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Elsevier, Journal of Magnetic Resonance, 2(200), p. 207-213, 2009

DOI: 10.1016/j.jmr.2009.07.001

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EPIC- and CHANCE-HSQC: Two 15N Photo-CIDNP-Enhanced Pulse Sequences for the Sensitive Detection of Solvent-Exposed Tryptophan

Journal article published in 2009 by Ashok Sekhar ORCID, Silvia Cavagnero
This paper is available in a repository.
This paper is available in a repository.

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Data provided by SHERPA/RoMEO

Abstract

Photochemically induced dynamic nuclear polarization (photo-CIDNP) of nuclei other than (1)H offers a tremendous potential for sensitivity enhancement in liquid state NMR under mild, physiologically relevant conditions. Photo-CIDNP enhancements of (15)N magnetization are much larger than those typically observed for (1)H. However, the low gyromagnetic ratio of (15)N prevents a full fruition of the potential signal-to-noise gains attainable via (15)N photo-CIDNP. Here, we propose two novel pulse sequences, EPIC- and CHANCE-HSQC, tailored to overcome the above limitation. EPIC-HSQC exploits the strong (1)H polarization and its subsequent transfer to non-equilibrium N(z) magnetization prior to (15)N photo-CIDNP laser irradiation. CHANCE-HSQC synergistically combines (1)H and (15)N photo-CIDNP. The above pulse sequences, tested on tryptophan (Trp) and the Trp-containing protein apoHmpH, were found to display up to 2-fold higher sensitivity than the reference NPE-SE-HSQC pulse train (based on simple (15)N photo-CIDNP followed by N-H polarization transfer), and up to a ca. 3-fold increase in sensitivity over the corresponding dark pulse schemes (lacking laser irradiation). The observed effects are consistent with the predictions from a theoretical model of photo-CIDNP and prove the potential of (15)N and (1)H photo-CIDNP in liquid state heteronuclear correlation NMR.