The use of a lyotropic liquid-crystalline medium and residual dipolar coupling constants for determination of the spatial structure of thiacalix[4]arenes in solutions

Application of RDC enhanced NMR spectroscopy in structural analysis of thiacalix[4]arene derivatives

The conformational behaviour of novel phenoxathiin-based skeletons was studied using the Residual Dipolar Coupling constant (RDC) method.

Use of residual dipolar couplings in conformational analysis of meta-disubstituted calix[4]arenes

Dimercuration of tetrapropoxy calix[4]arene followed by a reaction with isoamyl nitrite afforded dinitroso regioisomers with unique substitution patterns. The unusual conformational behaviour of these inherently chiral systems was revealed by the combination of dynamic NMR and residual dipolar coupling (RDC) techniques.

Disodium cromoglycate: exploiting its properties as a NMR weak-aligning medium for small organic molecules

Disodium cromoglycate (cromolyn) is an easy-to-prepare water-compatible NMR weak aligning medium for small molecules.

Ionic liquid crystals as alignment medium to measure residual dipolar couplings for carbohydrates

Ionic liquids consisting of N-dodecyl-N-methyl pyrrolidinium bromide [C12MPB] in a mixture with D2O, decanol, and DMSO were for the first time found to give anisotropic molecular alignment in magnetic fields and are useful to measure residual dipolar couplings (RDCs) from polar analytes, for example, glucose. The system shows less quadrupolar splitting of the deuterated solvent signal compared with other liquid crystal systems and hence less undesired line broadening.

Configuration verification via RDCs on the example of a tetra-substituted pyrrolidine ring

The configurational analysis of organic compounds is an important application for high resolution NMR spectroscopy. In the present study, a tetra-substituted pyrrolidine with four chiral carbon atoms is analyzed using classical methods based on (3) J and NOE data in solution and compared and verified with recently introduced alternative approaches via residual dipolar couplings (RDCs) in two weak anisotropic alignment media. The molecule shows sufficient rigidity in the five-membered ring for the configurational characterization with the various techniques. However, the flexibility caused by the many freely rotating bonds potentially poses problems for the interpretation of data. It is shown that RDCs measured in poly-γ-benzyl-l-glutamate and a stretched polydimethylsiloxane gel provide useful information for the distinction of diastereomers, but the success varies with the data interpretation strategy used. Although a general improvement of corresponding correlation factors is observed when limiting data to a subset of dipolar couplings directly connected to the central ring, the distinction power is reduced because of the smaller number of RDCs available for potential model falsification. Singular value decomposition for fitting experimental RDCs is able to distinguish in most cases the correct from incorrect configurations, but the differences in correlation factors can be relatively small. Surprisingly, predicting RDCs using the rod model as implemented in PALES gives best results in distinguishing the eight possible diastereomers. It is also found that the use of proton-phosphorus and carbon-phosphorus RDCs helps with the configurational analysis of the model compound.

MSpin-RDC. A program for the use of residual dipolar couplings for structure elucidation of small molecules

We developed a new program, MSpin-RDC for the analysis of residual dipolar coupling data. This software, specially designed for small molecule analysis, can directly read many molecular-modeling and popular chemistry file formats and accept RDC values as a simple free-format table. Alignment tensor can then be computed by singular value decomposition, as well as predicted using inertia and gyration tensor-based methodologies. Trial structures are then ranked according to their Cornilescu's quality factor (Q) values. Analysis of multiconformational problems and fitting of RDC data to relative populations can be accomplished using the single-tensor approximation.