Modeling of the Effects of Metal Complexation on the Morphology and Rheology of Xanthan Gum Polysaccharide Solutions

Abstract

Polysaccharide solutions commonly contain metal ions, which form cross-linking complexes with polymer ligands and significantly affect the polymer morphology and solution rheology. Here, we study by multiscale computational modeling complemented with atomic force microscopy (AFM) measurements the molecular mechanisms of metal complexation with examples of xanthan gum (XG) solutions containing ZnCl2. We develop original atomistic molecular dynamics (MD) and coarse-grained dissipative particle dynamics (DPD) models for XG chains of different compositions and Zn complexation. MD simulations reveal that Zn dramatically affects conformations of individual XG chains, causing a reduction in the radius of gyration by the formation of various types of intrachain cross-linking that are enhanced by the increased pyruvate content in the chains. DPD simulations at the static conditions and under the shear flow show that salt addition leads to gelation in XG systems via a sol–gel transition due to enhanced interchain cross-linking. Two morphological transitions occur in the shear flow: an orientational transition to a nematic phase with XG chains aligned in the direction of flow and a bundling transition accompanied by a reverse gel–sol transition at high Zn concentrations. The presence of the increased pyruvate content in the chains leads to stronger aggregation and stiffer aggregates, in qualitative agreement with AFM results. The proposed computational methodology of modeling the effects of metal complexation and chain composition on morphological and rheological properties may be extended and applied to various polysaccharide systems.

Evolutions of synergistic binding between konjac glucomannan and xanthan with high pyruvate group content induced by monovalent and divalent cation concentration

“…This was verified by simulations for the xanthan solution with divalent Zn 2+ (Santo, Fabijanic, Cheng, Potanin, & Neimark, 2021). The formation of complex structures inhibited the transition of xanthan chains from random coils to a helical structure and thus the interactions with KGM chains.…”

Biomolecular 1D Necklace-like Nanostructures Tailoring 2D Janus Interfaces for Controllable 3D Enteric Biomaterials

“…To elucidate the molecular mechanism of the electrostatic-driven coassembly of RPs and CMC, we performed mesoscopic simulations using the dissipative particle dynamics (DPD) method. − In these generic coarse-grained models as illustrated in Figure d, each amino acid in RPs or one glucose unit in CMC is coarse-grained as a single DPD particle, and five types of DPD particles are thus applied to represent the chain units of RPs and CMCs (see the Supporting Information for full details). In the simulations, the initial state was built as a dilute aqueous solution of 80 rice glutelin (the most representative subunit of RPs) in the presence of a preassembled CMC fibril frozen at the center of a rectangular simulation box.…”

Coarse-Grained Modeling of Ion-Containing Polymers

“…Addition of a salt into a polymer solution can also induce various cross-linking due to metal coordination, which gives rise to changes in membrane morphology, cluster formation, and rheological properties. Neimark et al − used DPD simulations of polymer solutions to gain mechanistic insight into the morphological and rheological changes due to metal coordination in the presence of multivalent cations. The coordinating metal was modeled as a 3D complex of planar, tetrahedral, or octahedral geometry, in which the metal cation was surrounded by either four or six dummy beads that correspond to coordination sites.…”