Physics & Astronomy - Quantum Nano Seminar - Stuart Elliott - Uni of Southampton
Title: "Long-Lived Nuclear Spin States in Monodeuterated Methyl Groups"
Abstract: Nuclear magnetic resonance (NMR) experiments are limited by relaxation dynamics. Observing non-equilibrium magnetization is restricted to timescales governed by the longitudinal relaxation time T1, which limits potential applications such as hyperpolarization or transport phenomena. Long-lived states (LLS) have relaxation times much longer than T1[1],2, providing a possible approach to overcome relaxation constraints. Often the duration of information capture is extended by an order of magnitude over T13. LLS commonly exist in symmetry-constrained homonuclear pairs termed singlet states, with some multi-spin variants established. Molecular systems exhibiting LLS include; parahydrogen4, parawater5, gamma-picoline6, peptides7, fumarates8 and naphthalenes9.
A recent addition to the LLS family is the monodeuterated methyl (CH2D) group10,11. The CH2D group’s interaction with the nitrogen lone pair significantly skews rotameric populations. Steric hindrance generated from the proximal methyl group then forces a small chemical inequivalence (14 ppb) between CH2D protons. Radio frequency pumping of NMR silent spin states is achieved using the spin-lock induced crossing (SLIC) pulse sequence12. A LLS decay constant (TS) of 27.0 ± 0.6 s was recorded13. A number of CH2D-2-x-piperidine derivatives are currently in synthesis to extend singlet lifetimes and to control chemical shift differences, the later of which are to be compared with computational predictions.
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13 S.J. Elliott, L.J. Brown and M.H. Levitt, In Preparation (2015).
