Nanotechnologies / Materials
Medical & healthcare, Separation/purification

Molecular recognition of polysaccharide derivatives
with highly branched architecture
Department of Macromolecular Science, Graduate School of Science
Professor Ken Terao
https://researchmap.jp/kenterao?lang=en

Nanotechnologies / Materials

Abstract
Highly branched polysaccharide derivatives consisting of rigid
rod-like chains were synthesized. Their dimensional and hydrodynamic properties in organic solvents were investigated by light and
X-ray scattering and viscometry. The obtained radius of gyrationand intrinsic viscosity were found to be much smaller than those oflinear chain with the same molar mass. The chiral columns with thishyperbranched sample coated on silica particles showed chiralrecognition ability for a number of racemic compounds, confirming its high chiral separation ability. It was also clarified that thechiral separation ability is appreciably different from those of linear
chains, indicating the difference in molecular recognition ability.
This is because the hyperbranched structure, consisting of rigid
and densely branched chains, distorts the rigid helical structure.

▍ Background & Results
Polysaccharide derivatives are used in a wide range of applications from foods and commodities to fibers and resins. Amongthem, carbamate derivatives of polysaccharides are widely usedas chiral stationary phase for chiral separation columns, which aredecisively important for purification and purity determination of
low-molecular-weight chiral compounds used in pharmaceuticals.
Since the chiral separation ability of polysaccharide derivatives isrelated to the helical structure of the polysaccharide main chain,it was expected that the separation ability would also be affected
when differences in the architecture of the polymer chain affectthe helical structure. Therefore, in this study, polysaccharide carbamate derivative samples with a hyperbranched structure weresynthesized using commercially available highly branched cyclic
dextrin samples. The above-mentioned difference in chiral separation ability was observed in the investigated carbamate derivatives.
Branched and cyclic polymers consisting of rigid chains have
not yet been studied extensively. Considering the recent development of novel polymer synthesis, it is expected that such polymers
will become readily synthesizable to develop novel functions.

Figure 1. (a) Chemical structure of the highly branched polysaccharide derivatives and (b) schematic image of the branching point.

▍ Significance of the research and Future perspective
The molecular size and viscosity in solution of the hyperbranched polymers are much smaller than those of the linear chain
with the same molar mass. This viscosity ratio becomes more
pronounced for rigid chains. In the case of the present study, theintrinsic viscosity was about 1/40 times that of the linear chains.
This low viscosity allows us to readily handle high molecular weight
polymer solutions. The distortion of the helical structure of the rigid
hyperbranched chains has a pronounced effect on the interaction
with solvent molecules as well as on the chiral separation. In fact,
phase separation was also observed for hyperbranched chainseven in a solvent at which the corresponding linear chain was fullydissolved. We expect to develop novel functions with the hyperbranched structure that cannot be achieved with only linear chains.

Figure 2. Schematic representation of the chiral column and the chemical structure of the polysaccharide derivatives used as chiral stationary phases.

P a t e n t
Kishimoto, Aika; Ryoki, Akiyuki; Terao, Ken et al. Molecular structure and chiral recognition ability of highly branched cyclic dextrin carbamate derivative.
Carbohydr. Polym. 2022, 290, 119491. doi: 10.1016/j.carbpol.2022.119491
Kishimoto, Aika; Ryoki, Akiyuki; Terao, Ken et al. Correlation between conformational feature in solution and chiral separation ability of linear and nonlinear
Tr e a t i s eamylose tris(alkylcarbamate)s. Polymer. 2023, 284, 126303. doi: 10.1016/j.polymer.2023.126303
Mizuguchi, Madoka; Umeda, Keisuke; Terao, Ken et al. Solution characterization of a hyperbranched polysaccharide carbamate derivative and specificphase separation behavior due to chain branching. Soft Matter. 2023, 19, 7781-7786. doi: 10.1039/d3sm01074k
UR
L https://www.chem.sci.osaka-u.ac.jp/lab/terao/K e y w o r d polysaccharide derivatives, branched polymers, stiff chains, molecular recognition, chiral separation