Pub Date : 2025-02-10DOI: 10.1021/acs.accounts.4c0069510.1021/acs.accounts.4c00695
Nanjun Chen, Chuan Hu and Young Moo Lee*,
Next-generation cost-effective anion exchange membrane (AEM) fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs) have emerged as promising alternatives to costly proton exchange membrane (PEM) fuel cells and water electrolyzers due to the possibility of utilizing platinum-group-metal (PGM)-free catalysts and phasing out unsustainable perfluorosulfonic acid polymers. Anion exchange polyelectrolytes (AEPs), which can be utilized as AEMs or ionomers, are pivotal materials in AEM devices. Despite extensive exploration in the past decade, the application of AEPs has been significantly impeded by their poor ionic conductivity, insufficient alkaline stability, and unfavorable mechanical properties. Therefore, developing highly conductive and robust AEPs is critical to the success of AEMFCs and AEMWEs. (i) Our group has developed a series of highly conductive and durable poly(aryl-co-aryl piperidinium) (c-PAP) AEPs to address the aforementioned issues. c-PAP AEMs and ionomers enable outstanding OH– conductivity (>160 mS cm–1 at 80 °C), alkaline stability (1 M NaOH at 80 °C > 2000 h), dimensional stability, and mechanical properties (tensile strength > 80 MPa), giving them all the properties required for applications in AEM devices. (ii) Based on c-PAP AEMs and ionomers, we have developed high-performance AEMFCs and AEMWEs, as well as provided insights into the ionomer research and the design of membrane electrode assemblies. Typically, c-PAP AEMFCs reached the topmost peak power densities (PPDs) of 2.7 W cm–2 at 80 °C in H2–O2 along with 1000 h cell durability. Moreover, cathode-dried AEMWEs achieved a record-breaking current density of 17 A cm–2 in 1 M KOH, and the cell can be run stably at a 1.5 A cm–2 current density for over 2000 h. The remarkable performances achieved by this new class of c-PAP AEPs identify them as the most promising candidates for practical applications in AEMFCs and AEMWEs. In this account, we will elaborate on our strategies and methodologies associated with c-PAP AEPs and AEM devices, covering the screening and identification of highly durable cation head groups and molecular-engineering approaches to design c-PAP AEMs and ionomers. Moreover, we underscore our strategy in terms of developing highly efficient and durable AEMFCs and AEMWEs. We also elucidate different approaches for further enhancing the ion conductivity and mechanical stability of c-PAP AEMs, including the design of backbones and side chains, cross-linking, and reinforcement. We firmly believe that our series of studies has made substantial contributions to the fields of AEM, ionomers, AEMFCs, and AEMWEs, which have advanced AEM technology to be on par with PEM technology, opening a new avenue for commercialization of AEMFCs and AEMWEs.
{"title":"Poly(Aryl-co-Aryl Piperidinium) Copolymers for Anion Exchange Membrane Fuel Cells and Water Electrolyzers","authors":"Nanjun Chen, Chuan Hu and Young Moo Lee*, ","doi":"10.1021/acs.accounts.4c0069510.1021/acs.accounts.4c00695","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00695https://doi.org/10.1021/acs.accounts.4c00695","url":null,"abstract":"<p >Next-generation cost-effective anion exchange membrane (AEM) fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs) have emerged as promising alternatives to costly proton exchange membrane (PEM) fuel cells and water electrolyzers due to the possibility of utilizing platinum-group-metal (PGM)-free catalysts and phasing out unsustainable perfluorosulfonic acid polymers. Anion exchange polyelectrolytes (AEPs), which can be utilized as AEMs or ionomers, are pivotal materials in AEM devices. Despite extensive exploration in the past decade, the application of AEPs has been significantly impeded by their poor ionic conductivity, insufficient alkaline stability, and unfavorable mechanical properties. Therefore, developing highly conductive and robust AEPs is critical to the success of AEMFCs and AEMWEs. (i) Our group has developed a series of highly conductive and durable poly(aryl-<i>co</i>-aryl piperidinium) (c-PAP) AEPs to address the aforementioned issues. c-PAP AEMs and ionomers enable outstanding OH<sup>–</sup> conductivity (>160 mS cm<sup>–1</sup> at 80 °C), alkaline stability (1 M NaOH at 80 °C > 2000 h), dimensional stability, and mechanical properties (tensile strength > 80 MPa), giving them all the properties required for applications in AEM devices. (ii) Based on c-PAP AEMs and ionomers, we have developed high-performance AEMFCs and AEMWEs, as well as provided insights into the ionomer research and the design of membrane electrode assemblies. Typically, c-PAP AEMFCs reached the topmost peak power densities (PPDs) of 2.7 W cm<sup>–2</sup> at 80 °C in H<sub>2</sub>–O<sub>2</sub> along with 1000 h cell durability. Moreover, cathode-dried AEMWEs achieved a record-breaking current density of 17 A cm<sup>–2</sup> in 1 M KOH, and the cell can be run stably at a 1.5 A cm<sup>–2</sup> current density for over 2000 h. The remarkable performances achieved by this new class of c-PAP AEPs identify them as the most promising candidates for practical applications in AEMFCs and AEMWEs. In this account, we will elaborate on our strategies and methodologies associated with c-PAP AEPs and AEM devices, covering the screening and identification of highly durable cation head groups and molecular-engineering approaches to design c-PAP AEMs and ionomers. Moreover, we underscore our strategy in terms of developing highly efficient and durable AEMFCs and AEMWEs. We also elucidate different approaches for further enhancing the ion conductivity and mechanical stability of c-PAP AEMs, including the design of backbones and side chains, cross-linking, and reinforcement. We firmly believe that our series of studies has made substantial contributions to the fields of AEM, ionomers, AEMFCs, and AEMWEs, which have advanced AEM technology to be on par with PEM technology, opening a new avenue for commercialization of AEMFCs and AEMWEs.</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 5","pages":"688–702 688–702"},"PeriodicalIF":16.4,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acs.accounts.4c00695","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143533680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-10DOI: 10.2174/1386207325666220629121318
Ning Yu, Shi-Kai Zhang, Jian Chen, Cheng Zhao, Ye-Min Cao, Ling Li, Yong-Bing Cao
Objective: Chemotherapy-induced phlebitis (CIP) is a side product of chemotherapy treatment for malignant tumors, which affects the therapeutic effect and quality of life of cancer patients, and still lacks a clear therapeutic means. In this study, we investigated the therapeutic effects of QLTMP on CIP using network pharmacology and verified the anti-inflammatory mechanism of QLTMP in a mice model induced by vinorelbine.
Methods: Network pharmacology analysis was performed to identify bioactive compounds in QLTMP. The protein-protein interaction network was used to identify the core therapeutic targets of QLTMP against CIP, analyze biological function and pathway enrichment based on the identified core therapeutic targets, and evaluate the therapeutic effect of QLTMP in a model of CIP induced by vinorelbine to confirm the reliability of the network pharmacological analysis. One hundred and sixty-five bioactive compounds of QLTMP matched the screening criteria and identified 19 core therapeutic targets of QLTMP against CIP. Biofunctional analysis showed that the therapeutic effect of QLTMP on CIP was mainly related to the inhibition of inflammation, while pathway enrichment analysis showed that the TNF signaling pathway was involved in the inflammatory process.
Results: Experimental confirmation in a mice model showed that QLTMP exerts anti-inflammatory effects through modulation of the PI3K/AKT/TNF signaling pathway, a discovery consistent with the network pharmacological analysis.
Discussion and conclusion: The network pharmacological analysis of the anti-inflammatory mechanism of QLTMP on CIP and its exploration of in vivo experiments provide a theoretical basis for the design of agents that can mitigate or cure CIP
{"title":"Mitigation of QingLuoTongMai Pills on Chemotherapy-induced Phlebitis: A Network Pharmacology Study and Experimental Validation","authors":"Ning Yu, Shi-Kai Zhang, Jian Chen, Cheng Zhao, Ye-Min Cao, Ling Li, Yong-Bing Cao","doi":"10.2174/1386207325666220629121318","DOIUrl":"10.2174/1386207325666220629121318","url":null,"abstract":"<p><strong>Objective: </strong>Chemotherapy-induced phlebitis (CIP) is a side product of chemotherapy treatment for malignant tumors, which affects the therapeutic effect and quality of life of cancer patients, and still lacks a clear therapeutic means. In this study, we investigated the therapeutic effects of QLTMP on CIP using network pharmacology and verified the anti-inflammatory mechanism of QLTMP in a mice model induced by vinorelbine.</p><p><strong>Methods: </strong>Network pharmacology analysis was performed to identify bioactive compounds in QLTMP. The protein-protein interaction network was used to identify the core therapeutic targets of QLTMP against CIP, analyze biological function and pathway enrichment based on the identified core therapeutic targets, and evaluate the therapeutic effect of QLTMP in a model of CIP induced by vinorelbine to confirm the reliability of the network pharmacological analysis.\u0000One hundred and sixty-five bioactive compounds of QLTMP matched the screening criteria and identified 19 core therapeutic targets of QLTMP against CIP. Biofunctional analysis showed that the therapeutic effect of QLTMP on CIP was mainly related to the inhibition of inflammation, while pathway enrichment analysis showed that the TNF signaling pathway was involved in the inflammatory process.</p><p><strong>Results: </strong>Experimental confirmation in a mice model showed that QLTMP exerts anti-inflammatory effects through modulation of the PI3K/AKT/TNF signaling pathway, a discovery consistent with the network pharmacological analysis.</p><p><strong>Discussion and conclusion: </strong>The network pharmacological analysis of the anti-inflammatory mechanism of QLTMP on CIP and its exploration of in vivo experiments provide a theoretical basis for the design of agents that can mitigate or cure CIP</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":" ","pages":""},"PeriodicalIF":16.4,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40410962","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}
Pub Date : 2025-02-07DOI: 10.1021/acs.accounts.4c0079410.1021/acs.accounts.4c00794
Zihao Zhao, Anze Li and Wang Zhang Yuan*,
<p >Nonconventional luminophores, characterized by the absence of extended (hetero)aromatic building blocks and alternating single–double/triple bonds, are composed primarily of electron-rich moieties, such as heteroatoms, double bonds, aliphatic amines, carbonyls, hydroxyls, cyano groups, amides, and their grouped functionalities. These unique structural features, coupled with their intriguing luminescent properties, have garnered significant interest for both fundamental research and promising applications, thus enabling widespread exploration. They generally benefit from abundant resources, simple synthesis, outstanding biocompatibility, and excellent photostability, empowering their potential applications in bioimaging, data storage and encryption, anticounterfeiting, bio- and chemosensing, etc. However, their research is preliminary, and the luminescence mechanisms remain elusive. For diverse systems, proposed conjectures, including tertiary amine oxidation, proton transfer, impurities, hydrogen bonding, and peptide bond electron delocalization, lack consistent correlation and universality, with some being subsequently invalidated. This lack of a unifying framework has hampered the development of effective guidelines for molecular design and photoluminescence (PL) regulation. To address these issues, a clustering-triggered emission (CTE) mechanism, focusing on the electron–molecule–aggregate multilevel structure–activity relationships, has been proposed. Specifically, it identifies the “clustered chromophores” of electron-rich moieties as emissive species. The CTE mechanism not only elucidates the emission behaviors of diverse nonconventional luminophores but also guides the PL regulation and further development of novel multifunctional luminescent materials.</p><p >This Account begins with a concise introduction to the proposed CTE mechanism, highlighting the significance of electron delocalization (through-space conjugation) within the “clustered chromophores” of electron-rich groups. It then delves into insights gained from various nonconventional luminescent systems, identifying three core components of the CTE mechanism: electron-rich moieties, their clustering, and the conformational rigidity of the resulting clusters. The CTE mechanism proves to be rational and universally applicable, encompassing natural products, (macro)biomolecules, and synthetic compounds and extending from singlet fluorescence to triplet phosphorescence. By strategically coordinating these elements, it is feasible to modulate intra/intermolecular interactions, through-space conjugation, and spin–orbit coupling within the clusters, thus enabling effective PL regulation and achieving red/near-infrared (NIR) room-temperature phosphorescence (RTP) in these systems through both internal/chemical (e.g., incorporating additional bridging units and heavy atoms) and external/physical (e.g., pressurization, conformation adjustments) methods. Furthermore, we investigate t
{"title":"Nonconventional Luminophores: Emission Mechanism, Regulation, and Applications","authors":"Zihao Zhao, Anze Li and Wang Zhang Yuan*, ","doi":"10.1021/acs.accounts.4c0079410.1021/acs.accounts.4c00794","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00794https://doi.org/10.1021/acs.accounts.4c00794","url":null,"abstract":"<p >Nonconventional luminophores, characterized by the absence of extended (hetero)aromatic building blocks and alternating single–double/triple bonds, are composed primarily of electron-rich moieties, such as heteroatoms, double bonds, aliphatic amines, carbonyls, hydroxyls, cyano groups, amides, and their grouped functionalities. These unique structural features, coupled with their intriguing luminescent properties, have garnered significant interest for both fundamental research and promising applications, thus enabling widespread exploration. They generally benefit from abundant resources, simple synthesis, outstanding biocompatibility, and excellent photostability, empowering their potential applications in bioimaging, data storage and encryption, anticounterfeiting, bio- and chemosensing, etc. However, their research is preliminary, and the luminescence mechanisms remain elusive. For diverse systems, proposed conjectures, including tertiary amine oxidation, proton transfer, impurities, hydrogen bonding, and peptide bond electron delocalization, lack consistent correlation and universality, with some being subsequently invalidated. This lack of a unifying framework has hampered the development of effective guidelines for molecular design and photoluminescence (PL) regulation. To address these issues, a clustering-triggered emission (CTE) mechanism, focusing on the electron–molecule–aggregate multilevel structure–activity relationships, has been proposed. Specifically, it identifies the “clustered chromophores” of electron-rich moieties as emissive species. The CTE mechanism not only elucidates the emission behaviors of diverse nonconventional luminophores but also guides the PL regulation and further development of novel multifunctional luminescent materials.</p><p >This Account begins with a concise introduction to the proposed CTE mechanism, highlighting the significance of electron delocalization (through-space conjugation) within the “clustered chromophores” of electron-rich groups. It then delves into insights gained from various nonconventional luminescent systems, identifying three core components of the CTE mechanism: electron-rich moieties, their clustering, and the conformational rigidity of the resulting clusters. The CTE mechanism proves to be rational and universally applicable, encompassing natural products, (macro)biomolecules, and synthetic compounds and extending from singlet fluorescence to triplet phosphorescence. By strategically coordinating these elements, it is feasible to modulate intra/intermolecular interactions, through-space conjugation, and spin–orbit coupling within the clusters, thus enabling effective PL regulation and achieving red/near-infrared (NIR) room-temperature phosphorescence (RTP) in these systems through both internal/chemical (e.g., incorporating additional bridging units and heavy atoms) and external/physical (e.g., pressurization, conformation adjustments) methods. Furthermore, we investigate t","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 4","pages":"612–624 612–624"},"PeriodicalIF":16.4,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143428307","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}
Pub Date : 2025-02-06DOI: 10.1021/acs.accounts.4c0076410.1021/acs.accounts.4c00764
Hui Zeng, Kang Liang, Lei Jiang, Dongyuan Zhao and Biao Kong*,
<p >Precise and rapid detection of key biomolecules is crucial for early clinical diagnosis. These critical biomolecules and biomarkers are typically present at low concentrations within complex environments, presenting significant challenges for their accurate and reliable detection. Nowadays, electrochemical sensors based on nanochannel membranes have attracted significant attention due to their high sensitivity, simplicity, rapid response, and label-free point-of-care detection capabilities. The confined arena provided by the nanochannels for target recognition and interactions facilitates detection and signal amplification, leading to enhanced detection performance. The nanochannel membranes also can act as filters to repel the interferents and enable target detection in more complex environments. Thus, sensors based on nanochannel membranes are considered promising platforms for biosensing applications. However, challenges such as uncontrollable structures and unstable performance in some materials limit their applications and theoretical advancements. To investigate the relationship between architecture and sensing performance and to achieve reliable and efficient performance, it is essential to construct sensors with precise nanostructures possessing stable properties. With the development of nanomaterials technology, mesoporous nanochannel membranes with robust, controllable, and ordered mesostructures, along with tunable surface properties and tailored ion transport dynamics, have emerged as promising candidates for achieving reliable and efficient biosensing performance. Additionally, investigating the sensing mechanisms and key influencing factors will provide valuable insights into optimizing sensor architecture and enhancing the efficiency and reliability of biosensing technologies. In this Account, we highlight substantial advancements in mesoporous nanochannel membranes, which are mainly based on the research work published by our group. In the first section, we explore the underlying mechanisms of the sensing processes, including the solid–liquid interfacial interactions and nanoconfinement effects (i.e., electrostatic interactions, hydrophilic/hydrophobic interactions, and steric hindrance effects). We also delve into the key parameters including geometry, materials, recognition elements, and external factors related to mesoporous nanochannel membranes and their impacts on sensing mechanisms and performance. In particular, we point out that mesoporous nanochannel membranes with three-dimensional interconnected networks can facilitate ion penetration and lead to an increased number of binding sites, contributing to high sensitivity. Additionally, composite or multilevel mesoporous nanochannel membranes, particularly when integrated with external stimuli such as pH, light, and heat, can introduce unexpected properties, enhancing the sensing performance. These understandings provide valuable insights into the fundamental principles
{"title":"Electrochemical Sensing Mechanisms and Interfacial Design Strategies of Mesoporous Nanochannel Membranes in Biosensing Applications","authors":"Hui Zeng, Kang Liang, Lei Jiang, Dongyuan Zhao and Biao Kong*, ","doi":"10.1021/acs.accounts.4c0076410.1021/acs.accounts.4c00764","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00764https://doi.org/10.1021/acs.accounts.4c00764","url":null,"abstract":"<p >Precise and rapid detection of key biomolecules is crucial for early clinical diagnosis. These critical biomolecules and biomarkers are typically present at low concentrations within complex environments, presenting significant challenges for their accurate and reliable detection. Nowadays, electrochemical sensors based on nanochannel membranes have attracted significant attention due to their high sensitivity, simplicity, rapid response, and label-free point-of-care detection capabilities. The confined arena provided by the nanochannels for target recognition and interactions facilitates detection and signal amplification, leading to enhanced detection performance. The nanochannel membranes also can act as filters to repel the interferents and enable target detection in more complex environments. Thus, sensors based on nanochannel membranes are considered promising platforms for biosensing applications. However, challenges such as uncontrollable structures and unstable performance in some materials limit their applications and theoretical advancements. To investigate the relationship between architecture and sensing performance and to achieve reliable and efficient performance, it is essential to construct sensors with precise nanostructures possessing stable properties. With the development of nanomaterials technology, mesoporous nanochannel membranes with robust, controllable, and ordered mesostructures, along with tunable surface properties and tailored ion transport dynamics, have emerged as promising candidates for achieving reliable and efficient biosensing performance. Additionally, investigating the sensing mechanisms and key influencing factors will provide valuable insights into optimizing sensor architecture and enhancing the efficiency and reliability of biosensing technologies. In this Account, we highlight substantial advancements in mesoporous nanochannel membranes, which are mainly based on the research work published by our group. In the first section, we explore the underlying mechanisms of the sensing processes, including the solid–liquid interfacial interactions and nanoconfinement effects (i.e., electrostatic interactions, hydrophilic/hydrophobic interactions, and steric hindrance effects). We also delve into the key parameters including geometry, materials, recognition elements, and external factors related to mesoporous nanochannel membranes and their impacts on sensing mechanisms and performance. In particular, we point out that mesoporous nanochannel membranes with three-dimensional interconnected networks can facilitate ion penetration and lead to an increased number of binding sites, contributing to high sensitivity. Additionally, composite or multilevel mesoporous nanochannel membranes, particularly when integrated with external stimuli such as pH, light, and heat, can introduce unexpected properties, enhancing the sensing performance. These understandings provide valuable insights into the fundamental principles","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 5","pages":"732–745 732–745"},"PeriodicalIF":16.4,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143533987","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}
Pub Date : 2025-02-05DOI: 10.1021/acs.accounts.4c0064410.1021/acs.accounts.4c00644
Shuizhong Wang, Xiancheng Li, Rumin Ma and Guoyong Song*,
<p >Lignin, a major component of lignocellulosic biomass, accounts for nearly 30% of organic carbon on Earth, making it the most abundant renewable source of aromatic carbon. The valorization of lignin beyond low-value heat and power has been one of the foremost challenges for a long time. On the other hand, aromatic compounds, constituting a substantial segment of the chemical industry and projected to reach a market value of $382 billion by 2030, are predominantly derived from fossil resources, contributing to increased CO<sub>2</sub> emissions. Integrating lignin into the aromatic chemical supply chain will offer a promising strategy to reduce the carbon footprint and boost the economic viability of biorefineries. Thus, depolymerizing lignin biopolymers into aromatic chemicals suitable for downstream processing is an important starting point for its valorization. However, owing to lignin’s complexity and heterogeneity, achieving efficient and selective depolymerization that yields desirable, isolable aromatic monomers remains a significant scientific challenge.</p><p >The structure of lignins varies significantly in terms of subunits and linkages across plant species, leading to considerable differences in their reactivity, in the distribution of resulting monomers, and in their subsequent utilization. In this context, this Account highlights our recent studies on the catalytic hydrogenolysis of lignin into serviceable products for preparing valuable materials, fuels, and chemicals. First, we designed a series of catalytic systems for lignin hydrogenolysis specifically tailored to the structural features of lignin from wood, grass, and certain seed coats. To reduce reliance on expensive commercial catalysts like Pd/C, Ru/C, and Pt/C, we advanced heterogeneous metal catalysts by shifting from high-loaded nanostructured metals to low-loaded, atomically dispersed metals and replacing precious metals with nonprecious alternatives. This approach significantly reduces the cost of catalysts, enhances their atomic economy, and improves their catalytic activity and/or selectivity. Then, using the developed catalysts, phenolic monomers tethering a distinct side chain were selectively generated from the hydrogenolysis of lignin (from various plants), achieving yields close to the theoretical maximum. The high selectivity allowed the separation and purification of monomeric phenols from lignin reaction mixtures readily. To gain deeper insights into the cleavage of lignin C–O bonds, we designed deuterium-incorporated β-O-4 mimics (dimers and one polymer) for a mechanistic study, which excluded the pathways involving the loss of linkage protons and led to the proposal of a concerted hydrogenolysis process for β-O-4 cleavage. Finally, to enable the utilization of depolymerized lignin phenolic monomers, unconventional feedstocks in the current chemical industry, we developed a series of methods to transform them into valuable bioactive molecules, functional
{"title":"Catalytic Hydrogenolysis of Lignin into Serviceable Products","authors":"Shuizhong Wang, Xiancheng Li, Rumin Ma and Guoyong Song*, ","doi":"10.1021/acs.accounts.4c0064410.1021/acs.accounts.4c00644","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00644https://doi.org/10.1021/acs.accounts.4c00644","url":null,"abstract":"<p >Lignin, a major component of lignocellulosic biomass, accounts for nearly 30% of organic carbon on Earth, making it the most abundant renewable source of aromatic carbon. The valorization of lignin beyond low-value heat and power has been one of the foremost challenges for a long time. On the other hand, aromatic compounds, constituting a substantial segment of the chemical industry and projected to reach a market value of $382 billion by 2030, are predominantly derived from fossil resources, contributing to increased CO<sub>2</sub> emissions. Integrating lignin into the aromatic chemical supply chain will offer a promising strategy to reduce the carbon footprint and boost the economic viability of biorefineries. Thus, depolymerizing lignin biopolymers into aromatic chemicals suitable for downstream processing is an important starting point for its valorization. However, owing to lignin’s complexity and heterogeneity, achieving efficient and selective depolymerization that yields desirable, isolable aromatic monomers remains a significant scientific challenge.</p><p >The structure of lignins varies significantly in terms of subunits and linkages across plant species, leading to considerable differences in their reactivity, in the distribution of resulting monomers, and in their subsequent utilization. In this context, this Account highlights our recent studies on the catalytic hydrogenolysis of lignin into serviceable products for preparing valuable materials, fuels, and chemicals. First, we designed a series of catalytic systems for lignin hydrogenolysis specifically tailored to the structural features of lignin from wood, grass, and certain seed coats. To reduce reliance on expensive commercial catalysts like Pd/C, Ru/C, and Pt/C, we advanced heterogeneous metal catalysts by shifting from high-loaded nanostructured metals to low-loaded, atomically dispersed metals and replacing precious metals with nonprecious alternatives. This approach significantly reduces the cost of catalysts, enhances their atomic economy, and improves their catalytic activity and/or selectivity. Then, using the developed catalysts, phenolic monomers tethering a distinct side chain were selectively generated from the hydrogenolysis of lignin (from various plants), achieving yields close to the theoretical maximum. The high selectivity allowed the separation and purification of monomeric phenols from lignin reaction mixtures readily. To gain deeper insights into the cleavage of lignin C–O bonds, we designed deuterium-incorporated β-O-4 mimics (dimers and one polymer) for a mechanistic study, which excluded the pathways involving the loss of linkage protons and led to the proposal of a concerted hydrogenolysis process for β-O-4 cleavage. Finally, to enable the utilization of depolymerized lignin phenolic monomers, unconventional feedstocks in the current chemical industry, we developed a series of methods to transform them into valuable bioactive molecules, functional","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 4","pages":"529–542 529–542"},"PeriodicalIF":16.4,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143428321","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}
Biomarkers play a vital role in the regulation of life processes, especially in predicting the occurrence and development of diseases. For the early diagnosis and precise treatment of diseases, it has become necessary and significant to detect biomarkers with sensitivity, accuracy, simplicity, convenience, and even visualization. Fluorescent-probe-based techniques have been recognized as one of the most powerful tools for the sensitive detection and real time imaging of biomarkers in biological samples. However, traditional optical probes, mainly including the visible probes (400–700 nm) and the near-infrared I (NIR-I, 700–900 nm) probes, suffer from low sensitivity, poor resolution, strong absorption and scattering, and high background fluorescence, which hinder effective monitoring of biomarkers.
Fortunately, the past decade has witnessed a remarkable evolution in the application fields of near-infrared II (NIR-II, 900–1700 nm) fluorescence, driven by its exceptional optical characteristics and the advancement of imaging technologies. Leveraging the superior penetration capabilities, negligible autofluorescence, and extended fluorescence emission wavelengths, NIR-II fluorescent probes significantly enhance the signal-to-noise ratio (SNR) of in vitro detection (IVD) and the temporal resolution of in vivo imaging. Our team has been committed to the design strategy, controlled synthesis, luminous mechanisms, and biomedical applications of NIR-II fluorescent probes. In this Account, we present the representative works in recent years from our group in the field of NIR-II fluorescent probes for analytical applications, ranging from in vitro detection of biomarkers to in vivo imaging monitoring of different biomarkers and various diseases, which also will further provide a general overview of analytical applications of NIR-II fluorescence probes. First, the in vitro analytical applications of NIR-II fluorescent probes are fully summarized, including tumor marker detection, virus and bacteria analysis, cell testing, and small-molecule sensing. Second, the in vivo imaging monitoring applications of NIR-II fluorescent probes are adequately discussed, including ROS detection, gas monitoring, pH sensing, small-molecule testing, receptor analysis, and the imaging diagnosis of some serious diseases. Finally, we further outline the application advantages of NIR-II fluorescent probes in analytical fields and also discuss in detail some challenges as well as their future development. There is a reasonable prospect that the in vitro detection technology and the in vivo imaging monitoring technology based on NIR-II fluorescent probes will exhibit great development potential in biomedical research and clinical disease diagnosis. We hope that this Account can expand their reach into an even broader spectrum of fields, further enhancing their impact on scientific discovery and medical practice.
{"title":"Near-Infrared-II Fluorescent Probes for Analytical Applications: From In Vitro Detection to In Vivo Imaging Monitoring","authors":"Sha Liu, Wenhong Dong, Hui-quan Gao*, Zhaorui Song* and Zhen Cheng*, ","doi":"10.1021/acs.accounts.4c0067110.1021/acs.accounts.4c00671","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00671https://doi.org/10.1021/acs.accounts.4c00671","url":null,"abstract":"<p >Biomarkers play a vital role in the regulation of life processes, especially in predicting the occurrence and development of diseases. For the early diagnosis and precise treatment of diseases, it has become necessary and significant to detect biomarkers with sensitivity, accuracy, simplicity, convenience, and even visualization. Fluorescent-probe-based techniques have been recognized as one of the most powerful tools for the sensitive detection and real time imaging of biomarkers in biological samples. However, traditional optical probes, mainly including the visible probes (400–700 nm) and the near-infrared I (NIR-I, 700–900 nm) probes, suffer from low sensitivity, poor resolution, strong absorption and scattering, and high background fluorescence, which hinder effective monitoring of biomarkers.</p><p >Fortunately, the past decade has witnessed a remarkable evolution in the application fields of near-infrared II (NIR-II, 900–1700 nm) fluorescence, driven by its exceptional optical characteristics and the advancement of imaging technologies. Leveraging the superior penetration capabilities, negligible autofluorescence, and extended fluorescence emission wavelengths, NIR-II fluorescent probes significantly enhance the signal-to-noise ratio (SNR) of <i>in vitro</i> detection (IVD) and the temporal resolution of <i>in vivo</i> imaging. Our team has been committed to the design strategy, controlled synthesis, luminous mechanisms, and biomedical applications of NIR-II fluorescent probes. In this Account, we present the representative works in recent years from our group in the field of NIR-II fluorescent probes for analytical applications, ranging from <i>in vitro</i> detection of biomarkers to <i>in vivo</i> imaging monitoring of different biomarkers and various diseases, which also will further provide a general overview of analytical applications of NIR-II fluorescence probes. First, the <i>in vitro</i> analytical applications of NIR-II fluorescent probes are fully summarized, including tumor marker detection, virus and bacteria analysis, cell testing, and small-molecule sensing. Second, the <i>in vivo</i> imaging monitoring applications of NIR-II fluorescent probes are adequately discussed, including ROS detection, gas monitoring, pH sensing, small-molecule testing, receptor analysis, and the imaging diagnosis of some serious diseases. Finally, we further outline the application advantages of NIR-II fluorescent probes in analytical fields and also discuss in detail some challenges as well as their future development. There is a reasonable prospect that the <i>in vitro</i> detection technology and the <i>in vivo</i> imaging monitoring technology based on NIR-II fluorescent probes will exhibit great development potential in biomedical research and clinical disease diagnosis. We hope that this Account can expand their reach into an even broader spectrum of fields, further enhancing their impact on scientific discovery and medical practice.</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 4","pages":"543–554 543–554"},"PeriodicalIF":16.4,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143428345","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}
Pub Date : 2025-02-05DOI: 10.1021/acs.accounts.4c0054610.1021/acs.accounts.4c00546
Kavita Matange, Eliav Marland, Moran Frenkel-Pinter and Loren Dean Williams*,
<p >A holistic description of biopolymers and their evolutionary origins will contribute to our understanding of biochemistry, biology, the origins of life, and signatures of life outside our planet. While biopolymer sequences evolve through known Darwinian processes, the origins of the backbones of polypeptides, polynucleotides, and polyglycans are less certain. We frame this topic through two questions: (i) Do the characteristics of biopolymer backbones indicate evolutionary origins? (ii) Are there reasonable mechanistic models of such pre-Darwinian evolutionary processes? To address these questions, we have established criteria to distinguish chemical species produced by evolutionary mechanisms from those formed by nonevolutionary physical, chemical, or geological processes. We compile and evaluate properties shared by all biopolymer backbones rather than isolating a single type. Polypeptide, polynucleotide, and polyglycan backbones are kinetically trapped and thermodynamically unstable in aqueous media. Each biopolymer forms a variety of elaborate assemblies with diverse functions, a phenomenon we call polyfunction. Each backbone changes structure and function upon subtle chemical changes such as the reduction of ribose or a change in the linkage site or stereochemistry of polymerized glucose, a phenomenon we call function-switching. Biopolymers display homo- and heterocomplementarity, enabling atomic-level control of structure and function. Biopolymer backbones access recalcitrant states, where assembly modulates kinetics and thermodynamics of hydrolysis. Biopolymers are emergent; the properties of biological building blocks change significantly upon polymerization. In cells, biopolymers compose mutualistic networks; a cell is an Amazon Jungle of molecules. We conclude that biopolymer backbones exhibit hallmarks of evolution. Neither chemical, physical, nor geological processes can produce molecules consistent with observations. We are faced with the paradox that Darwinian evolution relies on evolved backbones but cannot alter biopolymer backbones. This Darwinian constraint is underlined by the observation that across the tree of life, ribosomes are everywhere and always have been composed of RNA and protein. Our data suggest that chemical species on the Hadean Earth underwent non-Darwinian coevolution driven in part by hydrolytic stress, ultimately leading to biopolymer backbones. We argue that highly evolved biopolymer backbones facilitated a seamless transition from chemical to Darwinian evolution. This model challenges convention, where backbones are products of direct prebiotic synthesis. In conventional models, biopolymer backbones retain vestiges of prebiotic chemistry. Our findings, however, align with models where chemical species underwent iterative and recursive sculpting, selection, and exaptation. This model supports Orgel’s “gloomy” prediction that modern biochemistry has discarded vestiges of prebiotic chemistry. But there is
{"title":"Biological Polymers: Evolution, Function, and Significance","authors":"Kavita Matange, Eliav Marland, Moran Frenkel-Pinter and Loren Dean Williams*, ","doi":"10.1021/acs.accounts.4c0054610.1021/acs.accounts.4c00546","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00546https://doi.org/10.1021/acs.accounts.4c00546","url":null,"abstract":"<p >A holistic description of biopolymers and their evolutionary origins will contribute to our understanding of biochemistry, biology, the origins of life, and signatures of life outside our planet. While biopolymer sequences evolve through known Darwinian processes, the origins of the backbones of polypeptides, polynucleotides, and polyglycans are less certain. We frame this topic through two questions: (i) Do the characteristics of biopolymer backbones indicate evolutionary origins? (ii) Are there reasonable mechanistic models of such pre-Darwinian evolutionary processes? To address these questions, we have established criteria to distinguish chemical species produced by evolutionary mechanisms from those formed by nonevolutionary physical, chemical, or geological processes. We compile and evaluate properties shared by all biopolymer backbones rather than isolating a single type. Polypeptide, polynucleotide, and polyglycan backbones are kinetically trapped and thermodynamically unstable in aqueous media. Each biopolymer forms a variety of elaborate assemblies with diverse functions, a phenomenon we call polyfunction. Each backbone changes structure and function upon subtle chemical changes such as the reduction of ribose or a change in the linkage site or stereochemistry of polymerized glucose, a phenomenon we call function-switching. Biopolymers display homo- and heterocomplementarity, enabling atomic-level control of structure and function. Biopolymer backbones access recalcitrant states, where assembly modulates kinetics and thermodynamics of hydrolysis. Biopolymers are emergent; the properties of biological building blocks change significantly upon polymerization. In cells, biopolymers compose mutualistic networks; a cell is an Amazon Jungle of molecules. We conclude that biopolymer backbones exhibit hallmarks of evolution. Neither chemical, physical, nor geological processes can produce molecules consistent with observations. We are faced with the paradox that Darwinian evolution relies on evolved backbones but cannot alter biopolymer backbones. This Darwinian constraint is underlined by the observation that across the tree of life, ribosomes are everywhere and always have been composed of RNA and protein. Our data suggest that chemical species on the Hadean Earth underwent non-Darwinian coevolution driven in part by hydrolytic stress, ultimately leading to biopolymer backbones. We argue that highly evolved biopolymer backbones facilitated a seamless transition from chemical to Darwinian evolution. This model challenges convention, where backbones are products of direct prebiotic synthesis. In conventional models, biopolymer backbones retain vestiges of prebiotic chemistry. Our findings, however, align with models where chemical species underwent iterative and recursive sculpting, selection, and exaptation. This model supports Orgel’s “gloomy” prediction that modern biochemistry has discarded vestiges of prebiotic chemistry. But there is ","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 5","pages":"659–672 659–672"},"PeriodicalIF":16.4,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acs.accounts.4c00546","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143533986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-04DOI: 10.1021/acs.accounts.4c0083510.1021/acs.accounts.4c00835
Thomas Heine*, Mircea Dinca and Guangshan Zhou,
{"title":"Physical Phenomena in Porous Frameworks","authors":"Thomas Heine*, Mircea Dinca and Guangshan Zhou, ","doi":"10.1021/acs.accounts.4c0083510.1021/acs.accounts.4c00835","DOIUrl":"https://doi.org/10.1021/acs.accounts.4c00835https://doi.org/10.1021/acs.accounts.4c00835","url":null,"abstract":"","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":"58 3","pages":"327–329 327–329"},"PeriodicalIF":16.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143087934","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}
Pub Date : 2025-02-04Epub Date: 2025-01-27DOI: 10.1021/acs.accounts.4c00631
Christina M Zeng, Julien A Panetier
<p><p>ConspectusIn the search for efficient and selective electrocatalysts capable of converting greenhouse gases to value-added products, enzymes found in naturally existing bacteria provide the basis for most approaches toward electrocatalyst design. Ni,Fe-carbon monoxide dehydrogenase (Ni,Fe-CODH) is one such enzyme, with a nickel-iron-sulfur cluster named the C-cluster, where CO<sub>2</sub> binds and is converted to CO at high rates near the thermodynamic potential. In this Account, we divide the enzyme's catalytic contributions into three categories based on location and function. We also discuss how computational techniques provide crucial insight into implementing these findings in homogeneous CO<sub>2</sub> reduction electrocatalysis design principles. The CO<sub>2</sub> binding sites (e.g., Ni and "unique" Fe ion) along with the ligands that support it (e.g., iron-sulfur cluster) form the primary coordination sphere. This is replicated in molecular electrocatalysts via the metal center and ligand framework where the substrate binds. This coordination sphere has a direct impact on the electronic configuration of the catalyst. By computationally modeling a series of Ni and Co complexes with bipyridyl-<i>N</i>-heterocyclic carbene ligand frameworks of varying degrees of planarity, we were able to closely examine how the primary coordination sphere controls the product distribution between CO and H<sub>2</sub> for these catalysts. The secondary coordination sphere (SCS) of Ni,Fe-CODH contains residues proximal to the active site pocket that provide hydrogen-bonding stabilizations necessary for the reaction to proceed. Enhancing the SCS when synthesizing new catalysts involves substituting functional groups onto the ligand for direct interaction with the substrate. To analyze the endless possible substitutions, computational techniques are ideal for deciphering the intricacies of substituent effects, as we demonstrated with an array of imidazolium-functionalized Mn and Re bipyridyl tricarbonyl complexes. By examining how the electrostatic interactions between the ligand, substrate, and proton source lowered activation energy barriers, we determined how best to pinpoint the SCS additions. The outer coordination sphere comprises the remaining parts of Ni,Fe-CODH, such as the elaborate protein matrix, solvent interactions, and remote metalloclusters. The challenge in elucidating and replicating the role of the vast protein matrix has understandably led to a localized focus on the primary and secondary coordination spheres. However, certain portions of Ni,Fe-CODH's expansive protein scaffold are suggested to be catalytically relevant despite considerable distance from the active site. Closer studies of these relatively overlooked areas of nature's exceptionally proficient catalysts may be crucial to continually improve upon electrocatalysis protocols. Mechanistic analysis of cobalt phthalocyanines (CoPc) immobilized onto carbon nanotubes (CoPc/CN
{"title":"Computational Modeling of Electrocatalysts for CO<sub>2</sub> Reduction: Probing the Role of Primary, Secondary, and Outer Coordination Spheres.","authors":"Christina M Zeng, Julien A Panetier","doi":"10.1021/acs.accounts.4c00631","DOIUrl":"10.1021/acs.accounts.4c00631","url":null,"abstract":"<p><p>ConspectusIn the search for efficient and selective electrocatalysts capable of converting greenhouse gases to value-added products, enzymes found in naturally existing bacteria provide the basis for most approaches toward electrocatalyst design. Ni,Fe-carbon monoxide dehydrogenase (Ni,Fe-CODH) is one such enzyme, with a nickel-iron-sulfur cluster named the C-cluster, where CO<sub>2</sub> binds and is converted to CO at high rates near the thermodynamic potential. In this Account, we divide the enzyme's catalytic contributions into three categories based on location and function. We also discuss how computational techniques provide crucial insight into implementing these findings in homogeneous CO<sub>2</sub> reduction electrocatalysis design principles. The CO<sub>2</sub> binding sites (e.g., Ni and \"unique\" Fe ion) along with the ligands that support it (e.g., iron-sulfur cluster) form the primary coordination sphere. This is replicated in molecular electrocatalysts via the metal center and ligand framework where the substrate binds. This coordination sphere has a direct impact on the electronic configuration of the catalyst. By computationally modeling a series of Ni and Co complexes with bipyridyl-<i>N</i>-heterocyclic carbene ligand frameworks of varying degrees of planarity, we were able to closely examine how the primary coordination sphere controls the product distribution between CO and H<sub>2</sub> for these catalysts. The secondary coordination sphere (SCS) of Ni,Fe-CODH contains residues proximal to the active site pocket that provide hydrogen-bonding stabilizations necessary for the reaction to proceed. Enhancing the SCS when synthesizing new catalysts involves substituting functional groups onto the ligand for direct interaction with the substrate. To analyze the endless possible substitutions, computational techniques are ideal for deciphering the intricacies of substituent effects, as we demonstrated with an array of imidazolium-functionalized Mn and Re bipyridyl tricarbonyl complexes. By examining how the electrostatic interactions between the ligand, substrate, and proton source lowered activation energy barriers, we determined how best to pinpoint the SCS additions. The outer coordination sphere comprises the remaining parts of Ni,Fe-CODH, such as the elaborate protein matrix, solvent interactions, and remote metalloclusters. The challenge in elucidating and replicating the role of the vast protein matrix has understandably led to a localized focus on the primary and secondary coordination spheres. However, certain portions of Ni,Fe-CODH's expansive protein scaffold are suggested to be catalytically relevant despite considerable distance from the active site. Closer studies of these relatively overlooked areas of nature's exceptionally proficient catalysts may be crucial to continually improve upon electrocatalysis protocols. Mechanistic analysis of cobalt phthalocyanines (CoPc) immobilized onto carbon nanotubes (CoPc/CN","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":" ","pages":"342-353"},"PeriodicalIF":16.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143044845","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}
Pub Date : 2025-02-04Epub Date: 2025-01-22DOI: 10.1021/acs.accounts.4c00727
Trevor W Hayton, Jochen Autschbach
<p><p>ConspectusUnderstanding f element-ligand covalency is at the center of efforts to design new separations schemes for spent nuclear fuel, and is therefore of signficant fundamental and practical importance. Considerable effort has been invested into quantifying covalency in f element-ligand bonding. Over the past decade, numerous studies have employed a variety of techniques to study covalency, including XANES, EPR, and optical spectroscopies, as well as X-ray crystallography. NMR spectroscopy is another widely available spectroscopic technique that is complementary to these more established methods; however, its use for measuring 4f/5f covalency is still in its infancy. This Account describes efforts in the authors' laboratories to develop and validate multinuclear NMR spectroscopy as a tool for studying metal-ligand covalency in the actinides and selected lanthanide complexes. Thus far, we have quantified M-L covalency for a variety of ligand types, including chalcogenides, carbenes, alkyls, acetylides, amides, and nitrides, and for a variety of isotopes, including <sup>13</sup>C, <sup>15</sup>N, <sup>77</sup>Se, and <sup>125</sup>Te. Using NMR spectroscopy to probe M-C and M-N covalency is particularly attractive because of the ready availability of the<sup>13</sup>C and <sup>15</sup>N isotopes (both <i>I</i> = 1/2), and also because these elements are found in some of the most important f element ligand classes, including alkyls, carbenes, polypyridines, amides, imidos, and nitrides.The covalency analysis is based on the chemical shift (δ) and corresponding nuclear shielding constant (σ) of the metal-bound nucleus. The diamagnetic (σ<sub>dia</sub>), paramagnetic (σ<sub>para</sub>), and spin-orbit contributions (σ<sub>SO</sub>) to σ can be obtained and analyzed by relativistic density functional theory (DFT). Of particular importance is σ<sub>SO</sub>, which arises from the combination of spin-orbit coupling, the magnetic field, and chemical bonding. Its magnitude correlates with the amount of ligand s-character and metal <i>n</i>f (and (<i>n</i>+1)d) character in the M-L bond. In practice, Δ<sub>SO</sub>, the total difference between calculated chemical shift for the ligand nucleus including vs excluding SO effects, provides a more convenient metric for analysis. For the examples discussed herein, Δ<sub>SO</sub> accounts primarily for σ<sub>SO</sub> in an f-element complex, but also includes minor SO effects on the other shielding mechanisms and (usually) minor SO effects on the reference shielding. Δ<sub>SO</sub> can be very large, as in the case of [U(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>6</sub>] (348 ppm), which is not surprising as the An-C bonds in this example exhibits a high degree of covalency (e.g., 20% 5f character). However, even small values of Δ<sub>SO</sub> can indicate profound bonding effects, as shown by our analysis of [La(C<sub>6</sub>Cl<sub>5</sub>)<sub>4</sub>]<sup>-</sup>. In this case, Δ<sub>SO</sub> is only 9 ppm,
{"title":"Using NMR Spectroscopy to Evaluate Metal-Ligand Bond Covalency for the f Elements.","authors":"Trevor W Hayton, Jochen Autschbach","doi":"10.1021/acs.accounts.4c00727","DOIUrl":"10.1021/acs.accounts.4c00727","url":null,"abstract":"<p><p>ConspectusUnderstanding f element-ligand covalency is at the center of efforts to design new separations schemes for spent nuclear fuel, and is therefore of signficant fundamental and practical importance. Considerable effort has been invested into quantifying covalency in f element-ligand bonding. Over the past decade, numerous studies have employed a variety of techniques to study covalency, including XANES, EPR, and optical spectroscopies, as well as X-ray crystallography. NMR spectroscopy is another widely available spectroscopic technique that is complementary to these more established methods; however, its use for measuring 4f/5f covalency is still in its infancy. This Account describes efforts in the authors' laboratories to develop and validate multinuclear NMR spectroscopy as a tool for studying metal-ligand covalency in the actinides and selected lanthanide complexes. Thus far, we have quantified M-L covalency for a variety of ligand types, including chalcogenides, carbenes, alkyls, acetylides, amides, and nitrides, and for a variety of isotopes, including <sup>13</sup>C, <sup>15</sup>N, <sup>77</sup>Se, and <sup>125</sup>Te. Using NMR spectroscopy to probe M-C and M-N covalency is particularly attractive because of the ready availability of the<sup>13</sup>C and <sup>15</sup>N isotopes (both <i>I</i> = 1/2), and also because these elements are found in some of the most important f element ligand classes, including alkyls, carbenes, polypyridines, amides, imidos, and nitrides.The covalency analysis is based on the chemical shift (δ) and corresponding nuclear shielding constant (σ) of the metal-bound nucleus. The diamagnetic (σ<sub>dia</sub>), paramagnetic (σ<sub>para</sub>), and spin-orbit contributions (σ<sub>SO</sub>) to σ can be obtained and analyzed by relativistic density functional theory (DFT). Of particular importance is σ<sub>SO</sub>, which arises from the combination of spin-orbit coupling, the magnetic field, and chemical bonding. Its magnitude correlates with the amount of ligand s-character and metal <i>n</i>f (and (<i>n</i>+1)d) character in the M-L bond. In practice, Δ<sub>SO</sub>, the total difference between calculated chemical shift for the ligand nucleus including vs excluding SO effects, provides a more convenient metric for analysis. For the examples discussed herein, Δ<sub>SO</sub> accounts primarily for σ<sub>SO</sub> in an f-element complex, but also includes minor SO effects on the other shielding mechanisms and (usually) minor SO effects on the reference shielding. Δ<sub>SO</sub> can be very large, as in the case of [U(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>6</sub>] (348 ppm), which is not surprising as the An-C bonds in this example exhibits a high degree of covalency (e.g., 20% 5f character). However, even small values of Δ<sub>SO</sub> can indicate profound bonding effects, as shown by our analysis of [La(C<sub>6</sub>Cl<sub>5</sub>)<sub>4</sub>]<sup>-</sup>. In this case, Δ<sub>SO</sub> is only 9 ppm, ","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":" ","pages":"488-498"},"PeriodicalIF":16.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142995956","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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