We study the optical properties of amyloid aggregates relevant for neurodegenerative disease using experiments and computation. The low energy optical absorption in the near-UV range depends on conformations and involves charge-transfer excitations.

a Photosynthesis includes capturing sunlight by an assembly of molecules, called chlorophylls, and directing the harvested energy in the form of electronic excitations to the reaction center. Here we report, using realspace density functional theory and time-dependent density functional theory together with GW calculations, the optical and electronic properties of the two main chlorophylls in green plants, namely, chlorophylls a and b. Furthermore, we estimate the dipole and primitive quadrupole electric moments of these molecules. We employ Casida's assignment ansatz to study the absorption spectra of the chlorophylls in the two main red and blue regions at various environments with different exchangecorrelation functionals. In addition, we obtain the band gap of chlorophylls a and b, which are all in remarkable agreement with experimental observations.

<div>We combine absorption and fluorscence spectroscopy experiments and theoretical modeling to specifically examine the role of termini interactions on the optical properties.</div><div><div>Optical absorption and fluorescence is measured for a six-chain amino acid 2Y3J (AIIGLM) which forms a segment of the full amyloid beta 1-40. In order to explore the sensitivity of the optical properties to the termini interactions, the experiments were repeated by acetylating the N-terminus.</div><div>Although atomic force microscopy experiments indicate the formation of some form of fibrilar or crystal aggregates in both systems, the optical properties are strikingly different - acetylation significantly reduces optical activity between 280-350 nm.</div></div>

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