The use of ammonium hydroxide as an additive in supercritical fluid chromatography for achiral and chiral separations and purifications of small, basic medicinal molecules

This study describes using 0.1% of a 28-30% ammonium hydroxide solution as an additive to alcohol modifiers in SFC to improve chromatographic peak shapes for basic molecules. Ammonium hydroxide's high volatility leaves no residual additive in the purified sample unlike classical additives in preparative chromatography such as diethylamine and triethylamine. We demonstrate that the silica support is stable despite having ammonium hydroxide in the modifier by running a durability study for over 350 h (105 L of solvent, 105,000 column volumes) on an analytical Chiralcel OJ column and a second study for 30 h (7.2 L, 14,400 column volumes) on an analytical Lux Cellulose-1 column. The peak shape of small, basic molecules is greatly improved with the use of ammonium hydroxide and this improvement is very similar to those having 0.1% diethylamine as a mobile phase additive. Electrospray ionization is also enhanced with the presence of ammonium hydroxide compared with that of diethylamine. We have found that the age of the 28-30% bottle of ammonium hydroxide solution can have significant effects on the chromatography and we describe how this can be overcome. Finally, we analyzed 23 racemic and basic compounds on six different chiral stationary phases and found there to be very little chiral selectivity difference between ammonium hydroxide and diethylamine, triethylamine, ethanolamine and isopropylamine.     

Enhancing the photocatalytic efficiency of TiO(2) nanopowders for H(2) production by using non-noble transition metal co-catalysts

Co and Ni-nanoclusters are attractive alternatives to Pt catalysts for hydrogen generation. These earth abundant elements when loaded onto the TiO(2) nanopowders surface act as efficient co-catalysts. Co, Ni-decorated TiO(2) photocatalysts display only three (3) times lower catalytic activities for H(2) evolution under UV illumination compared with Pt-decorated TiO(2) photocatalysts.     

Determination of scandium in sea-water by atomic-absorption spectroscopy

A method for the determination of scandium in sea-water at the sub-microgram level has been developed. Scandium is coprecipitated with iron(III) hydroxide at pH 8-9, and then separated from the iron by ion-exchange. The final concentration is achieved by extracting the scandium into a solution of oxine in butanol. A nitrous oxide-acetylene flame is used for the determination by atomic-absorption spectroscopy. Recoveries of 99-100% are obtained. The storage of the solutions before analysis has been investigated by radiometric techniques with (46)Sc. The scandium concentration in surface waters of the South China Sea was found to be 0.01 +/- 0.005 microg/l .     

Fluorescent Bioprobes: Structural Matching in the Docking Processes of Aggregation‐Induced Emission Fluorogens on DNA Surfaces

Whereas most conventional DNA probes are flat disklike aromatic molecules, we explored the possibility of developing quadruplex sensors with nonplanar conformations, in particular, the propeller‐shaped tetraphenylethene (TPE) salts with aggregation‐induced emission (AIE) characteristics. 1,1,2,2‐Tetrakis[4‐(2‐triethylammonioethoxy)phenyl]ethene tetrabromide (TPE‐ 1 ) was found to show a specific affinity to a particular quadruplex structure formed by a human telomeric DNA strand in the presence of K⁺ ions, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Steady‐state and time‐resolved spectral analyses revealed that the specific binding stems from a structural matching between the AIE fluorogen and the DNA strand in the folding process. Computational modeling suggests that the AIE molecule docks on the grooves of the quadruplex surface with the aid of electrostatic attraction. The binding preference of TPE‐ 1 enables it to serve as a bioprobe for direct monitoring of cation‐driven conformational transitions between the quadruplexes of various conformations, a job unachievable by the traditional G‐quadruplex biosensors. Methyl thiazolyl tetrazolium (MTT) assays reveal that TPE‐ 1 is cytocompatible, posing no toxicity to living cells.     

Effect of pressure on the flow behavior of polybutene

The rheology of submicron thick polymer melt is examined under high normal pressure conditions by a recently developed photobleached‐fluorescence imaging velocimetry technique. In particular, the validity and limitation of Reynold equation solution, which suggests a linear through‐thickness velocity profile, is investigated. Polybutene (PB) is sheared between two surfaces in a point contact. The results presented in this work suggest the existence of a critical pressure below which the through‐thickness velocity profile is close to linear. At higher pressures however, the profile assumes a sigmoidal shape resembling partial plug flow. The departure of the sigmoidal profile from the linear profile increases with pressure, which is indicative of a second‐order phase/glass transition. The nature of the transition is confirmed independently by examining the pressure‐dependent dynamics of PB squeeze films. The critical pressure for flow profile transition varies with molecular weight, which is consistent with the pressure‐induced glass transition of polymer melt. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 708–715     

The role of dust charging frequency in the linear and nonlinear propagation of dust acoustic waves

The effect of dust charge fluctuation on the existence and propagation of dust acoustic waves in unmagnetized dusty plasma is studied. Dispersion relation for the dust acoustic waves with temporal dust charge fluctuations is calculated based on the reductive perturbation technique. By considering two different limiting cases of the dust charging frequency, it is shown that the dusty plasma system gives rise to linear or nonlinear dust acoustic waves. The well-known collisionless damping of two existing normal modes and one purely damped mode are recovered when the dust charging frequency is comparable to the dust acoustic wave frequency. On the other hand, when the dust charging frequency is considerably higher than the wave frequency, it is then possible to derive a nonlinear Schrödinger type equation with envelope soliton as solution.     

Expansion of the terrain input base for nepean tracked vehicle performance model, NTVPM, to accept swiss Rammsonde data from deep snow

A study of the correlation between the measured and predicted vehicle performance over undistributed and preconditioned snow using the Nepean Tracked Vehicle Performance Model, NTVPM, has been carried out. It is shown that on undisturbed snow in Fernie, British Columbia, the performance of a BV 206 predicted by NTVPM correlates very well with measured performance obtained in the field. On preconditioned snow, there is also a reasonable correlation between the measured vehicle performance and predicted one using NTVPM. It is found that predictions of vehicle performance made by NTVPM using pressure-sinkage data obtained with the Swiss Rammsonde and with the bevameter are comparable. This indicates that the pressure-sinkage data obtained using the Rammsonde can be used as input to the NTVPM for predicting tracked vehicle performance over snow. It is shown that in comparison with an earlier version, NTVPM-85, the latest version of the Nepean Tracked Vehicle Performance Model, NTVPM-86, which takes into account fully the characteristics of roadwheel suspension systems, provides improved predictions of vehicle performance over snow where track sinkage is significant. It is suggested that the computer simulation model NTVPM, using pressure-sinkage data obtained by the Rammsonde as input, could form a useful interface with cone based models, such as the NATO Reference Mobility Model, to provide them with an additional capability of predicting tracked vehicle performance over snow.     

Computer aided analysis of the effects of design parameters on the performance of tracked vehicles

This paper describes the application of a computer simulation model, known as NTVPM-85, to the evaluation of the effects of design parameters on the performance of tracked vehicles over various types of terrain. It demonstrates that the computer simulation model is a useful tool for the vehicle designer and the user in the evaluation of competing designs and in the examination of the effects on performance of design modifications and terrain conditions.