A new method for the acetalization of carbonyl compounds using chlorotrimethylsilane under mild conditions is described. Carbonyl compounds are acetalized by ethylene glycol with chlorotrimethylsilane. / Two isomeric methyl olivetolates were synthesised by the condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene with the corresponding electrophilic components. This reaction has clearly indicated the discriminative behaviour of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene towards different electrophilic sites thus leading to regio-selectivity. / A new method for the synthesis of olivetol is described. This method provides a shorter route to olivetol from acyclic precursors. / A new synthesis of (DELTA)('1)-tetrahydrocannabinol is described. The synthesis is patterned after biogenetic considerations. / A new method for the synthesis of poly (beta)-carbonyl compounds using diketene and enol silyl ethers is described. / The possibility of synthesising gossypol by the cyclo-aromatization procedure was investigated.

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Some new inorganic and organometallic derivatives of methylcyclosiloxanes have been prepared and characterized by IR, MS and ('1)H NMR. Compounds, {CH(,3)(Br)SiO}(,3) and {CH(,3)(Br)SiO}(,4) were prepared by cleavage of silicon-phenyl bond with bromine at low temperature. The reaction of {CH(,3)(Br)SiO}(,3) with Na(sec-butyl)(,3)BH at low temperature produced the highly reactive trimer, {CH(,3)(H)SiO}(,3). Compounds {CH(,3)(Co(CO)(,4))SiO}(,4), {CH(,3)(Fe(CO)(,2)(eta)('5)-C(,5)H(,5))SiO}(,4), and {CH(,3)(Co(CO)(,4)SiO}(,5) were prepared by the hydrogen elimination reaction of {CH(,3)(H)SiO}(,n), n = 4 and 5 with Co(,2)(CO)(,8) and {Fe(CO)(,2)(eta)('5)-C(,5)H(,5)}(,2). It was also possible to isolate the compound {CH(,3)(Co(CO)(,4))SiO}(,1){CH(,3)(Fe(CO)(,2)(eta)('5)-C(,5)H(,5))SiO}(,3) by reacting {CH(,3)(H)SiO}(,1){CH(,3)(Fe(CO)(,2)(eta)('5)-C(,5)H(,5))SiO}(,3) with a stoichiometric amount of Co(,2)(CO)(,8). A detailed study of mass spectra of {CH(,3)(R)SiO}(,n), where R = H, (n = 4, 5, and 6), R = C(,6)H(,5), (n = 3 and 4), R = Br, (n = 3 and 4), R = Co(CO)(,4), (n = 4 and 5) and R = Fe(CO)(,2)(eta)('5)-C(,5)H(,5), (n = 4) was achieved. Compounds R = Co(CO)(,4) show stepwise loss of all CO groups from ions {M}('+(.)), {M-Co(CO)(,4)}('+), and also {M}('++). A simple empirical approach based on the chemical environment of methyl protons was used to assign ('1)H NMR spectra of geometric isomers of substituted methylcyclosiloxanes. The total assignment of ('1)H NMR spectra allowed the determination of the isomeric composition of most new compounds mentioned above.

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No description available.

The behavior of biphenyl and naphthyl sulfinate and sulfoxylate esters under flash vacuum thermolytic and photolytic conditions was studied and a new tetrasubstituted dihydrophenanthrene was isolated. Several, 2,2'-biphenyl diols were synthesized including some with specifically deuterated alkyl chains. These diols were cyclized to give symmetrically substituted as well as cis-/trans- unsymmetrically substituted dibenzoxepins. The dynamic NMR properties of these dibenzoxepins were studied and the free energy barriers of conformational inversion were measured and related to the steric interactions of the alkyl substituents. The preferred conformations of the trans-dibenzoxepins were related to the relative stabilities of the alkyl substituents in the axial or equatorial position. The reaction of the 2,2'-biphenyl diols with trimethylsilylbromide yielded diolefinic biphenyls. In some other cases rearrangements to cyclized products were observed. The photolytic cyclization of the diolefinic biphenyls resulted in new tetrasubstituted tetrahydropyrenes and pyrenes.

No description available.

<p>In this study G. pallidus RAPc8 NHase mutants were screened for reduced substrate inhibition compared to the wild type enzyme. Wild type and mutant enzymes were expressed and purified using hydrophobic interaction chromatography. Amidase coupled enzyme stop assays were conducted using 3-cyanopyridine as a substrate, whereas continuous enzyme kinetics were conducted using acrylonitrile as a substrate.</p>

<p>Geobacillus pallidus RAPc8 is a thermophilic nitrile-degrading isolate, obtained from thermal sediment samples of a New Zealand hot spring. The G. pallidus RAPc8 NHase gene has been cloned and expressed in E. coli. The recombinant NHase exhibits nitrile-degrading activity at 50 &deg / C, capable of degrading branched, linear and cyclic heteroaromatic nitrile substrates. However, no activity was found on homoaromatic nitrile substrates such as benzonitrile. In the present study, high levels of activity on benzonitrile were detected with a double mutant &beta / F52G&beta / F55L. Kinetic analysis on the mutant enzyme showed an 8-fold decrease in KM with benzonitrile (0.3mM) compared to acrylonitrile (2.6mM). Specificity constants (kcat/KM) of 5900 and 450 s-1.mM-1 were obtained for the double mutant on benzonitrile and acrylonitrile respectively. The amino acid residues lining the substrate channel were identified and the geometric dimensions measured. Cavity calculations revealed a 29% increase in volume and a 13% increase in inner surface area for the substrate channel of the double mutant when compared to the wild type. Surface representation of the wild type structure revealed two extended, curved channels, which are accessible to the bulk solvent from two locations in the heterodimer. The removal of the &beta / F52 may have contributed to the presence of a single channel with two opposing openings across the dimers with no internal blockage. Normal Mode Analysis calculations also indicate a higher intrinsic flexibility of the mutant relative tothe wild type enzyme. The increased flexibility within the mutant NHase could have introduced a functionally relevant aromatic substrate recognition conformation</p>

Systematic kinetic and thermodynamic analyses of the substitution reactions of different Pt(II) complexes with a series of bio-relevant nucleophiles have been investigated as a function of concentration and temperature, using standard stopped-flow and UV–Vis Spectrophotometric methods. For this purpose, five different systems involving squareplanar Pt(II) complexes, viz. (i) mononuclear Pt(II) complexes with tridentate nitrogendonor ligands of varying degree of π-conjugation, and (ii) polynuclear Pt(II) complexes with azine, pyridyl units separated by S, S-S and CH2CH2 spacer groups, and α,ω- alkanediamine bridging ligands were synthesised and characterised by various spectroscopic methods. All substitution reactions of the Pt(II) chlorido complexes of the type [Pt(terpy)Cl]+ were studied in the presence of 10 mM LiCl to prevent spontaneous parallel reaction due to hydrolysis or solvolysis. The substitution reactions of the coordinated water molecules in the dinuclear Pt(II) complexes by thiourea nucleophiles of varying steric hindrance were studied under acidic conditions. The concentration of the nucleophile solution was prepared in 0.1 M NaClO4, at pH 2.0 and always at least 10- fold excess to provide pseudo first-order conditions. The pKa values of the coordinated aqua ligands of the dinuclear Pt(II) complexes were determined by Spectrophotometric acid-base titrations. DFT calculations were also performed in an effort to account for the observed reactivity of homologous analogues in each series of complexes, in terms of NBO charges and energies of frontier molecular orbitals. Substitution reactions of the Mononuclear Pt(II) complexes with tridentate ligands showed reactivity of the complexes is controlled by the π–acceptor characteristics of the chelate ligands. The fused rigid pyridyl system allows electronic interaction between the platinum centre and the pyridyl ligands, because of the extended conjugated π-system. This effect is controlled by how the fused ring system around the terpy moiety is structured. The isoquinoline moiety was found to reduce the effective π-backbonding and the lability of CH3PhisoqPtCl complex compared to 1,10-phenanthroline and terpyridine systems, indicating that isoquinoline ligand is a net σ-donor. The results obtained for the substitution reactions of the diaqua Pt(II) complexes with the thiourea and ionic (Br-, I- SCN-) nucleophiles demonstrate that reactivity increases with decreasing pKa values as well as decreasing distance between the Pt(II)centres. An increase in steric crowding at the Pt(II) centre imposed by the methyl groups on the azine linker decelerates the lability of the aqua ligands. The 1H and 195Pt NMR spectroscopic results confirmed degradation of the aromatic-based bridging ligand from the metal centre. The final cleavage of the complex linkers was only achieved after addition of excessive amounts of thiourea and other strong nucleophiles. The negative activation entropies and second-order kinetics for all the substitution reactions support the Associative mode of substitution mechanism. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.