Application of Electron Spin Resonance and Fluorescence Spectroscopies to the Study of Soil Humic Substances

Abstract

ABSTRACT Senesi, N., 1991. Application of electron spin resonance and fluorescence spectroscopies to the study of soil humic substances. In the first part of this review paper, applications of electron spin resonance (ESR) spectroscopy to the study of humic substances (HS) are considered. The nature and concentration of organic free radicals in HS and their changes as a function of several experimental factors, the relations existing between ESR results and structural and functional properties of HS, and the information that ESR data may provide on the interaction of HS with some herbicides, are discussed. ESR spectra and parameters of HS complexes with Fe(III), Cu(II), Mn(II), and V(IV) are discussed, with emphasis on the chemical and geometrical nature of the binding sites and the identity of HS ligands involved in the interaction, and on the stability of the metal-HS Complexes. In the second part of this paper, fluorescence spectra in the emission, excitation, and synchronous-scan excitation modes of representative HS are discussed for the possible distinction and classification of HS, on the basis of structures feasibly responsible for and factors affecting their fluorescence behaviour on dependence on their nature and origin. Finally, the use of fluorescence quenching method and fluorescence polarization technique for quantitative studies of the binding of metal ions and organic chemicals to HS and for conformational studies of HS is briefly summarized.