Residual dipolar couplings as a tool for structural analysis of ionic liquids.

An acrylonitrile/dimethylacrylamide cross-linked polymer could be swollen in different imidazolium ionic liquids. Mechanical compression of the obtained polymer gels inside an NMR tube allowed the measurement of residual dipolar couplings. Conformational analysis of the 1-methyl-3-butyl-imidazolium (BMIM) cation could be performed by including the measured RDCs as restraints in time-averaged molecular dynamics.

An Acrylonitrile-Based Copolymer Gel as an NMR Alignment Medium for Extraction of Residual Dipolar Couplings of Small Molecules in Aqueous Solution.

An NMR weakly-aligning polymer gel has been prepared by copolymerization of acrylonitrile and 2-acrylamide-2-methyl-1-propanesulfonic acid in the presence of 1,4-butanediol diacrylate as a cross-linker. The polymer readily swells in water in a large range of temperatures, although the swelling ratio is decreased in saline solutions. The swollen gel can be mechanically compressed, in a reversible way, generating anisotropy, as easily shown in 2 H NMR experiments, and allowing measurement of 1 DCH residual dipolar couplings (RDCs) through F1-coupled HSQC experiments. The performance of this gel as a NMR alignment medium was evaluated in several water-soluble organic molecules and, while it provided RDCs of proper size for sucrose and even such as small molecule as 5-norbornen-2-ol, in the case of azidothymidine and cefuroxime sodium salt the strong interaction of these molecules with the gel prevented successful extraction of the RDCs.

Chemically cross-linked polyacrylonitrile. A DMSO compatible NMR alignment medium for measurement of residual dipolar couplings and residual chemical shift anisotropies.

Chemically cross-linked polyacrylontrile polymer gels, have been prepared as an alignment medium compatible with DMSO-d6. These gels allow measurement of residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) with good accuracy as tested with brucine and α-santonin natural compounds. The gels can be reversibly compressed allowing easy measurement of RCSAs. They also present good physical homogeneity, clean HSQC spectra with little background 1H signals, and allow unambiguous referencing of 13C spectra for RCSA extraction.