title: Using nitrogen isotope fractionation to assess the oxidation of substituted anilines by manganese oxide.
abstract: We explored the N isotope fractionation associated with the oxidation of substituted primary aromatic amines, which are often the position of initial attack in transformation processes of environmental contaminants. Apparent (15)N-kinetic isotope effects, AKIE(N), were determined for the oxidation of various substituted anilines in suspensions of manganese oxide (MnO(2)) and compared to reference experiments in homogeneous solutions and at electrode surfaces, as well as to density functional theory calculations of intrinsic KIE(N)for electron and hydrogen atom transfer reactions. Owing to the partial aromatic imine formation after one-electron oxidation and corresponding increase in C-N bond strength, AKIE(N)-values were inverse, substituent-dependent, and confined to the range between 0.992 and 0.999 in agreement with theory. However, AKIE(N)-values became normal once the fraction of cationic species prevailed owing to (15)N-equilibrium isotope effects, EIE(N), of 1.02 associated with N atom deprotonation. The observable AKIE(N)-values are substantially modulated by the acid/base pre-equilibria of the substituted anilines and isotope fractionation may even vanish under conditions where normal EIE(N) and inverse AKIE(N) cancel each other out. The pH-dependent trends of the AKIE(N)-values provide a new line of evidence for the identification of contaminant degradation processes via oxidation of primary aromatic amino groups.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Marita
authors.initials: M
authors.lastname: Skarpeli-Liati
authors.forename: Martin
authors.initials: M
authors.lastname: Jiskra
authors.forename: Aurora
authors.initials: A
authors.lastname: Turgeon
authors.forename: Ashley N
authors.initials: AN
authors.lastname: Garr
authors.forename: William A
authors.initials: WA
authors.lastname: Arnold
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Cramer
authors.forename: René P
authors.initials: RP
authors.lastname: Schwarzenbach
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D005591:Chemical Fractionation / Q000379:methods*; D002853:Chromatography, Liquid; D004784:Environmental Monitoring / Q000379:methods*; D004785:Environmental Pollutants / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D006863:Hydrogen-Ion Concentration; D016014:Linear Models; D017895:Manganese Compounds / Q000737:chemistry*; D015394:Molecular Structure; D009587:Nitrogen Isotopes / Q000032:analysis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*
chemical_list: D000814:Aniline Compounds; D004785:Environmental Pollutants; D017895:Manganese Compounds; D009587:Nitrogen Isotopes; D010087:Oxides; C027424:manganese oxide