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The method of Nuclear Magnetic Resonance (NMR) relaxometry is proposed to be applied to investigate the kinetics of the recrystallization of a substance from the amorphous phase. The method is based on the determination and analysis of nuclear magnetization recovery Mz obtained from spin-lattice T1 relaxation time measurements as a function of time since sample amorphization. The formation of a biphasic (crystalline and amorphous) system in the process of recrystallization implies that the magnetization recovery Mz is biexponential and that the amplitudes of its components are proportional to the number of spins (protons) in the crystalline and amorphous phases, and, thus, also to the volume occupied by the phases. The method was tested for amorphous felodipine samples with grain sizes close to 0.1 or 1 mm, and the recrystallization process was confirmed by using Powder X-ray Diffraction (PXRD) and Fourier-Transform Infrared (FTIR) methods. Qualitative comparison of the results obtained with the data obtained earlier by PXRD and Raman methods for felodipine samples with grain sizes of 0.2 and 0.6 mm [U. S. Kestur, I. Ivanesivic, D. E. Alonzo, L. S. Taylor, Influence of particle size on the crystallization kinetics of amorphous felodipine powders, Powder Technology 236 (2013) 197–204] showed reasonable agreement. The method is fully extensive and can be applied to amorphous samples prepared in different ways, such as grinding, milling or melting, as well as for co-amorphous or amorphous solid dispersion samples.

The chemical structure of a yellow dye present in Mirabilis jalapa L., miraxanthin I, was characterized by NMR spectroscopy. The extract of M. jalapa was analysed by a high-performance liquid chromatographic system (LC-DAD-FL-ESI-MS/MS) and the presence of miraxanthin I among other betaxanthins was confirmed. This dye was synthesized from previously generated methionine-betaxanthin by oxidation with 10% H2O2. The E/Z stereoisomers of miraxanthin I were found by NMR analysis to occur in a 50 : 33 : 10 : 7 ratio in aqueous solution (7E,9E : 7Z,9E : 7E,9Z : 7Z,9Z configurations, respectively). Comparison of NMR data with chemical shifts obtained from quantum chemical calculations strongly suggests the presence of intramolecular hydrogen bonds which may favour a more rigid structure of the dye. This explains the highest fluorescence quantum yield among betaxanthins. The observed changes in the 1H NMR spectra during the measurements indicate on miraxanthin I hydrolysis for which a mechanism is proposed. The first step during the hydrolysis process is protonation of the nitrogen atom within the central bridge bond system which is observed in the ZE stereoisomer by NMR.

The application of ionic liquids (ILs) has grown enormously, from their use as simple solvents, catalysts, media in separation science, or electrolytes to that as task-specific, tunable molecular machines with appropriate properties. A thorough understanding of these properties and structure–property relationships is needed to fully exploit their potential, open new directions in IL-based research and, finally, properly implement the appropriate applications. In this work, we investigated the structure–properties relationships of a series of alkyltriethylammonium bis(trifluoromethanesulfonyl)imide [TEA-R][TFSI] ionic liquids in relation to their thermal behavior, structure organization, and self-diffusion coefficients in the bulk state using DSC, FT-IR, SAXS, and NMR diffusometry techniques. The phase transition temperatures were determined, indicating alkyl chain dependency. Fourier-transformed infrared spectroscopy studies revealed the structuration of the ionic liquids along with alkyl chain elongation. SAXS experiments clearly demonstrated the existence of polar/non-polar domains. The alkyl chain length influenced the expansion of the non-polar domains, leading to the expansion between cation heads in polar regions of the structured IL. 1H NMR self-diffusion coefficients indicated that alkyl chain elongation generally caused the lowering of the self-diffusion coefficients. Moreover, we show that the diffusion of anions and cations of ILs is similar, even though they vary in their size.

Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (J. Mol. Liq. 263 (2018) 274–281) at room temperature that mixtures of short aliphatic chains compounds, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, due to their ability to allow for phosphate-to-amine proton transfer, display ionic liquid–like behavior with composition-dependent enhanced conductivity, viscosity, and magnetically-induced birefringence. To understand the molecular mechanisms at the basis of this behavior, in the present study a combination of nuclear magnetic resonance (NMR) and dielectric spectroscopy investigations has been carried out for the same materials for different amine molar ratios. It was found that at certain compositions all studied dynamical processes (conformational changes, local hopping of “free” protons among neighboring polar headgroups, long-range charge migration) exhibit significant deviations from ideal mixing behavior. The microscopic origin of these deviations is discussed.

Many bacteria become progressively more resistant to antibiotics and it remains a challenging task to control their overall levels. Polymers combined with active biomolecules come to the forefront for the design of antibacterial materials that can address this encounter. In this work, we investigated the photo-crosslinking approach of UV-sensitive benzophenone molecule (BP) with polyvinylpyrrolidone (PVP) polymer within electrospun fibres. The BP and PVP solutions allowed fabricating polymer mats that were subsequently functionalised with antibacterial lysozyme. The physical properties of the crosslinked electrospun fibres were investigated by scanning electron microscopy and atomic force microscopy. The average diameter of the obtained fibres decreased from 290 ± 50 nm to 270 ± 70 nm upon the addition of the crosslinking molecules and then to 240 ± 80 nm and 180 ± 90 nm after subsequent crosslinking reaction at an increasing time: 3 and 5 h, respectively. The peak force quantitative nanomechanical mapping (PF-QNM) indicated the increase of DMT modulus of obtained cross-linked fibres from 4.1 ± 0.8 GPa to 7.2 ± 0.5 GPa. Furthermore, the successful crosslinking reaction of PVP and BP solution into hydrogels was investigated in terms of examining photo-crosslinking mechanism and was confirmed by rheology, Raman, Fourier transform infrared and nuclear magnetic resonance. Finally, lysozyme was successfully encapsulated within cross-linked PVP-BP hydrogels and these were successfully electrospun into mats which were found to be as effective antibacterial agents as pure lysozyme molecules. The dissolution rate of photo cross-linked PVP mats was observed to increase in comparison to pure PVP electrospun mats which opened a potential route for their use as antibacterial, on-demand, dissolvable coatings for various biomedical applications., Graphical Abstract

Recently, ionic liquids are very promising substances mentioned in electrochemistry as electrolytes in supercapacitors. Due to the fact the operation conditions for supercapacitors require low temperatures, an important issue is an investigation of melting behavior of ionic liquid applied as an electrolyte. In the presented work, we report the experimental studies of the melting behavior of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI); for this purpose the methods of dielectric spectroscopy (DS) and differential scanning calorimetry (DSC) in wide temperature ranges were applied. To investigate the structural properties of the system the temperature-controlled WAXS and Neutron Diffraction methods were adopted. The measurements of the complex permittivity of the studied EMIM TFSI allowed us to determine the relaxation of the system in wide temperature range from 140 K to 300 K. The results obtained from DSC and DS indicate that the ionic liquid on the heating process undergoes two phase transitions: solid-solid transition at temperature 230 K and the melting transition at 257 K, wherein the melting process is not homogeneous. Based on the structural studies results, performed in the temperatures range 10 K – room temperature, it was shown that in the temperature range 10 K–230 K EMIM TFSI forms a crystal monoclinic structure where the rotation motions of molecular groups are observed. At the higher temperature up to the melting temperature the crystal structure is undefined and the rotational motions of molecular groups are changed.

We have studied structural differences among tetrahedral and octahedral sodium Montmorillonite layer arrangements in naturally occurring and synthetic montmorillonite clay minerals, as well as their poly(ethylene oxide) and poly(ε-coprolatone) polymer nanocomposites.

Spin–lattice relaxation time constants, T1, were studied for low-molecular-weight linear and grafted polydimethylsiloxane over a wide temperature and frequency range. Quantitative evaluations of proton T1 measurements indicated two relaxation processes: anisotropic rotation of methyl groups around the Si–C bond (low temperature process) and motions of the PDMS side-chains connected with the glass transition (high temperature process). Additional analyses of the T1 relaxation dispersion profiles revealed specific local segment fluctuation times, which are characteristic of the coherent motions in the grafted polymer chains.

Rheological and dielectric behavior of linear PDMS and alkyl-modified PDMS melts has been studied. Molecular dynamics of linear PDMS, being a model of grafted polydimethylsiloxanes studied, has been examined carefully with particular attention paid to its ability to form the semicrystalline phase. Random incorporation of alkyl groups into PDMS chain has been shown to prevent the polymer crystallization. The glass transition temperature of the grafted PDMS changes proportionally to the modifier content. Both techniques allow characterization of the main α-relaxation, which is related to the glass transition and exhibits similar behavior in all systems. This relaxation is discussed in terms of the Vogel–Fulcher–Tammann–Hesse (VFTH) approach. The fragility of grafted PDMS materials was found to be higher as compared to the linear polymer. The analysis of the rheological data shows the existence of additional slow relaxation, which has been interpreted as the polymer chain motion.

The complex consisting of two piperidine-4-carboxylic acid, l -tartaric acid, water and methanol molecules has been synthesized and characterized by X-ray diffraction, 1 H, 13 C NMR, 13 C CP MAS NMR, FTIR spectra and DFT calculations. The title complex is composed of the following units: piperidinium-4-carboxylate (P4C), piperidinium-4-carboxylic acid (P4CH), semi-tartrate anion (TA), water and methanol; it crystallizes in orthorhombic space group P 2 1 2 1 2 1 . TA anions form infinite chains through the COOH···OOC hydrogen bond of 2.503(5) A. The zwitterionic P4C molecules are linked by the N + H···OOC hydrogen bond of 2.780(5) A into chains. The P4CH cation is a bridge between the TA and P4C chains. P4CH and P4C form a homoconjugated cation through the COOH···OOC hydrogen bonds of 2.559(5) A. Water interacts with TA and P4CH, while methanol interacts only with water. In the optimized molecule of the (P4C) 2 H·TA·H 2 O·HOCH 3 complex, the components form a cyclic oligomer through four O–H···O and four N–H···O hydrogen bonds. The 1 H and 13 C NMR spectra elucidate the structure of the title complex in the aqueous solution. The 13 C CP MAS NMR spectrum is consistent with the X-ray results. The FTIR spectrum confirms a very complex structure of the title compound.

Silico-phosphate glasses of NaCaPO 4 -SiO 2 and NaCaPO 4 -AlPO 4 -SiO 2 system have been the subject of the presented investigations. Glasses of these systems are the basis for the preparation of glassy-crystalline biomaterials [R.D. Rawlings, Clin. Mater. 14 (1993) 155]. Detailed knowledge of the precursor glass structure is necessary for proper design of the glassy-crystalline biomaterials preparation procedure. Since there is no long-range ordering in glasses, spectroscopic methods which make it possible to study the short range ordering should be applied. MIR studies carried out in the work have allowed to establish that the glasses of the systems studied show domain composition [L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, J. Biol. Res. Symp. 2 (1971) 117; L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, J. Biol. Res. 5 (1972) 117]. Domain structure is close to that of the corresponding crystalline phases. It has been shown that even small amount of aluminium in the glass (5 mol.% of AlPO 4 ) significantly influences both, its texture (microscopic and EDX studies) and its structure (spectroscopic studies). 27 Al NMR investigations have made it possible to establish unequivocally that aluminium occurs exclusively in tetrahedral coordination, i.e. it is involved in the formation of glass framework. Presence of aluminium results in significant changes in the [SiO 4 ] 4− and [PO 4 ] 3− tetrahedra environment which is reflected in 23 Na, 31 P and 29 Si NMR spectra. Changes in the shapes and positions of the bands in the NMR spectra of glasses belonging to the NaCaPO 4 -AlPO 4 -SiO 2 system confirm great influence of aluminium on silico-phosphate glasses structure.

The structure of the 4-hydroxy-1-methylpiperidine betaine has been determined by X-ray diffraction. The crystals belong to the monoclinic system, space group Pc and unit cell parameters a = 8.972(2), b = 9.747(2), c = 9.562(2) A and β = 96.10(3)o. Two molecules are present in the asymmetric unit. They are in two antipodal chair conformations, in the first (A) with the methyl and hydroxyl groups in the equatorial positions and the CH2COO substituent in the axial one, and in the second (B) with the methyl and hydroxyl groups in the axial positions and the CH2COO substituent in the equatorial one. The molecules A and B form two separated zigzag chains, parallel to the z-axis. In each chain, the molecules are linked by the O–H···OOC hydrogen bonds of 2.723(3) and 2.704(3) A, in A and B, respectively. The optimized structure of the A conformer, at the B3LYP/6-31G(d,p) approach, is by 2.09 kcal/mol more stable than B. Two resonance signals attributed to the CH3 group in 13C CP MAS NMR spectrum confirm the conformational equilibrium in the solid-state. Two bands at 1631 and 1618 cm−1 in the solid-state FTIR spectrum suggest the presence of two inequivalent COO groups. The calculated FTIR spectra of conformers A and B differ in the frequencies of the O–H and C–H modes.

Polycrystalline sample of pyridinium perchlorate was studied by NMR method in the temperature range from 133 to 313 K. Assuming a reorientation of pyridinium cations over inequivalent potential energy barriers in the low-temperature and intermediate phases a temperature dependence of an asymmetry parameter Δ was determined from analysis of 2 H line shape. By using the known potential shape and population of its minima, a temperature dependence of the spontaneous polarisation was calculated. The polarisation determined in this way compared with that measured by the pyroelectric effect revealed the mixed type of ferroelectricity in the crystal studied: the order-disorder and displacive one.

This paper reports a nuclear magnetic resonance study of the molecular motion in copolymers derived from glycolide and L-lactide in the solid state. Variation of T1 relaxation times with temperature reflects a local disorder and the fast segment conformational motions which can be quantified in terms of correlation times predicted by the Bloembergen–Purcell–Pound and Davidson–Cole models. At low temperatures, spin relaxation is dominated by the axial methyl rotation in lactide units described by an asymmetry parameter of the correlation time δ which takes a value of about 0.45 for all systems. Above the devitrification points the trans and gauche isomerization in glycolide segments occurs. In addition to the chemical structure characterization, solid-state magic-angle spinning spectroscopy gives an insight into the role of glycol segments in the chain mobility.

On the basis of occupancy factor data for nitrogen atoms in the pyridinium cation obtained from the structural study of PyHIO 4 by neutron diffraction, 4 the shape of the potential for cation reorientation about the axis perpendicular to its plane was found. The 2 H NMR spectra of d 5 PyHIO 4 taken over a wide range of temperatures have allowed the determination of potential minima populations. These data were used to obtain the temperature dependence of spontaneous polarization. The agreement between the spontaneous polarization calculated in this way and the measured values is very good and indicates that the ferroelectric crystal is of the order-disorder type.

Nuclear magnetic resonance (NMR) and broadband dielectric spectroscopies (BDS) were used to analyze the molecular dynamics in P10.3H Podand. The temperature studies of NMR line and magnetic spin-lattice relaxation times accompanied by DS investigation enabled us to distinguish three main dynamical processes connected with the motions of the P10.3H Podand chains. In the low-temperature region the magnetic relaxation was associated with fast axial C 3 rotation of methyl groups. Moreover, two other independent processes were observed and interpreted as (i) segmental motion of both oxyethylene and ethylene units, and (ii) the overall motion involved in the melting process.

Polymer-layered silicate nanocomposites belong to a new class of hybrid materials consisting of organic-synthetic polymer matrix and inorganic filler-layered structure clay minerals. The paper presents the results of FTIR, NMR, and SAXS studies of poly(e-caprolactone)/sodium montmorillonite nanocomposites. We observed a correlation between the concentration of poly(e-caprolactone) in nanocomposite samples and structural changes both of the clay mineral and the intercalated polymer. Stiffening of the clay structure appears as a result of poly(e-caprolactone) intercalation into a clay structure. Al NMR studies indicated in nanocomposites two non-equivalent sites of aluminium ions, i.e. in octahedral and tetrahedral coordination, whereas in the montmorillonite clay structure the aluminium ions are located in the interlayer space too. We found also that the temperatures of structural changes and softening process of poly(e-caprolactone) chains in the nanocomposites depend on the concentration of poly(e-caprolactone).

Detailed ICP, IR, Raman and NMR investigation were performed for more than 50 samples of beryls from pegmatites in the Sudety Mts. MIR spectra were measured at room (293 K), low up to 22 K and high up to 1273 K temperatures. The absorption bands for studied samples of beryl are correlated with chemical composition and structural parameters. The samples represent both alkali-poor (potassium-bearing, sodium-potassium-bearing) and alkali-rich (sodic and sodic-lithian) members of the beryl group. Two types of H 2 O molecules are discerned in all studied beryls. The I-type is not connected with alkali with bands at 3697/3690 cm −1 , 3647/3630/3610 cm −1 (3606 cm −1 in Raman spectra) and 1602/1550 cm −1 dominates over the II-type (hydrated anions of alkali) with bands at 3660 cm −1 , 3592/3590 cm −1 (3597 cm −1 in Raman spectra) and 1637/1630 cm −1 . CO 2 molecules (2360 cm −1 in MIR spectra, 1386 cm −1 , 1240 cm −1 in Raman spectra) and hydroxyl groups in subordinate quantities occur in structural channels of beryls, except for mentioned above. Main bands in the range of 1200–400 cm −1 are diagnostic in discerning of the three types of beryls according to lattice parameter classification. Studied beryls, in the most cases, belong to normal-type. Some samples are octahedral-type, and do not occur tetrahedral beryls in the Sudety Mts.

Glasses used for the fabrication of fibrous insulating materials are made from natural raw materials, mainly basalts. Basalt alloys, however, show relatively high crystallization capability, which is disadvantageous for throwing and durability of the fibres prepared. In the work new raw materials, such as melaphyres and diabase from the Silesia region of Poland were applied for the preparation of aluminosilicate alloys. In order to study their crystallization ability the glasses were heated in an electric furnace at various temperatures for various time periods. Depending on the raw material used as well as the temperature of heat-treatment amorphous or crystalline materials were obtained. Crystalline phases were identified based on X-ray diffraction studies. It was found that magnetite/titanomagnetite crystallized in the first step. Then pyroxenes phases of diopsides or augite type appeared in the systems. Spectroscopic investigations in the mid IR region were carried out for all the glasses. This made it possible to determine the influence of thermal treatment on the structural changes of glasses (changes in the spectra shapes). Locations of the bands due to Al–O–Si and Si–O–Si bridges vibrations suggested that in most cases the augite-type phases were present in the systems (aluminium coordination number equal to 4 and 6). Appearance of aluminium in coordination 4 and 6 was confirmed by NMR investigations (two clear bands in the spectra).

The aim of the work is to determine the internal structure of bioactive glasses based on structural studies. Due to the absence of the long-range order, the X-ray methods usually applied in the studies of crystalline materials are of low applicability in the investigations of glasses. Therefore, spectroscopic methods, such as IR and NMR, which make it possible to ‘see’ the short- and the middle-range order are extremely suitable in their studies. IR investigations have shown that the glasses studied exhibit non-uniform domain composition, which should facilitate their transformation into glass-crystalline state. Additionally, detailed NMR measurements have been carried out in order to determine the influence of glass structure on the course of its crystallization. These studies make it possible to verify the common opinions on the middle-range order (domains) in the glasses studied. The results obtained for 27 Al and 31 P are particularly promising. Changes in the environment of [SiO 4 ] 4− tetrahedra, which can be spatially connected with various numbers of [PO 4 ] 3− and [AlO 4 ] 5− tetrahedra cause the presence of various types of bridging bonds, such as Si–O–Si, Si–O–Al and Si–O–P. This in turn has significant impact on the number and the shape of the bands occurring in the spectra.

Spin-lattice NMR relaxation times T1 in the laboratory frame and T1rho(off) as well as T1rho(off) in the rotating frame off-resonance were employed to the study of molecular dynamics of both pristine PPS and thermally treated poly(p-phenylene sulfide) (PPS). The temperature dependence of T1 was exponential in the whole temperature range studied, whereas T1rho only in low temperatures. In the high temperature range the distribution of relaxation times T1rho and correlation times tau(c) as well as activation energy Ea was observed. The distribution of activation energy determined from T1 minima at 15 and 30 MHz and from low temperature slopes of T1rho dependence as well as from spectral density functions (estimated from proton off-resonance technique) was attributed to the reorientation of phenylene groups around the sulfur-phenyl-sulfur axis in amorphous and crystalline phases of PPS. Furthermore, it is suggested that an additional relaxation mechanism related to interactions of protons with paramagnetic centers is operative in a low temperature range. After thermal treatment of PPS the low temperature minima disappeared and the relaxation times shortened in the low temperature regime. Both these facts were attributed to an increased contribution of spin diffusion in the relaxation process.

Measurements of the 1H and 19F nuclear magnetic resonance (NMR) second moments were performed for a polycrystalline sample of (PyH)BF4, whereas the shape of the 2H NMR line was analysed for a polycrystalline sample of (d5PyH)BF4. Asymmetry parameter δ has been calculated for four models of pyridinium cation reorientation among inequivalent potential energy minima, using the experimental value of the 1H NMR second moment as well as the 2H NMR line width. From knowledge of the potential shape and the population of its minima, the temperature dependence of polarization for all the models has been found. From the comparison of the experimentally determined polarization with the calculated polarization, the most appropriate model of the pyridinium cation reorientation has been chosen.

In the work, the results of 27 Al MAS NMR studies carried out for structures of different framework aluminosilicates are presented. The spectra of natural clinoptilolite and its sodium and hydrogen forms were measured. The zeolite spectra were obtained before and after incorporation of heavy metal cations (Pb 2+ , Cd 2+ , Ni 2+ and Cr 3+ ) into the zeolite structure. After decomposition of the spectra into component peaks differences caused by ion exchange were observed. Additionally, NMR spectra of kalsilite (framework aluminosilicate, not belonging to zeolite group) and other zeolites (chabazite, heulandite and analcime) were measured. 27 Al MAS NMR spectra of all the samples studied were compared with the FTIR spectra measured in the middle infrared region. Based on the results obtained it has been proved that the interpretation of spectra obtained using these two different techniques can give some information concerning changes occurring in various framework aluminosilicate structures.

Solid poly[(R)-3-hydroxybutyric] acid was examined by high-resolution 13C MAS NMR, differential scanning calorimetry and infrared spectroscopy. The 13C methyl group resonance consists of three components: the rigid amorphous phase, the crystalline phase and the mobile amorphous phase. Spectral deconvolution, using the Lorentz function, reveals the relative amounts as 62% crystalline and 38% amorphous at 333 K, and 42% crystalline, 40% pure amorphous and 18% beta-orthorhombic at 413 K. NMR indicates a large difference in molecular mobility between the crystalline and amorphous regions of the sample. Infrared spectroscopy shows that the stretching at 1725 cm(-1) (characteristic of the alpha-form) comes from the crystalline region, and the bands at 1744 cm(-1) (characteristic of the beta-form) and 1800 cm(-1) come from the amorphous region.

The 2 H NMR spectra of the selectively deuterated polycrystalline n -dodecylammonium chloride as well as 13 C CPMAS spectra of this compound are studied over a wide range of temperature. The results reveal a variety of phase transitions occurring in this model bilayer system and make it possible to relate them to the local molecular dynamics of the alkyl chains.

The relation between molecular dynamics and phase properties of the bilayered compound C12H25NH3C1 is studied by differential scanning calorimetry, proton second moment, and spin-lattice relaxation times. In the low-temperature phase I of the compound methyl and ammonium groups execute a classical threefold reorientation, while the alkylammonium chains are rigid on the nuclear magnetic resonance time scale. In the intermediate-temperature phase δ a trans-gauche isomerization of the alkyl chains is observed. In the high-temperature phase α the reorientation of the whole chains about their long axes, which are parallel to the normal to the ionic layer is evidenced. In the metastable e phase the dynamics involves classical rotation of methyl and ammonium groups and CH2 groups motion of the trans-gauche isomerization type.

Nuclear magnetic resonance line shapes and spin-lattice relaxation timesT 1, of1H and2H nuclei of poly[(R)-3-hydroxybutyric acid] have been measured in the temperature range 100–413 K. The results provide information on the local dynamics of the compound. Activation parameters of the revealed motion are determined.

The crystal structure of bis(thiourea) pyridinium iodide (T2PyI) was previously determined at 295 and 110 K [Prout, Heyes, Dobson, McDaid, Maris, Mueller & Seaman (2000). Chem. Mater. 12, 3561–3569] and the two phases were described in the space groups Cmcm and P21 cn, respectively. Because differential scanning calorimetry revealed two phase transitions, at 161 and 141 K, a redetermination of the structure of T2pyI at 295, 155 and 110 K has been undertaken, and the following sequence of space groups obtained: Cmcm (I) → C2cm (II) → P21 cn (III). The high- (I) and low-temperature (III) phases confirmed the results reported in the previous study. In the new intermediate phase II, the mirror plane perpendicular to the x axis vanishes and the crystal structure loses the centre of symmetry. In phases I and II the pyridinium cations are strongly dynamically disordered, while in the low-temperature phase III the cations are well ordered. In all three phases the thiourea–iodine hydrogen-bonded sublattice is very well ordered. Dielectric measurements show that the intermediate and low-temperature phases are ferroelectric and that 161 K is the Curie point of a new ferroelectric crystal.

$^{11}\mathrm{B}$ NMR measurements on a single crystal of $\mathrm{Y}{\mathrm{B}}_{12}$ have been performed at room temperature at a frequency of $128.4\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. The electric-field-gradient (EFG) tensor components and the principal axes calculated previously by first-principles methods have been verified experimentally. Three magnetically different boron-atom groups in the ${\mathrm{B}}_{12}$ cluster were clearly observed for the crystal orientation used in this work. This distinction results from different EFG-tensor orientations with respect to magnetic field and not from different quadrupolar splittings $({\ensuremath{\nu}}_{Q})$ or asymmetry-parameter values $(\ensuremath{\eta})$. The magnetically different boron atoms have been identified through the calculated angle dependence of the satellite transitions (0\ifmmode^\circ\else\textdegree\fi{}--360\ifmmode^\circ\else\textdegree\fi{}). Very satisfactory agreement between the calculated and experimental angular dependencies of the EFG tensor has been obtained. Similarly, the quadrupolar splittings and asymmetry parameters agree very well with those previously determined from NMR measurements on a powder sample of $\mathrm{Y}{\mathrm{B}}_{12}$.

A new method, the immobilisation of ferroceneacetic acid (FAA) on various MCM-41 mesoporous molecular sieves (containing Si or Si+Al) followed by calcination at 773 K has been applied for the formation of ion active species. The structural, surface and catalytic properties of these materials, characterised by N2 adsorption/desorption, XRD, 27Al NMR, ESR, and Mossbauer spectroscopy as well as test reactions, were compared with those of materials prepared via commonly used impregnation methods. Contrary to Fe-impregnated samples, Fe oxides species were only slightly detected in the solids modified by FAA followed by calcination. It is evidenced that the new technique applied for Fe-modification gives rise to the significantly higher activity (in isopropanol decomposition and acetonylacetone cyclization) reached thanks to a better isolation and/or dispersion of Fe3+ species. The presence of Al, in the sample influences the Fe3+ reduction under vacuum.

The ordering of the anionic sublattice at the coexisting high orientational disorder of the cationic sublattice produces spontaneous polarization in imidazolium tetrafluoroborate $[{\mathrm{C}}_{3}{\mathrm{N}}_{2}{\mathrm{H}}_{5}{]}^{+}[{\mathrm{BF}}_{4}{]}^{\ensuremath{-}}.$ This ferroelectric crystal exhibits the Curie point at 297.0 K and undergoes two other polymorphic phase transitions at 213.6 and 187.8 K. In spite of its pentagonal ring the dynamically disordered polar cation is localized at a special position on the threefold axis of the highly symmetrical rhombohedral unit cell. Thus it does not contribute immediately to the spontaneous polarization which originates predominantly from the behavior of the distorted tetrahedral fluoroborate anion.

A prototype NMR probe for long RF pulse has been constructed. Its main elements are two coils mounted in the concentric position. The first bigger coil is wound around a glass dewar tube and the second smaller coil is placed inside the dewar. These two coils are thermally isolated by the dewar. A long and strong RF pulse is applied to the bigger coil. The smaller detection coil inside the dewar contains a sample and to this coil a short RF pulse is applied. The two coils are independently tuned and electrically isolated. During the operation of the strong RF pulse the smaller coil has a high resistance to ground (very low Q factor) and does not absorb energy from the bigger coil. During the operation of the short on-resonance RF pulse the bigger coil is detuned to a higher frequency, but the resonance circuit with the small coil is in the electrical resonance. The NMR probe may be used in off-resonance experiments in which long and strong RF pulses are applied to the bigger coil and thereby the problem of the sample overheating is avoided.

Molecular dynamics in n -dodecylammonium chloride/water solutions for concentrations of 34 and 45 wt% was studied by 2 H NMR and by 1 H NMR dispersion of spin–lattice relaxation in the 2 kHz–90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of 2 H NMR lineshapes of selectively deuterated DDACl molecules gave us an evidence for local trans–gauche conformational changes in the chains, whereas the dispersion of spin–lattice relaxation times T 1 explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin–lattice relaxation below 1 MHz and that local motions and translational diffusion are responsible for the spin–lattice relaxation in the higher Larmor frequency range.

A model of the methyl group dynamics of two steroid compounds: cholesterol and ergocalciferol was proposed on the grounds of complementary studies performed by inelastic incoherent neutron scattering, nuclear magnetic resonance and quantum chemistry calculation methods.

We have grown a single crystal of ReB2 and refined its crystal structure. Our structural studies confirmed the hexagonal structure (space group P63/mmc) with lattice parameters a=2.8982(1) A and c=7.4723(3) A. We also report the observation of first order satellites in the B11 nuclear magnetic resonance, which indicated the presence of a nonzero quadrupole coupling frequency, νQ=276±3 kHz, and an asymmetry parameter η=0 at the boron atom sites. These values are in excellent agreement with electric-field-gradient (EFG) tensor calculations based on first principles. These calculations showed that the principal axis of the most negative EFG-tensor component, VZZ, is parallel to the c-axis of the crystal. This behavior is in agreement with the observed excess of B pz charge (c direction) over the px and py charges and is related to stronger metal-boron bonds compared to previously studied YB12 and LaB6, where the B–B bonds are stronger. Finally, the bonding properties of ReB2 are discussed in terms of densiti...

B11 nuclear-magnetic-resonance measurements on a B11 enriched single crystal of LaB6 have been performed at room temperature at a frequency of 128.4MHz. The electric-field-gradient (EFG) tensor components have been determined from the angle dependence of the quadrupole splittings associated with (−3∕2↔−1∕2) and (3∕2↔1∕2) satellite transitions. These EFG components have been calculated using first-principles methods. Very satisfactory agreement with the experimental values has been obtained. The calculations show that the largest component of the EFG tensor mainly comes from the pp part of the so-called sphere component. The principal axis for the most negative EFG component is oriented in direction of the shortest and strongest bond between neighboring B atoms, which belong to two different B6 units (interoctahedral B–B bonds). The fact that these interoctahedral B–B bonds are aligned in three different directions is responsible for the observation of up to three satellite pairs, although all boron atoms ...

2H NMR (nuclear magnetic resonance) line-shape measurements were performed over a wide temperature range for pyridinium nitrate (d5PyH)NO3 and bis-thiourea pyridinium nitrate inclusion complex T2(d5PyH)NO3 in order to compare the dynamics of d5-pyridinium cation in both compounds. It was revealed that in both systems the pyridinium cation undergoes reorientations about the axis perpendicular to its plane, among inequivalent potential energy barriers. However, in (d5PyH)NO3 (no phase transition) the population of the deepest minima decreases monotonically up to the melting point, whereas in T2(d5PyH)NO3 (two phase transitions) this population decreases rapidly in a transition to the high-temperature phase and its value does not depend on temperature. In bis-thiourea pyridinium nitrate inclusion compound the out-of-plane motion of the cation is also found in the intermediate- and high-temperature phases, and the amplitudes of the motion are equal to 20° and 35°, respectively. On the basis of the assumptions of these models, it is possible to reproduce the experimental 2H NMR line shapes in an excellent way.