Figure 14. Proposed theoretical structural model for the localization of the cZc-previtamin D₃ in the phospholipids of a membrane. Based on the amphipathic nature and conformational mobility of previtamin D₃, we proposed the following model to show the spatial relationship between previtamin D₃ and phospholipids. We postulated that in the membrane, the cholesterol like cZc-previtamin D₃ is aligned parallel to its neighboring phospholipids, with its polar 3β-hydroxy interacting with the polar head groups of the phospholipids through hydrogen bonding, and the hydrophobic rings and side chain interacting with the nonpolar acyl chains of the lipids through hydrophobic and van der Waals interactions. A, phosphatidylcholine; B, cZc-previtamin D₃. Reproduced with permission from.²⁷