Molecular rotor as a structural probe of glucan polymers: Amylopectin, phytoglycogen, and their β-limit dextrins as models

Abstract

Fluorescence emissions of molecular rotors (MRs) are affected by local restrictions to molecular motion, and therefore it was considered that MRs can be used as structural probes of biopolymers. In this study, 9-(2-carboxy-2-cyanovinyl)-julolidine (CCVJ), a hydrophilic MR, was used to differentiate branched α-D-glucans, including amylopectin, phytoglycogen, and their β-limit dextrins. CCVJ emissions of glucan dispersions were correlated with dispersion viscosities and glucan branch structures. In diluted glucan dispersions, CCVJ emission showed essentially linear correlation with glucan content. In concentrated glucan dispersions, CCVJ emission correlated with viscosity in a double-logarithmic linear pattern, with phytoglycogen showing much greater sensitivities than amylopectin. In the plots of CCVJ emission vs. molar amount of branch, phytoglycogen materials showed greater slopes than their amylopectin counterparts, suggesting evident effects of branch structure on the restrictions to CCVJ molecules. Overall, CCVJ has demonstrated its fluorescent sensitivity with glucans, showing strong potentials as a structural probe of biopolymers.

Keywords: Amylopectin; Branching pattern; CCVJ; Molecular rotor; Phytoglycogen; Spatial restriction.