title: 3D ¹⁵N/¹⁵N/¹H chemical shift correlation experiment utilizing an RFDR-based ¹H/¹H mixing period at 100 kHz MAS.
abstract: Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While (13)C/(13)C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of (15)N nuclei in proteins has been a challenge. Previous studies have shown that the negligible (15)N-(15)N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a (15)N/(15)N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of (15)N, via the recoupled (1)H-(1)H dipolar couplings enable faster (15)N/(15)N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between (1)H and (15)N nuclei) steps. In fact, less than 300 nL (∼1.1 micromole quantity) sample is sufficient to acquire the 3D spectrum within 5 h. Our results also demonstrate that a 3D (15)N/(15)N/(1)H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D (15)N/(15)N/(1)H and 2D radio frequency-driven dipolar recoupling (RFDR)-based (1)H/(1)H experimental results obtained from a powder sample of N-acetyla-L-(15)N-valyl-L-(15)N-leucine at 70 and 100kHz MAS frequencies are presented.
authors.affiliation: JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nishiyama
authors.affiliation: JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan.
authors.forename: Michal
authors.initials: M
authors.lastname: Malon
authors.affiliation: JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ishii
authors.affiliation: Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA. Electronic address: ramamoor@umich.edu.
authors.forename: Ayyalusamy
authors.initials: A
authors.lastname: Ramamoorthy
mesh_terms: D000465:Algorithms; D009587:Nitrogen Isotopes / Q000032:analysis / Q000737:chemistry; D010449:Peptide Mapping / Q000379:methods*; D011506:Proteins / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods; D013223:Statistics as Topic
chemical_list: D009587:Nitrogen Isotopes; D011506:Proteins
keywords: Peptide; Proton-detection; RFDR; Solid-state NMR; Ultrafast MAS