Applications of high-resolution 13C and 15N n.m.r. of solids

1981 ◽  
Vol 299 (1452) ◽  
pp. 593-608 ◽  
Keyword(s):  
High Resolution ◽  
Spin Diffusion ◽  
Magic Angle Spinning ◽  
Spin Lattice Relaxation ◽  
Spatial Proximity ◽  
Magic Angle ◽  
Rotating Frame ◽  
Cross Polarization ◽  
Relaxation Rates ◽  
Relaxation Parameters

The combination of cross polarization, dipolar decoupling and magic angle spinning results in liquid-like high-resolution 13 C and 15 N n.m.r. spectra of a wide variety of solid materials. Structural determinations based on such 13 C n.m.r. spectra include the measurement of the extent to which pyrolysed polyacrylonitrile fibres (Orion) retain aliphatic character during the first step of the production of a carbon fibre, the determination of the chemical identity of the cross links formed from an acetyleneterminated polyimide resin, and the characterization of the metabolic products of a bacterial fermentation of wood lignin. All of these non-destructive analyses are performed on intact heterogeneous samples. The high resolution of the carbon experiment can also be exploited by obtaining proton spin-lattice relaxation parameters for chemically different protons in solids. Because of spin diffusion, these parameters are dependent on spatial proximity and so are helpful in measuring the homogeneity of solid blends of polymers such as poly(phenylene oxide) and polystyrene. High-resolution 13 C n.m.r. spectra of polymers can also be used for measuring microscopic chain dynamics. 13 C rotating-frame relaxation parameters observed for polycarbonate and poly (ethylene terephthalate) are related to the effects on motion of annealing, additives and structural substitutions. Individual relaxation rates are observed for individual carbons, so the behaviour of side groups is cleanly separated from that of the main chain. All of the line-narrowing and sensitivity-enhancing techniques applied to 13 C n.m.r. of solids work equally well for 15 N n.m.r. Use of 15 N rotating-frame and cross-polarization parameters leads to the assessment of the relative concentrations of 13 C - 15 N and 12 C - 15 N pair concentrations in the main chains of multiply labelled proteins. Such measurements can be used to characterize the rate of protein turnover in fully expanded soybean leaves, as well as the details of protein synthesis in cultured soybean cotyledons.

scholarly journals CP MAS kinetics and impedance spectroscopy studies of local disorder in low-dimensional H-bonded proton-conducting materials

2019 ◽  
Vol 59 (3) ◽  
Author(s):  
Laurynas Dagys ◽  
Sergejus Balčiūnas ◽  
Jûras Banys ◽  
Feliksas Kuliešius ◽  
Vladimir Chizhik ◽  
...  
Keyword(s):  
Impedance Spectroscopy ◽  
Spin Diffusion ◽  
Lattice Relaxation ◽  
Magic Angle Spinning ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Magic Angle ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Local Disorder

The 1H–13C cross-polarization magic angle spinning (CP MAS) kinetics was studied in poly(vinyl phosphonic acid) (pVPA), i.e. material with high degrees of freedom of proton motion along H-bonded chains. It has been shown that the CP kinetic data for the adjacent 1H–13C spin pairs can be described in the frame of the isotropic spin-diffusion approach. The rates of spin diffusion and spin-lattice relaxation as well as the parameters accounting for spin coupling and the effective size of spin clusters have been determined. The local order parameter S ≈ 0.63±0.02, determined as the ratio of the measured dipolar 1H–13C coupling constant and the calculated static dipolar coupling constant, is significantly lower than the values deduced for related sites in other polymers and in series of amino acids. This means that the local disorder of the C–H bonds in pVPA is between those for rather rigid C–H bond configurations having S = 0.8–1.0 and highly disordered –CH3 groups (S ~ 0.4). This effect can be attributed to the presence of the proton transfer path where proton motion is easy to activate. The activation energy for the proton motion Ea = 59±7 kJ/mol was determined from the impedance spectroscopy data analysing the temperature and frequency dependences of the complex dielectric permittivity of pVPA. The rates of proton spin-lattice relaxation and spin diffusion are of the same order and both run in the time scale of milliseconds.

scholarly journals Polydisperse methyl β-cyclodextrin–epichlorohydrin polymers: variable contact time 13C CP-MAS solid-state NMR characterization

2015 ◽  
Vol 11 ◽  
pp. 2785-2794 ◽  
Author(s):  
Isabelle Mallard ◽  
Davy Baudelet ◽  
Franca Castiglione ◽  
Monica Ferro ◽  
Walter Panzeri ◽  
...  
Keyword(s):  
Solid State ◽  
Contact Time ◽  
Magic Angle Spinning ◽  
Proton Spin ◽  
Fine Tuning ◽  
Spin Lattice Relaxation ◽  
Molar Ratio ◽  
Magic Angle ◽  
Cross Polarization ◽  
Nmr Characterization

The polymerization of partially methylated β-cyclodextrin (CRYSMEB) with epichlorohydrin was carried out in the presence of a known amount of toluene as imprinting agent. Three different preparations (D1, D2 and D3) of imprinted polymers were obtained and characterized by solid-state 13C NMR spectroscopy under cross-polarization magic angle spinning (CP-MAS) conditions. The polymers were prepared by using the same synthetic conditions but with different molar ratios of imprinting agent/monomer, leading to morphologically equivalent materials but with different absorption properties. The main purpose of the work was to find a suitable spectroscopic descriptor accounting for the different imprinting process in three homogeneous polymeric networks. The polymers were characterized by studying the kinetics of the cross-polarization process. This approach is based on variable contact time CP-MAS spectra, referred to as VCP-MAS. The analysis of the VCP-MAS spectra provided two relaxation parameters: T CH (the CP time constant) and T 1ρ (the proton spin-lattice relaxation time in the rotating frame). The results and the analysis presented in the paper pointed out that T CH is sensitive to the imprinting process, showing variations related to the toluene/cyclodextrin molar ratio used for the preparation of the materials. Conversely, the observed values of T 1ρ did not show dramatic variations with the imprinting protocol, but rather confirmed that the three polymers are morphologically similar. Thus the combined use of T CH and T 1ρ can be helpful for the characterization and fine tuning of imprinted polymeric matrices.

scholarly journals Secular and semi-nonsecular models of cross-polarization kinetics for remote spins: an application for nano-structured calcium hydroxyapatite

2021 ◽  
Vol 61 (1) ◽  
Author(s):  
V. Klimavičius ◽  
F. Kuliešius ◽  
E. Orentas ◽  
V. Balevičius
Keyword(s):  
Spin Diffusion ◽  
Dipolar Coupling ◽  
Calcium Hydroxyapatite ◽  
Magic Angle Spinning ◽  
Proton Conductors ◽  
Magic Angle ◽  
Cross Polarization ◽  
Proton Diffusion ◽  
High Anisotropy ◽  
Spin Pairs

The 1H → 31P cross-polarization (CP) kinetics in the nanostructured calcium hydroxyapatite (nano-CaHA) was measured under moderate (5 kHz) magic-angle spinning (MAS) rate. This material was chosen as it contains the distanced 1H–31P spin pairs and the interactions between them are characterized by a relatively low dipolar coupling (b) that could be comparable with the spin-diffusion rates (R). Therefore, the physical legitimacy to use the secular solution of the quantum Liouville–von Neumann equation is doubtful. The semi-nonsecular model of spin dynamics was applied, and the results were compared with those obtained by the secular approach. The comparable results obtained by both models show that the secular model is applicable, with certain reservation, also in the case of |b| ≈ R. The extremely high anisotropy of spin diffusion in the nano-CaHA was deduced. This can be a matter of the applied approach, as the interactions of the 31P spins with the proton bath were neglected in both models. The high anisotropy could also be caused by the physical reasons that stem from the structural and proton diffusion features of CaHA. This material belongs to low-dimensional proton conductors possessing a large motional freedom for protons along OH– chains.

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