Mazzei, Pierluigi (2011) NMR evaluation of the interactions between humic substances and three molecules of agrochemical interest: beta-D-glucosidase and alkaline phosphatase enzymes and glyphosate. [Tesi di dottorato] (Inedito)

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Abstract

This doctoral thesis presents results concerning the investigation, by liquid-state Nuclear Magnetic Resonance (NMR) technique, on interactions occurring among humic substances and three molecules largely diffused in soil: the herbicide glyphosate, the enzymes beta-D-Glucosidase and Alkaline Phosphatase. These agrochemical molecules were examined as a function of the increasing addition of humic substances. In detail, glyphosate was treated with both humic and fulvic acids (pH 5 and 7.2); the alkaline phosphatase with two different humic acids (pH 10.4) and beta-D-Glucosidase with fulvic acids (pH 5 and 7.2). All studied molecules interacted with employed humic substances and the complex formations were mainly driven by weak forces. These results were initially supported by the observation of resonance broadening and/ or chemical shift drift spectroscopic phenomena, as a function of the humic concentration. Then, by analyzing both the molecular spin relaxation and correlation times as well as the self-diffusion constants, significant and diagnostic variations emerged, thus, corroborating the hypothesis of the occurred interactions. Moreover, only in the case of glyphosate, it was possible to apply the saturation transfer difference (STD) NMR experiment and, by means of diffusion results, the fraction of herbicide bond to humic matter was calculated. Instead, concerning the soil enzymes, the attention was focused on a further purpose that consisted in researching possible modifications, due to humic interactions, affecting the enzymatic catalytic activity. Therefore, a progressive inhibition of the activity was detected in liquid-phase, as a function of both the molecular concentration and composition of humic substances. Finally, aiming to better reproduce a more realistic soil condition, the enzymatic inhibition, due to the interactions with natural organic matter, was further studied in liquid-solid phase. In fact, by preliminary experiments, beta-D-Glucosidase was immobilized on OH-Al-humate-montmorillonite complexes and a significant inhibition was again observed as well as its extents were more enhanced than the one detected for pure liquid catalysis.

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