Differential scanning calorimetry and optical properties of collagen-dichroic azo ponceau ss complexes

ABSTRACT

The purpose of this research was to find correlations between thermocalorimetric properties, linear dichroism and birefringence of collagen-Ponceaus SS complex as compared to pure collagen fibers. In this work, we show that the binding of the dichroic sulfo-azo dye Ponceau SS to highly oriented collagen fibers results in increased crystallinity, as measured by differential scanning calorimetry and optical anisotropy. Collagen fibers formed a complex with Ponceau SS that showed higher crystallinity and molecular order than the fibers alone. Differential scanning calorimetry revealed that the denaturation (peak) temperatures (Tm) of the complex were higher than for the pure collagen fibers. In addition, the dye-collagen complex showed high linear dichroism and stark interference colors in birefringence dispersion. These photo-optical properties are caused by periodic differences in the refractive indices along the molecules in the ordered collagen-dye complex, and indicate that this complex is a non-linear optical supramolecular chiral object.