ML and ML₂ complex formation between Ca(ii) and d-glucose derivatives in aqueous solutions

Area of Science:

• Carbohydrate Chemistry
• Coordination Chemistry
• Biophysical Chemistry

Background:

• Understanding metal-carbohydrate interactions is crucial for biological and chemical applications.
• Calcium (Ca2+) plays vital roles in biological systems, necessitating studies on its interactions with biomolecules.
• Carbohydrate derivatives offer diverse functionalities for complexation studies.

Purpose of the Study:

• To quantitatively characterize complex formation equilibria between Ca2+ and six d-glucose derivatives.
• To investigate the influence of ligand structure, particularly the carboxylate group, on complex stability.
• To determine the stoichiometry and stability of formed complexes using multiple analytical techniques.

Main Methods:

• Potentiometry was employed to determine complex formation constants.
• Freezing point depression measurements quantified the extent of complexation.
• Polarimetry assessed changes in optical activity upon complex formation.

Main Results:

• Complexation was not observed for d-glucose, with weak association for d-sorbitol and d-mannitol.
• Stronger Ca2+ complexes formed with d-gluconate and d-heptagluconate, attributed to the carboxylate group.
• Both 1:1 (ML) and 1:2 (ML2) species were detected, with ML2 formation favored for ligands with carboxylate groups and flexibility.

Conclusions:

• The stability of 1:1 Ca2+ complexes follows a specific order: mannitol < sorbitol < glucuronate < heptagluconate ≈ gluconate < glucarate.
• Ligands with carboxylate groups and conformational flexibility exhibit enhanced complexation with Ca2+.
• The study provides quantitative insights into the coordination chemistry of calcium with functionalized carbohydrates.