Interaction mechanisms between humic acids of different origin and nature and electron donor herbicides: A comparative IR and ESR study

Abstract

Products from reaction of four humic acids of different origin and nature (synthetic, coal, peat, compost) and four s-triazine and six substituted urea herbicides were studied. Elemental composition and infrared and electron spin resonance spectra were measured on original humic acids, pure herbicides and the reaction products. Elemental analysis data indicated that stable complexes were formed between humic acids and herbicides. Infrared analysis results showed the formation of ionic and hydrogen bonds between interacting molecules and suggested the possible occurrence of charge-transfer complexes. Electron spin resonance parameters and in particular the increases concentrations of paramagnetic centres in interaction products gave evidence that electron donor-acceptor processes involving free radical intermediates were among the most important binding mechanisms occurring. Structural and chemical properties of both humic acids and herbicides influenced the prevailing type(s) of interaction mechanism(s) which occurred.