EPIC- and CHANCE-HSQC: two 15N-photo-CIDNP-enhanced pulse sequences for the sensitive detection of solvent-exposed tryptophan.
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.
Sekhar
Ashok
A
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Cavagnero
Silvia
S
D000465:Algorithms; D008027:Light; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009590:Nitrogen Radioisotopes / Q000032:analysis* / Q000737:chemistry* / Q000528:radiation effects; D010777:Photochemistry / Q000379:methods*; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D012997:Solvents / Q000737:chemistry* / Q000528:radiation effects; D014364:Tryptophan / Q000032:analysis* / Q000737:chemistry* / Q000528:radiation effects
D009590:Nitrogen Radioisotopes; D012997:Solvents; D014364:Tryptophan