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