Real‐time homonuclear broadband and band‐selective decoupled pure‐shift ROESY

Abstract

Unambiguous spectral assignments in (1)H solution-state NMR are central, for accurate structural elucidation of complex molecules, which is often hampered by signal overlap, primarily because of scalar coupling multiplets, even at typical high magnetic fields. The recent advances in homodecoupling methods have shown powerful means of achieving high resolution pure-shift (1)H spectra in 1D and also in 2D J-correlated experiments, by effectively collapsing the multiplet structures. The present work extends these decoupling strategies to through-space correlation experiments as well and describes two new pure-shift ROESY pulse schemes with homodecoupling during acquisition, viz., homodecoupled broadband (HOBB)-ROESY and homodecoupled band-selective (HOBS)-ROESY. Furthermore, the ROESY blocks suppress the undesired interferences of TOCSY cross peaks and other offsets. Despite the reduced signal sensitivity and prolonged experimental times, the HOBB-ROESY is particularly useful for molecules that exhibit an extensive scalar coupling network spread over the entire (1)H chemical shift range, such as natural/synthetic organic molecules. On the other hand, the HOBS-ROESY is useful for molecules that exhibit well-separated chemical shift regions such as peptides (NH, Hα and side-chain protons). The HOBS-ROESY sensitivities are comparable with the conventional ROESY, thereby saves the experimental time significantly. The power of these pure-shift ROESY sequences is demonstrated for two different organic molecules, wherein complex conventional ROE cross peaks are greatly simplified with high resolution and sensitivity. The enhanced resolution allows deriving possibly more numbers of ROEs with better accuracy, thereby facilitating superior means of structural characterization of medium-size molecules.

Real-time broadband proton-homodecoupled CLIP/CLAP-HSQC for automated measurement of heteronuclear one-bond coupling constants

“…The central problem, spectral perturbations caused by the cumulative effect of successive imperfect pulse sequence elements, is one that is common to all experiments in which windowed acquisition, alternating spin manipulations and chunks of data acquisition, is used. In high resolution NMR this includes real-time heteronuclear J-scaling 22 (for which a detailed analysis of the effects of pulse imperfections has been presented), 23 real-time pure shi NMR, 8,9,12,14,15,19,24 and J-up-and down-scaling. [25][26][27] With one honorable exception, 14 such problems have largely been ignored in the literature.…”

perfectBASH: Band‐selective homonuclear decoupling in peptides and peptidomimetics

“…Initially developed for broadband BIRD homonuclear decoupling by Lupulescu and Frydman, real‐time decoupling variants using the Zangger–Sterk element and soft pulses for band‐selective decoupling were also presented. The band‐selective variant of the real‐time homonuclear decoupling (HOBS) has been implemented into homonuclear and heteronuclear 2D experiments as well as experiments for the measurement of relaxation times . Again, major applications of these band‐selective homodecoupling techniques are the analysis of α‐peptides and proteins .…”

“…The band‐selective variant of the real‐time homonuclear decoupling (HOBS) has been implemented into homonuclear and heteronuclear 2D experiments as well as experiments for the measurement of relaxation times . Again, major applications of these band‐selective homodecoupling techniques are the analysis of α‐peptides and proteins . Nevertheless, applications in the analysis of oligosaccharides, small DNA fragments, or the determination of the enantiomeric and diastereomeric excess are also reported using band‐selective decoupled 1D and 2D NMR experiments.…”

“…[25] Again, major applications of these band-selective homodecoupling techniques are the analysis of α-peptides and proteins. [17,21,23] Nevertheless, applications in the analysis of oligosaccharides, [12] small DNA fragments, [22] or the determination of the enantiomeric and diastereomeric excess [26,27] are also reported using band-selective decoupled 1D and 2D NMR experiments. It is common to these BASH decoupling techniques that they can only be used successfully in the stated applications, if the proton region, which should be decoupled, is well defined and free of mutually coupled protons.…”

HOBS methods for enhancing resolution and sensitivity in small DNA oligonucleotide NMR studies

“…On the one hand, homonuclear band-selective (HOBS) decoupling allows data acquisition at full sensitivity but only on part of the NMR spectrum under special conditions. [13,14] On the other hand, pure shift yielded by chirp excitation gives the full 1 H-{ 1 H} BB NMR spectrum reportedly with tenfold greater sensitivity compared with the spatially encoded pure shift approach. [15] HOBS is effective only if resonances from specific types of proton occur in a region of the spectrum that is relatively isolated from scalar coupling partners and allows full sensitivity to be maintained.…”