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Running head: MODULATION OF HYDRIDE TRANSFER REACTIONS
Chemistry paper: Modulating the mechanism of hydride transfer reactions
(Name)
(Course)
(Date)
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MODULATION OF HYDRIDE TRANSFER REACTIONS
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Chemistry paper: Modulating the mechanism of hydride transfer reactions
Relevance of the study
Despite the importance that hydrogen bonds had in the fields of both chemistry and
biology, the exact mechanism of the hydride transfer reactions was not wholly understood. In this
regard, Archipowa et al. (2018) have elucidated the mechanism of the hydride transfer reactions
in biological systems. By following the exact steps involved in the reaction process, the chemists
can now design different experiments oriented to the modulation of the process, which may
result in multiple technological advances such as the manufacturing of more efficient fuel cells.
Methodology
Previous experiments carried out to try to establish the exact mechanism involved in the
hydride transfer during redox reactions failed as a result of the impossibility to detect the
theoretically formed intermediate radicals due to their extremely low lifetime. To overcome this
problem, Archipowa et al. focused on the evaluation of the hydride transfer redox reaction
between NADPH and protochlorophyllide.
Main results
Archipowa et al. (2018) demonstrated the formation of a relatively stable intermediate
radical during the hydride transfer reaction between NADPH and protochorophyllide, catalyzed
by the protochlorophyllide reductase enzyme. The intermediate radical formed during the
reaction process was identified and quantified by fluorescence emission spectroscopy.
The precise identification of this intermediate radical demonstrates that the hydride
transfer reaction is a stepwise process, in which:
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An electron is transferred between NADPH and the C17-C18 double bond, activating
protochlorophyllide by creating an anionic radical
MODULATION OF HYDRIDE TRANSFER REACTIONS
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The activated anionic radical created in protochlorophyllide reacts with the labile
hydrogen atom of NADPH, which is added to the C17-C18 double bond
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A second electron transfer reaction takes place between NADPH and the reduced
protochlorophyllide, resulting in the formation of NADP+ and anionic reduced
chlorophyllide.
Future research plans
The methodology developed by Archipowa et al. (2018) can be adapted to evaluating
other hydride transfer reaction mechanisms. In this regard, it is of utmost importance if the same
3-steps stepwise hydride transfer reaction mechanism is presented in different faster reaction
systems to evaluate its generalizability. If this mechanism is confirmed in other hydride transfer
reaction processes, the chemists now have the necessary starting point to design highly efficient
fuel cells through, e.g., the modulation of the reaction process by the introduction of different
functional groups that either stabilize or destabilize the radical intermediate formed during the
reaction process.
MODULATION OF HYDRIDE TRANSFER REACTIONS
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Work cited
Archipowa, N., Kutta, R. J., Heyes, D. J., & Scrutton, N. S. (2018). Stepwise Hydride Transfer in
a Biological System: Insights into the Reaction Mechanism of the Light-Dependent
Protochlorophyllide Oxidoreductase. Angewandte Chemie International Edition, 57, In
press. doi:10.1002/anie.201712729. Retrieved February 23, 2018, from
http://onlinelibrary.wiley.com/doi/10.1002/anie.201712729/epdf
Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201712729
German Edition:
DOI: 10.1002/ange.201712729
Hydride Transfer
Stepwise Hydride Transfer in a Biological System: Insights into the
Reaction Mechanism of the Light-Dependent Protochlorophyllide
Oxidoreductase
Nataliya Archipowa+, Roger J. Kutta+,* Derren J. Heyes, and Nigel S. Scrutton*
Abstract: Hydride transfer plays a crucial role in a wide range
of biological systems. However, its mode of action (concerted
or stepwise) is still under debate. Light-dependent NADPH:
protochlorophyllide oxidoreductase (POR) catalyzes the stereospecific trans addition of a hydride anion and a proton
across the C17C18 double bond of protochlorophyllide. Timeresolved absorption and emission spectroscopy were used to
investigate the hydride transfer mechanism in POR. Apart
from excited states of protochlorophyllide, three discrete
intermediates were resolved, consistent with a stepwise mechanism that involves an initial electron transfer from NADPH.
A subsequent proton-coupled electron transfer followed by
a proton transfer yield distinct different intermediates for wild
type and the C226S variant, that is, initial hydride attaches to
either C17 or C18, but ends in the same chlorophyllide
stereoisomer. This work provides the first evidence of a stepwise
hydride transfer in a biological system.
Hydride transfers (H T) play a crucial role in a wide range
of biological and chemical systems. Over 400 enzymecatalyzed HT reactions depend on the cofactor nicotinamide
adenine dinucleotide (phosphate), NAD(P)H, which acts as
a source of two electrons and one proton (equivalent to
a hydride ion).[1] Therefore, reaction with a substrate results in
the oxidized form, NAD(P)+, and the reduced substrate.[2] In
theory, HT consists of three elementary steps as shown in
Scheme 1.[1, 3] Depending on the rate constants involving the
necessary electron transfer (eT) and proton transfer (PT)
[*] N. Archipowa,[+] Dr. R. J. Kutta,[+] Dr. D. J. Heyes,
Prof. Dr. N. S. Scrutton
Manchester Institute of Biotechnology and School of Chemist...