Direct Nuclear Magnetic Resonance Research Articles

Phosphorylated and carbamylated Kraft lignin for improving fire- and biological-resistance of Scots pine wood

In this study, Kraft lignin was modified by ammonium dihydrogen phosphate (ADP) and urea for achieving phosphorylation and carbamylation, aiming to protect wood against biological and fire attack. Scots pine (Pinus sylvestris L.) sapwood was impregnated with a water solution containing Kraft lignin, ADP, and urea, followed by heat treatment at 150 °C, resulting in changes in the properties of the Kraft lignin as well as the wood matrix. Infrared spectroscopy, 13C cross-polarisation magic-angle-spinning (MAS) nuclear magnetic resonance (NMR), and direct excitation single-pulse 31P MAS NMR analyses suggested the grafting reaction of phosphate and carbamylate groups onto the hydroxyl groups of Kraft lignin. Scanning electron microscopy with energy dispersive X-ray spectroscopy indicated that the condensed Kraft lignin filled the lumen as well as partially penetrating the wood cell wall. The modified Kraft lignin imparted fire-retardancy and increased char residue to the wood at elevated temperature, as confirmed by limiting oxygen index, microscale combustion calorimetry, and thermogravimetric analysis. The modified wood exhibited superior resistance against mold and decay fungi attack under laboratory conditions. The modified wood had a similar modulus of elasticity to the unmodified wood, while experiencing a reduction in the modulus of rupture.

Gradient-based surface nuclear magnetic resonance for groundwater investigation

In medical magnetic resonance imaging, spatial localization (imaging) is based upon the application of controlled magnetic field gradients on top of the main magnetic field to spatially modulate the frequency and/or phase of the nuclear magnetic resonance (NMR) signal across the volume of investigation. In this work, we have applied similar physical principles to produce controlled magnetic field gradients during surface NMR-based groundwater investigations. In this approach, a gradient pulse of variable amplitude or duration is applied immediately after the excitation pulse to cause predictable phase encoding of the NMR signal as a function of depth. This approach is also applicable to emerging surface NMR detection methods that use a prepolarization field with fast nonadiabatic turn-off to generate detectable NMR signals from the shallow subsurface. In this case, the gradient pulse is applied after terminating the prepolarization field and provides a heretofore unavailable means of localizing the NMR response as a function of depth. The application of gradients can also be combined with tip-angle-based modulation to yield higher imaging resolution than can be achieved through either gradient- or tip-angle-based imaging alone. We implemented this new gradient-based capability into a surface NMR gradient generation accessory that is compatible with the GMR-Flex instrument and developed surface NMR-specific forward modeling and linear inverse models. We validated the accuracy of this novel gradient-based sNMR technology using computer simulations, experiments using a small pool filled with a discrete layer of bulk water, and field experiments at well-characterized groundwater test sites along Ebey Island, WA, and Larned, KS. The gradient-based sNMR imaging observations were compared with high-resolution direct push NMR results observed at these sites. The results of computer simulations and field experiments indicate improvements in both the detection (signal-to-noise ratio) and spatial resolution of shallow subsurface water content using gradient-based surface NMR, compared with traditional surface NMR imaging methods.

Review on NMR as a tool to analyse natural products extract directly: Molecular structure elucidation and biological activity analysis.

Natural products, the small organic molecules produced by plants, microbes and invertebrates, often present in the form of a mixture, this leads to the structural characterisation of natural extracts often requiring time-consuming multistep purification procedures. Nuclear magnetic resonance (NMR) technology is traditionally utilised as a tool for the structural elucidation of pure compounds. Contemporarily, an up-to-date trend in the application of NMR in natural product research is shifting to the direct NMR analysis of crude mixtures, to obtain molecular structure and biological activity information without performing cumbersome separation. To review works of literature on the evolution, principle and progress of NMR technologies for analysing mixtures, we focus on the successful application of NMR technologies in direct analysis of natural product extracts. Based on our research experience, academic tracking and extensive literature search, which involved, but not limited to, the use of various databases, like Web of Knowledge and PubMed. The keywords used, in various combinations, to retrieve recent literature on the successful application of NMR technologies to sheer natural product extracts, and excluded artificially natural product mixture and biofluid. NMR technologies for direct natural extracts analysis, including two-dimensional J-resolved spectroscopy (2D-JRES), pure shift NMR, diffusion-ordered NMR spectroscopy (DOSY), statistical correlation spectroscopy (STOCSY), concentration-ordered NMR spectroscopy (CORDY), saturation transfer difference (STD) and water-ligand observed via gradient spectroscopy (WaterLOGSY) were illustrated. By these methods, molecular structure and biological activity information will be directly obtained from NMR analysis of natural products extract, aiming to save experimental time and expenses.

Direct and Indirect DNP NMR Uncovers the Interplay of Surfactants with Their Mesoporous Host Material

Two different mesoporous silica materials (SBA-15 and MCM 41) were impregnated with four different, commercially available surfactants, namely, E5, PEG 200, C10E6, and Triton X-100. Differential scanning calorimetry was employed to confirm the confinement of the surfactants in the pores of their host materials. Dynamic nuclear polarization enhanced solid state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were recorded for these materials, showing that both the direct as well as the indirect polarization transfer pathways are active for the carbons of the polyethylene glycol moieties of the surfactants. The presence of the indirect polarization pathway implies the presence of molecular motion with correlation times faster than the inverse Larmor frequency of the observed signals. The intensities of the signals were determined, and an approach based on relative intensities was employed to ensure comparability throughout the samples. From these data, the interactions of the surfactants with the pore walls could be determined. Additionally, a model describing the surfactants’ arrangement in the pores was developed. It was concluded that all carbons of the hydrophilic surfactants, E5 and PEG 200, interact with the silica walls in a similar fashion, leading to similar polarization transfer pathway patterns for all observed signals. For the amphiphilic surfactants C10E6 and Triton X-100, the terminal hydroxyl group mediates the majority of the interactions with the pore walls and the polarizing agent.

Triple-pulse excitation: An efficient way for suppressing background signals and eliminating radio-frequency acoustic ringing in direct polarization NMR experiments

Direct polarization using a single pulse is the simplest excitation scheme in nuclear magnetic resonance (NMR) experiments, capable of quantifying various compositions in many materials applications. However, this single-pulse excitation generally gives rise to NMR spectra with a severely distorted baseline due to the background signals arising from probe components and/or due to the radio-frequency (RF) acoustic ringing, especially in low-γ nuclei and wide-line NMR. In this work, a triple-pulse excitation scheme is proposed to simultaneously suppress the background signals and eliminate the RF acoustic ringing. The acoustic ringing is cancelled through subtraction in any two consecutive scans by alternating the receiver phase while keeping the phase of the pulse right before acquisition the same. While the triple-pulse scheme generates an additional flip-angle dependent scaling to the traditional single-pulse excitation profile in such a way that the scaling is one when the flip-angle is ∼90° but becomes almost zero when the flip-angle is very small. Therefore, the background signals arising from the materials outside the sample coil experiencing a very small fraction of the RF flip-angles can be effectively suppressed. Various samples containing 1H and quadrupolar nuclei (17O, 25Mg, and 23Na) have been used to demonstrate the effectiveness of this newly proposed triple-pulse excitation in terms of suppressing the background signals and eliminating the acoustic ringing effects.

Role of NMR in High Ordered Structure Characterization of Monoclonal Antibodies.

Obtaining high ordered structure (HOS) information is of importance to guarantee the efficacy and safety of monoclonal antibodies (mAbs) in clinical application. Assessment of HOS should ideally be performed in a non-invasive manner under their formulated storage conditions, as any perturbation can introduce unexpected detritions. However, most of the currently available techniques only indirectly report HOS of mAbs and/or require a certain condition to conduct the analyses. Besides, the flexible multidomain architecture of mAbs has hampered atomic-resolution structural analyses using X-ray crystallography and cryo-electron microscopy. In contrast, the ability of nuclear magnetic resonance (NMR) spectroscopy to structurally analyze biomolecules in various conditions in a non-invasive and quantitative manner is suitable to meet the needs. However, the application of NMR to mAbs is not straightforward due to the high molecular weight of the system. In this review, we will discuss how NMR techniques have been applied to HOS analysis of mAbs, along with the recent advances of the novel 15N direct detection NMR strategy that allows for obtaining the structural fingerprint of mAbs at lower temperatures under multiple formulation conditions. The potential application of these NMR strategies will benefit next-generation mAbs, such as antibody-drug conjugates and bispecific antibodies.

Direct NMR T1 distribution measurement without using ill-posed fitting methods.

The usual Nuclear Magnetic Resonance (NMR) experiments for measuring spin-lattice relaxation time (T1) distributions are Inversion-Recovery (IR) and Saturation-Recovery (SR), followed by data processing based on ill-posed multi-exponential curve fitting methods. Recently, a new method combining SR and IR, called Saturation-Inversion-Recovery (SIR), has been proposed to obtain sharper T1-dependences than IR and SR. In this article, we propose an appropriate combination of SIR signals to directly obtain T1 distributions without using any multi-exponential fitting methods.

Inter-Active Site Communication Mediated by the Dimer Interface β-Sheet in the Half-the-Sites Enzyme, Thymidylate Synthase.

Thymidylate synthase (TS) is a dimeric enzyme conserved in all life forms that exhibits the allosteric feature of half-the-sites activity. Neither the reason for nor the mechanism of this phenomenon is understood. We used a combined nuclear magnetic resonance (NMR) and molecular dynamics approach to study a stable intermediate preceding hydride transfer, which is the rate-limiting and half-the-sites step. In NMR titrations with ligands leading to this intermediate, we measured chemical shifts of the apoenzyme (lig0), the saturated holoenzyme (lig2), and the typically elusive singly bound (lig1) states. Approximately 40 amides showed quartet patterns providing direct NMR evidence of coupling between the active site and probes >30 Å away in the distal subunit. Quartet peak patterns have symmetrical character, indicating reciprocity in communicating the first and second binding events to the distal protomer. Quartets include key catalytic residues and map to the dimer interface β-sheet, which also represents the shortest path between the two active sites. Simulations corroborate the coupling observed in solution in that there is excellent overlap between quartet residues and main-chain atoms having intersubunit cross-correlated motions. Simulations identify five hot spot residues, three of which lie at the kink in the unique β-bulge abutting the active sites on either end of the sheet. Interstrand cross-correlated motions become more organized and pronounced as the enzyme progresses from lig0 to lig1 and ultimately lig2. Coupling in the apparently symmetrical complex has implications for half-the-sites reactivity and potentially resolves the paradox of inequivalent TS active sites despite the vast majority of X-ray structures appearing to be symmetrical.

Endogenous dynamic nuclear polarization NMR of hydride-terminated silicon nanoparticles

Silicon nanoparticles (SiNPs) are intriguing materials and their properties fascinate the broader scientific community; they are also attractive to the biological and materials science sub-disciplines because of their established biological and environmental compatibility, as well as their far-reaching practical applications. While characterization of the particle nanostructure can be performed using 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy, poor sensitivity due to low Boltzmann population and long acquisition times hinder in-depth studies of these potentially game-changing materials. In this study, we compare two dynamic nuclear polarization (DNP) NMR protocols to boost 29Si sensitivity in hydride-terminated SiNPs. First, we assess a traditional indirect DNP approach, where a nitroxide biradical (AMUPol or bCTbk) is incorporated into a glassing agent and transferred through protons (e− → 1H → 29Si) to enhance the silicon. In this mode, electron paramagnetic resonance (EPR) spectroscopy demonstrated that the hydride-terminated surface was highly reactive with the exogenous biradicals, thus decomposing the radicals within hours and resulting in an enhancement factor, ε, of 3 (TB = 15 s) for the 64 nm SiNP, revealing the surface components. Secondly, direct DNP NMR methods were used to enhance the silicon without the addition of an exogenous radical (i.e., use of dangling bonds as an endogenous radical source). With radical concentrations <1 mM, 29Si enhancements were obtained for the series of SiNPs ranging from 3 to 64 nm. The ability to use direct 29Si DNP transfer (e− → 29Si) shows promise for DNP studies of these inorganic nanomaterials (ε = 6 (TB = 79 min) for 64 nm SiNPs) with highly reactive surfaces, showing the sub-surface and core features. These preliminary findings lay a foundation for future endogenous radical development through tailoring the surface chemistry, targeting further sensitivity gains.

Oxidatively stressed mitochondria-mimicking membranes: A molecular insight into their organization during apoptosis

Mitochondria are crucially involved in the removal of eukaryotic cells by the intrinsic pathway of programmed cell death (apoptosis). The mitochondrion's outer membrane (MOM) is the platform where this pathway takes place. Upon oxidative stress triggering apoptotic action, the MOM undergoes permeabilization and release of cytochrome c, ultimately causing cell death. This membrane perforation is regulated not only by opposing members of the Bcl-2 protein family meeting at the MOM but also actively the membrane itself. Upon oxidative damage, the membrane undergoes severe reorganization causing an increase in cell death-causing apoptotic Bcl-2 proteins. To understand the active role of MOM, we provided a detailed molecular view of its structural and dynamic reorganization upon oxidative stress by solid-state 13C MAS NMR (magic angle spinning nuclear magnetic resonance) accompanied by calorimetric studies. By focusing on MOM-like vesicles doped with oxidized lipid species, direct polarization 13C MAS NMR provided a quantitative overview and identification of all lipid moieties across the membrane. 1H-13C cross polarization and insensitive nuclei enhanced by polarization transfer MAS NMR generated a dynamic - mobile versus restricted – membrane profile. Oxidized phospholipids significantly perturb the structural membrane organization and increase membrane dynamics. These perturbations are not uniformly distributed as the hydrophobic core is reflecting the melting of lipid chains and increase in molecular disorder directly, whereas the interface and headgroup region undergo complex dynamical changes, reflecting increased intra-molecular flexibility of these moieties. These changes are potentially crucial in augmenting pro-apoptotic action of proteins like Bax.

Direct 1H NMR evidence of spin-rotation coupling as a source of para → ortho-H2 conversion in diamagnetic solvents.

At ambient temperature, conversion from 100% enriched para-hydrogen (p-H2; singlet state) to ortho-hydrogen (o-H2; triplet state) leads necessarily to the thermodynamic equilibrium proportions: 75% of o-H2 and 25% of p-H2. When p-H2 is dissolved in a diamagnetic organic solvent, conversion is very slow and can be considered as arising from nuclear spin relaxation phenomena. A first relaxation mechanism, specific to the singlet state and involving a combination of auto-correlation and cross correlation spectral densities, can be retained: randomly fluctuating magnetic fields due to inter-molecular dipolar interactions. We demonstrate here that (i) this dipolar mechanism is not sufficient for accounting for the para→ortho conversion rate, (ii) spin-rotation interaction, an intra-molecular mechanism, behaves similarly to random-field interaction and, thus, may be involved in the singlet relaxation rate. Also, as the para→ortho conversion is monitored by proton nuclear magnetic resonance (NMR) of dissolved o-H2 (p-H2 is NMR-silent), one has to account for H2 exchange between the liquid phase and the gas phase within the NMR tube, as well as for dissolution effects. Experimental evidence of the above statements is brought here in the case of two organic solvents: acetone-d6 and carbon disulfide. The observed temperature dependence of the para→ortho conversion rate shows that spin-rotation can be the dominant contribution to the p-H2 relaxation rate in the absence of tangible dipolar interactions. Our findings shed new light on the "mysterious" mechanism of the para→ortho conversion which has been searched for several decades.

Science meets regulation

Ethnopharmacological relevance: The European Pharmacopoeia (Ph. Eur.) is a standard reference for both European and non-European countries and defines requirements for the qualitative and quantitative composition of medicines. Herbal drug (HD) monographs state which aspects have to be considered for quality assurance through the relevant chapters “Definition”, “Characters”, “Identification”, “Tests”, and “Assay”. Identification of botanical material is achieved by macroscopic and microscopic morphology, generally examined by a trained expert. Content or assay is the most difficult area of quality control to perform, since in most herbal drugs the active constituents are unknown and markers should be used which cannot be really related to the quality. The other critical points are represented by the purity tests, in particular some tests such as heavy metals, aflatoxins and pesticides are laborious and time intensive, requiring a significant investment in equipment, materials, and maintenance.Material and methods: A literature survey concerning alternative and/or complementary tools for quality control of botanicals has been performed by searching the scientific databases Pubmed, SciFinder, Scopus and Web of Science.Results: Diverse analytical methods including DNA fingerprinting, Nuclear Magnetic Resonance (NMR), Near Infra Red (NIR) and (bio)sensors have been reported in the literature to evaluate the quality of botanical products. Identification of plants at the species level can be successfully based on genome-based methods, using DNA barcodes, the nucleotide sequence of a short DNA fragment. NMR can provide direct NMR fingerprint determination (complete assignment of the signals by 1D and 2D experiments), quantitative NMR and chemometric analysis (the metabolite fingerprint is based on the distribution of intensity in the NMR spectrum to provide sample classification). NIR spectroscopy is a fast qualitative and quantitative analytical method, getting knowledge about plant species and/or its geographic origin. Finally, the development of chemical and biological sensors is currently one of the most active areas of analytical research. Immobilization of specific enzymes led to recognize definite class of compounds such as cysteine sulfoxides, glucosinolates, cyanogenic glycosides, and polyphenols. Other recognition elements are nucleic acids to evaluate the ability of different molecules to bind DNA. Sensors have also been developed for the detection of heavy metals in botanicals. Moreover, the analysis of micotoxins and pesticides, could represent another field of possible application.Conclusions: These alternative/complementary analytical methods represent tools which appear to be an analyst’s dream: they are able to give rapid analysis responses; to operate directly on complex matrices, in many cases; to be selective and sensitive enough for the required application; to be portable and sometimes also disposable; and to have fast analysis times.

Single Domain Metallothioneins: Supermetalation of Human MT 1a

Metallothioneins are a family of small, cysteine rich proteins that have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as metallochaperones involved in the homeostasis of both essential zinc and copper. We report that human metallothionein 1a, well-known to coordinate 7 Zn(2+) or Cd(2+) ions with 20 cysteinyl thiols, will bind 8 structurally significant Cd(2+) ions, leading to the formation of the supermetalated Cd(8)-βα-rhMT 1a species, for which the structure is a novel single domain. ESI-mass spectrometry was used to determine the exact metalation status of the βα-rhMT. The derivative-shaped CD envelope of Cd(7)-βα-rhMT [peak extrema (+) 260 and (-) 239 nm] changed drastically upon formation of the Cd(8)-βα-rhMT with the appearance of a sharp monophasic CD band centered on 252 nm, a feature indicative of the loss of cluster symmetry. The structural significance of the eighth Cd(2+) ion was determined from a combination of direct and indirect (113)Cd nuclear magnetic resonance (NMR) spectra. In the case of Cd(8)-βα-rhMT, only four peaks were observed in the direct (113)Cd NMR spectrum. Significantly, while both of the isolated domains can be supermetalated forming Cd(4)-β-rhMT and Cd(5)-α-rhMT, Cd(8)-βα-rhMT and not Cd(9)-βα-rhMT was observed following addition of excess Cd(2+). We propose that both domains act in concert to coordinate the eighth Cd(2+) atom, and furthermore that this interaction results in a coalescence of the two domains leading to collapse of the two-domain structure. This is the first report of a possible single-"superdomain" metallothionein structure for Zn(2+) and Cd(2+) binding mammalian proteins. A computational model of a possible single-domain structure of Cd(8)-βα-rhMT is described.

Probing multimodal ligand binding regions on ubiquitin using nuclear magnetic resonance, chromatography, and molecular dynamics simulations

Site-directed mutagenesis, nuclear magnetic resonance (NMR) chemical shift perturbation experiments, and molecular dynamics (MD) simulations are employed in concert with chromatographic experiments to provide insight into protein–ligand interactions in multimodal chromatographic systems. In previous studies, a preferred binding region was identified on the surface of the protein ubiquitin for binding with a multimodal ligand. In this study, site-directed mutagenesis is used to enable direct NMR evaluation of the mutant protein as compared to the wild type. It is found that reversing the charge of a key residue (K6E) in the proposed preferred binding region results in substantial decreases in the magnitude of the ligand-induced NMR chemical shift perturbations relative to those detected for the wild type protein, particularly for residues located within the preferred binding region. These NMR results also indicate a decrease in ligand affinity, consistent with the weaker chromatographic retention observed for the mutant as compared to the wild type on a multimodal cation exchange resin. MD simulation results provide additional insight at a molecular level and demonstrate that many residues located within the preferred binding region exhibit weaker binding interactions due to the mutation. The analysis suggests that multimodal ligand binding consists of initial localization of the ligand by long-ranged electrostatic interactions followed by multiple short-ranged synergistic interactions to attain high affinities of the ligand to specific residues.

NMR evaluation of total statin content and HMG-CoA reductase inhibition in red yeast rice (Monascus spp.) food supplements

BackgroundRed yeast rice (i.e., rice fermented with Monascus spp.), as a food supplement, is claimed to be blood cholesterol-lowering. The red yeast rice constituent monacolin K, also known as lovastatin, is an inhibitor of the hydroxymethylglutaryl-CoA (HMG-CoA) reductase. This article aims to develop a sensitive nuclear magnetic resonance (NMR) method to determine the total statin content of red yeast rice products.MethodsThe total statin content was determined by a 400 MHz 1H NMR spectroscopic method, based on the integration of the multiplet at δ 5.37-5.32 ppm of a hydrogen at the hexahydronaphthalene moiety in comparison to an external calibration with lovastatin. The activity of HMG-CoA reductase was measured by a commercial spectrophotometric assay kit.ResultsThe NMR detection limit for total statins was 6 mg/L (equivalent to 0.3 mg/capsule, if two capsules are dissolved in 50 mL ethanol). The relative standard deviations were consistently lower than 11%. The total statin concentrations of five red yeast rice supplements were between 1.5 and 25.2 mg per specified daily dose. A dose-dependent inhibition of the HMG-CoA reductase enzyme activity by the red yeast rice products was demonstrated.ConclusionA simple and direct NMR assay was developed to determine the total statin content in red yeast rice. The assay can be applied for the determination of statin content for the regulatory control of red yeast rice products.

Experimental Verification of the Theory of Nuclear Quadrupole Relaxation in Liquids over the Entire Range of Molecular Tumbling Motion

Nuclearmagneticresonance(NMR)spectraofquadrupolarnuclei(I>1/2)in liquids often consist of broad resonances, making it difficult to obtain useful chemical information. The poor NMR spectral resolution commonly observed for quadrupolar nuclei isadirectconsequenceofnuclearquadrupolerelaxationprocesses.Althoughallkeyaspectsof nuclear quadrupole relaxation processes have been known for decades within the framework of the Redfield relaxation theory, direct experimental NMR relaxation data that cover a wide range of molecular motion in liquids for quadrupolar nuclei are generally lacking. Here we reportacompletesetofexperimentalnuclearquadrupolerelaxationdatathatareobtainedfor 17 O, a half-integer quadrupolar nucleus, over the entire range of molecular motion within the limit of the Redfield theory. Ageneral approachutilizing the quadrupole relaxation properties in the slow motion limit will be particularly beneficial for studies of quadrupolar nuclei in biomolecules of medium and large sizes.

Direct 1H NMR spectroscopy of dissolved organic matter in natural waters

Nuclear magnetic resonance (NMR) spectroscopy arguably provides the greatest insight into the overall chemical composition of dissolved organic matter (DOM). However, in a standard 5 mm NMR probe, a sample of sea water at natural abundance only contains ca. 500-600 ng of organic matter, distributed among the heterogeneous components of DOM. Additionally, the intensity of the water signal, which may be many orders of magnitude greater than the signals from DOM, makes the detection and analysis of DOM at natural abundance extremely demanding. Here, we demonstrate, that although challenging, the application of an improved water suppression technique allows NMR spectra of DOM to be obtained directly (i.e without pre-concentration) for major bodies of water, including rivers, lakes and the ocean. The technique described here provides a compositional overview of an intact sample, permitting researchers to investigate and assess the impact of concentration, isolation and extraction procedures that are employed routinely. Also the technique permits NMR to be performed on 'precious' samples for which traditional isolations are not possible, for example, water from ice cores and pore water, which are key in hydrology and for paleoclimatic reconstruction.

Direct NMR measurement of rotation rates: solvent effects on rotation barriers

Abstract2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐dialkoxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. The IR spectra of the solids display a broad OH absorption at 3320 cm−1, corresponding to an intermolecularly hydrogen‐bonded syn rotamer, probably a dimer, as well as absorptions around 3500 cm−1 of the intramolecularly hydrogen‐bonded anti form. Well‐crystallized samples of these derivatives go into solution in the syn form but undergo rotation to the anti rotamer at a rate which can be measured directly by proton Nuclear Magnetic Resonance (NMR) spectroscopy. The diethoxy derivative was studied in a wide variety of solvents. The activation energy for syn→anti rotation is practically solvent‐independent, whereas that of the reverse reaction falls in hydrogen‐bonding solvents, by more than 2 kcal mol−1 on going from chloroform or benzene to dimethylsulfoxide (DMSO). By combining direct measurements at low temperature and Dynamic Nuclear Magnetic Resonance (DNMR) results at high temperature, rotation rates were evaluated over a range of more than 100 K, and significantly large negative activation entropies determined. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Electric-field gradients in thin face-centered-tetragonal Co films observed by nuclear magnetic resonance

Thin tetragonally strained fcc-Co films grown epitaxially on Cu(001) single crystals have been investigated by $^{59}\mathrm{Co}$ nuclear magnetic resonance (NMR). The ultrahigh structural quality and the homogeneity of the strain result in the direct NMR observation of electric-field gradients, which is unique in thin films. The structural quality and the homogeneity and size of the strain are analyzed by means of the very small NMR linewidths, the hyperfine field anisotropies, and the uniform electric-field gradients. A quantitative agreement with the observed strain is found. The strain, and thus the tetragonal distortion, in the films is found to be surprisingly stable, showing less than 10% strain relief for 80 ML Co films.

Direct NMR evidence for ethanol binding to the lipid-water interface of phospholipid bilayers.

The mechanisms behind the membrane-mediated effects of ethanol were examined via the interaction of ethanol with phospholipid bilayers at hydration levels of 10-12 water molecules per lipid. 2H and 31P nuclear magnetic resonance (NMR) spectroscopy was used to monitor deuterated water and ethanol and the headgroups and acyl chains of neutral phospholipids. Ethanol was found to interact strongly with both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) bilayers, giving 2H NMR quadrupolar splittings for CH3CD2OH between 6.3 and 9.4 kHz. The quadrupolar splittings for ethanol in gel-phase lipids remained well resolved and were not significantly larger than those in the L alpha phase, suggesting that little or no ethanol was bound in the hydrocarbon interior of the bilayer. Ethanol binding significantly altered the orientation of the lipid headgroups, as shown with headgroup-deuterated PC bilayers. The entire lengths of the acyl chains were significantly disordered by the ethanol interaction, evidenced by significant reductions in the 2H NMR order parameters of the chains. The disordering corresponds to an increase in the area per lipid by an estimated 6% with one ethanol molecule per lipid, and a total of 18% with a second ethanol per lipid. This pronounced area increase is presumably caused by the disruption of lipid packing in the rigid region of the glycerol backbone rather than in the acyl chains, since the order of hydrocarbon chains is not affected to a significant degree by incorporation of alkanes and long-chain alcohols into the hydrocarbon interior.(ABSTRACT TRUNCATED AT 250 WORDS)