Browsing by Author "Pispisa, Basilio"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Binding-induced Conformational Transition of Sodium Poly-L-Glutamate by Iron(ni) Complex Ions in Aqueous Solution
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (2), 1977) Branca, Mario; Pispisa, Basilio
    The binding of pseudo-octahedral trans- and cis-FeIII complex ions by sodium poly-L-glutamate (PLG) and dextransulphate (DS) in aqueous solution at about pH 7 has been studied. Equilibrium dialysis and “phase-separation” data show that the affinity for the complex counterions by both polyelectrolytes follows the order trans-[Fe(tetpy)(OH)2]+ > cis-[Fe(pmen)(OH)2]+. Evidence of a specific site binding, leading to a marked “renaturation” effect on the charged polypeptide, is produced in the case of the trans-FeIII-quaterpyridine compound. The binding isotherm of the trans-complex + PLG system and the circular dichroism patterns of the polypeptide as a function of the bound-trans-complex to polymer-residue ratio were successfully treated by a two-state model for the polyelectrolyte and a preferential association of the complex ions to the helical conformation of the polymeric matrix. All these features are examined in the light of the structural characteristics of the interacting species. The implications of the different stereochemistry of the other complex ions studied on the binding process with PLG are also discussed.
  • No Thumbnail Available
    Item
    Environmental Control of Reactions: Influence of Poly(L-glutamate) on the Kinetics of Decomposition of Hydrogen Peroxide Catalysed by Quaterpyridineiron (m) Complex Ions
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Barteri, Mario; Farinella, Marcello; Pispisa, Basilio; Splendorini, Luciano
    The decomposition of hydrogen peroxide catalysed by quatcrpyridineiron(ni) complex ions has been studied within the pH range 6.5-8. The reaction obeys total third-order kinetics with a partial order of two with respect to the substrate. At pH Rs 7.6, where the reaction velocity exhibits a maximum asymptotic value, the apparent activation energy is 29.3±2.9 kJ mol-1. Addition of poly (L-glutamate) (PLG) in solution determines a change in the overall kinetics. In this case, the process follows a total second-order equation and has an apparent activation energy of 53.1 ±6.3 kJ moly . At a fixed concentration of complex, saturation phenomena are observed in all cases on increasing the concentration of substrate. As expected, the Lineweaver-Burk plot of the polymer- free complex-catalysed reaction is nonlinear, whereas it is linear when the complex + PLG system is us5.d', At 25°C, the rate constant for the irreversible decomposition of the Michealis “ complex ”, which represents the rate-determining step, is k3 = 4.9 ±0.2 and 2.7 ± 0.2 s-1 for [Fe(tctpy) X2]nF and 1 c(. etpy)X2]"++PLG catalytic systems, respectively. Implications of the role played by the poly- pep ice matrix as environmental controller of the catalysis under study are briefly discussed.