Dynamics of Humic Acid and Its Interaction with Uranyl in the Presence of Hydrophobic Surface Implicated by Molecular Dynamics Simulations

Abstract

This work targeted a molecular level of understanding on the dynamics of humic acid (HA) and its interaction with uranyl in the presence of hydrophobic surface mimicked by a carbon nanotube (CNT), which also represents a potential intruder in the environment accompanying with the development of nanotechnology. In aqueous phase, uranyl and HA were observed to build close contact spontaneously, driven by electrostatic interaction, leading to a more compact conformation of HA. The presence of CNT unfolds HA via π-π interactions with the aromatic rings of HA without significant perturbation on the interaction strength between HA and uranyl. These results show that the hydrophilic uranyl and the hydrophobic CNT influence the folding behavior of HA in distinct manners, which represents two fundamental mechanisms that the folding behavior of HA may be modulated in the environment, that is, uranyl enhances the folding of HA via electrostatic interactions, whereas CNT impedes its spontaneous folding via van der Waals (vdW) interactions. The work also provides molecular level of evidence on the transformation of a hydrophobic surface into a hydrophilic one via noncovalent functionalization by HA, which in turn affects the migration of HA and the cations it binds to.

Surface Properties of Nanoparticles Dictate Their Toxicity by Regulating Adsorption of Humic Acid Molecules

“…The all-atom model of the Leonardite HA was transferred to the CG model using the four-to-one mapping rule (Figure S1a,b), similar to the martinize.py script provided by the Martini force field . Although it is hard to expect a single type of model compound to represent the full features of HAs, the model used in our simulations has the typical features of real HAs, such as aromatic rings, hydroxy groups, and carboxyl groups that enable it to be amphiphilic with a flexible backbone. − NP was constructed by arranging CG beads into a sphere of 10 nm in diameter. Types of CG beads on the NP surface were set according to the defined surface property (Figure S1c–f).…”

From Adsorption to Precipitation of U(VI): What is the Role of pH and Natural Organic Matter?

“…Several experimental and modeling studies reported the effect of humic acid (HA) and fulvic acid on U mobility through adsorption and complexation. 13,14,24,31 However, there are limited studies reporting adsorption and desorption of U onto NOM. 24,32 The adsorption of U−humic complexes onto quartz was enhanced between pH 3 and 6.…”

A contribution of molecular modeling to supramolecular structures in soil organic matter#

“…The TNB monomeric model was used in FFMD simulation of interactions of HAs with several explosive species (e.g., trinitrotoluene) by Schutt and Shukla (2020). The older Stevenson HA model (Stevenson, 1994) was used in the FFMD simulation of HA interactions with uranyl and graphene oxide (Lan et al, 2016(Lan et al, , 2019.…”