Surface charge response of the phosphatidylcholine head group in bilayeredmicelles from phosphorus and deuterium nuclear magnetic resonance

Solid-state phosphorus (P-31) and deuterium (H-2) nuclear magnetic resonanc e (NMR) spectroscopy over the temperature range of 25-50 degrees C were use d to investigate bilayered micelles (bicelles) composed of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphoc holine (DHPC) in the presence of either the anionic lipid 1,2-dimyristoyl-s n-3-phosphoglycerol (DMPG) or the cationic lipid 1,2-dimyristoyl-3-trimethy lammonium-propane (DMTAP). The P-31-NMR spectra demonstrate that bicellar s tructures form with DMPG/DMPC ratios ranging from 0 to 50/50 and with DMTAP /DMPC ratios from 0 to 40/60, while the overall concentration of DHPC remai ns constant. The formation of bicelles containing charged amphiphiles is co ntingent upon the presence of NaCl, with 50 mM NaCl being sufficient for bi celle formation at all concentrations of charged amphiphile investigated, w hile 150 mM NaCl affords better resolution of the various P-31-NMR resonanc e signals. The H-2-NMR spectra demonstrate that the quadrupolar splittings (Delta v) of head group-deuterated DMPC change inversely as a function of t he amount of negative versus positive charge present, and that the changes for deuterons on the ex-carbon are opposite in sense to those for deuterons on the beta-carbon. This indicates that head group-deuterated phosphatidyl choline functions as a molecular voltmeter in bicelles in much the same fas hion as it does in spherical vesicles. (C) 1999 Elsevier Science B.V. All r ights reserved.