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

Weakly aligned Ti3C2Tx MXene liquid crystals: measuring residual dipolar coupling in multiple co-solvent systems

Residual Dipolar Coupling (RDC), acquired relying on weakly alignment media, is highly valuable for the structural elucidation of organic molecules. Arising from the striking features of no background signals and low critical concentrations, two-dimensional (2D) liquid crystals (LCs) show the clear advantages of acting as alignment media to measure RDCs. So far, creating multisolvent compatible 2D LC media through a simple and versatile method is still formidably challenging. Herein, we report the rapid creation of aligned media based on the Ti₃C₂T_x MXene, which self-aligned in multiple co-solvents including CH₃OH-H₂O, DMSO-H₂O, DMF-H₂O, and acetone-H₂O. We demonstrated the applicability of these aligned media for the RDC measurement of small organic molecules with different polarities and solubilities. Notably, Ti₃C₂T_x MXene LCs without chemical modification enabled RDC measurements on aromatic molecules. The straightforward preparation of Ti₃C₂T_x media and its compatibility with multiple solvents will push RDC measurement as a routine methodology for structural elucidation. It may also facilitate the investigation of solvation effects on conformational dynamics.

Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics

Self-assembled graphene oxide lyotropic liquid crystal (GO LLC) structures are mostly formed in aqueous medium; however, most GO derivatives are water insoluble, so processing GO LLCs in water poses a practical limitation. The use of polar aprotic solvent (like dimethyl sulfoxide) for the formation of GO LLC structures would be interesting, because it would allow incorporating additives, like photoinitiators or cross-linkers, or blending with polymers that are insoluble in water, which hence would expand its scope. The well-balanced electrostatic interaction between DMSO and GO can promote and stabilize the GO nanosheets' alignment even at lower concentrations. With this in mind, herein we report mechanically robust, chlorine-tolerant, self-assembled nanostructured GO membranes for precise molecular sieving. Small-angle X-ray scattering and polarized optical microscopy confirmed the alignment of the modified GO nanosheets in polar aprotic solvent, and the LLC structure was effectively preserved even after cross-linking under UV light. We found that the modified GO membranes exhibited considerably improved salt rejection for monovalent ions (99%) and water flux (120 LMH) as compared to the shear-aligned GO membrane, which is well supported by forward osmosis simulation studies. Additionally, our simulation studies indicated that water molecules traveled a longer path while permeating through the GO membrane compared to the GO LLC membrane. Consequently, salt ions permeate slowly across the GO LLC membrane, yielding higher salt rejection than the GO membrane. This begins to suggest strong electrostatic repulsion with the salt ions, causing higher salt rejection in the GO LLC membrane. We foresee that the ordered cross-linked GO sheets contributed to excellent mechanical stability under a high-pressure, cross-flow, chlorine environment. Overall, these membranes are easily scalable, exhibit good mechanical stability, and represent a breakthrough for the potential use of polymerized GO LLC membranes in practical water remediation applications.

Residual Dipolar Coupling Based Conformational Analysis Allows the Configurational Assessment of Steroids with up to Eight Stereocenters

Residual dipolar couplings (RDCs) induced by anisotropic media have been proved as a powerful tool for the structure elucidation of organic molecules in solution in nuclear magnetic resonance (NMR) based analysis. The value of dipolar couplings to solve complex conformational and configurational problems represents indeed an appealing analytical tool for the pharmaceutical industry particularly focusing on the stereochemistry characterization of NCEs since the early phase of the drug development process. In our work, RDCs were used for the conformational and configurational study of synthetic steroids with multiple stereocenters - prednisone and beclomethasone dipropionate (BDP) -. For both molecules the correct relative configuration was identified among all the possible diastereoisomers (32 and 128 respectively) arising from the compounds stereogenic carbons. Only for prednisone the use of additional experimental data (i. e. rOes) was necessary to resolve the right stereochemical structure.

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 D_CH 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.

Self-Assembled Oligopeptide (FK)4 as a Chiral Alignment Medium for the Anisotropic NMR Analysis of Organic Compounds

Anisotropic NMR parameters have been proven to be powerful for the structural elucidation of organic molecules. Herein, we present an alignment medium based on the self-assembled (FK)₄ oligopeptide, showing excellent properties in measurements of anisotropic NMR parameters in both D₂O and CD₃OD. The preparation of the (FK)₄-based alignment medium is simple and rapid. The low viscosity of the anisotropic phase makes it easy to be transferred to the NMR tube. The alignment of the oligopeptide is fast, stable, and homogeneous, with weak background signals, permitting the acquirement of high-quality NMR spectra. The performance of this alignment medium in residual dipolar coupling measurements and diastereomer discriminations is demonstrated by analyzing several different analytes. The enantiodiscrimination property of the (FK)₄ oligopeptide is revealed by the difference of residual chemical shift anisotropy of the two enantiomers in the 1D ¹³C spectrum, granting its potential use for the quantification and identification of enantiomers of small molecules.

A supramolecular and liquid crystalline water-based alignment medium based on azobenzene-substituted 1,3,5-benzenetricarboxamides

A supramolecular, lyotropic liquid crystalline alignment medium based on an azobenzene-containing 1,3,5-benzenetricarboxamide (BTA) building block is described and investigated. As we demonstrate, this water-based system is suitable for the investigation of various water-soluble analytes and allows for a scaling of alignment strength through variation of temperature. Additionally, alignment is shown to reversibly collapse above a certain temperature, yielding an isotropic solution. This collapse allows for isotropic reference measurements, which are typically needed in addition to those in an anisotropic environment, to be performed using the same sample just by varying the temperature. The medium described thus provides easy access to anisotropic NMR observables and simplifies structure elucidation techniques based thereon.

Ti3C2Tx MXene Liquid Crystal: Access to Create Background-Free and Easy-Made Alignment Medium

The formation of lyotropic liquid crystals (LCs) in two-dimensional (2D) colloidal dispersions enables the production of mesoscopic/macroscopic ordered materials from nanoscale building blocks. In contrast to graphene oxide (GO) LCs, the practical applications of MXene LCs are less exploited. This study bridges the gap by utilizing a simple and versatile fabrication method to prepare Ti₃C₂T_x MXene LC that can be applied as a background-free alignment medium for the residual dipolar coupling (RDC) measurement of organic molecules. Ti₃C₂T_x LC displays the size- and concentration-dependent alignment degree. Ti₃C₂T_x nanoflakes with an average size of around 600 nm can provide the quadrupolar ²H splitting of 71 Hz at a concentration of 50 mg/mL and show excellent fluidity at such a high concentration. Compared with other alignment media, Ti₃C₂T_x LC exhibits the features of no-background and narrow line broadening, which actualizes the acquirement of clean and high-quality NMR spectra for the accurate RDC extraction. Notably, the alignment of LCs is determined to be maintainable in the redispersed solution after freeze-drying, providing the great convenience for the preparation of alignment Ti₃C₂T_x media, long-term sample preservation, and quantitative evaluation of alignment degree. Meanwhile, the alignment LC media for RDC measurement can be established in other MXenes such as Ti₂CT_x and Ti₃CNT_x. Collectively, our findings demonstrate the potential of creating various alignment media from the fascinating MXene family.

Poly(arylisocyanides) as Versatile, Enantiodiscriminating Alignment Media for Small Molecules

Lyotropic liquid crystalline (LLC) phases of amino acid derived polyarylisocyanides were employed as chiral alignment media for the measurement of residual dipolar couplings (RDCs) of small chiral organic molecules. Anisotropic samples in CDCl3 displayed quadrupolar splittings of the deuterium signal in the range of several hundreds of Hertz. The LLC phases showed excellent orienting properties for a broad range of analytes bearing various functional groups. The precise extraction of RDCs in the range of up to ±40 Hertz from F2-coupled HSQC spectra was possible. Additionally, the chiral environment offers the opportunity for diastereomorphous interactions with the enantiomers of chiral analytes leading to two different sets of RDCs. This differential order effect was particularly pronounced with ketones and alcohols.

Model free analysis of experimental residual dipolar couplings in small organic compounds

Residual dipolar couplings (RDCs) contain information on the relative arrangement and dynamics of internuclear spin vectors in chemical compounds. Classically, RDC data is analyzed by fitting to structure models, while model-free approaches (MFA) directly relate RDCs to the corresponding internuclear vectors. The recently introduced software TITANIA implements the MFA and extracts structure and dynamics parameters directly from RDCs to facilitate de novo structure refinement for small organic compounds. Encouraged by our previous results on simulated data, we herein focus on the prerequisites and challenges faced when using purely experimental data for this approach. These concern mainly the fact that not all couplings are accessible in all media, leading to voids in the RDC matrix and the concomitant effects on the structure refinement. It is shown that RDC data sets obtained experimentally from currently available alignment media and measurement methods are of sufficient quality to allow relative configuration determination even when the relative configuration of the analyte is completely unknown.

TITANIA: Model-Free Interpretation of Residual Dipolar Couplings in the Context of Organic Compounds

Residual dipolar couplings (RDCs) become increasingly important as additional NMR parameters in the structure elucidation of organic compounds but are usually used in fitting procedures to discriminate between (computed) structures that are in accordance with RDCs and others that can be ruled out. Thus, the determination of configurations requires prior structural information. The direct use of RDCs as restraints to construct structures based on RDCs has only recently begun also in organic compounds. No protocol has been published though that uses the vector and dynamics information available in multialignment data sets directly for the joint determination of conformation and configuration of organic compounds. This is proposed in the current study. We show that by employing these data, even a flat or random start structure converges into the correctly configured structure when employing multiple alignment data sets in our iterative procedure. The requirements in terms of the number of RDCs and alignment media necessary are discussed in detail.

Valine derived poly (acetylenes) as versatile chiral lyotropic liquid crystalline alignment media for RDC-based structure elucidations

Anisotropic samples of lyotropic liquid crystalline (LLC) phases of valine derived polyaryl acetylenes were employed as chiral alignment media for the measurement of residual dipolar couplings (RDCs) of 12 small, chiral, organic molecules. The quadrupolar splitting of the deuterium signal of CDCl₃ can be adjusted by temperature and concentration changes from 0 to 350 Hz. The LLC phases showed excellent orienting properties for all analytes bearing various functional groups. The precise extraction of RDCs in the range of up to ±30 Hz from F2-coupled HSQC spectra was possible. Additionally, the chiral environment led to diastereomorphous interactions with the enantiomers of chiral analytes leading to two different sets of RDCs. This differential order effect was particularly pronounced with H-bond donors like alcohols and 2° amines.

Single experiment measurement of residual dipolar couplings in aqueous solution using a biphasic bisperylene imide chromonic liquid crystal

The use of the biphasic isotropic/nematic region in a bisperylene imide-based lyotropic liquid crystal system allows the extraction of proton-carbon ¹ D_CH residual dipolar couplings in aqueous solution from a single F1-coupled HSQC experiment. The method was successfully applied to the RDC-based conformational analysis of sucrose.

Determination of Configuration and Conformation of a Reserpine Derivative with Seven Stereogenic Centers Using Molecular Dynamics with RDC-Derived Tensorial Constraints*

NMR-based determination of the configuration of complex molecules containing many stereocenters is often not possible using traditional NOE data and coupling patterns. Making use of residual dipolar couplings (RDCs), we were able to determine the relative configuration of a natural product containing seven stereocenters, including a chiral amine lacking direct RDC data. To identify the correct relative configuration out of 32 possible ones, experimental RDCs were used in three different approaches for data interpretation: by fitting experimental data based singular value decomposition (SVD) using a single alignment tensor and either (i) a single conformer or (ii) multiple conformers, or alternatively (iii) using molecular dynamics simulations with tensorial orientational constraints (MDOC). Even though in all three approaches one and the same configuration could be selected and clear discrimination between possible configurations was achieved, the experimental data was not fully satisfied by the methods based on single tensor approaches. While these two approaches are faster, only MDOC is able to fully reproduce experimental results, as the obtained conformational ensemble adequately covers the conformational space necessary to describe the molecule with inherent flexibility.

Water-Soluble Glycosylated Resveratrol for Measuring Residual Dipolar Coupling in NMR

Residual dipolar coupling (RDC) is a newly emerging technique for obtaining more precise conformational features of molecules in nuclear magnetic resonance (NMR), which can be observed when the molecules are oriented in NMR sample solutions. Unlike the case of solubilization of resveratrol (Res) in aqueous media by surfactants, multiglycosylated resveratrol (GlyRes) was dispersed in aqueous media forming nanoparticles with an extremely small size. In the presence of an NMR alignment medium of bacteriophage, GlyRes molecules were efficiently oriented in the strong magnetic field allowing for observations of RDCs in NMR. Structural refinement using the observed RDC values enabled differentiation of trans and cis forms of Res.

The Advanced Floating Chirality Distance Geometry Approach-How Anisotropic NMR Parameters Can Support the Determination of the Relative Configuration of Natural Products

The configurational analysis of complex natural products by NMR spectroscopy is still a challenging task. The assignment of the relative configuration is usually carried out by analysis of interproton distances from NOESY or ROESY spectra (qualitative or quantitative) and scalar (J) couplings. About 15 years ago, residual dipolar couplings (RDCs) were introduced as a tool for the configurational determination of small organic molecules. In contrast to NOEs/ROEs which are local parameters (distances up to 400 pm can be detected for small organic molecules), RDCs are global parameters which allow to obtain structural information also from long-range relationships. RDCs have the disadvantage that the sample needs a setup in an alignment medium in order to obtain the required anisotropic environment. Here, we will discuss the configurational analysis of five complex natural products: axinellamine A (1), tetrabromostyloguanidine (2), 3,7-epi-massadine chloride (3), tubocurarine (4), and vincristine (5). Compounds 1-3 are marine natural products whereas 4 and 5 are from terrestrial sources. The chosen examples will carefully work out the limitations of NOEs/ROEs in the configurational analysis of natural products and will also provide an outlook on the information obtained from RDCs.

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

Practical aspects of the oligopeptide AAKLVFF as an alignment medium are discussed, including large-scale synthesis of the oligopeptide, detailed description of preparation of the alignment medium, and acquisition of the RDCs. The resulting orienting medium is stable and highly homogeneous with tunable alignment strength in methanol.

Lyotropic liquid crystal to measure residual dipolar couplings in dimethyl sulfoxide based on modified cellulose nanocrystals

A novel lyotropic liquid crystal was developed for the measurement of RDCs of organic molecules with no background signals.

Configuration determination by residual dipolar couplings: accessing the full conformational space by molecular dynamics with tensorial constraints

Residual dipolar couplings (RDCs) and other residual anisotropic NMR parameters provide valuable structural information of high quality and quantity, bringing detailed structural models of flexible molecules in solution in reach. The corresponding data interpretation so far is directly or indirectly based on the concept of a molecular alignment tensor, which, however, is ill-defined for flexible molecules. The concept is typically applied to a single or a small set of lowest energy structures, ignoring the effect of vibrational averaging. Here, we introduce an entirely different approach based on time averaged molecular dynamics with dipolar couplings as tensorial orientational restraints that can be used to solve structural problems in molecules of any size without the need of introducing an explicit molecular alignment tensor into the computation. RDC restraints are represented by their full 3D interaction tensor in the laboratory frame, for which pseudo forces are calculated using a secular dipolar Hamiltonian as the target. The resulting rotational averaging of each individual tensorial restraint leads to structural ensembles that best fulfil the experimental data. Using one-bond RDCs, the approach has been implemented in the force field procedures of the program COSMOS and extensively tested. A concise theoretical introduction, including the special treatment of force fields for stable and fast MD simulations, as well as applications regarding configurational analyses of small to medium-sized organic molecules with different degrees of flexibility, is given. The observed results are discussed in detail.

Cromolyn/gelatin mixtures as aqueous alignment media and utilization of their mechanical stability for a layering technique

In this study, aqueous blends of cromolyn and gelatin ("cromogels") are introduced as anisotropic media. The addition of gelatin enables an advantageous adjustability of the strength, the homogeneity, and the stability of the cromolyn alignment. The mechanical stability of these polymer-dispersed liquid crystals is further utilized by stacking layers of D₂ O/cromolyn/gelatin with varying component ratio. The resulting distinct phases with correspondingly different degrees of alignment can be targeted by spatially resolved NMR techniques. As a case study, we investigated sucrose in a two-phase system with neat D₂ O and analyte layered over the anisotropic medium. A recently presented spatially selective coupled-type HSQC experiment allows the determination of one-bond C-H splitting in both phases.

Residual Dipolar Couplings in Structure Determination of Natural Products

The determination of natural products stereochemistry remains a formidable task. Residual dipolar couplings (RDCs) induced by anisotropic media are a powerful tool for determination of the stereochemistry of organic molecule in solution. This review will provide a short introduction on RDCs-based methodology for the structural elucidation of natural products. Special attention is given to the current availability of alignment media in organic solvents. The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized. This review provides a short introduction on RDCs-based methodology for the structural elucidation of natural products. Special attention is given to the current availability of alignment media in organic solvents. The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized.

A practical strategy for the accurate measurement of residual dipolar couplings in strongly aligned small molecules

Accurate measurement of residual dipolar couplings (RDCs) requires an appropriate degree of alignment in order to optimize data quality. An overly weak alignment yields very small anisotropic data that are susceptible to measurement errors, whereas an overly strong alignment introduces extensive anisotropic effects that severely degrade spectral quality. The ideal alignment amplitude also depends on the specific pulse sequence used for the coupling measurement. In this work, we introduce a practical strategy for the accurate measurement of one-bond ¹³C-¹H RDCs up to a range of ca. -300 to +300 Hz, corresponding to an alignment that is an order of magnitude stronger than typically employed for small molecule structural elucidation. This strong alignment was generated in the mesophase of the commercially available poly-γ-(benzyl-L-glutamate) polymer. The total coupling was measured by the simple and well-studied heteronuclear two-dimensional J-resolved experiment, which performs well in the presence of strong anisotropic effects. In order to unequivocally determine the sign of the total coupling and resolve ambiguities in assigning total couplings in the CH₂ group, coupling measurements were conducted at an isotropic condition plus two anisotropic conditions of different alignment amplitudes. Most RDCs could be readily extracted from these measurements whereas more complicated spectral effects resulting from strong homonuclear coupling could be interpreted either theoretically or by simulation. Importantly, measurement of these very large RDCs actually offers significantly improved data quality and utility for the structure determination of small organic molecules.

A Self-Assembled Oligopeptide as a Versatile NMR Alignment Medium for the Measurement of Residual Dipolar Couplings in Methanol

Residual dipolar coupling (RDC) is a powerful structural parameter for the determination of the constitution, conformation, and configuration of organic molecules. Herein, we report the first liquid crystal-based orienting medium that is compatible with MeOH, thus enabling RDC acquisitions of a wide range of intermediate to polar organic molecules. The liquid crystals were produced from self-assembled oligopeptide nanotubes (AAKLVFF), which are stable at very low concentrations. The presented alignment medium is highly homogeneous, and the size of RDCs can be scaled with the concentration of the peptide. To assess the accuracy of the RDC measurement by employing this new medium, seven bioactive natural products from different classes were chosen and analyzed. The straightforward preparation of the anisotropic alignment sample will offer a versatile and robust protocol for the routine RDC measurement of natural products.

Graphene and Other 2D Colloids: Liquid Crystals and Macroscopic Fibers

Two-dimensional colloidal nanomaterials are running into renaissance after the enlightening researches of graphene. Macroscopic one-dimensional fiber is an optimal ordered structural form to express the in-plane merits of 2D nanomaterials, and the formation of liquid crystals (LCs) allows the creation of continuous fibers. In the correlated system from LCs to fibers, understanding their macroscopic organizing behavior and transforming them into new solid fibers is greatly significant for applications. Herein, we retrospect the history of 2D colloids and discuss about the concept of 2D nanomaterial fibers in the context of LCs, elaborating the motivation, principle and possible strategies of fabrication. Then we highlight the creation, development and typical applications of graphene fibers. Additionally, the latest advances of other 2D nanomaterial fibers are also summarized. Finally, conclusions, challenges and perspectives are provided to show great expectations of better and more fibrous materials of 2D nanomaterials. This review gives a comprehensive retrospect of the past century-long effort about the whole development of 2D colloids, and plots a clear roadmap - "lamellar solid - LCs - macroscopic fibers - flexible devices", which will certainly open a new era of structural-multifunctional application for the conventional 2D colloids.

Complete NMR assignment and conformational analysis of 17-α-ethinylestradiol by using RDCs obtained in grafted graphene oxide

The ¹ H and ¹³ C NMR spectra of 17-α-ethinylestradiol (EE2), a well-known contraceptive, including diastereotopic methylene groups, were fully assigned with the help of residual dipolar couplings (RDC) measured in the recently developed grafted graphene oxide orienting medium. RDC analysis, which included all ¹ D_CH couplings and the long-range ² D_CH¹ H-C≡¹³ C coupling, also pointed to the presence of a minor conformation arising from pseudo-rotation of the steroid B ring. Saturation-transfer difference (STD) measurements revealed that the most likely interaction between EE2 and orienting medium occurred on the C and D ring. Copyright © 2016 John Wiley & Sons, Ltd.

Di(ethylene glycol) methyl ether methacrylate (DEGMEMA)-derived gels align small organic molecules in methanol

Residual dipolar couplings (RDCs) constitute an important NMR parameter for structural elucidation in all areas of chemistry. In this study, di(ethylene glycol) methyl ether methacrylate (DEGMEMA)-based gels are introduced as alignment media for the measurement of RDCs of small organic molecules in polar solvents such as methanol. The low viscosity of methanol permits the execution of J-scaled BIRD HSQC experiments that yield very sharp lines in anisotropic conditions. The gels have excellent mechanical properties, and their compression and expansion in the swollen state can be reversed and performed multiple times. This process enables the easy loading and release of analytes. The excellent performance of these new aligning gels is demonstrated by analyzing the structure of the alkaloid retrorsine. Copyright © 2016 John Wiley & Sons, Ltd.

Perspectives in the application of residual dipolar couplings in the structure elucidation of weakly aligned small molecules

This perspective article aims to review the general methodology in the application of residual dipolar couplings (RDCs) in the structure elucidation of small molecules and give the author's view on challenges for future applications. Recent improvements in the availability of alignment media, new pulse sequences for the measurement of couplings and improvements in the analysis software have garnered widespread interest in the technique. However, further generalization is needed in order to make RDC analysis into a truly "routine" method. Copyright © 2016 John Wiley & Sons, Ltd.

Phase-Separated Polyaniline/Graphene Composite Electrodes for High-Rate Electrochemical Supercapacitors

Polyaniline/graphene hydrogel composites with a macroscopically phase-separated structure are prepared. The composites show high specific capacitance and excellent rate performance. Further investigation demonstrates that polyaniline inside the graphene hydrogel has low rate performance, thus a phase-separated structure, in which polyaniline is mainly outside the graphene hydrogel matrix, can enhance the rate performance of the composites.

Q.E.COSY: determining sign and size of small deuterium residual quadrupolar couplings using an extended E.COSY principle

Residual quadrupolar couplings contain important structural information comparable with residual dipolar couplings. However, the measurement of sign and size of especially small residual quadrupolar couplings is difficult. Here, we present an extension of the E.COSY principle to spin systems consisting of a Spin 1 coupled to a spin ½ nucleus, which allows the determination of the sign of the quadrupolar coupling of the Spin 1 nucleus relative to the heteronuclear coupling between the spins. The so-called Q.E.COSY approach is demonstrated with its sign-sensitivity using variable angle NMR, stretched gels and liquid crystalline phases applied to various CD and CD3 groups. Especially the sign-sensitive measurement of residual quadrupolar couplings that remain unresolved in conventional deuterium 1D spectra is shown.

Graphene Oxide Liquid Crystals: Discovery, Evolution and Applications

The discovery and relevant research progress in graphene oxide liquid crystals (GOLCs), the latest class of 2D nanomaterials exhibiting colloidal liquid crystallinity arising from the intrinsic disc-like shape anisotropy, is highlighted. GOLC has conferred a versatile platform for the development of novel properties and applications based on the facile controllability of molecular scale alignment. The first part of this review offers a brief introduction to LCs, including the theoretical background. Particular attention has been paid to the different types of LC phases that have been reported thus far, such as nematic, lamellar and chiral phases. Several key parameters governing the ultimate stability of GOLC behavior, including pH and ionic strength of aqueous dispersions are highlighted. In a relatively short span of time since its discovery, GOLCs have proved their remarkable potential in a broad spectrum of applications, including highly oriented wet-spun fibers, self-assembled nanocomposites, and architectures for energy storage devices. The second part of this review is devoted to an exclusive overview of the relevant applications. Finally, an outlook is provided into this newly emerging research field, where two well established scientific communities for carbon nanomaterials and liquid crystals are ideally merged.

CLIP-ASAP-HSQC for fast and accurate extraction of one-bond couplings from isotropic and partially aligned molecules

Fast measurement of heteronuclear one-bond couplings, a class of NMR parameters valuable for structure elucidation, is highly desirable, especially if samples undergo chemical reactions or dynamic processes are observed. Methods presented so far face severe limitations in terms of resolution, accessible bandwidth, and sensitivity. We present the CLean InPhase-Acceleration by Sharing Adjacent Polarization-HSQC (CLIP-ASAP-HSQC) pulse sequence that allows fast acquisition of spectra with clean inphase multiplets in about 25 s. The performance in terms of accurate extraction of one-bond couplings is demonstrated on three test samples including partially aligned molecules.