Executive Summary : | Anisotropic NMR spectroscopy has emerged as a powerful tool to investigate the 3D structure and specifically the configuration and constitution of small synthetic and natural compounds. It has led to success when the classical NMR parameters, scalar couplings, and NOE fall short. The measurement of anisotropic parameters such as residual dipolar coupling (RDC) and residual chemical shift anisotropy (RCSA) require the partial alignment of a molecule of interest, for which an alignment medium such as aligning gel or liquid crystal is necessary. The practical and routine use of anisotropic NMR spectroscopy has been mainly determined by the development of suitable, ready-to-use, reusable, and multi-solvent compatible alignment media. Though there are several aligning gels available, most of them work either in a polar or apolar solvent limiting their applications. Therefore, there is a need to develop aligning gels with multi-solvent compatibility, which will allow the investigation of different classes of compounds. The RDC (D) data collection suffers from the necessity of two measurements: one isotropic solvent to obtain scalar coupling (J) and one in anisotropic solvent to get access to the sum of RDC and J. The difference in these coupling constants simply provides D. Therefore, an ideal strategy would be to measure J and D simultaneously from a single F2-coupled HSQC experiment. This can be accomplished by realizing a gel that can produce both isotropic and anisotropic signals. Therefore, one objective of the proposal is to develop multi-solvent compatible aligning gels to measure single-shot RDCs. Concerning RCSAs, proton RCSA was measured using only perdeuterated and chloroform swollen poly(methyl methacrylate) gel. With such gel, for a very minute sample amount, background polymer signals overlap with some proton resonances, hindering their RCSA measurement. To address this problem, a suitable NMR experiment will be adapted for polymer signal suppression. The fully deuterated gel has not been developed yet for proton RCSA, which can bring down the sample amount to a few micrograms as the spectrum will be devoid of background signals completely. Thus, one objective is to develop a fully deuterated gel for proton RCSAs. If RDC or RCSA alone is not sufficient to investigate the structure of the molecule under study, then the combination of RDC and RCSA will be used. RDCs and RCSAs will be measured for natural compounds using designed gels and will be analysed for configuration assignment. Many non-crystallizable natural compounds are not known even today as they are isolated from nature in a few micrograms quantities. The use of fully deuterated gel for proton RCSA can provide practical solutions for such molecules. The structure determination of peptides by NMR often struggles with limited information about long-range orientation. Thus, utilization of RDC and RCSA will be a big boost in peptide structure refinement. |