High Resolution Solid State Research Articles

Structural characterization of silver dialkylphosphite salts using solid‐state 109Ag and 31P NMR spectroscopy, IR spectroscopy and DFT calculations

High-resolution solid-state (109)Ag and (31)P NMR spectroscopy was used to investigate a series of silver dialkylphosphite salts, Ag(O)P(OR)(2) (R = CH(3), C(2)H(5), C(4)H(9) and C(8)H(17)), and determine whether they adopt keto, enol or dimer structures in the solid state. The silver chemical shift, CS, tensors and |J((109)Ag, (31)P)| values for these salts were determined using (109)Ag (Xi = 4.652%) NMR spectroscopy. The magnitudes of J((109)Ag, (31)P) range from 1250 +/- 10 to 1318 +/- 10 Hz and are the largest reported so far. These values indicate that phosphorus is directly bonded to silver for all these salts and thus exclude the enol structure. All (31)P NMR spectra exhibit splittings due to indirect spin-spin coupling to (107)Ag (I = 1/2, NA = 51.8%) and (109)Ag (I = 1/2, NA = 48.2%). The (1)J((109)Ag, (31)P) values measured by both (109)Ag and (31)P NMR spectroscopy agree within experimental error. Analysis of (31)P NMR spectra of stationary samples for these salts allowed the determination of the phosphorus CS tensors. The absence of characteristic P=O stretching absorption bands near 1250 cm(-1) in the IR spectra for these salts exclude the simple keto tautomer. Thus, the combination of solid-state NMR and IR results indicate that these silver dialkylphosphite salts probably have a dimer structure. Values of silver and phosphorus CS tensors as well as (1)J((109)Ag, (31)P) values for a dimer model calculated using the density functional theory (DFT) method are in agreement with the experimental observations.

Perturbations to 27Al Electric Field Gradients in Nanocrystalline α-Al2O3 Studied by High-Resolution Solid-State NMR

(27)Al solid-state NMR has been employed to study the perturbations to (27)Al electric field gradients for the aluminum environments in nanocrystalline alpha-alumina. Triple quantum magic angle spinning experiments show that the octahedral aluminum coordination remains unchanged down to 12 nm, although severe perturbations to (27)Al electric field gradients are noticed at 28 nm and below. 3Q-MAS and SATRAS experimental data of nano alpha-alumina have been analyzed through extensive spectral simulations to probe (27)Al electric field gradients of aluminum in the grains and grain boundaries. While the aluminum in the grains has a unique field gradient tensor, the same octahedrally coordinated aluminum environments in the grain boundaries suffer a distribution of electric field gradients. This is evidenced by data analysis of both 3Q-MAS and SATRAS spectra. By invoking the Gaussian isotropic model, in which the (C(Q), eta(Q)) parameter space is discretely sampled by the Czjzek distribution, we have been able to analyze the (27)Al SATRAS spectra of nanocrystalline alpha-alumina samples having grain sizes of 52, 28, 20, and 12 nm. Good agreement between experimental and simulated spectra has led to the quantitative determination of grain and grain boundary components in these materials.

Molecular Dynamics of Regioregular Poly(3-hexylthiophene) Investigated by NMR Relaxation and an Interpretation of Temperature Dependent Optical Absorption

The molecular structure and dynamics of regioregulated poly(3-hexylthiophene) (P3HT) were investigated using high-resolution solid-state (13)C nuclear magnetic resonance (NMR) and optical absorption spectroscopies. A crystal (C)-plastic crystal (PC) transition induced by the molecular motion of the aliphatic side group was observed for P3HT in the temperature dependence analysis of (13)C NMR spectra and spin-lattice relaxation time (T(1C)). The aliphatic side group motion in the crystalline state weakened intermolecular pi-pi interaction, resulting in the blue shift of the characteristic absorption of the interchain exciton. Above the transition temperature, the thiophene twisting motion induces not only further collapsing of the intermolecular interaction but also localizing of the intrachain exciton, leading to the blue shift of the absorption of both the inter- and intrachain exciton.

Effects of hydration on the acid–base interactions and secondary structures of poly-l-lysine probed by 15N and 13C solid state NMR

Using high resolution solid state (15)N and (13)C NMR spectroscopy we have studied the effects of successive hydration on the (15)N labeled side chain amino groups of solid poly-L-lysine (PLL) in the presence of acids. Generally, hydration leads to the formation of local "ionic fluid" phases composed by flexible side chain ammonium groups, acid anions and small amounts of water. The associated local dynamics reduces the widths of the inhomogeneously broadened (15)N amino signals found for the dry states. The hydration of free base PLL--which consists of mixtures of alpha-helices and beta-pleated sheets--is monitored by a small low-field shift of the amino group signal arising from hydrogen bonding with water, reaching eventually the value of PLL in water at pH 13. No difference for the two conformations is observed. PLL x HF adopts a similar secondary structure with isolated NHF hydrogen bonds; hydration leads only to small low-field shifts which are nevertheless compatible with the formation of ammonium groups in aqueous solution. PLL doped with small amounts of HCl contains ammonium groups which are internally solvated by neighboring free amino groups. Both nitrogen environments are characterized by different chemical shifts. Hydration with less than one water molecule per amino group leads already to a chemical shift averaging arising from fast proton motions along NHN-hydrogen bonds and fast side chain and anion motions.By contrast, the hydration of fully doped PLL x HBr and PLL x HCl is more complex. These systems exist only in beta-pleated sheet conformations forming alkyl ammonium salt structures. Separate (15)N signal components are observed for (i) the dry states, for (ii) wet beta-pleated sheets and for (iii) wet alpha-helices which are successively formed upon hydration. Exchange between these environments is slow, but water motions lead to averaged amino group signals within each of the two wet environments. These results indicate that the different environments form domains. As the replacement of NHBr or of NHCl hydrogen bonds by NHO hydrogen bonds leads to high-field shifts the observation of separated signals is the result of different water content in the three domains. In agreement with previous X-ray powder diffraction studies we observe a dominance of the alpha-helical regions at above 3 water molecules per amino group in the case of PLL x HBr and at about 5 water molecules in the case of PLL x HCl, an effect arising from the limited space between beta-pleated sheets and the larger volume of bromide as compared to chloride.

Do Cation-PI Interactions Occur in Lipid Bilayers Between Phosphatidylcholine Headgroups and Interfacially Localized Tryptophans?

Lipids can modulate membrane protein activity in many different ways. To understand the basic priciples governing this complex lattice of interactions between lipids and membrane proteins, simple model peptides have been created. Among those are the families of WALP and KALP peptides, which consist of a poly-(leucine-alanine) stretch flanked by tryptophans and lysines, respectively.Here we focused on studying how electrostatic interactions between these flanking residues and the lipid polar head groups can affect the behavior of the peptides and the lipids. We used 2H NMR on Ala-d4 labeled peptides to map changes in the orientation of the peptides in phosphatidylcholine bilayers in the absence and presence of the anionic lipid phosphatidylglycerol and we used 14N NMR to monitor changes in structure and dynamics of the phosphocholine head groups. Surprisingly, we found that WALP peptides, which are uncharged, are more sensitive to incorporation of negatively charged lipids, than their positively charged equivalents, the KALP peptides. As a possible explanation we raised the hypothesis that WALP peptides are sensitive to the concentration of phosphatidylcholine lipids in the membrane, due to favorable cation-pi interactions between the tryptophans and the choline moieties of the lipids. This hypothesis was supported by results from high resolution solid state NMR experiments, designed to monitor Trp-choline interactions. The existence of such a favorable interaction may shed new light on understanding the behavior of membrane proteins, in particular since in such proteins Trp frequently occurs as flanking residue at the lipid/water interface.

過酸化物架橋エチレンプロピレンゴムの残存過酸化物による劣化機構の解析

The chemical structures of aged dicumyl peroxide(DCP)-crosslinked EPDMs were investigated with FT-IR and 13C high-resolution solid state NMR. The mechanism of degradation induced by residual DCP was studied in DCP-crosslinked EPDMs.The thermal degradation of DCP-crosslinked EPDMs occurred with the disappearance of C=C bond of ethylidene norbornene and generation of carbonyl, carboxy and hydroxy groups and the scission of polymer chains. It can be considered that the residual DCP in DCP-crosslinked EPDMs accelerated the production of peroxide and hydroperoxide. The peroxide and hydroperoxide are extremely unstable, thereby causing various degradation reactions such as production of radicals, chain scission, and oxidation reactions of EPDM polymer.

Structural characterization of metal–metal bonded polymer [Ru(L)(CO)2]n (L = 2,2′-bipyridine) in the solid state using high-resolution NMR and DFT chemical shift calculations

The metal bonded ruthenium polymer [Ru(0)(bpy)(CO)(2)](n) (bpy = 2,2'-bipyridine) is known to be a very promising and efficient solid material for catalysis applications, such as carbon dioxide electroreduction in pure aqueous media and the water-gas shift reaction. It also exhibits potential application for molecular electronics as a conductive molecular wire. The insolubility and relative air-sensitivity of [Ru(0)(bpy)(CO)(2)](n) as well as the lack of monocrystals make its structural characterization very challenging. A first approach to determine the structure of this polymer has been obtained by ab initio X-ray powder diffraction, based on the known X-ray structure of [Ru(CO)(4)](n). In order to refine this structure, a non-conventional solid-state NMR study was performed. The results of this study are presented here. The comparison of high-resolution solid-state (13)C NMR spectra of the polymer with those of the corresponding monomeric [Ru(bpy)(CO)(2)Cl(2)] or dimeric [Ru(bpy)(CO)(2)Cl](2) precursor complexes has shown a clear shift and splitting of carbonyl ligand resonances, which turns out to be linearly correlated with the redox state of the Ru (ii, i or 0, respectively). Bipyridine resonances are also affected but in a non-trivial way. Finally, in the case of the dimer, it was found that the CO peak splitting (2.7 ppm) contains structural information, e.g. the ligand staggering angle. Based on DFT chemical shift calculations on corresponding model molecules (n = 1-2), all the described experimental observations could be reproduced. Moreover, upon extending these calculations to models of increasing length (n = 3-5), it turns out that information about the staggering angle between successive ligands is actually retained in the CO NMR computed peak splitting. Turning back to experiments, the CO broad signal measured for the wire could be decomposed into a major component (at 214.9 ppm) assigned to the internal CO ligands, and a minor doublet component (216.9 and 218.1 ppm) whose splitting (2.8 ppm) contains the staggering angle information. Finally, from the relative integrals of these three components, expected to be in the ratio 1 : 1 : n-2, it was possible to tentatively estimate the length n of the polymetallic wire (n = 7).

Microscopic structure of heterogeneous lipid-based formulations revealed by 13C high-resolution solid-state and 1H PFG NMR methods

Lipid-based formulations such as lip glosses that are very alike on the base of their components may have significant differences in their expected macroscopic properties as cosmetics. To differentiate such formulations, high-resolution 13C NMR was performed under magic angle spinning to investigate the properties at both molecular and microscopic levels. Temperature studies were carried out and no polymorphism in the solid domains could be evidenced after the thermal treatment performed for obtaining the commercial lip glosses. 13C NMR spectra also showed that some waxes remain partially solubilized in the oils of formulations. The microscopic structure of the wax-oil liquid domains was worked out on the basis of restricted diffusion properties obtained with proton pulsed-field gradient NMR. Changing a single wax component, in two identical formulations, yields significant morphological differences. In the first one the liquid phase appears as a continuum whereas in the second one, the liquid phase is fractionated into micrometric droplets.

Study of alkaline metal ions and glass-formers in glasses with advanced NMR methods and quantum mechanic calculations

Silicate, calcium-silicate, and phosphosilicate glasses of the composition 80 SiO 2–(20 − x) Na 2O − x Me 2O (where x = 0, 10 and Me = Li or K), 48.7 SiO 2–26.9 CaO–(24.4 − x) Na 2O − x Me 2O (where x = 0, 12.2 and Me = Li or K), and 46.1 SiO 2–2.6 P 2O 5–26.9 CaO–(24.4 − x) Na 2O − x Me 2O (where x = 0, 12.2 and Me = Li or K) have been studied with high resolution solid state NMR methods. The quantification of the different Q n species was obtained for each sample by 29Si MAS–NMR analysis. The 23Na MQ-MAS–NMR was used to distinguish the different 23Na sites present in the glasses. The presence of phosphorus in the Na 2O phosphosilicate revealed the presence of three Na ionic sites, while the mixed alkali effect resulted in the absence of the third and most ionic site. Quantum mechanical calculations were performed for the identification of the structures observed in our glasses detected by MAS–NMR and MQ-MAS–NMR.

Structural Elucidation of Alkali Fluorozirconate Glasses Using High-Resolution Solid State NMR

Abstract The structure of two compositional series of ZrF4-LaF3-BaF2-MF (M = Li or Na) glasses has been examined by 19F magic-angle spinning (MAS)-NMR spectroscopy. From a detailed lineshape analysis, the fractions of corner-bridging (CBF) and non-bridging fluoride (NBF) species were extracted. With increasing LiF (or NaF) content, the fraction of NBF increases significantly, producing an increased spectral contribution of the low-frequency lineshape components. 19F{7Li} rotational echo double resonance (REDOR) experiments reveal that this part of the MAS-NMR lineshape interacts most closely with the 7Li nuclei. The compositional dependence of the NBF fractions is discussed in the context of various scenarios, describing the transformation of CBF units into NBF units, and affecting the average coordination number of the Zr ions. The results indicate that the evolution of the NBF fraction cannot be described by a single scenario over the entire composition range.

Proton Distributions and Hydrogen Bonding in Crystalline and Glassy Hydrous Silicates and Related Inorganic Materials: Insights from High‐Resolution Solid‐State Nuclear Magnetic Resonance Spectroscopy

Solid‐state 1H nuclear magnetic resonance (NMR) spectroscopy has developed into a versatile, high‐resolution method for elucidating the detailed structures of both crystalline and amorphous materials. Here, we summarize our recent endeavors in applying this method to crystalline and glassy silicates and related inorganic materials. We first present updated correlations between 1H chemical shift and O⋯O and H⋯O distances of O–H⋯O hydrogen bonds, derived from a comprehensive 1H chemical shift database containing both original high‐quality fast magic angle spinning (MAS) and two‐dimensional combined rotation and multiple pulse spectroscopy (CRAMPS)‐MAS NMR data and literature MAS NMR data for a large number of inorganic compounds, including phosphates, silicates, (oxy)hydroxides, borates, sulfates, and carbonates. These correlations may be used to estimate hydrogen‐bonding distances for inorganic oxide materials of unknown structures. We then present case studies for the application of high‐resolution two‐dimensional 1H CRAMPS‐MAS NMR to unravel the order/disorder of proton distributions in crystalline high‐pressure hydrous silicates. Finally, we summarize some of our results on the water speciation in hydrous (alumino)silicate glasses of a range of compositions obtained through comprehensive 1H MAS NMR, and 29Si–1H and 27Al–1H double‐resonance NMR experiments, and analyze them in the framework of a quasi‐chemical model.

High resolution Solid state NMR structure of Kaliotoxin bound to Potassium channel

High resolution Solid state NMR structure of Kaliotoxin bound to Potassium channel

High-Resolution Solid-State NMR Investigation of the Phase Transition in Decamethylferrocene−Acenaphthenequinone Charge-Transfer Complex

A charge-transfer complex composed of decamethylferrocene (D) and acenaphthenequinone (A) was prepared. The material was a 1:1 neutral complex with a mixed-stack structure and exhibited a phase transition at -16 degrees C. High-resolution (13)C and (1)H NMR spectroscopy revealed that an inclination of A with respect to D occurs below the phase-transition temperature. The (1)H spin-diffusion rates of the complex undergoing high-speed magic-angle spinning (MAS) were measured to determine the shortest (1)H-(1)H distance r between D and A. To analyze the experimental results, we derived the analytical expression of the spin-diffusion rate W(z) for a homonuclear multispin system undergoing MAS. It was found that W(z) for the complex is proportional only to 1/r(6) under high-speed MAS conditions. On the basis of this relationship and the crystal structure at 20 degrees C, it was determined that the shortest (1)H-(1)H distance r at -27.7 degrees C (below the phase transition temperature) is 0.4 A shorter than that at 20 degrees C. Given this information, a plausible model of the low-temperature structure is discussed.

Thermodynamics in Conformational Transition of Poly(β-benzyl l-aspartate) As Studied by High-Resolution Solid-State 13C NMR Spectroscopy

The thermodynamic characteristics associated with conformational change of poly(β-benzyl l-aspartate) (PBLA) in the solid state are studied by using 13C high-resolution solid-state NMR. PBLA was chosen because four different conformations, i.e., the right-handed (αR-) and left-handed α-helices (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet), can be prepared separately, and the thermally induced transition occurs among them. In this work, we analyze spectral changes due to conformational transformation of PBLA and determine the enthalpic and entropic changes associated with the transformation of αR-helix to other conformations; the enthalpic change ΔH per residue becomes ca. 1.4 kJ mol−1, and the entropic change ΔS per residue becomes ca. 3.5 J K−1 mol−1. With using these ΔH and ΔS values, we show that the observed transition curve can be reproduced by a simple statistical model.

The concentration of polysaccharides and proteins in EPS of Pseudomonas putida and Aureobasidum pullulans as revealed by 13C CPMAS NMR spectroscopy

Extracellular polymeric substances were extracted from the bacterial strain Pseudomonas putida and the fungal species Aureobasidium pullulans using three different methods (formaldehyde-NaOH, ethylenediaminetetraacetic acid (EDTA) and cation-exchange-resin). The composition of the extracellular polymeric substances (EPS) was analysed by biochemical and high-resolution solid state 13C nuclear magnetic resonance (NMR) spectroscopic methods. The EPS yield was strongly dependent on the extraction method, with the formaldehyde-NaOH method showing the best extraction efficiency. The NMR method revealed that when using the EDTA extraction method, about 40% of the EDTA accumulated in the EPS and that was responsible for the apparent high extraction yields. EPS protein content determined by the NMR method was up to 30% higher than the protein content determined using the biochemical (Lowry) method for P. putida and for A. pullulans. The average protein carbon content determined by the NMR method was approximately 70% of the total carbon content. NMR results could be supported by elemental analysis, which showed a high nitrogen content (approximately 10%) in the EPS. The carbohydrate carbon content detected with both methods in the cell aggregates and the EPS was approximately 20% in each. In this study, quantitative 13C cross-polarisation magic angle spinning NMR spectroscopy was conducted on unlabeled cell strains, and EPS and could be used to quantify protein and carbohydrate of different samples.

Structural and mechanical properties of a-C:H and Si doped a-C:H thin films grown by LF-PECVD

Abstract Amorphous hydrogenated carbon (a-C:H) and Silicon doped a-C:H (Si-DLC) and a-C:H/Si-DLC multilayered films were deposited by low frequency plasma enhanced chemical vapour deposition (LF PECVD). Influences of plasma power and substrate temperature were first investigated on structural and mechanical properties of a-C:H films elaborated from cyclohexane–hydrogen mixtures. The hybridation ratio, Csp 2 /Csp 3 , was evaluated by means of Raman spectroscopy and High Resolution Solid-State Nuclear Magnetic Resonance (SSNMR). Stress measurements were realised by the substrate bending method. Nanoindentation and ball on disk tribometer were used in order to determine nanohardness, Young modulus and friction behaviours respectively. Si-DLC films were then elaborated by incorporating tetramethylsilane in the previous gas mixtures. Those layers revealed a significantly reduced stress level comparing to a-C:H films without a dramatic loss of mechanical properties. Finally a-C:H and Si-DLC layers were associated to elaborate a multilayered system which presents mechanical and tribological properties equivalent to an a-C:H monolayer properties while maintaining a lower residual stress level.

Investigation of Trans Content in Amorphous Phase of stretched Polyethylene Terephthalate by Solid-state High resolution 13C NMR Spectroscopy

Crystalline, constrained noncrystalline, and amorphous phase structures for polyethylene terephthalate (PET) stretched at 75, 80, and 90°C were investigated by solid-state high resolution 13 C NMR. Saturation recovery pulse sequence is a very powerful tool for investigating not only the molecular structure but also the molecular mobility. Spin-lattice relaxation behavior of trans methylene carbon was decomposed by three components, which are assignable to crystalline, constrained noncrystalline, and amorphous phases. The weight content of each component can be estimated by the relaxation behavior. The stretching process induced the transformation from gauche to trans conformation. The trans content with the longest T 1c corresponds to the crystallinity, which was in good agreement with DSC measurement. The trans content in the amorphous phase was also estimated by the ratio between the gauche content assignable to the amorphous phase and the amorphous component of the trans conformer decomposed by relaxation measurement. The trans content of unstretched PET was as low as 21%, whereas that for five-times stretched PET was about 60%.

Access to Local Structures of HS-AlF3 and Its Precursor Determined by High-Resolution Solid-State NMR

High-surface aluminum fluoride (HS-AlF3) is an interesting catalytic material and possesses high surface areas compared to crystalline aluminum fluorides and strong Lewis acidity. HS-AlF3 and its precursor aluminum isopropoxide fluoride are X-ray amorphous, which makes precise structural elucidations very difficult, which is, in turn, the prerequisite for understanding its extraordinary properties. For this reason 27Al NMR using magic angle sample spinning (MAS) and multiple quantum NMR (MQMAS) has been carried out at different magnetic field strengths up to 19.9 T in order to gain maximum information about the various AlF6−xOx (x = 0, 1, 2, ...) octahedra present in the precursor and HS-AlF3 structure. The 27Al NMR spectra are almost featureless irrespective of the applied B0 fields because of distributions of isotropic chemical shifts and second order quadrupolar effects. Nevertheless, it was possible to verify the presence of four different octahedra in the materials following the results of earlier investigations of the sol−gel of these HS-AlF3 samples. Different oxygen-containing AlF5O and AlF4O2 are found in the precursor structure, whereas AlF6 sites determine the HS-AlF3 structure besides residual AlF5O and AlF4O2 octahedra after postfluorination of the precursor.

Acid-Induced Amino Side-Chain Interactions and Secondary Structure of Solid Poly-l-lysine Probed by 15N and 13C Solid State NMR and ab Initio Model Calculations

The acid-base and base-base interactions of the (15)N-labeled side-chain amino groups of dry solid poly-L-lysine (PLL) and the consequences for the secondary structure have been studied using high-resolution solid state (15)N and (13)C CPMAS NMR spectroscopy. In a previous study we had shown that at acid/base ratios of 1 per amino group the halogen acids HI, HCl and HBr form PLL salts in the beta-pleated sheet but not in the alpha-helical structure, whereas HF and various oxygen acids form 1:1 acid-base hydrogen-bonded complexes in both secondary structures. In the present study we performed NMR experiments at reduced acid/base ratios in order to elucidate whether also 1:2 and 1:3 acid-base complexes are formed under these conditions. Generally, the PLL samples containing HF, HBr, HCl, HI, CH(3)COOH, H(3)PO(4), H(2)SO(4), or HNO(3) were obtained by lyophilization at different pH. For comparison, samples were also obtained by letting dry acid-free PLL interact with gaseous HCl. In a theoretical section we first study the probability of the different acid-base complexes as a function of the acid/base ratio and the equilibrium constants of the complex formation. Using this information, the (15)N NMR spectra of acid doped PLL obtained were analyzed and assigned. Indeed, evidence for the formation of 1:2 and 1:3 acid-base complexes at lower acid/base ratios could be obtained. Moreover, the salt structures of the halides of PLL are already destroyed at acid/base ratios of about 0.8. By contrast, when acid-free poly-L-lysine is exposed to HCl gas, a biexponential conversion of amino groups into ammonium groups is observed without formation of 1:2 and 1:3 complexes. (13)C NMR reveals that the beta-pleated sheet environments of acid-free PLL react rapidly with HCl, whereas the alpha-helices first have to be converted in a slow reaction to beta-pleated sheets before they can react. Interestingly, after partial doping with HCl, exposure to gaseous H(2)O catalyzes the interconversion of the ammonium and amino groups into a mixture of 1:1, 1:2 and 1:3 complexes. Finally, the (15)N NMR assignments were assisted by DFT calculations on methylamine-acid model complexes.

Solid State NMR Study and Density Functional Theory (DFT) Calculations of Structure and Dynamics of Poly(p-xylylenes)

High resolution solid state (13)C nuclear magnetic resonance (SS NMR) measurements were carried out on poly(p-xylylene) (PPX). The samples comprised vapor-deposited specimens as well as pure alpha and beta polymorphs of this polymer. The measurements were performed using cross-polarization and magic angle spinning (CP/MAS) techniques. Density functional theory gauge-including-atomic-orbital (DFT GIAO) calculations of NMR shielding parameters (13)C sigma(ii) were performed for the optimized geometry and structure of a xylylene trimer, acquired from the X-ray data, including intermolecular interactions. Two-dimensional phase adjusted spinning sideband (2D PASS) correlation was employed for the assignment of the values of the principal elements (13)C delta(ii) of the chemical shift tensor (CST). A comparative analysis of shielding (sigma(ii)) versus chemical shift (delta(ii)) parameters showed substantial differences between the molecular dynamics of alpha and beta polymorphs. This observation was further supported by the measurements of (13)C T(1) relaxation times and the analysis of cross-polarization kinetics. Frequency switched Lee-Goldburg heteronuclear correlation (FSLG HETCOR) for the (1)H-(13)C system was used in order to analyze molecular packing in both polymorphs. As a result of all of the above measurements, new insight into the mechanism of thermal phase transition from the alpha to the beta polymorph of poly(p-xylylene) is presented.