Deuterium Quadrupole Splittings Research Articles

ChemInform Abstract: DEUTERIUM MAGNETIC RESONANCE IN THE DISCOTIC COLUMNAR MESOPHASES OF HEXAALKYLOXYTRIPHENYLENES: THE CONFORMATION OF THE ALIPHATIC SIDE CHAINS

Deuterium NMR spectra of chain perdeuterated hexa‐pentyloxy, ‐hexyloxy, ‐heptyloxy, and ‐octyloxy triphenylene (THE5, THE6, THE7, and THE8) were studied as functions of temperature in the mesophase region. The deuterium quadrupole splittings exhibited several characteristic features, in particular a steplike decrease in the splitting along the alkyl chain and an even–odd alteration in the methyl splittings within the homologous series. The results are interpreted in terms of possible conformational distributions of the alkyl chain. It is found that there is bending of the alkyl chains out of the aromatic plane, and a considerable degree of chain disorder.

Deuterium magnetic resonance in the discotic columnar mesophases of hexaalkyloxytriphenylenes: The conformation of the aliphatic side chains

Deuterium NMR spectra of chain perdeuterated hexa-pentyloxy, -hexyloxy, -heptyloxy, and -octyloxy triphenylene (THE5, THE6, THE7, and THE8) were studied as functions of temperature in the mesophase region. The deuterium quadrupole splittings exhibited several characteristic features, in particular a steplike decrease in the splitting along the alkyl chain and an even–odd alteration in the methyl splittings within the homologous series. The results are interpreted in terms of possible conformational distributions of the alkyl chain. It is found that there is bending of the alkyl chains out of the aromatic plane, and a considerable degree of chain disorder.

Headgroup interactions in mixed phospholipid bilayers.

(2)H NMR methods have been used to study how bilayer-forming phospholipids interact with each other at the membrane surface. Aqueous dispersions of dimyristoyl-sn-phosphatidylcholine (Myr(2)-PtdCho), dimyristoyl-sn-phosphatidylethanolamine (Myr(2)-PtdEtn), and dimyristoyl-sn-phosphatidyl-3-glycerol, specifically deuterated at different positions in their headgroups, give well-resolved (2)H NMR powder spectra. These spectra are characteristic of a lipid bilayer with quadrupole splittings that are sensitive to the amplitude of headgroup motion. In binary mixed bilayers of deuterated lipids with an unlabeled component, all parts of the deuterated headgroup monitor the presence of the second lipid from changes in the measured quadrupole splittings. The headgroups of the charged lipids, dimyristoyl-sn-phosphatidylserine and dimyristoyl-sn-phosphatidyl-3-glycerol, interact to the largest extent with the choline moiety of Myr(2)-PtdCho and the ethanolamine moiety of Myr(2)-PtdEtn, whereas a somewhat smaller but still marked alteration in headgroup motion was observed in Myr(2)-PtdCho/Myr(2)-PtdEtn mixtures. The large changes in the deuterium quadrupole splittings for the zwitterionic lipids after addition of a charged lipid suggest that either a strong perturbation in the hydrogen bonding occurs or changes take place in the water structure at the membrane surface, or possibly both.

Solubilization of some related para-substituted benzenes in Type II DM mesophases

A series of chemically related para-disubstituted aromatic solutes have been dissolved in two type II DM systems. The Saupe matrix elements of order have been determined for the solutes and the degrees of order of some segments in the amphiphiles have been derived from deuterium quadrupole splittings. The comparison of deuterium quadrupole splittings in uncontaminated mesophases with those containing the solutes leads to the conclusion that four solutes are located in the bilayer disk of the component micelles of one meosphase. A consideration of the structure and alignment of the disc micelles leads to absolute sign attribution for degrees of order of detergent segments and matrix elements for solute axes. A consideration of the orientations of the solute axes with respect to the mesophase director suggests the type of molecular interactions and motions which apply to solutes.

Nitrogen‐14 NMR of Solutes in Liquid Crystals: NH4NO3 and (CH3)4N NO3 in the DSCG–Water System

AbstractMeasurements of the nitrogen‐14 and deuterium quadrupolar splittings in NH4NO3 and (CH3)4 N NO3 dissolved in the disodiumcromoglycate–water liquid crystalline system are presented. Nitrogen‐14 T1 values in aqueous solutions for these salts are also given. The results are discussed and compared with similar studies on solutes containing 14N in ordered media.

Chain ordering and molecular orientational order in liquid crystals

We have extended the scheme for computing deuterium quadrupolar splittings of a flexible solute in a nematic solvent [Ferroelectrics 30, 83 (1980)] to study chain ordering in the 4-n-alkyl-4′-cyanobiphenyl liquid crystals (nCB). All possible configurations {φ} of the nCB molecule are generated by the rotational isomeric state model of Flory. Each {φ} has a separate ordering matrix whose diagonal elements are assumed to scale with the shape anisotropy of the molecule as prescribed by the principal moments of inertia of the configuration I{φ}. Two models for identifying the molecular-fixed-frame are considered: (1) The frame diagonalizes I{φ}; (2) the frame is stationary on the nCB core. The variation of deuterium quadrupolar splittings along the alkyl chain can be satisfactorily explained by the calculations, however, the detailed behavior of the computed splittings are sensitive to the assumptions about the placement of the molecular-fixed-frame.

Anisotropic Translational Diffusion of Methane and Chloroform in Thermotropic Nematic and Smectic Liquid Crystals

Abstract Nuclear magnetic resonance pulsed-gradient spin-echo measurements are reported for the anisotropic translational diffusion coefficients and their temperature dependence, of methane, monodeuteromethane and chloroform dissolved in several thermotropic liquid crystals exhibiting nematic, smectic A and smectic B phases. For methane, in those liquid crystals forming only nematic phases, the diffusion parallel to the director (D ⊥) is greater than the perpendicular diffusion (D); the magnitude of the diffusional anisotropy (D ⊥/D ⊥) depends on the nature of the nematic medium. In the nematic phases of smectic-forming materials, D ⊥/D ⊥ < 1. In the smectic A phases, D ⊥/D ⊥ ≪ 1 with a much larger activation energy for D ⊥. In the smectic B phase, D ⊥/D ⊥ ≪ 1 with similar activation energies. Chloroform exhibits similar behavior with deviations in the nematic phases of a polymorphic liquid crystal. A qualitative interpretation of these results is given in terms of several factors which govern the diffusion behavior: different diffusion characteristics in aliphatic and aromatic regions of the ordered medium, expulsion of methane (and possibly chloroform) from the aromatic cores into the aliphatic end chains as a result of the smectic layering behavior and pronounced pretransitional ordering effects in nematic phases of the polymorphic liquid crystals. In addition to the diffusion measurements, proton dipolar and deuterium quadrupolar splittings in these systems are reported for CH4 and CH3D. These splittings are related to the strength of solute-solvent interaction and consequently to the diffusion patterns. Complementary data is presented for methane proton spin-lattice relaxation measurements in these systems.

The interaction of cholesterol with bilayers of phosphatidylethanolamine

The interaction of cholesterol with the glycerol backbone segments of phospholipids was studied in bilayers of phosphatidylethanolamine containing equimolar amounts of cholesterol. Glycerol selectively deuterated at various positions was supplied to the growth medium of Escherichia coli strain 131 GP which is defective in endogeneous glycerol synthesis. The procedure enables the stereospecific labeling of the three glycerol backbone segments of the membrane phospholipids. Phosphatidylethanolamine with wild-type fatty acid composition was purified from E. coli cells and deuterium magnetic resonance spectra were obtained either from dispersions of pure phosphatidylethanolamine or from equimolar mixtures of phosphatidylethanolamine with cholesterol. For comparative purposes 1,2-di[9,10- 2H 2]elaidoyl- sn-glycero-3-phosphoethanolamine and [3-α- 2H]cholesterol were synthesized in order to monitor the behavior of the fatty acyl chains and of the cholesterol molecule itself. For all deuterated segments the deuterium quadrupole splittings as well as the deuterium spin-lattice ( T 1) relaxation times were measured as a function of temperature. The glycerol backbone was found to be a remarkably stable structural element of the phospholipid molecule. The quadrupole splittings of the backbone segments changed only by at most 2 kHz upon incorporation of 50 mol % cholesterol. This was in contrast to the fatty acyl chains where the same amount of cholesterol increased the quadrupole splitting by more than 20 kHz. The glycerol segments exhibited the shortest T 1 relaxation times of all CH 2 segments indicating that the glycerol backbone is the slowest motional moiety of the lipid molecule. Addition of cholesterol has no effect on the backbone motion but the fast reorientation rate of the trans-double bonds in 1,2-dielaidoyl- sn-glycero-3-phosphoethanolamine is increased dramatically.

Deuterium NMR of water in immobilized protein systems

Deuterium NMR spectra are reported for lysozyme crystals, powders, and frozen solutions. At high water contents the spectrum is a superposition of a narrow central component and a quadrupole doublet. The quadrupole splitting and the relaxation rates of both components, monitored as a function of water content and temperature, are discussed in terms of models for the water-protein interaction. The anisotropy of the water molecule motion is clearly demonstrated by the deuterium quadrupole splitting observed in the protein single crystal, but such splittings were not found in protein powders and frozen protein solutions. We therefore suggest that the most useful view of such data is to consider the water-protein interactions at the surface to be mixed rapidly and that a distribution of interactions be invoked rather than an oversimplified view often taken of a two or n-site mixing where n is small.

Solvation sites in mesophases of discotic liquid crystals

The deuterium quadrupole splitting, νQ, of C6D 6 dissolved in a number of discotic liquid crystals has been measured over the temperature range of the mesophase stability. Three different types of mesophases were used : (i) Dho, which is a columnar hexatic phase with ordered molecular stacking; (ii) Drd, which is a rectangular biaxial columnar phase with disordered molecular stacking ; (iii) a nematic discotic, ND. The three types of mesophases exhibit different temperature dependence of ν Q : In the Dho phase the splittings are relatively small and strongly temperature dependent. This behaviour is interpreted in terms of a fast dynamic equilibrium between two solvation sites consisting of (1) molecules intercalated within the discotic columns, and (II) molecules dissolved in the aliphatic side chain region between the columns. In the Drd phase the splittings are considerably larger and fairly constant with temperature indicating that solvation in this phase is predominantly in the intercalation site. Finally in the nematic phase the splittings are large and follow a Maier-Saupe type temperature dependence. This is consistent with the structure of the nematic phase where no different sites are expected.

A deuterium nmr study of solute molecules dissolved in the discotic mesophase of p-n-hexahexyloxytriphenylene

Deuterium NMR spectra of twelve, mostly aromatic, deuterated compounds dissolved in the discotic mesophase of normal p-n-hexahexyloxytriphenylene are reported. The solute deuterium quadrupole splittings are in general much smaller than normally observed in thermotropic liquid crystals and at the same time they exhibit a conspicuous dramatic temperature dependence, often changing sign as the temperature is varied within the mesophase region. The results are interpreted in terms of a model in which the solute molecules can occupy two sites having order parameters of opposite signs. The two sites are tentatively identified with (I) molecules intercalated within the columnar structures, and (II) molecules within the aliphatic region of the mesogen side chains. The results are consistent with a model in which there is fast dynamic equilibrium (on the NMR timescale) between the two sites, which shifts from site I to site II with increasing temperature. The results also indicate that the magnetic parameters in the two sites are different.

Local anesthetics and divalent cations have the same effect on the headgroups of phosphatidylcholine and phosphatidylethanolamine

The effects of the local anesthetic dibucaine on the membrane headgroup conformations of phosphatidylcholine and phosphatidylethanolamine were determined using 2H- and 31P-NMR. The size of the deuterium quadrupole splittings of the two methylene segments of the choline and ethanolamine groups changed dramatically and the 31-phosphorus chemical shift anisotropy of the phosphatidylcholine headgroup decreased by about 7 ppm in the presence of local anesthetic. The quadrupole splittings of the 3-glycerol and choline methyl segments were relatively insensitive to the addition of dibucaine. The headgroup data for dibucaine addition paralleled similar data for the addition of various cations. These NMR results agree with the previous observation that these drugs displace calcium from phospholipids. The effects of this local anesthetic on these headgroups were distinctly different from the changes induced by cholesterol, heat and the general anesthetic chloroform.

Detection of deuterium quadrupole splittings by odendor in the excited triplet state of benzophenone

Using a fully deuterated sample of benzophenone, optically detected ENDOR transitions reveal line splittings due to deuterium quadrupole interaction in the excited triplet state. The line splittings were used to determine the ring-carbonyl-ring bond angle 2θ = 138(1.5)° and the phenyl-ring twist ansle ψ = 28.5(1.5)° of benzophenone in its metastable excited state.

Bilayers of phosphatidylglycerol. A deuterium and phosphorus nuclear magnetic resonance study of the head-group region

The structural properties of the phosphoglycerol polar head group in bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol have been studied with deuterium and phosphorus-31 nuclear magnetic resonance. For this purpose, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol was deuterated chemically or biosynthetically at all three segments of the glycerol head group. Both the D and the L configurations of the glycerol head group have been synthesized, and the correct stereochemical configuration of the polar group was verified by an enzymtic assay, as direct measurement of the optical rotation was insufficiently sensitive to distinguish between these diastereomers. The phosphatidylglycerol sodium salts were dispersed in excess buffer (0.1 M NaCl, pH 7.0), and the bilayer properties were characterized by small-angle X-ray diffraction and differential scanning calorimetry. The deuterium quadrupole splittings, delta vQ, and the phosphorus-31 chemical shielding anisotropy, delta sigma, were measured as a function of temperature in the range 20-60 degrees C, yielding the following results. (1) Well-resolved deuterium signals were obtained for all head-group segments and could be assigned unambiguously. (2) Almost identical spectra were obtained for 1,2-dipalmitoyl-sn-glycero-3-phospho-1'-glycerol (natural L,D configuration) and 1,2-dipalmitoyl-sn-glycero-3-phospho-3'-glycerol (L,L configuration), suggesting very similar head-group motions and orientations for both diastereomers. (3) The spatial anisotropy of motion and the segmental fluctuations of the negatively charged phosphoglycerol are similar to those of the zwitterionic phosphocholine and phosphoethanolamine head groups but differ distinctly from those of phosphoserine which also carries a net negative charge. (4) The motional inequivalence of geminal deuterons in 1,2-dipalmitoyl-sn-glycero-3-phospho-3'-glycerol was demonstrated by synthesis of a stereospecifically monolabeled analogue.

The fidelity of response by nitroxide spin probes to changes in membrane organization: The condensing effect of cholesterol

The response of doxyl fatty acid spin probes in egg lecithin bilayers to added cholesterol is compared with results from 2H-NMR. Large differences are found between the profiles of order parameter vs. label position and cholesterol concentration. At constant cholesterol content, the ESR spin probe order parameter decreases continuously as the label position is moved toward the terminal methyl region of the bilayer whereas an order parameter ‘plateau’ is observed for the upper region of the bilayer by 2H-NMR. In addition, the spin probe order parameters are smaller than those observed by 2H-NMR. Differences are also observed in the profiles of order parameter vs. cholesterol content for each label position. The spin probes detect a maximal response to added cholesterol for the central portion of the chains with much weaker responses near both ends of the chains. In contrast, the 2H-NMR results indicate a large, approximately constant response for the first ten positions in the chains with a decreasing response toward the terminal methyl group. For all the positions examined, the spin probes show a weaker response than that observed by 2H-NMR. A direct measure of the perturbing effect of a spin label is made by comparing the deuterium quadrupole splittings in egg lecithin-cholesterol bilayers for stearic acid with and without an attached doxyl moiety. The spin-labelled fatty acid has a much reduced quadrupole splitting and an opposite response to cholesterol addition.

The temperature dependence of molecular order and the influence of cholesterol in Acholeplasma laidlawii membranes

2H nuclear magnetic resonance (NMR) of Acholesplasma laidlawii membranes grown on a medium supplemented with perdeuterated palmitic acid shows that at 42°C or above, the membrane lipids are entirely in a fluid state, exhibiting the characteristic ‘plateau’ in the variation of deuterium quadrupolar splitting with chain position. Between 42 and 34°C there is a well-defined gel-to-fluid phase transition encompassing the growth temperature of 37°C, and at lower temperatures the membranes are in a highly ordered gel state. The 2H-NMR spectra of the gel phase membranes are similar to those of multilamellar dispersions of chain perdeuterated dipalmitoyl phosphatidylcholine (Davis, J.H. (1979) Biophys. J. 27, 339) as are the temperature dependences of the spectra and their moments. The incorporation of large amounts of cholesterol into the membrane removes the gel to fluid phase transition. Between 20 and 42°C, the position dependence of the orientational order of the hydrocarbon chains of the membranes is similar to that of the fluid phase of the membranes without cholesterol, i.e., they exhibit the plateau in the deuterium quadrupolar splittings. However, the cholesterol-containing membranes have a higher average order, with the increases in order being greater for positions near the carbonyl group of the acyl chains. Below 20°C the 2H spectra of the membranes containing cholesterol change dramatically in a fashion suggestive of complex motional and/or phase behaviour.

Micelle Motion in Lyotropic Nematic Phases

Abstract Aqueous lyotropic liquid crystalline systems of Type I (Δχ > 0), composed of finite cyclindrical micelles, and Type II (Δχ < 0) composed of finite disc shaped micelles have been prepared in thermodynamic equilibrium with the parent mesophases Hexagonal Hα” and “Lamellar Lχ” respectively. The degree of order profile has been measured for all hydrocarbon segments by substitution of perdeuteriated amphiphiles in the mesophases and the determination of their deuterium quadrupole splittings. The related co-existent phases have degrees of order profile in the chains, which differ by a constant factor in each of the two cases. The order profile is lowered in the nematic liquid crystal because the micelles are finite in size and their symmetry axes can oscillate about the director of the mesophase. An upper limit for the oscillation angle has been estimated. For the case of Type II with finite bilayer disc micelles, the normal to the discs deviates a maximum of 27° from the director. For Type I with fin...

Protein-lipid interactions. High-field deuterium and phosphorus nuclear magnetic resonance spectroscopic investigation of the cytochrome oxidase-phospholipid interaction and the effects of cholate

Deuterium quadrupole-echo Fourier transform nuclear magnetic resonance spectra (at 34 MHz) and phosphorus-3 1 Fourier transform nuclear magnetic resonance spectra (at 60.7 MHz) have been obtained of 1-(6,6-dideuteriopalmitoyl)-2-oleyl-sn-glycero-3-phosphocholine dispersions in excess water in the absence of, and complexed with, the membrane enzyme cytochrome oxidase (cytochrome c:02 oxidoreductase, EC 1.9.3.1). Thereby, we have investigated the effects of the detergent sodium cholate, and of temperature, on protein-lipid interactions in this system. Our results strongly suggest that residual detergent in these protein-lipid complexes causes a significant disordering of hydrocarbon chain and head group organization as determined by deuterium quadrupole splittings (AvQ) and phosphorus chemical shielding anisotropies (Aa). At low (-2 wt %) cholate levels, C6 AuQ and 31P ha values in the protein-lipid complexes (containing T h e nature of the interactions between proteins and lipids in biological membranes is a topic of considerable current t From the Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (D.M.R. and E.O.), and the Department of Chemistry and the Laboratory for Bioenergetics, State University of New York at Albany, Albany, New York 12222 (J.C.H. and T.E.K.). Received April I I , 1979; revised manuscript received Augusl 15, 1979. This work was supported by the National Institutes of Health (Grant HL-19481 to E.O. and Grants GM-16767 and HL12576 to T.E.K.) and in part by the Alfred P. Sloan Foundation (E.O.). *Correspondence should be addressed to this author. He is an Alfred P. Sloan Research Fellow, 1978-1980. *Supported in part by a National Institutes of Health, Cell and Molecular Biology Training grant (Grant GM-07283). -70 wt % protein) are only about 8% smaller than in pure phospholipid bilayers at the same temperature, between 20 and 35 “C, suggesting rather similar structural organization. There are, however, significant line-width increases, especially on approaching T, in both deuterium and phosphorus spectra, indicating increased correlation times, in the region of the membrane surface. These results obtained on protein-lipid complexes containing an unsaturated phospholipid are in agreement with those of a previous study utilizing a disaturated phospholipid [Kang, S . Y., Gutowsky, H. S . , Hsung, J. C., Jacobs, R., King, T. E., Rice, D., & Oldfield, E. (1979) Biochemistry 18, 3257-32671 but differ significantly from those of a similar study employing 1-(5,5-dideuteriopalmitoyl)-2-oleyl-sn-glycero-3-phosphocholine [Seelig, A,, & Seelig, J . (1978) Hoppe-Seyler’s 2. Physiol. Chem. 359, 1747-17561. interest due to the frequent observation that a variety of membrane enzymes appear to require lipids in order to express their full biological activity [e.g., Yu et al. (1975), Gennis & Jonas (1977), Tanford & Reynolds (1976), Bennett et al. (1978), and Vik & Capaldi (1977)l. The most frequent model for the nature of the protein-lipid interaction is that the lipids are somehow immobilized (Jost et al., 1973a,b, 1977; Marsh et al., 1978; Warren et al., 1974, 1975; Longmuir et al., 1977) by the rigid protein “wall” (Moore et al., 1978), a cholesterol-like effect (Hong & Hubbell, 1972; Kleemann & McConnell, 1976), and that as a result the lipid hydrocarbon chain organization becomes far more restricted, leading to increased molecular order parameters (Dahlquist et al., 1977; MarEelja, 1976; Jost & Griffith, 1978; Scott & Cherng, 1978). 0006-2960/79/0418-5885S01 .OO/O , 1

Orientational order and rotational diffusion of the head group in the bilayer membrane. A nuclear magnetic resonance study

An order parameter-based interpretation is applied to the temperature dependence of the deuterium magnetic resonance splittings and the anisotropic contribution to the chemical shift for 31P from the head groups of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). It is shown that the rotational motion of the molecule about its long axis is not a free rotational motion as normally assumed, but instead a biased one. Changes in the degree of biasing appear to be primarily responsible for the variation of the NMR spectra with temperature. The degree of biasing is described by orientational order parameters. With the use of these order parameters, it is shown that the temperature dependence of the anisotropic contribution to the chemical shift for 31P can be predicted from that of the deuterium quadrupole splittings.

End-chain ordering and even-odd effects in nematic thermotropic liquid crystalline mesophases studied by deuterium magnetic resonance

Deuterium quadrupole splittings are reported for the nematic mesophases of all isomers of 4,4′-di- n-octyl- d 4( d 6)-oxyazoxybenzene with CD 2(CD 3) groups at corresponding segments in the two end chains. These splittings do not decrease monotonically with increasing separation of the chain segment from the aromatic core as has previously been assumed. Comparison with similar measurements for 4,4′-di- n-heptyloxyazoxybenzene reveals an “even—odd” effect in the chain ordering, but only in so far as to reflect differences in the molecular order in the two mesophases. The results are used to test earlier theoretical calculations by Marčelja.