Which feature supports ionic interactions in the active conformation of acetylcholine?

Which feature supports ionic interactions in the active conformation of acetylcholine?

• A. Methyl groups support van der Waals interactions
• B. Positively charged N supports ionic interactions
• C. Ester O is an H-bond acceptor
• D. Several freely rotatable single bonds leading to many possible conformations

Answer: (B)

The feature being tested is the presence of a permanent positive charge on the molecule. In acetylcholine, the nitrogen carries a quaternary ammonium positive charge. This charged center enables ionic (electrostatic) interactions with negatively charged sites in the active receptor, helping to stabilize the ligand in the binding pocket. Methyl groups can contribute mainly van der Waals contacts, which are nonpolar and not ionic. The ester oxygen can participate in hydrogen bonding as an acceptor, but hydrogen bonds are different from ionic interactions. The many rotatable single bonds indicate conformational flexibility, which affects how the molecule fits, but by itself doesn’t provide ionic attraction.

The feature being tested is the presence of a permanent positive charge on the molecule. In acetylcholine, the nitrogen carries a quaternary ammonium positive charge. This charged center enables ionic (electrostatic) interactions with negatively charged sites in the active receptor, helping to stabilize the ligand in the binding pocket.

Methyl groups can contribute mainly van der Waals contacts, which are nonpolar and not ionic. The ester oxygen can participate in hydrogen bonding as an acceptor, but hydrogen bonds are different from ionic interactions. The many rotatable single bonds indicate conformational flexibility, which affects how the molecule fits, but by itself doesn’t provide ionic attraction.