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<p>This work examined the systematic approach to protein crystallization, exploring some of the techniques that have been developed to enhance the success rate of crystallization. The work was centered on two proteins / namely Vaccinia virus complement control protein (VCP) and glutamate dehydrogenase (GDH) from Bacteriodes fragilis. The crystal structures of the full lengthe native VCP and VCP bound to heparin had already been determined. In the same way, the structure of GDH from Bacteriodes fragilis is not known, even though structures of other GDHs from different organisms have been determined.</p>

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M.Tech. / The study into the effect of additives used in nickel powder precipitation by sodium hypophosphite has been carried out. Reduction experiments were conducted in a 10 L stainless steel batch reactor fitted with 3 baffles, 4-bladed axial impeller, heating element, thermocouple and thermostat. Nickel seed was used to initiate the reduction process, sodium hypophosphite was used as a reducing agent, and ammonia solution was used to adjust pH, poly(ethylene-comaleic anhydride) (EMA) was used as the first additive and poly(acrylic acid) (PA) as the second additive. Reduction experiments were conducted at a temperature between 60oC to 70oC, pH around 8 and a reaction time of 3 min. Synthetic nickel sulfate solution and sodium hypophosphite solutions at concentration of 0.5 g/L were used as nickel feed solution and reducing agent, respectively. Additives were investigated at high and low concentrations of 5 mg/L and 10 mg/L. The effect of additives on reduction behavior of nickel was investigated by studying the evolution of the volume distribution, moments, specific surface area, and rate of reduction and purity of the powder product. EMA was found to be a growth promoter and PA was found to be a growth inhibitor. The highest reduction rate was observed in the presence of EMA and the lowest in the presence of PA. The SEM micrographs of the powder obtained in the presence of EMA and PA showed that the powder was spherical shaped, open, dentritic and more porous compared with that of the seed particles. Both additives were found to increase the pore size of the powder particles. The presence of particle fragments observed in the scanning electron micrographs confirmed breakage as one of the major particulate process. The addition of additives significantly affected the volume distribution at lower concentrations of 5 mg/L. The extent of aggregation increased with increasing dosages of PA and decreased with increasing dosages of EMA. The highest specific surface area was obtained in the presence of 5 mg/L of EMA.

Thesis (Master of Applied Science in Chemistry)--Cape Peninsula University of Technology, 2018. / The prediction of the single crystal structure that will form due to the combination of two or more compounds to form a multicomponent crystal is one of the important areas of research in crystal engineering. Since these compounds display different properties when combined as a single crystal, knowledge of synthesis and design of the resulting compound is essential. The formation of a multicomponent crystal, such as a salt or a cocrystal generally depends on the complementarity of the functional groups present on both components. This means that basicity and acidity of the functional groups present on the selected compounds need to be considered. This study investigated salts and cocrystals of 3-chloro-4-hydroxyphenylacetic acid (CHPAA) using the ΔpKa rule. The calculated ΔpKa values were recorded and correlated with the experimental analysis in predicting the outcome of the crystallisation experiments ie. salt or cocrystal formation. This was further confirmed by the analysis of the C-O bond lengths found in the crystal structures. Salts were obtained by combinations of CHPAA with several organic bases (co-formers) such as diethylamine, dibutylamine, 2-aminopyridine, 2-amino-4-methylpyridine, 2-amino-6-methylpyridine and 4-dimethylaminopyridine. The calculated ΔpKa values were within the range of salt formation. Furthermore, the experimental analysis also showed that all resulting compounds were salts. Cocrystals were obtained by reactions of nicotinamide, isonicotinamide, phenazine and 4,4’-bipyridine with CHPAA. Again, the calculated ΔpKa values predicted cocrystals as the new solid forms. Experimental analysis carried out also confirmed cocrystal formation. For all resulting compounds, the comparison of intermolecular interactions as well as supramolecular synthons were reported. All compounds were synthesised by slow evaporation techniques using various organic solvents and characterised by single crystal X-ray diffraction, powder X-ray diffraction, thermal analysis and Fourier transformer infrared spectroscopy. From the structural analysis, it was found that all resulting structures displayed strong N-H•••O and O-H•••O intermolecular interactions including weak interactions of C-H•••Cl, C-H•••O and C-H•••π for a few of the structures. Furthermore, comparison of the crystal structures showed that no packing arrangement similarity existed between the compounds.

" We are investigating resolution of chiral drugs via crystallization on self-assembled monolayers functionalized with achiral and chiral molecules that exhibit varying hydrophobicity/hydrophilicity as a means to bring about enantioseparation. Two goals of this work are to determine (1) whether chiral surfaces can act as templates that bias molecular aggregation at the surface to favor single enantiomers thereby inducing nucleation of conglomerates over racemic crystals, and (2) whether chiral templating can be used to induce selective nucleation of one enantiomer leading to high enantiomeric excess. Racemic compounds being investigated include the antibiotic 3-phenyllactic acid(3PLA) and the muscle-tissue repairing amino acid N-acetylleucine(NAL). Achiral and chiral alkanethiols were self-assembled onto 2D gold substrates by overnight immersion of the gold slides in ethanolic solution of the alkanethiols. The functional groups deposited on the SAM were characterized by grazing incidence IR spectroscopy, contact angle goniometry and ellipsometry. The contact angle and ellipsometry measurements showed that the cysteine SAMs form a bilayer consisting of monolayers of cysteine covalently bonded to gold covered by an overlayer of cysteine. The approach of using chiral templates to induce enantioselective nucleation of racemic drugs on the chiral surface via crystallization was first demonstrated for 3-phenyllactic(3PLA). Homochiral crystals (1), and conglomerates (3) formed from aqueous solution as needles, whereas heterochiral racemic crystals (2) formed from 3:1 hexanes-ethyl acetate as rectangular blocks. A comparison of the thermal stability of the three crystalline forms showed that the crystals of 1 and 3 exhibit greater thermal stability than crystals of 2 such that the racemic form does not appear in the phase diagram. We showed that chiral SAMs of cysteine were able to resolve enantiomers of racemic 3PLA effectively with up to 30% enantiomeric excess in bulk samples of crystals, and that the enantiomer in excess could be controlled based on the choice of D- or L-cysteine as the chiral template. Moreover, crystals of D- or L-3PLA grew oriented with a high degree of selectivity for attachment on the (004) face. We show that the presence of the excess enantiomer (D- or L-3PLA) present in solution acts as an additive to cause a change in the habit of L- or D-3PLA on L- or D-cysteine SAM. We also demonstrated the enantioselective crystallization on chiral SAMs for N-acetylleucine (NAL) which gave a higher enantiomeric enrichment with upto 80% ee. A novel approach of using chiral drugs as templates to amplify the chirality for better self-recognition was designed and SAMs were formed from cysteamine with an overlayer of L-3PLA. As a proof of concept, crystallization of racemic 3PLA on L-3PLA/cysteamine SAMs gave 24% enantiomeric enrichment and our results are comparable to cysteine SAMs. These results confirm our hypothesis that the molecular aggregation on D- and L-cysteine occurs via specific diastereomeric hydrogen-bonding interactions that discriminate between the two enantiomers, thereby promoting enantioselective nucleation and facial selectivity of chiral drugs. "

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This thesis documents the development and application of a computer model for gibbsite, an aluminium tri-hydroxide polymorph. In particular, the work has emphasized the idea of computer modelling techniques combining with ex- observations to provide greater insight than either could separately. Chapter One provides an overview and introduction to the fields of solid state chemistry, crystallization and computer modelling. These ideas are extended in Chapter Two to include a more detailed discussion of the theoretical principles behind the modelling in this project. The development of transferable oxalate and hydroxide potential models, intended primarily for sodium oxalate and gibbsite, is described in Chapter Three. Both ab initio hypersurface fitting and lattice fitting techniques were utilized, with an average structural fitting error of under two percent. In addition, the potentials were used to successfully reproduce several (related) crystal structures, thus establishing the quality of the model. In Chapter Four, the model for gibbsite was employed in generating equilibrium and growth morphologies. The equilibrium morphology was found to give excellent agreement with experiment, with all observed faces present. However, the importance of the prismatic planes is underestimated. Also discussed in the chapter is a method for predicting the phenomenon of crystalline twinning. This technique was successfully applied to a number of systems, including gibbsite and sodium oxalate. In Chapter Five, the equilibrium morphology calculations performed earlier were extended by probing the effects of cation incorporation on the habit of gibbsite. This study was conducted in order to provide a first step in estimating the role of the crystallizing solution. Calculations of the change in surface energy caused by the replacement of a surface proton with a cation from solution ++ / were made. Different crystal habits were constructed by applying a range of defect surface coverage values to each of the faces appearing in the morphology. The resulting defect morphologies were in excellent agreement with crystal habits commonly observed by experimentalists. Also, the work provided an explanation for the earlier underestimation of the prismatic faces. Chapter Six documents molecular simulations of solutions containing the major species known to be present in industrial and experimental Bayer liquors. The structuring in two solutions, one containing sodium hydroxide and the other potassium hydroxide, was probed by constructing graphs of the radial distribution functions. These plots indicated that a significant degree of ion pairing was occurring between the alkali metal cations (Na+ and K+) and the aluminate monomer ([Al(OH)4(subscript)]-). Furthermore, these cations were found to be acting as 'bridges' which stabilize multiple aluminate monomers, allowing them to form clusters. This data was used to assist in explaining vibrational spectra, and to postulate that clustering may be the origin of the fine particle suspensions noted during the induction period.

Thesis (M. Sc.)(Chemical Eng.)--University of Pretoria, 2004. / Title from opening screen (viewed June 14, 2004). Includes bibliographical references.

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