Fluorine-19 nuclear magnetic resonance investigation of fluorine-19-labeled phospholipids. 1. A multiple-pulse study

Abstract

A multiple-pulse nuclear magnetic resonance technique has been used to measure the order parameter, SFF, at 40 MHz for dimyristoylphosphatidylcholine labeled with a difluoromethylene group at the 4-, 8-, or 12-position of the sn-2-acyl chain dispersed in water in the liquid-crystalline phase. The Carr-Purcell-Meiboom-Gill multiple-pulse sequence can resolve the homonuclear dipolar coupling between the two fluorine nuclei, thus making a direct determination of the order parameter, SFF, for the F-F internuclear vector possible. Other interactions, such as the 19F chemical shift anisotropy, heteronuclear dipolar couplings, and field inhomogeneity, which normally obscure the dipolar splitting, are effectively canceled. The order parameters obtained in this work compare well with those obtained by 19F nuclear magnetic resonance line-shape analysis of the 19F-labeled phospholipids reported in the following paper [Dowd, S. R., Simplaceanu, V., & Ho, C. (1984) Biochemistry (following paper in this issue)] as well as comparable SCD order parameters, determined for the deuterium-carbon internuclear vector of deuterium-labeled phospholipids [Oldfield, E., Meadows, M., Rice, D., & Jacobs, R. (1978) Biochemistry 17, 2727-2740]. The present results clearly show the usefulness of using nuclear magnetic resonance spectroscopy to investigate lipid-lipid and protein-lipid interactions, especially for those systems containing a difluoromethylene group in the acyl chain of a phospholipid molecule.

Structural Parameters from19F Homonuclear Dipolar Couplings, Obtained by Multipulse Solid-State NMR on Static and Oriented Systems

“…The reduced value of 3.1 kHz measured here is due to the long-axial rotation and further chain fluctuations of the lipid molecule, which are described by an order parameter S FF ϭ ⌬ FF /⌬ 0 . In good agreement with previous reports on DMPC-F 2 (S FF ϭ 0.19), we evaluate S FF as 0.20, which is also reasonably similar to the order parameter of the deuterated DMPC analogue (S CD ϭ 0.22) (8,26). Knowing the order parameter, it follows from the total width of the spectrum (Fig.…”

“…, which carries two geminal fluorine labels in one chain, was a gift from Chien Ho, Carnegie Mellon University of Pittsburgh (8,25,26). The doubly fluorinated sterol diflucortolon-21-valerate (DFC) was a gift from Schering AG, Berlin.…”

“…Alternatively, r and can also be determined from a single oriented sample by varying its align- ment in the external magnetic field (42). The technique used in this study to measure the dipolar coupling is based on the CPMG sequence (32,33), which has already been successfully applied to determine internuclear distances and to evaluate motionally averaged order parameters (23,24,26,34,35). Oriented samples of fluorinated lipid bilayers have also been used previously for solid-state NMR investigations (25).…”

“…Many fluorinated proteins have been investigated in terms of their structure and function, and in most cases the perturbation of the system was negligible (10 -13 (17,18), and heteronuclear couplings from 19 F to 31 P, 13 C, or 15 N have been used for structural studies on various polymers and biological systems (19 -22). Many years back, Post et al determined segmental order parameters from the homonuclear dipolar coupling between geminal 19 F-labels on acyl chains in liquid crystals and membranes (8,(23)(24)(25)(26). In each case it was necessary to isolate the desired dipolar interaction from all other interactions, such that the coupling strength could be interpreted in terms of internuclear distance or orientation.…”

Orientation-Dependent 19F Dipolar Couplings within a Trifluoromethyl Group Are Revealed by Static Multipulse NMR in the Solid State

“…Pure dipolar spectra were acquired with a modified CarrPurcell-Meiboom-Gill (CPMG) experiment (15,18,40,41). Instead of 180°pulses we used composite pulses with 90°-180°9 0°-90° (42,43).…”