Unusual rate enhancement in metal ion catalysis of phosphate transfer

Abstract

NH3, and cyclohexylimine, since only the imine can be readily explained by radical attack on the parent amine.2C6HnNH2 + 2HN -> C6HuNHNH2 + CeH10NH + NH3 The difference in chemical behavior between the two azide salts may be ascribed to the difference in structure and ease of diffusion through the crystal lattice of the two initially formed radicals, amino and cyclohexylamino, and the corresponding bases. The large and structurally complex cyclohexylamino radical results in stable products, such as imine and cyclohexyl-substituted hydrazines, while surfacing. Heterogeneous reaction depends upon the ability of survival or regeneration of reactive species, like the amino radical, within the solid azide such that they can finally diffuse to the surface and react. Figure 2. Log /tobad vs.

Synthesis and phosphatase activity of a Cobalt(II) phenanthroline complex

“…Rate of acceleration for the catalytic phenomenon is observed when multiple assisting parameters are working concurrently. [35][36][37][38] After rigorous review of the scientific literature, herein, we propose the plausible catalytic cycle having reasonably good agreement with our kinetic result. The generation of nucleophile from coordinated water molecules at the metal centres in the reaction medium remains the fundamental aspect in this catalysis which later follows the attack of metal bound nucleophile on phosphorous atom, as a representative mechanism (Scheme 3).…”

“…We have taken careful measure to propose the cleavage mechanism of PNPP for our cobalt(II) complex from the reported scientific literature. [35][36][37][38][39] It is seen that metal catalysts can take significant initiative for catalytic cleavage of PNPP through Lewis acid activation, metal-nucleophile attack and leaving group activation (Scheme 2), and exhibit remarkably fast rates of phosphate hydrolysis. Rate of acceleration for the catalytic phenomenon is observed when multiple assisting parameters are working concurrently.…”

Catalysis of phosphoryl group transfer. Role of divalent metal ions in the hydrolysis of lactic acid O-phenyl phosphate and salicylic acid O-aryl phosphates

“…The only appreciable deviation is the second-order rate constant for the Cu2+-catalyzed reaction. This is not unusual, in the sense that Cu2+ is often the only effective metal ion, or vastly superior, in reactions of phosphate esters where metal ion effects are observed (Hofstetter et al, 1962;Murakami and Takagi, 1969;Benkovic and Dunikoski, 1971;Benkovic and Miller, 1972). The basis for the unusual efficiency of Cu2+ is not understood.…”

Phosphoryl transfer to anionic oxygen nucleophiles. Nature of the transition state and electrostatic repulsion

“…Stabilization of this negative charge by proton transfer from a general acid, or by metal ions, can provide catalysis.65 Examples in nonenzymic reactions include the following: the hydrolysis of phosphate monoester monoanions with poor leaving groups, which is much faster than that of the corresponding dianions because the proton is transferred to the oxygen leaving group in the transition state;% Herschlag and Jencks catalysis of -20-fold by Mg2+ of the reaction of acetyl phosphate dianion with pyridines through stabilization of the large negative charge on the acetate leaving group;" catalysis of -105-fold by Zn2+ for the hydrolysis of pyridine-2-carbaldoximyl phosphate d i a n i ~n , ~~ which is equivalent to an increase in the acidity of the leaving group by lo4; and catalysis by Cu2+ of the hydrolysis of 2-(4(5)-imidazoly1)phenyl phosphate by a similar factor of > 104-fold. 67 The species RO(H+)P032-is an unfavorable substrate for the reverse reaction, if it exists at all, because it is a high-energy species that may not be present at a sufficient concentration to diffuse to the active site and account for the observed rate of catalysis.…”