Avance 3 200 spectrometer

Solid-state ¹³C NMR spectra were obtained on a Bruker Avance™ III 200 spectrometer (Bruker BioSpin GmbH, Karlsruhe, Germany). Cross-polarization magic angle spinning (CPMAS) was applied with a ¹³C-resonance frequency of 50.32 MHz and a spinning speed of 5 kHz. Contact time was 1 ms and recycle delay was 2 s. Approximately 5000 scans were accumulated and no line broadening was applied. For calibration of the ¹³C chemical shifts, tetramethylsilane was used and set to 0 ppm. Spectral analysis were performed using the spectrometer software. The crystallinity index (CrI) was then calculated by the NMR C4 peak separation method, that assigns peaks at about 87 and 82 ppm in the NMR spectra to the C4 carbons in ordered cellulose structures (“crystalline”; C4c) and non-crystalline domains (“amorphous”; C4a), respectively [47 (link), 52 (link), 55 (link)].
We would like to note that the CrI might have been underestimated for Alphacel, since we used a simple drying process instead of solvent-exchange drying, which might have given numbers more representative of the swollen state in the liquid broth. However, the measured differences have found to be less of an issue at high CrIs [41 (link)]. The CrIs of the MCCs were thus probably less affected, and that of Avicel was well in line with previously reported values [58 (link)].

Solid state CP-MAS (Cross Polarization-Magic Angle Spinning) ¹³C Nuclear Magnetic Resonance spectra were acquired at 50.3 MHz on a Bruker Avance III 200 spectrometer (Bruker BioSpin, Germany) fitted with a 4 mm solid state MAS probe (Bruker BioSpin, Switzerland). The samples were packed into a 4 mm rotor and spun at 5 kHz. Each 3 μs, a 90° proton preparation pulse was followed by a 1 ms contact time and a 30 ms acquisition time, with proton decoupling, and a 1.5 s recycle delay. All spectra were calibrated so that the cellulose Iβ interior C4 peak was assigned a value of 89.3 ppm relative to tetramethylsilane (Newman et al., 1993 (link)).

Infrared spectra were measured on a Perkin Elmer Spectrum 100 Optica (Perkin Elmer, Wellesley, MA, USA). ¹H- and ¹³C-NMR spectra were recorded on a Bruker Avance III 200 spectrometer at 200 MHz and 50 MHz respectively, Bruker Avance I 300 at 300 MHz and 75 MHz respectively, on a Bruker Advance II 400 spectrometer at 400 MHz and 100 MHz respectively, on a Bruker Advance III 600 spectrometer at 600 MHz and 150 MHz respectively (Bruker, Billerica, MA, USA). Shifts (δ) are given in parts per million with respect to solvent residual peak and coupling constants (J) are given in Hertz. HRMS (FD) spectra were performed by CESAMO (Bordeaux, France). The measurements were carried out on a TOF mass spectrometer AccuTOFGCv using an FD emitter with an emitter voltage of 10 kV. One to two microliters solution of the compound is deposited on a 13 μm emitter wire. Elemental analyses were carried out by the “Institut de Chimie des Substances Naturelles” (Gif-sur-Yvette, France). Melting points were measured on Stuart SMP 10.DSC measures were carried out on Mettler Toledo DSC 1 STAReSystem (Mettler, Greifensee, Switzerland).