Kinetics of xanthan in denaturation and renaturation process in dilute aqueous NaCl solution*

Denaturation and renaturation processes of xanthan in 5 mM or 10 mM aqueous NaCl were investigated with abruptly heated from 20 to 80 °C or quenched from 80 to 20 °C by using small-angle X-ray scattering (SAXS) and circular dichroism (CD) measurements. The time-development of CD signal took place more rapidly than that of the SAXS profile in denaturation process, while the SAXS intensity changed much more rapidly than the CD data in the renaturation process, indicating that the conformation of the side chain changes more rapidly than the melting of the double helical structure in the denaturation process. In contrast, the formation of double helical structure is faster than the orientation of the side chain in the renaturation process, while the CD spectra after 24 h were identical to the original solution, suggesting that the conformation of side chain after renaturation is the same as the native state. Our research suggests that the slow deformation and rapid recovery of ordered structure of the main chain may contribute to maintain the functionality derived from the polymer conformation.