High-resolution Solid-state NMR Spectroscopy Research Articles

Effect of chemical compositional distribution on solid-state structures and properties of poly(3-hydroxybutyrate- co-3-hydroxyvalerate)

Solid-state structures and crystallization kinetics were compared between poly(3-hydroxybutyrate- co-3-hydroxyvalerate) [PHB-HV] and PHB/PHB-HV blends exhibiting the cocrystallization. As cocrystallizable blends, both the blends showing complete cocrystallization, i.e. the PHB content in the crystalline phase is the same as that of the whole blends, and the blends forming a PHB-rich crystalline phase were used. The PHB and HV content in the cocrystalline phase were determined by high-resolution solid-state 13C NMR spectroscopy. In order to determine these contents with a minimum experimental error, site-specific 13C-labeled PHB/PHB-HV blends and PHB-HV copolymers were used. The crystallinity, lamellar structures, spherulite growth rate, and melting behavior were analyzed by wide-angle X-ray diffraction, small-angle X-ray scattering, polarized microscope, and differential scanning calorimetry, respectively. In these data, no difference was observed between the complete-cocrystallizable PHB/PHB-HV blends and the PHB-HV copolymers with the same overall HV content. On the other hand, the PHB/PHB-HV blends forming a PHB-rich crystalline phase has the amorphous layers thicker than that of the PHB-HV copolymers with the same overall HV content. Based on the collected data, the similarity and differences in the solid-state structures and properties between PHB-HV copolymers and cocrystallizable PHB/PHB-HV blends were discussed.

Biexponential 13C spin–lattice relaxation behavior of the crystalline region of ethylene copolymers and its origin

In this work, two series of ethylene–dimethylaminoethylmethacrylate (EDAM) and ethylene–methyl acrylate copolymers (EMA) with different comonomer content were studied by high-resolution solid-state 13C NMR spectroscopy. Biexponential 13C spin–lattice relaxation behaviors of the crystalline region were observed for all copolymer samples either melt-quenched or isothermally crystallized. The relative content of the shorter 13C T 1 component to that of the longer 13C T 1 component was found to increase with comonomer content. By employing a new pulse sequence which can be considered as a combination of Goldman–Shen's and Torchia's pulse sequences, it was demonstrated that the shorter 13C T 1 component is corresponding to the intermediate part of the crystalline region. The thickness of the intermediate part is estimated to be about 0.85 nm.

Interactions between fullerene(C 60) and poly(ethylene oxide) in their complexes as revealed by high-resolution solid-state 13C NMR spectroscopy

A series of poly(ethylene oxide) (PEO)/fullerene(C 60) complexes are prepared by lyophilization. The intermolecular interaction and molecular motion in the complex are investigated by solid-state 13C NMR spectroscopy. An intense C 60 signal due to the intermolecular cross-polarization is observed in the 13C CP/MAS spectra of the complex samples, indicating a high degree of dispersion of C 60s in the complexes. By measuring the 13C spin-lattice relaxation times and 1H transverse relaxation times of the complex sample and by comparing the static 13C spectrum of the pure C 60 sample with that of the complex sample, it is demonstrated that there exist n–π interactions between the n-orbitals of the PEO ether oxygen and the π-system of C 60. The C 60 molecules act as physical cross-links in the amorphous region of PEO, which greatly inhibit the mobility of the surrounding PEO chains, while the rapid isotropic rotation of C 60 molecules is also reduced to some extent due to the interactions with the polymer chains.

A new approach in 1D and 2D 13C high-resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning.

Novel 1D and multidimensional solid-state NMR (SSNMR) methods using very fast magic-angle spinning (VFMAS) (spinning speed > 20 kHz) for performing 13C high-resolution SSNMR of paramagnetic organometallic complexes are discussed. VFMAS removes a majority of 13C-1H and 1H-1H dipolar couplings, which are often difficult to remove by RF pulse techniques in paramagnetic complexes because of large paramagnetic shifts. In the first systematic approach using the unique feature of VFMAS for paramagnetic complexes, we demonstrate a means of obtaining well-resolved 1D and multidimensional 13C SSNMR spectra, sensitivity enhancements via cross polarization, and signal assignments, and applications of dipolar recoupling methods for nonlabeled paramagnetic organometallic complexes of moderate paramagnetic shifts ( approximately 800 ppm). Experimental results for powder samples of small nonlabeled coordination complexes at 1H frequencies of 400.2-400.3 MHz show that highly resolved 13C SSNMR spectra can be obtained under VFMAS, without requirements of 1H decoupling. Sensitivity enhancement in 13C SSNMR via cross polarization from 1H spins was demonstrated with an amplitude-sweep high-power CP sequence using strong RF fields ( approximately 100 kHz) available in the VFMAS probe. 13C CPMAS spectra of nonlabeled Cu(II)(dl-alanine)2.(H2O) and V(III)(acetylacetonate)3 (V(acac)3) show that it is possible to obtain high-resolution spectra for a small quantity ( approximately 15 mg) of nonlabeled paramagnetic organometal complexes within a few minutes under VFMAS. Experiments on Cu(II)(dl-alanine)2.(H2O) demonstrated that 1H-13C dipolar recoupling for paramagnetic organometal complexes can be performed under VFMAS by application of rotor-synchronous pi-pulses to 1H and 13C spins. The results also showed that signal assignments for 13CH, 13CH3, and 13CO groups in paramagnetic complexes are possible on the basis of the amount of 13C-1H dipolar dephasing induced by dipolar recoupling. Furthermore, the experimental 2D 13C/1H chemical-shift correlation NMR spectrum obtained for nonlabeled V(acac)3 exhibits well-resolved lines, which overlap in 1D 13C and 1H spectra. Signals for different chemical groups in the 2D spectrum are distinguished by the 13C-1H dipolar dephasing method combined with the 2D 13C/1H correlation NMR. The assignments offer information on the existence of nonequivalent ligands in the coordination complex in solids, without requiring a single-crystal sample.

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.

Chain Dynamics, Conformations, and Phase Transformations for Form III Polymorph of Isotactic Poly(1-butene) Investigated by High-Resolution Solid-State13C NMR Spectroscopy and Molecular Mechanics Calculations

High-resolution solid-state 13C NMR spectroscopy and MM3 molecular mechanics calculations have been applied to investigate side-chain conformations, side- and main-chain dynamics, and phase transformations of the form III polymorph of isotactic-poly(1-butene) (i-PB). MM3 calculations indicate that the t−g‘ side-chain conformation is much more stable than the g‘−g and g−t side-chain conformations in the crystal lattices of form III. The 13C cross-polarization magic-angle spinning (CPMAS) NMR spectrum at 199 K shows that the methyl group in the side chain adopts only the t−g‘ conformation. Upfield shift for the 13C methyl signal above 338 K indicates dynamic disorder in the side-chain conformations. The 13C two-dimensional exchange NMR reveals that the polymer chains in form III consist of two components. The 74% polymer chains execute the 90° helical jump motion with an activation energy of 79.3 ± 5.6 kJ/mol, while the residual chains are immobile. It is found that the 90° helical jump motion begins to occur at the temperature very close to the glass-transition temperature (Tg). Upfield shifts for the 13C main-chain signals at 338 K indicate the motional mode change from the 90° helical jump motion to “more or less” rotational or jump motion with different angle displacements. Above 338 K, two phase transformations from form III to forms II and I‘ are confirmed in the 13C CPMAS spectra. The 1H spin−lattice relaxation times in the rotating frame show that the transformation from form III to form I‘ proceeds within the form III phase via the crystal-to-crystal process, whereas the line-shape analyses of the 13C direct-polarization magic-angle spinning (DPMAS) NMR spectra indicate that the transformation from form III to form II proceeds via the quasi-melting/recrystallization process. The frozen chain conformations in the amorphous phase below Tg are also investigated on the basis of the 13C chemical shifts. It is suggested that most of the main chains adopt the helical (tg‘)n conformation, and the residual part adopts the (tt) conformation.

New Opportunities for High-Resolution Solid-State NMR Spectroscopy of Oxide Materials at 21.1- and 18.8-T Fields

We present here high-resolution solid state NMR spectra of several oxide and silicate materials that illustrate the improvements obtainable with very high external fields (18.8 and 21.1 T), with probes capable of tuning to a wide frequency range that allow observations of nuclides from high to low magnetogyric ratio. We discuss 27Al MAS spectra for the zeolite scolecite (CaAl2Si3O10·3H2O), 17O MAS data for analcime (NaAlSi2O6·H2O), calcium monoaluminate (CaAl2O4), and titanite (CaTiSiO5), 39K spin–echo spectra for leucite (KAlSi2O6), microline (KAlSi3O8), muscovite (KAl2(AlSi3O10)(OH2) and a potassium aluminosolicate glass, and preliminary 73Ge spin–echo MAS spectra for crystalline and glassy germanium dioxide (GeO2).

Mineralization followup with the use of NMR spectroscopy and others.

High-resolution solid state NMR spectroscopy appears to be a powerful method for a better understanding of bone structures and bone substitutes and implants. It is particularly efficient to estimate osteoformation via bioceramic bone colonization. Pathological calcification occurring in bioprosthetic heart valves and breast prostheses can be characterized as a complement to X-ray spectrometry.

Thermal decomposition chemistry of starch studied by 13C high-resolution solid-state NMR spectroscopy

The chemical structure and thermal reaction pathway of four native and modified starch samples after being heated up to 600 °C have been examined by 13C high-resolution solid-state NMR spectroscopy. Chemical reactions for the samples started around 300 °C to generate ether and ethylene segments via thermal condensation and dehydration mechanisms. Heating at increased temperatures generated substituted phenol/benzene and furan structures with methylene or ether linkages between these aromatic rings. Varied thermal reactivity was observed for starch samples around 300 °C due to their difference in molecular weight, pH or structural modification. However, the reaction pathway was similar. Above 400 °C, the starch structure was destroyed and the product appeared structurally similar to thermally cross-linked/decomposed phenolic/furfuryl alcohol resins, thereafter, the thermal reaction of the systems followed a similar pathway as these resins. No significant difference of chemical structures was obtained for the four samples after heating above 350 °C and identical carbon structures were generated at 600 °C.

Structural Transition of Lamella Crystals in a Isomorphous Copolymer, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The structure of the isomorphous crystals of P(HB-co-HV) in the PHB crystalline lattice is examined in detail, and a structural transition at ca. 10 mol % HV is found for the first time. By analyzing a series of P(HB-co-HV) samples prepared by the same treatment, the effect of the thermal history was removed from the results, and the composition dependence of the crystal formation and of the resultant crystalline structure was highlighted. The crystallinity, unit cell dimensions, and lamella thickness of P(HB-co-HV) were determined by X-ray analysis. The HV content in the crystalline phase was determined by high-resolution solid-state 13C NMR spectroscopy. The thermal properties were studied by DSC. The crystallization kinetics was analyzed through the measurement of spherulite growth rate. It has been shown that the composition dependence of spherulite growth rate, crystallinity, lamella thickness, HV content in the crystalline phase, and melting temperature change discontinuously at ca. 10 mol % HV, indicating the occurrence of a structural transition at this composition. To explain these results, we have introduced two models of lamellar crystals containing counits, i.e., sandwich lamella and uniform lamella. We have concluded that P(HB-co-HV) with HV content below and above 10 mol % can be described by the sandwich lamella model the uniform lamella model, respectively.

Recent Advances in High-Resolution Solid-State NMR Spectroscopy

Diverse complex systems may be studied by the new methods in solid-state NMR spectroscopy described herein. These methods use magic-angle spinning (MAS) on samples in oriented bilayers (right picture) and in orientationally disordered samples (left picture). Systems as diverse as uniformly 13C,15N-labeled proteins, model membrane systems, and silk, as produced by the silkworm, can be structurally characterized.

Recent Advances in High-Resolution Solid-State NMR Spectroscopy.

Diverse complex systems may be studied by the new methods in solid-state NMR spectroscopy described herein. These methods use magic-angle spinning (MAS) on samples in oriented bilayers (right picture) and in orientationally disordered samples (left picture). Systems as diverse as uniformly 13 C,15 N-labeled proteins, model membrane systems, and silk, as produced by the silkworm, can be structurally characterized.

Investigation of the crystallization process of syndiotactic polypropylene quenched at 0°C from the melt or concentrated solutions by solid-state 13C NMR spectroscopy

The crystallization process of syndiotactic polypropylene (sPP) quenched from the melt or concentrated solutions has been investigated by high-resolution solid-state 13C NMR spectroscopy in order to make clear the formation of the planar zigzag form at 0°C. The sPP film just after quenching at 0°C from the melt is in the noncrystalline state, but when the film is left at room temperature, crystals with sPP in the t 2g 2 conformation are quickly produced. The 13C NMR spectral shape of the CH 2 resonance line is similar to that of the sPP gels previously obtained. For the gels quenched at 0°C from concentrated solutions, T 1C and T 2C measurements reveal that segmental mobility remarkably decreases with increasing polymer concentration in the noncrystalline phase, whereas it stays unchanged in the crystalline phase as a result of lack of penetration of solvent molecules. Increase of viscosity in the noncrystalline phase results in the decrease of molecular mobility. In particular, molecular mobility is extremely restricted in the noncrystalline phase for the solvent-free sample, compared with the case of the gels. A line shape analysis of the CH 3 resonance line indicates that the trans fraction of the noncrystalline component is significantly increased above about 70 wt% concentration. These results lead to the conclusion that the molecular mobility in solutions below about 70 wt% is fast enough to take the almost random chain conformation as expected, but the sPP chains in solutions above about 70 wt% including in the bulk state tend to take trans-rich conformations, probably due to some kind of intermolecular interaction. As a result, crystallization from solutions with appropriate concentrations produces crystals with the most stable t 2g 2 sequences, whereas form III with the planar zigzag conformation is induced around 0°C in the solvent-free bulk state.

Preparation and characterization of lithium ion-conducting oxysulfide glasses

The properties and structure of the lithium ion-conducting oxysulfide glasses in the systems Li 2S–SiS 2–Li x MO y (Li x MO y : lithium ortho-oxosalt, M=Si, P, Ge, B, Al, Ga and In) are reviewed. The Li 2S–SiS 2 glass added with small amounts of Li x MO y exhibited high glass stability against crystallization, high conductivity of 10 −3 S cm −1 at room temperature, and wide electrochemical window. Further addition of Li x MO y reduced these superior properties in any system. High-resolution solid-state NMR and X-ray photoelectron spectroscopy revealed that the silicon atoms coordinated with both bridging oxygen atoms and nonbridging sulfur atoms were mainly present in the glasses with small amounts of Li x MO y . The presence of these unique structural units brought about high conductivities and high thermal stability of these glasses. The solid state battery with the oxysulfide glass worked as a lithium secondary battery and performed excellent cycling behaviors.

Crystal Transformation Behavior and Structural Changes of the Planar Zigzag Form for Syndiotactic Polypropylene

Crystal transformation behavior and structural changes for the planar zigzag form (form III) of syndiotactic polypropylene, which is spontaneously crystallized at 0 °C from the melt, have been investigated in the heating process by DSC, wide-angle X-ray diffractometry, and high-resolution solid-state 13C NMR spectroscopy. The DSC curve for the sample containing only form III crystallites, which is crystallized at 0 °C for 5000 h, shows an evident endothermic peak at about 20 °C and an additional exothermic peak at about 100 °C prior to melting at about 150 °C. The endothermic peak, which is shifted up to about 40 °C by annealing at room temperature, is found to be ascribed to the crystal transformation from form III with the planar zigzag conformation to form II composed of isochiral helices with the ttgg conformation by wide-angle X-ray diffractometry. Moreover, the CH3 resonance lines of the dipolar decoupling/MAS 13C NMR spectra measured at different temperatures for the sample with almost the same str...

Understanding the structural properties of a homologous series of bis-diphenylphosphine oxides

A homologous series of bis-diphenylphosphine oxides (C6H5)2PO(CH2)(n)PO(C6H5)2 (with n = 2-8; denoted 2-8] have been investigated to explore the effects of a range of competing and cooperative intermolecular and intramolecular interactions on the structural properties in the solid state. The important factors influencing the structural properties include intramolecular aspects such as the conformation of the aliphatic chain and the intramolecular interaction between the two P=O dipoles in the molecule, and intermolecular aspects such as long-range electrostatic interactions (dominated by the arrangement of the P=O dipoles), C-H...O interactions, C-H...pi interactions and pi...pi interactions. Compounds 3 and 5 could be crystallized only as solvate co-crystals (3 water and 5 x (toluene)2], whereas the crystal structures of all the other compounds contain only the bis-diphenylphosphine oxide molecule. The crystal structures have been determined from single-crystal X-ray diffraction data, with the exception of 7 (which has been determined here from powder X-ray diffraction data) and 4 (which was known previously). The compounds with even n represent a systematic structural series, exhibiting characteristic, essentially linear P=O...P=O...P=O dipolar arrays, together with C-H...O and C-H...pi interactions. For the compounds with odd n, on the other hand, uniform structural behaviour is not observed across the series, although certain aspects of these crystal structures contribute in a general sense to our understanding of the structural properties of bis-diphenylphosphine oxides. Importantly, for the compounds with odd n, there is "frustration" with regard to the molecular conformation, as the preferred all-anti conformation of the aliphatic chain gives rise to an unfavourable parallel alignment of the two P=O dipoles within the molecule. Clearly the importance of avoiding a parallel alignment of the P=O dipoles becomes greater as n decreases. Local structural aspects (investigated by high-resolution solid-state 31P NMR spectroscopy) and thermal properties of the bis-diphenylphosphine oxide materials are also reported.

Spontaneous Crystallization Process of the Planar Zigzag Form at 0 °C from the Melt for Syndiotactic Polypropylene

The spontaneous crystallization process of the planar zigzag form (form III) of syndiotactic polypropylene has been investigated at 0 °C for samples quenched from the melt by real-time wide-angle X-ray diffractometry and high-resolution solid-state 13C NMR spectroscopy. The X-ray diffraction profile just after quenched from the melt is in good accord with that of the melt, indicating that the sample is in the noncrystalline state. With increasing crystallization time, broad diffraction peaks assignable to form III are found to evidently appear for the diffraction profile obtained after the subtraction of the noncrystalline contribution. The spontaneous crystallization of form III is also confirmed by high-resolution solid-state 13C NMR spectroscopy; for example, the CH3(I) line assigned to the tt conformation really increased in intensity with increasing crystallization time in concomitancy with the decrease of the CH3(II) line ascribed to the tg conformation. The line shape analysis of these CH3 lines re...

Comparison of residual dipolar interactions in uncross-linked and cross-linked natural rubber by high-resolution solid-state NMR spectroscopy

It is shown that local residual dipolar broadening of protons coupled to 13C is a sensitive way to observe motional constraints from networks and entanglements in cross-linked and uncross-linked rubber systems. This may be easily obtained from the indirect observation of proton spin system through 13C resonance in the conditions of slow magic-angle spinning. The method has been used to visualise the changes in the amount of physical constraints induced during mechanical treatment, which precedes the vulcanisation process.

Structural characterization of 13C-labeled n-tetracosane adsorbed on the surface of silica gel by high-resolution solid-state 13C NMR spectroscopy

13C CP/MAS and PST/MAS spectra of 10% 13C-labeled n-tetracosane adsorbed on the surface of silica gel were measured by means of high-resolution solid-state 13C NMR. From these experimental results, it is found that adsorbed n-tetracosane is in three regions with different molecular motion. In the immobile region, n-tetracosane takes a layer structure with triclinic-like form. In the mobile region, n-tetracosane is undergoing fast transition between trans and gauche conformations and fast rotation along the chain axis.

X-ray diffraction and phosphorus-31 NMR studies of the dynamically disordered 3:2 phenol–triphenylphosphine oxide complex

The 3:2 phenol–triphenylphosphine oxide (phenol–TPPO) adduct was studied by means of X-ray diffraction together with high-resolution solid-state 31P NMR spectroscopy. The X-ray results showed that the crystalline structure, which belongs to the triclinic P[1 with combining macron] space group, involves disorder. There are two molecules of TPPO and three phenol molecules per unit cell. One of the latter is disordered across an apparent inversion centre. Analysis of NMR data in conjunction with the crystal structure allowed the origin of such disorder to be established, showing that it is dynamic in nature. Variable-temperature NMR experiments were performed and a coalescence temperature was found at 247 K. Spectra recorded below this temperature showed two phosphorus signals. The kinetics for the phenol residue exchanging between two different TPPO moieties (two-site exchange with equal populations) were determined. Thermodynamic parameters for the motion were calculated from Eyring plots. For temperatures ranging from 262.9 to 221.5 K, the bandshape analysis technique was used to derive the required data. For lower temperatures, the selective polarisation inversion experiment (SPI) was performed, whilst high temperature values were derived from variable-temperature T1ρ studies. The activation enthalpy (ΔH‡), calculated using the results obtained by bandshape analysis, T1ρ and SPI, was determined as 38 kJ mol−1, while the activation entropy (ΔS‡) was found to be −23 J mol−1 K−1 (assuming the transmission coefficient is ½). Phosphorus-31 shielding tensor anisotropies have been derived for this system by spinning sideband analysis at both fast and slow-exchange limits and it has been shown that the tensor is axially symmetric. Single-crystal experiments show that the symmetry axis of the tensor is along the P[double bond, length half m-dash]O bond (within experimental error).