Hydration effects on photophysical properties of collagen

Collagen structure, in which water molecules mediate some networks of intra-chain and inter-chain hydrogen bonds, appears to be a promising model system to investigate in great detail the relationships between biological organization and the characteristics of Delayed Luminescence (DL), the phenomenon consisting of the prolonged ultra-weak emission of optical photons after excitation of the system by illumination. Samples of type I collagen molecules from tendons have been studied on varying their hydration state. Comparison of their dielectric properties with the DL response, along with the acquisition of excitation and emission spectra of tendon collagen, in its native and dried state have gathered additional information allowing to test hypothesis on the origin and/or the mechanisms of photoinduced DL emission. The peculiar structure of collagen, where a relevant role is played by the hydrogen bonded water network, suggested that collective excitations could be generated in this macromolecule. Upon hydration, changing of the phonon spectrum could significantly affect the type of the ground electron states which can be excited in the collagen, as evaluated by applying a variational method. Changing in the ground electron states could take into account for the different regimes of the DL decays, in turn.