Wide-line NMR Research Articles

Toward Bicelle Stability with Ether-Linked Phospholipids: Temperature, Composition, and Hydration Diagrams by2H and31P Solid-State NMR

Phosphorus and deuterium wide line NMR was used to determine diagrams of binary mixtures of 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (DIOMPC) and 1,2-di-O-hexyl-sn-glycero-3-phosphocholine (DIOHPC) ether-phospholipids. By varying the hydration, h, the temperature, T, and the mole fraction, X, of long-chain ether-phospholipids, we delineated the conditions for which such systems are oriented by the magnetic field, in the presence of 100 mM KCl. The 3D domain is found for X = 62-90%, T = 27-50 degrees C, and h = 70-98%. At 80% hydration, the domain shape (X = 70-90% and T = 27-42 degrees C) is close to that already observed for ester-phospholipids mixtures (Raffard, G.; Steinbruckner, S.; Arnold, A.; Davis, J. H.; Dufourc, E. J. Langmuir 2000, 16, 7655-7662) where disc-shaped bicelles of 300-600 A have been found by electron microscopy (Arnold, A.; Labrot, T.; Oda, R.; Dufourc, E. J. Biophys. J. 2002, 83, 2667-2680). Systems made of ether-linked lipids are much more stable on time and acidic conditions than those made of ester lipids. Assuming that the disc-shaped species are also found with ether lipids, their diameter as determined from integration of phosphorus NMR lines ranges from 240 to 440 A +/- 10%; it is generally independent of hydration and temperature but decreases with decreasing long-chain lipid content, X. The structure and the dynamics of water in the DIOMPC-DIOHPC were characterized by (2)H NMR. Water exchanges between the membrane surface where it is bound and a bulk isotropic pool lead to an average ordered state for temperatures in the bicelle region and above, thus offering a larger thermal span for structural studies of dissolved molecules.

Microscopic study on spin state of nano-particles of antiferromagnet: ND4MnF3

Abstract The magnetic behavior of small size grains of antiferromagnet of ND 4 MnF 3 with 30 nm diameter is particularly compared with that of bulk. To elucidate the low temperature property of a magnetic nano-particle, we characterized bulk sample of ND 4 MnF 3 , nano-particle of ND 4 MnF 3 with ca. 30 nm diameter, and magnetically diluted compound of ND 4 Mn 0.5 Zn 0.5 F 3 in bulk with using powder X-ray diffractometry, scanning electron microscopy (SEM), SQUID magnetometry, and particularly with solid-state deuterium NMR. The magnetic properties of these materials are discussed from the difference of magic angle spinning deuterium NMR spectra in the paramagnetic phase and from internal magnetic field determined by deuterium NMR spectra in the antiferromagnetic phase. It was found that critical behavior of the nano-particles with approaching the Neel temperature is clearly different from the bulk sample, while internal magnetic field of the nano-particles in the low temperature limit is almost the same as that of bulk sample. Near-surface spins of nano-particles in the antiferromagnetic phase were distinguished from the inner spins by wide-line deuterium NMR spectrum.

Study of the thermal elimination process of sulphinyl-based PPV precursors by solid state NMR

A sensitive protocol to judge the completeness of the elimination reaction for soluble and insoluble conjugated polymers prepared via precursor routes is presented based on UV/vis and 1H wideline NMR relaxometry in the solid state. Especially the proton spin–lattice decay time in the rotating frame, T 1 ρH , has proven to be suitable for an accurate determination of the completeness of the elimination reaction. Especially for long side-chain substituted PPV derivatives, UV/vis seems to be limited due to thermochromic effects. Furthermore, it is shown by solid state 2H wideline NMR spectroscopy that incomplete elimination results in an enhanced polymer backbone chain mobility. Both the completeness of elimination and insight into the molecular dynamics can be of significant importance toward the performance of photovoltaic devices.

Structural role of fluorine in amorphous silica

The composition and temperature dependence of the coordination environments of F atoms in fluorinated silica glasses have been studied using high-resolution 19F and 29Si NMR spectroscopies. 19F MAS and wideline NMR spectra have revealed the presence of two distinct types of fluorine environments in glasses containing 1–3.3wt% fluorine. The majority of the fluorine environments are formed by replacing one of the bridging oxygens around a silicon atom with a non-bridging fluorine atom, forming SiO3/2F polyhedra. The less abundant species is found to be highly unusual in that it involves bonding of a non-bridging fluorine to a silicon atom that is already coordinated to four bridging oxygens, yielding a fivefold coordinated silicon of the type SiO4/2F. The relative concentration of the SiO4/2F species in these glasses is found to increase with both increasing fluorine content and fictive temperature. The possible role of these structural elements in controlling diverse physical properties of these glasses such as the optical absorption edge and viscosity is discussed.

Solid state NMR study of segmented polymer networks: fine-tuning of phase morphology via their molecular design

Segmented polymer networks (SPNs) based on thermo-sensitive poly(N-isopropyl acryl amide) (PNIPAA) and poly(tetrahydrofuran) (PTHF) have been synthesized by free radical copolymerization of PTHF bis-macromonomers with N-isopropyl acrylamide. The nature of the polymerizable end group on the bis-macromonomer has been varied, respectively from acrylate to acrylamide end groups. The multiphase behaviour of the corresponding SPNs has been examined as a function of the nature of the end group by making use of solid-state 13C CP/MAS NMR relaxometry, 1H wideline NMR relaxometry and dynamic mechanical analysis (DMA). When PTHF with acrylate end groups was used during the SPN formation, analysis of proton spin-lattice relaxation times (T1H) and proton spin-lattice relaxation times in the rotating frame (T1ρH) revealed phase separation with domain sizes larger than 5nm when the PTHF fraction exceeds 10wt%. Only for lower PTHF-amounts, the SPNs were homogeneous on the nanometer scale. On the other hand, when PTHF with acrylamide end groups was used as macromolecular cross-linker, the NMR results showed the absence of any domain formation for SPNs with PTHF fractions up to 50wt%. The major impact of the molecular design on the ultimate phase morphology of bicomponent polymer networks has been confirmed in all cases by DMA-analysis.

A Solid-State NMR Experiment: Analysis of Local Structural Environments in Phosphate Glasses

The solid state 31P NMR wideline spectra of a series of student-prepared sodium phosphate glasses can easily be measured using a standard multinuclear FTNMR spectrometer available in many chemistry departments. The observed spectra can be simulated by spectral addition of reference solid-state spectra obtained for pure pyrophosphate and metaphosphate salts. Students measure the relative fractions of these phosphorus environments in the glasses and can study the effect on the depolymerization of phosphate as P2O5 when a network modifier as Na2O is added. They learn the principles of solid-state NMR, gain experience of measuring the NMR spectrum of a solid glass, and interpret the spectrum in terms of the composition and localized phosphate environment in this glass.

NMR methods for studying the structure and dynamics of oncogenic and antihistaminic peptides in biomembranes

We present several applications of both wide-line and magic angle spinning (MAS) solid-state NMR of bicelles in which are embedded fragments of a tyrosine kinase receptor or enkephalins. The magnetically orientable bicelle membranes are shown to be of particular interest for studying the functional properties of lipids and proteins in a state that is very close to their natural environment. Quadrupolar, dipolar and chemical shielding interactions can be used to determine minute alterations of internal membrane dynamics and the orientation of peptides with respect to the membrane plane. MAS of bicelles can in turn lead to high-resolution proton spectra of hydrated membranes. Using deuterium-proton contrast methods one can then obtain pseudo-high-resolution proton spectra of peptides or proteins embedded in deuterated membranes and determine their atomic 3D structure using quasi-conventional liquid-state NMR methods.

Another approach to protons with constricted mobility in white matter: pilot studies using wideline and high-resolution NMR spectroscopy.

We report a new approach for the identification of an independent method of studying the semi-solid pool of protons, i.e., protons with constrained motion as a result of being bound to lipid and protein matrices. These protons cannot be observed using conventional imaging techniques since their transverse relaxation times are much shorter than the minimum echo times that are currently available on clinical scanners. In this pilot study, in vitro multicomponent transverse relaxation experiments were made on human white matter slices, fixed in formalin (7 normal and 5 with multiple sclerosis). The transverse relaxation decay curves were multiexponential and were decomposed to yield three primary components. The shortest T(2) component that we obtained (a component too short to be seen by in vivo methods) was of the order of microseconds. We hypothesize that this might correspond to the macromolecular pool of lipid protons trapped within the myelin sheaths. To our knowledge, this is the first attempt at extracting this ultra short T(2) component from human white matter. Subsequently, an attempt was made to directly detect the lipid protons in a proton NMR spectrum and, if possible, measure their concentration in some of the tissues, using the technique of magic angle spinning.

Latent methane in fossil coals

It is established experimentally using 1H NMR wide line spectroscopy that methane can exist in coals not only in open or closed porosity and fracture systems but also in solid solutions in coal substance, in particular, under methane pressure 2 MPa or higher. Methane dissolved in coal minerals reversibly modifies their lattice parameters as determined from X-ray diffraction analysis. Co-existence of these methane forms in fossil coals causes multi-step desorption kinetics. It is shown experimentally that the long-term latent methane desorption is effected mainly by closed porosity, which in turn is determined by coal rank.

Magnetic Resonance Study of a Series of Phosphorus‐Containing Zintl Compounds: Ca14AlP11, Ca14MnP11, and Eu14MnP11.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Magnetic Resonance Study of a Series of Phosphorus-Containing Zintl Compounds: Ca14AlP11, Ca14MnP11, and Eu14MnP11

The compounds Ca14AlP11, Ca14MnP11, and Eu14MnP11 have been synthesized and are isostructural to the Zintl compound, Ca14AlSb11. Eu14MnP11 is a ferromagnet showing colossal magnetoresistance at TC = 52 K, Ca14MnP11 shows paramagnetic behavior down to 5 K, and Ca14AlP11 is nonmagnetic. The formula unit for these Zintl compounds is A14MPn11 and comprises 14 A cations, a MPn4 tetrahedron, four isolated Pn anions, and a Pn3 linear unit. The central Pn of the Pn3 unit is believed to be positionally disordered, and it has been speculated that the disorder is static rather than dynamic. To address this issue, 31P solid-state NMR was applied to these new compounds to provide insight into the magnetic ordering and structural changes. The NMR chemical shift anisotropy and the dipolar coupling for the 31P nuclei as well as the quadrupolar coupling for the 27Al nucleus in the diamagnetic compound Ca14AlP11 provide structural details consistent with the Zintl structure. Wide-line 31P NMR and EPR were applied to the paramagnetic compounds Ca14MnP11 and Eu14MnP11 to obtain similar structural information. The lack of any EPR spectra for the Eu-substituted compound below 50 K confirms the assigned paramagnetic-to-ferromagnetic transition temperature of 52 K. Hyperfine couplings in the Eu-substituted compound suggests localization of the electron density above 50 K.

Solid-state NMR study on the structure and mobility of the noncrystalline region of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate- co-3-hydroxyvalerate)

The noncrystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) copolymers were studied by variable temperature solid-state wide-line 1H NMR and solid-state high-resolution 13C NMR spectroscopy. It is found that at room temperature there exists a rich and rigid component in the noncrystalline region of PHB and PHBV. The content of this component decreases with the increase in 3-hydroxyvalerate content in PHBV and with the increase in temperature. The brittleness of PHB may be partly attributed to the rigidness of the noncrystalline region at room temperature, while the improvement of the properties of PHBV may come from the enhanced mobility of the noncrystalline region.

Dynamics and orientation of N+(CD3)3-bromoacetylcholine bound to its binding site on the nicotinic acetylcholine receptor.

Dynamic and structural information has been obtained for an analogue of acetylcholine while bound to the agonist binding site on the nicotinic acetylcholine receptor (nAcChoR), using wide-line deuterium solid-state NMR. Analysis of the deuterium lineshape obtained at various temperatures from unoriented nAcChoR membranes labeled with deuterated bromoacetylcholine (BAC) showed that the quaternary ammonium group of the ligand is well constrained within the agonist binding site when compared with the dynamics observed in the crystalline solids. This motional restriction would suggest that a high degree of complementarity exists between the quaternary ammonium group of the ligand and the protein within the agonist binding site. nAcChoR membranes were uniaxially oriented by isopotential centrifugation as determined by phosphorous NMR of the membrane phospholipids. Analysis of the deuterium NMR lineshape of these oriented membranes enriched with the nAcChoR labeled with N(+)(CD(3))(3)-BAC has enabled us to determine that the angle formed between the quaternary ammonium group of the BAC and the membrane normal is 42 degrees in the desensitized form of the receptor. This measurement allows us to orient in part the bound ligand within the proposed receptor binding site.

Structural Analysis of the Protein/Lipid Complexes Associated with Pore Formation by the Bacterial Toxin Pneumolysin

Pneumolysin, a major virulence factor of the human pathogen Streptococcus pneumoniae, is a soluble protein that disrupts cholesterol-containing membranes of cells by forming ring-shaped oligomers. Magic angle spinning and wideline static (31)P NMR have been used in combination with freeze-fracture electron microscopy to investigate the effect of pneumolysin on fully hydrated model membranes containing cholesterol and phosphatidylcholine and dicetyl phosphate (10:10:1 molar ratio). NMR spectra show that the interaction of pneumolysin with cholesterol-containing liposomes results in the formation of a nonbilayer phospholipid phase and vesicle aggregation. The amount of the nonbilayer phase increases with increasing protein concentration. Freeze-fracture electron microscopy indicates the coexistence of aggregated vesicles and free ring-shaped structures in the presence of pneumolysin. On the basis of their size and analysis of the NMR spectra it is concluded that the rings are pneumolysin oligomers (containing 30-50 monomers) complexed with lipid (each with 840-1400 lipids). The lifetime of the phospholipid in either bilayer-associated complexes or free pneumolysin-lipid complexes is > 15 ms. It is further concluded that the effect of pneumolysin on lipid membranes is a complex combination of pore formation within the bilayer, extraction of lipid into free oligomeric complexes, aggregation and fusion of liposomes, and the destabilization of membranes leading to formation of small vesicles.

Interaction of the lantibiotic nisin with mixed lipid bilayers: a 31P and 2H NMR study.

Nisin is a positively charged antibacterial peptide which binds to the negatively charged membranes of Gram-positive bacteria. The initial interaction of the peptide with model membranes of neutral (phosphatidylcholine) and negatively charged (phosphatidylcholine/phosphatidylglycerol) model lipid membranes was studied using nonperturbing solid state magic angle spinning (MAS) (31)P NMR and (2)H wide-line NMR. In the presence of nisin, the coexistence of two bilayer lipid environments was observed both in charged and in neutral membranes. One lipid environment was found to be associated with lipid directly interacting with nisin and one with noninteracting lipid. Solid state (31)P MAS NMR results show that the acidic membrane lipid component partitions preferentially into the nisin-associated environment. Deuterium NMR ((2)H NMR) of the selectively headgroup-labeled acidic lipid provides further evidence of a strong interaction between the charged lipid component and the peptide. The segregation of acidic lipid into the nisin-bound environment was quantified from (2)H NMR measurements of selectively headgroup-deuterated neutral lipid. It is suggested that the observed lipid partitioning in the presence of nisin is driven, at least initially, by electrostatic interactions. (2)H NMR measurements from chain-perdeuterated neutral lipids indicate that nisin perturbs the hydrophobic region of both charged and neutral bilayers.

Molecular Relaxation and Local Motion of Hyperbranched Poly(ether ketone)s with Reference to Their Linear Counterpart. 1. Effect of Degrees of Branching

Three different fluoro-terminated hyperbranched poly(ether ketone)s (FHBPEKs) with variable degrees of branching and their linear analogous poly(ether ketone) (LPEK) whose chemical structure and molecular weight were similar to those of the FHBPEKs were synthesized. Cyano-terminated hyperbranched poly(ether ketone), CHBPEK, in which the terminal groups of FHBPEK were modified with cyanophenol was also prepared as a reference. The local relaxation and motion of the three FHBPEKs, in conjunction with their hyperbranched structure and the degrees of branching, were characterized by the solid-state 1H pulsed wide-line NMR spectroscopy and compared to that of the linear counterpart, LPEK. From the measurements of the spin−lattice relaxation times in the rotating frame, T1ρ's, over the temperature range 140−400 K, the correlation times, τc's, and the corresponding activation energies, Ea's, were determined, providing a direct evaluation for the local molecular motion. FHBPEKs were found to be structurally heterogeneous because they had two different motions throughout the system; with aid of the τc results of CHBPEK, each was assigned as originating from the linear and from the terminal/branched portion, respectively. In contrast, LPEK exhibited single relaxational and motional behavior, indicating that it was structurally homogeneous. The molecular mobility of the linear portion of FHBPEKs was higher than that of LPEK and enhanced with increasing degree of branching in the entire range of experimental temperatures. For the terminal/branched portion of the FHBPEKs, the local mobility was little affected by the degree of branching, especially at the temperature range from 140 K to room temperature, but increased afterward as was for the linear portion.

Solid-State Vanadium-51 NMR Studies of Supported V2O5−WO3/TiO2 Catalysts

Solid-state wide-line vanadium-51 NMR spectra of supported V2O5−WO3/TiO2 catalysts were obtained under ambient conditions. A distorted tetrahedral vanadium unit is favored at low vanadia loadings i...

Relationship between Viscoelastic Properties and Characteristics of Filler-Gel in Filled Rubber System

Abstract The wide-line NMR and viscoelastic measurements were carried out for the filled rubber systems. NMR results revealed that the filler-gel in the filled rubber composites had a multi-component system depending on the mobility of rubber molecules. The fraction and the spin-spin relaxation time of each component were well correlated with the viscoelastic properties such as dynamic storage modulus (E′) and loss-tangent (tan δ) of the filled rubber systems. Such findings turned out to be useful in designing new tread materials with well-balanced wet traction and rolling resistance in tires.

Characterization of the Interface in Polymer−Silica Composites Containing an Acrylic Silane Coupling Agent

Microscopic dynamics of the interfacial layer and macroscopic mechanical properties of [3-(acryloxy)propyl]trimethoxysilane (APMS) at a polymer−silica interface were studied using NMR and three-point bending tests. Wide-line deuterium NMR studies of deuterium-enriched [3-(acryloxy)propyl]trimethoxysilane-d (APMS-d), showed that when chemically bonded to silica, the acrylic group of APMS moved rapidly at the interface with air, more slowly when coated with a poly(methyl methacrylate) (PMMA) overlayer, and slowest when copolymerized with methyl methacrylate. A two-component line shape was found for the coated composite and these were assigned to relative immobile and mobile surface groups. From three-point bend tests, the PMMA/glass-fiber composite, made from glass laminates treated with APMS, had almost two times the flexural strength of a composite made from glass laminates not treated with APMS. Electron micrographs of the fracture surfaces revealed that the untreated fibers were smooth, while those from the APMS-treated glass were rougher, indicating the presence of polymer at the interface.

Characterization of V2O5−TiO2Catalysts Prepared by Milling by ESR and Solid State1H and51V NMR

The interaction between V2O5 and TiO2 under milling in a ball mill (an alternative procedure of catalyst preparation) was characterized by 1H, 51V MAS, and 51V static (wide line) NMR spectroscopy supplemented by simulations of 51V NMR spectra. Additionally, ESR and magnetic susceptibility measurements were carried out for the characterization of the paramagnetic V4+ and V3+ sites. It has been shown that after milling, two different types of octahedrally coordinated vanadium (V5+) species (V5+(I) and V5+(II)) strongly bonded to TiO2 are formed. At the same time, the appearance of V3+ ions and an increase of their concentration is observed during milling−calcination processes, along with the formation of at least three different types of paramagnetic V4+ species corresponding to (i) V4+ centers in O-deficient V2O5-x; (ii) VO2+ vanadyl species (V4+(I)) with the vanadium centers in octahedral symmetry with axial distortion; (iii) V4+(II) species with vanadium centers also in octahedral symmetry, but with diff...