Biomaterial Database

Kinetics and mechanism of the oxidation of N-acetyl homocysteine thiolactone with aqueous iodine and iodate. 2013

Ashley Sexton, and Wilbes Mbiya, and Moshood K Morakinyo, and Reuben H Simoyi

Department of Chemistry, Portland State University , Portland, Oregon 97207-0751, United States.

The kinetics of N-acetyl homocysteine thiolactone (NAHT) oxidation by aqueous iodine and iodate were studied by spectrophotometric techniques. The iodate-NAHT reaction is slow and results in the formation of N-acetyl homocysteine thiolactone sulfoxide as the sole product (NAHTSO). The stoichiometry of the reaction was deduced as: IO3(-) + 3NAHT → I(-) + 3NAHTSO (S1). In excess iodate conditions, the iodide produced in S1 is oxidized to give iodine: IO3(-) + 5I(-) + 6H(+) → 3I2 + 3H2O (S2). Thus in excess iodate conditions the overall stoichiometry of the reaction is a linear combination of S1 and S2 that eliminates iodide, 5S1 + S2: 2IO3(-)+ 5NAHT+ 2H(+) → I2 + 5NAHTSO + H2O. There was a 1:1 stoichiometry for the NAHT - I2 reaction: NAHT+ I2 + H2O → NAHTSO +2I(-) + 2H(+) (S3). All reactions, S1, S2 and S3 occur simultaneously and since they are all comparable in rate; complex dynamics were observed. Iodide catalyzes S1 and S2 but inhibits S3. Iodide is a product of both S1 and S3. It has the most profound effect on the overall global dynamics observed. The overall reaction scheme which involved S1, S2 and S3 was modeled by a simple 12-reaction mechanistic scheme which gave a very good fit to experimental data.

UI	MeSH Term	Description	Entries
D007452	Iodates	Inorganic salts of iodic acid (HIO3).	Iodate
D007455	Iodine	A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126.90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically.	Iodine-127,Iodine 127
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008968	Molecular Conformation	The characteristic three-dimensional shape of a molecule.	Molecular Configuration,3D Molecular Structure,Configuration, Molecular,Molecular Structure, Three Dimensional,Three Dimensional Molecular Structure,3D Molecular Structures,Configurations, Molecular,Conformation, Molecular,Conformations, Molecular,Molecular Configurations,Molecular Conformations,Molecular Structure, 3D,Molecular Structures, 3D,Structure, 3D Molecular,Structures, 3D Molecular
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D013237	Stereoisomerism	The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)	Molecular Stereochemistry,Stereoisomers,Stereochemistry, Molecular,Stereoisomer
D013876	Thiophenes	A monocyclic heteroarene furan in which the oxygen atom is replaced by a sulfur.	Thiophene
D014867	Water	A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Hydrogen Oxide