FIGURE 2.

Deuterium and phosphorus-31 NMR spectra of POPC liposomes deuterated at the α-position of the choline headgroup (−POCD₂CH₂N⁺). Approximately twenty-five milligrams of POPC was suspended in 50 μL buffer (25 mM, MES 0.1 M NaCl, pH 5.5, deuterium-depleted water) containing different concentrations of verapamil. The two top spectra correspond to pure POPC membranes without verapamil. The spectra below are characterized by increasing drug concentrations. The verapamil/POPC molar ratio from top to bottom is: 0, 0.02, 0.04, 0.07, 0.11, and 0.14. Virtually all verapamil is incorporated into the membrane. (Number of FIDs: ²H NMR spectra 8 K, ³¹P NMR 2 K.)