19926-71-7Relevant academic research and scientific papers
The effects of Mg2+, hydrogen bonding, and steric factors on rate and equilibrium constants for phosphoryl transfer between Carboxylate Ions and Pyridines
Herschlag, Daniel,Jencks, William P.
, p. 1942 - 1950 (2007/10/02)
The reaction of bicarbonate ion with phosphorylated γ-picoline monoanion (PicP), which presumably gives carboxyphosphate, is faster than the reactions of acetate and carbonate by factors of 40 and 6, respectively (25°C, I = 1.5). The rate increase is attributed to hydrogen bonding of the bicarbonate hydroxyl group to a phosphoryl oxygen atom; phosphate monoanion and dianion show similar increases. The reaction of acetate ion with PicP and the reverse reaction of γ-picoline with acetyl phosphate dianion are catalyzed ～20-fold by Mg2+. The reaction of PicP with formate ion is 20-fold faster than with acetate ion and shows no catalysis by Mg2+. This indicates that the rate increases with bicarbonate and with Mg2+ arise from overcoming unfavorable electrostatic, solvation, or steric interactions. Catalysis of the reaction of γ-picoline with acetyl phosphate (AcP), in both directions, is described by chelation of Mg2+ to the transition state, with Ka? = 97 M-1, and binding to the ground states with Ka = 5 and 4.4 M-1 for PicP and AcP, respectively. Equilibrium constants are reported for phosphoryl transfer between pyridines, imidazole, ammonia, and acetate ion; the favorable transfer from pyridine to acetate, by ～100-fold, shows that the P-O bond is stronger than the P-N bond, relative to H-O and H-N bonds.
