title: Photolysis of phenylalanine in the presence of oxidized carbon nanotubes.
abstract: Photolyses at 254 nm of phenylalanine (Phe) in aqueous solutions, were carried out in the presence of oxidized carbon nanotubes modified by the reaction with SO2 (mNTO). Kinetics of the photolyses were followed by UV spectrophotometry at 220 nm, and the products were characterized by HPLC, XPS, and (13)C-SSNMR. The ratio of the initial rates of photolysis in the presence and absence of mNTO, k*/ko*, showed a systematic decrease. The photolytic decay of Phe occurs with minor formation of tyrosine. The mass of nanotubes produced an exponential attenuation of the photolytic decomposition of Phe. Total carbon analyses (TCA) showed no inorganic carbon formation after the photolyses. The first-order rate constant of photofunctionalization of mNTO by the insertion of phenylalanine onto the nanotube matrix was calculated from TCA to be kin = 30.1 min(-1). Comparison of the XPS spectra of the mNTO before and after the photolysis, using the atom inventory technique, suggests the insertion of Phe along with the extrusion of a sulfide radical anion ((•)S(-)) which undergo subsequent oxidation to SO4(2-). The obtained results show the effects of mNTO on the photolysis of Phe and provide a new method of photofunctionalization of carbon materials, modified by the intermediates of the reduction of SO2, with an organic moiety.
authors.affiliation: Departamento de Química and ‡ Departamento de Engenharia Química e Engenharia de Alimentos, Universidade Federal de Santa Catarina , 88040-670 Florianópolis, Santa Catarina Brazil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Humeres
authors.forename: Eduardo Pinheiro
authors.initials: EP
authors.lastname: de Souza
authors.forename: Nito Angelo
authors.initials: NA
authors.lastname: Debacher
authors.forename: Regina de F P M
authors.initials: Rde F
authors.lastname: Moreira
authors.forename: Cristiane Nunes
authors.initials: CN
authors.lastname: Lopes
authors.forename: Ma Isabel
authors.initials: MI
authors.lastname: Fernández
authors.forename: J Arturo
authors.initials: JA
authors.lastname: Santaballa
authors.forename: Moisés L
authors.initials: ML
authors.lastname: Canle
authors.forename: Wido H
authors.initials: WH
authors.lastname: Schreiner
authors.forename: Abil E
authors.initials: AE
authors.lastname: Aliev
mesh_terms: D007700:Kinetics; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000737:chemistry*; D010782:Photolysis; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D037742:Nanotubes, Carbon; D010649:Phenylalanine; D012822:Silicon Dioxide