Deuterium nuclear magnetic resonance spectra of dimyristoylphosphatidylcholines specifically labeled in positions 2', 3', 4', 6', 8', 10', 12', and 14', of the 2 chain, of an N-deuteriomethylphosphatidylcholine, and of cholesterol-3alpha-d1, have been obtained by the Fourier transform method at 5.46 and 3.52 T on two "home-built" widebore superconducting magnet spectrometers, as a function of temperature and composition. Data on the specifically deuterium-labeled cholesterol molecule (in nonsonicated membrane systems) permits an estimate of the most probable angle of tilt of the sterol in the membrane, and evaluation of the order parameter (Salpha) describing rigid body motions in the bilayer. Segmental order parameters derived from the data presented allow calculation of individual chain segment projections onto the director axis and, consequently, estimation of effective chain length. It is shown that mathematical models which include chain tilt as well as those which neglect this type of rigid body motion give essentially identical results when applied to the dimyristoylphosphatidylcholine and dimyristoylphosphatidylcholine-cholesterol bilayer systems (in excess water, between 23 and 60 degrees C). Results of calculations of chain length and membrane thickness of a dimyristoylphosphatidylcholine-30 mol % cholesterol membrane system at 23 degrees C give excellent agreement when compared with recent high-resolution neutron diffraction data obtained on specifically deuterium labeled lecithin-cholesterol systems. No evidence for formation of lecithin-cholesterol complexes having lifetimes of approximately 30 ms has been found. Below the pure-lipid gel-liquid crystal phase transition temperature Tc but in the presence of cholesterol, we have obtained further evidence for 1-chain/2-chain nonequivalence. At 10 degrees C, the 2' segment of the 2 chain, but not the 2' segment of the 1 chain or the 3', 6', or 12' segments of the 2 chain, is broadened almost beyond detection. These results are in agreement with similar effects reported recently for the dipalmitoylphosphatidylcholine-cholesterol system and may indicate a bent configuration for the 2 chain, in the lecithin-cholesterol system. Further cooling below Tc results in loss of the 1-chain 2'-position signal intensity plus 2-chain 3', 6', and 12' signals simultaneously. The increase in length of the 2 chain of dimyristoylphosphatidylcholine upon addition of 30 mol % cholesterol of 23 degrees C is about 2.3 A. Addition of cholesterol to a choline-labeled lecithin results in complex behavior of the head group deuterium quadrupole splitting as a function of temperature, and cholesterol mole fraction. Above approximately 20 mol % cholesterol, the main effect is a decrease in quadrupole splitting as cholesterol content increases, the opposite effect to that observed with hydrocarbon chains.
Deuterium Fourier-transform nuclear magnetic resonance spectra have been obtained of 1-myristoyl 2-(14,14,14-trideutero)myristoyl phosphatidylcholine bilayers at 34.1 MHz by using the quadrupole echo pulse technique. Thereby, we have investigated the effects upon the deuterated dimyristoyl phosphatidylcholine bilayers of the following proteins and polypeptides: gramicidin A, bacteriophage f1 coat protein, beef brain myelin proteolipid apoprotein, cytochrome b 5 , and cytochrome c oxidase (ferrocytochrome c :oxygen oxidoreductase, EC 1.9.3.1). Above T c , the transition temperature between the gel and liquid crystal phases, the quadrupole splitting of the deuterium-labeled methyl group is reduced or collapsed in the presence of protein or polypeptide. No evidence has been found for ordered “boundary lipid.” Below T c , the spectra show that the hydrocarbon chains are prevented from crystallizing by the protein (or polypeptide) incorporated in the membrane. Similar disordering effects above T c are also seen when an unsaturated lipid, 1-(16,16,16-trideutero)palmitoyl 2-palmitoleyl phosphatidylcholine is complexed with cytochrome oxidase.
molecule lies along the z axis and the second molecule lies along the intermolecular y axis. The most important contribution to the dispersion energy involves a pure dx2-yi virtual orbital of the first molecule. The dxy orbital of the first molecule is also important. Other important virtual orbitals of the first molecule generally have a large coefficient corresponding to some d components. The d functions are of less interest when the molecule lies along the intermolecular}' axis. For instance in the linear case, the largest contribution involves the first 5U virtual orbital of each molecule. In this orbital the coefficient corresponding to the dyy component is only 0.27. Other important virtual orbitals are of the type pxu or pzu, the coefficient corresponding to a d component {dxy or dyz, respectively) being not very large in such orbitals. Thus, though the importance of the d functions may not be negligible in the linear case, it is obviously of less importance than in the T-shaped configuration. This probably explains why the linear configuration is more stable than the "T" configuration in ref 3. Since the stability of the (Chh dimer is due mainly to the dispersion energy, a bad description of this dispersion energy may lead to misleading results.Finally, we can see from the total energy Elol (Table I) that the T-shaped configuration exhibits a much deeper van der Waals minimum (about -1.68 kcal/mol) than the linear configuration (about -0.511 kcal/mol). The corresponding intermolecular distance is about 3.44 Á. This is compatible with the observed polar character of this dimer.1•3 Work on the L-shaped configuration is in progress. From our preliminary results, it seems that the L-shaped configuration is slightly more stable than the T-shaped one.
We report the observation of high-resolution solid-state NMR spectra of 23Na (I = 3/2), 27AM (I = 5/2) and 51V (I = 7/2) in various inorganic systems. We show that, contrary to popular belief, relatively high-resolution (="10 ppm linewidth) spectra may be obtained from quadrupolar systems, in which electric quadrupole coupling constants (e2qQ/h) are in the range -1-5MHz, by means of observation of the (1/2, -1/2) spin transition. The (1/2, -1/2) transition for all nonintegral spin quadrupolar nuclei (I = 3/2, 5/2, 7/2, or 9/2) is only normally broadened by dipolar, chemical shift (or Knight shift) anisotropy or second-order quadrupolar effects, all of which are to a greater or lesser extent averaged under fast magic-angle sample rotation. In the case of 23Na and 27Al, high-resolution spectra of 23NaNO3 (e2qQ/h :300 kHz) and a-27A1203 (e2qQ/h a2-3 MHz) are presented; in the case of 51V205 (e2qQ/h '800 kHz), rotational echo decays are observed due to the presence of a 103-ppm chemical shift anisotropy. The observation of high-resolution solid-state spectra of systems having spins I = 3/2, 5/2, and 7/2 in asymmetric environments opens up the possibility of examining about two out of three nuclei by solid-state NMR that were previously thought of as "inaccessible" due to the presence of large (a few megahertz) quadrupole coupling constants. Preliminary results for an I = 9/2 system, 93Nb, having e2qQ/h -19.5 MHz, are also reported.During the past 20 years or so there has been considerable interest in obtaining high-resolution NMR spectra of solids (1-6). One particularly widespread technique, originally introduced by Andrew et al. (1, 2) and Lowe (3) for averaging of dipolar interactions, involves high-speed sample rotation at the so-called magic angle. In the past 5 years the technique has enjoyed great popularity for investigating spin I = 1/2 nuclei such as 13C (7) and 31p (8), and more recently the technique has been applied to the spin I = 1 nucleus deuterium (9, 10).In the case of spin I = 1/2 species, considerable narrowing is achieved for spinning rates in excess ofthe static linebreadth. However, such rapid spinning rates are sometimes not feasible-e.g., for some 13C nuclei at very high field-in which case spinning or rotational beats or echoes-i. e., well-resolved sidebands-are formed in the NMR spectrum (8)(9)(10)(11)(12)(13)(14). Such is the case, of course, for all rigid 2H-labeled species (9, 10). In the case of 2H, magic-angle experiments have been carried out by using synchronous sampling methods (9, 10, 13, 14), but the minute angle adjustments required for efficient averaging make it unlikely that the technique will be useful for narrowing integral spin quadrupolar powder patterns .200 kHz in breadth (9, 10).The general belief, therefore, based on the work done to date, is that it is unlikely to be practical to obtain high-resolution spectra of quadrupolar nuclei in the solid state for systems having large (41-5 MHz) quadrupole interactions, not only for the technical reason outlined above...
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