permaculture

[Lawrence London <lfljvenaura@gmail.com>]

Quantum mechanics explains efficiency of photosynthesis
http://www.sciencedaily.net/releases/2014/01/140109092008.htm

Quantum mechanics explains efficiency of photosynthesis
Date:
January 9, 2014
Source:
University College London
Summary:
 Light-gathering macromolecules in plant cells transfer energy by taking
advantage of molecular vibrations whose physical descriptions have no
equivalents in classical physics, according to the first unambiguous
theoretical evidence of quantum effects in photosynthesis.

Light-gathering macromolecules in plant cells transfer energy by taking
advantage of molecular vibrations whose physical descriptions have no
equivalents in classical physics, according to the first unambiguous
theoretical evidence of quantum effects in photosynthesis.
*Credit: © lily / Fotolia*

Light-gathering macromolecules in plant cells transfer energy by taking
advantage of molecular vibrations whose physical descriptions have no
equivalents in classical physics, according to the first unambiguous
theoretical evidence of quantum effects in photosynthesis published today
in the journal *Nature Communications*.







 The majority of light-gathering macromolecules are composed of
chromophores (responsible for the colour of molecules) attached to
proteins, which carry out the first step of photosynthesis, capturing
sunlight and transferring the associated energy highly efficiently.
Previous experiments suggest that energy is transferred in a wave-like
manner, exploiting quantum phenomena, but crucially, a non-classical
explanation could not be conclusively proved as the phenomena identified
could equally be described using classical physics.

Often, to observe or exploit quantum mechanical phenomena systems need to
be cooled to very low temperatures. This however does not seem to be the
case in some biological systems, which display quantum properties even at
ambient temperatures.

Now, a team at UCL have attempted to identify features in these biological
systems which can only be predicted by quantum physics, and for which no
classical analogues exist.

"Energy transfer in light-harvesting macromolecules is assisted by specific
vibrational motions of the chromophores," said Alexandra Olaya-Castro (UCL
Physics & Astronomy), supervisor and co-author of the research. "We found
that the properties of some of the chromophore vibrations that assist
energy transfer during photosynthesis can never be described with classical
laws, and moreover, this non-classical behaviour enhances the efficiency of
the energy transfer."

Molecular vibrations are periodic motions of the atoms in a molecule, like
the motion of a mass attached to a spring. When the energy of a collective
vibration of two chromphores matches the energy difference between the
electronic transitions of these chromophores a resonance occurs and
efficient energy exchange between electronic and vibrational degrees of
freedom takes place.

Providing that the energy associated to the vibration is higher than the
temperature scale, only a discrete unit or quantum of energy is exchanged.
Consequently, as energy is transferred from one chromophore to the other,
the collective vibration displays properties that have no classical
counterpart.

The UCL team found the unambiguous signature of non-classicality is given
by a negative joint probability of finding the chromophores with certain
relative positions and momenta. In classical physics, probability
distributions are always positive.

"The negative values in these probability distributions are a manifestation
of a truly quantum feature, that is, the coherent exchange of a single
quantum of energy," explained Edward O'Reilly (UCL Physics & Astronomy),
first author of the study. "When this happens electronic and vibrational
degrees of freedom are jointly and transiently in a superposition of
quantum states, a feature that can never be predicted with classical
physics."

Other biomolecular processes such as the transfer of electrons within
macromolecules (like in reaction centres in photosynthetic systems), the
structural change of a chromophore upon absorption of photons (like in
vision processes) or the recognition of a molecule by another (as in
olfaction processes), are influenced by specific vibrational motions. The
results of this research therefore suggest that a closer examination of the
vibrational dynamics involved in these processes could provide other
biological prototypes exploiting truly non-classical phenomena.
 ------------------------------

*Story Source:*

The above story is based on
materials<http://www.ucl.ac.uk/news/news-articles/0114/090114-Quantum-mechanics-explains-efficiency-of-photosynthesis>provided
by *University
College London* <http://www.ucl.ac.uk>. *Note: Materials may be edited for
content and length.*
 ------------------------------

*Journal Reference*:

   1. Edward J. O’Reilly, Alexandra Olaya-Castro. *Non-classicality of the
   molecular vibrations assisting exciton energy transfer at room 
temperature*.
   *Nature Communications*, 2014; 5 DOI:
10.1038/ncomms4012<http://dx.doi.org/10.1038/ncomms4012>

------------------------------

*Cite This Page*:

   - 
MLA<http://www.sciencedaily.net/releases/2014/01/140109092008.htm#citation_mla>
   - 
APA<http://www.sciencedaily.net/releases/2014/01/140109092008.htm#citation_apa>
   - 
Chicago<http://www.sciencedaily.net/releases/2014/01/140109092008.htm#citation_chicago>

University College London. "Quantum mechanics explains efficiency of
photosynthesis." ScienceDaily. ScienceDaily, 9 January 2014. <
www.sciencedaily.com//releases/2014/01/140109092008.htm>.