Oxidation of L-cysteine by FeIII-1,10-phenanthroline complex : A kinetic study

Department of Chemistry, Utkal University, Vani Vihar, Bhubaneswar-751 004, Orissa, India
E-mail : sandhya_panda2002@yahoo.com
Hydro- and Electro-Metallurgy Department, Regional Research Laboratory (CSIR), Bhubaneswar-751 013, Orissa, India
Manuscript received 19 October 2006, revised 19 April 2007, accepted 24 May 2007

Electron transfer reaction of lron(III)-1,10-phananthrollne by I.-cysteine has been studied spcctrophotometrlcnlly over the range 1.1 ≤ pH ≤ 2.26, 25 ≤ t ≤ 40 ^oC, 0.1 ≤ 0.2, 4.5 ≤ 10⁵ [Fe"']_T. ≤ 6.5, 1.5 ≤ 10³ [phcn]_T ≤ 6.0 and 3.0 ≤ 10³ [H₃A⁺] ≤ 7.0 mol dm-3, The products of the reaction are Fe" and cystine. The ∆H^#- and ∆S^#-values for the electron transfer reaction are (4.5 :± 1) kJ/mol and (-149 :± 3) JK^-1 mol^-1• The electron transfer reaction between the oxidant [Fc(phen)₂(OH₂)2]³⁺ and the zwitterlonlc form of the amino acid follows the rate law : k_obs = K₂K₃ [Sub]_T [Hphen] (k₁ + k₂K₁[H⁺)/([H+] + K₁ [H+]² + K₂ K₃ [Hphcn]_e + K₁K₂K3 [H+] [Hphcn]).