Interaction Pathways and Structure–Chemical Transformations of Alginate Gels in Physiological Environments

Abstract

The remarkably diverse affinity of alginate (ALG) macromolecules for polyvalent metal ions makes cross-linked alginate gels an outstanding biomaterial. Surprisingly, however, very little is known about their interactions and structural transformations in physiological environments. To bridge this gap, we prepared a set of ALG gels cross-linked by various ions and monitored their structural changes at different media simulating gastric and intestinal fluids and cellular environments. For these studies, we used multinuclear solid-state NMR (ss-NMR) spectroscopy, which revealed a range of competitive ion-exchange and interconversion reactions, the rate of which strongly depended on the nature of the cross-linking metal ions. Depending on the environment, ALG chains adopted different forms, such as acidic (hydro)gels stabilized by strong hydrogen bonds, and/or weakly cross-linked Na/H-gels. Simultaneously, the exchanged polyvalent ions extensively interacted with the environment even forming in some cases insoluble phosphate microdomains directly deposited in the ALG bead matrix. The extent of the transformations and incorporation of secondary phases into the alginate beads followed the size and electronegativity of the cross-linking ions. Overall, the applied combination of various macroscopic and biological tests with multinuclear ss-NMR revealed a complex pathway of alginate beads transformations in physiological environments.

On the Molecular Mechanism of the Calcium-Induced Gelation of Pectate. Different Steps in the Binding of Calcium Ions by Pectate

“…This mode of binding, largely focused on detailed stereochemical arrangement at the binding site, had always been supposed to hold for all values of the extent of binding. In the more recent years, both theoretical approaches , and advanced experimental ones , introduced a slightly different perspective, essentially looking at a wider scale, whole-chain, approach. Nevertheless, the older point-of-view did not lose interest and applications.…”

Structural Changes of Sodium Warfarin in Tablets Affecting the Dissolution Profiles and Potential Safety of Generic Substitution

“…When analyzing the considerably different extents of the API transformation and API–excipient interactions, one must consider the chemical origin and activity of the excipients used. Specifically, Di-Cafos, a CaHPO 4 phosphate-based system, can easily participate in ion-exchange reactions [ 45 ]. Typically, the ion-exchange interaction of CaHPO 4 with warfarin sodium can create mixed ionic species such as NaCaPO 4 and the acidic form of warfarin.…”

Tuning Xanthan Viscosity by Directed Random Coil-to-Helix Transition

“…A similar effect has been demonstrated in ion-cross-linked alginates where the coordination of cations bridges adjacent carbohydrates within the polymer backbone and restricts the steric flexibility of the polymers. These intramolecular bonds also lead to increased persistence length and improved viscosifying properties. − …”