Graphene Oxide Liquid Crystals as a Versatile and Tunable Alignment Medium for the Measurement of Residual Dipolar Couplings in Organic Solvents

• Published in: Journal of the American Chemical Society Vol. 136; no. 32; pp. 11280 - 11283
• Main Authors: Lei, Xinxiang, Xu, Zhen, Sun, Han, Wang, Shun, Griesinger, Christian, Peng, Li, Gao, Chao, Tan, Ren X
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.08.2014
• Subjects: Anisotropy; Dimethyl Sulfoxide - chemistry; Graphite - chemistry; Hydrogen - chemistry; Hydrogen-Ion Concentration; Liquid Crystals; Magnetic Resonance Spectroscopy; Molecular Weight; Organic Chemicals - chemistry; Oxides - chemistry; Proline - chemistry; Salts - chemistry; Solutions; Solvents - chemistry; Sucrose - chemistry; Temperature; Water - chemistry
• DOI: 10.1021/ja506074a
• ISSN: 0002-7863

Residual dipolar couplings (RDCs) have proven to be an invaluable anisotropic NMR parameter for the structural elucidation of complex biopolymers and organic molecules. However, a remaining bottleneck limiting its wider use by organic and natural product chemists is the lack of a range of easily applicable aligning media for diverse organic solvents. In this study, graphene oxide (GO) liquid crystals (LCs) were developed to induce partial orientation of organic molecules to allow RDC measurements. These LCs were determined to be maintainable at very low concentrations (as low as 1 mg/mL, corresponding to quadrupolar 2H splittings ranging from 2.8 to 30 Hz and maximum 13C–1H dipolar couplings of 20 Hz for camphor in a CH3COCH3/water system) and to be remarkably stable and broadly compatible with aqueous and organic solvents such as dimethyl sulfoxide, CH3COCH3, and CH3CN. Moreover, compared with those for other alignment media, very clean and high-quality NMR spectra were acquired with the GO molecules in solution because of their rigidity and high molecular weight. The developed medium offers a versatile and robust method for RDC measurements that may routinize the RDC-based structure determination of organic molecules.