Shear flow affects secondary and tertiary structures in hyaluronan solution as shown by rheo-NMR

C-13 NMR spectra of hyaluronan (HA) in aqueous solution have been recorded under shear in a Couette viscometer. In shear-thinning conditions as determined in mechanical rheometry experiments the chemical shifts of glycosidic linkage carbons moved to higher frequency. This result is consistent with a more stretched conformation for the chain. Shear-dependant broadening and extension to downfield of the acetamido C=O resonance are compatible with a partial switch from P-sheet (tertiary structure) NH H-bonded forms to non-H-bonded states, suggestive of some disruption of the P-sheet. By contrast, the chemical shifts of sugar ring carbons did not deviate from values found in the solution at rest. (C) 2002 Elsevier Science B.V. All rights reserved.