Non-enzymatic hydrolysis of creatine ethyl ester

Abstract

The rate of the non-enzymatic hydrolysis of creatine ethyl ester (CEE) was studied at 37 °C over the pH range of 1.6–7.0 using 1H NMR. The ester can be present in solution in three forms: the unprotonated form (CEE), the monoprotonated form (HCEE +), and the diprotonated form (H 2CEE 2+). The values of p K a1 and p K a2 of H 2CEE 2+ were found to be 2.30 and 5.25, respectively. The rate law is found to be Rate = - dC CEE / dt = k + + [ H 2 CEE 2 + ] [ OH - ] + k + [ HCEE + ] [ OH - ] + k 0 [ CEE ] [ OH - ] where the rate constants k ++, k +, and k 0 are (3.9 ± 0.2) × 10 6 L mol −1 s −1, (3.3 ± 0.5) × 10 4 L mol −1 s −1, and (4.9 ± 0.3) × 10 4 L mol −1 s −1, respectively. Calculations performed at the density functional theory level support the hypothesis that the similarity in the values of k + and k 0 results from intramolecular hydrogen bonding that plays a crucial role. This study indicates that the half-life of CEE in blood is on the order of one minute, suggesting that CEE may hydrolyze too quickly to reach muscle cells in its ester form.