Paramagnetic molecular centers in the gamma-irradiated precipitates obtained in the system AlCl3-beta-alanine-NaOH

The presented results are the continuation of our work on paramagnetic molecular centers in the model clay compounds. Here it was attempted to incorporate β-alanine in the aluminium hydroxide matrix. A series of precipitates were prepared with the highest ratio of β-alanine/Al = 0.22 obtained at pH = 7.

X-ray diffraction analysis revealed in addition to amorphous precipitates, microcrystalline samples of four different X-ray patterns in nine precipitates, indicating variations in the structure of aluminium hydroxide matrix with incorporated β-alanine. Selected samples were exposed to γ-irradiation at 77 K, and at room temperature (293 K) in the presence and in the absence of air. In all the samples of amorphous structure no stable paramagnetic centers were determined by ESR after γ-irradiation in air.

In all samples of microcrystalline structure similar stable paramagnetic centers were determined by ESR after γ-irradiation in air and in the evacuated tubes. These paramagnetic centers that we were unable to identify due to the poor resolution of the lines in the ESR spectrum can be most probably ascribed to structural defects introduced into the aluminium hydroxide matrix by β-alanine.

In all amorphous samples γ-irradiated in the absence of air, the radical C̊H₂CH₂COOH formed by abstraction of amino group from the β-alanine was determined by ESR. The radical was unstable in air. Thus in the absence of air β-alanine may be considered as a storage site for the γ-irradiation energy in the amorphous aluminium hydroxides.