No description available.

Abstract Ionic liquids and microwave heating have been studied in four different reactions namely esterifications, etherifications and ene and sulfonylation reactions. These techniques revealed several advantages over conventional methods. In esterification of alcohols with anhydrides in ionic liquid solvents, the low boiling acid by-product could be removed before product recovery. The acid by-product could be regenerated back to the anhydride. Similar or higher yields were observed from esterifications with acetic anhydride of carbohydrates than with conventional methods. Even cellulose and starch could be esterificated in ionic liquids in the homogenous phase. The etherification reaction in ionic liquid was challenging, due to the basic reaction conditions needed. 1-Methyl-3-butylimidazolium -cations ([BMIM]) could not be used in basic conditions. The new information was that [BMIM]-cation could not be used with epichlorohydrin. The ene reaction was carried out with microwave heating in various solvents. Ionic liquids could be used as a solvent, but the ene reaction between allyl benzene. The best results were obtained without additional solvent. The yields by using microwave heating were high and reaction times were relatively short. The sulfonylation reaction of aromatics could be catalyzed by metal bistriflimide complexes. Even chlorobenzene could be sulfonylated when Bi-complex was used as a catalyst. Ionic liquids could be used as a solvent, but sulfonylations were best carried out without additional solvents.

In 1970, Freiser made the theoretical prediction that a biaxial nematic phase could exist. In auniaxial nematic, only one particle axis is aligned but with a biaxial nematic, all three molecular axes are aligned. This phase is expected to occur for particle whose shape is intermediate between that of a disc and a rod. Board and bent-core particles are examples of such structures. Despite extensive experimental investigation, however, very few biaxial nematic systems have been found. Yu and Saupe [21] have shown the occurrence of a biaxial nematic phase generated for a lyotropic system. Similarly van der Pol observed a biaxial nematic phase in a colloidal suspension of board-like goethite particles [22]. For thermotropic, molecular systems, however, the situation is less clear-cut. Merkel et al., [23] and Figueirinhas et al., [24] claim that Tetrapodes have can exhibit a biaxial nematic phase, whilst Acharya et al., [25] and Prasad et al., [26] have also suggested the occurrence of this same phase with bent-core molecules, though experimental uncertainty still exist. With regards to theoretical predictions of the biaxial nematic transition, one notes in particular the work of Taylor and Herzfeld [13] on hard sphero-platelets, which predicts a rich phase diagram, notably containing an unusual discotic smectic phase. To date there are few simulations of board-like models, such as Vanakaras et al., [27] being arecent exception, developing a phase diagram for hard board-like colloids. Similarly, Escobedo[28] has produced a phase diagram of hard cuboids. We present molecular dynamics simulation results on a short range repulsive fused-hexagonmodel, somewhat resembling hard boards. Depending on the geometry of the board, we observe uniaxial and biaxial nematics, smectics A and C, a biaxial smectic phase and a columnar phase. Possibly the most interesting result is the existence of the theoretically predicted discoticsmectic. We further investigated the effect of applying both external fields and shears to several of the structures. The former, among other things, aided the alignment of the particles in the phase, removing dislocations. The shear was also seen to increase biaxial ordering, however, it also demonstrates an ability to introduce clear layer fractures, seen when shearing forces became overly dominant. An applied electrical field was able to induce isotropic!biaxial nematic and biaxial smectic switching. Finally we consider briefly less-symmetric arrangements of fused hexagons, including chiral particles. These systems proved hard to equilibrate but discotic nematic phases were observed for certain structures. Chiral clusters were also observed, however, no globally chiral phase was found. Columnar structures were also seen, but showing a weak overall alignment as columnstended to point along several directions.

No description available.

The evaluation of the potential to use Ultra Performance Liquid Chromatography (UPLC) for the simultaneous quantification of all the actives in a multi-active tablet is described in this work. Part of the evaluation was to ensure that the necessary regulatory requirements were adhered to by ascertaining that an analytical method is suitable for a specific purpose through analytical method validation for the specific multi-active tablet. The UPLC method was also tested for the analysis of similar products, namely tablet formulations that contain similar active ingredients in the same proportions but with an additional active ingredient. A method for the simultaneous determination of paracetamol, caffeine and codeine phosphate was developed using UPLC technology. The UPLC developed method was more efficient than the existing in-house HPLC method. The UPLC method was then validated in accordance to ICH and USP guidelines. The application of this UPLC method for the analysis of similar products containing paracetamol, caffeine, codeine phosphate and one extra active ingredient was very challenging. The low concentration of the additional component, differences in sample matrix and differences in formulations added to the challenges. The direct application for the analysis of products Y and Z was not successful; however the method could be used as a platform for further research. A cost comparison between the UPLC and HPLC methods showed the UPLC method to be more cost effective. Thus, while maintenance costs are higher for the UPLC instrument, column costs are comparable to HPLC columns, but solvent and waste disposal charges decrease considerably due to lower solvent use. The reduction in instrument time dramatically improves the cost effectiveness of UPLC over HPLC due to a concurrent reduction in analyst time requirement. The results of this study show that the analytical costs associated with the analysis of multi-active drugs using HPLC procedures can be reduced substantially by the CONFIDENTIAL INTELLECTUAL PROPERTY OF ASPEN PHARMACARE implementation of UPLC technology. The hypothesis that the enhanced chromatographic power of UPLC can be leveraged to provide faster analysis times hence increased product throughput rates, and lower operating costs for the analysis of multi-active drugs was accepted. These advantages were achieved whilst meeting all regulatory requirements for analytical methods as required by regulatory bodies.

No description available.

No description available.

[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate

We have analyzed the NMR spectra of a series of 19 di-halobenzenes having Cs or C₂v symmetry dissolved in a special mixture of nematic liquid crystals, i.e., 55 wt% 1132/EBBA-d₂. This mixture has the unique feature that dideuterium dissolved in it experiences a zero average electric field gradient. Therefore one can assume that for this mixture the contribution to the molecular order due to the interaction between the average electric field gradient and the quadrupole moment of the molecule can be neglected. It has been suggested that the orientational order also depends on the size and shape of the solutes and a model has been used to calculate the order parameters. Another model relates the ordering to the molecular polarizability anisotropy. A description of the ordering of molecules having Cs symmetry requires 3 independent order parameters and thus provides a strong test for the different models of orientational order. Comparisons are made between our experimentally determined order parameters and the theoretical values obtained using the size and shape, and the polarizability models. Very good agreement is obtained for the size and shape model. However, it is found that any mechanism, involving a molecular property which is approximately bond additive, can not predict the differences found between the ortho- and meta-dihalobenzenes. Consequently, a poor agreement results from the polarizability model when a bond-additive scheme is used to calculate the molecular polarizability. Further investigation of the correlation between order parameters and solute molecules suggests that the molecular shape dominates the orientational behavior. / Science, Faculty of / Chemistry, Department of / Graduate

While endeavouring to produce macroscopic vortex rings in liquid helium by a drop method, a general study of the formation of vortex rings when a liquid drop falls into a stationary bath of the same liquid was made. Preliminary investigations were made using room temperature liquids with a wide range of surface tensions, densities and viscosities. A cryostat was designed to study vortex ring formation in liquid nitrogen, liquid helium I, and liquid helium II. A numerical method, involving vorticity and Stokes stream function as parameters, for the solution of non-steady, rotational, viscous flows is outlined. Experimental results confirm the reported existence of optimum dropping heights from which the drop develops into a superior vortex ring. These optimum heights are analysed, by a photographic study, in terms of the liquid drop oscillation. It is found that optimum vortex rings are formed, if the drop is spherical at the moment of contact with the bath, and is changing from an oblate spheroid to a prolate spheroid. Vortex rings were detected in liquid nitrogen but not in liquid helium. / Science, Faculty of / Physics and Astronomy, Department of / Graduate