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.

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.

Turrigiano lab uncovers sources of neuronal heterogeneity

High activity neurons have greater instrinsic excitability and response to local inputs, but no difference in total input type or amount

Mammalian cortex has long been one of the most widely studied systems in neuroscience, dating back to the pioneering work of Santiago Ramon y Cajal in the late 19th century. The cortex is much larger in primates than other mammals, and is thought to be responsible for the advanced cognitive abilities of humans. Today, models of cortical connections and computations form the basis for some of the most powerful deep learning paradigms. However, despite this success, there is still much that is unknown about how cortex functions. One feature of cortex that has recently been discovered is that neurons that appear to be similar to each other can have very different baseline activity levels: some neurons are 100x more active than their neighbors. We don’t know how neurons that are otherwise highly similar in shape and genetic makeup can maintain such different activity levels, or if the neurons with high and low activity levels have different functions in the brain. These neurons are otherwise so similar to each other that it is difficult to tell them apart without recording their activity directly, and current techniques for recording the activity of many neurons simultaneously in live animals do not allow us to later re-identify them for further study.

In a paper recently published in Neuron, the Turrigiano lab, led by postdoctoral researcher Nick Trojanowski, reported a new approach for permanently labeling high and low activity neurons in live animals, and then determining what makes them different. To do this they used a fluorescent protein called CaMPARI2 that changes from green to red as activity increases, but only when exposed to UV light. By shining UV light into the brain, they caused neurons with high activity to turn red, while neurons with low activity remained green. This procedure allowed them to run a series of tests on high and low activity neurons to identify differences between them. They found that high activity neurons would intrinsically generate more activity than low activity neurons when presented with the same stimulus. These high activity neurons also receive more excitatory input specifically from nearby neurons of the same type. Surprisingly, however, they found that the total amount of excitatory and inhibitory input that high and low activity neurons received from other neurons was not a major factor in determining their activity levels. Together, these results tell us that the differences in activity between neurons are due to intrinsic differences, as well as their pattern of connectivity to their nearby partners. This has deep implications for how the networks that underlie cortical computations are built and maintained.

With these tools in hand, it is now possible to further explore the differences between high and low activity neurons. Do these neurons serve different functions? Are the baseline activity levels specified from birth? How do these activity levels affect the mechanisms of plasticity that are responsible for learning and memory? The recently published results represent just the tip of the iceberg of information that can be learned with this new technique, in the mammalian cortex as well as other brain regions.

Learning from how viruses assemble

Capsid image from paper

credit: eLife

Michael Hagan, Professor of Physics, is quoted extensively in the Chemical & Engineering News article, Lessons learned from watching viruses assemble. The paper discusses how scientists are studying the ability for viruses to self-assemble. During a viral infection, infected cells manufacture the genetic material and other components of the virus. These components then self-assemble, or build themselves into complex shapes, to form new viruses capable of infecting additional cells.

Many viruses contain their genetic material within a protective shell known as a capsid. Michael Hagan is one of the scientists studying how these capsids are formed by modeling the conditions and chemical properties that allow viruses to build themselves. Once understood, researchers hope this will help in drug design and delivery.

Article: Lessons learned from watching viruses assemble, Laura Howes, Chemical & Engineering News-C&EN,  December 15, 2020.

Grace Han named Landsman Career Development Chair in the Sciences

Grace Han, Assistant Professor of Chemistry, has been appointed the Landsman Career Development Chair in the Sciences. Lisa Lynch, Provost and Dorothy Hodgson, Dean of Arts and Sciences, noted that Han’s work as a “scholar, a teacher, and an advisor, makes [her] highly deserving of the Landsman Chair.”

Grace directs the Han Group at Brandeis. This lab, whose scientific inquiry focuses on light-matter interaction in various material systems that range from photo-switching molecules to inorganic 2D crystals.  Her team seeks to develop optically-controlled molecular switches for energy conversation and storage and optoelectronic applications.

Grace’s research has resulted in a project, “Optically-Controlled Functional Heat Storage Materials,” which was featured in Chemical and Engineering News upon being granted Brandeis SPROUT Awards in 2019 and again in 2020.  In this work, the Han Group developed materials that recycle waste heat from a running engine and warm up frozen oil upon triggering to facilitate car startups in northern climes.  The Han Group is currently developing the initial prototype for the device containing the functional energy material.

At Brandeis, Grace teaches “Inorganic Chemistry,” “Polymer and Inorganic Materials Chemistry,” and “Chemistry Colloquium.”  She is co-chair of the Graduate Student Admissions Committee and of the Departmental Colloquium Committee and is also a member of the Graduate Studies Committee. Grace has most recently co-authored articles for the Journal of the American Chemical Society, Chemistry of Materials, and ACS Nano.

The Landsman Chair was established in 2015 through a gift from Dr. Emanuel Landsman. The Landsman Chair reflects his deep commitment to nurturing rising young scientists.

Longtime supporters of the University, Manny and his wife, Sheila Landsman, also gifted the funds used to build the Landsman Research Facility. This is the structure that houses an 800 MHz magnetic resonance spectrometer. The 15,000-pound superconducting magnet is used by scientists to search for solutions to neurodegenerative diseases and cancer.  Dr. Landsman co-founded the American Power Conversion Corporation, served on the Brandeis University Science Advisory Council for many years, and was named a Brandeis Fellow in 2008.  The Landsmans’ grandson, Wiley Krishnaswamy, is a member of the Class of 2020.

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