Functional hybrid co-crystals of humic substances: a growth forecastElectronic supplementary information (ESI) available: Force field validation and principal structural features of the computed structures, as well as the sketches of their crystal packing and their relative computed cif files. See DOI: 10.1039/c4ce00191e

Basing our reasoning on the only known and available crystalline structure of a hybrid co-crystal of caffeic acid, we extended our study to the analysis of the behaviour of another humic substance, the protocatechuic acid. The abilities and tendencies of both these compounds to give rise to stable hybrid co-crystals with the elements of group I were studied by predicting, via molecular dynamics simulations, their crystalline setups on the basis of a detailed energetic analysis, which allows the detection of the most stable possible structures and their layouts. Without claiming to have performed an ab initio crystal structure prediction, we tried instead to determine the tendencies of a specific set of humic substances to give rise to a particular type of hybrid co-crystals. Basing our reasoning on the only known and available crystalline structure of a hybrid co-crystal of caffeic acid, we extended our study to the analysis of the behaviour of another humic substance, the protocatechuic acid.