College of Chemistry

Proton transfer at electrochemical interfaces is fundamentally important across science and technology, yet kinetic measurements of this elementary step at electrode|electrolyte interfaces are convoluted with other electron-transfer steps and by inhomogeneous electrode surfaces. We use facilitated proton transfer at the interface between two immiscible electrolyte solutions (ITIES) as a platform to study proton-transfer kinetics in the absence of interfacial electron transfer and without the defects at solid|electrolyte interfaces. Diffusion-controlled micropipette voltammetry revealed that 2,6-diphenylpyridine (DPP) facilitates proton transfer across the HCl(aq)|trifluorotoluene interface, while voltammetry at nanopipette-supported interfaces yielded activation-controlled ion-transfer currents. We extract kinetic parameters k_app⁰ and α_app, 3.0 ± 1.8 cm/s and 0.3 ± 0.2, respectively, for DPP-facilitated proton transfer by fitting quasi-reversible voltammograms to a mixed diffusive-kinetic model. Finite-element simulations highlighted regimes of direct proton transfer and sequential proton transfer, where the current divided between these two possible pathways was shown to favor direct proton transfer when the neutral partitioning step DPP(org) → DPP(aq) was rate-determining. Atomistic molecular-dynamics simulations were used to compute the free energy change to move DPP and its protonated analogue within, and across, the liquid|liquid interface. The most-likely location for proton transfer is predicted to be in the surface region where significant interpenetration of the two liquids occurs. Understanding the kinetics of ion transfer at the ITIES illustrated here is important in the development of general theories of ion transfer in electrochemical science and technology.

The efficacy of electrochemical systems is governed by the cation transference number, which represents the fraction of current carried by the working ion. Energy is wasted when field-induced motion also drives anions and solvent molecules, decreasing the transference number to near-zero. We present a systematic study of cation transference in a series of electrolytes: tetraglyme (TG), octaglyme (OG), and poly(ethylene oxide) (PEO) mixed with lithium bis(trifluoromethanesulfonyl)imide. In all three electrolytes, starting from the dilute salt concentration limit, the experimentally measured cation transference number decreases with increasing concentration, reaching a minimum between -0.1 and -0.2, before rising back to positive values. Explicit measurements of field-induced species' velocities by electrophoretic nuclear magnetic resonance indicate that negative cation transference numbers in TG and OG electrolytes are dictated by solvation interactions with minimal contribution from anion-cation interactions. Simulation-based solvation structures indicate that OG serves as a bridge between TG and PEO. Multi-charge positive clusters, which are negligible in TG, become increasingly important at higher chain lengths (OG and PEO). As migrating cations drag their solvation shells, this solvation-induced motion is amplified in glyme electrolytes because of covalent interactions between solvating glyme molecules and free glyme molecules.

Streptomyces tsukubaensis NRRL 18488, the primary producer of the immunosuppressant FK506, was analyzed to elucidate regulatory features of secondary metabolism. Completion of its 7.9-Mb linear genome enabled accurate re-annotation of the FK506 biosynthetic gene cluster (BGC). Transcriptome analysis during BGC activation revealed major transcriptional shifts from primary to secondary metabolism, especially in genes involved in FK506 biosynthesis and lysine metabolism. Primary transcriptome mapping identified 1,225 transcription units and uncovered post-transcriptional regulation of allylmalonyl-CoA production, a key FK506 precursor. Ribosome profiling demonstrated that AT-rich codons reduce translational efficiency in S. tsukubaensis, with pronounced ribosome pausing at the TTA codon within the FK506 BGC. Substituting this codon relieved pausing and improved FK506 production. Together, these integrative genomic, transcriptomic, and translatomic analyses highlight how multi-level regulatory mechanisms shape secondary metabolism in Streptomyces. This work offers insights into metabolic control that could inform future efforts in strain improvement for efficient natural products production.

This work presents a computational screening approach to identify Li-rich transition-metal oxide sacrificial cathode additives and provides experimental validation of antifluorite-structured Li6MnO4 as a potential candidate. Initial attempts to synthesize this compound result in low purity (≤40% by weight) owing to close thermodynamic competition with Li2O and MnO at low temperature. However, it is shown that a much higher purity of 85% by weight can be achieved by combining Li excess with rapid cooling from high temperature, which effectively stabilizes the Li6MnO4 phase. The synthesized product delivers a high irreversible Li release capacity that exceeds 700 mAh g⁻¹ by utilizing combined Mn oxidation (Mn^2+/3+ and Mn^3+/4+) and O oxidation. These results demonstrate that Li6MnO4 may therefore be useful as a potential sacrificial cathode additive in Li-ion batteries and motivate further investigation of other structurally-related compounds. While attempts were made to synthesize two additional compounds among computationally screened candidates, it was not successful to experimentally realize the two candidates. The difficulty of experimental realization of the newly predicted materials remains a challenge and it is suggested that more efforts need to be devoted to developing computational techniques to precisely predict synthesizability and propose potential synthetic routes of the predicted materials.

Cu-based oxides and hydroxides represent an important class of materials from a catalytic and corrosion perspective. In this study, we investigate the formation of bulk and surface Cu³⁺ species that are stable under water oxidation catalysis in alkaline media. So far, no direct evidence existed for the presence of hydroxides (CuOOH) or oxides, which were primarily proposed by theory. This work directly places CuOOH in the oxygen evolution reaction (OER) Pourbaix stability region with a calculated free energy of -208.68 kJ/mol, necessitating a revision of known Cu-H₂O phase diagrams. We also predict that the active sites of CuOOH for the OER are consistent with a bridge O* site between the two Cu³⁺ atoms with onset at ≥1.6 V vs the reversible hydrogen electrode (RHE), aligning with experimentally observed Cu^2+/3+ oxidation waves in cyclic voltammetry of Fe-free and Fe-spiked copper in alkaline media. Trace amounts of Fe (2 μg/mL (ppm) to 5 μg/mL) in the solution measurably enhance the catalytic activity of the OER, likely due to the adsorption of Fe species that serve as the active sites . Importantly, modulation excitation X-ray absorption spectroscopy (ME-XAS) of a Cu thin-film electrode shows a distinct Cu³⁺ fingerprint under OER conditions at 1.8 V vs RHE. Additionally, in situ Raman spectroscopy of polycrystalline Cu in 0.1 mol/L (M) KOH revealed features consistent with those calculated for CuOOH in addition to CuO. Overall, this work provides direct evidence of bulk electrochemical Cu³⁺ species under OER conditions and expands our longstanding understanding of the oxidation mechanism and catalytic activity of copper.

Anion-exchange-membrane water electrolyzers (AEMWEs) are a possible low-capital-expense, efficient, and scalable hydrogen-production technology with inexpensive hardware, earth-abundant catalysts, and pure water. However, pure-water-fed AEMWEs remain at an early stage of development and suffer from inferior performance compared with proton-exchange-membrane water electrolyzers (PEMWEs). One challenge is to develop effective non-platinum-group-metal (non-PGM) anode catalysts and electrodes in pure-water-fed AEMWEs. We show how LaNiO₃-based perovskite oxides can be tuned by cosubstitution on both A- and B-sites to simultaneously maintain high metallic electrical conductivity along with a degree of surface reconstruction to expose a stable Co-based active catalyst. The optimized perovskite, Sr_0.1La_0.9Co_0.5Ni_0.5O₃, yielded pure-water AEMWEs operating at 1.97 V at 2.0 A cm^-2 at 70 °C with a pure-water feed, thus illustrating the utility of the catalyst design principles.

Lithium (Li)-excess transition metal oxide materials which crystallize in the cation-disordered rock salt (DRX) structure are promising cathodes for realizing low-cost, high-energy-density Li batteries. However, the state-of-the-art electrolytes for Li-ion batteries cannot meet the high-voltage stability requirement for high-voltage DRX cathodes, thus new electrolytes are urgently demanded. It has been reported that the solvation structures and properties of the electrolytes critically influence the performance and stability of the batteries. In this study, the structure-property relationships of various electrolytes with different solvent-to-diluent ratios are systematically investigated through a combination of theoretical calculations and experimental tests and analyses. This approach guides the development of electrolytes with unique solvation structures and characteristics, exhibiting high voltage stability, and enhancing the formation of stable electrode/electrolyte interphases. These electrolytes enable the realization of Li||Li_1.094Mn_0.676Ti_0.228O₂ (LMTO) DRX cells with improved performance compared to the conventional electrolyte. Specifically, Li||LMTO cells with the optimized advanced controlled-solvation electrolyte deliver higher specific capacity and longer cycle life compared to cells with the conventional electrolyte. Additionally, the investigation into the structure-property relationship provides a foundational basis for designing advanced electrolytes, which are crucial for the stable cycling of emerging high-voltage cathodes.

Topochemical polymerization (TCP) represents an essential route to create regio- and stereoregular polymers through solid-state transformations. Herein, we present an innovative strategy for controlling topochemical polymerization pathways by tailoring the terminal group aromaticity in the para-azaquinodimethane (AQM) ring system. Substituting phenyl groups with less aromatic furyl units extends significant spin density delocalization across the conjugated core upon thermal activation, inducing significant diradicaloid characters at furyl positions and enabling unconventional reactivities in both solution and solid states. Thermal treatment in toluene yields a unique cyclophane dimer formed via furyl-methine C-C coupling, confirmed by X-ray crystallography, while solid-state reactions produce polymers formed via both intercolumnar furyl-methine coupling and intracolumnar methine-methine coupling. The spin-center-directed mechanism underlying these transformations is validated through theoretical modeling and isotopic labeling experiments. This study highlights the prowess of aromaticity modulation in functional pro-aromatic systems, which enables the synthesis of polymers with main chain structures that are otherwise difficult to access.

Amphiphilic copolypeptoids are known to form a variety of nanostructures (fibers, tubes, sheets, etc.), but the assembly mechanisms and key intermediates remain underexplored. This study investigates the intermediate structures formed during the early stages of self-assembly in diblock copolypeptoids using cryo-transmission electron microscopy (cryo-TEM). We focused on two diblock copolypeptoids, one with a free N-terminus and the other with a capped N-terminus, which ultimately form less-ordered nanofibers and well-ordered nanosheets, respectively. Through cryo-TEM imaging of vitrified solutions at various time points during the self-assembly process, the study identified micelles and vesicles as key intermediate structures. Notably, the formation of vesicles as intermediates is unusual in crystallization-driven self-assembly and suggests a unique pathway in polypeptoid self-assembly. The study provides direct imaging evidence of key intermediates in polypeptoid self-assembly, advancing the understanding of their self-assembly mechanisms.