View
9
Download
0
Category
Preview:
Citation preview
Experimental Quantum Biophysics Group
Uncovering the fundamental physics in photosynthesis:
Lightharvesting, energy transport and charge separation
Yes! One water located in the protein
pocket, bound to oxyluciferin, can affect
the difference between the ground and
excited states enough to explain why
light emitted from fireflies is yellow-
green, while it is orange from click
beetles and red from railroad worms.
We thank Lundbeckfonden, Villumfonden, Carlsbergfondet and FNU for generous funding.
The questions we seek to answer:
The molecules of life (DNA and peptides) are highly photostable: How is dangerous electronic energy converted to harmless heat? Can we speak
of “survival of the fittest” at a molecular level?
Near 100%-efficiency of light-harvesting in photosynthesis: How do the many pigments (chlorophylls) in the photoprotein talk to each other?
How is energy transferred to the reaction center where charge separation occurs (nature’s solar cell)?
How does the microenvironment affect photoactive biomolecules and electron acceptors?
This is all governed by nontrivial quantum physics!
Bottom-up approach: Start with one molecular unit and gradually add complexity (single water molecules or other photoactive molecules).
Isolated light
absorber + one water molecule
hν hν
Ground state
Excited state
hν hν ?
Ground state
First excited state
Second excited state
En
erg
y
ϕ10ϕ2
0
ϕ11ϕ2
0 ϕ10ϕ2
1 Ψ𝑒𝑥𝑐𝑖𝑡𝑜𝑛+ = ϕ1
1ϕ20+ϕ1
0ϕ21
Ψ𝑒𝑥𝑐𝑖𝑡𝑜𝑛− = ϕ1
1ϕ20-ϕ1
0ϕ21
?
Separate
light absorbers
Coupled
light absorbers
Gas-phase ion spectroscopy
Angew. Chem. Int. Ed. 51, 10256-10260 (2012)
J. Am. Chem. Soc. 135, 6485-6493 (2013)
J. Am. Chem. Soc. 135, 6818-6821 (2013)
Angew. Chem. Int. Ed. 54, 2170–2173 (2015)
Light-emitting insects:
They are red, orange, or yellow-green even
though they use the same molecule:
Oxyluciferin!
Is a nearby water molecule sufficient to
explain the color modulation ?
or hν
Our results clearly show that
communication between two
or more pigments is needed
to account for the protein
absorption.
Two chlorophylls together
causes a redshift of 0.06 eV.
In the right direction!
Solu
tion
-phas
e ab
sorp
tion
Gas
-phas
e ab
sorp
tion
Chlorophyll a
monomer dimer
Red shift
0 100 200 300 400 500 600 700 800 900 1000
0
200
400
600
800
1000
1200
Chl a + acetylcholine = 600 nm
Counts
m/zFragment mass
Wavelength (nm)
A quinone is produced in an
electronically excited state after
near-resonant electron transfer
from pheophytin. We have shown
that the separation between ground
and excited states in the anion is
surprisingly independent of the
microenvironment (H2O). Quinone
is a robust electron acceptor.
Nature has worked it out!
In the future we want to see the
light!
OxyLuciferin
OxyLuciferin + H2O
Simon, Karin, Mark, Steen, Jørgen and Christina
Recommended