Study of dynamic behavior of EDTA molecule in solution using perturbed gamma-gamma angular correlation spectroscopy

In this work, PAC spectroscopy has been used to obtain the hyperfine parameters in EDTA molecules in solutions with pH 4.3 and pH 10.5 both measured at 77 K and 295 K using 181Hf(181Ta) as probe nuclei. Both dynamic and static interactions were measured in aqueous solution, crystallized and re-hydrated samples in order to examine the motion and structure of EDTA-molecules. The hyperfine parameters, quadrupole interaction frequency (νQ), asymmetry (η), and the dynamic interaction frequency (λ) were obtained. The outcomes show that the rotational correlation time (τCR) is larger than the half-life of the intermediate state of probe nuclei. For samples with pH 4.3 and pH 10.5, it was observed an increase in νQ when the temperature decreases, as expected, and also a variation of η, which is an evidence of a change in the EDTA molecule structure. 181Hf is bound only to a single molecule site when the pH was 4.3, differently from the results for pH 10.5 sample, which showed two fractions with different νQ indicating the possibility of 181Hf being bonded to two different sites of the molecule. Measurements of the dehydrated sample presented different results leading us to conclude that the preparation procedure can causes alterations in the chemical bounds. Concluding, these results showed a systematic behavior of the 181Hf-EDTA, with the variation of pH from 4 to approximately 11, and they are important to the knowledge of the dynamic behavior of this molecule. (author)