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

Abstract

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 2 H splittings ranging from 2.8 to 30 Hz and maximum 13 C− 1 H dipolar couplings of 20 Hz for camphor in a CH 3 COCH 3 /water system) and to be remarkably stable and broadly compatible with aqueous and organic solvents such as dimethyl sulfoxide, CH 3 COCH 3 , and CH 3 CN. 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. have been widely used to determine the 3D structures of biopolymers and organic molecules. Among these parameters, RDCs can reflect long-range structural restraints of global character and thus have been demonstrated to improve the precision and accuracy of NMR structures of biomolecules and to provide deeper insight into their internal dynamics. 4 In the past few years, RDC-enhanced structure analysis for organic molecules has attracted increasing attention because it allows the determination of the relative configuration of organic molecules in addition to constitution and conformation.

Advances in liquid crystalline nano-carbon materials: preparation of nano-carbon based lyotropic liquid crystal and their fabrication of nano-carbon fibers with liquid crystalline spinning

“…The viscosity of the SWNTs solution in 102% H 2 SO 4 plotted against GO and improve the dispersion and stability of the GO in a polar solvent without any additive [71][72][73].…”

Liquid Crystalline Anisotropic Nanoparticles: From Metallic and Semiconducting Nanoparticles to Carbon Nanomaterials

“…Residual dipolar couplings have proven to be an invaluable anisotropic (NMR) parameter for the structural elucidation of complex biopolymers and organic molecules. Lei et al demonstrated that GO LCs can act as versatile and tunable alignment medium for the measurement of residual dipolar couplings in organic solvents [123]. The LCs were found to be maintainable at very low concentrations and to be remarkably stable and broadly compatible with both aqueous and organic solvents.…”

Practical aspects of oligopeptide AAKLVFF as an alignment medium for the measurements of residual dipolar coupling of organic molecules

“…Cross‐linked polystyrene (PS), poly (vinylacetate) (PVAc), cross‐linked poly (dimethylsiloxane) (PDMS), poly (methyl methacrylate) (PMMA), and the cross‐linked poly (ethylene oxide) (PEO) are the gel‐based alignment media that have been developed in recent years . The liquid crystals include the high‐molecular weight homopolypeptides represented by poly‐ γ ‐benzyl‐L/D‐glutamate (PBLG/PBDG), poly‐γ‐ethyl‐L/D‐glutamate (PELG/PEDG), poly‐ε‐carboxybenzoyl‐L/D‐lysine (PCBLL/PCBDL), and helically chiral polymers such as polyguanidines exemplified by poly‐( N ‐methyl‐ N ′‐(( R )‐1‐phenylethyl)guanidine(( R )‐PPEMG), polyarylacetylenes, polyarylisocyanides, polyisocyanopeptides, as well as carbon‐based graphene oxide (GO) sheets …”