✍ Scribed by Mario Piccioli; Luisa Poggi
No coin nor oath required. For personal study only.
The presence of a paramagnetic center may disturb both coherent and incoherent communication between nuclear spins that are affected, to some extent, by the hyperfine interaction. This is a limiting factor to an extensive use of paramagnetic probes in NMR spectroscopy to enhance partial alignment and to exploit cross correlation effects and pseudocontact shifts. We propose here an HCCH-TOCSY experiment tailored to identify spin systems involving resonances that are partly or completely affected by hyperfine interaction. The efficiency of polarization transfer steps when fast relaxing nuclei are involved is discussed. The sequence is tested for the protein Calbindin D 9k , in which one of the two native Ca 2+ ions is replaced by the paramagnetic Ce 3+ ion as well as for the oxidized form of cytochrome b 562 .
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