Protolysis kinetics of some amino-acids studied by the nuclear magnetic resonance spin echo technique

Abstract

Proton magnetic relaxation times have been measured as a function of pH and temperature for aqueous solutions of amino-acids in the series H₃[graphic omitted]—[CH₂]_n—CO₂ where n= 1, 2, 3, 5 and 7 and also for solutions of α-alanine, sarcosine, L-proline, picolinic acid and 2-pyrrolidone. The T₁ values were independent of pH but T₂ had a minimum value near to pH 6 at room temperature for most of the solutions studied. In many cases, a second minimum occurred close to pK_al for the amino-acid. The data are analysed in terms of proton exchanges between amino groups and sites which are oxygen attached. Kinetic parameters are derived for some exchange reactions which have not previously been considered in connection with amino-acid solutions.