Yohei Cho, Mengya Yang, Junyi Cui, Yue Yang, Surya Pratap Singh, Salvador Eslava, Daniele Benetti, James R Durrant, Akira Yamaguchi, Masahiro Miyauchi, Fumiaki Amano
Photoelectrochemical water splitting offers a promising pathway for green hydrogen production, but its efficiency is limited by electron−hole recombination. Overcoming this challenge requires detailed analysis of the relationship between charge separation and charge transfer kinetics under operando conditions. Here, we applied intensity-modulated photocurrent spectroscopy (IMPS) combined with distribution of relaxation times (DRT) analysis to the photoanodic process under varying light intensities. This approach revealed three distinct applied potential regions: a high-potential region with constant admittance independent of light intensity; a midpotential region strongly influenced by light intensity; and a low-potential region with back electron−hole recombination (BER). Crucially, our analysis demonstrated that what has traditionally been viewed as a single bulk recombination process can be resolved into distinct mechanisms based on light intensity dependence. Additionally, we identified satellite peaks in the slow kinetic regions for the first time. These peaks, influenced by light intensity and reaction conditions, revealed novel insights into surface-trapped hole dynamics. Based on these insights, we propose tailored band bending models for each kinetic scenario and discuss the implications of satellite peaks for reaction bottlenecks. These results offer new perspectives on understanding and optimizing photoelectrochemical systems.
{"title":"Analysis of the TiO2 Photoanode Process Using Intensity Modulated Photocurrent Spectroscopy and Distribution of Relaxation Times","authors":"Yohei Cho, Mengya Yang, Junyi Cui, Yue Yang, Surya Pratap Singh, Salvador Eslava, Daniele Benetti, James R Durrant, Akira Yamaguchi, Masahiro Miyauchi, Fumiaki Amano","doi":"10.1021/jacs.4c17345","DOIUrl":"https://doi.org/10.1021/jacs.4c17345","url":null,"abstract":"Photoelectrochemical water splitting offers a promising pathway for green hydrogen production, but its efficiency is limited by electron−hole recombination. Overcoming this challenge requires detailed analysis of the relationship between charge separation and charge transfer kinetics under operando conditions. Here, we applied intensity-modulated photocurrent spectroscopy (IMPS) combined with distribution of relaxation times (DRT) analysis to the photoanodic process under varying light intensities. This approach revealed three distinct applied potential regions: a high-potential region with constant admittance independent of light intensity; a midpotential region strongly influenced by light intensity; and a low-potential region with back electron−hole recombination (BER). Crucially, our analysis demonstrated that what has traditionally been viewed as a single bulk recombination process can be resolved into distinct mechanisms based on light intensity dependence. Additionally, we identified satellite peaks in the slow kinetic regions for the first time. These peaks, influenced by light intensity and reaction conditions, revealed novel insights into surface-trapped hole dynamics. Based on these insights, we propose tailored band bending models for each kinetic scenario and discuss the implications of satellite peaks for reaction bottlenecks. These results offer new perspectives on understanding and optimizing photoelectrochemical systems.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"11 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143470646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Francois Nkurunziza, Saudagar Dongare, Soumya Chatterjee, Bhavi Shah, Manu Gautam, Baleeswaraiah Muchharla, Bijandra Kumar, Michael J. Janik, Burcu Gurkan, Robert L. Sacci, Joshua M. Spurgeon
Imidazolium-based ionic liquids have led to enhanced CO2 electroreduction activity due to cation effects at the cathode surface, stabilizing the reaction intermediates and decreasing the activation energy. In aqueous media, alkali cations are also known to improve CO2 reduction activity on metals such as Ag, with the enhancement attributed to electrical double layer effects and trending with the size of the alkali cation. However, the effect of a mixed catholyte solution of alkali cations in the presence of an imidazolium-based ionic liquid has not been well-explored. Herein, 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF4], in water was investigated with alkali salts to unravel the interaction effects for CO2 electroreduction on Ag. Although both [EMIM]+ and alkali cations have individually improved CO2 to CO conversion on Ag in water, electrochemical results showed that alkali cations hindered imidazolium-mediated CO2 electroreduction in most conditions. Li+, in particular, was sharply inhibitory compared to other alkali cations and strongly redirected the selectivity to hydrogen evolution. The nature of the alkali cation inhibition was investigated with spectroscopic techniques, including in situ surface-enhanced Raman spectroscopy (SERS) and dynamic electrochemical impedance spectroscopy (DEIS). Along with computational insights from density functional theory (DFT), the electrochemical and spectroscopic data suggest that alkali cations inhibit [EMIM]-mediated CO2 reduction by competing for surface adsorption sites, preventing the potential-dependent structural reorientation of imidazolium, and promoting hydrogen evolution by bringing solvated water to the cathode surface.
{"title":"Alkali Cation Inhibition of Imidazolium-Mediated Electrochemical CO2 Reduction on Silver","authors":"Francois Nkurunziza, Saudagar Dongare, Soumya Chatterjee, Bhavi Shah, Manu Gautam, Baleeswaraiah Muchharla, Bijandra Kumar, Michael J. Janik, Burcu Gurkan, Robert L. Sacci, Joshua M. Spurgeon","doi":"10.1021/jacs.4c16635","DOIUrl":"https://doi.org/10.1021/jacs.4c16635","url":null,"abstract":"Imidazolium-based ionic liquids have led to enhanced CO<sub>2</sub> electroreduction activity due to cation effects at the cathode surface, stabilizing the reaction intermediates and decreasing the activation energy. In aqueous media, alkali cations are also known to improve CO<sub>2</sub> reduction activity on metals such as Ag, with the enhancement attributed to electrical double layer effects and trending with the size of the alkali cation. However, the effect of a mixed catholyte solution of alkali cations in the presence of an imidazolium-based ionic liquid has not been well-explored. Herein, 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF<sub>4</sub>], in water was investigated with alkali salts to unravel the interaction effects for CO<sub>2</sub> electroreduction on Ag. Although both [EMIM]<sup>+</sup> and alkali cations have individually improved CO<sub>2</sub> to CO conversion on Ag in water, electrochemical results showed that alkali cations hindered imidazolium-mediated CO<sub>2</sub> electroreduction in most conditions. Li<sup>+</sup>, in particular, was sharply inhibitory compared to other alkali cations and strongly redirected the selectivity to hydrogen evolution. The nature of the alkali cation inhibition was investigated with spectroscopic techniques, including in situ surface-enhanced Raman spectroscopy (SERS) and dynamic electrochemical impedance spectroscopy (DEIS). Along with computational insights from density functional theory (DFT), the electrochemical and spectroscopic data suggest that alkali cations inhibit [EMIM]-mediated CO<sub>2</sub> reduction by competing for surface adsorption sites, preventing the potential-dependent structural reorientation of imidazolium, and promoting hydrogen evolution by bringing solvated water to the cathode surface.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"65 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143470649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Boyu Wang, Cheng Chen, Yani Huo, Hongyu Ju, Wanqi Sun, Xiao-Ye Wang, Chuancheng Jia, Jinying Wang, Xuefeng Guo
Developing effective structural design strategies for regulating charge transport is a central focus in molecular electronics. The interplay between molecular symmetry and orbital distribution, facilitated by heteroatom substitution, presents opportunities for direct modulation in both resonant and off-resonance tunneling processes. In this study, scanning tunneling microscopy-break junction techniques and the first-principles calculations are employed to investigate the electronic properties of boron-embedded acenes. Compared to the parent acene, boron incorporation shifts the transport-dominating molecular orbital from a centrally localized distribution to a delocalized configuration across the orthogonal molecular backbone. This shift results in a 10-fold increase in conductance in the off-resonance region near zero bias and a 50-fold enhancement in conductance through near-resonant tunneling at high bias voltages. Notably, expanding the central acene fragment increases orbital asymmetry within molecular junctions, thereby compromising transport efficiency. However, applying a bias voltage gradually mitigates the symmetry-breaking effect, leading to through-backbone orbital distribution and a recovery in the near-resonant tunneling conductance. This orthogonal control of electronic transport channels provides a distinct strategy for the effective regulation of molecular conductance.
{"title":"Orthogonal Control of Transport Channels in Boron-Embedded Acenes","authors":"Boyu Wang, Cheng Chen, Yani Huo, Hongyu Ju, Wanqi Sun, Xiao-Ye Wang, Chuancheng Jia, Jinying Wang, Xuefeng Guo","doi":"10.1021/jacs.4c17477","DOIUrl":"https://doi.org/10.1021/jacs.4c17477","url":null,"abstract":"Developing effective structural design strategies for regulating charge transport is a central focus in molecular electronics. The interplay between molecular symmetry and orbital distribution, facilitated by heteroatom substitution, presents opportunities for direct modulation in both resonant and off-resonance tunneling processes. In this study, scanning tunneling microscopy-break junction techniques and the first-principles calculations are employed to investigate the electronic properties of boron-embedded acenes. Compared to the parent acene, boron incorporation shifts the transport-dominating molecular orbital from a centrally localized distribution to a delocalized configuration across the orthogonal molecular backbone. This shift results in a 10-fold increase in conductance in the off-resonance region near zero bias and a 50-fold enhancement in conductance through near-resonant tunneling at high bias voltages. Notably, expanding the central acene fragment increases orbital asymmetry within molecular junctions, thereby compromising transport efficiency. However, applying a bias voltage gradually mitigates the symmetry-breaking effect, leading to through-backbone orbital distribution and a recovery in the near-resonant tunneling conductance. This orthogonal control of electronic transport channels provides a distinct strategy for the effective regulation of molecular conductance.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"14 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143470657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jialun Mao, Jiashun Liang, Yunan Li, Xuan Liu, Feng Ma, Shuxia Liu, Hao Ouyang, Zhao Cai, Tanyuan Wang, Yufei Zhao, Yunhui Huang, Qing Li
Designing a rational electrocatalyst/electrolyte interface with superb active hydrogen supply is of significant importance for the alkaline hydrogen evolution reaction (HER) and anion exchange membrane water electrolyzers (AEMWEs). Here, we propose a strategy to tune the interfacial active hydrogen supply via inducing dissoluble cation into electrocatalysts to boost HER in alkali, with electrochemical lithiated sub-2 nm RuSn0.8 nanowires (NWs) as a proof of concept. It is found that a part of Li+ could dissolve in situ from lithiated RuSn0.8 NWs during HER, which tends to affect the interfacial structure and facilitate the proton transport. Among all the Li–Ru–Sn and Ru–Sn NWs, the best-performing Li3.0RuSn0.8 NWs exhibit the lowest initial overpotential of 66 mV at 100 mA cm–2 in 1.0 M KOH, which could be further reduced to 38 mV after the 30 000 cycles accelerated stability test (AST). In situ Raman spectroscopy and operando X-ray adsorption spectroscopy indicate that the pristine Li3.0RuSn0.8 NWs are highly active toward water dissociation and the dissolved Li+ during AST could further enhance the flexibility of the hydrogen bond network for proton transportation. Ab initio molecular dynamics simulations and density functional theory calculations disclose that the incorporation of Li into the Ru–Sn lattice is beneficial to lower the water dissociation barrier, while dissolved Li+ at the interface significantly increases the population of interfacial water molecules, thereby providing sufficient active hydrogens for H2 production. The AEMWE equipped with the Li3.0RuSn0.8 NWs cathode delivers an extremely low cell voltage (1.689 V) at an industrial-scale current density (1 A cm–2) and outstanding stability (56 μV h–1 loss at 1 A cm–2 after 1000 h galvanostatic test), representing one of the best alkaline HER electrocatalysts ever reported.
{"title":"Electrochemical Lithiation Regulates the Active Hydrogen Supply on Ru–Sn Nanowires for Hydrogen Evolution Toward the High-Performing Anion Exchange Membrane Water Electrolyzer","authors":"Jialun Mao, Jiashun Liang, Yunan Li, Xuan Liu, Feng Ma, Shuxia Liu, Hao Ouyang, Zhao Cai, Tanyuan Wang, Yufei Zhao, Yunhui Huang, Qing Li","doi":"10.1021/jacs.4c17373","DOIUrl":"https://doi.org/10.1021/jacs.4c17373","url":null,"abstract":"Designing a rational electrocatalyst/electrolyte interface with superb active hydrogen supply is of significant importance for the alkaline hydrogen evolution reaction (HER) and anion exchange membrane water electrolyzers (AEMWEs). Here, we propose a strategy to tune the interfacial active hydrogen supply via inducing dissoluble cation into electrocatalysts to boost HER in alkali, with electrochemical lithiated sub-2 nm RuSn<sub>0.8</sub> nanowires (NWs) as a proof of concept. It is found that a part of Li<sup>+</sup> could dissolve in situ from lithiated RuSn<sub>0.8</sub> NWs during HER, which tends to affect the interfacial structure and facilitate the proton transport. Among all the Li–Ru–Sn and Ru–Sn NWs, the best-performing Li<sub>3.0</sub>RuSn<sub>0.8</sub> NWs exhibit the lowest initial overpotential of 66 mV at 100 mA cm<sup>–2</sup> in 1.0 M KOH, which could be further reduced to 38 mV after the 30 000 cycles accelerated stability test (AST). In situ Raman spectroscopy and operando X-ray adsorption spectroscopy indicate that the pristine Li<sub>3.0</sub>RuSn<sub>0.8</sub> NWs are highly active toward water dissociation and the dissolved Li<sup>+</sup> during AST could further enhance the flexibility of the hydrogen bond network for proton transportation. Ab initio molecular dynamics simulations and density functional theory calculations disclose that the incorporation of Li into the Ru–Sn lattice is beneficial to lower the water dissociation barrier, while dissolved Li<sup>+</sup> at the interface significantly increases the population of interfacial water molecules, thereby providing sufficient active hydrogens for H<sub>2</sub> production. The AEMWE equipped with the Li<sub>3.0</sub>RuSn<sub>0.8</sub> NWs cathode delivers an extremely low cell voltage (1.689 V) at an industrial-scale current density (1 A cm<sup>–2</sup>) and outstanding stability (56 μV h<sup>–1</sup> loss at 1 A cm<sup>–2</sup> after 1000 h galvanostatic test), representing one of the best alkaline HER electrocatalysts ever reported.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"134 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143470650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alexander I. P. Taylor, Yong Xu, Martin Wilkinson, Pijush Chakraborty, Alice Brinkworth, Leon F. Willis, Anastasia Zhuravleva, Neil A. Ranson, Richard Foster, Sheena E. Radford
Amyloid formation is involved in widespread health conditions such as Alzheimer’s disease, Parkinson’s disease, and type-2 diabetes. Amyloid fibrils have a similar cross-β architecture, but fibrils formed by a single protein sequence can have diverse structures, varying with time, self-assembly conditions, and sequence modifications. Fibril structure has been proposed to be diagnostic of disease, but why different structures result under different conditions, especially in vitro, remains elusive. We previously identified a small molecule, YX-I-1, which inhibits in vitro amyloid formation by islet amyloid polypeptide (IAPP), a peptide hormone whose amyloid formation is involved in type-2 diabetes. Here, using YX-I-1 as a lead, we identified regulator-approved drugs with similar structures by chemical similarity analysis and substructure searches and monitored the effect of 24 of these potential ligands on IAPP amyloid assembly in vitro. We show that one such compound, canagliflozin (Invokana), a type-2 diabetes drug already in clinical use, can strongly delay the kinetics of IAPP amyloid formation, an activity independent of its intended mode of action [sodium-glucose linked transporter 2 (SGLT2) inhibitor] that may have important therapeutic implications. Combining analysis of amyloid self-assembly kinetics, biophysical characterization of monomer and fibril binding, and cryo-EM of the assembly products, we show that YX-I-1 and canagliflozin target IAPP early in aggregation, remodeling the energy landscape of primary nucleation and profoundly altering the resulting fibril structures. Early binding events thus imprint long-lasting effects on the amyloid structures that form.
{"title":"Kinetic Steering of Amyloid Formation and Polymorphism by Canagliflozin, a Type-2 Diabetes Drug","authors":"Alexander I. P. Taylor, Yong Xu, Martin Wilkinson, Pijush Chakraborty, Alice Brinkworth, Leon F. Willis, Anastasia Zhuravleva, Neil A. Ranson, Richard Foster, Sheena E. Radford","doi":"10.1021/jacs.4c16743","DOIUrl":"https://doi.org/10.1021/jacs.4c16743","url":null,"abstract":"Amyloid formation is involved in widespread health conditions such as Alzheimer’s disease, Parkinson’s disease, and type-2 diabetes. Amyloid fibrils have a similar cross-β architecture, but fibrils formed by a single protein sequence can have diverse structures, varying with time, self-assembly conditions, and sequence modifications. Fibril structure has been proposed to be diagnostic of disease, but why different structures result under different conditions, especially in vitro, remains elusive. We previously identified a small molecule, YX-I-1, which inhibits in vitro amyloid formation by islet amyloid polypeptide (IAPP), a peptide hormone whose amyloid formation is involved in type-2 diabetes. Here, using YX-I-1 as a lead, we identified regulator-approved drugs with similar structures by chemical similarity analysis and substructure searches and monitored the effect of 24 of these potential ligands on IAPP amyloid assembly in vitro. We show that one such compound, canagliflozin (Invokana), a type-2 diabetes drug already in clinical use, can strongly delay the kinetics of IAPP amyloid formation, an activity independent of its intended mode of action [sodium-glucose linked transporter 2 (SGLT2) inhibitor] that may have important therapeutic implications. Combining analysis of amyloid self-assembly kinetics, biophysical characterization of monomer and fibril binding, and cryo-EM of the assembly products, we show that YX-I-1 and canagliflozin target IAPP early in aggregation, remodeling the energy landscape of primary nucleation and profoundly altering the resulting fibril structures. Early binding events thus imprint long-lasting effects on the amyloid structures that form.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"274 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143470652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Samuel I. Mann, Zhi Lin, Sophia K. Tan, Jiaqi Zhu, Zachary X. W. Widel, Ian Bakanas, Jarrett P. Mansergh, Rui Liu, Mark J. S. Kelly, Yibing Wu, James A. Wells, Michael J. Therien, William F. DeGrado
De novo protein design provides a framework to test our understanding of protein function and build proteins with cofactors and functions not found in nature. Here, we report the design of proteins designed to bind powerful photooxidants and the evaluation of the use of these proteins to generate diffusible small-molecule reactive species. Because excited-state dynamics are influenced by the dynamics and hydration of a photooxidant’s environment, it was important to not only design a binding site but also to evaluate its dynamic properties. Thus, we used computational design in conjunction with molecular dynamics (MD) simulations to design a protein, designated NBP (NDI Binding Protein), that held a naphthalenediimide (NDI), a powerful photooxidant, in a programmable molecular environment. Solution NMR confirmed the structure of the complex. We evaluated two NDI cofactors in this de novo protein using ultrafast pump–probe spectroscopy to evaluate light-triggered intra- and intermolecular electron transfer function. Moreover, we demonstrated the utility of this platform to activate multiple molecular probes for protein labeling.
{"title":"De Novo Design of Proteins That Bind Naphthalenediimides, Powerful Photooxidants with Tunable Photophysical Properties","authors":"Samuel I. Mann, Zhi Lin, Sophia K. Tan, Jiaqi Zhu, Zachary X. W. Widel, Ian Bakanas, Jarrett P. Mansergh, Rui Liu, Mark J. S. Kelly, Yibing Wu, James A. Wells, Michael J. Therien, William F. DeGrado","doi":"10.1021/jacs.4c18151","DOIUrl":"https://doi.org/10.1021/jacs.4c18151","url":null,"abstract":"<i>De novo</i> protein design provides a framework to test our understanding of protein function and build proteins with cofactors and functions not found in nature. Here, we report the design of proteins designed to bind powerful photooxidants and the evaluation of the use of these proteins to generate diffusible small-molecule reactive species. Because excited-state dynamics are influenced by the dynamics and hydration of a photooxidant’s environment, it was important to not only design a binding site but also to evaluate its dynamic properties. Thus, we used computational design in conjunction with molecular dynamics (MD) simulations to design a protein, designated NBP (<u>N</u>DI <u>B</u>inding <u>P</u>rotein), that held a naphthalenediimide (NDI), a powerful photooxidant, in a programmable molecular environment. Solution NMR confirmed the structure of the complex. We evaluated two NDI cofactors in this <i>de novo</i> protein using ultrafast pump–probe spectroscopy to evaluate light-triggered intra- and intermolecular electron transfer function. Moreover, we demonstrated the utility of this platform to activate multiple molecular probes for protein labeling.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"2 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jakob A. Meckes, Zachary W. Schroeder, Diganta Sarkar, Riley W. Hooper, Clara E. Faraday-Smith, Alex Brown, Rik R. Tykwinski, Vladimir K. Michaelis
High-field dynamic nuclear polarization nuclear magnetic resonance (DNP NMR) spectroscopy transfers polarization from unpaired electrons in polarizing agents to nuclei of interest to boost NMR sensitivity. Verdazyl biradicals are a promising choice as polarizing agents because they have been found to generate narrower electron paramagnetic resonance (EPR) signals compared to nitroxide biradicals; an advantageous characteristic for high-field DNP when operating above 400 MHz/263 GHz. The use of verdazyl radicals as DNP polarizing agents has been very limited to date, yet, recent numerical simulations have predicted that verdazyl-nitroxide hybrid biradicals could be more effective polarizing agents than nitroxide-nitroxide biradicals. Herein, the syntheses of a series of verdazyl mono- and biradicals, as well as verdazyl-nitroxide biradicals are described. These radicals were examined in high-field DNP NMR experiments (600 MHz/395 GHz), by measuring 1H signal enhancements directly and through 13C{1H} cross-polarization experiments. X-band EPR, 1H DNP field profiles, and experiments to determine the nuclear build-up times were performed for verdazyl-nitroxide biradicals VerTEMPol and VerTEKol. These hybrid biradicals provide enhancements of up to 100-fold increased signal intensities (i.e., representing >104-fold time savings), approximately four times higher than that of the nitroxide biradical TEKPol, a commonly used polarizing agent in the field.
{"title":"Verdazyl-Based Radicals for High-Field Dynamic Nuclear Polarization NMR","authors":"Jakob A. Meckes, Zachary W. Schroeder, Diganta Sarkar, Riley W. Hooper, Clara E. Faraday-Smith, Alex Brown, Rik R. Tykwinski, Vladimir K. Michaelis","doi":"10.1021/jacs.4c13374","DOIUrl":"https://doi.org/10.1021/jacs.4c13374","url":null,"abstract":"High-field dynamic nuclear polarization nuclear magnetic resonance (DNP NMR) spectroscopy transfers polarization from unpaired electrons in polarizing agents to nuclei of interest to boost NMR sensitivity. Verdazyl biradicals are a promising choice as polarizing agents because they have been found to generate narrower electron paramagnetic resonance (EPR) signals compared to nitroxide biradicals; an advantageous characteristic for high-field DNP when operating above 400 MHz/263 GHz. The use of verdazyl radicals as DNP polarizing agents has been very limited to date, yet, recent numerical simulations have predicted that verdazyl-nitroxide hybrid biradicals could be more effective polarizing agents than nitroxide-nitroxide biradicals. Herein, the syntheses of a series of verdazyl mono- and biradicals, as well as verdazyl-nitroxide biradicals are described. These radicals were examined in high-field DNP NMR experiments (600 MHz/395 GHz), by measuring <sup>1</sup>H signal enhancements directly and through <sup>13</sup>C{<sup>1</sup>H} cross-polarization experiments. X-band EPR, <sup>1</sup>H DNP field profiles, and experiments to determine the nuclear build-up times were performed for verdazyl-nitroxide biradicals <b>VerTEMPol</b> and <b>VerTEKol</b>. These hybrid biradicals provide enhancements of up to 100-fold increased signal intensities (i.e., representing >10<sup>4</sup>-fold time savings), approximately four times higher than that of the nitroxide biradical <b>TEKPol</b>, a commonly used polarizing agent in the field.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"34 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jules Schleinitz, Alba Carretero-Cerdán, Anjali Gurajapu, Yonatan Harnik, Gina Lee, Amitesh Pandey, Anat Milo, Sarah E. Reisman
The development of machine learning models to predict the regioselectivity of C(sp3)–H functionalization reactions is reported. A data set for dioxirane oxidations was curated from the literature and used to generate a model to predict the regioselectivity of C–H oxidation. To assess whether smaller, intentionally designed data sets could provide accuracy on complex targets, a series of acquisition functions were developed to select the most informative molecules for the specific target. Active learning-based acquisition functions that leverage predicted reactivity and model uncertainty were found to outperform those based on molecular and site similarity alone. The use of acquisition functions for data set elaboration significantly reduced the number of data points needed to perform accurate prediction, and it was found that smaller, machine-designed data sets can give accurate predictions when larger, randomly selected data sets fail. Finally, the workflow was experimentally validated on five complex substrates and shown to be applicable to predicting the regioselectivity of arene C–H radical borylation. These studies provide a quantitative alternative to the intuitive extrapolation from “model substrates” that is frequently used to estimate reactivity on complex molecules.
{"title":"Designing Target-specific Data Sets for Regioselectivity Predictions on Complex Substrates","authors":"Jules Schleinitz, Alba Carretero-Cerdán, Anjali Gurajapu, Yonatan Harnik, Gina Lee, Amitesh Pandey, Anat Milo, Sarah E. Reisman","doi":"10.1021/jacs.4c15902","DOIUrl":"https://doi.org/10.1021/jacs.4c15902","url":null,"abstract":"The development of machine learning models to predict the regioselectivity of C(sp<sup>3</sup>)–H functionalization reactions is reported. A data set for dioxirane oxidations was curated from the literature and used to generate a model to predict the regioselectivity of C–H oxidation. To assess whether smaller, intentionally designed data sets could provide accuracy on complex targets, a series of acquisition functions were developed to select the most informative molecules for the specific target. Active learning-based acquisition functions that leverage predicted reactivity and model uncertainty were found to outperform those based on molecular and site similarity alone. The use of acquisition functions for data set elaboration significantly reduced the number of data points needed to perform accurate prediction, and it was found that smaller, machine-designed data sets can give accurate predictions when larger, randomly selected data sets fail. Finally, the workflow was experimentally validated on five complex substrates and shown to be applicable to predicting the regioselectivity of arene C–H radical borylation. These studies provide a quantitative alternative to the intuitive extrapolation from “model substrates” that is frequently used to estimate reactivity on complex molecules.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"14 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Joël Benninga, Bert Gebben, Rudy Folkersma, Vincent S. D. Voet, Katja Loos
Back-to-monomer chemical recycling of polymers is crucial in achieving a circular plastics economy. Herein, we report the rapid microwave-assisted depolymerization of poly(p-phenylene terephthalamide) (PPTA), also known as Twaron or Kevlar. The alkaline hydrolysis of PPTA was conducted in a microwave reactor at temperatures ranging from 240 to 260 °C with reaction times of 1–15 min. The highest conversion (96%) was found after 15 min at 260 °C. The resulting monomers terephthalic acid and p-phenylenediamine were successfully purified (>99% purity) in good yields using extraction and precipitation methods. This work presents the fastest depolymerization of PPTA to date under relatively mild conditions, thereby encouraging a circular value chain for PPTA.
{"title":"Rapid Microwave-Assisted Chemical Recycling of Poly(p-Phenylene Terephthalamide)","authors":"Joël Benninga, Bert Gebben, Rudy Folkersma, Vincent S. D. Voet, Katja Loos","doi":"10.1021/jacs.4c17791","DOIUrl":"https://doi.org/10.1021/jacs.4c17791","url":null,"abstract":"Back-to-monomer chemical recycling of polymers is crucial in achieving a circular plastics economy. Herein, we report the rapid microwave-assisted depolymerization of poly(<i>p</i>-phenylene terephthalamide) (PPTA), also known as Twaron or Kevlar. The alkaline hydrolysis of PPTA was conducted in a microwave reactor at temperatures ranging from 240 to 260 °C with reaction times of 1–15 min. The highest conversion (96%) was found after 15 min at 260 °C. The resulting monomers terephthalic acid and <i>p</i>-phenylenediamine were successfully purified (>99% purity) in good yields using extraction and precipitation methods. This work presents the fastest depolymerization of PPTA to date under relatively mild conditions, thereby encouraging a circular value chain for PPTA.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"2 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Para-aramid nanofibers, one of the newest high-performance building blocks at the nanoscale, have attracted great attention due to their hard-to-find property sets and ability to form high-porosity solids. However, there are great difficulties in their scalable and sustainable production because the strong intermolecular hydrogen bonds and other interactions of aramid macromolecules lead to lengthy processes with highly corrosive solvents. Taking advantage of uniquely efficient delamination of polymer nanocrystallites, here we show that the preparation time of para-aramid nanofibers can be reduced by 2520 times (from 1 week to four min), while their concentration can be increased by 10 times. Through this molecule intercalation-induced method, novel ribbon-like aramid nanofibers are prepared. The multiscale modeling indicated that delamination of nanofibers occurs via intercalation of alcohols at nanoscale interfaces. 1000 kg nanofiber dispersions were successfully prepared within half an hour in a pilot-scale test. These findings demonstrate the realism of effective aramid recycling into a wide range of multifunctional nanofiber composites.
{"title":"Fast and Massive Production of Aramid Nanofibers via Molecule Intercalation","authors":"Zi-Meng Han, YuanZhen Hou, Hao-Cheng Liu, Qing-Fang Guan, Huai-Bin Yang, Kun-Peng Yang, Chong-Han Yin, Zhang-Chi Ling, Yu-Xiang Zhao, Jun Xia, YinBo Zhu, HengAn Wu, Kody Whishant, Nicholas A. Kotov, Shu-Hong Yu","doi":"10.1021/jacs.4c18620","DOIUrl":"https://doi.org/10.1021/jacs.4c18620","url":null,"abstract":"Para-aramid nanofibers, one of the newest high-performance building blocks at the nanoscale, have attracted great attention due to their hard-to-find property sets and ability to form high-porosity solids. However, there are great difficulties in their scalable and sustainable production because the strong intermolecular hydrogen bonds and other interactions of aramid macromolecules lead to lengthy processes with highly corrosive solvents. Taking advantage of uniquely efficient delamination of polymer nanocrystallites, here we show that the preparation time of para-aramid nanofibers can be reduced by 2520 times (from 1 week to four min), while their concentration can be increased by 10 times. Through this molecule intercalation-induced method, novel ribbon-like aramid nanofibers are prepared. The multiscale modeling indicated that delamination of nanofibers occurs via intercalation of alcohols at nanoscale interfaces. 1000 kg nanofiber dispersions were successfully prepared within half an hour in a pilot-scale test. These findings demonstrate the realism of effective aramid recycling into a wide range of multifunctional nanofiber composites.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":"127 1","pages":""},"PeriodicalIF":15.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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