58 Search Results

Carbon dioxide (CO₂) capture and storage represents an important technological challenge. A mechanistic understanding of interactions involved in the capture process is necessary not only for technological development but also for efficient conversion of captured CO₂ into value-added materials. Herein, we present a novel contained secondary electrospray ionization platform for studying the interactions of gaseous amines and CO₂ gas under microdroplet reaction conditions, which enables mass spectrometry (MS) characterization of CO₂ capture products and intermediates in real time. We detected [2 M + CO₂ + H]⁺ species, which corresponds to a six-membered intermediate. DFT calculations confirmed the high stability ofmore » the protonated six-membered ring intermediate. This finding provides a plausible concerted mechanism in the microdroplet environment that excludes the involvement of thermodynamically disfavored ionic species. The carbamic acid counterpart of the final product/salt was readily characterized by tandem MS. The carbamic acid/amine salt was also isolated and characterized by Fourier transform infrared spectroscopy. By virtue of the fact that headspace vapors of amines are sampled, we were able to establish a high-throughput platform that enabled the CO₂ capture capacity of five different amines to be studied in under 2 min. The same device also enabled the absolute quantification of capture capacity.« less

High-temperature, high-pressure (HPHT) nanodiamond (ND) hosts nitrogen-vacancy (NV) centers, solid-state qubits that enable room-temperature quantum sensing by all-optical magnetometry, electrometry, and thermometry. However, the covalent surface functionalization of nanoscale diamond remains largely limited to carboxylate-based chemistries. Amine termination is particularly attractive because theoretical studies predict suppression of midgap states and extended electron-spin coherence times. Recently, chemical activation of alcohol-terminated NDs to alkyl bromides (ND-Br) using SOBr2 has enabled nucleophilic substitution through a carbocation intermediate, allowing formation of simple amine terminations. Here, we evaluate whether sterically demanding amines can form covalent diamond−nitrogen bonds on ND-Br surfaces. ND-Br was reacted with branched,more » linear, and cyclic amines, including polyethylenimine, diethylenetriamine, and melamine. X-ray spectroscopies were used to confirm successful and to probe the resulting electronic structure at the diamond−amine interface. These results expand the chemical toolbox for tuning diamond surface dipoles and electron affinity, providing new pathways for engineering nanodiamond surfaces for quantum sensing and photocatalysis applications.« less

Targeted protein degradation can be induced by recruiting a protein of interest to an E3 ligase, resulting in its ubiquitination and subsequent proteasome-mediated degradation. However, only a small number of E3 ligases have been utilized for degradation. Expansion of the repertoire of useful E3 ligases via the identification of ligands to those ligases could broaden the scope and applicability of the degradation paradigm. We have identified KLHL12 as an E3 ligase with higher expression in cancer over normal tissues. We report here the use of NMR-based screening to identify fragments that bind to KLHL12, and X-ray structures of a fragmentmore » hit bound to KLHL12. Using this structural information, we optimized the hits, leading to the first reported small molecules that bind to KLHL12 with submicromolar affinity. Derivatives of these compounds may be useful for the construction of PROTACs to selectively degrade protein targets in tumors while sparing normal cells.« less

Textile waste, dominated by polyester-cotton blends, largely evades recycling and ends up in landfills or incinerators. Here, we demonstrate an aqueous ionic liquid–mediated route for selective depolymerization of textile waste, including polyester and polycotton (polyester/cotton blend). Using aqueous cholinium lysinate ([Ch][Lys]), we depolymerized poly(ethylene terephthalate) (PET) textiles with over 95 % terephthalic acid (TPA) yields, comparable to virgin PET resin. Notably, colored fabrics showed no inhibitory effect from dyes. While protic ionic liquids such as ethanolammonium acetate showed limited efficiency, their precursor amine enabled near-complete PET conversion—ethanolamine promoted aminolysis with byproduct formation whereas butylamine achieved higher TPA recovery through combinedmore » hydrolysis and aminolysis. Importantly, polycotton blends achieved complete PET depolymerization with TPA yield above 85 % and preserved cotton. These results establish aqueous ionic liquids as efficient, selective agents for deconstructing polyester in blended textiles, offering flexible product and ionic liquid management pathways toward scalable and facile textile recycling.« less

Solid amine sorbents have shown promise in the removal of ultradilute CO₂ from the atmosphere. Despite being a promising candidate material type for this application, these sorbents are prone to degradation during long-term exposure to environmental components such as CO₂, O₂, and H₂O, with amine oxidation being a particularly challenging problem. In this study, we investigate the potency of different radical scavengers and additives in mitigating the degradation of a model poly- (ethylenimine) (PEI)/Al₂O₃ sorbent under direct air capture (DAC)-relevant conditions. The results reveal that a 4,4′-bis(α,α- dimethylbenzyl)diphenylamine (BDDPA)-incorporated PEI/Al₂O₃ sorbent showed the most resistance toward oxidative degradation at varyingmore » exposure times and BDDPA loadings under CO₂-free air (21% O₂/balance N₂) at 120 °C. Interestingly, under humid (∼43% relative humidity (RH) at 26 °C) and dry 0.04% CO₂-air, the BDDPA/PEI/Al₂O₃ sorbent showed enhanced sorbent stability both at 70 and 120 °C after 4.5 h of exposure. Under humid CO₂-free air, at 120 °C, the antioxidant performance slightly declined (in comparison to the dry CO₂-free air condition) but displayed a much higher stability than the pristine sorbent. Overall, the ability of BDDPA to inhibit sorbent degradation under dry and humid, CO₂-free and CO₂-containing (0.04%) air at intermediate (70 °C) and elevated (120 °C) temperatures is promising in prolonging sorbent stability and underscores the importance of performing accelerated oxidation studies in the presence of all species that are expected to be present in DAC processes to identify suitable stabilization treatments for sorbent materials.« less

Extrusion 3D printing has advanced the manufacturing of complex liquid crystal elastomer (LCE) architectures. In parallel, donor–acceptor Stenhouse adducts (DASAs), a class of white-light-responsive photoswitches, have enabled both photochemical and photothermal LCE actuation. However, DASA–LCEs have yet to be extruded and 3D-printed. Two key challenges exist: DASA’s inherent sensitivity to heat and radicals can lead to degradation during ink preparation and printing, and small changes in the concentration of the added DASA component impact the properties of the extrudable ink, requiring reoptimization of well-established 3D-printing protocols. To overcome these challenges, we present a post-printing functionalization strategy that circumvents these limitations.more » Residual secondary amines, inherent to inks synthesized via standard aza-Michael addition, serve as active sites for covalent attachment of DASA photoresponsive groups following printing and cross-linking. Our method means that DASAs can be directly grafted onto 3D-printed aza-Michael LCEs without modifying the ink formulation or processing. The resulting DASA–LCEs exhibit wavelength tunability within the visible range and a variety of photothermal and photochemical responses. The post-functionalization can occur within 2 min and enables spatial control of the DASA concentration, producing films with tunable color gradients and locally varied photothermal and photochemical responses under visible light. In conclusion, this approach enables the rapid fabrication of DASA-based light-responsive LCEs using established ink formulations with the potential for the design of complex 3D architectures.« less

The activity of aqueous-based carbon dioxide reduction (CO₂R) reactions is often limited by the solubility of CO₂. The addition of amines can increase the total dissolved carbon in water through the formation of bicarbonate and carbamate species, which has been used to a great effect to capture CO₂ from dilute streams. Here, in this study, we explore the effect of 12 primary and secondary amines of varying Brønsted basicity, steric profile, and hydrogen-bonding capabilities on the aqueous CO₂R to CO activity of a molecular Ni(cyclam)Cl₂ catalyst with a Hg electrode. Addition of some of the amines results in greater activitymore » and selectivity for CO production compared to equivalent aqueous solutions without added amines. Under optimal conditions (0.4 M 3-amino-propionitrile), there is an over sevenfold increase in partial current density and greater selectivity for CO compared to equivalent conditions with no amine. Interestingly, the increase in activity did not correlate to any single property across the 12 amines. To elucidate the effect of the amine additives on catalysis, we used vapor–liquid equilibrium modeling (VLE), ¹³C NMR spectroscopy, and computational analysis to determine the carbon speciation of the solutions. These results indicate that for amines without ethylalcohol functionalities, CO₂R activity correlates with carbamate concentration, which is in turn governed by amine basicity and steric effects. However, this correlation does not persist for amines with ethylalcohol functionalities, which can form more stable carbamates through intramolecular-hydrogen bonding. These studies demonstrate that amine additives can enhance aqueous CO₂R activity and selectivity and describe amine properties that lead to these higher performance metrics.« less

Understanding the impact of O₂ during a carbon capture process is vital for designing robust, cost-effective materials for carrying it out. However, mechanistic studies of the O₂-induced degradation of materials are not easily undertaken owing to the complex sequential reaction pathways that arise. Here, we report comprehensive mechanistic investigations of the O₂-induced degradation of diamine-appended metal−organic frameworks (MOFs) exhibiting cooperative CO₂ adsorption. Oxygen exposure experiments were performed on seven different diamine-appended MOFs, including e-2−Mg₂(dobpdc) (e-2 = N-ethylethylenediamine, dobpdc⁴⁻ = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), under various temperatures and O₂ pressures. These experiments show that diamine degradation inhibits CO₂ chemisorption and that the degradation ratemore » is significantly influenced by the diamine structure. In contrast, the parent frameworks remain essentially intact upon O₂ exposure. Detailed characterization of O₂-exposed e-2−Mg₂(dobpdc) revealed the formation of various degradation products, including acetaldehyde, carbon dioxide, water, ethylamine, and other aldehyde- and imine-containing species. Together, these observations suggest that diamine degradation occurs via C−N bond cleavage through pathways involving C-centered radicals. Furthermore, computational evaluation of the initiation and propagation pathways for amine degradation in diamine-appended MOFs indicates that (i) degradation is likely initiated by OH^•, (ii) carbon-centered radicals generated via radical transfer reactions react with O₂, leading to amine degradation, and (iii) the ratelimiting step of the degradation reactions likely involves O−O bond cleavage. Overall, these mechanistic insights could inform strategies for mitigating O₂-induced amine degradation in next-generation carbon capture technologies.« less

This study explores the CO₂ capture characteristics of hyperbranched poly(ethylenimine) (HB-PEI) and poly- (propyleneimine) (HB-PPI) through molecular dynamics simulations using density functional theory-calibrated force fields. Key features such as density, free volume, glass transition temperature, CO₂/H₂O distribution, and molecular diffusion are systematically investigated to elucidate structure−function relationships under dry and hydrated conditions. HB-PEI demonstrates a slightly higher density and lower free volume compared to HB-PPI yet shows superior CO₂ capture due to the high amine concentration. Glass transition analysis indicates a higher thermal mobility in HBPEI, enhancing the CO₂ diffusivity. Pair correlation and coordination analyses confirm a stronger affinity ofmore » CO₂ with primary and secondary amines, particularly in hydrated environments where water competes with CO₂ for binding sites. Despite its more compact structure, HB-PEI outperformed HB-PPI in CO₂ and H₂O transport, as confirmed by higher diffusion coefficients across all hydration levels. These findings highlight a critical balance among polymer architecture, amine accessibility, and hydration in designing next-generation solid amine sorbents for efficient direct air capture applications.« less

Here, we report the role of pendant amine basicity on the proton-coupled electron transfer (PCET) reactivity for the conversion of [Co^IIICp(P^Ph₂N^R₂)(CH₃CN)]²⁺ complexes to [HCo^IIICp(P^Ph₂N^R₂)]⁺, which is a key transformation involved in catalytic CO₂ conversion to formate and in H₂ evolution. Three complexes were studied, where the amine substituent (R) varies from benzyl, methoxyphenyl, or phenyl. In previous work on the benzyl system, we showed that the amine on the P^Ph₂N^Bn₂ ligand serves as a kinetically accessible protonation site and enables three participating hydride formation mechanisms. In this work, a combination of electrochemical measurements and theoretical calculations were used to showmore » that the electronic donation at the pendant amine influences the accessible PCET mechanism and proton transfer kinetics related to cobalt hydride formation under analogous reaction conditions. Notably, the amine with the most electron-donating substituent correlates to the lowest barrier for amine protonation, and specific cobalt hydride formation mechanisms can be shut off for the amine with the least electron-donating substituent. The mechanistic and kinetic changes upon modulation of the amine substituent have great implications for overall catalytic efficiency and selectivity, especially to generate the cobalt hydride intermediate involved in selective CO₂ reduction to formate. This work shows how to exploit kinetic basicity using ligand-cooperative design to facilitate PCET reactions involved in energy related transformations.« less