The rate of the non-enzymatic hydrolysis of creatine ethyl ester (CEE) was studied at 37 degrees C over the pH range of 1.6-7.0 using H-1 NMR. The ester can be present in solution in three forms: the unprotonated form (CEE), the monoprotonated form (HCEE+), and the diprotonated form (H2CEE2+). The values of pK(a1) and pK(a2) of H2CEE2+ were found to be 2.30 and 5.25, respectively. The rate law is found to be Rate = -dC(CEE)/dt = k(++)[H2CEE2+][OH-] + k(+)[HCEE+][OH-] + k(0)[CEE][OH-] where the rate constants k(++), k(+), and k(0) are (3.9 +/- 0.2) x 10(6) L mol(-1) s(-1), (3.3 +/- 0.5) x 10(4) L mol(-1) s(-1), and (4.9 +/- 0.3) x 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. (C) 2009 Elsevier Inc. All rights reserved.