conformations with the COO(-) group in the same plane as the ring(s). This structural preference can be attributed to either intramolecular hydrogen bonding (o-hydroxyl derivatives) or pi-conjugation effects (m- and p-halogenated derivatives). In the former case the barrier to rotation is 40-50 kcal/mol, whereas in the latter case the threshold value is around 3.0 kcal/mol. Propensity for the planar conformation correlates with a greater depth of counterion penetration into the micelle surface, as inferred from NMR experiments, compared to the anions with less hindered carbonyl rotation. This points to favorable hydrophobic interactions between the surfactant methylene groups and the aromatic ring(s) of the anion as a possible explanation for the rapid growth of cationic micelles observed upon addition of certain aromatic carboxylates.     

Some symmetry-induced isotope effects in the kinetics of recombination reactions

Symmetry-induced isotope effects in recombination and collision-induced dissociation reactions are discussed. Progress on understanding the anomalous isotope effects in ozone is reviewed. Then, calculations are performed for the simpler reaction xNe+yNe+H<-->xNeyNe+H, where x and y label either identical or different isotopes. The atomic masses in the model are chosen so that symmetry is the only difference between the systems. Starting from a single potential energy surface, the properties of the bound, quasibound, and continuum states of the neon dimer are calculated. Then, the vibration rotation infinite order sudden approximation is used to calculate cross sections for all possible inelastic and dissociative processes. A rate constant matrix that exactly satisfies detailed balance is constructed. It allows recombination to occur both via direct three-body collisions and via tunneling into the quasibound states of the energy transfer mechanism. The eigenvalue rate coefficients are determined. Significant isotope effects are clearly found, and their behavior depends on the pressure, temperature, and mechanism of the reaction. Both spin statistics and symmetry breaking produce isotope effects. Under most conditions the breaking of symmetry enhances the rates, but a wide spectrum of effects is observed; they range from isotope effects with a normal mass dependence to huge, mass-independent isotope effects to cancellation and even to reversal of the isotope effects. This is the first calculation of symmetry-induced isotope effects in recombination rates from first principles. The relevance of the present effects to ozone recombination is discussed.     

An improved microwave plasma torch for atomic spectrometry

The analytical performance of a microwave plasma torch was improved through mechanical alterations. Several problems reported in earlier designs were addressed: the ignition and stabilization of a helium plasma in the MPT was difficult; high powers were required to both ignite and operate the plasma; otherwise, the plasma would erratically change from an annular to a filament type discharge. In the new torch, the helium discharge was stabilized by replacing the copper central tube with one made of quartz. In addition, air entrainment was alleviated through use of a sheathing gas. This modification simplified the background mass spectrum and raised the effective ionization temperature of the discharge. A detailed schematic diagram of the new microwave plasma torch is presented.     

A diastereoselective intramolecular hydroamination approach to the syntheses of (+)-, (+/-)-, and (-)-pinidinol

A diastereoselective, lanthanocene-catalyzed, intramolecular hydroamination reaction was applied to the preparation of 2,6-disubstituted piperidines. Various metal/ligand arrays in the catalysts were examined using a model substrate to allow optimization of the diastereoselectivity. It was determined that the relationship between metal size and ligand bulk plays an integral role in the transformation. The complex Cp2NdCH(TMS)2 converted 2-substituted 8-nonen-4-amines to 2,6-disubsituted piperidines with greater than 100:1 selectivity for the formation of the cis isomer. A short synthesis of pinidinol, an alkaloid isolated from various pine and spruce species, was then carried out to exploit this stereoselective reaction.     

A multiplex single nucleotide polymorphism genotyping method using ligase‐based mismatch discrimination and CE‐SSCP

Accuracy, simplicity, and cost‐effectiveness are the most important criteria for a genotyping method for SNPs compatible with clinical use. One method developed for SNP genotyping, ligase‐based discrimination, is considered the simplest for clinical diagnosis. However, multiplex assays using this method are limited by the detection method. Although CE has been introduced as an alternative to error prone microarray‐based detection, the design process and multiplex assay procedure are complicated because of the DNA size‐dependent separation principle. In this study, we developed a simple and accurate multiplex genotyping method using reaction condition‐optimized ligation and high‐resolution CE‐based SSCP. With this high‐resolution CE‐SSCP system, we are able to use similar‐sized probes, thereby eliminating the complex probe design step and simplifying the optimization process. We found that this method could accurately discriminate single‐base mismatches in SNPs of the tp53 gene, used as targets for multiplex detection.     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.