NMR Study of a Reversible Hydrolysis Reaction

The hydrolysis of pyruvic acid to 2,2-dihydroxypropanoic acid is a reversible reaction giving rise to the following equilibrium in aqueous solution  

In this experiment, nuclear magnetic resonance (NMR) techniques will be used to determine the specific rate constants and for the forward and reverse reactions as well as the value for the equilibrium constant K. Like the hydrolysis of many other organic compounds, this reaction can be acid catalyzed and the effect of hydrogen-ion concentration on the kinetics can be studied. Furthermore, the dependence of y, , and K on temperature will be measured and used to evaluate activation energies. 

The reversible pyravic acid hydrolysis proceeds kinetically along both an uncatalyzed and an acid-catalyzed path  

CH3C—COOH -H H+t— CH3C+—COOH very rapid to equil. (3) 

Introducing an abbreviated notation for convenience such that A = CH3COCOOH, B = CH3C(0H)2C00H, and AH+ = CH3C+(OH)COOH, one finds 

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A number of studies on photochemistry of the nucleic acid bases in aqueous solutions demonstrated that while uracil undergoes reversible hydration under exposure to UV irradiation, the other bases (thymine, adenine, and guanine) were stable [41,42], However, the sensitivity of dissolved thymine to UV irradiation can be significantly increased if the solution is rapidly frozen [43]. In 1960 the thymine photoproduct was isolated from irradiated frozen aqueous solution of thymine. Elemental analysis, molecular weight measurements, powder X-ray diffraction, NMR and IR spectroscopy confirmed that the most likely photoproduct is a thymine dimer [20]. Similar photoproduct was obtained by hydrolysis of irradiated DNA. Its formation was attributed to reaction between two adjacent thymine groups on the same DNA chain [44], Independently an identical compound was isolated from DNA of UV-irradiated bacteria [45]. 

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