A detailed analysis of the properties of radiolyzed proteinaceous amino acids

Abstract

The thermal behaviour of 21 proteinaceous l-amino acids either as pristine samples and also as radiolyzed (3.2 MGy) samples was studied with the differential scanning calorimeter. The onset and peak melting point as well as the melting enthalpy of all samples before and after the radiation treatment was measured and reported. The residual amount of each amino acid survived to the radiation dose of 3.2 MGy (N _γ) was measured from the melting enthalpies before and after radiolysis and hence the radiation resistance of each amino acid has been determined. The radiolysis causes a systematic reduction of the melting enthalpy and a shift of the onset and peak melting point to lower values. It is shown that N _γ does not correlate with the melting points of the amino acids but shows a correlation with the entity of the shift of the melting point peaks occurred after radiolysis. Such correlation instead does not exist between the N _γ parameter and the onset melting points of the amino acids. An explanation of such lack of correlation was given. Furthermore, a general relationship has been found between the amino acids melting point peak measured on pristine samples and the melting point peaks after solid state radiolysis. Such relationship can be used to predict roughly the expected melting point after radiolysis at 3.2 MGy of any given amino acid. The last part of the study was dedicated in the attempt to find a correlation between the N _γ parameter and the amount of the amino acids survived the radiolysis R _γ as measured by spectropolarimetry (ORD spectroscopy). A general trend was found in the connection between the N _γ and R _γ parameters but not a very strong correlation.