Deuterium NMR Spectra Research Articles

Proton-decoupled deuterium NMR study of an asymmetric liquid crystal dimer having two nematic phases.

Proton-decoupled deuterium NMR spectra were obtained for an asymmetric liquid crystal dimer 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) containing a single -CD_{2}- group. The sample has two nematic liquid crystal phases: a twist-bend nematic, N_{TB}, at the lowest temperature followed by a uniaxial nematic, N_{U}, on increasing the temperature. Proton decoupling reduces the linewidths of the peaks in the deuterium spectrum from kHz to ∼100Hz, enabling quadrupolar splittings, Δν, to be obtained with enhanced precision as well as the dipolar coupling between deuterium nuclei within the CD_{2} group, hence enhancing the information content.

Fragmentation of DMPC Membranes by a Wedge-Shaped Amphiphilic Cyclodextrin into Bicellar-like Aggregates.

Small bilayer lipid aggregates such as bicelles provide useful isotropic or anisotropic membrane mimetics for structural studies of biological membranes. We have shown previously by deuterium NMR that a wedge-shaped amphiphilic derivative of trimethyl βcyclodextrin anchored in deuterated DMPC-d27 bilayers through a lauryl acyl chain (TrimβMLC) is able to induce magnetic orientation and fragmentation of the multilamellar membranes. The fragmentation process fully detailed in the present paper is observed with 20% cyclodextrin derivative below 37 °C, where pure TrimβMLC self-assembles in water into large giant micellar structures. After deconvolution of a broad composite 2H NMR isotropic component, we propose a model where the DMPC membranes are progressively disrupted by TrimβMLC into small and large micellar aggregates depending whether they are extracted from the outer or inner layers of the liposomes. Below the fluid-to-gel transition of pure DMPC-d27 membranes (Tc = 21.5 °C), the micellar aggregates vanish progressively until complete extinction at 13 °C, with a probable release of pure TrimβMLC micelles leaving lipid bilayers in the gel phase doped with only a small amount of the cyclodextrin derivative. Bilayer fragmentation between Tc and 13 °C was also observed with 10% and 5% of TrimβMLC, with NMR spectra suggesting possible interactions of micellar aggregates with fluid-like lipids of the Pβ' ripple phase. No membrane orientation and fragmentation was detected with unsaturated POPC membranes, which are able to accommodate the insertion of TrimβMLC without important perturbation. The data are discussed in relation to the formation of possible DMPC bicellar aggregates such as those known to occur after insertion of dihexanoylphosphatidylcholine (DHPC). These bicelles are in particular associated with similar deuterium NMR spectra exhibiting identical composite isotropic components which were never characterized before.

Examination of pH dependency and orientation differences of membrane spanning alpha helices carrying a single or pair of buried histidine residues

We have employed the peptide framework of GWALP23 (acetyl-GGALWLALALALALALALWLAGA-amide) to examine the orientation, dynamics and pH dependence of peptides having buried single or pairs of histidine residues. When residue L8 is substituted to yield GWALP23-H8, acetyl-GGALWLAH8ALALALALALWLAGA-amide, the deuterium NMR spectra of 2H-labeled core alanine residues reveal a helix that occupies a single transmembrane orientation in DLPC, or in DMPC at low pH, yet shows multiple states at higher pH or in bilayers of DOPC. Moreover, a single histidine at position 8 or 16 in the GWALP23 framework is sensitive to pH. Titration points are observed near pH 3.5 for the deprotonation of H8 in lipid bilayers of DLPC or DMPC, and for H16 in DOPC. When residues L8 and L16 both are substituted to yield GWALP23-H8,16, the 2H NMR spectra show, interestingly, no titration dependence from pH 2–8, yet bilayer thickness-dependent orientation differences. The helix with H8 and H16 is found to adopt a transmembrane orientation in thin bilayers of DLPC, a combination of transmembrane and surface orientations in DMPC, and then a complete transition to a surface bound orientation in the thicker DPoPC and DOPC lipid bilayers. In the surface orientations, alanine A7 no longer fits within the core helix. These results along with previous studies with different locations of histidine residues suggest that lipid hydrophobic thickness is a first determinant and pH a second determinant for the helical orientation, along with possible side-chain snorkeling, when the His residues are incorporated into the hydrophobic region of a lipid membrane-associated helix.

Cobalt porphyrin immobilized on the TiO2 nanotube electrode for CO2 electroreduction in aqueous solution

Herein we report CO2 electrochemical reduction reaction (CO2ERR) on the cobalt tetraphenylporphyrin (CoTPP) modified TiO2 nanotube (TNT) electrode. It was found the axial coordination of drop-casting solvent to CoTPP and the porphyrin structure are the major factors that have significant effects on the catalytic performance of the electrode. As confirmed by spectrophotometric titration, pyridine has a stronger coordination bond to CoTPP than DMF and THF thus leading to the highest efficiency among the drop-casting solvents tested in the study. Based on the spectrophotometric analysis, possible coordination mechanism between drop-casting solvents and CoTPP is put forward. On the other hand, introduction of –COOMe substituents in phenyl rings of CoTPP weakens the coordination bond between pyridine and CoTPP as clearly evidenced by deuterium NMR spectra, resulting in a detrimental effect on CO2ERR. Therefore, the manipulation of the coordination environment around the metal center of immobilized catalyst is crucial in designing an efficient electrocatalytic system.

Cholesterol-binding site of the influenza M2 protein in lipid bilayers from solid-state NMR

The influenza M2 protein not only forms a proton channel but also mediates membrane scission in a cholesterol-dependent manner to cause virus budding and release. The atomic interaction of cholesterol with M2, as with most eukaryotic membrane proteins, has long been elusive. We have now determined the cholesterol-binding site of the M2 protein in phospholipid bilayers using solid-state NMR spectroscopy. Chain-fluorinated cholesterol was used to measure cholesterol proximity to M2 while sterol-deuterated cholesterol was used to measure bound-cholesterol orientation in lipid bilayers. Carbon-fluorine distance measurements show that at a cholesterol concentration of 17 mol%, two cholesterol molecules bind each M2 tetramer. Cholesterol binds the C-terminal transmembrane (TM) residues, near an amphipathic helix, without requiring a cholesterol recognition sequence motif. Deuterium NMR spectra indicate that bound cholesterol is approximately parallel to the bilayer normal, with the rough face of the sterol rings apposed to methyl-rich TM residues. The distance- and orientation-restrained cholesterol-binding site structure shows that cholesterol is stabilized by hydrophobic interactions with the TM helix and polar and aromatic interactions with neighboring amphipathic helices. At the 1:2 binding stoichiometry, lipid 31P spectra show an isotropic peak indicative of high membrane curvature. This M2-cholesterol complex structure, together with previously observed M2 localization at phase boundaries, suggests that cholesterol mediates M2 clustering to the neck of the budding virus to cause the necessary curvature for membrane scission. The solid-state NMR approach developed here is generally applicable for elucidating the structural basis of cholesterol's effects on membrane protein function.

Cover Picture: Integrated Computational Protocol for the Analysis of Quadrupolar Splittings from Natural‐Abundance Deuterium NMR Spectra in (Chiral) Oriented Media (ChemPhysChem 10/2017)

Cover Picture: Integrated Computational Protocol for the Analysis of Quadrupolar Splittings from Natural‐Abundance Deuterium NMR Spectra in (Chiral) Oriented Media (ChemPhysChem 10/2017)

Integrated Computational Protocol for the Analysis of Quadrupolar Splittings from Natural‐Abundance Deuterium NMR Spectra in (Chiral) Oriented Media

AbstractThe front cover artwork is provided by Dr. Armando Navarro‐Vázquez from the department of fundamental chemistry of the Universidade Federal de Pernambuco (Brazil) as well as Dr. Philippe Berdagué and Dr. Philippe Lesot (DR CNRS), both from the Institut de Chimie Moléculaire et des Matériaux d'Orsay of the Université de Paris‐Sud/Paris‐Saclay (France). Graphically inspired by the famous word game «Scrabble», the image illustrates, through selected keywords, the analytical potential of a hyphenated computational protocol for investigating (achiral, prochiral or chiral) organic molecules by combining deuterium NMR spectroscopy at natural abundance level and chiral oriented systems, as described in their article. Read the full text of the article at 10.1002/cphc.201601423.

Integrated Computational Protocol for the Analysis of Quadrupolar Splittings from Natural-Abundance Deuterium NMR Spectra in (Chiral) Oriented Media.

Despite its low natural abundance, deuterium NMR spectroscopy in weakly oriented (chiral) solvents gives easy access to deuterium residual quadrupolar couplings (2 H-RQCs). These are formally equivalent to one-bond residual dipolar couplings ((13 C-1 H)-RDCs) for calculation of the Saupe tensor, and provide similar information for the study of molecular structure and orientational behavior. Because the quadrupolar interaction is one order of magnitude larger than the dipolar one, 2 H-RQC analysis is a much more sensitive tool for the detection of subtle structural differences and also tiny differences in molecular alignment, such as those observed for different enantiomers in chirally aligned media. To promote the analytical advantages of anisotropic, natural-abundance deuterium NMR (NAD NMR) spectroscopy in the organic chemistry community, we describe a 2 H-RQC/DFT-based integrated computational protocol for the evaluation of the order parameters of aligned solutes by using singular-value decomposition. Several examples of 2 H-RQC-assisted analysis of chiral and prochiral molecules dissolved in various polypeptide lyotropic chiral liquid crystals are reported. The role of the molecular shape in the ordering mechanism was investigated through the determination of intertensor angles between alignment tensors and inertia tensors by using the proposed protocol.

Benzene at 1 GHz. Magnetic field-induced fine structure

The deuterium NMR spectrum of benzene-d6 in a high field spectrometer (1GHz protons) exhibits a magnetic field-induced deuterium quadrupolar splitting Δν. The magnitude of Δν observed for the central resonance is smaller than that observed for the 13C satellite doublets Δν′. This difference, Δ(Δν)=Δν′−Δν, is due to unresolved fine structure contributions to the respective resonances. We determine the origins of and simulate this difference, and report pulse sequences that exploit the connectivity of the peaks in the 13C and 2H spectra to determine the relative signs of the indirect coupling, JCD, and Δν. The positive sign found for Δν is consonant with the magnetic field biasing of an isolated benzene molecule—the magnetic energy of the aromatic ring is lowest for configurations where the C6 axis is normal to the field. In the neat liquid the magnitude of Δν is decreased by the pair correlations in this prototypical molecular liquid.

NMR of bent-core nematogens: a mini-review.

This review focuses on two of our studied bent-core liquid crystals 2-methyl-3-[4-(4-octylbenzoyloxy)-benzylidene]-amino-benzoic acid 4-(4-dodecylphenylazo)-phenyl ester A131, and a shape-persistent fluorenone mesogen, F1a by means of temperature-dependent (13)C NMR spectra and deuterium NMR spectra, respectively. Orientational order parameters, molecular packing, and/or conformations in the nematic phases or nematic glass can be extracted from the observed NMR spectra. These will be discussed in terms of certain motional models. In particular, F1a has been found to form a biaxial nematic glass. The derived orientational order parameters would put the biaxial system of phase symmetry lower than orthorhombic.

New Solvates of an Old Drug Compound (Phenobarbital): Structure and Stability

The solvent formation of phenobarbital, an important drug compound with an unusually complex polymorphic behavior, was studied in detail. Monosolvates with acetonitrile, nitromethane, dichloromethane, and 1,4-dioxane were produced and characterized by single-crystal and powder X-ray diffraction, thermoanalytical methods, FT-IR, Raman, and solid-state NMR spectroscopy. Thermal desolvation of these compounds yields mainly mixtures of polymorphs III, II, and I. At a low relative humidity (25 °C) the solvates transform to polymorph III, and at higher relative humidity the monohydrate and the metastable polymorphs IV and VI can be present as additional desolvation products. These results highlight the potential complexity of desolvation reactions and illustrate that a tight control of ambient conditions is a prerequisite for the production of phase-pure raw materials of drug compounds. Transformation in aqueous media results in the monohydrate. Below room temperature, the 1,4-dioxane monosolvate undergoes a reversible single-crystal-to-single-crystal phase transition due to the ordering/disordering of 50% of its solvent molecules. Dipolar-dephasing NMR experiments show that the solvent molecules are relatively mobile. Deuterium NMR spectra reinforce that conclusion for the dioxane solvent molecules. The crystal structure of an elusive 1,4-dioxane hemisolvate was also determined. This study clearly indicates the existence of "transient solvates" of phenobarbital. The formation of unstable phases of this kind must be considered in order to better understand how different solvents affect the crystallization of specific polymorphs.

Characterizing Moderately Short Antimicrobial Tryptophan/Arginine-Rich Peptides

Antimicrobial peptides offer attractive alternatives to the problem of increasing bacterial drug resistance. To address this issue, we have engineered moderately short “hybrid” peptides that are somewhat longer than the antimicrobial surface-acting lactoferrin-derived LfB6 (RRWQWR-NH2), yet shorter than the inert model transmembrane helical peptide RWALP23 (acetyl-GRALW(LA)6LWLARA-NH2). Previously we observed that a 15-residue peptide with 4 arginines, acetyl-GRRW(LA)3LWRRA-NH2 (designated RRWALP15) exhibits significant activity against E. coli and S. aureus (MIC ∼10 μg/ml). To further interrogate the importance of peptide length and detailed amino acid sequence, we have synthesized additional LfB-RWALP hybrid peptides that have between 9 and 15 total residues and differing numbers of arginine and tryptophan residues. Into peptides such as, acetyl-GRRWWAWWRRA-NH2, acetyl-GRRWLALWRRA-NH2, and acetyl-GRWLALALALWRA-NH2, we incorporate 2H-labeled alanine residues and seek to compare the biophysical properties and the antimicrobial potencies of several such peptides. Solid-state deuterium (2H) NMR spectra suggest peptide conformational heterogeneity in several different mechanically aligned lipid bilayers of varying lipid thickness. The circular dichroism spectra of the new LfB-KWALP hybrid peptides in lipid vesicles furthermore reveal, in most cases, a mixture α-helical and β-like conformations. The antimicrobial activity typically is higher when four arginines are present, yet the activity does not appear to correlate directly with folding or secondary structure.

The Chirality of a Twist–Bend Nematic Phase Identified by NMR Spectroscopy

One of the defining characteristics of the twist-bend nematic phase, formed by the methylene-linked liquid crystal dimer 1″,7″-bis(4-cyanobiphenyl-4'-yl) heptane (CB7CB), is its chirality. This new nematic phase, predicted by Dozov, is of particular interest because although the constituent molecules are achiral the phase itself is chiral. Here, we describe the use of NMR spectroscopy to determine experimentally whether in reality the phase is chiral or not. The basis of this novel procedure is that the equivalence of the protons or deuterons in a prochiral methylene group in a nematic phase with D∞h symmetry is lost in a chiral phase because its symmetry is reduced to D∞ on removal of the mirror plane. Recording proton-enhanced local field (PELF) NMR experiments shows that in the standard nematic phase all of the methylene groups in the heptane spacer have equivalent pairs of C-H groups but this equivalence is lost for the six prochiral methylene groups with their enantiotopic protons on passing to the twist-bend nematic. Strikingly, this equivalence is not lost for the central methylene group where the two protons are homotopic. We also show how the phase chirality can be demonstrated with probe molecules which contain deuteriated prochiral methylene groups, using 4-octyl-4'-cyanobiphenyl-d2, perdeuteroacenaphthene-d10, and acenaphthene-d4 as examples. For the standard nematic phase deuterium, NMR shows that the deuterons in these methylene groups are equivalent but, as expected, in the twist-bend nematic phase this equivalence is lost. The deuterium NMR spectra of these probe molecules dissolved in CB7CB have been recorded from the isotropic phase, through the nematic and deep into the supercooled twist-bend nematic.

Probing the Lipid-Protein Interface Using Model Transmembrane Peptides with a Covalently Linked Acyl Chain

The aim of this study was to gain insight into how interactions between proteins and lipids in membranes are sensed at the protein-lipid interface. As a probe to analyze this interface, we used deuterium-labeled acyl chains that were covalently linked to a model transmembrane peptide. First, a perdeuterated palmitoyl chain was coupled to the Trp-flanked peptide WALP23 (Ac-CGWW(LA)8LWWA-NH2), and the deuterium NMR spectrum was analyzed in di-C18:1-phosphatidylcholine (PC) bilayers. We found that the chain order of this peptide-linked chain is rather similar to that of a noncovalently coupled perdeuterated palmitoyl chain, except that it exhibits a slightly lower order. Similar results were obtained when site-specific deuterium labels were used and when the palmitoyl chain was attached to the more-hydrophobic model peptide WLP23 (Ac-CGWWL17WWA-NH2) or to the Lys-flanked peptide KALP23 (Ac-CGKK(LA)8LKKA-NH2). The experiments showed that the order of both the peptide-linked chains and the noncovalently coupled palmitoyl chains in the phospholipid bilayer increases in the order KALP23 < WALP23 < WLP23. Furthermore, changes in the bulk lipid bilayer thickness caused by varying the lipid composition from di-C14:1-PC to di-C18:1-PC or by including cholesterol were sensed rather similarly by the covalently coupled chain and the noncovalently coupled palmitoyl chains. The results indicate that the properties of lipids adjacent to transmembrane peptides mostly reflect the properties of the surrounding lipid bilayer, and hence that (at least for the single-span model peptides used in this study) annular lipids do not play a highly specific role in protein-lipid interactions.

Enantiotopic discrimination in the deuterium NMR spectrum of solutes with S4 symmetry in chiral liquid crystals

Enantiotopic discrimination in the NMR spectra of prochiral rigid solutes in chiral liquid crystals (CLC), by the ordering mechanism, is limited to molecules possessing one of the four, so called, "allowed" symmetries, D(2d), C(2v), C(s), and S(4). So far, such spectral discrimination was demonstrated only for solutes possessing one of the first three symmetries. In this work, we present deuterium NMR measurements on a rigid S(4) compound dissolved in a chiral nematic solvent and demonstrate, for the first time, enantiotopic discrimination in such symmetry. The measurements were performed on the isotopically normal icosane derivative (1) and on its isotopomer (1-d(8)), specifically deuterated in its four core methylene groups. As a CLC solvent, a lyotropic mesophase, consisting of a solution of poly-γ-benzyl-L-glutamate (PBLG) in pyridine, was employed. For comparison with a corresponding achiral liquid crystal (ALC) solvent, a solution of a racemic mixture of poly-γ-benzylglutamate (PBG) of similar composition in the same co-solvent was used. The spectra were recorded at 92.1 MHz using the 2D Q-COSY Fz sequence with proton decoupling. In the CLC solvents they exhibited clear discrimination due to different enantiotopic sites, with components displaced symmetrically, at frequencies below and above those in the corresponding ALC, as expected for discrimination by ordering. Two procedures were employed for correlating the enantiotopic sites in the CLC spectra. For 1-d(8) the dipolar cross-peaks in a 2D (2)H-(2)H COSY-90 experiment provided identification of signals belonging to the same methylene (and hence the same enantiotopic) groups. For 1 the correlation was achieved using a least-square-deviation fitting of the experimental quadrupole splittings with respect to those expected from the molecular geometry. These results, with appropriate symmetry considerations were used to determine the symmetric (S(zz)) and antisymmetric (S(xy) and S(xx)-S(yy)) components of the Saupe ordering matrix. Interpretation of the NMR spectra of prochiral solutes in CLC suffers from the ambiguity in identifying the signals with specific enantiotopic groups. For this reason only the relative (but not the absolute) signs of the antisymmetric elements of the ordering matrix can be determined. For the S(4) group this leads to sign ambiguity in the rhombic term in the diagonalized ordering matrix. Similar (but not identical) ambiguities occur for solutes belonging to the other allowed groups. In a concluding section of the paper, the ambiguities in the antisymmetric order parameters for the various allowed groups are compared and their physical meaning are discussed.

Detecting Critical Fluctuations in Ternary Lipid and Cholesterol Mixtures

Mixtures of long chain saturated and unsaturated phospholipids with cholesterol have attracted a lot of attention because of the formation of two coexisting fluid bilayer phases over a broad range of temperatures and compositions of these systems. Davis et al. and Veatch et al. have presented phase diagrams for ternary mixtures of two phospholipids (DOPC and DPPC-d62) and cholesterol. These ternary mixtures show evidence of critical fluctuations in composition [1,2]. A preliminary investigation of the linewidth of the deuterium NMR spectrum of powder samples under magic angle spinning (MAS) has been done and shows a large increase (5 or 6 fold) in the spectral linewidths as we approach the critical temperature. We also looked at the MAS spectral linewidths for these samples using proton NMR but found that the effect is very minimal and inconclusive. We are undertaking to explore these systems in more detail using static solid-state NMR techniques. We are using a Jeener Echo pulse sequence which probes the relaxation of the nuclear magnetic dipolar spin energy to the lattice. The Jeener Echo pulse sequence makes dipolar order, which ordinarily is much smaller than the Zeeman order, detectable by NMR [3]. Dipolar order relaxes by fluctuations in the local fields of the nuclei which are typically a few kHz in strength. Critical fluctuations would cause changes in the local fields and in turn changes in the rate of relaxation of dipolar order. This technique is sensitive to slow motions which makes it useful for investigating the existence of fluctuations near a critical point.[1] Davis, J.H. et al. (2009) Biophys. J. 96:521-539. [2] Veatch, S.L. et al. (2007) Proc. Natl. Acad. Sci. USA 104:17650-17655. [3] Jeener, J. and Broekaert, P. (1966)Phys. Rev. 157:232-240.

2H NMR calculations on polynuclear transition metal complexes: on the influence of local symmetry and other factors

It is now well-known that (2)H solid-state NMR techniques can bring a better understanding of the interaction of deuterium with metal atoms in organometallic mononuclear complexes, clusters or nanoparticles. In that context, we have recently obtained experimental quadrupolar coupling constants and asymmetry parameters characteristic of deuterium atoms involved in various bonding situations in ruthenium clusters, namely D(4)Ru(4)(CO)(12), D(2)Ru(6)(CO)(18) and other related compounds [Gutmann et al., J. Am. Chem. Soc., 2010, 132, 11759], which are model compounds for edge-bridging (μ-H) and face-capping (μ(3)-H) coordination types on ruthenium surfaces. The present work is in line with density functional theory (DFT) calculations of the electric field gradient (EFG) tensors in deuterated organometallic ruthenium complexes. The comparison of quadrupolar coupling constants shows an excellent agreement between calculated and observed values. This confirms that DFT is a method of choice for the analysis of deuterium NMR spectra. Such calculations are achieved on a large number of ruthenium clusters in order to obtain quadrupolar coupling constants characteristic of a given coordination type: terminal-D, η(2)-D(2), μ-D, μ(3)-D as well as μ(4)-D and μ(6)-D (i.e. interstitial deuterides). Given the dependence of such NMR parameters mainly on local symmetry, these results are expected to remain valid for large assemblies of ruthenium atoms, such as organometallic ruthenium nanoparticles.

ChemInform Abstract: Cope Rearrangement and Molecular Reorientation in Solid Bullvalene: A Single Crystal Deuterium NMR Study.

Deuterium NMR spectra of single crystals of deuterated bullvalene were recorded in the temperature range -13 0C to +80 0 C. The measurements were performed with the magnetic field parallel to the crystallographic 6-axis where all four molecules in the unit cell are magnetically equivalent. Below about 5 0C the spectrum consists of ten almost symmetrical doublets due to the ten distinct deuterons per bullvalene molecule. Above 5 0C dynamic line broadening effects set in which were quantitatively interpreted in terms of two independent thermally activated processes: (i) symmetric 3-fold jumps about the molecular C3 axis and (ii) Cope rearrangement combined with molecular reorientation that preserves the crystal symmetry. The kinetic equations for the rates of the 3-fold jumps and the Cope rearrangement processes are respectively, k3 = 13.6 X 10 exp(-19.1//?r> and £c = 4.02 X 1014 exp(~\5.\/RT), where R is in kcal/mol-deg and the k's are in s1. Deuterium NMR measurements on a powder sample of deuterated bullvalene were also performed and found consistent with those obtained from the single crystals. The results are discussed in comparison with earlier solid state proton and 13C NMR and structural crystallographic measurements. We also show that the bullvalene molecules undergo an inde­ pendent 3-fold jump process, and we determine the rate of this process as well. It thus turns out that solid bullvalene is at the same time a highly order crystalline system and also highly fluxional. It exhibits, both whole-molecule jumps and valence-bond tautomerism but using pathways that leave the site symmetry in the crystal completely unchanged. The experimental details including the mounting and NMR measurements of the bullvalene single crystals are described in the Experimental Section. The single crystal measurements at low temperatures and in the temperature range where dynamic effects are observed, are then presented and compared with theoretically calculated lineshapes from which kinetic parameters are derived. These parameters are subsequently used to simulate and analyze the spectra obtained from a powder sample of bullvalene. We close with a short summary and conclusions which

Computer Simulation of the Deuterium NMR Spectra Reflecting the Director Distribution for Multi-Domains in a Thin Nematic Cell

Deuterium NMR spectroscopy is widely employed to investigate the static and dynamic director alignment for low molar mass nematics contained in a thin sandwich cell. When the director is not uniformly aligned the appearance of the deuterium NMR spectra, recorded in the measurements, reflects the form of the director distribution. This occurs because the observed spectrum is a weighted sum of the spectra from all director orientations in the sample. In order to obtain the form of the director distribution function by simulating the spectra it is necessary to know how the spectral lineshape varys with the director orientation. As well as being of practical relevance, when the director distributes thermally with the average director orientation in multi domains, this contribution to the lineshape is of fundamental interest for nematic behaviour. Here we explore ways to vary the aveage director orientation using an electric field and employ this to measure the voltage dependence of the NMR lineshapes for the nematic phase of 5CB-d2. This approach is investigated by using a computer simulation of the NMR lineshapes.

Observation of Backbone Cα-Deuteron Signals in Solid-State NMR Spectra of Labeled Alanines in Oriented Transmembrane Peptides

Solid-state deuterium NMR spectra combined with the Geometric Analysis of Labeled Alanines (GALA) method provide information about the average apparent tilt and dynamics of membrane-spanning peptides in oriented, hydrated lipid bilayer membranes. When Ala-d4 labels are used, the side-chain methyl (CD3) signals are readily detected, but the weaker backbone Cα-D resonances are often problematic to observe (van der Wel, Biophys J, 83, 1479) for peptides of the WALP family [GWW(LA)nLWWA]. In spite of this difficulty, we recently have begun to observe surprisingly intense backbone Cα-D resonances in the 2H NMR spectra for some oriented transmembrane peptides, particularly in cases where the (LA)n core sequence of WALP is interrupted by a “guest” residue such as Pro, Lys or Arg. Examples will be discussed. In some cases, the Cα-D signal intensities appear to depend upon the macroscopic orientation of the lipid bilayers with respect to the external magnetic field. The sequence and orientation dependence of the backbone Cα-D signals may therefore reflect the local and global peptide dynamics in ways that are incompletely understood. A selection of spectral examples will be presented and interpreted.