Accelerated Chlorophyll Reaction in Microdroplets to Reveal Secret of Photosynthesis
Accelerated Chlorophyll Reaction in Microdroplets to
Reveal Secret of Photosynthesis
- The research team of DGIST’s fellow Hong Gil Nam, discovered
the natural control of chlorophyll activity
- New mechanisms to protect photosynthesis organisms and control
its efficiency are expected
Figure 1. When the chlorophyll encounters an acid, a demetallation reaction occurs in which the magnesium metal ions of the chlorophyll are converted into hydrogen ions. This reaction occurs in many different types of chlorophyll, and the optical, electrical and chemical properties of the chlorophyll are changed by this reaction.
DGIST announced that the research team of the fellow Hong Gil Nam (Head of Center for Aging Research,
Institute for Basic Science) at the Department of New Biology and the
research team of Professor Richard N. Zare of Stanford University have found in
their joint research that chlorophyll demetallation is naturally accelerated a thousand times faster in microdroplets without any help of enzymes.
Chlorophyll is a green pigment molecule found in photosynthetic
organisms and plays a key role in the first step of photosynthesis, which
absorbs light and converts it into chemical energy.
In recent years, several research groups have reported the
phenomenon of accelerated chlorophyll reactions in microdroplets. Mostly,
evaporation of the solvent or low voltage was pointed as the main causes of the
acceleration. However, this study conducted experiments to verify various
hypotheses without accepting existing assertions and found that the limitation
effect of physical space of micro-sized droplets is the cause of accelerated
The team paid attention to the chemical reaction of chlorophyll in
order to reveal the control secret of the absorption and transfer of solar energy.
In the acidic condition, chlorophyll demetallation reaction occurs in which the
magnesium ions at the center of the chlorophyll are replaced with the hydrogen
ions. So far, the importance of this reaction in photosynthesis has been
overlooked as the reaction rate of the demetallation in bulk solution was very
slow compared to the absorption and transfer rate of solar energy in many
The research team has found that the chlorophyll demetallation
reaction gets a thousand times faster in microdroplets by applying the method
to measure the reaction rate of biochemicals in microdroplets which was
developed in 2015. This suggests the possibility of a new mechanism of
photosynthesis control by rediscovering the importance of chlorophyll reaction.
In living organisms, a variety of biochemical reactions take place
in physically confined spaces. Photosynthesis also occurs in the organelles,
the chloroplasts of plants, and the smaller structures called "grana" in
chloroplasts absorb light. The team observed the reaction kinetics of
biochemical reactions by creating microdroplets to look at the reaction of
chlorophyll under the similar environment to the actual physical space of a
The research team collided water droplets containing chlorophyll
with water droplets containing hydrochloric acid at high speed to make micro-sized
fused droplets. Then, they recorded kinetics of acid-induced chlorophyll
demetallation by controlling the travelling distance of the fused
Figure 2. Experimental setup for chlorophyll
demetallation kinetics using microdroplet fusion mass spectrometry.
As a result, it was found that chlorophyll demetallation occurs at a
time of several tens of microseconds, which is about a thousand times faster
than that measured in bulk solution. This result is presumed to be due to the
limitation of the physical space of microdroplets as well as the surface effect
of droplets themselves.
DGIST’s Hong Gil Nam said "When chlorophyll is oxidized, it
loses its photosynthesis function. However, the demetallation reaction can
protect the chlorophyll as it prevents the oxidation of chlorophyll." He
added "This study suggests that the demetallation reaction of chlorophyll
can be a new mechanism which can protect photosynthetic organisms or control
photosynthetic efficiency and that the reaction can be fast enough without any enzymatic
action unlike conventional thinking."
The team expects that the discovery of a new mechanism of
photosynthesis would bring better understanding of the operation of
photosynthesis and contribute to further studies to find elements and methods
for more efficient photosynthesis.
Meanwhile, this study was published on January 1, 2017 in the online
edition of Quarterly Reviews of
Biophysics, an international academic journal in the field of biophysics.
Kyoo Lee, Hong Gil Nam and Richat N. Zare, “Microdroplet Fusion Mass
Spectrometry : Accelerated Kinetics of Acid-Induced Chlorophyll Demetallaton”
Quarterly Reviews of Biophysics, 2017.
Kinetics of acid-induced chlorophyll
demetallation was recorded in microdroplets by fusing a stream of microdroplets
containing 40 μM chlorophyll a or b dissolved in
methanol with a stream of aqueous microdroplets containing 35 mM hydrochloric
acid (pH = 1·46). The kinetics of the demetallation of
chlorophyll in the fused microdroplets (14 ± 6 μm diameter; 84 ± 18 m s−1
velocity) was recorded by controlling the traveling distance of the
fused microdroplets between the fusion region and the inlet of a mass
spectrometer. The rate of acid-induced chlorophyll demetallation was
about 960 ± 120 times faster in the charged microdroplets compared with that
reported in bulk solution. If no voltage was applied to
the sprayed microdroplets, then the acceleration factor was about 580 ± 90,
suggesting that the applied voltage is not a major factor
determining the acceleration. Chlorophyll a was more rapidly demetallated than
chlorophyll b by a factor of ∼26 in bulk solution and ∼5 in charged microdroplets. The demetallation kinetics was second
order in the H+ concentration, but the acceleration factor of microdroplets compared with bulk
solution appeared to be unchanged in going from pH = 1·3 to 7·0. The
water:methanol ratio of the fused microdroplets was varied
from 7:3 to 3:7 causing an increase in the reaction rate of chlorophyll a
demetallation by 20%. This observation demonstrates that the solvent
composition, which has different evaporation rates, does not significantly
affect the acceleration. We believe that a major portion of the
acceleration can be attributed to confinement effects involving surface
reactions rather than either to evaporation of solvents or to the introduction of