Abstract not available

Abstract not available

Abstract not available

No description available.

The availability of complete sequences for the genomes of many organisms changes the researcher's attention from genome sequencing to finding the function of gene products, the proteins. The three dimensional (3D) structure of a protein is helpful to understand its function, because tertiary structure is more conserved in evolution than sequence. The 3D structures can be found quickly by using high-throughput (HT) methods for protein expression, purification, characterization and structure determination. This process is very challenging in every step. Therefore we selected nearly 200 cancer related proteins as targets to see the difficulties in trying to determine the web predicted structural properties that make the protein easy to produce and crystallize using current technologies. Selection of targets, gene carriers or vectors and the expression strains of Escherichia coli K12-MG1655 (EC) are very important to obtain soluble expression clones and pure protein for crystallization and structure determination. Identification of protein function based on 3D structural analysis comes after the structure determination. We described a new calculation method called frame method to characterize the proteins in the mu-crystallin fold family. Two functionally characterized proteins, ornithine cyclodeaminase (OCD) and alanine dehydrogenase (AlaDH), are used as frames in order to annotate the activity of OCD like 1 from thermophilic Sulfolobus solfataricus P2 (Ss) and the human mu-crystallin enzyme. OCD like 1 seems to have OCD activity, but the human enzyme does not, as described in the literature. In the meantime, OCD like 1 expression was tested and purified to test for OCD activity to validate our calculations. We were not able to purify OCD like 1; therefore the determination of catalytic activity of it will require future studies. Crystallization, structure determination and identification of protein function are dependent on each other; therefore we started crystallization studies of Phosphoinositide-specific phospholipase C (PI-PLC) from Streptomyces antibioticus (Sa) to better understand the mechanism of action of the PLC protein family. SaPLC is purified by affinity, gel filtration and ion exchange chromatographies. SaPLC crystals are obtained using the hanging drop crystallization technique at concentrations of 20-24 % polyethylene glycol (PEG) 17500 and 1.5- 2 % 1,4- dioxane for 35-40 mg/mL protein. The main major barrier to success of structure determination is the preparation of well-diffracting crystals for X-ray diffraction studies, which we are currently optimizing.

No description available.

Unsaturated aldehydes are widely used in the synthesis of natural products and pharmaceutical molecules.18,19,20 Among various methods available in the literature, carbon homologation is a common reaction employed for the synthesis of unsaturated aldehydes. Wittig reaction has emerged as a very useful method for making homologated unsaturated aldehydes. The use of classical Wittig reaction is not desirable on a commercial scale due to the formation of the by-product triphenylphosphine oxide which is insoluble in water and generally difficult to remove. Use of alkyl phosphine reagents is one of the research interests in our group. Previously in our group, alkylphosphonium salts were successfully used in the Wittig reaction for the one and two carbon homologations.15 The trialkylphosphine oxide by-product is water soluble and can be easily removed. In this thesis, the three carbon homologation of aldehydes using (2-(1, 3-dioxolan-2-yl)ethyl)tripropylphosphonium bromide is described. The ylide formation is highly regioselective. A variety of aromatic and hetero aromatic aldehydes are homologated with good stereo selectivity. An attempt to synthesize the cytotoxic natural product (2R,3R,4R)-3,4-dihydro-3,4-dihydroxy-2-(3-methylbut-2-enyl)-1(2H)-naphthalenone using the homologated aldehyde is also illustrated. Finally, the development of new synthetic routes for tricyclohexylphosphine is described. Tricyclohexylphosphine is used as a ligand in many important complexes which include the olefin metathesis Grubbs' catalyst and the homogeneous hydrogenation Crabtree's catalyst. It is synthesized generally from phosphorus trichloride and cyclohexylmagnesium bromide. It is also synthesized by hydrogenation of triphenyl phosphine with a niobium catalyst. Nevertheless, a new commercially viable synthesis possesses greatest advantage in the use of tricyclohexylphosphine. / Thesis / Master of Science (MSc)

Nitronyl nitroxides bearing substituents with hydrogen bonding potential were synthesized and characterized by magnetism and crystallography. Most of the radicals showed antiferromagnetic interactions at low temperatures. The magnetism of the radicals were rationalized with their crystal packing. In two of the systems, mAmPN and pAcPN, strong antiferromagnetic interactions were observed which was attributed to spin-pairing resulting from antiparallel stack of the nitroxide N-Os. In pAmPN radical, there appeared to be two opposing interactions going on at low temperatures with the ferromagnetic interactions dominating the antiferromagnetic interactions at temperatures lower than 2 K. Two amine salt radicals were made from acidification of para -aminophenyl nitronyl nitroxide. These two systems showed extremely strong antiferromagnetic interactions throughout the temperature range of 1.8 K to 300 K. UV-vis absorption experiments at variable concentrations on the salt radicals displayed aggregation of the molecules at about 0.2 mM concentrations and above. The huge antiferromagnetic interaction was attributed to aggregation. Mixed crystal or alloy of two nitronyl nitroxides H4BImNN and F4BImNN was studied by crystallography and magnetism. The two components individually showed ferromagnetic interactions The alloy also exhibited ferromagnetic interactions that was rationalized with its hydrogen-bonded packing. Biradicals with different interspin distances were synthesized and analyzed by four pulse double electron electron spectroscopy (DEER) using Jeschke's DEER analysis program. The DEER interspin distances for two of the systems 26TAnt and 14TTer were in excellent agreement with their theoretically predicted values derived from molecular modeling. Thus the two systems are good candidates as standards for DEER experiments on spin-labeled biomolecules.

Cholesterol is a major component of plasma membranes, a precursor for bile acids and steroid hormones, and a structural component of serum lipoproteins. Although cholesterol is essential for normal cell function, it oxidizes under a variety of conditions. The resulting oxides are known to produce varying degrees of toxicity. The oxidation of cholesterol in foods or cell membranes is influenced significantly by the interactions among cholesterol, its neighboring molecules and other environmental factors. The purpose of this study was to examine the role of such interactions in cholesterol oxidation. Such examinations were carried out by monitoring the destruction of cholesterol and the formation and destruction of cholesterol oxides in dry and aqueous model systems as well as in the milk fat globule membrane. In cell membranes, a delicate balance exists between the various antioxidative and oxidative factors present. Numerous factors can influence such balance. In dry model systems, the amino acids and sugars tested inhibited, and triacylglycerols and free fatty acids accelerated, cholesterol oxidation. The added phospholipids were protective and/or destructive depending on their head groups, fatty acyl chains and temperature. In aqueous systems, amino acids were protective but added sugars accelerated cholesterol oxidation in the early stages of incubation. The effects of phospholipids were significantly influenced by their head groups, acyl chains, concentration, sonication and pH. In dry model systems, added lipid components significantly changed not only the oxidation rate, but also the oxidation pathway. However, in the aqueous model systems, cholesterol oxidation patterns and the resulting oxide profiles were common in most of the conditions tested. Cholesterol in turn, also influenced the oxidation of mixed lipid. The milk fat globule membrane exhibited high protective effect on cholesterol oxidation in aqueous environment. It contains a non-lipid fraction that protects, and a lipid fraction that accelerates cholesterol oxidation. In the absence of water, the net balance between these two opposing factors is destructive. The presence of water tips this balance in favor of protection. The results in this study indicate that certain physicochemical factors exist in biological membranes so as to protect the membrane against destruction.

Diaryliodonium salts have received much attention as photoactivated curing agents for many applications. Irradiation of a film containing a diaryliodonium salt leads to the formation of a strong Bronsted acid, which initiates secondary reactions within the film. Examples of such secondary reactions include; acid catalyzed polymerization, depolymerization, and crosslinking. Thus, irradiation of a diaryliodonium salt in the presence of a polymer containing epoxy groups in the main chain would yield an insoluble, crosslinked material. Diaryliodonium salts have also been incorporated into the main chain of polymeric materials. Such materials have been shown to make effective photosensitive films. We have studied the incorporation of diaryliodonium salts into polyamides. Bis (4-(2-aminoethyl)phenyl) iodonium bromide was caused to react with sebacoyl chloride to yield a polyamide, which was insoluble in most solvents making the preparation of films difficult. Our attention then turned to the preparation of diaryliodonium salts which contained polymerizable functional groups. Such salts were thought to be potential photohardening agents in polymeric materials. Irradiation of a film containing Bis (3((2-methacroyloxyethoxycarbonyl))phenyl) iodonium bromide and polyvinyl alcohol gave a material which was resistant to a solvent wash. GPC and DSC results suggested the presence of high molecular weight species which may have contributed to the films' solvent resistance. We also undertook a mechanistic reinvestigation of the thermal decomposition of diphenyliodonium salts and found products not previously reported in the literature. Diphenyliodonium tetrafluoroborate, when heated, gives fluorobenzene, iodobenzene, biphenyl, three iodobiphenyl isomers, terphenyl, other polyaromatics and Bronsted acids. A mechanism involving free radicals and radical cations is proposed to account for the formation of these products. For example, homolytic cleavage of the C-I bond gives a phenyl radical/iodobenzene radical cation geminate pair. Recombination of this pair leads to the formation of the iodobiphenyl isomers. A secondary reaction of an iodobiphenyl isomer with a phenyl radical leads to an iodoterphenyl isomer. The formation of the other polyaromatic compounds is proposed to follow similar coupling reactions.