title: Hydrogen-bonding interactions between water and the one- and two-electron-reduced forms of vitamin K1: applying quinone electrochemistry to determine the moisture content of non-aqueous solvents.
abstract: Vitamin K(1) (VK(1)) was shown by voltammetry and coulometry to undergo two chemically reversible one-electron reduction processes in acetonitrile (CH(3)CN) containing 0.2 M Bu(4)NPF(6) as the supporting electrolyte. The potential separation between the first and second electron-transfer steps diminished sequentially with the addition of water, so that at a H(2)O concentration of approximately 7 M (approximately 13% v/v) only one process was detected, corresponding to the reversible transfer of two electrons per molecule. The voltammetric behavior was interpreted on the basis of the degree of hydrogen bonding between the reduced forms of VK(1) with water in the solvent. It was found that the potential separation between the first and second processes was especially sensitive to water in the low molar levels (0.001-0.1 M); therefore, by measuring the peak separation as a function of controlled water concentrations (accurately determined by Karl Fischer coulometric titrations) it was possible to prepare calibration curves of peak separation versus water concentration. The calibration procedure is independent of the type of reference electrode and can be used to determine the water content of CH(3)CN between 0.01 and 5 M, by performing a single voltammetric scan in the presence of 1.0 mM VK(1). The voltammetry was also investigated in dichloromethane, dimethylformamide, and dimethyl sulfoxide. The reduction processes were monitored by in situ electrochemical UV-vis spectroscopy in CH(3)CN over a range of water concentrations (0.05-10 M) to spectroscopically identify the hydrogen-bonded species.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371.
authors.forename: Yanlan
authors.initials: Y
authors.lastname: Hui
authors.forename: Elaine Lay Khim
authors.initials: EL
authors.lastname: Chng
authors.forename: Cheryl Yi Lin
authors.initials: CY
authors.lastname: Chng
authors.forename: Hwee Ling
authors.initials: HL
authors.lastname: Poh
authors.forename: Richard D
authors.initials: RD
authors.lastname: Webster
mesh_terms: D055664:Electrochemical Techniques; D004583:Electrons; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011809:Quinones / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*; D013053:Spectrophotometry; D010837:Vitamin K 1 / Q000032:analysis* / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D011809:Quinones; D012997:Solvents; D014867:Water; D010837:Vitamin K 1