4 mm hrmas probe

HRMAS ¹H NMR data acquisition was performed on a Bruker 600 MHz instrument with a 4 mm HRMAS probe. All the spectra were obtained using TOPSPIN 2.5 Bruker software and at a spin rate of 3000 Hz and a sample temperature of 4 °C. A water-suppressed pulse sequence with a repetition time of 8 s, 128 transients and 64 K time domain points was used to get the metabolite spectrum. The corresponding water spectrum was acquired with 8 s repetition time, eight transients and 64 K time domain points. A water-suppressed CPMG pulse sequence with acquisition parameters of 8 s repetition time, 128 transients and 64 K time domain points was used with a T₂ filter (T₂ filter times with 50 ms, 100 ms and 200 ms) to acquire metabolite spectra with suppression of the broad lipid and macromolecule signals. The total data acquisition time for each sample was about 1 h 30 min.

NMR spectra were collected at 600 MHz for ¹H on a Bruker Avance II spectrometer (Bruker Biospin, Coventry, UK) with a 4 mm HR-MAS probe at 310 K while spinning at 5 kHz. ¹H NMR spectra were acquired using a Carr-Purcell Meiboom-Gill pre-saturation (cpmgpr1d) pulse sequence with a spectrum width of 16.0 ppm and 9615 data points using 64 transients. Free induction decay was multiplied by an exponential function with 0.293 Hz line broadening. 2D ¹H–¹H correlation spectroscopy (COSY) and ¹H–¹³C Heteronuclear Single Quantum Correlation (HSQC) experiments were performed on representative datasets using standard Bruker settings.

A total of 5 wt% raw curdlan powder was dissolved in 0.4 wt% and 2 wt% NaOH aqueous solution, respectively, then loaded in 5 mm NMR tubes and measured using a Bruker 600 MHz Advance III spectrometer equipped with a BBO probe. Chopped small pieces of dry S gel or C gel (~3 mg) were first placed into a 4 mm HR-MAS zirconia rotor and weighed; then, 15 times the weight of water was added and the sample was sealed in the rotor for one day to maintain equilibrium swelling. The ¹³C high-resolution MAS (HRMAS) NMR experiments were performed on a Bruker 600 MHz Advance III spectrometer equipped with a 4 mm HR-MAS probe at spinning rate of 3 kHz. The temperature was controlled by a Bruker cooling unit with an accuracy of 0.1 °C. A 15 min equilibrium time was required for each NMR experiment to maintain the temperature balance.