Stabilizing Capacity of Water Bridges in Nanopore Segments of Humic Substances: A Theoretical Investigation

Molecular simulations using density functional theory (DFT/PBE and DFT/tight-binding (DFTB)) have been performed to study wetting processes of model nanopore segments in humic substances (HS). A complex of two poly(acrylic acid) trimers (trimer complex, TC) arranged in parallel alignment was used to provide the structural example for supramolecular contact of two HS chains by means of hydrogen bonds. Their interaction with a local network of water molecules represented the influence of wet spots. Displaced TC structures were constructed by horizontal motion of the chains relative to each other in order to study the capacity of the water cluster to hold the two chains together even though their distance is too far for direct hydrogen bonding between the carboxyl groups. Geometry optimizations and molecular dynamics simulations were used to investigate the hydrogen-bonded structures formed and to compute their energetic stabilities. At shorter distances between the two oligomer chains an outer solvation was...