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A spectroscopic mimic of the oxygen evolving complex

February 27, 2020

The oxygen evolving complex (OEC) of photosystem II catalyzes the oxidation of water to form molecular oxygen. The S₃-state is currently the last observable intermediate prior to O–O bond formation. Its electronic structure has been assigned to a homovalent Mn(IV)₄ core with an S = 3 ground state. In a recent publication (Lee, Marchiori, et al. JACS), the Agapie (Caltech) and Britt labs synthesized and characterized via XAS and multifrequency EPR spectroscopy a Mn(IV)₄O₄ cuboidal complex.

EPR spectroscopy of iron- and nickel-doped [ZnAl]-layered double hydroxides: modeling active sites in heterogeneous water oxidation catalysts

January 14, 2020

In a new JACS article (https://pubs.acs.org/doi/10.1021/jacs.9b10273) describing a collaboration between the Britt and Gray (Caltech) labs, Sayler et al. describe a set of model materials that facilitate the understanding of individual active sites in the highly active heterogeneous water oxidation catalyst, [NiFe] LDH.  Heterogeneous catalysts often have a high magnetic density of active sites, complicating the interpretation of EPR spectroscopic data.

Thermoelectric composite with improved mechanical and transport properties

January 14, 2020
Synthesis of the composite of the high performance Yb₁₄MgSb₁₁ thermoelectric phase with iron to improve mechanical and transport properties

Thermoelectric materials have been used to provide electricity to spacecraft for decades. In this work the Kauzlarich lab (Perez, et al., ACS Appl. Energy Mater., 2020) in collaboration with Thermal Energy Conversion Research and Advancement Group at NASA-JPL have shown that Yb₁₄MgSb₁₁, one of the candidates for NASA’s next generation of thermoelectric materials, can be composited with iron without reaction upon thermal cycling.

The biosynthetic origins of [FeFe] hydrogenase active site unraveled

January 04, 2020

Hydrogenases are nature’s machines to metabolize H₂. The [FeFe] hydrogenase subtype catalyzes the rapid turnover at its six-iron active site cofactor, the H-cluster, which contains CO, cyanide and a unique azadithiolate (adt) ligand essential for catalysis. In a recent publication (Rao and coworkers, Chemical Science, 2019) the Britt lab identified the biosynthetic precursor of the adt ligand.

Discovery of metastability in the active phase of perovskite solar cells

November 01, 2019

Cesium lead iodide (CsPbI₃) has long been a promising light absorbing material for perovskite solar cells. Researchers from the Navrotsky lab, in a recently published study (J. Am. Chem. Soc. 2019, 141, 14501) conducted calorimetric studies on cubic(α) and orthorhombic(δ) CsPbI₃ polymorphs, obtaining their enthalpies of formation from binary iodides, and discussing the relative stabilities. Cubic phase CsPbI₃, the desirable phase for light absorbing material, is confirmed to be metastable under ambient conditions.

New insights into hydrogenase active site biosynthesis

October 14, 2019

[FeFe]-hydrogenases catalyze H₂ evolution at extraordinary rates at low overpotential using base metal (not platinum). In the field of renewable energy, the biosynthesis of these enzymes’ active sites, the H-cluster, is of intense interest. Among its many cofactors, the azadithiolate is unique, and its biosynthesis remains enigmatic. Three Fe–S proteins, HydE, HydF, and HydG, are essential for the H-cluster bioassembly. This paper describes an in vitro assembly approach where a synthetic [Fe(cysteine)(CO)₂(CN)] complex, “syn-B,” allows HydG- free biosynthesis of the active enzyme.

A radical enzyme intermediate trapped using non-native substrates

October 01, 2019

In a recent publication "Trapping and Electron Paramagnetic Resonance Characterization of the 5′dAdo• Radical in a Radical S-Adenosyl Methionine Enzyme Reaction with a Non-Native Substrate", Rick Sayler and coworkers in R. David Britt's Lab at UC Davis used non-natural substrates in the HydG radical SAM enzyme to trap and characterize the hot 5'deoxyadenosyl radical for the first time in such an enzyme reaction.

More information at https://pubs.acs.org/doi/10.1021/acscentsci.9b00706

A new Zintl phase for direct thermal to electrical energy conversion

September 27, 2019

Thermoelectric materials have shown promise as a clean energy alternative to fossil fuels that can convert waste heat into electrical power.  The Kauzlarich lab (He et al., Chem. Mater., 2019), in collaboration with Prof. Donadio and NASA-JPL, have been able to elucidate the structural and physical properties of a new material, Yb₂₁Mn₄Sb₁₈, showing large thermoelectric efficiency in the mid-to-high temperature regime.  The favorable properties of Yb₂₁Mn₄Sb₁₈ come intrinsically from its unique crystal structure, highlighted below. 

CO₂ reduction promoted by metal-promoted Mo₆S₈ clusters

September 05, 2019

In a recent publication (Perryman and coworkers, Materials Horizons, 2019) the Velázquez Lab describes for the first time experimental evidence of CO₂ reduction (CO₂R) activity over the compositionally modular Chevrel-Phase chalcogenide framework. In this unique framework, “promotion” of Mo₆S₈ units by a ternary metal species allows for electronic tuning of CO₂R-active sites, and further acts to stabilize anionic domains of key reaction intermediates, thereby providing an avenue toward controllable catalytic selectivity.

A Closer Look at Time Tested Reactions

May 29, 2019

In a recent publication (Zhu, Li, Tsui and coworkers, J. Am. Chem. Soc. 2019, 141, 6247-6253), the Tantillo and Kurth labs reinvestigated the mechanism of the Davis–Beirut reaction and Cadogan cyclization for 2H-indazole synthesis. At last, the elusive 2H-indazole N-oxide has been isolated, characterized, and modelled. This work highlights the amount of mechanistic insights gained when synthetic chemistry is coupled with computational support!

Metals influence C-peptide, a hormone related to insulin

May 20, 2019

A recently accepted publication by Heffern and coworkers in ChemBioChem details how metals like zinc, copper, and chromium affect a peptide hormone known as C-peptide. C-peptide is made during insulin production in the pancreas and may help with sugar transport, kidney disease, and nerve damage in patients with diabetes. Their findings show that copper and chromium stop C-peptide from being taken up by cells but zinc does not.

DMT Microdosing Produces Antidepressant and Anxiolytic Effects

March 04, 2019

In a recent publication (Cameron and coworkers, ACS Chemical Neuroscience, 2019), the Olson Lab demonstrates for the first time that psychedelic microdosing—the practice of administering subhallucinogenic doses on a chronic, intermittent schedule—may reduce depression and ease anxiety.  This work suggests that the hallucinogenic properties of psychedelic compounds like DMT might not be necessary for their therapeutic effects.

Thermodynamics of H₂O and CO₂ Absorption and Guest-induced Phase Transitions in Zeolite RHO

February 09, 2019
Scientific Achievement

The zeolite RHO structure is unusually flexible in response to guest molecule occupancy. Gas absorption calorimetry determined the energetics of H₂O and CO₂ interaction with the framework as a function of loading from near zero coverage to saturation for several cation exchanged zeolite RHO materials. Framework flexibility and an associated “gate opening” phase transition from the dehydrated acentric form to the hydrated centric form during water absorption are clearly detected and quantified. The interactions with CO₂ are weaker than with H₂O.