Cautionary Note: The Thermal Decomposition of Amino Acids in the Solid State

Abstract

The Arrhenius parameters governing the pyrolysis rates for 19 amino acids in the solid state presented in the paper listed as reference 1 were developed in a dynamic TGA–DSC procedure employing single heating rate techniques and appear to be untrustworthy. The incongruities resulting from the parameters include clearly implausible half-lives for glycine and alanine at 25 °C of respectively 8 min and 2.5 years. A simulation of an experimental run for glycine employing the recorded parameters and the procedure described in the paper reveals that the amino acid should be fully consumed at temperatures well below the recorded region of thermolysis. The recorded parameters for alanine are significantly different from those reported 3 decades earlier in a kinetic study that utilized conventional isothermal techniques and provided acceptable estimates of alanine’s stability. The source of the problem is the use of a single heating rate rather than multiple rates in the determinations, and it is suggested that the parameters listed in reference 1 be avoided.

Highlights

► The Arrhenius parameters presented in the often cited paper listed as reference 1 appear to be untrustworthy.

► The incongruities resulting from the parameters include implausible half-lives for glycine and alanine at 25 °C.

► The recorded parameters for alanine are significantly different from those reported more than 3 decades.

► It is suggested that the parameters listed for the amino acids dealt with in reference 1 cannot be relied upon and should be applied with caution.