The document discusses a conjectured derivative morphology of pheophytin that could facilitate proton conduction and hydrogen decomposition. Quantum simulations showed the derivative structure was energetically favorable. Spectral analyses of extracted pheophytin matched the simulated derivative structure more than the textbook structure. Battery experiments demonstrated pheophytin-catalyzed electrodes produced more discharge than non-catalyzed electrodes, providing evidence pheophytin can catalyze hydrogen decomposition. The findings suggest a derivative pheophytin form may exist that could better explain experimental observations than the accepted textbook structure.

1. A Suspected Derivative Morphology for
pheophytin (脫鎂葉綠素) and
the Enhanced Hydrogen Decomposition It Caused
Jyun-Lin Huang,2 Wen-Bing Lai,2 Chungpin Liao,1,2,* Li-Shen Yeh2
（黃均霖） （賴玟柄） （廖重賓） （葉立紳）
1Graduate School of Electro-Optic and Materials Science,
National Formosa University (NFU), Huwei, Taiwan 632, ROC.
2Advanced Research & Business Laboratory (ARBL),
Taichung, Taiwan 407, ROC.
*Corresponding Author: cpliao@alum.mit.edu and Speaker
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Outline
• What’s the role of pheophytin (pheo) in photosynthesis?
• What might be pheo’s other structure-related roles?  things we
bumped into in the original low-power chlorophyll battery
• A conjectured derivative morphology and associated
proton conduction path within pheophytins (pheo’s)
• Experimental evidence in pheo-catalyzed decomposition of
hydrogen gas
• Summary and conclusions
• Porphyrin-ring family and their uses
• Spectral comparison among: 1st-principle quantum simulation,
measurement on ethanol-extracted pheo, and existing literature

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• What’s the role of pheophytin (pheo) in photosynthesis?
Pheo as:
-1st acceptor of light-
excited electrons
-Accelerator of such
electrons (~1.14 eV)

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• Background and motivation
– the success of pheophytin (pheo, 脫鎂葉綠素) catalyst
Pheophytin a
(textbook)
textbook
Porphyrin ring
E ~ 1.14 eV was used in our metal-air chemical batteries, but the number wasn’t right.
?
?

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Chlorophyll batteries
Some “products” were made back then, without paying attention to the real mechanism.

6. However, the oxygen evolving complex (OEC) is far from clear morphologically and
functionally.
To get back electrons for those ionized chlorophyll antennas, OEC’s have to oxidize
water under the room temperature, i.e., H2O  2H+ + ½ O2 + 2e-
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7. OEC morphology and function
OEC itself is already a battery….
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• What might be pheo’s other structure-related roles?  things we
bumped into in the original low-power chlorophyll battery
The original low-power chlorophyll (葉綠素) battery demonstrated that electricity can be
extracted from wetted chlorophyll powder which apparently had pre-stored the optical
energy from sun.
Primitive chl battery structure:
(-) Al foil | MgO powder | fiber paper | chl powder |
active carbon powder | (+) graphite paper
After the burn-out of battery, all chlorophyll became yellow brown in color, signifying
the conversion of all chlorophyll (chl) into pheophytin (pheo).
Namely, the chl-pheo chains within the wetted chlorophyll powder (i.e., electrolyte)
should have fulfilled their mission in accelerating returning electrons near the positive
electrode.
However, this scenario alone fell short of explaining the significantly more electricity
generated, as observed.
Pheo’s appeared to have shown their catalyzing capability too. See below.

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MgO + H2O  Mg(OH)2
(slightly soluble
in water)
 Mg2+ + 2OH-
MgO + 2OH-  Mg(OH)2 + 2e-
½ O2 + 2H+ + 2e-  H2O (acidic)
½ O2 + H2O + 2e-  2OH- (basic)
Catalysis by pheo?
If so, how?

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• Porphyrin-ring family and their uses
Porphyrins are compounds composed of four modified pyrrole subunits
interconnected at their α carbon atoms via methine bridges (=CH−).
The parent porphyrin is porphin, and substituted porphines are called porphyrins.
The porphyrin ring structure is aromatic (芳香族的), with a total of 26 electrons in
the conjugated system.
Porphyrin molecules typically have very intense absorption bands in the visible
region and hence may be deeply colored.
Porphyrins have been evaluated in the context of photodynamic therapy since they
strongly absorb light, which is then converted to energy and heat in the illuminated
areas.
For example, a structurally-modified porphyrin: verteporfin
porphin

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Verteporfin (trade name Visudyne) is a medication used as
a photosensitizer for photodynamic therapy to eliminate the
abnormal blood vessels in the eye associated with conditions
such as the wet form of macular degeneration (黃斑性病變).
* Scott, L. J.; Goa, K. L. (2000). "Verteporfin". Drugs & aging 16 (2): 139–146; discussion 146–8. and,
Adelman, R.; Adelman, R. A. (2013). "Profile of verteporfin and its potential for the treatment of central serous chorioretinopathy". Clinical
Ophthalmology 7: 1867–1875.
Verteporfin accumulates in these abnormal
blood vessels and, when stimulated by
nonthermal red light with a wavelength
of 689 nm in the presence of oxygen,
produces highly reactive
short-lived singlet oxygen and other
reactive oxygen radicals,
resulting in local damage to
the endothelium (內皮) and blockage of the
vessels.*
verteporfin

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Also, porphyrin-based compounds are of interest in molecular electronics and
supramolecular building blocks.
Synthetic porphyrin dyes that are incorporated in prototype dye-sensitized
solar cells (DSSCs)+.
As a porphyrin derivative, phthalocyanines (酞菁)
form coordination complexes with most elements
of the periodic table. These complexes are also
intensely colored and also are used as dyes or pigments.
phthalocyanine
+ Michael G. Walter; Alexander B. Rudine; Carl C. Wamser (2010). "Porphyrins and phthalocyanines in solar photovoltaic cells". Journal of Porphyrins
and Phthalocyanines 14 (9): 759–792.
Aswani Yella; Hsuan-Wei Lee; Hoi Nok Tsao; Chenyi Yi; Aravind Kumar Chandiran; Md.Khaja Nazeeruddin; Eric Wei-Guang Diau; Chen-Yu Yeh; Shaik M
Zakeeruddin; Michael Grätzel (2011). "Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent
Efficiency". Science 334 (6056): 629–634.

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Although never commercialized, metalloporphyrin complexes are widely
studied as catalysts for the oxidation of organic compounds.
Particularly popular for such laboratory research are complexes of meso-
tetraphenylporphyrin (H2TPP), e.g., the iron(III) chloride complex (TPPFeCl),
catalyze a variety of reactions of potential interest in organic synthesis.
H2TPP
TPPFeCl
Some other complexes emulate the action of various heme enzymes such
as cytochrome (細胞色素) P450, lignin peroxidase.#
# Zucca, Paolo; Rescigno, Antonio; Rinaldi, Andrea C.; Sanjust, Enrico (July 2014). "Biomimetic metalloporphines and metalloporphyrins as potential
tools for delignification: Molecular mechanisms and application perspectives". Journal of Molecular Catalysis A: Chemical. 388–389: 2–34.
Guilard, edited by Karl M. Kadish, Kevin M. Smith & Roger (2012). Handbook of porphyrin science. with applications to chemistry, physics, materials
science, engineering, biology and medicine. Singapore: World Scientific. ISBN 9789814335492.

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Figure 1. N-H tautomeric equilibria in porphyrins. Nonconcerted mechanism
(ab, bc) with both N-H protons exchanging independently, and concerted
mechanism with N—H exchanging simultaneously between neighboring
(de, df), or, opposite nitrogen atoms (ef).
• A conjectured derivative morphology and associated
proton conduction path within pheophytins (pheo’s)
First of all, tautomeric (互變異構的) dynamics is believed to be constantly going on
within the porphyrin ring.
Usually, you see
only one of them
in the textbooks.

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Figure 2. Seemingly stationery orthodox morphology of pheophytin-a (pheo-a)
It was pointed out that in order for the 1st-principle simulated chemical shift
spectra of a porphyrin-based molecule to match those of NMR (nuclear magnetic
resonance) measurements, such proton-movement-caused ring current was
necessary.&
Therefore, there is likely tautomeric dynamics taking place actively within the
porphyrin ring of pheo-a, in some way.
& Iwamoto, H.; Hori, K.; Fukazawa, Y. A model of porphyrin ring current effect. Tetrahedron Letters 2005, Vol. 46, 731–734.

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However, a single pheo molecule in its orthodox morphology (Figure 2, below)
does NOT seem to possess any capability in transporting protons across or
around within the porphyrin ring.
Namely, how can the seemingly needed tautomeric dynamic ring current owing
to the proton movement be initiated at all?
These double
bonds make the
proton movement
very hard.

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Figure 3. Suspected derivative morphology of pheophytin
(pheo), without showing its tail
It is suspected, therefore, that if proper electron movements can be arranged
such that all double bonds attaching to nitrogen (N) atoms become single ones
(with each associated carbon atom now carrying one positive formal charge),
and all 4 N atoms are saturated with hydrogen atoms, the situation will be
utterly different.

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Figure 4. Proposed proton (H+) transport scenario
across, or around within, a derivative pheophytin
molecule (tail not shown)
The suspected mechanism for proton internal transport within a derivative pheo,
which leads to the tautomeric ring current:
H+
H+
H+

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Q: Can most existing spectra for standard (orthodox)
pheo be actually those of “derivative” pheo instead?

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Figure 5. Spectral comparison among (a) standard morphology plus 2 free protons
simulation, (b) derivative morphology with 4 N-H bonds in porphyrin ring simulation,
(c) measurement on ethanol-extracted pheo, and (d) existing data in literature
[courtesy of Milenković S. M. et al. (2012)]
• Spectral comparison among: 1st-principle quantum simulation,
measurement on ethanol-extracted pheo, and existing literature
Standard pheo
simulation
Derivative
pheo simulation
To our dismay, the
wiggly features
were not complete
still.
More structures?
Even different
weighting percent?

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1st-principle QM simulated spectrum of orthodox morphology of pheo does NOT
show the key little features as demonstrated by measurements, existent data, and
simulated derivative morphology.
Can existing textbooks or literatures about pheo morphology
be rigorously in error? If so, so what?
What can molecular geometry optimization reveal to us further?
More importantly:
Can such derivative morphologies facilitate hydrogen oxidation reaction (i.e.,
Orienting and splitting of H2 molecule, ionization of H atoms, as a catalyst for HOR)?
What about conducting energy simulations and a battery-related experiment?

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Figure 6. A reasonable scenario to convert the entering hydrogen molecule and form the
derivative morphology of pheo with 4 N-H bonds formed under the acidic chemical battery
action, wherein yellow spots = electron lone pair, white = H, grey = C, blue = N, red = O, and
numbers on atoms = formal charges. 1 Ha (Hartree) = 27.2116 eV.
Suspected
derivative
morphology
 most stable
Energetic
DMol3 simulation
on pheo
bc = 0.18 eV
( H2  13.36 eV)
By a more rigorous
calculation wherein
H2 were
perpendicular to
the porphyrin plane.

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Figure 7. Hydrogen production by electrolysis for the intended hydrogen-fueled
battery (after the gas transfer was completed, the connection was disabled.)
• Experimental evidence in pheo-catalyzed decomposition of
hydrogen gas

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Figure 8. Battery discharge cases with pheo-catalyzed and reference
(without pheo) negative electrodes.

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The 1st-principle quantum mechanical simulations following the above steps
demonstrated that such proposed scenario involving pheo derivative
morphologies was energetically favorable.
It is noted, however, that the total energy increase (0.4911 Ha, or 13.36 eV) from
step (b) to step (c) (i.e., with two H’s becoming 2H+’s) has to come from the
battery action and eventually a lowest energy state –the derivative morphology—
can be achieved.
This was only made possible by the “catalytic” presence of both the N atoms in
the new pheo derivative structure.
Otherwise, the minimum price to remove a single electron from a stand-alone H
atom is known to be as large as 13.58 eV.
Pheo-catalyzed chemical batteries (or, fuel cells) are promising for room-
temperature operation.
What’s significant?

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0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
H2molenumberinthecontainer(mmol)
Time(Hr)
Hydrogen gas adsorption experiments
paper
paper with P
paper with P200
Reference Group_P Group_P200
H2 mole number after 55-min
electrolysis (mmol)
5.25392 5.05739 4.8768
H2 mole number after 24 hr. 5.23208 3.93935 3.7819
Adsorbed hydrogen amount
(mmol)
0.02184 1.11804
(22.11%)
1.0949
(22.45%)
Further related evidence: hydrogen adsorption by pheo
Though invisible for
the real situation,
this extra info
may serve as an
indirect evidence.

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• Summary and conclusions
It was conjectured that a derivative form of pheophytin had existed all along
which may provide the internal proton conductive path to account for the
observed NMR spectral features.
Then, such derivative form was suspected to facilitate its role as a general
catalyst, particularly to hydrogen gas decomposition.
Results from spectral analyses, quantum simulations, and chemical battery
experiments all pointed to the viability of such a conjecture.
Pheo-catalyzed H2 fuel cell can be a new possibility.
H2 storage in pheo can be a new fuel transport alternative after proper tailoring
of pheo structures.