Title

Complexation effects on novel catalyst and thiol-disulfide equilibrium

Date of Award

2004

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

The supramolecular chemistry of cyclodextrins and cucurbiturils is fascinating because of their remarkable binding properties. This thesis covers the complexation effect on cyclodextrin-capped Pd nanoparticles used in the Suzuki reaction and complexation effects of cucurbit[6]uril (CB6) on thiol-disulfide equilibria. Cyclodextrin-capped Pd nanoparticles (dia. ∼ 3.5 nm) were used as heterogeneous catalysts for Suzuki cross-coupling reactions. The results demonstrate that the nanoparticles are effective catalysts for the coupling of iodoaromatics with phenylboronic in an aqueous medium. Bromoaryl compounds were found to be less reactive under similar conditions. We also found conditions in which the nanoscopic heterogenous catalysts improved the yield of iodoferrocene with phenylboronic acid versus those obtained with homogenous catalysts. The formation of iodoferrocene-cyclodextrin inclusion complexes on the surface of Pd catalysts appears to be responsible for the improved yield of iodoferrocene.Complexation effects of CB6 on thiol molecules and disulfides were studied by 1H NMR spectroscopy. A new thiol molecule with a secondary ammonium center and a bulky benzyl group was synthesized and encapsulation in CB6 was observed through the thiol molecular end. Oxidants such as FeCl 3 and thricloronitromethane (Cl3CNO2) were used to oxidize the thiol molecule and provide symmetrical disulfide products. Upon encapsulation of the guest by CB6 no dimerization occurred, indicating that the host protects the thiol group.Two biological molecules such as cystamine and cysteamine were investigated in the presence of CB6. The thiol group in the cysteamine-CB6 complex is protected from dimerization in the presence of FeCl3. Cystamine was reduced by dithiothreitol (DTT) to its monothiol, but in the presence of the CB6 host the disulfide bond is protected. Thiol/disulfide reactions between cystamine and monothiols, and L-cysteine methylester, were also investigated and found to produce a mixture of disulfides, as previously shown. However, encapsulation of cystamine inside CB6 prevents the thiol/disulfide scrambling reactions.

Keywords

Chemistry, Analytical; Chemistry, Inorganic

Link to Full Text

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