DREAMTIME NMR Spectroscopy: Targeted Multi‐Compound Selection with Improved Detection Limits

Abstract

NMR/MRI are critical tools for studying molecular structure and interactions but suffer from relatively low sensitivity and spectral overlap. Here, a Nuclear Magnetic Resonance (NMR) approach, termed DREAMTIME, is introduced that provides “a molecular window” inside complex systems, capable of showing only what the user desires, with complete molecular specificity. The user chooses a list of molecules of interest, and the approach detects only those targets while all other molecules are invisible. The approach is demonstrated in whole human blood and urine, small living aquatic organisms in 1D/2D NMR, and MRI. Finally, as proof‐of‐concept, once overlap is removed via DREAMTIME, a novel “multi‐focusing” approach can be used to increase sensitivity. In human blood and urine, sensitivity increases of 7–12 fold over standard 1H NMR are observed. Applicable even to unknowns, DREAMTIME has widespread application, from monitoring product formation in organic chemistry to monitoring/identifying suites of molecular targets in complex media or in vivo.

Targeted Compound Selection with Increased Sensitivity in 13C-Enriched Biological and Environmental Samples Using 13C-DREAMTIME in Both High-Field and Low-Field NMR

“…DREAMTIME (Designed Refocused Excitation And Mixing for Targets In Vivo and Mixture Elucidation), is a recently introduced NMR technique that can be used to improve sensitivity and reduce spectral overlap in the analysis of complex samples. In simple terms, the original 1 H-DREAMTIME allows the user to target desired compounds in a sample; the user chooses a list of molecules of interest, and the approach detects only those targets.…”

“…The sequence works via a double refocused echo (DRE) that targets pairs of J-coupled protons in a given compound using a phase-modulated waveform. By passing the magnetization through a phase-cycled double quantum filter during the DRE, only the J-coupled magnetization is refocused, while all other unwanted signals cancel . The approach is extremely selective as a compound is only selected if it contains signals at both the frequencies targeted and if these two protons are coupled over a coupling constant similar to that selected for.…”

“…By passing the magnetization through a phasecycled double quantum filter during the DRE, only the Jcoupled magnetization is refocused, while all other unwanted signals cancel. 5 The approach is extremely selective as a compound is only selected if it contains signals at both the frequencies targeted and if these two protons are coupled over a coupling constant similar to that selected for. The result is that numerous compounds can be cleanly selected even if they were buried beneath many other compounds in a mixture and thus not visible in standard 1D The sensitivity of DREAMTIME is up to 50% of that of standard 1 H NMR as the double quantum filter is at most 50% efficient.…”

“…This approach focuses one multiplet (per compound) into an ultrasharp spike that has exhibited between 700 and 1200% higher SNR than in the standard 1 H NMR spectrum in samples of human blood and urine. 5 While focusing of single compounds is similar to the SHARPER approach, 6 multi-focusing is more challenging and requires correction of the frequency-dependent phase offsets that evolve during acquisition for "off-resonance" signals. 5 This is achieved by modulating the phases of the different frequency components for each refocusing pulse in the echo train.…”

“…However, as the approach overcomes spectral overlap, it also allows peak “focusing” to be performed to increase SNR in the targets. This approach focuses one multiplet (per compound) into an ultrasharp spike that has exhibited between 700 and 1200% higher SNR than in the standard 1 H NMR spectrum in samples of human blood and urine . While focusing of single compounds is similar to the SHARPER approach, multi-focusing is more challenging and requires correction of the frequency-dependent phase offsets that evolve during acquisition for “off-resonance” signals .…”