What is the mechanism of action of best carmine?

• A. Hydrogen bonding (phenol groups ionize to the oxide and bind to the glycol groups of glycogen)
• B. Ionic bonding between carmine and glycogen
• C. Covalent bonding with glycogen
• D. Hydrophobic interactions with glycogen

Answer: (A)

Best carmine binds glycogen mainly through noncovalent hydrogen bonding between the dye’s phenolic groups and the hydroxyl groups of glycogen. Under staining conditions, some phenolic groups can deprotonate to form phenoxide, which strengthens these hydrogen-bond–based interactions and helps the dye adhere to the glycogen-rich structures. Because glycogen is a neutral, highly hydrated polymer with many hydroxyls, ionic or covalent bonding isn’t the driving mechanism, and hydrophobic interactions aren’t favorable. The mordant in the stain supports adherence, but the binding remains noncovalent hydrogen-bond–driven, making hydrogen bonding the best explanation for how best carmine works.