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 pKal 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.