Proton conducting ionic liquid organization as probed by NMR: self-diffusion coefficients and heteronuclear correlations

The structure and local organization of new proton conducting ionic liquids (PCILs) obtained by reacting alkylamine with various acids were deciphered by complementary 1- and 2-D heteronuclear NMR experiments. One the one hand, PFG NMR yielded the self-diffusion coefficients of the PCIL components (and thus information on their possible concerted translational motions), while on the other hand, 13C, 1H, and 15N, 1H correlation and intermolecular Overhauser experiments gave insight into the nature of protonic species and ion-pairing behavior.     

Dynamically corrected transition state theory calculations of self-diffusion in anisotropic nanoporous materials

We apply the dynamically corrected transition state theory to confinements with complex structures. This method is able to compute self-diffusion coefficients for adsorbate-adsorbent systems far beyond the time scales accessible to molecular dynamics. Two example cage/window-type confinements are examined: ethane in ERI- and CHA-type zeolites. In ERI-type zeolites, each hop in the z direction is preceded by a hop in xy direction and diffusion is anisotropic. The lattice for CHA-type zeolite is a rhombohedral Bravais lattice, and diffusion can be considered isotropic in practice. The anisotropic behavior of ERI-type cages reverses with loading, i.e., at low loading the diffusion in the z direction is two times faster than in the xy direction, while for higher loadings this changes to a z diffusivity that is more than two times slower. At low loading the diffusion is impeded by the eight-ring windows, i.e., the exits out of the cage to the next, but at higher loadings the barrier is formed by the center of the cages.     

NMR measurement of self-diffusion coefficients by slice selection

Most of the time, so-called inversion-recovery experiments concern longitudinal nuclear magnetization of the whole sample, the region of interest being limited by the transmitting-receiving coil. Here we address the question of what occurs if the region of interest is purposely limited to a thin slice selected by means of procedures employing magnetic field gradients. Gradients of both magnetic fields (B(0), the static magnetic field, and B(1), the radio-frequency magnetic field) can be used. In this study we resorted essentially to B(1) gradients and novel procedures, based on the natural inhomogeneity of the B(1) field delivered by a saddle coil, are described. It is obvious that molecules leaving and entering the slice during the evolution (recovery) period should influence the magnetization recovery. Molecular self-diffusion is responsible for such effects, experimentally visible and accounted for by an appropriate theory which has been approximated for by permitting an easy physical assessment. This approach should lead to alternative methods for measuring self-diffusion coefficients.     

Nondestructive evaluation of polymer materials by solid state NMR imaging

Many polymer products are heterogeneous. Examples of heterogeneities are the chemical composition, distributions of mechanical stress, and variations in flexibility or molecular orientation. Applications of NMR imaging to polymers are summarized and investigations of the aging of rubber are reported as well as novel deuteron NMR techniques to image molecular order and mobility of polymers below the glass transition temperature.     

The state of ruthenium in nitrite-nitrate nitric acid solutions as probed by NMR

The state of ruthenium in nitric acid solutions treated with sodium nitrite has been studied by ¹⁴N, ¹⁵N, ¹⁷O, and ⁹⁹Ru NMR. In the acidity range 2.7-0.12 mol/L, the dominating ruthenium species are the [RuNO(NO₂)₂(NO₃)(H₂O)₂]⁰ and [RuNO(NO₂)₂(H₂O)₃]⁺ complexes. When the acidity is decreased to 0.06 mol/L, trinitro-and tetranitronitrosoruthenium(II) complexes predominate in solution. In an acidic medium, the trinitro-and tetranitronitrosoruthenium(II) complexes exhibit catalytic activity toward oxidation with air of nitrite to nitrate.     

重质稠环芳烃的固体核磁共振光谱研究

以固体核磁共振光谱为主要分析手段,比较研究了两种合成中间相沥青吡啶不溶组分的结构。结果表明：均四甲苯基中间相沥青吡啶不溶组分具有较低的芳香度和缩合度,富含甲基和环烷结构,分子呈渺位结合实际合构型;与此相反,四氢萘基中间相沥青则呈现很高的芳香度和缩合度,芳环上仅带有一些甲基取代基,平均分子为完全迫位缩合构型,造成这种结构差异的原因在于前驱齐聚物的结构及缩聚程度的不同。     

Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid‐state 2H NMR Spectroscopy†

Solid‐state NMR spectroscopy gives a powerful avenue for investigating G protein‐coupled receptors and other integral membrane proteins in a native‐like environment. This article reviews the use of solid‐state ²H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site‐specific ²H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability ²H NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three‐fold (C₃) axes with an order parameter for the off‐axial motion of For the dark state, the ²H NMR structure of 11‐cis‐retinal manifests torsional twisting of both the polyene chain and the β‐ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11‐cis to trans isomerization. In addition, ²H NMR has been applied to study the retinylidene dynamics in the dark and light‐activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the β‐ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the β‐ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid‐state ²H NMR thus provides information about the flow of energy that triggers changes in hydrogen‐bonding networks and helix movements in the activation mechanism of the photoreceptor.     

Characterization of annealed isotactic polypropylene in the solid state by 2D time‐domain 1H NMR

Two‐dimensional time‐domain ¹H NMR was used to investigate annealed isotactic polypropylene in the solid phase. The spin–lattice relaxation in the laboratory frame and in the rotating frame were correlated with the shape of the free induction decay to identify and characterize relaxation components over the temperature range −120 to 120 °C. Several phase transitions were observed, and three distinct solid phases, with different chain mobilities, were detected. Two of these phases were identified as regions with different mobilities within the crystalline phase. The third phase was characterized by a high degree of isotropy in molecular motion. This phase, identified as the amorphous phase, appeared as the polymer was heated above a low‐temperature (−45 °C) phase transition. All transitions observed at higher temperatures occurred exclusively in this phase. About one‐third of the polymer chains reside between crystalline lamellae, whereas the majority form amorphous regions outside fibrils of multilamellar structure. Furthermore, the glass‐to‐rubber transition, occurring above −15 °C, consists of three stages. During the first stage, between −15 °C and 15 °C, regions with an increased segment mobility (labeled intermediate phase) appear gradually within the amorphous phase. At 15 °C, the intermediate phase consists of ∼10% of the polymer units, or one‐third of the polymer units constituting the amorphous phase. Between 15 °C and 25 °C, the intermediate phase increases rapidly to 18%. This is associated with the appearance of semiliquid and liquid regions, likely within the intermediate phase. Polymer chain segments (and possibly entire chains) involved in the liquidlike phases exhibit heterogeneous molecular motion with a correlation frequency higher than 10⁶ Hz. These two stages of glass‐to‐rubber transition occur within amorphous regions outside multilamellar structures. The third stage of the glass transition, appearing above 70 °C, is associated with the upper glass transition and occurs within the interlamellar amorphous phase. Finally, on a timescale of 100 ms or less, spin diffusion does not couple the amorphous regions outside fibrils with crystalline and amorphous regions within multilamellar fibrils. However, on a timescale of hundreds of milliseconds to seconds, all different regions within isotactic polypropylene are partially coupled. It is proposed that the relative magnitude of the crystalline magnetization, as observed in the T_1ρ experiment, is a good measure of polymer crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2487–2506, 2000     

NMR Studies on the structure of cellulose. 2-dimensional solid state NMR approach

Two-dimensional C-H correlation NMR spectra are presented for the native cellulose types Iα and Iβ from Cladophora sp. A remarkable difference of correlation peaks between Iα and Iβ was observed, which indicates an essential structure difference between the two types of native cellulose.     

Structure investigations of solid organosilicon polymers by high resolution solid state Si NMR

The high resolution ²⁹Si NMR spectra of five solid silicon polymers of different structure have been studied and the ²⁹Si chemical shifts of characteristic structure units determined. ²⁹Si---¹H cross-polarization in combination with high speed magic angle sample spinning and high power proton decoupling was used to achieve high resolution in the solid state spectra. Comparison of the latter with the results obtained in the liquid state clearly indicates that no special solid state effects on ²⁹Si chemical shifts arise and the relations between δ(Si) and the molecular structure, well known from investigations of liquids, can be used for interpretation of the solid state spectra. It is shown that high resolution solid state ²⁹Si NMR spectroscopy offers detailed information about the structural units of the siloxane resin framework, and this opens up new possibilities for structural determinations of solid organosilicon polymers.     

NMR line-width, self-diffusion and relaxation studies of neopentanol in liquid and solid phases

The translational and rotational dynamics of the liquid and disordered (solid I) phases of neopentanol are investigated using high-field multinuclear NMR. The extensive line-narrowing of the ¹H resonances for solid I is ascribed to the onset of translational diffusion whereas the line-narrowing of the deuteron and carbon-13 signals is dominated by molecular reorientations. The activation energy of the molecular self-diffusion is 34 and 71 kJ mol⁻¹ for the liquid and solid I phases, respectively. The self-diffusion coefficient of solid I is 3.2 × 10⁻¹³ m² s⁻¹ at the melting point.

A thorough analysis of the multinuclear T₁ data is presented. The activation energy of the overall tumbling motion in the liquid and solid I phases, obtained from the hydroxyl deuteron T₁ data, is 36 and 52 kJ mol⁻¹, respectively. The internal reorientations have a profound effect on the spin-lattice relaxation times of the methyl and methylene groups by reducing the effective correlation time by an order of magnitude relative to the overall tumbling motion in solid I. The long correlation time (22 and 58 ps of liquid and solid neopentanol at the melting point) and high activation energy suggest that the overall tumbling motion in the liquid and disordered phases involves hydrogen-bonded aggregates.     

Solid state analysis in mechanochemistry by high resolution 27Al solid state NMR spectroscopy

Modern solid state NMR techniques [one-dimensional magic angle spinning (MAS) and two-dimensional quadrupole nutation experiments with MAS] are applied for the characterization of mechanochemically activated inorganic powders such as hydrargillite [γ-Al(OH)₃] and pseudo-boehmite [synthetic γ-AlO(OH)]. The materials were activated in a vibration mill.     

Gas-induced solid state transformation of an organic lattice: from nonporous to nanoporous

A well-known organic host, tris-o-phenylenedioxycyclotriphosphazene, exists in two polymorphic guest-free forms: the thermodynamic nonporous high-density phase and the kinetic nanoporous low-density phase. Simple pressurization of the high density phase with CO(2) brings a solid-state transformation to the low density phase, resulting in significant expansion of the crystal volume by 23%.     

固体核磁共振研究分子筛的新进展

分子筛由于具有独特的孔道及可调控酸碱性等特征,被作为离子交换剂、吸附剂及催化剂而广泛应用于石油化工的各种催化过程中。固体核磁共振是研究分子筛结构、酸性及主客体相互作用的强有力谱学手段之一。简单概述了固体核磁共振研究分子筛的最近进展。     

A space group assignment of ZrP2O7 obtained by 31P solid state NMR

2-D 31P dipolar recoupling magic angle spinning NMR has been used to determine the true symmetry of the low temperature structure of ZrP2O7 for the first time.     

Lamellar thickness of crystallizable ethene runs in ethene-propene copolymers by solid state NMR

Crystallizable runs of ethene in ethene-propene copolymers can be identified in ¹³C CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a ¹H spin lock will reflect the intrinsic T^H_1ρ. Spin diffusion leads to a more complex relaxation decay, which reflects the local polymer morphology. Simulations of the spin diffusion process have been carried out for a simplified two-phase model for the morphology with the aim of determining whether the lamellar thickness of the crystalline and amorphous regions can be found from the T^H_1ρ observed via the ¹³C NMR spectrum. Calculations covering the expected range of the input parameters, namely the spin diffusion coefficients, domain lengths, and intrinsic relaxation times, show that, providing the intrinsic relaxation time in the amorphous phase is known, an accurate estimate of the crystalline and amorphous lamellar thicknesses can be made. Analysis of simulated T^H_1ρ decays indicate that, in general, the time constant of the fastest decaying component can be identified with the intrinsic relaxation time of the amorphous phase. © 1994 John Wiley & Sons, Inc.     

Helix change of polypeptides in the solid state as studied by NMR spectroscopy

The conformational characterization of solid polypeptides has been carried out by means of high-resolution solid-state NMR. It has been demonstrated that high-resolution solid-state NMR spectroscopy is a very useful means for elucidating the structure of polypeptides and proteins in the solid state.     

Characterization of dextrin hydrogels by FTIR spectroscopy and solid state NMR spectroscopy

Fourier transform infrared (FTIR) and ¹³C solid state nuclear magnetic resonance (NMR) spectroscopy were used to study dextrin structural changes occurring upon hydrogel formation by vinyl acrylate (VA) grafting and subsequent free radical polymerization. The degrees of VA substitution (DS) and polymerization (DP) were quantified up to 40%VA by FTIR intensity measurements and partial least squares (PLS)/FTIR, the latter being a faster and less error-prone method. Above 40%VA, both parameters are underestimated by FTIR. A spin counting NMR experiment showed high carbon observabilities for hydrogels and improved PLS/NMR models were achieved for DS and DP determination. Alternative NMR integration methods are hindered by the broad VA peaks and need for area correction, due to their CP dynamics. NMR changes in C1 profile showed that a single helical conformation predominates at lower %VA, being replaced by disordered conformations as %VA increases. Furthermore, a correlation FTIR/NMR study indicated that ring conformations are significantly affected in hydrogels, compared to unpolymerized dextrin.     

2H-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials

Solid state deuterium NMR has been used to study the molecular motion of d(6)-isobutyric acid (d(6)-iBA) in the pure (unconfined) state and confined in the cylindrical pores of two periodic mesoporous silica materials (MCM-41, pore size 3.3 nm and SBA-15, pore size 8 nm), and in a controlled pore glass (CPG-10-75, pore size ca. 10 nm). The line shape analysis of the spectra at different temperatures revealed three rotational states of the iBA molecules: liquid (fast anisotropic reorientation of the molecule), solid I (rotation of the methyl group) and solid II (no rotational motion on the time scale of the experiment). Transition temperatures between these states were determined from the temperature dependence of the fraction of molecules in these states. Whereas the solid I-solid II transition temperature is not affected by confinement, a significant lowering of the liquid-solid I transition temperature in the pores relative to the bulk acid was found for the three matrix materials, exhibiting an unusual dependence on pore size and pore morphology. Complementary DSC measurements on the same systems show that the rotational melting (solid I-liquid) of d(6)-iBA in the pores occurs at a temperature 20-45 K below the thermodynamic melting point. This finding indicated that the decoupling of rotational and translational degrees of freedom in phase transitions in confined systems previously found for benzene is not restricted to molecules with non-specific interactions, but represents a more general phenomenon.