Solvent contribution to the stability of a physical gel characterized by quasi-elastic neutron scattering

The dynamics of a physical gel, namely the Low Molecular Mass Organic Gelator {\textit Methyl-4,6-O-benzylidene-$\alpha$ -D-mannopyranoside ($\alpha$-manno)} in water and toluene are probed by neutron scattering. Using high gelator concentrations, we were able to determine, on a timescale from a few ps to 1 ns, the number of solvent molecules that are immobilised by the rigid network formed by the gelators. We found that only few toluene molecules per gelator participate to the network which is formed by hydrogen bonding between the gelators' sugar moieties. In water, however, the interactions leading to the gel formations are weaker, involving dipolar, hydrophobic or $\pi-\pi$ interactions and hydrogen bonds are formed between the gelators and the surrounding water. Therefore, around 10 to 14 water molecules per gelator are immobilised by the presence of the network. This study shows that neutron scattering can give valuable information about the behaviour of solvent confined in a molecular gel.Comment: Langmuir (2015

Low-Molecular-Weight Organogelators Based on <i>N</i>-dodecanoyl-L-amino Acids—Energy Frameworks and Supramolecular Synthons

Lauric acid was used to synthesize the low-molecular-weight organogelators (LMOGs), derivatives of two endogenous (L)-alanine, (L)-leucine, and three exogenous (L)-valine, (L)-phenylalanine, and (L)-proline amino acids. The nature of processes responsible for the gel formation both in polar and in apolar solvents of such compounds is still under investigation. Knowing that the organization of surfactant molecules affects the properties of nano scale materials and gels, we decided to elucidate this problem using crystallographic diffraction and energy frameworks analysis. The single crystals of the mentioned compounds were produced successfully from heptane/tBuOMe mixture. The compounds form lamellar self-assemblies in crystals. The energetic landscapes of single crystals of a series of studied amphiphilic gelators have been analyzed to explore the gelling properties. The presented results may be used as model systems to understand which supramolecular interactions observed in the solid state and what energy contributions are desired in the designing of new low-molecular-weight organic gelators

An attempt to predict the gelation ability of hydrogen-bond-based gelators utilizing a glycoside library

The correlation between the saccharide crystal structure and its gelating ability seems to be a useful tool for finding promising gelators. By analogy to the other types of the hydrogen-bond-based gelators the tendency to form one-dimensional hydrogen-bonded networks may be essential as a prerequisite for good gelators. The gelation abilities were tested for four configurational isomers (methyl-4,6-O-benzylidyne-α-D-glucopyranoside, methyl-4,6-O-benzylidyne-α-D-allopyranoside, methyl-4,6-O-benzylidyne-α-D-altropyranoside, and methyl-4,6-O-benzylidyne-α-D-idopyranoside) which exhibit quite different hydrogen-bonded networks in their crystal structures. Only in the case of one-dimensional hydrogen-bonded architecture the good gel systems were found.\ud \u

Molecular Conformation and Excited-State Dipole Moments of Di- and Tetramethylaminobenzonitrile (DMABN and TMABN)

The conformational analysis of TMABN by three different methods X-ray analysis, photoelectron spectroscopy, and UV molar absorption coefficient yields a twist angle of the dimethylamino group of 60-70° in the ground state, whereas DMABN is not far from planar in qualitative agreement with the predictions from force field calculations (QCFF/PI and MM3). Dipole moment determinations by the thermochromic method agree with those from other methods (solvatochromism, electrochromism and time resolved microwave absorption) in that the excited state dipole moment of TMABN is very large, as well as that of the TICT state of DMABN. Its value increases somewhat with solvent polarity. This is explained by a nuclear polarizability model. The force field calculations are used to predict twist angle values for various sterically hindered DMABN derivatives

The Solvent–Gelator Interaction as the Origin of Different Diffusivity Behavior of Diols in Gels Formed with Sugar-Based Low-Molecular-Mass Gelator

Organogels are soft materials consisting of low-molecular-mass gelators (LMOGs) self-assembled through noncovalent interactions into 3D structures, in which free spaces are filled by organic solvents. 4,6,4′,6′-<i>O</i>-terephthylidene-bis­(methyl-α-d-glucopyranoside) (<b>1</b>) is found to be a new LMOG. It gelatinizes only a limited number of solvents. Here, the gels of <b>1</b> with ethylene glycol (EG) and 1,3-propanediol (PG) are investigated with FT-IR, Raman, and UV–vis spectroscopies, the NMR relaxometry and diffusometry methods, and microscopic observation. The chemical structures of both solvents are closely related, but the variety of physical characteristics of the gels is large. The <b>1</b>/PG gels are thermally more stable compared to <b>1</b>/EG gels. The types of aggregates are most likely the H- and J-type in <b>1</b>/EG gels and the J-type in <b>1</b>/PG gels. Different microstructures are observed: bundles of crossing fibers for <b>1</b>/EG and a honeycomb-like matrix for <b>1</b>/PG gels. The diffusivity of the EG solvent in gels with <b>1</b> behaves as expected, decreasing with increasing gelator concentration, whereas the opposite behavior is observed for the PG solvent. This is a most fascinating result. To explain the diffusion enhancement, we suggest that a dynamic hydrogen bonding network of PG solvent in gel matrixes is disrupted due to solvent–gelator interaction. The direct proof of this interaction is given by the observed low frequency dispersion of the spin–lattice relaxation time of solvents in the gel matrixes

Crystal structure and thermodynamic stability of the [Hg(Pyridine)\u2084(NO\u2083)\u2082] \ub7 2(Pyridine) inclusion compound

The studied compound belongs to the family of [MPy\u2084X\u2082] c5 2Py isomorphous clathrates. Its crystal structure exhibits a van der Waals architecture formed by neutral [HgPy\u2084(NO\u2083)\u2082] host molecules, with the guest pyridine molecules included in the cavities of the host lattice. The host complex is formed by coordination of four pyridines, located near the equatorial plane, and two nitrates, located axially, to the Hg(II) cation. One of nitrates ligates as a monodentate ligand and another as a bidentate. The coordination polyhedron is 'HgN\u2084O\u2083', with average Hg-NPy and Hg-Onitrate distances of 2.38(5) and 2.68(1) \uc5, respectively. The crystal structure is complicated with a superlattice and the crystal symmetry reduced to monoclinic, as compared to the structure usually occurring in the [MPy\u2084X\u2082] c5 2Py clathrates. The pyridine vapor pressure over the clathrate was measured in the 293-369 K temperature range by the static tensimetric method. Thermodynamic parameters of the clathrate dissociation were calculated from these data. For the reaction 1/3[HgPy\u2084(NO\u2083)\u2082] c5 2Pysolid=1/3[HgPy\u2083(NO\u2083)\u2082] solid + Pygas the parameters are as follows: \u394H\ubaav = 49.4(2) kJ/mol, \u394S\ubaav = 127(2) J/(mol K) and \u394G\uba\u2082\u2089\u2088=11.4(3) kJ/mol. The results are compared with previously reported data on compounds of the [MPy\u2084(NO\u2083)\u2082] c5 2Py series.NRC publication: Ye