Inversion Recovery Cross Polarization Research Articles

Structural Characterization of Hydrothermal Carbon Spheres by Advanced Solid-State MAS 13C NMR Investigations

The local structure of carbon spheres obtained via the hydrothermal carbonization process is characterized by using a combination of advanced solid-state 13C NMR techniques. Glucose was chosen as the starting product because it offers the possibility of 13C isotopic enrichment and is regarded as a model compound for more complex polysaccharides and biomass, as reported in recent studies. A number of 13C solid-state MAS NMR techniques (single-pulse, cross-polarization, inversion recovery cross-polarization, INEPT, 13C−13C proton-driven magnetization exchange, and 13C−13C double-quantum−single-quantum correlation experiments) were combined to retrieve information about binding motifs and C−C closest neighbor relations. We found that the core of the carbonaceous scaffold is composed of furan rings cross-linked by domains containing short keto-aliphatic chains instead of otherwise expected graphene-type sheets, as mainly reported either for hydrothermal carbon spheres or for biomass-related carbons obtained b...

Molecular dynamics of chiral semi-crystalline poly( R)-(3-hydroxyalkanoates)

The inversion-recovery cross-polarization (IRCP) sequence used for measuring cross-relaxation time ( T CH) is modified to obtain signals that show exponential or spin-lock (SL) decay to zero. The new sequence may, therefore, be analogously abbreviated as SLCP. Poly( R)-(3-hydroxybutyrate- co-3-hydroxyhexanoate) {P(HB-HHx) (85:15)} is found to be more mobile than poly( R)-(3-hydroxybutyrate) {PHB} in the crystalline regions. The molecular-level evidence by solid state nuclear magnetic resonance (NMR) that the P(HB-HHx) chain is more flexible than PHB is echoed by the dynamic frequency sweep measurements of the biopolymer melts, which show that the PHB melt has an unusual rheological response with the dynamic loss moduli dominating the storage moduli at all frequencies. This is most likely to be caused by the local anisotropic melt structures due to the long persistence length of PHB in the melt. Upon cooling the PHB melt to the solid state, such high levels of anisotropy may be frozen into the solid causing lower chain mobility, and hence giving rise to lower toughness. The incorporation of longer side chain unit to the main chain gives rise to a dynamic rheological response in P(HB-HHx) similar to that of an isotropic melt. This is believed to be due to the enhanced chain flexibility, and hence reduced persistence length. This further allows P(HB-HHx) to be processed into a more uniform isotropic morphology, and hence with improved mechanical toughness.

Partitioning of Main and Side-Chain Units between Different Phases: A Solid-State 13C NMR Inversion-Recovery Cross-Polarization Study on a Homogeneous, Metallocene-Based, Ethylene-1-Octene Copolymer

13C NMR inversion-recovery cross-polarization experiments are used to study the phase structure and partitioning of main and side-chain groups in a homogeneous, metallocene-based, ethylene-1-octene copolymer. The results provide strong evidence for a three-phase model, i.e. a rigid, (imperfect) crystalline phase, which is mainly composed of long sequences of methylene carbon atoms of the main chain, a semi-rigid, amorphous interphase (also denoted as ‘rigid amorphous’), which is enriched by chain segments bearing methylene and methine carbon atoms of the main chain, and a soft fraction of the amorphous phase (also denoted as ‘mobile amorphous’), which is largely composed of side chains and short methylene sequences of the main chain.

Synthesis and characterization of a novel cyclic aluminophosphinate: structure and solid-state NMR study.

We present the structure and a multinuclear solid-state NMR study of a new cyclic aluminophosphinate. The crystallographic structure of [Al(2)(HC(6)H(5)PO(2))(2)(C(4)H(9)OH)(8)]Cl(4) (compound 1) was obtained at low temperature (a = 11.830(7) A, b = 14.216(6) A, c = 17.790(6) A, beta = 91.25(4) degrees, monoclinic, P21/c, Z = 2). (13)C IRCP (inversion recovery cross polarization) and NQS (non quaternary suppression) NMR experiments allowed the complete assignment of the quaternary carbon atom of the phenyl ring and the precise determination of the isotropic /(1)J(P-C)/ coupling constant. (31)P CP MAS dynamics was carefully studied by varying the contact time. Dipolar oscillations even at slow MAS were observed. Up to 11 kHz, these oscillations were more pronounced, and the P-H distance was easily extracted. (27)Al NMR quadrupolar parameters for 1 were obtained with very good accuracy, and unusual satellite transition splitting was observed. Furthermore, the isotropic lines of the inner and outer transitions were clearly observable, leading to the unambiguous determination of the quadrupolar parameters.

Structural Investigation of the First Stages of Pyrolysis of Si-C-O Preceramic Polymers Containing Si–H Bonds

The polymer-to-glass transformation in the Si-C-O system usually involves cross-linking reactions at the C sites, which transform for example ≡Si–\(\underline {\text{C}} \)H3 sites into \(\underline {\text{C}} \)(Si)4 sites, leading to the formation of a silicon oxycarbide network. Identification of the various C sites that form during pyrolysis under inert atmosphere is rather difficult from 13C MAS-NMR spectra, due to strong overlap of resonance lines, which prevents an accurate determination of the chemical shift values. This paper reports on the use of a spectral editing technique called Inversion Recovery Cross Polarization (IRCP), which, when combined with Cross Polarization (CP) technique, allows us to identify and quantify the formation of Si-\(\underline {\text{C}} \)H2-Si bridges during the early stages of the pyrolytic transformation of a polysiloxane containing Si–CH3 and Si–H groups. Several Si-C-O systems characterized by the same initial number of Si–CH3 bonds but with increasing number of Si–H bonds, have been investigated by MAS-NMR as well as thermogravimetric analysis coupled with mass spectrometry (TG/MS). The Si—H bonds play clearly an active role in the insertion of C atoms within the silica network.

Nuclear Magnetic Resonance Detection of Two Distinctly Different Chains in the Orthorhombic Crystalline Phase of Polyethylenes.

Several commercial and noncommercial, high- and low-density and ultraoriented polyethylene samples, as well as polyethylene samples with inorganic fillers, have been investigated by inversion-recovery cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (NMR). In all these samples two types of all-trans chains in orthorhombic crystalline domains are detected, which give two overlapping carbon-13 lines with different line widths and different relaxation times. From the NMR relaxation parameters we conclude that one type of the crystalline chains, which composes 60-90% of the crystalline fraction in all samples, can execute at room temperature 180 degrees flips with a frequency in the kilohertz domain. The other crystalline chains are more rigid and probably are found in more perfect structures in which such chain flips do not occur or occur on a much slower time scale. Adding kaoline filler particles to polyethylene enhances the contribution of the more mobile crystalline chains. The presence of the two distinctly different types of crystalline environments is found in all polyethylene samples investigated so far (more than 25 samples).

15N cross‐polarization using the inversion–recovery cross‐polarization technique and 11B magic angle spinning NMR studies of reference compounds containing B—N bonds

Borane–ammonia complexes, trialcynylborazine and N-trimethylcycloborazane were characterized by 15N and 11B solid-state magic angle spinning (MAS) NMR. They are representative of compounds containing B—N bonds and presenting various N and B environments, either tri- or tetracoordinated. Inversion–recovery cross-polarization (IRCP), a spectral editing technique first introduced for 13C, was extended to 15N. For all compounds, characterized by either weak or strong 15N–1H dipolar couplings, the polarization inversion behavior follows the theoretical equations describing the spin dynamics associated with the IRCP sequence. This technique thus proved to be an excellent tool for identifying 15N sites according to their proton environments. The isotropic chemical shift, quadrupolar coupling constant and asymmetry factor were extracted from the 11B MAS NMR spectra. However, the unusual shape of the center band was tentatively related to the presence of residual 11B–14N dipolar coupling, which could be possibly reduced at higher fields. © 1998 John Wiley & Sons, Ltd.

15N cross-polarization using the inversion-recovery cross-polarization technique and11B magic angle spinning NMR studies of reference compounds containing B—N bonds

Borane–ammonia complexes, trialcynylborazine and N-trimethylcycloborazane were characterized by 15N and 11B solid-state magic angle spinning (MAS) NMR. They are representative of compounds containing B—N bonds and presenting various N and B environments, either tri- or tetracoordinated. Inversion–recovery cross-polarization (IRCP), a spectral editing technique first introduced for 13C, was extended to 15N. For all compounds, characterized by either weak or strong 15N–1H dipolar couplings, the polarization inversion behavior follows the theoretical equations describing the spin dynamics associated with the IRCP sequence. This technique thus proved to be an excellent tool for identifying 15N sites according to their proton environments. The isotropic chemical shift, quadrupolar coupling constant and asymmetry factor were extracted from the 11B MAS NMR spectra. However, the unusual shape of the center band was tentatively related to the presence of residual 11B–14N dipolar coupling, which could be possibly reduced at higher fields. © 1998 John Wiley & Sons, Ltd.

Cross-polarization dynamics and proton dipolar local field measurements in some organic compounds

Hartmann–Hahn inversion–recovery cross-polarization magic-angle spinning experiments were performed for all types of protonated carbons (CHn with n=1, 2 and 3). The resulting non-exponential decays were analyzed using both a simple memory function approach and density matrix calculations. Although the memory function approach provides a useful analytical description of the cross-polarization dynamics, the density matrix method is required to account better for the details of the spin dynamics. 13C-detected dipolar local fields of protons were measured using the wideline separation experiment. It was observed that the resulting local free induction decays may be quantitatively described by their local second moment. Moreover, the local spin diffusion process controlling the second stage of the cross-polarization dynamics is directly related to the strength of the local dipolar field of protons. © 1997 John Wiley & Sons, Ltd.

ADRF Differential Cross Polarization Spectroscopy of Synthetic Calcium Phosphates and Bone Mineral

An adiabatic demagnetization in the rotating frame (ADRF) differential cross polarization (DCP), or inversion recovery cross polarization (IRCP), technique has been developed to study synthetic calcium phosphates and bone mineral. ADRF of the protons followed by a remagnetization of the phosphorus-31 spins results in an equalization of the dipolar and phosphorus Zeeman nuclear spin temperatures. By shifting the phase of the phosphorus RF by 180° during the forward cross polarization it is possible to invert the temperature of this reservoir and initiate reverse cross polarization. Transient Strombotne–Hahn oscillations were observed on inverting the temperature. The presence of these oscillations complicates the determination of a null point on the basis of cross polarization times. It is necessary to shift the phase of the RF only after a Zeeman spin temperature can be defined, and to use an RF field strength that is slightly smaller than the equivalent S-spin local dipolar field in order to produce a zero crossing after the transient oscillations have decayed.

NMR Characterization of Hybrid Systems Based on Functionalized Silsesquioxanes

In this paper, the authors present recent NMR investigations on several silsesquioxanes (RSiO{sub 1.5}){sub 8} with R = H, CH{sub 3}, CH{double_bond}CH{sub 2}, OSi(CH{sub 3}){sub 2}R{prime} (R{prime} = H, CH{sub 3}, CH{double_bond}CH{sub 2}). The octameric polyhedral cubane like derivatives were analyzed by means of high resolution {sup 13}C and {sup 29}Si solid state NMR including CP (Cross-Polarization) and MAS (Magic Angle Spinning) techniques. The CP sequence including variable contact time was used in order to extract quantitative data. The 1D IRCP sequence (Inversion Recovery Cross Polarization), based on the standard CP scheme, allowed them to investigate the CP dynamics of the involved sites and to propose a complete spectral editing of the spectra. Furthermore, local molecular motions were determined through the careful analysis of CP dynamics. Finally, the NMR results related to crystalline cubane derivatives were extended to hybrid systems obtained by cross-coupling of monomeric entities (via hydrosilylation).

29Si and13C NMR Investigation of the Polysilane-to-Poly(carbosilane) Conversion of Poly(methylchlorosilanes) Using Cross-Polarization and Inversion Recovery Cross-Polarization Techniques

The polysilane-to-polycarbosilane transformation of polymethylchlorosilane prepared from based-catalyzed disproportionation of 1,1,2,2-tetrachlorodimethyldisilane has been characterized in detail by 29Si and 13C magic angle spinning nuclear magnetic resonance, using cross-polarization as well as inversion recovery cross-polarization techniques. These techniques allow a clear insight in the protonated environment of a given nucleus, in particular to distinguish between strongly coupled nuclei such as 13CH2 and moderately coupled ones such as 13CH3. For the first time, the IRCP sequence was also used to probe the environment of 29Si nuclei in such systems and proved to be very effective in distinguishing the silane and carbosilane sites. The 180−450 °C temperature range was investigated: the formation of carbosilane units was clearly demonstrated by 13C and also 29Si NMR experiments. The various 29Si and 13C sites were thus identified due to their polarization inversion behavior and quantified. Comparison ...

Solid-state carbon-13 nuclear magnetic resonance investigations of bismuth citrate complexes and crystal structure of Na2[Bi2(cit)2]·7H2O

The complex Na2[Bi2(cit)2]·7H2O (H4cit = 3-carboxy-3-hydroxypentane-1,5-dioic acid) crystallized during reactions of the antiulcer drug ranitidine bismuth citrate with the tripeptide glutathione (γ-L-Glu-L-Cys-Gly) at low pH. X-Ray analysis showed one [Bi(cit)]– fragment per asymmetric unit with Bi3+ chelated to a terminal carboxylate group; citrate also binds, in tridentate mode, to the bismuth of an equivalent [Bi(cit)]– unit (related to the first by a C2 axis)via one oxygen donor from each of the remaining two carboxylate groups and the alkoxy group. Both ends of the resultant dimeric anion {Bi(µ-cit)2Bi}2– bind to adjacent dimers, related by n-glide plane symmetry, via double carboxylate bridges, to form a continuous polymeric anionic chain [{Bi(µ-cit)2Bi}n]2n– running throughout the crystal. In this way each bismuth atom achieves six-co-ordination [Bi–O 2.210(10)–2.505(10)A] with a nido-pentagonal-bipyramidal geometry, the vacant axial site providing evidence for a stereochemically active lone pair and the second axial site being occupied by the alkoxy donor. The parallel polyanionic chains are linked by anion–cation interactions [Na ⋯ O (cit) 2.37–2.50 A] and by bonds of largely ionic character (Bi ⋯ O 3.003–3.095 A) to give the overall three-dimensional solid-state structure which incorporates seven water molecules per dianionic subunit. The solid-state cross-polarization magic angle spinning 13C NMR spectrum of this complex is assigned with the aid of dipolar-dephasing and inversion-recovery cross-polarization experiments, and compared to those of ranitidine bismuth citrate and bismuth citrate Bi(Hcit). The IR and solid-state 13C NMR data suggested that the alkoxy group is protonated in Bi(Hcit) but deprotonated in ranitidine bismuth citrate, and that the latter contains similar dimeric units to Na2[Bi2(cit)2]·7H2O. The general modes of aggregration of dimeric [{Bi(µ-cit)2Bi}n]2n– units and the relevance to antiulcer activity are discussed.

Studies of model organic and inorganic compounds by 15N CP MAS NMR using Inversion Recovery Cross Polarization

In this paper, a study of simple organic/inorganic compounds by 15 N and 13 C CP MAS NMR using a selective sequence (Inversion Recovery Cross Polarization, IRCP) is presented. Such a sequence allows a precise insight in the CP dynamic of various 15 NHx (x = 0 → 4) sites. It allows also the selection of the different NMR lines according to the number of directly bonded protons. This technique appears extremely useful for the study of inorganic polymerisation, starting from protonated precursors (borazines) and leading to non-protonated boron nitride (BN) phases.

NMR investigation of the polysilane-polycarbosilane transformation of poly(methylchlorosilanes)

The pyrolysis of poly(methylchlorosilanes) prepared by catalytic disproportionation of disilanes leads to the formation of silicon carbide. The first step of the process is a polysilanc to polycarbosilane transformation, which occurs with the insertion of methylene groups into Si-Si bonds. For the first time, this transformation was studied by 13 C MAS-NMR, using cross polarization (CP) and Inversion Recovery Cross Polarization (IRCP) techniques.

13C CP–MAS NMR study of absorbed water in polyimide film

AbstractSolid‐state nuclear magnetic resonance (NMR) relaxation studies were performed on Kapton H polyimide films in order to determine the location of water absorption within the polymer lattice and its effects on the microdomain properties of the polymer. Carbon spin lattice relaxation (13CT1), spin lattice relaxation in the rotating frame (T1ρ), and inversion recovery cross polarization (IRCP) experiments were performed to analyze wet and dry Kapton films and films exposed to D2O. The conventional pulse sequences for these experiments were modified with a TOSS acquisition sequence in order to remove spinning side bands from the 13C‐NMR spectra. The data indicates that the water molecules aggregate near the carbonyl group of the imide ring and are most probably bound via hydrogen bonding. Additionally the water molecules plasticize the polymer network by increasing the amplitude of low‐frequency motions. © 1994 John Wiley & Sons, Inc.

Cross-polarization dynamics and spin diffusion in some aromatic compounds

The inversion-recovery cross-polarization (IRCP) magic-angle spinning experiment has been applied to study the 13C 1H cross-polarization dynamics of protonated aromatic carbons in ferrocene, 5,6-dimethoxyindole (DMI) and some indole derivatives. Using the 13C-detected proton spin diffusion (SD) experiment recently developed by Zhang et al. [Solid State Nucl. Magn. Reson., 1 (1992) 313], the slow decaying or incoherent stage of the IRCP experiment is shown to be controlled by the spin diffusion process at the directly bound proton. Moreover, a simple phenomenological model treating spin diffusion as a relaxation process provides an excellent agreement with both the IRCP and SD experimental data for all the different CH pairs of DMI and its derivatives. The resulting time constants of the non-exponential spin diffusion decays are related to the local intra- and intermolecular network of dipolar interactions. This model is nevertheless found to be inadequate for ferrocene because intramolecular spin diffusion then has an inhomogeneous character.

Studies of polymer mobility in composite blends of poly(vinyl butyral) and alumina

AbstractSolid‐state NMR and thermal analysis techniques were used to compare the mobility of poly(vinyl butyral) (PVB) in the presence and absence of both alumina filler particles and plasticizer. The relative mobility of main‐chain and side‐chain carbons increases in the presence of both plasticizer and alumina as seen from an increase in the average cross‐polarization rates, 〈TCH〉, and from a general decrease in the rotating frame spin‐lattice relaxation rates, CT1ρ. Unlike the main‐chain carbons, inversion recovery cross‐polarization (IRCP) data on solution cast composites show that the side‐chain methyl groups in neat PVB samples are best characterized by a monoexponential cross‐polarization model. However, in the presence of alumina, a fraction of the methyl groups becomes less mobile as indicated by the biexponential IRCP behavior. Polymer phase mobility also increases below the critical pigment volume concentration (CPVC) as seen from decreasing transition temperatures using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). This is accompanied by an increase in the rigidity of a portion of the polymer phase above the CPVC as indicated by an increase in the apparent Tg, along with an increase in the mobility of another portion as indicated by the appearance of a low‐temperature DMA transition. These trends are consistent with an increase in polymer chain packing heterogeneity in the presence of alumina. © 1993 John Wiley & Sons, Inc.

A preliminary correlation between macroscopic and microscopic polymer properties: Dynamic storage modulus vs. CPMAS NMR cross polarization rates

AbstractA correlation has been established between the dynamic storage modulus (E') and the mean cross polarization time constants 〈TCH〉 for a set of five morphologically diverse polymers, including one at two temperatures and one at two plasticizer concentrations. The correlation is only possible when the TCH values for all of the motional environments within the polymers are considered. An inversion recovery cross polarization (IRCP) NMR technique is used to obtain motional and morphological information from the main chain carbons of each polymer. After comparing simplified correlation functions for the two parameters, an experimental relationship between them is established that suggests that TCH and E' are both modulated by a similar distribution of molecular motions.

AntiPlasticization in the Glassy States of Poly(Vinyl Butyral) and Poly(2,6-Dimethyl Phenylene Oxide)

AbstractSolid state NMR and dynamic mechanical analysis (DMA) techniques have been used to study the “antiplasticization” effects of dihexyladipate (DHA) and tricresylphosphate (TCP) on poly(vinyl butyral-co-vinyl alcohol) (PVB) and poly(2,6-dimethyl phenylene oxide) (PPO) respectively. The DHA and TCP diluents decrease the primary viscoelastic transition temperatures (ax processes) along with their apparent activation energies [1,2] However, glassy state mechanical transitions (P processes) are characterized by increased activation energies. Similarly, carbon T1, T1p, and inversion recovery cross polarization (IRCP) experiments generally show that DHA and TCP suppress motion in the MHz, KHz, and near static frequency regimes. These results collectively suggest that the extent of antiplasticization is dependent on both the frequency regime of observation, and the morphology of the polymers.