33 research outputs found
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- -D-mannopyranoside (-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
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
In Situ Studies of Monosaccharide Gelation Using the Small-Angle X-ray Scattering Time-Resolved Method
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
Molecular conformation and excited-state dipole moments of di- and tetramethylaminobenzonitrile (DMABN and TMABN)
1H Spin–Lattice Relaxation Study of Dynamical Inequivalence of Methyl Groups in Solid 1,2-O-(1-Ethylpropylidene)-α-d-Glucofuranose
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