Solid-state 2H NMR Spectroscopy Research Articles

Solid State NMR Characterisation of Encapsulated Molecules in Mesoporous Silica

Ibuprofen molecules have been encapsulated in mesoporous MCM-41 type-silica functionalised or not by amino groups. They have been characterised by 13C and 1H solid state NMR spectroscopy. The 13C MAS single pulse or cross polarization NMR spectra, as well as the 1H MAS NMR spectra demonstrate an extremely high mobility of the ibuprofen molecules when the matrix is not functionalised. On the contrary, when the silica matrix is functionalized by amino groups, the 13C NMR response shows less mobility suggesting the existence of interactions between the amino groups and the carboxylic groups. Benzoic acid as well as benzamide have also been encapsulated and their NMR responses compared to that of ibuprofen.

Solid-state NMR spectroscopic studies of an integral membrane protein inserted into aligned phospholipid bilayer nanotube arrays.

This communication demonstrates for the first time that solid-state NMR spectroscopic studies can be used to investigate aligned phospholipid bilayer nanotube arrays. Also, an integral membrane peptide can be successfully incorporated into the oriented phospholipid bilayer nanotube arrays and studied with 2H solid-state NMR spectroscopy.

Dependence of Thermal Properties on the Copolymer Sequence in Diacetylene-Containing Polycarboranylenesiloxanes

Diacetylene-containing polycarboranylenesiloxane copolymers were prepared by two different methods to yield either alternating or block copolymers with respect to the diacetylene distribution along the backbone. With each method, a set of copolymers was prepared with trisiloxane:carborane:diacetylene molar ratios of 10:9:1, 5:4:1, and 3:2:1. Both sets of copolymers yielded networks upon thermal curing. Even though the two methods produced materials of comparable molecular weights and overall compositions, the variation in the copolymer sequence caused noticeable differences in the calorimetric glass transitions for the copolymers in which the diacetylene group was most concentrated (i.e., the 3:2:1 and 5:4:1 copolymers). The copolymers were characterized by differential scanning calorimetry, thermogravimetric analysis, and 1H solid-state NMR spectroscopy.

Two-dimensional double-quantum 2H NMR spectroscopy in the solid state under OMAS conditions: correlating 2H chemical shifts with quasistatic line shapes.

Solid-state 2H NMR spectroscopy is a well-established and versatile method to study molecular orientation and dynamics in selectively deuterated samples. Herein, we introduce a 2D 2H double-quantum (DQ) NMR experiment performed under fast magic-angle spinning with a slight offset of the magic angle (OMAS). The experiment combines 2H chemical-shift resolution with DQ-filtered quasistatic 2H line shapes. In this way, it is possible to separate 2H resonances and to independently determine 2H quadrupole couplings at multiple sites. While 2H chemical shifts are resolved in the 2H DQ dimension, the quadrupole parameters can be obtained from characteristic line shapes which are reintroduced in the second dimension by the magic-angle offset. The 2D 2H DQ OMAS experiment is demonstrated on L-histidine which was deuterated at multiple sites by recrystallisation from D2O.

Characteristics of Water Adsorbed on TiO2 Photocatalytic Systems with Increasing Temperature as Studied by Solid-State 1H NMR Spectroscopy

The time profiles of the intensities, line widths, and chemical shifts of 1H NMR signals of adsorbed water at 358 K were investigated for six different TiO2 photocatalysts with different properties by solid-state 1H NMR spectroscopy. The apparent single water peak was found to comprise the signals with different line widths and chemical shifts, which correspond to those of the water molecules with different structures and mobility. The adsorbed water region observed with NMR is characterized by three layers: (I) the innermost layer with rigid water molecules with highly restricted mobility and/or hydroxyl groups on the solid surface; (II) the intermediate layer with relatively mobile water molecules; and (III) the outermost layer with highly mobile water molecules. The thickness of the water layer is almost the same for the six photocatalysts. The ratio of the number of the water molecules contained in each layer could be roughly estimated to be 3(I):2(II):5(III). The surface properties of the individual photocatalysts are distinctly reflected in the water molecules in layer I but not in those in layer III.

A simple method for the characterization of OHO-hydrogen bonds by 1H-solid state NMR spectroscopy

A set of OHO hydrogen bonded systems with known neutron diffraction structure has been studied by fast 1H-MAS echo spectroscopy. It is shown that the application of a simple rotor synchronized echo sequence combined with fast MAS allows a faithful determination of the chemical shift of the proton in the hydrogen bond. Employing the empirical valence bond order model, the experimental 1H chemical shifts of the hydrogen bonded protons are correlated to the hydrogen bond geometries. The resulting correlation between the proton chemical shift and the deviation of the proton from the center of the hydrogen bond covers a broad range of substances. Deviations from the correlation curve, which are observed in certain systems with strong hydrogen bonds, are explained in terms of proton tautomerism or delocalization in low-barrier hydrogen bonds. These deviations are a highly diagnostic tool to select potential candidates for further experimental and theoretical studies. Thus, the combination of the 1H-MAS echo sequence with the correlation curve yields a simple and versatile tool for the structural analysis of OHO hydrogen bonds.

Evaluation of Reactions of a Dilute Cross-Linker Using Solution Nuclear Magnetic Resonance Spectroscopy with Isotopically Labeled Cross-Linkers

Cross-linked poly(methyl methacrylate) (PMMA) was synthesized to high conversion with 0.02−0.5 wt % 13C- or 2H-labeled ethylene glycol dimethacrylate (EGDMA). Samples were analyzed with a variety of NMR techniques to examine different cross-linker reaction products (or architectures), i.e., pendant EGDMA methacrylates, cyclized EGDMA, and cross-linked EGDMA. Solid-state 13C NMR spectroscopy was not applicable because poor peak resolution masked the cross-linker architecture peaks. Solid-state 2H NMR spectroscopy of deuterium-labeled EGDMA was also not useful because the deuterium line shape was convoluted by signals from natural abundance deuterium in the polymer. Solution 13C NMR analysis of solvent swollen polymers (gel-state 13C NMR spectroscopy) produced well-resolved spectra of copolymers containing less than 0.5 wt % 13C-labeled EGDMA. These spectra confirm that significant amounts of EGDMA were singly reacted, resulting in large numbers of pendant methacrylate units. Non-cross-linked and completely soluble model PMMA copolymers containing 0.1 wt % 13C-labeled pendant EGDMA methacrylates units (incorporated in a postpolymerization reaction) were used to identify the 13C NMR signals characteristic of EGDMA pendant units. Signals from the stereochemical triads (syndio- and heterotactic) were identified, but specific peaks for nine-membered cyclic EGDMA units were not observed. The detection limit of gel-state 13C NMR analysis on these MMA/EGDMA copolymers was as low as 0.02 wt % 13C-labeled EGDMA, which demonstrates the utility of this approach for characterizing lightly cross-linked polymers.

Investigating fatty acids inserted into magnetically aligned phospholipid bilayers using EPR and solid-state NMR spectroscopy

This is the first time 2H solid-state NMR spectroscopy and spin-labeled EPR spectroscopy have been utilized to probe the structural orientation and dynamics of a stearic acid incorporated into magnetically aligned phospholipid bilayers or bicelles. The data gleaned from the two different techniques provide a more complete description of the bilayer membrane system. Both methods provided similar qualitative information on the phospholipid bilayer, high order, and low motion for the hydrocarbon segment close to the carboxyl groups of the stearic acid and less order and more rapid motion at the end towards the terminal methyl groups. However, the segmental order parameters differed markedly due to the different orientations that the nitroxide and C–D bond axes transform with the various stearic acid acyl chain conformations, and because of the difference in dynamic sensitivity between NMR and EPR over the timescales examined. 5-, 7-, 12-, and 16-doxylstearic acids spin-labels were used in the EPR experiments and stearic acid-d 35 was used in the solid-state NMR experiments. The influence of the addition of cholesterol and the variation of temperature on the fatty acid hydrocarbon chain ordering in the DMPC/DHPC phospholipid bilayers was also studied. Cholesterol increased the degree of ordering of the hydrocarbon chains. Conversely, as the temperature of the magnetically aligned phospholipid bilayers increased, the order parameters decreased due to the higher random motion of the acyl chain of the stearic acid. The results indicate that magnetically aligned phospholipid bilayers are an excellent model membrane system and can be used for both NMR and EPR studies.

Investigating Structural Changes in the Lipid Bilayer upon Insertion of the Transmembrane Domain of the Membrane-Bound Protein Phospholamban Utilizing 31P and 2H Solid-State NMR Spectroscopy

Phospholamban (PLB) is a 52-amino acid integral membrane protein that regulates the flow of Ca 2+ ions in cardiac muscle cells. In the present study, the transmembrane domain of PLB (24–52) was incorporated into phospholipid bilayers prepared from 1-palmitoyl-2-oleoyl- sn-glycero-phosphocholine (POPC). Solid-state 31P and 2H NMR experiments were carried out to study the behavior of POPC bilayers in the presence of the hydrophobic peptide PLB at temperatures ranging from 30°C to 60°C. The PLB peptide concentration varied from 0 mol % to 6 mol % with respect to POPC. Solid-state 31P NMR spectroscopy is a valuable technique to study the different phases formed by phospholipid membranes. 31P NMR results suggest that the transmembrane protein phospholamban is incorporated successfully into the bilayer and the effects are observed in the lipid lamellar phase. Simulations of the 31P NMR spectra were carried out to reveal the formation of different vesicle sizes upon PLB insertion. The bilayer vesicles fragmented into smaller sizes by increasing the concentration of PLB with respect to POPC. Finally, molecular order parameters ( S CD) were calculated by performing 2H solid-state NMR studies on deuterated POPC ( sn-1 chain) phospholipid bilayers when the PLB peptide was inserted into the membrane.

Solid-State NMR Studies of the Preparation of Si−Al−C−N Ceramics from Aluminum-Modified Polysilazanes and Polysilylcarbodiimides

Multinuclear (13C, 29Si, 27Al, 1H) solid-state NMR spectroscopy and EPR and FT IR experiments are employed to investigate the thermolysis of aluminum-modified poly(hydridovinylsilazane), [Al(C2H4−SiHNH)3]n, from which Si−Al−C−N ceramics can be formed. In addition, a comparative study is provided for different aluminum-modified polysilazanes and polysilylcarbodiimides in the amorphous state at 1400 °C. The investigation primarily aims at the structural characterization of the amorphous intermediates, where such spectroscopic techniques have demonstrated their particular suitability. It is shown that the transformation of the polymeric precursor to the (amorphous) preceramic network is completed at around 500 °C. At this temperature AlN domains, as well as Si−C−N clusters of mixed composition, are formed. Above this temperature a continuous transformation to the ceramic material takes place. In addition, above 700 °C a considerable amount of free carbon-centered radicals is detectable. Eventually, three mai...

Photochemistry and mobility of stilbenoid dendrimers in their neat phases.

Selectively deuterated, dodecyloxy substituted stilbenoid dendrimers of the first and second generation were synthesized by a convergent synthesis, using the Wittig-Horner reaction. The photochemistry and the fluorescence in the different crystalline and liquid crystalline phases were investigated. Molecules deuterated at the alpha-position of the alkoxy chains were used to study the photoreactions in the neat phases by 1H NMR. Reactions of the double bonds are exclusively observed in the liquid crystal phases. No photoreactions occur in the crystalline state. The mobility of the dendrimers was studied by means of 2H solid-state NMR spectroscopy. The onset of the photochemistry for dendrimer 1 [all-(E)-1,3,5-tris[2-(3,4,5-tridodecyloxyphenyl)ethenyl]benzene] corresponds to the increasing mobility at the Cr/LC transition. The first generation dendrimers still show large angle motion, whereas dendrimers of the second generation 2 [all-(E)-1,3,5-tris(2-[3,5-bis[2-(3,4,5-tridodecyloxyphenyl)ethenyl]phenyl]ethenyl)benzene] are restricted to librational motions. Photochemical conversion and fluorescence quenching for first and second generation dendrimers 1 and 2 increase with increasing molecular motion and reach a maximum in the isotropic phase.

Supramolecular assembly of dendritic polymers elucidated by 1H and 13C solid-state MAS NMR spectroscopy.

Advanced solid-state NMR methods under fast magic-angle spinning (MAS) are used to study the structure and dynamics of large supramolecular systems, which consist of a polymer backbone with dendritic side groups and self-assemble into a columnar structure. The NMR experiments are performed on as-synthesized samples, i.e., no isotopic enrichment is required. The analysis of (1)H NMR chemical-shift effects as well as dipolar (1)H-(1)H or (1)H-(13)C couplings provide site-specific insight into the local structure and the segmental dynamics, in particular, of phenyl rings and -CH(2)O- linking units within the dendrons. Relative changes of (1)H chemical shifts (of up to -3 ppm) serve as distance constraints and allow protons to be positioned relative to aromatic rings. Together with dipolar spinning sideband patterns, pi-pi packing phenomena and local order parameters (showing variations between 30% and 100%) are selectively and precisely determined, enabling the identification of the dendron cores as the structure-directing moieties within the supramolecular architecture. The study is carried out over a representative selection of systems which reflect characteristic differences, such as different polymer backbones, sizes of dendritic side groups, or length and flexibility of linking units. While the polymer backbone is found to have virtually no effect on the overall structure and properties, the systems are sensitively affected by changing the generation or the linkage of the dendrons. The results help to understand the self-assembly process of dendritic moieties and aid the chemical design of self-organizing molecular structures.

Solid-state 1H and 27Al NMR studies of amorphous aluminum hydroxides

Two kinds of amorphous aluminum hydroxides, a sample precipitated from admixing AlCl 3 and NaOH aqueous solutions and the commercial product, were measured by 27Al and 1H solid-state NMR spectroscopy. Pentahedral and tetrahedral coordinations, as well as octahedral coordination of oxygen atoms for aluminum, are observed in 27Al magic angle spinning (MAS) spectra of both amorphous samples. In contrast, octahedral coordination is only observed in gibbsite, bayerite, and boehmite. According to 1H MAS-NMR spectra under conditions of high spinning rate (35 kHz) and high field (14.09 T), free waters and OH groups coupled with aluminum for amorphous samples are observed at ∼5 and ∼4.5 ppm, respectively, the latter peak being broader. This is consistent with the differential spectra between spin echo and transfer of populations in double resonance. We conclude that the subunits of AlO 4, AlO 5, and AlO 6 in amorphous aluminum hydroxides are bound through hydrogen bonds with a wide distribution of bonding strength.

Magnetically aligned phospholipid bilayers in weak magnetic fields: optimization, mechanism, and advantages for X-band EPR studies

Our lab is developing a spin-labeled EPR spectroscopic technique complementary to solid-state NMR studies to study the structure, orientation, and dynamics of uniaxially aligned integral membrane proteins inserted into magnetically aligned discotic phospholipid bilayers, or bicelles. The focus of this study is to optimize and understand the mechanisms involved in the magnetic alignment process of bicelle disks in weak magnetic fields. Developing experimental conditions for optimized magnetic alignment of bicelles in low magnetic fields may prove useful to study the dynamics of membrane proteins and its interactions with lipids, drugs, steroids, signaling events, other proteins, etc. In weak magnetic fields, the magnetic alignment of Tm 3+-doped bicelle disks was thermodynamically and kinetically very sensitive to experimental conditions. Tm 3+-doped bicelles were magnetically aligned using the following optimized procedure: the temperature was slowly raised at a rate of 1.9 K/min from an initial temperature being between 298 and 307 K to a final temperature of 318 K in the presence of a static magnetic field of 6300 G. The spin probe 3β-doxyl-5α-cholestane (cholestane) was inserted into the bicelle disks and utilized to monitor bicelle alignment by analyzing the anisotropic hyperfine splitting for the corresponding EPR spectra. The phases of the bicelles were determined using solid-state 2H NMR spectroscopy and compared with the corresponding EPR spectra. Macroscopic alignment commenced in the liquid crystalline nematic phase (307 K), continued to increase upon slowly raising the temperature, and was well-aligned in the liquid crystalline lamellar smectic phase (318 K).

Photocatalytic Reaction Sites at the TiO2 Surface as Studied by Solid-State 1H NMR Spectroscopy

The adsorption and photodecomposition of ethanol that was employed as a model substrate of organic pollutants were investigated in the presence of adsorbed water with TiO2 by solid-state 1H NMR spectroscopy in order to obtain information about the actual photocatalytic reaction sites of organic pollutants on TiO2 photocatalysts. Consequently it was revealed that ethanol molecules in practical conditions as contaminants were firmly captured in mobile physisorbed water layers to be photodecomposed to CO2 and water after photoillumination, suggesting that actual photocatalytic reactions should proceed in physisorbed water layers.

High‐Temperature, High‐Pressure Hydrothermal Synthesis, Crystal Structure, and Solid State NMR Spectroscopy of a New Vanadium(IV) Silicate: Rb2(VO)(Si4O10)×xH2O.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel Gallium Phosphatooxalate with Pendant Oxalate Ligands: Preparation, Crystal Structure, NMR Spectroscopy, and Thermal Stability

A new gallium phosphatooxalate hybrid material, (C10H28N4)[Ga6(OH)2(PO4)2(HPO4)4(C2O4)3]·3.5H2O (1), has been synthesized under mild hydrothermal conditions (150 °C) in the presence of the amine 1,4-bis(3-aminopropyl)piperazine (APPIP) as a structure-directing agent. The compound was structurally characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and 1H, 2H, 13C, 31P, and 71Ga solid-state NMR spectroscopy. The structure of (1) consists of gallium phosphate double layers formed of GaO6 octahedra, GaO4 tetrahedra, and HPO4 and PO4 groups sharing corners. The double layers are cross-linked by oxalate ligands to form a three-dimensional framework with intersecting channels where the amine and water molecules are located. The oxalate units play a dual role as nonbridging mono-bidentate ligands with two terminal C−O groups pendant inside the channels and bis-bidentate ligands bridging the double layers. Crystal data are as follows: triclinic P1 (No. 2), a = 9.0220(7) A, b = 9.1864(...

Hydrogen Bond Dynamics in Solid Triphenylsilanol

Dynamic properties of the hydroxyl groups in a selectively deuterated polycrystalline sample of triphenylsilanol (Ph3SiOD) have been studied using variable-temperature solid-state 2H NMR spectroscopy. The crystal structure of triphenylsilanol contains eight crystallographically independent molecules, which are arranged in two tetrameric building units. Within each of these tetrameric units, the four silicon atoms are arranged in the form of a slightly distorted square, with the O atoms of the four hydroxyl groups involved in O−H···O hydrogen bonding. The temperature dependence of the quadrupole echo 2H NMR line shape in the temperature range 213−358 K and 2H NMR spin−lattice relaxation time measurements at 368 K demonstrate that the hydrogen-bonding arrangement is dynamic. From the 2H NMR line-shape analysis, the dynamic process is interpreted as interconversion between “clockwise” and “anticlockwise” hydrogen-bonding arrangements within each tetrameric unit, via a two-site jump motion of each hydroxyl de...

Structural characterization of nylon 4 in the solid state by high-resolution solid-state 1H NMR spectroscopy

High-resolution solid-state 1H NMR spectra of nylon 4 melt-quenched sample and single crystal sample in the solid state were measured in a wide range of temperatures from room temperature to 505K by using solid state 300MHz NMR with the FSLG-2 homo-nuclear dipolar decoupling method combined with high speed magic angle spinning method. From the experimental results, structural characterization on the crystalline and non-crystalline components was carried out. Further, intermolecular interaction between nylon 4 and water contained in the sample was discussed.

Proton NMR and Dynamic Studies of Hydrous Ruthenium Oxide

A series of hydrous ruthenium oxide (RuO2·xH2O) samples annealed at different temperatures have been studied by solid-state 1H NMR spectroscopy. The proton dynamics of the RuO2·xH2O samples was characterized for the first time through variable-temperature 1H spin−lattice relaxation time (T1) measurements. For the RuO2·xH2O samples annealed at temperatures lower than 100 °C and higher than 200 °C, a high proton activation energy was obtained, implying that the proton dynamics/diffusive motion is relatively restrained, whereas the samples annealed at temperatures between 100 and 200 °C exhibited relatively low proton activation energies, indicating that the protons can easily diffuse into the bulk of the material. Therefore, the proton activation energy correlates strongly with the hydrogen transfer and storage ability of the proton-conducting materials. In combination with electrochemical measurements, our NMR data also suggest that the coexistence of the Ru2+, Ru3+, and Ru4+ valency states in the local st...