Recovering Invisible Signals by Two‐Field NMR Spectroscopy

Abstract

Nuclear magnetic resonance (NMR) studies have benefited tremendously from the steady increase in the strength of magnetic fields. Spectacular improvements in both sensitivity and resolution have enabled the investigation of molecular systems of rising complexity. At very high fields, this progress may be jeopardized by line broadening, which is due to chemical exchange or relaxation by chemical shift anisotropy. In this work, we introduce a two-field NMR spectrometer designed for both excitation and observation of nuclear spins in two distinct magnetic fields in a single experiment. NMR spectra of several small molecules as well as a protein were obtained, with two dimensions acquired at vastly different magnetic fields. Resonances of exchanging groups that are broadened beyond recognition at high field can be sharpened to narrow peaks in the low-field dimension. Two-field NMR spectroscopy enables the measurement of chemical shifts at optimal fields and the study of molecular systems that suffer from internal dynamics, and opens new avenues for NMR spectroscopy at very high magnetic fields.

Field-cycling long-lived-state NMR of 15N2 spin pairs

“…NMR experiments for measuring the LLS relaxation rate of 15 N 2 -I at low magnetic field (LF, 0.33 T) were performed using a dedicated two-field NMR spectrometer [42,43]. The sample was transported from HF to LF using a pneumatic shuttling device [44].…”

Recommended strategies for spectral processing and post-processing of 1D 1H-NMR data of biofluids with a particular focus on urine

“…Even today there are more than 600 papers published each year that describe the use of NMR in metabolomics studies. Continuing improvements in NMR technology, such as increased magnet field strength (> 1 GHz) (Cousin et al 2016 ; Tkac et al 2009 ; Abdul-Hamid M.; Emwas et al 2013 ), cryogenically cooled probe technology (Keun et al 2002 ), microprobe design advances (Miao et al 2015 ; Nagato et al 2015 ; Grimes and O’Connell 2011 ) and dynamic nuclear polarization (Emwas et al 2008 ; Ludwig et al 2010 ) have significantly improved the sensitivity of NMR for metabolomics applications. Now samples as small as 50 µL are being handled and nanomolar concentrations are now detectable.…”

Full Correlations across Broad NMR Spectra by Two‐Field Total Correlation Spectroscopy

“…Here, we demonstrate a universal solution to this problem by using different magnetic fields for chemical shift labelling and detection on the one hand, and for TOCSY mixing on the other hand. This can be achieved with a two‐field NMR spectrometer …”

“…We have recently introduced a two‐field NMR spectrometer that combines two magnetic centers at greatly different fields. Spin systems can be manipulated by applying rf pulses at these two magnetic fields.…”

“…Detection is performed at high field. In systems were chemical exchange leads to line‐broadening, we have shown that our two‐field spectrometer allowed us to recover signals that were broadened beyond detection at high fields . Here, we exploit the dramatically reduced spectral width for carbon‐13 nuclei at low fields to obtain efficient isotropic mixing across the entire carbon‐13 spectrum.…”