Polypentapeptide (PPP) elastin undergoes a reversible transparent-opaque optical transition in the visible spectrum when the temperature is changed across a transition temperature, Tt. To discover the mechanism of this transition, transmissivity and reflectivity measurements of a PPP membrane were made in the wavelength region of 500–1050 nm. Analysis of the measured data using a two-flux radiative transfer model showed that above the transition temperature the scattering albedo varied with wavelength as that of a Rayleigh scattering particle. It is proposed that the optical transition occurs due to scattering by three-dimensionally folded chains of PPP which are formed above the transition temperature when water pentamers are broken and intramolecular hydrophobic interactions are induced.

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