Complexation of Trivalent Metal Cations to Mannuronate Type Alginate Models from a Density Functional Study

Area of Science:

• Materials Science
• Computational Chemistry
• Biochemistry

Background:

• Alginates are biopolymers with diverse applications, including metal chelation.
• Understanding metal-alginate interactions is crucial for applications in drug delivery, water treatment, and tissue engineering.
• Trivalent metal cations are of particular interest due to their strong binding potential.

Purpose of the Study:

• To investigate the complexation of alginate models with various trivalent metal cations (Al3+, Sc3+, Cr3+, Fe3+, Ga3+, La3+).
• To determine the preferred binding modes, energies, and electronic contributions in these metal-alginate complexes.
• To compare the complexation behavior with divalent cations.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model alginate chains of varying lengths.
• Quantum chemical methods were used to obtain binding modes and energies for hydrated metal-alginate complexes.
• Orbital population analysis was performed to assess the nature of the metal-carboxylate bond.

Main Results:

• Monodentate binding was the most energetically favorable mode for all hydrated structures.
• Coordination bond lengths were cation-specific and minimally influenced by hydration or chain length.
• A distinct binding energy trend was observed: Fe3+ ≈ Cr3+ > Al3+ ≈ Ga3+ ≫ Sc3+ ≥ La3+.
• Significant covalent character was found in the M(3+)···O(COO-) bonds, arising from charge donation.
• Exothermic chain-chain association was predicted based on enthalpy variations.

Conclusions:

• The study elucidates the fundamental interactions between trivalent metal cations and alginate at a molecular level.
• DFT calculations provide valuable insights into the specificity and strength of these complexation reactions.
• The findings contribute to a better understanding of alginate's potential in applications involving metal sequestration and delivery.