Interaction and Thermal Stability of Oxidized Carboxymethyl Cellulose/Collagen Based on Two-Dimensional Infrared Spectroscopy

Collagen was modified by oxidized carboxymethyl cellulose (OCMC) and then their interaction and thermal stability were investigated by two-dimensional infrared spectroscopy (2D-IR). One-dimensional infrared spectra showed that the positions and intensities of the main characteristic absorption peaks (amide I , II and bands) for collagen had no significant change upon cross-linking; additionally, all the absorption ratios of amide III bands to 1 455 cm(-1) (A(III)/A(1455)) of native and cross-linking collagen were close to 1. 000. These results indicated that the triple helix of collagen was not demolished by the introduction of cross-linking. The 2D-IR spectra were constructed from OCMC amount-dependent infrared spectra, and then the interaction between OCMC and collagen was further analyzed. The response sensitivity and order of collagen structure and the groups of OCMC showed that electrostatic interaction formed firstly between carboxyl groups of OCMC and guanidine or amino groups of collagen. Then Schiff's base reaction occurred between aldehyde groups of OCMC and amino groups of collagen, which was the dominated interaction. As a result, the thermal stability of cross-linked collagen increased. With the increase of temperature, the red-shift of absorption bands and the decreased A(III)/A(1455) value reflected that hydrogen bonds were weakened, and the unwinding of triple helix occurred for both native and cross-linked collagens; whereas the fewer changes in red-shift and A(III)/A(1455) value for cross-linked collagen also confirmed the increase in thermal stability. Furthermore, the 2D-IR spectra were constructed from the temperature-dependent infrared spectra and provided information about the thermally induced structural changes. It could be conjectured that the triple helix was transformed into random coils for the native and cross-linked collagen, resulting in the loss of secondary structure with increasing the temperature. Nevertheless, the response sensitivity and order of the triple helix to temperature changed significantly. (1) For native collagen, the most temperature-sensitive structure was triple helix; whereas, it was random coils for cross-linked collagen, demonstrating that the triple helix of cross-linked collagen was less sensitive to temperature than that of native collagen. (2) Moreover, the response order of the triple helix for cross-linked collagen to the increased temperature lagged. It was illustrated that the stabilization of collagen by OCMC was due to the reinforcement of the triple helix.