State NMR Research Articles

Synthesis, dynamic properties and electrochemical stability of organic-inorganic hybrid polymer electrolytes with double core branched structures based on polyether, cyanuric chloride and alkoxysilane

A new organic-inorganic solid hybrid electrolyte based on 2,4,6-trichloro-1,3,5-triazine, triblock co-polymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether), poly(ethylene glycol) diglycidyl ether, and 3-(glycidyloxypropyl)trimethoxysilane doped with LiClO4 salt is synthesized by a sol-gel process. Fourier transform infrared spectroscopy and 13C NMR results reveal the successful synthesis of the organic-inorganic hybrid electrolyte. The conductivity of the hybrid electrolyte follows a VTF (Vogel-Tamman-Fulcher)-like behavior, implying that the diffusion of charge carriers is assisted by the segmental motions of polymer chains. The Li-ion mobility is determined from 7Li static NMR linewidth and diffusion coefficient measurements; both are correlated with their ionic conductivities. The maximum ionic conductivity of 9.5×10−5Scm−1 at 30°C is obtained for the hybrid electrolyte with the [O]/[Li] ratio of 32. The electrochemical stability window of 4V ensures the hybrid electrolyte as a potential candidate for low voltage lithium ion batteries.

Structure and solid-state NMR spectroscopy of the ternary pnictides Li3LaX 2 (X = P, As, Sb, Bi)

The ternary pnictides Li3LaX 2 (X = P, As, Sb, Bi) were synthesized by the reaction of the elements in sealed niobium ampoules in a resistance furnace. The new phase Li3LaAs2 was obtained for the first time and completes this pnictide series. The structure of Li3LaAs2 was investigated by X-ray diffraction on a single crystal: Li3LaSb2 type, $$P \bar{3}$$ m1, a = 435.68(6) pm, c = 710.8(1) pm, wR2 = 0.1033, 162 F 2 values, and ten variables. The structure is a filled derivative of the CaAl2Si2 type. The Li2 atoms have tetrahedral arsenic coordination. These Li2As4 tetrahedra are condensed via common edges forming layers in the ab plane which are separated by lanthanum atoms. The “filling” Li1 atoms are placed within the Li2-As polyanionic network. The chemical shift values of the 7Li solid-state MAS NMR spectra show that the lithium atoms are fully ionized and the compound can be described by the Zintl–Klemm concept as (3Li+)(La3+)(2As3−). The static 7Li solid-state NMR spectra show no lithium mobility.

Critical Behaviour in DOPC/DPPC/Cholesterol Mixtures: Static 2H NMR Line Shapes Near the Critical Point

Static 2H NMR spectroscopy is used to study the critical behavior of mixtures of 1,2-dioleoyl-phosphatidylcholine/1,2-dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol in molar proportion 37.5:37.5:25 using either chain perdeuterated DPPC-d62 or chain methyl deuterated DPPC-d6. The temperature dependence of the first moment of the 2H spectrum of the sample made with DPPC-d62 and of the quadrupolar splittings of the chain-methyl-labeled DPPC-d6 sample are directly related to the temperature dependence of the critical order parameter η, which scales as [(Tc−T)/Tc]βc near the critical temperature. Analysis of the data reveals that for the chain perdeuterated sample, the value of Tc is 301.51 ± 0.1 K, and that of the critical exponent, βc = 0.391 ± 0.02. The line shape analysis of the methyl labeled (d6) sample gives Tc = 303.74 ± 0.07 K and βc = 0.338 ± 0.009. These values obtained for βc are in good agreement with the predictions of a three-dimensional Ising model. The difference in critical temperature between the two samples having nominally the same molar composition arises because of the lowering of the phase transition temperature that occurs due to the perdeuteration of the DPPC.

15N chemical shift referencing in solid state NMR

Solid-state NMR spectroscopy has much advanced during the last decade and provides a multitude of data that can be used for high-resolution structure determination of biomolecules, polymers, inorganic compounds or macromolecules. In some cases the chemical shift referencing has become a limiting factor to the precision of the structure calculations and we have therefore evaluated a number of methods used in proton-decoupled 15N solid-state NMR spectroscopy. For 13C solid-state NMR spectroscopy adamantane is generally accepted as an external standard, but to calibrate the 15N chemical shift scale several standards are in use. As a consequence the published chemical shift values exhibit considerable differences (up to 22ppm). In this paper we report the 15N chemical shift of several commonly used references compounds in order to allow for comparison and recalibration of published data and future work. We show that 15NH4Cl in its powdered form (at 39.3ppm with respect to liquid NH3) is a suitable external reference as it produces narrow lines when compared to other reference compounds and at the same time allows for the set-up of cross-polarization NMR experiments. The compound is suitable to calibrate magic angle spinning and static NMR experiments. Finally the temperature variation of 15NH4Cl chemical shift is reported.

Electron Localization of Polyoxomolybdates with ε-Keggin Structure Studied by Solid-State 95Mo NMR and DFT Calculation

We report electron localization of polyoxomolybdates with ε-Keggin structure investigated by solid-state (95)Mo NMR and DFT calculation. The polyoxomolybdates studied are the basic ε-Keggin crystals of [Me3NH]6[H2Mo12O28(OH)12{MoO3}4] · 2H2O (1), the crystals suggested to have a disordered {ε-Mo12} core of [PMo12O36(OH)4{La(H2O)2.75Cl1.25}4]·27H2O (2), and the paramagnetic Keggin crystals of [H2Mo12O30(OH)10{Ni(H2O)3}4] · 14H2O (3). The spectra of (95)Mo static NMR of these samples were measured under moderate (9.4 and 11.7 T) and ultrahigh magnetic fields (21.8 T). From spectral simulation and quantum chemical calculation, the NMR parameters of the chemical shift and quadrupole interactions for (95)Mo were estimated. By the analysis based on the result for 1, it was found for 2 that although the {ε-Mo12} core is disordered, the eight d(1) electrons in it are not completely localized on four Mo-Mo bonds. Furthermore, it was shown for 3 that the d(1) electrons are localized to make the Mo-Mo bonds, while the unpaired electrons are also almost localized on the paramagnetic Ni(II) ions.

Study of phase transition mechanisms in [N(CH3)4]2ZnCl4 by static NMR and MAS NMR

The temperature dependences of chemical shifts, intensities, the spin-lattice relaxation time in laboratory frame T1, and in rotating frame T1ρ were measured for 1H and 13C in [N(CH3)4]2ZnCl4 by single-crystal NMR and MAS NMR. The unit cell in phase I contains two chemically inequivalent types of N(CH3)4 ions. However, the two chemically different ions N(CH3)4 cannot be practically identified from the 13C NMR spectrum. The structural changes for 1H and 13C were measured near Ti and TC4. The existence of chemically equivalent N(CH3)4 ions in phase I and the existence of the ferroelastic characteristic of the N(CH3)4 ions in phases IV and V are discussed.

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds

Two hexanuclear niobium halide cluster compounds with a [Nb6X12]2+ (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable Bo field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of 95Mo nuclei in structurally related compounds containing [Mo6Br8]4+ cluster cores. Experimentally determined δiso(93Nb) values are in the range from 2400 to 3000ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (Vzz and δ33) coinciding with the molecular four-fold axis of the [Nb6X12]2+ unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (Vzz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (Vyy) and the largest CS principal axis (δ11) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by 79/81Br NQR and 35Cl solid-state NMR measurements.

Bicelles Exhibiting Magnetic Alignment for a Broader Range of Temperatures: A Solid-State NMR Study

Bicelles are increasingly used as model membranes to suitably mimic the biological cell membrane for biophysical and biochemical studies by a variety of techniques including NMR and X-ray crystallography. Recent NMR studies have successfully utilized bicelles for atomic-resolution structural and dynamic studies of antimicrobial peptides, amyloid peptides, and membrane-bound proteins. Though bicelles composed with several different types of lipids and detergents have been reported, the NMR requirement of magnetic alignment of bicelles limits the temperature range in which they can be used and subsequently their composition. Because of this restriction, low-temperature experiments desirable for heat-sensitive membrane proteins have not been conducted because bicelles could not be aligned. In this study, we characterize the magnetic alignment of bicelles with various compositions for a broad range of temperatures using (31)P static NMR spectroscopy in search of temperature-resistant bicelles. Our systematic investigation identified a temperature range of magnetic alignment for bicelles composed of 4:1 DLPC:DHexPC, 4:1:0.2 DLPC:DHexPC:cholesterol, 4:1:0.13 DLPC:DHexPC:CTAB, 4:1:0.13:0.2 DLPC:DHexPC:CTAB:cholesterol, and 4:1:0.4 DLPC:DHexPC:cholesterol-3-sulfate. The amount of cholesterol-3-sulfate used was based on mole percent and was varied in order to determine the optimal amount. Our results indicate that the presence of 75 wt % or more water is essential to achieve maximum magnetic alignment, while the presence of cholesterol and cholesterol-3-sulfate stabilizes the alignment at extreme temperatures and the positively charged CTAB avoids the mixing of bicelles. We believe that the use of magnetically aligned 4:1:0.4 DLPC:DHexPC:cholesterol-3-sulfate bicelles at as low as -15 °C would pave avenues to study the structure, dynamics, and membrane orientation of heat-sensitive proteins such as cytochrome P450 and could also be useful to investigate protein-protein interactions in a membrane environment.

Crystal engineering the clathrate hydrate lattice with NH4F

There have been very few attempts to apply crystal engineering approaches to modify the clathrate lattice with the aim of modifying structure and properties. To this end, solutions of ammonium fluoride in water were used to prepare clathrate hydrates with ammonium fluoride replacing water molecules in the hydrate lattice. Both modified structure I Xe and structure II tetrahydrofuran/Xe hydrates were prepared, with the hydrate lattices consisting of NH4F-water solid solutions containing up to ~19 and 25 mole% NH4F, respectively. The lattice constants for both hydrates decreased with increase of the amount of NH4F incorporated, and guest positions and cage occupancies were determined from the PXRD patterns with direct space methods and Rietveld analysis. The 129Xe NMR spectra for Xe in the small cavities of each hydrate showed NH4F concentration-dependent fine structure, not evident in the pure water clathrates, and characteristic of the presence of cage configurations with different distributions of ions. Analysis of the spectra along with density functional theory calculations of the chemical shifts allowed reasonable assignments to be made of the ion distribution. As a test of the altered function of the clathrate upon modification, a clathrate of methanol was prepared, something which has not been possible to do with a pure water clathrate. Structural analysis of the PXRD pattern by direct space methods showed that the methanol OH was hydrogen-bonded to one or both of the NH4+ and F− ions in the lattice, a conclusion corroborated by the absence of molecular motion (except for methyl group rotation) of the methanol guest in the clathrate cages, as determined by static 2H NMR and molecular dynamics simulations. The stability of the modified methanol clathrate can be attributed to the strong methanol CH3OH⋯F− or CH3OH⋯NH4+ hydrogen bonding which leaves the water–water hydrogen bonding network intact, as opposed to the situation in a pure water clathrate where the methanol–water hydrogen bonding disrupts the lattice and a stable clathrate cannot be made.

Dynamics in the Transmembrane Segment of the Influenza a M2 Proton Channel

Influenza A virus, responsible for the flu, infects respiratory tract epithelial cells. M2 is a tetrameric proton channel essential for the virus life cycle. The antiviral drug amantadine (Amt) used to block M2 channel prior to the recent S31N mutation. With the known backbone structure of the M2 transmembrane (TM) domain, polypeptide backbone and side chains dynamics can be characterized.Peptides corresponding to M2TM wild-type (M2TM) and M2TM S31N (S31N_TM) domains were chemically synthesized. M2TM peptides were labeled at: d4-Ala29/15N-Ile42, or d8-Val27/15N-Ala29, or d2-Gly34/15N2-Trp41, or d5-Trp41/15N-Ile39. An S31N_TM peptide was labeled at d8-Val27/15N-Ala29. 2H and 15N static NMR spectra of the peptides reconstituted in DOPC:DOPE bilayer at pH 7.5 were acquired.Analysis of the spectra of M2TM(d4-Ala29) at various temperature and echo times indicates that above the phase transition temperature of the lipids M2TM channel is undergoing rotation motion about the bilayer normal and channel axis on the ms time scale. The spectra of M2TM(d4-Ala29 and d8-Val27) in the absence and presence of Amt indicate that drug binding doesn't affect spectral line shape and is proposed to have no significant influence on backbone and side chain dynamics of these sites. The S31N mutation lead to narrowing of the spectrum of S31N_TM(d8-Val27) in comparison to M2TM(d8-Val27). This mutation was reported to increase the splay between helices which could lead to a less tight packing of Val27 side chains and an increase of side chain dynamics. The collapsed 2H powder patterns of M2TM(d2-Gly34 and d5-Trp41) at 288 K indicates that both sites are undergoing motions on µs/ms time scale. Moreover, at 297 K the collapsed powder pattern of 15Ne-Trp41 indicates that the indole ring is undergoing large amplitude motions, possibly about χ1 and χ2.

The biaxial nematic phase of oxadiazole biphenol mesogens

Herein we review the attributes of the cluster biaxial nematic exhibited by bent-core mesogens derived from the oxadiazole biphenol mesogenic core. We present an array of static 2H NMR spectra as well as 2D powder spectra generated by rotating the nematic phase of directly labelled mesogens. Analysis of these motionally averaged NMR observations requires the nematic phase to have monoclinic symmetry. X-ray diffraction data, in particular the effects of electric and magnetic field effects, are also consonant with the cluster picture of this biaxial nematic phase.

ChemInform Abstract: From Molecular Complexes to Complex Metallic Nanostructures ‐ 2H Solid‐State NMR Studies of Ruthenium‐Containing Hydrogenation Catalysts

In the last years, the combination of (2)H solid-state NMR techniques with quantum-chemical calculations has evolved into a powerful spectroscopic tool for the characterization of the state of hydrogen on the surfaces of heterogeneous catalysts. In the present minireview, a brief summary of this development is given, in which investigations of the structure and dynamics of hydrogen in molecular complexes, clusters and nanoparticle systems are presented, aimed to understand the reaction mechanisms on the surface of hydrogenation catalysts. The surface state of deuterium/hydrogen is analyzed employing a combination of variable-temperature (2)H static and magic-angle spinning (MAS) solid-state NMR techniques, in which the dominant quadrupolar interactions of deuterium give information on the binding situation and local symmetry of deuterium/hydrogen on molecular species. Using a correlation database from molecular complexes and clusters, the possibility to distinguish between terminal Ru-D, bridged Ru2-D, three-fold Ru3-D, and interstitial Ru6-D is demonstrated. Combining these results with quantum-chemical density functional theory (DFT) calculations allows the interpretation of (2)H solid-state data of complex real world nanostructures, which yielded new insights into reaction pathways at the molecular level.

Structure of 1,5-benzodiazepinones in the solid state and in solution: Effect of the fluorination in the six-membered ring

Two novel tetrafluorinated 1,5-benzodiazepinones were synthesized and their X-ray structures determined. 6,7,8,9-Tetrafluoro-4-methyl-1,3-dihydro-2H-1,5-benzodiazepin-2-one crystallizes in the monoclinic P21/c space group and 6,7,8,9-tetrafluoro-1,4-dimethyl-1,3-dihydro-2H-1,5-benzodiazepin-2-one in the triclinic P−1 space group. Density functional theory studies at the B3LYP/6-311++G(d,p) level were carried out on these compounds and on four non-fluorinated derivatives, allowing to calculate geometries, tautomeric energies and ring-inversion barriers, that were compared with the experimental results obtained by static and dynamic NMR in solution and in solid state.

1H and 13C MAS NMR analysis for the role of chemically inequivalent a-N(CH3)4 and b-N(CH3)4 ions in [N(CH3)4]2CuCl4

The spin–lattice relaxation times in the laboratory frame, T1, and in the rotating frame, T1ρ, for 1H and 13C in [N(CH3)4]2CuCl4 were measured by static NMR and magic angle spinning (MAS) NMR as functions of temperature. The intensities of the 1H and 13C signals changed near phase transition temperatures TC1 and TC3, which indicated that N(CH3)4 plays an important role in these phase transitions. It was thus apparent that the T1 and T1ρ for 1H are governed by the same molecular motions. Two inequivalent ions, a-N(CH3)4 and b-N(CH3)4, were identified by 13C cross-polarization (CP)/MAS NMR. From these results, the behaviors of these two chemically inequivalent N(CH3)4 groups in the paraelastic and ferroelastic phases are discussed.

Determination of structural topology of a membrane protein in lipid bilayers using polarization optimized experiments (POE) for static and MAS solid state NMR spectroscopy.

The low sensitivity inherent to both the static and magic angle spinning techniques of solid-state NMR (ssNMR) spectroscopy has thus far limited the routine application of multidimensional experiments to determine the structure of membrane proteins in lipid bilayers. Here, we demonstrate the advantage of using a recently developed class of experiments, polarization optimized experiments, for both static and MAS spectroscopy to achieve higher sensitivity and substantial time-savings for 2D and 3D experiments. We used sarcolipin, a single pass membrane protein, reconstituted in oriented bicelles (for oriented ssNMR) and multilamellar vesicles (for MAS ssNMR) as a benchmark. The restraints derived by these experiments are then combined into a hybrid energy function to allow simultaneous determination of structure and topology. The resulting structural ensemble converged to a helical conformation with a backbone RMSD ~0.44 Å, a tilt angle of 24° ± 1°, and an azimuthal angle of 55° ± 6°. This work represents a crucial first step toward obtaining high-resolution structures of large membrane proteins using combined multidimensional oriented solid-state NMR and magic angle spinning solid-state NMR.

T2 distribution spectra obtained by continuum fitting method using a mixed Gaussian and exponential kernel function

Static 1H NMR Free Induction Decay (FID) signals of polymer solids contain a lot of information about the molecular dynamics. A T2 analysis of the FID has generally been performed in terms of discrete two- or three-component models. However, this requires a priori assumption of the number of proton species before analysis. This paper presents a method of analyzing the FIDs of the polymer solid samples in terms of a continuous T2 distribution. A mixed Gaussian and Exponential kernel function was used to represent the true characteristic of FIDs of the polymer solids. A simple and realistic assumption has been made to reduce the number of degrees of freedom in the continuum fitting and to make the fitting stable. An experimental static 1H NMR FID of a typical polymer solid sample was analyzed as an example in the end to demonstrate the application of this method.

A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

A series of transition-metal organometallic complexes with commonly occurring metal-chlorine bonding motifs were characterized using (35)Cl solid-state NMR (SSNMR) spectroscopy, (35)Cl nuclear quadrupole resonance (NQR) spectroscopy, and first-principles density functional theory (DFT) calculations of NMR interaction tensors. Static (35)Cl ultra-wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST-QCPMG pulse sequence. The (35)Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. (35)Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of (35)Cl SSNMR spectra. (35)Cl EFG tensors obtained from first-principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a (35)Cl SSNMR spectrum of a transition-metal species (TiCl4) diluted and supported on non-porous silica is presented. The combination of (35)Cl SSNMR and (35)Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine-containing transition-metal complexes, in pure, impure bulk and supported forms.

Synthesis, structure and electrochemical characterization, and dynamic properties of double core branched organic–inorganic hybrid electrolyte membranes

Organic–inorganic hybrid electrolyte membranes based on the reaction of tri-block copolymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether), 3-isocyanatepropyltriethoxysilane and central core 2,4,6-trichloro-1,3,5-triazine doped with LiClO4 were synthesized by a sol–gel process to obtain a double core branched structure. The structural and dynamic properties of the materials thus obtained were systematically investigated by a variety of techniques including alternate current impedance, Fourier transform infrared spectroscopy, differential scanning calorimetry, multinuclear solid-state NMR and 7Li diffusion coefficient measurements. A VTF (Vogel–Tamman–Fulcher)-like temperature dependence of ionic conductivity was observed for solid hybrid electrolyte membranes, implying that the diffusion of charge carriers was assisted by the segmental motions of the polymer chains. The Li-ion mobility was determined from 7Li static NMR linewidth and diffusion coefficient measurements and correlated with their ionic conductivities. A maximum ionic conductivity of 6.2×10−5Scm−1 was obtained at 30°C for the solid hybrid electrolyte membrane with a [O]/[Li] ratio of 32. After swelled in electrolyte solvent, the plasticized hybrid membrane exhibited a maximum ionic conductivity of 7.2×10−3Scm−1 at 30°C. The good value of electrochemical stability window (~5V) makes the plasticized hybrid electrolyte membrane promising for lithium-polymer battery applications.

Optimizing the Kinetics and Thermodynamics of DNA i‐Motif Folding

Under slightly acidic conditions, single cytidine-rich DNA strands can form four-stranded structures called i-motifs. The stability of the i-motif structure is based on the intercalation of hemiprotonated C-C(+) base pairs. In addition, the stability of these structures is influenced by pH, temperature, salt concentration, number of cytidines per C-rich stretch, and length of sequence; it also depends on the nucleotides in the connecting loop regions. Here, we investigated the influence of the loop nucleotides on i-motif stability, structure, and kinetics of folding, in five structures with the same loop-size but different adenosine and thymidine residues within the loop. The stabilities of the i-motif structures were determined by CD melting, and structure and kinetics of folding were studied by static and time-resolved NMR experiments.

From Molecular Complexes to Complex Metallic Nanostructures—2H Solid‐State NMR Studies of Ruthenium‐Containing Hydrogenation Catalysts

In the last years, the combination of (2)H solid-state NMR techniques with quantum-chemical calculations has evolved into a powerful spectroscopic tool for the characterization of the state of hydrogen on the surfaces of heterogeneous catalysts. In the present minireview, a brief summary of this development is given, in which investigations of the structure and dynamics of hydrogen in molecular complexes, clusters and nanoparticle systems are presented, aimed to understand the reaction mechanisms on the surface of hydrogenation catalysts. The surface state of deuterium/hydrogen is analyzed employing a combination of variable-temperature (2)H static and magic-angle spinning (MAS) solid-state NMR techniques, in which the dominant quadrupolar interactions of deuterium give information on the binding situation and local symmetry of deuterium/hydrogen on molecular species. Using a correlation database from molecular complexes and clusters, the possibility to distinguish between terminal Ru-D, bridged Ru2-D, three-fold Ru3-D, and interstitial Ru6-D is demonstrated. Combining these results with quantum-chemical density functional theory (DFT) calculations allows the interpretation of (2)H solid-state data of complex "real world" nanostructures, which yielded new insights into reaction pathways at the molecular level.