Modulation of Optical Properties of Dissolved Humic Substances by their Molecular Complexity

R.A. MIGNONE; M.V. MARTIN; F.E. MORÁN VIEYRA; V. I. PALAZZI; B. LÓPEZ DE MISHIMA; D. MÁRTIRE; C. D. BORSARELLI

PHOTOCHEMISTRY AND PHOTOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2012 vol. 88 p. 792 - 800

0031-8655

In the present work, we present several UV-VIS absorbance, steady-state and time-resolved fluorescence parameters of a series of dissolved humic substances (DHS) from different sources and nature (e.g. terrestrial fulvic and humic acids, and humic acid-like substances extracted from composted and vermicomposted wastes). Several spectroscopic parameters correlated with the molar absorptivity at 280 nm per mole of organic carbon (e280), which in turns is proportional to the molecular complexity (molecular size, aromaticity and oxidation degree, etc.) of the DHS. Both absorbance and fluorescence spectral responses were very sensitive to the molecular complexity associated with the maturation degree of the DHS. Therefore, depending on the molecular complexity of the DHS, different emitting responses by excitation at the UVA (360 nm) and VIS (460 nm) regions of the absorption spectra of DHS were observed. The results were explained in terms of the increment of intramolecular low-energy absorbing and emitting energy/electron-transfer states formed by donor moieties groups, e.g. polyhydroxylated aromatics, indoles, etc. and more oxidized acceptor groups (e.g. quinones or other oxidized aromatics, etc.) as the molecular complexity of the DHS increased.