¹H and¹³C NMR study of phase transition and molecular motion in ionic liquids forming lyotropic liquid-crystalline ionogels

Abstract

The room temperature ionic liquid (RTIL) 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], dissolved in water, was studied using 1 H and 13 C NMR spectroscopy. The manifestation of phase transitions and fine features of molecular motion in NMR spectra upon changing temperature and composition have been analysed. The 1 H NMR line shape typical for anisotropic fluids with zero biaxiality (asymmetry) of magnetic shielding and the chemical shift anisotropy (CSA) of ca 0.33 ppm was observed and attributed to water molecules. CSA values for 13 C nuclei have been found in the range of 1.2-1.7 ppm. The difference between lyotropic liquid-crystalline (LC) ionogel phase and the solid one has been revealed, where the motions of RTIL and water molecules have been found to be dynamically segregated. The anisotropic 13 C NMR signal shape at 16.89 ppm shows the difference between LC ionogel and the lamellar phases, where usually the decreasing order parameter moving along hydrocarbon chain from the polar head is observed. It indicates, that the terminal −CH3 groups are more ordered and the supramolecular structures of [C10mim][Br], similar to some higher micellar RTIL aggregates are expected. In order to explain the experimental observations, the quantum chemistry DFT calculations of 1 H and 13 C magnetic shielding tensors of [C10mim] [Br] and various H-bond structures of H2O were performed.

Experimental Evidence of Intramolecular CAr–H···O=C Hydrogen Bonds in the Structure of (Diaryl)tetrahydrofuranones Using Spectroscopic Tools

“…The peculiarity of H o ‐ H‐atoms in the structure of regioisomers 1a – d is also evident from the effect of solvent permittivity ( ε ) and dipole moment ( D ) on the difference in chemical shifts of the H o ‐ and H m ‐H‐atoms of regioisomers 1 and 2 (see SI, p. S4, Figs and ). For all ortho ‐H o ‐atoms, the dependence of this difference on the permittivity of the solvent (macroscopic feature) is consistent with the logarithmic function Δ δ = A ln( ε ) + B, which is in a good agreement with the literature data for various H‐bonding systems . Similar dependence of a chemical shift on the dipole moments of solvents (microscopic property) is also in good agreement with literature data and in a similar way has linear relationship Δ δ = a D + b.…”

“…For all ortho ‐H o ‐atoms, the dependence of this difference on the permittivity of the solvent (macroscopic feature) is consistent with the logarithmic function Δ δ = A ln( ε ) + B, which is in a good agreement with the literature data for various H‐bonding systems . Similar dependence of a chemical shift on the dipole moments of solvents (microscopic property) is also in good agreement with literature data and in a similar way has linear relationship Δ δ = a D + b. As for the meta ‐H‐atoms, their chemical shifts are practically independent on the solvent polarity (Δ δ (H m ) < 0.06 ppm), while the dependence on the dielectric permittivity of the solvent can be fitted by the linear function (see SI, p. S4, Fig.…”

NMR and Raman Spectroscopy Monitoring of Proton/Deuteron Exchange in Aqueous Solutions of Ionic Liquids Forming Hydrogen Bond: A Role of Anions, Self-Aggregation, and Mesophase Formation

“…This highly diluted state (below ∼0.05−0.08 mole fraction of RTIL) was called as the aqueous solution. 23 The coexisting solid and liquid phases can appear only below ∼290 K. 26 It is obvious that the rates of H/D exchange process in such RTILs can be crucially influenced by the phase behavior when different molecular sites and peculiar environments in the microscopic or mesoscopic scales appear. For example, the imidazolium groups can get blocked inside of inverted hexagonal structures, if such formed, or the formation of the regions with confined water (D 2 O as deuteron donor) is enhanced due to the interplay between hydrophilic and hydrophobic segments, as well as the formation of the layered structures in the case of the lamellar phase.…”

Biological assays and theoretical density functional theory calculations of Rh(I), Ir(III), and Ru(II) complexes of chiral phosphinite ligand

“…[ 29 ] In the present study, we describe the synthesis of four rhodium, iridium, and ruthenium complexes of IL‐OPPh 2 and free radical scavenging, reducing power, antimicrobial, and DNA‐binding studies of these complexes. In addition, computational tools have been applied to imidazolium‐based ILs, [ 30–33 ] phosphinites, and their complexes [ 34–37 ] in recent years. Therefore, we started to investigate the computational aspects of the complexes that we have synthesized.…”