Broadband inversion of ¹J_CC responses in 1,n-ADEQUATE spectra

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• 作者：Mikhail Reibarkh ; R. Thomas Williamson ; Gary E. Martin ; Wolfgang Bermel
• 关键词：1 ; n-ADEQUATE ; 1 ; 1-ADEQUATE ; Pulse sequence ; Broadband inversion ; Strychnine
• 刊名：Journal of Magnetic Resonance
• 出版年：November, 2013
• 年：2013
• 卷：236
• 期：Complete
• 页码：126-133
• 全文大小：1371 K

文摘

Establishing the carbon skeleton of a molecule greatly facilitates the process of structure elucidation, both manual and computer-assisted. Recent advances in the family of ADEQUATE experiments demonstrated their potential in this regard. 1,1-ADEQUATE, which provides direct ¹³C-¹³C correlation via ¹J_CC, and 1,n-ADEQUATE, which typically yields ³J_CC and ¹J_CC correlations, are more sensitive and more widely applicable experiments than INADEQUATE and PANACEA. A recently reported modified pulse sequence that semi-selectively inverts ¹J_CC correlations in 1,n-ADEQUATE spectra provided a significant improvement, allowing ¹J_CC and ⁿJ_CC correlations to be discerned in the same spectrum. However, the reported experiment requires a careful matching of the amplitude transfer function with ¹J_CC coupling constants in order to achieve the inversion, and even then some ¹J_CC correlations could still have positive intensity due to the oscillatory nature of the transfer function. Both shortcomings limit the practicality of the method. We now report a new, dual-optimized inverted ¹J_CC 1,n-ADEQUATE experiment, which provides more uniform inversion of ¹J_CC correlations across the range of 29-82 Hz. Unlike the original method, the dual optimization experiment does not require fine-tuning for the molecule鈥檚 ¹J_CC coupling constant values. Even more usefully, the dual-optimized version provides up to two-fold improvement in signal-to-noise for some long-range correlations. Using modern, cryogenically-cooled probes, the experiment can be successfully applied to samples of 鈭? mg under favorable circumstances. The improvements afforded by dual optimization inverted ¹J_CC 1,n-ADEQUATE experiment make it a useful and practical tool for NMR structure elucidation and should facilitate the implementation and utilization of the experiment.