Michał Bielejewski

Solvent Effect on 1,2-O-(1-Ethylpropylidene)-α-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.

Novel supramolecular organogels based on a hydrazide derivative: non-polar solvent-assisted self-assembly, selective gelation properties, nanostructure, solvent dynamics

In this work, we report the complementary studies of supramolecular organogels composed of a newly synthesized low molecular mass gelator 4-(4-morpholinyl)-3-nitro-benzoylhydrazide (1) with benzene, toluene, and p-xylene. Intermolecular hydrogen bonding and π–π stacking interactions are the main driving forces promoting gelation of the system and the self-assembly of the new gelator molecules. The former interactions were revealed by the FT-IR and Raman studies, whereas the latter ones were postulated on the basis of the molecular structure of the gelator, UV-Vis spectra and comparison with the previously published data for other hydrazide derivatives. The strengths of the hydrogen bonding interactions are comparable as indicated by the FT-IR spectra analysis. Therefore, we correlated the differences in the calculated enthalpies of the gelator aggregates of 1 in the gels studied with the differences in the strengths of the π–π stacking interactions. The gel of 1 with benzene is characterized by the highest value of enthalpy. The images taken by the SEM and POM methods reveal differences in the architecture of gelator 1 aggregates, which are lamellar-like in toluene and fibrillar in benzene and p-xylene. The dispersion of spin–lattice relaxation times of solvents in the gel phase, observed by the NMR relaxometry method at low frequencies, is an indicator of the solvent–gelator interactions. As a result of this interaction, a significant slowing down of the motion (5 orders of magnitude as compared to bulk solvents) of the fraction of solvent molecules at the pore surface in the gel phase takes place. The diffusion of solvents in gels is restricted as shown by PGSE NMR. The apparent diffusion coefficient measured as a function of diffusion time can be used to estimate the pore size of the gel matrix, which for the gel of 1 with toluene is about 22 μm.

Evidence of Solvent-Gelator Interaction in Sugar-Based Organogel Studied by Field-Cycling NMR Relaxometry

The dynamics of bulk toluene and toluene confined in the 1,2-O-(1-ethylpropylidene)-α-D-glucofuranose gel was studied using (1)H field-cycling nuclear magnetic resonance relaxometry. The proton spin-lattice relaxation time T(1) was measured as a function of the magnetic field strength and temperature. The observed dispersion in the frequency range 10(4)-10(6) Hz for the relaxation rate of toluene in the gel system give evidence of the interaction between the toluene and the gelator aggregates. The data were interpreted in terms of the two-fraction fast-exchange model. Additionally it was also shown that a cooling rate during gel preparation process influences the gel microstructure and leads to different gelator-solvent interactions as reflected in a different behavior of the proton spin-lattice relaxation rate of toluene within the gel observed at the low frequency range.

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.

Molecular interactions in high conductive gel electrolytes based on low molecular weight gelator.

Organic ionic gel (OIG) electrolytes, also known as gel electrolytes or ionogels are one example of modern functional materials with the potential to use in wide range of electrochemical applications. The functionality of OIGs arises from the thermally reversible solidification of electrolytes or ionic liquids and their superior ionic conductivity. To understand and to predict the properties of these systems it is important to get the knowledge about the interactions on molecular level between the solid gelator matrix and the electrolyte solution. This paper reports the spectroscopic studies (FT-IR, UV-Vis and Raman) of the gel electrolyte based on low molecular weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside and solution of quaternary ammonium salt, tetramethylammonium bromide. The solidification process was based on sol-gel technique. Below characteristic temperature, defined as gel to sol phase transition temperature, Tgs, the samples were solid-like and showed high conductivity values of the same order as observed for pure liquid electrolytes. The investigations were performed for a OIGs in a wide range of molar concentrations of the electrolyte solution.

Thermally reversible solidification of novel ionic liquid [im]HSO4 by self-nucleated rapid crystallization: investigations of ionic conductivity, thermal properties, and catalytic activity

In recent years, the growing concern for the environment has triggered the search for new materials that meet the criteria for the preservation of natural habitats. Among these materials are ionic liquids, the new generation of which has contributed substantially to the rapid development of green chemistry. In this paper, we report the synthesis and characterization of an ionic liquid of imidazolium hydrogen sulphate ([im]HSO4), which displays multifunctional properties. The [im]HSO4 ionic liquid can be used either as an efficient catalyst in the preparation of hexahydroquinolines under green conditions or as a thermally reversible ionogel. Investigations of its catalytic properties showed that [im]HSO4 can be reused at least four times without appreciable loss of activity, and the reaction yields are in the range of 92% to 98% referred to the isolated pure products. On the other hand, the ionogels formed by [im]HSO4 showed high ionic conductivity (up to 25 mS cm−1 in the solid phase) and melting points of approximately 54 °C. The process responsible for gelation was found to be solidification by self-nucleated crystallization. The structure of [im]HSO4 was fully characterized using FT-IR, 1H NMR, 13C NMR, XRD, SEM, TGA, and DTA. The physical properties important from an application point of view (e.g., ionic conductivity, thermal stability, phase transitions and microstructure) were investigated by thermal scanning conductometry (TSC), differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The results of this work support the rational design, synthesis and application of task-specific ionic liquids for various purposes.