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1. Cyanobacteria from marine oxygen-deficient zones encode both form I and form II Rubiscos

   https://doi.org/10.1073/pnas.2418345121  

   Jaffe, Alexander L; Harrison, Kaitlin; Wang, Renée Z; Taylor-Kearney, Leah J; Jain, Navami; Prywes, Noam; Shih, Patrick M; Young, Jodi; Rocap, Gabrielle; Dekas, Anne E (November 2024, Proceedings of the National Academy of Sciences)

   Cyanobacteria are highly abundant in the marine photic zone and primary drivers of the conversion of inorganic carbon into biomass. To date, all studied cyanobacterial lineages encode carbon fixation machinery relying upon form I Rubiscos within a CO₂-concentrating carboxysome. Here, we report that the uncultivated anoxic marine zone (AMZ) IB lineage of Prochlorococcus from pelagic oxygen-deficient zones (ODZs) harbors both form I and form II Rubiscos, the latter of which are typically noncarboxysomal and possess biochemical properties tuned toward low-oxygen environments. We demonstrate that these cyanobacterial form II enzymes are functional in vitro and were likely acquired from proteobacteria. Metagenomic analysis reveals that AMZ IB are essentially restricted to ODZs in the Eastern Pacific, suggesting that form II acquisition may confer an advantage under low-O₂conditions. AMZ IB populations express both forms of Rubisco in situ, with the highest form II expression at depths where oxygen and light are low, possibly as a mechanism to increase the efficiency of photoautotrophy under energy limitation. Our findings expand the diversity of carbon fixation configurations in the microbial world and may have implications for carbon sequestration in natural and engineered systems. 

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2. Synthesis of Ln ^II ‐in‐Cryptand Complexes by Chemical Reduction of Ln ^III ‐in‐Cryptand Precursors: Isolation of a Nd ^II ‐in‐Cryptand Complex

   https://doi.org/10.1002/anie.202006393  

   Huh, Daniel N.; Ciccone, Sierra R.; Bekoe, Samuel; Roy, Saswata; Ziller, Joseph W.; Furche, Filipp; Evans, William J. (June 2020, Angewandte Chemie International Edition)

   Abstract Lanthanide triflates have been used to incorporate Nd^IIIand Sm^IIIions into the 2.2.2‐cryptand ligand (crypt) to explore their reductive chemistry. The Ln(OTf)₃complexes (Ln=Nd, Sm; OTf=SO₃CF₃) react with crypt in THF to form the THF‐soluble complexes [Ln^III(crypt)(OTf)₂][OTf] with two triflates bound to the metal encapsulated in the crypt. Reduction of these Ln^III‐in‐crypt complexes using KC₈in THF forms the neutral Ln^II‐in‐crypt triflate complexes [Ln^II(crypt)(OTf)₂]. DFT calculations on [Nd^II(crypt)]²⁺], the first Nd^IIcryptand complex, assign a 4f⁴electron configuration to this ion. 

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3. Electrochemical Preparation of Sm(II) Reagent Facilitated by Weakly Coordinating Anions

   https://doi.org/10.1002/chem.202301045  

   Ware, Skyler_D; Zhang, Wendy; Charboneau, David_J; Klein, Channing_K; Reisman, Sarah_E; See, Kimberly_A (July 2023, Chemistry – A European Journal)

   Abstract Samarium diiodide (SmI₂) is widely used as a strong one‐electron reducing agent and is often employed to form C−C bonds in complex systems. Despite their utility, SmI₂and related salts suffer from several drawbacks that render the use of Sm reducing agents in large‐scale synthesis impractical. Here, we report factors influencing the electrochemical reduction of Sm(III) to Sm(II), towards the goal of electrocatalytic Sm(III) reduction. We probe the effect of supporting electrolyte, electrode material, and Sm precursor on Sm(II)/(III) redox and on the reducing power of the Sm species. We find that the coordination strength of the counteranion of the Sm salt affects the reversibility and redox potential of the Sm(II)/(III) couple and establish that the counteranion primarily determines the reducibility of Sm(III). Electrochemically generated SmI₂performs similarly to commercial SmI₂solutions in a proof‐of‐concept reaction. The results will provide fundamental insight to facilitate the development of Sm‐electrocatalytic reactions. 

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4. Diverse Coordination Geometries Derived from Trisaminocyclohexane Ligands with Appended Outer‐Sphere Hydrogen Bond Donors

   https://doi.org/10.1002/ejic.202300434  

   Ekanayake, Danushka_M; Sheridan, Patrick_E; Lindeman, Sergey_V; Fiedler, Adam_T (September 2023, European Journal of Inorganic Chemistry)

   Abstract With the aim of constructing hydrogen‐bonding networks in synthetic complexes, two new ligands derived fromcis,cis‐1,3,5‐triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer‐sphere H‐bond donors. The TACH framework offers a facial arrangement of threeN‐donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X‐ray structural characterization of a series of Cu^I‐X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H₃L^R, R=pyrrole or indole) coordinate in the intended facialN₃manner, yielding four‐coordinate complexes with idealizedC₃symmetry. The N−H units of the outer‐sphere heterocycles form a hydrogen‐bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H₃L^pyrroleand H₃L^indolewith divalent transition metal chlorides (M^IICl₂, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer‐sphere H‐bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH‐based ligands with pendant H‐bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H‐bonding interactions. 

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5. Influence of the Anions and Oxalic Acid on the Electrochemical Reduction of Cr(VI) on Au and Magnetite Surfaces

   https://doi.org/10.1149/1945-7111/ae15c1  

   Tsui, Lok-Kun; Benavidez, Angelica; Garzon, Fernando; Cerrato, José_M (October 2025, Journal of The Electrochemical Society)

   Hexavalent chromium, Cr(VI), is a highly toxic carcinogen occurring in natural and industrial environments. Pathways to economical reduction to the more benign trivalent form, Cr(III), are necessary for treatment of contaminated groundwater. Magnetite’s (Fe₃O₄) mixture of Fe(II) and Fe(III) make it a promising material for remediation. This study investigated the mechanisms for reduction of Cr(VI) catalyzed by Fe₃O₄as a redox mediator in the presence of oxalic acid in HClO₄and SO₄²⁻solutions, a system where the interactions among these species are not fully understood. The reduction of Cr(VI) in different anion environments is first measured on an Au rotating disk electrode. SO₄²⁻inhibits the formation of a passivation layer and Cl^-partially inhibits passivation. The reduction of Cr(VI) on Fe₃O₄is limited by the availability of Fe(II) surface sites. Addition of oxalic acid works synergistically through liberation of Fe(II)-oxalate and soluble Cr(III)-oxalate products. A combination of Fe₃O₄activated by exposure to oxalic acid and use of an oxalic acid solution as a medium for reduction of Cr(VI) produces over 97% removal of Cr(VI). These results provide relevant insights regarding interactions of Fe₃O₄with organic acids and the anion environment which lead to the effective reduction of Cr(VI). 

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