Interaction study in homogeneous collagen/chondroitin sulfate blends by two-dimensional infrared spectroscopy

The neutral homogeneous collagen/chondroitin sulfate (Col/CS) blends were prepared when using 0.25 mol/L NaCl to stabilize the blends. Composition-dependent Fourier transform-infrared (FTIR) spectra were analyzed by generalized two-dimensional (2D) correlation spectroscopy to investigate the conformational changes of collagen and the specific interactions between collagen and CS. When adding CS to the collagen solution, C–H bending vibration of collagen varies firstly, then collagen skeleton, and finally the specific interactions between collagen and CS. The Col/CS ratios influence the kinds of specific interactions. Only hydroxyl groups of CS interact with CO group of collagen owing to the charge shielding effect of NaCl when the CS content is less than 50 wt%. Besides hydrogen bond, the electrostatic interactions between ionized carboxyl group or sulfate group of CS and ɛ-amino group of lysine or guanidine group of arginine appear when the CS content is more than 50 wt%.