Adam Rachocki

Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry

Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(ω) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.

Structure, hydrogen bond network and proton conductivity of new benzimidazole compounds with dicarboxylic acids

Dicarboxylic acids are interesting for crystal engineering due to their ability of hydrogen bond formation. To find a relationship between the molecular structure and the properties of proton conducting materials, we synthesized two compounds of benzimidazole with dicarboxylic acids of different chain length: glutaric and pimelic acids. The structure of the compounds was determined by X-ray diffraction and compared with molecular arrangement studied by 13C CP/MAS NMR spectroscopy supported by Density Functional Theory computations for benzimidazole. Benzimidazole was found to form salt with glutaric acid in a 1 : 1 ratio and monoclinic layer-type structure with P21/n space group. Flat layers, parallel to (−102) plane, are built of glutaric acid molecules linked into rectangular-type chains by O–H⋯O bonds and benzimidazole molecules attached to the chains by N–H⋯O bonds. The molecule of the benzimidazole compound with pimelic acid contains two benzimidazole rings and one pimelic acid chain. The structure with alternating layers, built of two groups of benzimidazole dimers and layers of pimelic acid chains, belongs to P21/n space group. The acid layers are built of pimelic acid molecules linked by O–H⋯O hydrogen bonds into chains parallel to [30−1] direction and the benzimidazole dimers are linked to the acid layers by N–H⋯O bonds. Impedance spectroscopy studies in wide frequency and temperature range of pellets made of powdered compounds enabled to separate the contributions of crystalline and grain boundary parts to the electric conductivity. The conductivity (averaged over all directions) of the crystalline compounds of benzimidazole with glutaric and pimelic acid is characterized by activation energy of 2.5 eV and 1.6 eV, respectively, which is in an agreement with the hydrogen bond network in the materials.

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.

The structural dynamics in the proton-conducting imidazolium oxalate

The 1H spin–lattice relaxation times and high-resolution solid-state nuclear magnetic resonance (NMR) under fast magic spinning were used to study the structural dynamics in the proton-conducting material imidazolium oxalate. The measurements provide evidence for the ordered and disordered domains within the studied material. The two components drastically differ in their 1H spin–lattice relaxation times and 1H–13C cross-polarization magic-angle-spinning (CP/MAS) spectra. The coalescence phenomenon of the resonances of the basal carbons of the imidazole ring undergoing a reorientation is observed only for mobile molecules in the disordered domains. Therefore, only these molecules can be responsible for proton conductivity allowing for the Grotthus mechanism.

Effect of gel matrix confinement on the solvent dynamics in supramolecular gels.

Supramolecular gels formed by the sugar gelator of methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside (1) with 1,3-propanediol (PG) and 1-butanol (BU) were prepared with different gelator concentrations. The solvent dynamics within gels, characterized by the diffusion coefficient (D) and the spin-lattice relaxation time (T1), was the subject of NMR diffusometry and relaxometry studies. The diffusion was studied as a function of diffusion time and gelator concentrations. The relaxation time was measured as a function of Larmor frequency. The decrease of the diffusion coefficient was observed as a function of diffusion time for both gels and for all studied gelator concentrations. It is indicative of the confinement effect due to the geometrical restrictions of the gel matrix. The relaxation data for PG solvent confined in 1/PG gel revealed the low frequency dispersion (in kHz region) which is a fingerprint of a specific interaction experienced by PG solvents in the presence of the rigid structure of gelator 1 aggregates. The relaxation model, well known from the interpretation of liquid confined in nanopores as reorientations mediated by translational displacements (RMTD), was successfully applied to analyze the data of studied solvents confined in matrices of supramolecular gels. The microstructures of gel matrices were imaged by Polarized Microscopy.

The crystal structure and evidence of the phase transition in D-amphetamine sulfate, as studied by X-ray crystallography, DSC and NMR spectroscopy

X-Ray crystallography, DSC and NMR spectroscopy methods have been used to study the phase transition of D-amphetamine sulfate. The phase transition temperature occurs at about 325 K, and belongs to the discontinuous type with a large temperature hysteresis. A change in the space group is observed from monoclinic P21 in the low temperature phase to monoclinic C2 in the high temperature phase. The transformation from phase I to phase II is a result of the ordering of the SO42−groups, allowing a T-shape interaction between D-amphetamine molecules. Proton relaxation rate data obtained for the studied compound have been analysed by assuming two dynamically-inequivalent methyl groups below the phase transition and only one type of ammonium group above the phase transition. The activation energies for the C3 reorientation of the methyl groups have been determined to be 7.31 and 11.89 kJ mol−1, whereas for the ammonium group it is 27.29 kJ mol−1.

Morphology, molecular dynamics and electric conductivity of carbohydrate polymer films based on alginic acid and benzimidazole.

The present paper describes a preparation method and molecular investigations of new biodegradable proton-conducting carbohydrate polymer films based on alginic acid and benzimidazole. Electric conductivity was studied in a wide temperature range in order to check the potential application of these compounds as membranes for electrochemical devices. Compared to pure alginic acid powder or its film, the biodegradable film of alginic acid with an addition of benzimidazole exhibits considerably higher conductivity in the range above water boiling temperature (up to approximately 10(-3) S/cm at 473 K). Due to this important feature the obtained films can be considered as candidates for application in high-temperature electrochemical devices. The microscopic nature and mechanism of the conduction in alginate based materials were studied by proton nuclear magnetic resonance (NMR). The results show specific changes in morphology and molecular dynamics between pure alginate powders and the films obtained without and with the addition of benzimidazole molecules.

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.

The indications of tautomeric conversion in amorphous bicalutamide drug

Abstract The investigation of tautomerization phenomenon in pharmaceutically relevant materials has important implications. The lack of knowledge about tautomeric preferences may negatively impact the formulation and manufacturing process as well as performance of drug product. In this paper we performed theoretical calculations to verify the occurrence of proton transfer in popular anti‐androgen drug bicalutamide (BIC). Density functional theory (DFT) calculations determine the activation energy values for possible tautomeric paths providing a basis for comparison with experimental data. To find the indication of the presence of imidic acid and amide tautomers in amorphous BIC we applied infrared spectroscopy (IR). Finally, we performed isothermal broadband dielectric spectroscopy studies (BDS) to select the most likely mechanism of proton transfer in supercooled BIC. We found out that thermal processing applied during glass preparation via vitrification method results in the presence of amide and imidic acid forms in glassy BIC. Further heating leads to re‐equilibration of supercooled BIC manifested by the growth of viscosity and effective dipole moment. Based on the value of activation energy determined in theoretical and experimental BDS studies we recognized that the observed time evolution of dielectric parameters likely reflects the increasing amount of more stable amide tautomer. The results presented herein indicate that in amorphous BIC in particular conditions the temperature‐dependent changes in tautomeric composition due to intramolecular proton transfer are possible. Graphical abstract Figure. No Caption available.

A novel method of recognizing liquefied honey

The content of glucose, fructose, sucrose, maltose and water were determined for multiflorous honey of Great Poland. The measurements were carried out for different fractions of honey and also for the liquefied honey at 40 °C. Water activity and pH were both determined for all samples. A new method of recognizing liquefied honey is proposed based on the water influence on pH and the monosaccharides and disaccharides contents. The simple function of quadratic polynomial enabled to reveal the different character of the liquefied honey. The electrical conductivity behavior of different dry matter samples of honey are presented in the wide range of temperature. The proton spin-lattice relaxation measurements were recorded for the crystalline fraction in the magnetic field range covering the proton Larmor frequencies from 0.01 to 25 MHz and in the wide range of temperature. Heating the honey at 30 °C results in the irreversible molecular structure changes.