The Suprahumic research group is based at Federico II University, in Portici (Naples).
Humic substances are ubiquitous natural compounds, arising from the chemical and biological degradation of plant and animal residues and occurring in soils, sediments, coals, waters, and other natural materials. Approximately 40-60% of dissolved organic carbon (DOC) in freshwaters and 60-70% of the total soil C occurs in humic materials, thereby representing the largest reservoir of carbon in the biosphere.
Humic substances are a major part of the Natural Organic Matter (NOM). The name is traditionally associated to the organic matter, outside the living cell, that is not directly related to recognizable biopolymers such as proteins, polysaccharides and plant and animal polyesters. However, these biopolymers are still to be found in the humic fractions usually isolated form waters and soils. Though humus is one of the natural materials that have been most studied since the onset of modern chemistry, their chemical and conformational structure has been for long elusive. Even their definition, that goes back to the early chemical studies, is still commonly based on the operational classification in general humic and fulvic acids. However, it is clear from more modern studies that the separation in these main classes does not have any chemical meaning.
Since about the sixties of the XX° century, a general consensus was spread in the scientific community on assuming that humic substances were formed of a unique type of molecules that should be linearly polymerised in the environment up to 50,000 Da for fulvic and more than 300,000 Da for humic acid. This paradigma had never been univocally demonstrated to be true in real conditions of waters and soils, but had strongly influenced the scientific community up to the mid of the nineties.
Following some experimental evidence, first observed by the Agricultural Chemists of the University of Padova, Piccolo, Nardi, and Concheri (European Journal of Soil Science, 47, 319-328, 1996), based on gel permeation experiments, doubted that the humic molecules could be polymers but, rather, an associations of relatively small molecules arranged in a sort of an irregular micelle in as much as it had been argued some years before by Wershaw (Journal of Contaminants Hydrology, 1, 29-45, 1986). However, while Wershaw had not questioned the polymeric nature of humic molecules in his micellar aggregates, the new understanding called for a supramolecular structure of humic substances in which the relatively small and heterogeneous molecules would have self associated mainly by dispersive weak forces such as van der Waals, p-p , CH-p .
This new model, though somewhat opposed at the beginning, has been progressively gaining a widespread consensus, the more experimental evidence have been produced in the literature by our group and many other scientists to confirm it. Its acceptance has been concomitantly sustained by the absence of modern experimental evidence supporting the traditional macropolyeric model. Several works can be found now in literature that explain results based on the supramolecular theory. Moreover, advanced physical-chemical instrumentation such as NMR and Mass Spectrometry have ascertained that the average mass of single humic molecules is hardly larger than 1000 Da.
It is our opinion that the supramolecular model of humic matter has promoted a new insurgence of awarness on how humic substances can be used to improve our understanding of environmental processes. The major areas in which humic research based on the supramolecular chemical concept can make a breakthrough are manyfolds.