Unravelling the intrinsic color of chlorophyll

Angewandte Chemie International Edition 127, 2198–2201 (2015)

Unravelling the intrinsic color of chlorophyll

Bruce F. Milne,Yoni Toker,Angel Rubio, Steen Brøndsted Nielsen

The exact color of light absorbed by chlorophyll (Chl) pigments, the lightharvesters in photosynthesis, is tuned by the protein microenvironment but without knowledge of the intrinsic color of Chl it remains unclear how large this effect is. Here we report experimental first absorption energies of Chl a and b isolated in vacuo and tagged with quaternary ammonium cations. The energies are largely insensitive to details of the tag structure, a finding supported by first–principles calculations using time-dependent density functional theory. Absorption is significantly blueshifted compared to that of Chlcontaining proteins (by 30 – 70 nm). A single redshifting perturbation such as axial ligation or the protein medium is insufficient to account even for the smallest shift; the largest requires pigment-pigment interactions.

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B.F.M. thanks DIPC and CFM (UPV/EHU) and the Laboratory for Advanced Computation (University of Coimbra) for support. S.B.N. acknowledges support from Lundbeckfonden. A.R. acknowledges support from ERC Advanced Grant DYNamo (ERC-2010-AdG-267374), Spanish Grant (FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), and EC FP7 CRONOS (Grant 280879-2).

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