posted on 2024-02-27, 10:05authored bySayan Maity, Vangelis Daskalakis, Thomas L. C. Jansen, Ulrich Kleinekathöfer
Diatoms are one of
the most abundant photosynthetic organisms on
earth and contribute largely to atmospheric oxygen production. They
contain fucoxanthin and chlorophyll-a/c binding proteins (FCPs) as
light-harvesting complexes with a remarkable adaptation to the fluctuating
light on ocean surfaces. To understand the basis of the photosynthetic
process in diatoms, the excitation energy funneling within FCPs must
be probed. A state-of-the-art multiscale analysis within a quantum
mechanics/molecular mechanics framework has been employed. To this
end, the chlorophyll (Chl) excitation energies within the FCP complex
from the diatom Phaeodactylum tricornutum have been
determined. The Chl-c excitation energies were found to be 5-fold
more susceptible to electric fields than those of Chl-a pigments and
thus are significantly lower in FCP than in organic solvents. This
finding challenges the general belief that the excitation energy of
Chl-c is always higher than that of Chl-a in FCP proteins and reveals
that Chl-c molecules are much more sensitive to electric fields within
protein scaffolds than in Chl-a pigments. The analysis of the linear
absorption spectrum and the two-dimensional electronic spectra of
the FCP complex strongly supports these findings and allows us to
study the excitation transfer within the FCP complex.