title: Micelle-catalyzed reaction between ninhydrin and nickel dipeptide complex [Ni(II)-Gly-Tyr]+.
abstract: The interaction of nickel dipeptide complex [Ni(II)-Gly-Tyr](+) with ninhydrin has been investigated in the absence and presence of cationic cetyltrimethylammonium bromide (CTAB) and gemini (16-s-16, s=4, 5, 6) surfactants spectrophotometrically at 80°C and pH 5.0. The product formed was the same and the reaction followed first- and fractional-order kinetics with respect to [Ni(II)-Gly-Tyr](+) and [ninhydrin], respectively, in both aqueous as well as micellar media. In the presence of CTAB, rate increased and reached up to a maximum, then decreased. Also, whereas typical rate constant (k(Ψ)) increase and leveling-off regions, just like CTAB, were observed with geminis, the latter produced a third region of increasing k(Ψ) at higher concentrations. This unusual third-region effect of the gemini micelles is assigned to changes in their micellar morphologies. The micellar catalysis is explained in terms of pseudo-phase model. The binding constants and the values of activation parameters such as activation energy (E(a)), enthalpy of activation (ΔH(#)) and entropy of activation (ΔS(#)) have been evaluated.
authors.affiliation: Department of Chemistry, Aligarh Muslim University, Aligarh, UP, India. drmohdakram@rediffmail.com
authors.forename: Mohd
authors.initials: M
authors.lastname: Akram
authors.forename: Dileep
authors.initials: D
authors.lastname: Kumar
authors.lastname: Kabir-ud-Din
mesh_terms: D002384:Catalysis; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008823:Micelles; D009532:Nickel / Q000737:chemistry*; D009555:Ninhydrin / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D013053:Spectrophotometry; D013501:Surface-Active Agents / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D002593:Cetrimonium Compounds; D056831:Coordination Complexes; D004151:Dipeptides; D008823:Micelles; D009942:Organometallic Compounds; D013501:Surface-Active Agents; D014867:Water; D009532:Nickel; D009555:Ninhydrin; D000077286:Cetrimonium