Analysis of13C NMR chemical shielding and XPS for cellulose and chitosan by DFT calculations using the model molecules

Abstract

13C NMR chemical shielding and XPS of cellulose and chitosan were analyzed by deMon DFT calculations using the model dimers. The calculated 13C chemical shifts of (α-D-glucose, β-D-glucose, and β-D-glucosamine) and cellobiose with DZVP basis are in considerably good accordance with the experimental values in the average absolute deviations (AAD) of ±3.1 and 2.0 ppm, respectively. The calculated shifts of the dimer models for cellulose and chitosan also correspond well to the experimental ones of both solid biopolymers in the AAD of ±3.1 ppm. In order to simulate the valence XPS and to calculate core-electron binding energies (CEBE)s of cellulose and chitosan, we used the restricted diffuse ionization (rDI) and generalized transition-state (GTS) methods, respectively, due to Slater's transition-state (TS) concept. The simulated valence spectra of the dimer models showed good agreement with the experimental ones of cellulose and chitosan. We also estimated as 5.9 and 5.7 eV for WD (work function and the other energies) values of cellulose and chitosan, respectively from the differences between calculated CEBE values for the model molecules and experimental ones on the solid polymers.