Proton conductivity and proton dynamics in nanocrystalline cellulose functionalized with imidazole.

In the present study, we report the synthesis, electrical and dynamic properties of a new generation bio-based nanocomposite, that is a proton-exchange membrane based on nanocrystalline cellulose (CNC) and imidazole (Im). CNC serves as supporting material and imidazole acts as a proton donor and proton acceptor at the same time. The nanocomposite (1.3 CNC-Im) was synthesized as a film and shows proton conductivity equal to 4.0 × 10-1 S/m at 160 °C in anhydrous conditions. Analysis of impedance measurements and NMR spectra provided some insight into the macroscopic and microscopic processes involved in proton transport in 1.3 CNC-Im. Local processes such as reorientation of imidazole rings and breaking of hydrogen bonds are identified and their activation energies are calculated. The energies of the macroscopic and microscopic proton transport in CNC-Im film are correlated. The percolation model used confirmed the percolation nature of conductivity in cellulose composites with imidazole.

Comparison of structural, thermal and proton conductivity properties of micro- and nanocelluloses.

Our search for a cellulose-based proton conducting material is continued. This paper presents selected physicochemical properties of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) together with cellulose microcrystals (CMCs) and cellulose microfibrils (CMFs), determined by X-ray diffraction (XRD), thermogravimetric analysis (TGA + DTA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and electrical impedance spectroscopy (EIS). The CNCs and CNFs were studied in the forms of powder and film. They were produced in the process of transition metal catalyzed oxidative process or by TEMPO-mediated oxidation. It has been shown that regardless of the production method and the form of the sample the celluloses retained the cellulose Iß crystalline structure, the cellulose films showed similar thermal properties in the relevant temperature range from room temperature to about 200 °C, and the TEMPO-oxidized CNF film showed the highest proton conductivity when compared with those of the other samples studied.

The gelation influence on diffusion and conductivity enhancement effect in renewable ionic gels based on a LMWG.

This paper reports the interdisciplinary study on molecular dynamics, ionic interactions and electrical conductivity in a quaternary ammonium salt (TMABr) ionogel based on a low molecular weight gelator (LMWG) in a wide range of electrolyte molar concentrations. The thermal scanning conductometry (TSC) was used to investigate the electric properties of the ionogels. The prepared TMABr/H2O/LMWG ionogel exhibits better ion transport properties than the dissociated TMA+ cation in solution. The enhanced ionic conductivity effect (EICE) was observed in the concentration range of the TMABr salt up to 1 M. To investigate the transport properties of the TMA+ cation and solvent molecules in the gel and sol phase, the NMR diffusiometry method was used. The field-cycling relaxometry method (FFC NMR) was applied to study the local motions of the electrolyte at the surface of the gelator matrix. On the basis of the obtained data, the higher ionic conductivity observed in the gel phase has been related to the microstructure of the gel matrix. The possible explanation for the origin of this effect has been given. The investigated system is a thermally reversible physical gel, all registered data were reproducible upon transforming the sample from gel to sol and back to the gel state, confirming the enhancement effect as a permanent property of the investigated ionogels. Therefore, the EICE has been proposed to be used as an internal sensor to monitor the condition of the ionogel phase, thus making them smart materials.

Novel application of NMR relaxometry in studies of diffusion in virgin rape oil.

Field cycling (FC) proton nuclear magnetic resonance ((1)H NMR) relaxometry was applied to study the dynamics of rape oil molecules. The spin-lattice relaxation data, measured in the frequency range from 0.01 to 30 MHz, were analysed by applying relaxation theory combined with the force-free-hard-sphere (FFHS) diffusion model. In the low frequency range, the relaxation was dominated by the translational diffusion contribution. Therefore, the diffusion coefficient of rape oil was determined from a linear dependence of the (1)H NMR relaxation dispersion drawn as a function of the square root of Larmor frequency. The results are consistent with those obtained from the pulse gradient spin echo (PGSE) NMR method. To estimate the density of oil protons, a parameter required to derive the diffusion coefficient from NMR relaxometry, a single point imaging (SPI) NMR experiment was proposed.

Dynamic processes and chemical composition of Lepidium sativum seeds determined by means of field-cycling NMR relaxometry and NMR spectroscopy.

Proton nuclear magnetic resonance (NMR) techniques, such as field-cycling relaxometry, wide-line NMR spectroscopy, and magic angle spinning NMR spectroscopy, were applied to study the seeds of cress, Lepidium sativum. Field-cycling NMR relaxometry was used for the first time to investigate the properties of the whole molecular system of dry cress seeds. This method not only allowed the dynamics to be studied, but was also successful in the differentiation among the solid (i.e., carbohydrates, proteins, or fats forming a solid form of lipids) and liquid-like (oil compounds) components of the seeds. The (1)H NMR relaxation dispersion of oils was interpreted as a superposition of intramolecular and intermolecular contributions. The intramolecular part was described in terms of a Lorentzian spectral density function, whereas a log-Gaussian distribution of correlation times was applied for the intermolecular dipole-dipole contribution. The models applied led to very good agreement with the experimental data and demonstrate that the contribution of the intermolecular relaxation to the overall relaxation should not be disregarded, especially at low frequencies. A power-law frequency dependence of the proton relaxation dispersion was used for the interpretation of the solid components. From the analysis of the (1)H wide-line NMR spectra of the liquid-like component of hydrated cress seeds, we can conclude that the contribution of oil protons should always be taken into account when evaluating the spin-lattice relaxation times values or measuring the moisture and oil content. The application of (1)H magic angle spinning NMR significantly improves resolution in the liquid-like spectrum of seeds and allows the determination of the chemical composition of cress seeds.

Solvent effect on 1,2-O-(1-ethylpropylidene)-alpha-D-glucofuranose organogel properties.

The solvent effect on organogel formation in nitrobenzene and chlorobenzene using 1,2-O-(1-ethylpropylidene)-alpha-d-glucofuranose (1) as the gelator is presented. Fourier transform infrared (FTIR) spectroscopy revealed that hydrogen bonding between the molecules of gelator 1 is the main driving force for gelator self-aggregation. The gels are characterized by different hydrogen-bonding patterns, which are reflected in a different microstructure of the networks. The morphology of fibers of nitrobenzene organogel consists of straight, rod-like, and thinner fibers, in comparison to the elongated but generally not straight and thicker fibers in chlorobenzene organogel. The thermal stability of gels also differs, and the DeltaH is equal to 50.1 and 65.0 kJ/mol for nitrobenzene and chlorobenzene gels, respectively. The properties of the gels reported here were compared to benzene and toluene gels of 1 presented in previous work and correlated with different solvent parameters: epsilon, delta, and E(T)(30). We have shown that the polarity of the solvent influences the thermal stability of the gel, the hydrogen-bonding network, and finally the structure of gel network. Therefore, in the studied sugar-based gelator, the hydrogen bonding alone is insufficient to fully describe the gelation process.

Spin-lattice relaxation study of the methyl proton dynamics in solid 9,10-dimethyltriptycene (DMT).

Proton spin-lattice relaxation studies are performed for powder samples of 9,10-dimethyltriptycene (DMT) and its isotopomer DMT-d(12) in which all the non-methyl protons in the molecule are replaced by deuterons. The relaxation data are interpreted in terms of the conventional relaxation theory based on the random jump model in which the Pauli correlations between the relevant spin and torsional states are discarded. The Arrhenius activation energies, obtained from the relaxation data, 25.3 and 24.8 kJ mol(-1) for DMT and DMT-d(12), respectively, are very high as for the methyl groups. The validity of the jump model in the present case is considered from the perspective of Haupt theory in which the Pauli principle is explicitly invoked. To this purpose, the dynamic quantities entering the Haupt model are reinterpreted in the spirit of the damped quantum rotation (DQR) approach introduced recently for the purpose of NMR lineshape studies of hindered molecular rotators. Theoretical modelling of the relevant methyl group dynamics, based on the DQR theory, was performed. From these calculations it is inferred that direct assessments of the torsional barrier heights, based on the Arrhenius activation energies extracted from relaxation data, should be treated with caution.

Proton magnetic resonance microimaging of human trabecular bone.

Proton magnetic resonance (1H magnetic resonance imaging (MRI)) images of human trabecular bone were acquired and discussed for two samples with different porosity. Three-dimensional 3D Spin Echo (3D SE) and Multi-Slice Multi-Echo (MSME) pulse sequences were examined. A very high slice resolution of (38 microm)2 was achieved (MSME). The intensity histograms were found useful for the characterization of the bone porosity. A spatial distribution of the spin-spin relaxation time T2 was monitored with the MSME pulse program. The work demonstrates the great potential of the proton MRI technique in the study of the trabecular bone morphology.

A nuclear magnetic resonance study of molecular motion in solid tris (n-propylammonium) enneachlorodiantimonate (III) (n-C3H7NH3)3Sb2Cl9.

Proton magnetic resonance second moment and spin-lattice relaxation time were carried out on polycrystalline tris (n-propylammonium) enneachlorodiantimonate (III), (n-C3H7NH3)3Sb2Cl9, in the temperature range of 10-370 K. The second moment measurements show that the structure is not rigid on the NMR scale at 10 K, the lowest temperature studied, and that CH3 and NH3 groups execute rotations about C3 axis. The proton spin-lattice relaxation measurements reveal two minima due to the motions of the amino and methyl groups. Analysis of the relaxation data yields the activation energy barriers of 11.0 kJ mol(-1) and 5.8 kJ mol(-1), respectively, for the NH3 and CH3 groups' motion. NMR data confirm the phase transition at Tc = 232 K, known from different studies.

Nuclear magnetic resonance proton dynamics study of [N(CH3)2H2]3Bi2I9 at low temperature.

The phase transitions of dimethylammonium nonaiododibismuthate [N(CH3)2H2]3Bi2I9 were studied by investigating the temperature dependence of the line widths and proton spin-lattice relaxation times in the nuclear magnetic resonance spectrum. Two phase transitions appeared to be connected with motions of the cationic and CH3 group in the molecule, while the third one seemed to be connected with the dynamics of the Bi2I9 group.

Molecular motions in solid [N(CH3)2H2]3Sb2I9 studied by proton nuclear magnetic resonance spectroscopy.

Molecular motions and phase transition in [N(CH3)2H2]3Sb2I9 was studied by measuring the temperature dependencies of the proton spin-lattice relaxation times T1 and the second moment M2. The results are interpreted in terms of the C'3 reorientation of the methyl groups and the whole cationic reorientation about the C2 axis. The activation parameters for these motions have been determined. The phase transition has no influence on the M2 and the T1 values, thus suggesting that it is not directly connected to the motion of the cation but rather to the dynamics of the inorganic subsystem [Sb2I9]3-.

Molecular motions and phase transitions in solid bis-n-propylammonium pentabromoantimonate.

The proton nuclear magnetic resonance (NMR) second moment and spin-lattice relaxation time for polycrystalline bis-n-propylammonium pentabromoantimonate (nPBA) have been measured from 70 to 290 K. The results are interpreted in terms of the CH3 and NH3 group reorientations for which the activation parameters have been determined. A structural phase transition evidenced at about 220 K is found in the polycrystalline sample of nPBA.

17O, 14N and 15N n.m.r. studies of the Co2+ complexes of cyclo(Pro17O-Gly15N) and cyclo(Gly17O-Pro) in aqueous solution.

The complexation of cyclo(Pro17O-Gly15N) and cyclo(Gly17O-Pro) with Co2+ ions has been studied by 17O, 14N and 15N n.m.r. spectroscopy in aqueous solution. 17O, 14N and 15N transverse relaxation times and chemical shifts were measured as a function of temperature. The 17O n.m.r. studies unequivocally demonstrate that the cobaltous ion binds to the peptide oxygen of both compounds. The hyperfine coupling constant and the peptide residence times were found to be A = -0.165 MHz and -0.145 MHz, tau m = 16, and 92 microseconds for cyclo(Pro17O-Gly15N) and cyclo(Gly17O-Pro), respectively. The 14N and 15N studies of labeled cyclo(Pro17O-Gly15N) do not indicate binding at either the Gly15N or the Pro14N site.

17O n.m.r. studies of amino acids in the solid state, in single- and polycrystalline forms.

A single crystal of 17O enriched alpha-glycine was grown by slow evaporation of aqueous solution. 17O n.m.r. studies of the alpha-glycine molecule in single crystalline form revealed five 17O transitions each consisting of two lines due to inequivalency of the oxygen atoms in the unit cell, with each of these lines revealing a dipolar interaction between the 17O and the nearest hydrogen atom. The spectral width was found to be of the order of magnitude of MHz and the linewidths of the order of magnitude of 2 kHz.

17O and 14N n.m.r. studies of the Co (II) interaction with cyclo(Ala*-Ala) in aqueous solution.

The complexation of cyclo(Ala*-Ala) with the cobaltous ions in aqueous solution was investigated by 17O and 14N n.m.r. spectroscopy. The 17O and 14N transverse relaxation time (T2p) and chemical shift (delta omega a) of cyclo(Ala*-Ala) were measured as a function of the temperature at pH = 7.03 +/- 0.02, and pH = 6.45 +/- 0.02, and as a function of pH at room temperature. No effects of pH on the transverse relaxation time and chemical shift were observed. Complementary 17O studies of the solvent water molecules were also carried out. The hyperfine coupling constant and the entropy and enthalpy of activation for the exchange of cyclo(Ala*-Ala) and water molecules between the coordinated and noncoordinated states were determined by least-square fit of theoretical equation for the chemical shift delta omega a to experimental data. The hyperfine coupling constant of the peptide bound oxygen was determined to be (-1.6 +/- 0.1) X 10(5) Hz and the entropy and enthalpy (32.0 +/- 3.0) kJ/mol and (-12.0 +/- 1.0) e.u, respectively. Information obtained from 17O n.m.r. study allows some inferences concerning the probable coordination sphere of the cobaltous ion. There are three types of complexes: Co(H2O)6(2+), CoL X 5H2O and CoL2 X 4H2O, with relative concentrations 19.9%, 2.9%, and 77.2%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)