Study On The Interaction Mechanism Between Organic Arsenic Drugs And Dissolved Organic Matter (DOM)

In this thesis, the interaction between humic acid (HA)-a kind of typical dissolved organic matter (DOM) and organic arsenic, such as roxarsone (ROX), p-arsenilic acid (p-ASA) and o-arsenilic acid (o-ASA) were researched. The methods of three dimensional fluorescence spectrum, synchronous-scan fluorescence spectra, transient fluorescence spectrum and fourier transform infrared spectroscopy were used to identify the interaction between HA and organic arsenic. Fluorescence spectroscope and fluorescence quenching titration technique were used to investigate the effects of HA concentration, pH, and temperature on the bonding strength between HA and organic arsenic. HA-Fe-organic arsenic was studied to clarify the function of Fe. The main conclusions are as follows:1. HA could be quenched by ROX, p-ASA, o-ASA.The equilibrium between them could be achieved within0.5hours. Four fluorescence peaks of HA were Ex/Em=300nm/480nm,370nm/480nm,420nm/500nm,460nm/520nm respectly. For ROX, the extent of decreases in fluorescence intensities of different peaks was different and followed an order of C>A>D. For p-ASA and o-ASA, it was A>B=C=D.2. Transient-fluorescence spectrum analyses and liner model simulations revealed that single static quenching was the main mechanism between ROX (p-ASA, o-ASA) and the functional groups of fluorescence peak A, B, D in HA, and combined dynamic and static quenching were the main mechanism between ROX and the functional groups of peak C in HA.3. Fourier transform infrared spectroscopy analyses indicated an interaction between groups of arsenic acid in ROX (p-ASA, o-ASA) and negative ion of carboxylic acid in HA. In HA-Fe-ROX, Fe3+played a role of bridge connection.4. Compared with HA-ROX and o-ASA-HA, the increasing of HA concentration could inhibit apparently the interaction between HA and p-ASA. It meansed that the equilibrium could be rebuilded for different concentration of HA in p-ASA-HA. The common logarithm value of association constants (1g K) were far larger than the bimolecular quenching constant of O2.5. pH could change the formation of ROX (p-ASA, o-ASA, Fe3+) and conformation of phenolic hydroxyl groups and carboxyl groups in HA. When pH=7, the interaction between p-ASA and HA was easier. When pH<7, the interaction between o-ASA and HA was easier.6. The1gK values of HA-ROX (p-ASA, o-ASA) decreased with the increase of temperature ranging from25.0℃to55.0℃(for p-ASA, o-ASA, from15.0℃to35.0℃), which further confirmed the static quenching interaction between HA and ROX (p-ASA, o-ASA). Δ H0values obtained from van’t Hoff equation showed that the interactions between ROX (p-ASA,o-ASA) and HA were hydropobic effect and hydrogen bond, and the strengths of the interaction between ROX and HA, between p-ASA and HA were larger than that of between o-ASA and HA.7. Adding Fe3+into the reactive system of HA and ROX, the fluorescence quenching of humic-like and fluvic-like groups in HA by ROX could be quickened, while the strength of fluorescence of HA-Fe-ROX reduced apparently. No competition occurred between Fe3+and ROX on the surface binding site of HA.