College of Chemistry

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.

In vivo genetic diversifiers have previously enabled efficient searches of genetic variant fitness landscapes for continuous directed evolution. However, existing genomic diversification modalities for mammalian genomic loci exclusively rely on deaminases to generate transition mutations within target loci, forfeiting access to most missense mutations. Here, we engineer CRISPR-guided error-prone DNA polymerases (EvolvR) to diversify all four nucleotides within genomic loci in mammalian cells. We demonstrate that EvolvR generates both transition and transversion mutations throughout a mutation window of at least 40 bp and implement EvolvR to evolve previously unreported drug-resistant MAP2K1 variants via substitutions not achievable with deaminases. Moreover, we discover that the nickases mismatch tolerance limits EvolvRs mutation window and substitution biases in a gRNA-specific fashion. To compensate for gRNA-to-gRNA variability in mutagenesis, we maximize the number of gRNA target sequences by incorporating a PAM-flexible nickase into EvolvR. Finally, we find a strong correlation between predicted free energy changes underlying R-loop formation and EvolvRs performance using a given gRNA. The EvolvR system diversifies all four nucleotides to enable the evolution of mammalian cells, while nuclease and gRNA-specific properties underlying nickase fidelity can be engineered to further enhance EvolvRs mutation rates.

Although synthetic biology can produce valuable chemicals in a renewable manner, its progress is still hindered by a lack of predictive capabilities. Media optimization is a critical, and often overlooked, process which is essential to obtain the titers, rates and yields needed for commercial viability. Here, we present a molecule- and host-agnostic active learning process for media optimization that is enabled by a fast and highly repeatable semi-automated pipeline. Its application yielded 60% and 70% increases in titer, and 350% increase in process yield in three different campaigns for flaviolin production in Pseudomonas putida KT2440. Explainable Artificial Intelligence techniques pinpointed that, surprisingly, common salt (NaCl) is the most important component influencing production. The optimal salt concentration is very high, comparable to seawater and close to the limits that P. putida can tolerate. The availability of fast Design-Build-Test-Learn (DBTL) cycles allowed us to show that performance improvements for active learning are rarely monotonous. This work illustrates how machine learning and automation can change the paradigm of current synthetic biology research to make it more effective and informative, and suggests a cost-effective and underexploited strategy to facilitate the high titers, rates and yields essential for commercial viability.

Chemical recycling of commodity and specialty polymers presents a multifaceted challenge for industrial societies. On one hand, macromolecular architectures must be engineered to yield durable products that, on the other hand, rapidly deconstruct to recyclable monomers under pre-determined conditions. Polymer deconstruction is a chemical process that requires deep understanding of molecular reactivity in heterogeneous media, where porous material architectures evolve in both space and time. To build this understanding, we develop herein experimental and analytical methods describing sets of diffusive eigenmodes that exist within time-varying, non-Euclidean boundary conditions, a situation commonly encountered in the reactive deconstruction of polymers where chain fragments splay, alter their local dynamics, and evolve in their confinement of reacting media. Diffusion power spectra, discerned experimentally by NMR, yield polymer and solvent frequency-domain velocity autocorrelation functions that are analyzed in the context of physical models for chemical reactions parameterized with fractal mathematics. The results connect local motion in polymers to chemical reactivity during acidolysis of circular elastomers.

Dry reforming of methane was studied over Ni/Al2O3 catalyst at 600 °C with varying CO2/CH4 ratios (0.2, 0.5, 1, 2, 5). 13CO2 as well as 12CO2 were used along with 12CH4 and resulting carbon was characterized with 13C solid state NMR spectroscopy in order to elucidate the role of CO2 in carbon build up. 13C NMR results revealed that carbon in the deposited coke not only came from CH4, but also from CO2. CO2 saturation coverage is determined by adsorption calorimetry as 0.02 mole/site at 323 K, populated on Al2O3. The critical CO2/CH4 ratio for the onset of carbon growth at atmospheric pressure was determined as 1.8 in good agreement with the literature. The effect of CO2/CH4 ratio on the type of carbon formation was investigated by HCTEM. Long-term reaction tests resulted in octopus carbon structure with several fibers growing from one nickel crystal. Above the critical CO2/CH4 ratio, carbon growth was inhibited, only a small amount of amorphous carbon could form. At CO2/CH4 ratios below the critical value, whisker formation was clearly observed. When the steady state operation of reforming reaction was changed to a transient operation by injecting pure CO2 flow to the reactor, coke deposition could be inhibited at the expense of hydrogen stoichiometry.

Biotechnology offers a sustainable route to manufacturing, but closing the loop towards safeguarding biodiversity remains challenging. Here, we explore how partnerships with Indigenous Peoples and Local Communities (IP&LC) can promote an ethical and circular bioeconomy.

The efficient removal of CO₂ from exhaust streams and even directly from air is necessary to forestall climate change, lending urgency to the search for new materials that can rapidly capture CO₂ at high capacity. The recent discovery that diamine-appended metal-organic frameworks can exhibit cooperative CO₂ uptake via the formation of ammonium carbamate chains begs the question of whether simple organic polyamine molecules could be designed to achieve a similar switch-like behavior with even higher separation capacities. Here, we present a solid molecular triamine, 1,3,5-tris(aminomethyl)benzene (TriH), that rapidly captures large quantities of CO₂ upon exposure to humid air to form the porous, crystalline, ammonium carbamate network solid TriH(CO₂)_1.5·xH₂O (TriHCO₂). The phase transition behavior of TriH converting to TriHCO₂ was studied through powder and single-crystal X-ray diffraction analysis, and additional spectroscopic techniques further verified the formation of ammonium carbamate species upon exposing TriH to humid air. Detailed breakthrough analyses conducted under varying temperatures, relative humidities, and flow rates reveal record CO₂ absorption capacities as high as 8.9 mmol/g. Computational analyses reveal an activation barrier associated with TriH absorbing CO₂ under dry conditions that is lowered under humid conditions through hydrogen bonding with a water molecule in the transition state associated with N-C bond formation. These results highlight the prospect of tunable molecular polyamines as a new class of candidate absorbents for high-capacity CO₂ capture.

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.

The temperature for complete disintegration of spent lithium-ion battery (LIB) cathode materials is typically in a range of 750-1400 °C, resulting in intensive energy consumption and high carbon emissions. Here, we promote the bond activation of oxygen in LiNi0.5Co0.2Mn0.3O2 and carbon in graphite electrodes, achieving rapid gasification and thermal decomposition of active crystals at lower temperatures in the absence of other activating agents. The activation of C and O bond leads to the storage of internal energy and the transition of the crystalline phase (single crystal to polycrystal) of the active crystals. Density functional theory modeling confirms that the CO adsorption energy is significantly higher with Ca-Oa (-3.35 eV, C and O activation) than with no activation (-1.66 eV). The differential charge results show that the bond activation model has the highest charge accumulation and consumption, improving the electron transfer. The Bader charge transfer between Ca-Oa and CO is also the largest, with a value of 0.433 |e|. Therefore, synchronous activation of C and O bonds can reduce the decomposition temperature of active crystals by 200 °C and allows a low-temperature pyrolysis recycling of retired LIB cathode materials. Our research provides a potential strategy for low-carbon recycling of retired LIBs worldwide.

The delivery of biomolecules to target cells has been a longstanding challenge in biotechnology. DNA viruses naturally evolved the ability to deliver genetic material to cells and modulate cellular processes. As such, they inherently possess requisite characteristics that have led to their extensive study, engineering, and development as biotechnological tools. Here, we overview the application of DNA viruses to biotechnology, with specific implications in basic research, health, biomanufacturing, and agriculture. For each application, we review how an increasing understanding of virology and technological methods to genetically manipulate DNA viruses has enabled advances in these fields. Additionally, we highlight the remaining challenges to unlocking the full biotechnological potential of DNA viral technologies. Finally, we discuss the importance of balancing continued technological progress with ethical and biosafety considerations.