New Chiral Alignment Media based on Helically Chiral Synthetic Polymers and Graphene Oxides and Applications to Stereochemistry Elucidation

点击翻译按钮获取中文摘要

For many decades, the NMR-spectroscopic determination of the configuration and conformation of compounds in general and chiral compounds in particular was dominated by the evaluation of J-couplings and NOEs. At the end of the 90s, anisotropic NMR-parameters such as residual dipolar couplings (RDCs) started to being applied for struc-ture elucidation of biomolecules[1] and were later adopted in organic structure determination. RDCs are very powerful global parameters because they contain angular and distance information without the need for parametrization. How-ever, for their measurement an anisotropic environment preventing the analyte from tumbling isotropically, is neces-sary. This can be achieved either by stretched polymer gels or by lyotropic liquid crystalline (LLC) phases.[2] Some of these so called alignment media have been prepared in optically active form aiming at enantiomer differentiating orientation (sometimes called DOE: differential order effect) of chiral analytes to finally determine their absolute configuration. Preliminary studies around this topic have been conducted on three aspects in our groups: (i) develop-ment of graphene oxide liquid crystals as versatile and tunable alignment media in organic solvents (Conducted by Xinxiang Lei and Han Sun);[3] (ii) development of polyacetylenes and polyguanidines as enantiodifferentiating align-ment media (Conducted by Michael Reggelin);[4] (iii) methods development of absolute configurational determination in polyacetylene phases using MD simulations (Conducted by Han Sun and Michael Reggelin). The presented pro-posal will aim at transfering the strong enantiomer differentiating effect to other orienting systems and minimizing the amount of polymer needed per measurement (ca. 120 mg!) through a long-term established Sino-German research group. Both goals may possibly be attained by combining the favorable properties of graphene oxide with the ones offered by the polyarylacetylenes. To reach the final goal, the determination of absolute configurations, Han Sun will contribute with her expertise in modeling the polymer/analytes interactions.