Thermodynamic characteristics of L-arginine oscillating system catalyzed by tetraazamacrocyclic nickel(II) complex

Abstract

A novel oscillating system with L-arginine (Arg) as organic substrate, catalyzed by a tetraazamacrocyclic nickel(II) complex (NiL(ClO₄)₂, (L: 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazabutadecacyclo-7,14-diene) is reported for the first time. The system has been quantitatively characterized by kinetic parameters, including the rate constants (k_in, k_p), the apparent activation energies (E_in, E_p), the pre-exponential constants (A_in, A_p), and the thermodynamic functions (∆H_in, ∆G_in, ∆S_in, ∆H_p, ∆G_p, ∆S_p). The results indicate that the NiL(ClO₄)₂ can catalyze the Arg oscillating reaction, exhibiting features of irreversible thermodynamics as shown by the negative entropy of the oscillating system. Further, the two active groups of the Arg oscillating system can be activated at higher acidity. A possible mechanism is also proposed for the Arg oscillating system catalyzed by NiL(ClO₄)₂.