Solution-state structures of the cellulose model pullulan in lithium chloride/N,N-dimethylacetamide

Pullulan is soluble in both N,N-dimethylacetamide (DMAc) and LiCl/DMAc. Here, the solution-state structures of pullulan in these two solvents were studied by size-exclusion chromatography with multi-angle laser light scattering (SEC/MALLS) and nuclear magnetic resonance (NMR) analyses. SEC/MALLS and off-line refractive index analyses revealed that the hydroxy groups of pullulan interact with LiCl in DMAc, as observed previously for cellulose. The nine different C-OH protons of pullulan in DMAc and LiCl/DMAc appeared independently in NMR spectra and were successfully assigned. When LiCl was present, the degree of dissociation of all C-OH protons of pullulan was increased by Li+ and Cl- ions, and the conformations of the C-O-H groups became stable and restricted in DMAc. Based on the obtained results, the solution-state structures of cellulose in LiCl/DMAc are hypothesized to contain similar interactions between the cellulose hydroxy groups, and Li+ and Cl- in LiCl/DMAc to those observed for pullulan. (C) 2017 Elsevier B.V. All rights reserved.