Dsx 400 spectrometer

The pre-wet NMR samples (with approximately 55% water content) were
prepared with isolated cellulose packed into a 4-mm cylindrical ceramic MAS rotor
(Bruker, Billerica, MA, United States). Repetitive steps of packing samples into
the rotor were performed to fully compress and load the maximum amount of sample.
Solid-state NMR measurements were carried out on a Bruker DSX-400 spectrometer
(Bruker, Billerica, MA, United States) operating at frequencies of 100.55 MHz for
carbon-13 in a Bruker double-resonance MAS probe head (Bruker, Billerica, MA,
United States) at spinning speeds of 10 kHz. CP/MAS experiments utilized a 5 μs
(90°) proton pulse, 1.5 ms contact pulse, 4.0 second recycle delay and 4–8 K
scans. All spectra were recorded on wet samples (with approximately 55% water
content), and the line-fitting analysis of spectra was performed using NUTS NMR
Data Processing software (Acorn NMR, Inc., Livermore, CA, United States). Error
analysis was conducted by performing three individual isolations, NMR
acquisitions, and line-fit data processing [59 (link),60 (link)].

Solid-state NMR experiments were carried out on a wide-bore Bruker AVANCE-600 spectrometer (14.1 T) and a Bruker DSX-400 spectrometer (Karlsruhe, Germany) on 4-mm triple-resonance MAS probes. The drying His, Zn²⁺–His, and Cu²⁺–His powders were obtained by freezing and lyophilized from corresponding saturated solutions.