Nav: Home

Hydrogen transfer: One thing after the other

February 14, 2018

Hydride transfer is an important reaction for chemistry (e.g., fuel cells), as well as biology (e.g., respiratory chain and photosynthesis). Often, one partial reaction involves the transfer of a hydride ion (H(-)). But does this hydride transfer involve one step or several individual steps? In the journal Angewandte Chemie, scientists have now provided the first proof of stepwise hydride transfer in a biological system.

An important step in the biosynthesis of chlorophyll is the light-dependent hydrogenation of protochlorophyllide to chlorophyllide. This involves the reduction of a double bond between carbon atoms 17 and 18 in this complex ring system to a single bond as both carbon atoms bind to an additional hydrogen atom. This step is catalyzed by the enzyme protochlorophyllide oxireductase and requires irradiation with light. Technically speaking, however, this reaction does not add one hydrogen atom to each carbon. Instead, there is first addition of a hydride ion (H(-)) to C17 and then addition of a proton (H(+)) to C18. The first partial reaction, the hydride transfer, requires the cofactor nicotinamide adenine dinucleotide phosphate (NADPH). NADPH serves as a source for two electrons and a proton (H(+)), the equivalent of a hydride anion, H(-).

Hydride transfer reactions play a key role in many biological systems. However, their mechanism is still disputed. Do the three elementary steps--transfer of an electron, a proton, and another electron from NADPH to the substrate--occur simultaneously, or stepwise?

Because of the short lifetime of the intermediates, direct proof of a stepwise mechanism has not previously been possible. Light-dependent reactions--such as the hydrogenation that occurs in the biosynthesis of chlorophyll--that can be triggered by a short laser pulse have solved this problem. By using time-resolved absorption and emission spectroscopy, researchers working with Roger J. Kutta and Nigel S. Scrutton at the University of Manchester (UK) have been able to characterize the mechanism of this hydride transfer.

In addition to excited states of protochlorophyllide, the researchers were able to resolve three discrete intermediates that are consistent with a partially stepwise mechanism: an initial electron transfer from NADPH to protochlorophyllide that has been excited (to the singlet state) by light is followed by the coupled transfer of a proton and an electron. As expected, the final step is transfer of the second proton.

Interestingly, the researchers found different intermediates for the wild type of the enzyme and a mutated version (C226S): While the initial hydride binds to C17 in the wild type, it is transferred to C18 in the mutant version. However, the end result is the same chlorphyllide stereoisomer.

The insights gained from these experiments provide a deeper understanding of how light energy can be used for chemical reactions involving hydrogen transfer, particularly with regard to the design of light-activated catalysts.
About the Author

Nigel Scrutton is a full professor in the School of Chemistry at the University of Manchester and is the Director of the Manchester Institute of Biotechnology (MIB). His main research interests are in the mechanisms and structures of enzymes, with particular reference to redox and cofactor dependent enzyme catalysis. He also has major interests in biological photochemistry, biocatalysis and metabolic engineering. He is a Fellow of the Royal Society of Chemistry and the Royal Society of Biology and has received a number of research awards and prizes over a research career spanning 30 years.


Related Fuel Cells Articles:

Iodide salts stabilise biocatalysts for fuel cells
Contrary to theoretical predictions, oxygen inactivates biocatalysts for energy conversion within a short time, even under a protective film.
Instant hydrogen production for powering fuel cells
Researchers from the Chinese Academy of Sciences, Beijing and Tsinghua University, Beijing investigate real-time, on-demand hydrogen generation for use in fuel cells, which are a quiet and clean form of energy.
Ammonia for fuel cells
Researchers at the University of Delaware have identified ammonia as a source for engineering fuel cells that can provide a cheap and powerful source for fueling cars, trucks and buses with a reduced carbon footprint.
Microorganisms build the best fuel efficient hydrogen cells
With billions of years of practice, nature has created the most energy efficient machines.
Atomically precise models improve understanding of fuel cells
Simulations from researchers in Japan provide new insights into the reactions occurring in solid-oxide fuel cells by using realistic atomic-scale models of the electrode active site based on microscope observations instead of the simplified and idealized atomic structures employed in previous studies.
New core-shell catalyst for ethanol fuel cells
Scientists at Brookhaven Lab and the University of Arkansas have developed a highly efficient catalyst for extracting electrical energy from ethanol, an easy-to-store liquid fuel that can be generated from renewable resources.
The 'Batman' in hydrogen fuel cells
In a study published in Nature on Jan. 31, researchers at the University of Science and Technology of China (USTC) report advances in the development of hydrogen fuel cells that could increase its application in vehicles, especially in extreme temperatures like cold winters.
New catalysts for better fuel cells
Researchers in Korea have fabricated nano-sized catalysts that could improve the performance and production of clean energy fuel cells.
Scientists identify new fuel-delivery route for cells
Scientists at Washington University School of Medicine in St. Louis have identified a previously unknown route for cellular fuel delivery, a finding that could shed light on the process of aging and the chronic diseases that often accompany it.
Argonne scientists maximize the effectiveness of platinum in fuel cells
In new research from the U.S. Department of Energy's Argonne National Laboratory and published in Science, scientists have identified a new catalyst that uses only about a quarter as much platinum as current technology by maximizing the effectiveness of the available platinum.
More Fuel Cells News and Fuel Cells Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

One of the most consistent questions we get at the show is from parents who want to know which episodes are kid-friendly and which aren't. So today, we're releasing a separate feed, Radiolab for Kids. To kick it off, we're rerunning an all-time favorite episode: Space. In the 60's, space exploration was an American obsession. This hour, we chart the path from romance to increasing cynicism. We begin with Ann Druyan, widow of Carl Sagan, with a story about the Voyager expedition, true love, and a golden record that travels through space. And astrophysicist Neil de Grasse Tyson explains the Coepernican Principle, and just how insignificant we are. Support Radiolab today at