Reactions of Muonium with simple biochemical solutes in water and micelles

• Published in: Canadian journal of chemistry Vol. 69; no. 8; pp. 1252 - 1258
• Main Authors: Barnabas, Mary V, Walker, David C
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.08.1991; National Research Council of Canada
• Subjects: Bioinorganic chemistry; Chemistry; Exact sciences and technology; Inorganic chemistry and origins of life; Solvent effect; Isotope effect; Biochemical compound; Hydrogen Isotopes; Aqueous solution; Rate constant; Muonium; Micellar solution; Organic compounds
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v91-187

Rate constants are reported for the reaction of muonium atoms in water with some 36 organic compounds, many of interest in biology. These k M values range from < l0 5 to 7 × 10 10  M −1 s −1 , according to the type of reaction involved, with the sugar-phosphate backbones of nucleic acids being at the low end and their bases at the high end. They are compared with corresponding published H-atom data (k H ), where possible, and show kinetic-isotope-effects ranging over five orders of magnitude. Since all k H data were obtained at pH = 1, while k M values refer to pH ~ 7 of the natural state, the pH-dependence of k M was examined in representative cases. The changes found result from protonation of the solute rather than a changed reactivity of Mu on being converted to MuH + . On localizing the solutes in the hydrophobic phase of dilute micelles, the reactivity of Mu was again measured (k M(mic) ). The resulting "enhancement" factor was considered in terms of: the reaction mechanism, its dependence on microenvironment (solvation), and the concentrating effect of mutual confinement to small sections of a biphasal system. Key words: kinetic isotope effects, muonium, biochemicals, micelles.