Schmidt-Rohr examines why plants need two different photosystems

In a recent paper in Life (Basel), Klaus Schmidt-Rohr, Professor of Chemistry, introduces a self-explanatory description of the energetics of photosynthesis in plants, the so-called EZ-scheme. It shows the energies of molecules in kJ/mol instead of the classical Z-scheme’s shifted energy differences that are misleadingly encrypted in volts. Unlike its predecessor, the EZ-scheme includes the Kok cycle in the water-splitting complex, charge separation after photon absorption, and the Calvin cycle with carbohydrate synthesis (in a simplified form). It also shows O2 correctly as a high-energy product, due to its relatively weak double bond, and demonstrates that Photosystem II pumps more of the absorbed photon energy into O2 than into the plant.

This paper provides the first valid explanation of why plants need two different photosystems: PSII mostly extracts hydrogen (as protons plus electrons) from H2O, producing PQH2 (plastoquinol), and generates the energetically expensive product O2, providing little energy directly to the plant. PSI is needed to produce significant chemical energy for the organism, in the form of ATP, and to generate a less reluctant hydrogen donor, NADPH. This work fundamentally revises received notions of the energetics of photosynthesis, by pointing out the classical Z-scheme’s bewildering implication that H2O gives off electrons spontaneously to chlorophyll while releasing energy, and by showing that the concept of energy transport by “high-energy electrons” in photosynthesis is misguided, since energy and electrons flow in opposite directions.

Figure #1 from Schmidt-Rohr paper

Figure 1 Simplified EZ-scheme of the energetics of photosynthesis in plants, converting H2O and CO2 to O2 and carbohydrate, [CH2O]. The direction of energy transfer and release is indicated by straight red arrows at the top, formal hydrogen transfer by blue dashed curved arrows at the bottom of the diagram. Three dots … indicate omitted redox reactions.

Schmidt-Rohr K. O2 and Other High-Energy Molecules in Photosynthesis: Why Plants Need Two Photosystems. Life (Basel). 2021 Nov 5;11(11):1191.

Han paper describes electrochemical switching of arylazopyrazole & heat release

Research image from paperMihael Gerkman and Prof. Grace Han in the Department of Chemistry report the first demonstration of redox-induced energy release from molecular solar thermal (MOST) compounds in condensed phases, in collaboration with a team of Prof. Matthew Fuchter at Imperial College London. MOST compounds that utilize light-induced chemical isomerization for harnessing solar photon energy have emerged as an alternative to photovoltaics and artificial photosynthesis, enabling a closed-system solar photon energy storage and controlled release. Despite the discovery of various photoswitch systems that show improved photon energy storage efficiencies, the efficient and complete energy release from such photoswitches has remained a major challenge.

This work describes electrochemically-induced switching of arylazopyrazole-based photoswitches. The switching itself is electrocatalytic, requiring only a substoichiometric amount of charge, and its efficiency is improved by over an order of magnitude in the condensed phase compared to in solution. Moreover, electrochemically-induced switching affords a significantly higher completeness of switching than what could be achieved photochemically, which addresses the critical limitation of various azoheteroarene-based MOST materials. We envision that this work will promote exploration of the use of an electrical trigger for MOST material applications for a wide variety of photoswitches.

Jake L. Greenfield‡, Mihael A. Gerkman‡, Rosina S. L. Gibson, Grace G. D. Han*, and Matthew J. Fuchter* J. Am. Chem. Soc. 2021, 143, 37, 15250–15257. (‡ equal contributions) Publication Date: September 14, 2021.

Brandeis Receives Grant to Further Collaboration with Hampton University

Irving EpsteinIn collaboration with Hampton University, an historically Black institution in Hampton, VA, Brandeis has received a $250,000 grant from the Alfred P. Sloan Foundation’s Equity-Minded Pathways to STEM Graduate Education program to create a route for Hampton students to enroll in masters degree programs at Brandeis. The program will comprise summer research internships at Brandeis for Hampton juniors and a senior-year course at Hampton jointly developed and taught by Brandeis and Hampton faculty, as well as cohort-based mentoring during the students’ masters study.  It extends the existing Brandeis-Hampton collaboration associated with our Materials Research Science and Engineering Center (MRSEC) and will be led by Profs. Irving Epstein at Brandeis and Demetris Geddis at Hampton.

Grace Han Receives Young Investigator Award

Grace HanGrace Han, Landsman Assistant Professor of Chemistry, has received a Young Investigator Research Program award from the Air Force Office of Scientific Research (AFOSR). The award will support her research on the optically-controlled catalyst recycling for 3 years.

Catalysis is one of the core processes in chemical industry and essential for achieving many products critical to the Department of Defense’s mission – from medicines to counter threats, to radiation-resistant polymeric coatings, and advanced fuels for aircraft. Catalysts are the key components that serve to improve reaction rates and product yields, and these costly compounds are generally disposed after one use. Various concepts for catalyst recycling, particularly using fluorous biphasic systems, have been developed to achieve cost-effective and sustainable synthetic procedures. However, the heating and cooling steps employed in the recycling process are only compatible with a limited scope of reactions and solvents.

To address this challenge, the Han group is developing a new class of biphasic catalysts that are optically activated, or precipitated, at a constant temperature by the incorporation of a photoswitch unit in the catalyst structure. Photoswitches are novel organic molecules that respond to light by changing their shape and physical properties including polarity. The significant shape and polarity change of the photoswitch unit will drastically change the solubility of catalysts in an organic solvent, which regulates the activity and recovery of catalysts. This new method of catalyst recycling is anticipated to reduce the costs as well as environmental impact of the conventional use of catalysts in various industries.

Chemistry alum receives the Volvo Environmental Prize 2021

Photo: Yale School of Public Health

Paul Anastas, MA’87, PhD’90, aka the “Father of Green Chemistry,” has received the Volvo Environmental Prize for 2021. This award is given annually to those who have made “outstanding innovations or scientific discoveries, which in broad terms fall within the environmental field.” In Volvo’s press release, the prize jury stated that the research of Paul Anastas “is revolutionizing the chemical industry, a key contribution to meeting the sustainability challenge”.

Over the course of his career, Anastas has worked as a staff chemist at the Environmental Protection Agency, served as an advisor in the Obama White House and co-authored the book 12 Principles of Green Chemistry This book is used by high school, college and graduate students around the world. He is currently the director of Yale University’s Center for Green Chemistry and Green Engineering.

He received the 2012 Alumni Achievement Award from Brandeis.

Anastas did his graduate work in synthetic organic chemistry in the lab of the late Robert Stevenson, Professor Emeritus. He earned his B.S. in chemistry from the University of Massachusetts Boston and his M.A. and Ph.D. in chemistry from Brandeis University.

Gieseking Receives NSF CAREER Award

Figure from Rebecca GiesekingRebecca Gieseking, Assistant Professor of Chemistry, has received an NSF CAREER award from the Chemical Theory, Models and Computational Methods program. This award will enable her research group to develop computational models that provide chemical understanding of how light interacts with metal nanoclusters.

Harnessing solar energy is crucial to reduce humanity’s dependence on fossil fuels and alleviate the environmental impact of our ever-increasing demand for energy. Noble metal nanoclusters containing tens to hundreds of metal atoms have the potential to revolutionize solar energy technologies by harnessing light to produce chemical fuels. These nanoclusters strongly absorb light because they support plasmons, which are collective oscillations of the electrons. Understanding, controlling, and manipulating the plasmon properties is key to improving the efficiency of solar energy storage.

Rebecca has shown that efficient computational models can accurately model the light absorption of metal nanocluster, and her group is now extending these models to understand the decay processes after metal nanoclusters absorb light. They are using these models to understand how these decay processes change as a function of nanocluster size, shape, and composition to design metal nanoclusters with controllable decay time scales for efficient solar energy storage.

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