Using the FT-IR linear dichroism method for molecular order determination of tendon collagen bundles and nylon 6

Polarized Fourier transform-infrared (FT-IR) was used to compare the orientation of vibrational chemical groups of bovine tendon collagen bundles (CBs) to that of nylon 6, a simpler polyamide model, in terms of linear dichroism (LD). Subtraction of spectral profiles identified the most significant differences regarding the amide regions. At 1630 cm−1, the CBs displayed higher peak areas and absorbance when positioned perpendicularly (A⊥) to the plane of polarized light, in comparison with nylon 6. In contrast, at the 1526 cm−1 amide II spectral region the inverse occurred. In the amide III region (1232 cm−1), the LD was positive and higher for CBs. Dichroic ratios (DR = A||/A⊥) calculated from the average of ten measured spectra for CBs and nylon 6 revealed that the values for CBs were <1.0 in the 3298–1655 cm−1 wavenumber range and >1.0 in the 1536–1234 cm−1 wavenumber range. From 1535 to 1120 cm−1, nylon 6 displayed DR values higher than those of CBs. The LD band integrated areas were higher in CBs than in nylon 6. The LD differences between CBs and nylon 6 are probably due to a more complex chemical composition and supramolecular oriented architecture in CBs in comparison to nylon 6.