Chiroptical properties of reporter-modified or reporter-complexed highly 1,6-glucose-branched beta-1,3-glucan

摘要

The macromolecular structure of highly 1,6-glucose-branched beta-1,3-glucan (6BG3) was elucidated spectroscopically by modification and complexation with chromophoric reporters. The circular dichroism spectra of 4-(dimethylamino)benzoic acid (DABz)-modified 6BG3 showed a relatively small but obvious bisignate couplet in an aqueous DMSO solution; however, in DMSO, 6BG3 forms a random coil. These chiroptical properties and the AFM images revealed that reporter-modified 6BG3 goes through a random coil-to-globule conversion process upon solvent switching. The macromolecular structure of native, nonchromophoric 6BG3 was further examined by complexation with 2,5-poly(3-(6-pyridiniohexyl)thiophene) (PyPT) in situ. The 6BG3 random-coil strand complexed with PyPT to afford a heteroduplex with a small amount of a heterotriplex, showing a large exciton coupling for the pi,pi* transition of PyPT. The amount of the heteroduplex hybridization was enhanced at higher pH due to further complexation of single strands of partially deprotonated 6BG3 with free PyPT.