Hofmeister effect on the viscosity properties of gelatin in dilute solutions

Abstract

The effect of various Hofmeister anions on the molecular conformation of gelatin in dilute solutions was investigated by viscosity, optical rotation and dynamic light scattering (DLS). The results showed that the intrinsic viscosity of gelatin decreased in the presence of the kosmotropic anions such as Citrate3−, SO42−, H2PO4− and MeCOO−, whereas it was increased with the addition of chaotropes such as Cl− and KSCN−. Furthermore, the intrinsic viscosity of gelatin was directly correlated to the hydration entropy of kosmotropic anions, suggesting that the decrease of the intrinsic viscosity was attributed to the strong hydration effect of kosmotropes. The strong dehydration of gelatin facilitated the folding of the polymer chains into helix bundles, validated by the results of optical rotation. On the contrary, the chaotropic anions could interact directly with polypeptide backbones, and the intrachain hydrogen bonds were destroyed. As a result, the polymer chains expanded, which was confirmed by DLS data, and the intrinsic viscosity was increased. These observations indicate that the molecular conformation of gelatin can be modulated by Hofmeister anions.