Selective Excitation of Long-Lived Nuclear Spin States

Abstract

Nuclear magnetization storage, once limited by longitudinal and transverse relaxation lifetimes, T 1 and T 2, can be prolonged by symmetry-adapted nuclear spin order, i.e. long-lived states (LLS) and long-lived coherences (LLC), which have significantly extended relaxation time constants compared to T 1 and T 2, respectively. Excitation and/or detection of LLS currently involves pulses covering wide frequency ranges in high-magnetic-field spectrometers. This leads to excitation of unwanted signals that may overlap and interfere with the resonances of interest. Herein, we present a new pulse sequence that converts longitudinal magnetization to LLS and further to detectable magnetization using only frequency-selective pulses. We demonstrate the suitability of this sequence for different J-coupled spin pairs in dipeptide AlaGly and protein Ubiquitin. The newly developed method is adapted for investigations of LLS in complex systems such as proteins and mixtures of metabolites where selected molecular groups are to be investigated separately.

Multiple Stroboscopic Detection of Long-Lived Nuclear Magnetization for Glutathione Oxidation Kinetics

“…Methods to excite long-lived nuclear spin states on protons have been developed − for several endogenous molecules − to act as magnetization carriers while circumventing costly molecular enrichment in carbon-13 or nitrogen-15. Herein, long-lived states were excited and detected using a stroboscopic version of the “SELLS” procedure we have proposed recently. , The detection starts by a small flip-angle pulse used to convert a fraction of the singlet state into detectable magnetization (Figure B). This converts only a fraction of magnetization into detectable terms and is designed to preserve LLS for further storage and reading in an interleaved manner by subsequent pulses (Figure C).…”

“…(D) Hyperpolarization of GSH signals by dissolution-DNP at 6.7 T, necessitating a polarization time of 1 h starting from 20 mM TEMPOL; GSH signals had to be deconvoluted from signals of cryo-protectant. (E) Stack of experimental spectra acquired using StroboSELLS for an AlaGly dipeptide showing the decay of long-lived state of the glycine protons only across 32 loops with a total experimental time of 35 s. One resonance, the signature of SELLS, is present in each spectrum 21. Gaussian pulses were employed with a maximum amplitude of ν 1 max = 5 Hz and durations τ 1 = 270 ms (α 1 = 180°) and τ 2 = 19.5 ms (α 2 = 15°), respectively.…”

“…We preserved magnetization in symmetry-adapted long-lived spin states in GSH/GSSG Gly-(H α1,α2 ) and Cys-(H α H β1,β2 ) aliphatic protons (Figure A) in order to ensure the lifetimes necessary for on-the-fly stroboscopic detection. Methods to excite long-lived nuclear spin states on protons have been developed − for several endogenous molecules − to act as magnetization carriers while circumventing costly molecular enrichment in carbon-13 or nitrogen-15. Herein, long-lived states were excited and detected using a stroboscopic version of the “SELLS” procedure we have proposed recently. , The detection starts by a small flip-angle pulse used to convert a fraction of the singlet state into detectable magnetization (Figure B).…”

“…Experimentally, StroboSELLS was tested on AlaGly, a dipeptide that contains a pair of chemically inequivalent protons, Gly-H α1,α2 (Figure E). The first frequency-selective inversion pulse applied at the most downfield resonance (“D resonance”, see Supporting Information for assignment) excited the long-lived state on glycine’s protons, while the following selective pulses have a shorter duration (smaller flip angle) generating detectable magnetization for a total of 32 s. The resulting spectra consist of a single peak that corresponds to another multiplet component (“B resonance” in Figure S1 of the Supporting Information) of glycine’s pair of doublets …”

“…Herein, long-lived states were excited and detected using a stroboscopic version of the "SELLS" procedure we have proposed recently. 20,21 The detection starts by a small flip-angle pulse used to convert a fraction of the singlet state into detectable magnetization (Figure 1B). This converts only a fraction of magnetization into detectable terms and is designed to preserve LLS for further storage and reading in an interleaved manner by subsequent pulses (Figure 1C).…”