Portland State University. Department of Environmental Sciences and Resources
Reuben H. Simoyi
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Sciences and Resources
Contact dermatitis, Nitric oxide -- Physiological effect, Thiols
1 online resource (2, xiv, 203 pages)
Two biologically-active thiols, N-acetylpenicillamine (NAP) and 2-mercaptobenzothiazole (MBT), were studied in this thesis. NAP is known to combine with nitric oxide (NO) to produce S-nitroso-N-acetylpenicillamine (SNAP) and MBT is a known allergen.
The formation, reaction dynamics, and detailed kinetics and mechanism of the reaction between nitrous acid (HNO2), prepared in situ, and NAP to produce SNAP were studied. The reaction is first order in nitrite, NAP and acid in pH conditions at or slightly higher than the pKa of HNO2. Both HPLC and quadrupole time-of-flight mass spectrometry techniques confirmed the formation of SNAP and the absence of any other products. Cu(I) ions were found to be effective SNAP-decomposition catalysts. The formation of SNAP occurs through two distinct pathways. One involves the direct reaction of NAP and HNO2 to form SNAP and eliminate water, and the second pathway involved the initial formation of the nitrosyl cation, NO+, which then nitrosates the thiol. The bimolecular rate constant for the reaction of NAP and HNO2 was derived as 2.69 M-1 s-1, while that of direct nitrosation by the nitrosyl cation was 3.00 x 104 M-1 s -1. A simple reaction network made up of four reactions was found to be sufficient in simulating the formation kinetics and acid-induced decomposition of SNAP.
The chemical mechanism leading to MBT's allergenicity is unknown. It was hypothesized that the thiol group is critical to MBT's covalent binding/haptenation to nucleophilic protein residues. Hypochlorous acid oxidized MBT to the disulfide, 2, 2'-dithiobis(benzothiazole) (MBTS), within the glove matrix. Cysteine reduced MBTS to MBT with subsequent formation of the mixed disulfide 2-amino-3-(benzothiazol-2-yl disulfanyl)-propionic acid. Simultaneous reduction of MBTS and disulfide formation with Cys34 on bovine serum albumin was observed, suggesting a potential route of protein haptenation through covalent bonding between cysteinyl residues on proteins and the MBT/MBTS thiol moiety. Guinea pigs were sensitized to MBT using a modified guinea pig maximization assay (GPMT) and cross-reactivity towards MBTS and the free thiol-lacking or blocked compounds benzothiazole (BT), 2-hydroxybenzothiazole (HBT) and 2-(methylthio)benzothiazole (MTBT) assessed. MBT and MBTS, but not BT, HBT or MTBT elicited allergic contact dermatitis (ACD) in MBT-sensitized animals.
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Chipinda, Itai, "Selected Chemistry of Biologically-Active Thiols : N-acetylpenicillamine and 2-mercaptobenzothiazole in Nitrosothiol Formation and Role in Allergic Contact Dermatitis Respectively" (2007). Dissertations and Theses. Paper 6177.