Unravelling a Direct Role for Polysaccharide b-Strands in the Higher Order Structure of Physical Hydrogels.
Rüther, A.; Forget, A.; Roy, A.; Carballo, C.; Mießmer, F.; Dukor, R. K.; Nafie, L. A.; Johannessen, C.; Shastri, V. P.; Lüdeke, S.
Angew. Chemie Int. Ed. 2017, 56 (16), 4603–4607
The mechanical properties of agarose-derived hydrogels depend on the scaffolding of the polysaccharide network. To identify and quantify such higher order structure, we applied Raman optical activity (ROA)-a spectroscopic technique that is highly sensitive toward carbohydrates-on native agarose and chemically modified agarose in the gel phase for the first time. By spectral global fitting, we isolated features that change as a function of backbone carboxylation (28, 40, 50, 60, 80, and 93 %) from other features that remain unchanged. We assigned these spectral features by comparison to ROA spectra calculated for different oligomer models. We found a 60:40 ratio of double- and single-stranded α-helix in the highly rigid hydrogel of native agarose, while the considerably softer hydrogels made from carboxylated agarose use a scaffold of unpaired β-strands.