Figure 4.

Stick models of (A) cholic acid and (B) glycocholic acid. The sterol ring structure is the same in both cholic acid and glycocholic acid. The tail structure and its interactions with the core affect the cross section. (A) With cholic acid, the tail forms a hydrogen bond with the oxygen on carbon 3. This is similar in (B) glycocholic acid, where the tail structure folds over to form a hydrogen bond with the same oxygen on carbon 3, stabilizing the tail and limiting its motion. Even though glycocholic acid is 57 Da greater in mass, it has a similar collision cross section because it forms a hydrogen bond on the same carbon (carbon 3), collapsing the tail. Colors represent atoms, with beige representing carbon, red representing oxygen, blue representing nitrogen, and white representing hydrogen.