Influence of Tyrosine-Derived Moieties and Drying Conditions on the Formation of Helices in Gelatin

Abstract

The single and triple helical organization of protein chains strongly influences the mechanical properties of gelatin-based materials. A chemical method for obtaining different degrees of helical organization in gelatin is covalent functionalization, while a physical method for achieving the same goal is the variation of the drying conditions of gelatin solutions. Here we explored how the introduction of desaminotyrosine (DAT) and desaminotyrosyl tyrosine (DATT) linked to lysine residues of gelatin influenced the kinetics and thermodynamic equilibrium of the helicalization process of single and triple helices following different drying conditions. Drying at a temperature above the helix-to-coil transition temperature of gelatin (T > Tc, called vshort) generally resulted in gelatins with relatively lower triple helical content (Xc,t = 1−2%) than lower temperature drying (T < Tc, called vlong) (Xc,t = 8−10%), where the DAT(T) functional groups generally disrupted helix formation. While different helical contents affected the thermal transition temperatures only slightly, the mechanical properties were strongly affected for swollen hydrogels (E = 4−13 kPa for samples treated by vlong and E = 120−700 kPa for samples treated by vshort). This study shows that side group functionalization and different drying conditions are viable options to control the helicalization and macroscopic properties of gelatin-based materials.