Highly Oxygenated Biomolecules: Carbohydrates, Boron Complexes, and Their Biological Interfaces

Carbohydrates are among the most highly oxygenated biomolecules in nature, possessing dense arrays of hydroxyl, ether, carbonyl, carboxylate, phosphate, and sulfate functionalities that govern hydration, hydrogen bonding, molecular recognition, and supramolecular organization. Their stereochemically organized oxygen-donor groups provide numerous appropriately oriented diol motifs capable of selective and reversible coordination with boric acid and borate ions. This review examines the structural and physicochemical principles underlying carbohydrate–borate interactions, with particular emphasis on oxygen-rich biological interfaces. Pentoses, hexoses, oligosaccharides, polysaccharides, glycolipids, and membrane-associated glycoconjugates are considered to illustrate how hydroxyl-group orientation, molecular conformation, pH, hydration, and local environment determine borate recognition, complex stability, and dynamic assembly. Evidence from NMR and other spectroscopic methods, crystallography, mass spectrometry, calorimetry, and molecular simulations demonstrates that borate coordination follows common stereochemical and thermodynamic principles despite the remarkable structural diversity of carbohydrates. Biological examples include borate-mediated crosslinking in plant cell walls and interactions involving microbial carbohydrates, marine polysaccharides and glycoconjugates, photosynthetic membrane lipids, and cyanobacterial heterocyst glycolipids. Particular attention is given to distinguishing experimentally established borate complexes from membrane-associated interactions that remain proposed and require further characterization. Reversible borate crosslinking of oxygen-rich carbohydrate networks also provides the chemical basis for emerging applications in responsive hydrogels, biosensors, supramolecular assemblies, drug-delivery systems, and functional biomaterials. Collectively, the available evidence indicates that the spatial organization of oxygen donor atoms within carbohydrates provides the molecular basis for selective borate recognition, whereas boron can convert this functionality into reversible higher-order organization. This oxygen-centered perspective integrates coordination chemistry, glycobiology, membrane biology, and materials science into a unified framework for understanding carbohydrate–borate interactions in natural and engineered systems.