Anisotropy of Chemical Bonds in Collagen Molecules Studied by X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Collagen type I fibrils are the major building blocks of connective tissues. Collagen fibrils are anisotropic supramolecular structures, and their orientation can be revealed by polarized light microscopy and vibrational microspectrometry. We hypothesized that the anisotrophy of chemical bonds in the collagen molecules, and hence their orientation, might also be detected by X-ray photoemission electron spectromicroscopy (X-PEEM) and X-ray absorption near-edge (XANES) spectroscopy, which use linearly polarized synchroton light. To test this hypothesis, we analyze sections of rat tail tendon, composed of parallel arrays of collagen fibrils. The results clearly indicate that XANES-PEEM is sensitive to collagen fibril orientation and more specifically to the orientation of carbonyl and amide bonds in collagen molecules. These data suggest XANES-PEEM is a promising technique for characterizing the chemical composition and structural organisation at the nanoscale of collagen-based connective tissues, including tendons, cartilage and bone.