Pub Date : 2024-09-19DOI: 10.26434/chemrxiv-2024-35kds-v4
Henmei, Ni
The laws of classical mechanics are rebuilt in the frame of new thermodynamics. Heat is the sum of kinetic energy, system work, and system potential of gas, while force is the linear gradients of heat variation. Exporters and importers of force are evident in terms of exotherm and endotherm. Temperature and volume gradients create asymmetric forces driving rotation and spin (self-rotation). It verifies that force transfer doesn’t need a medium. As an outstanding achievement, a brief and general equation is derived to predict the equilibrium distance of molecular interaction: L_e=∛((3π^(α-1) M_A g)/(4N_A kT)), without using any assumption, such as van der Waals force and dispersion forces. In addition, the origins and attributes of repulsion and attraction are disclosed. Predicting results is applausive. For example, at 298 K, Le for N2, O2, and CH4 are 3.11, 3.11, and 3.68 Å, comparable to the data adopted in MD simulations of the literature. Furthermore, the relationship between electricity and mass is established. An electron is characterized as a particle with a large α dependent on the interaction distance. Two electrons are mutually attractive from a distance depending on temperature. The electromagnetic phenomena are integrated.
经典力学定律在新热力学的框架内得以重建。热量是气体的动能、系统功和系统势的总和，而力则是热量变化的线性梯度。力的输出者和输入者在放热和内热方面显而易见。温度梯度和体积梯度产生了驱动旋转和自旋（自转）的非对称力。它验证了力的传递不需要介质。作为一项杰出成就，我们推导出了一个简明的一般方程，用于预测分子相互作用的平衡距离：L_e=∛((3π^(α-1) M_A g)/(4N_A kT))，而无需使用任何假设，如范德华力和分散力。此外，还揭示了斥力和吸引力的起源和属性。预测结果令人称赞。例如，在 298 K 时，N2、O2 和 CH4 的 Le 分别为 3.11、3.11 和 3.68 Å，与文献中 MD 模拟所采用的数据相当。此外，还建立了电量与质量之间的关系。电子的特点是粒子的α很大，取决于相互作用距离。两个电子相互吸引的距离取决于温度。电磁现象是综合的。
{"title":"From new thermodynamics to classical mechanics","authors":"Henmei, Ni","doi":"10.26434/chemrxiv-2024-35kds-v4","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-35kds-v4","url":null,"abstract":"The laws of classical mechanics are rebuilt in the frame of new thermodynamics. Heat is the sum of kinetic energy, system work, and system potential of gas, while force is the linear gradients of heat variation. Exporters and importers of force are evident in terms of exotherm and endotherm. Temperature and volume gradients create asymmetric forces driving rotation and spin (self-rotation). It verifies that force transfer doesn’t need a medium. As an outstanding achievement, a brief and general equation is derived to predict the equilibrium distance of molecular interaction: L_e=∛((3π^(α-1) M_A g)/(4N_A kT)), without using any assumption, such as van der Waals force and dispersion forces. In addition, the origins and attributes of repulsion and attraction are disclosed. Predicting results is applausive. For example, at 298 K, Le for N2, O2, and CH4 are 3.11, 3.11, and 3.68 Å, comparable to the data adopted in MD simulations of the literature. Furthermore, the relationship between electricity and mass is established. An electron is characterized as a particle with a large α dependent on the interaction distance. Two electrons are mutually attractive from a distance depending on temperature. The electromagnetic phenomena are integrated.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.26434/chemrxiv-2024-ll505
Massimo, Bocus, Elias, Van Den Broeck, Xian, Wu, Mathias, Bal, Jeroen, Bomon, Louis, Vanduyfhuys, Bert F., Sels, Bert U. W., Maes, Veronique, Van Speybroeck
New lignocellulose biorefinery technologies that enable the conversion of lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In this study, we investigate the Brønsted acid-catalyzed O-demethylation of guaiacol in hot-pressurized water (HPW) as a model reaction for transforming lignin-derived phenolic substrates featuring ortho methoxy groups. We compare the effects of Brønsted mineral acid (HCl) and microporous solid acid (H-BEA zeolite) in water to elucidate the hydrolysis mechanism and the impact of zeolite microporosity on reaction rates. Operando molecular modeling combined with experimental kinetic studies reveals that, regardless of the catalyst type, O-demethylation follows a concerted, one-step O-activated SN2 mechanism. This mechanism involves a strong hydrogen bond between guaiacol and a hydronium ion as an ionic contact pair. Protons confined within the zeolite form more active undercoordinated hydronium ions, which are associated with lower enthalpic requirements and thus accelerate the hydrolysis. The molecular organization of solvent and reactants around the confined catalytic active site plays a crucial role in modulating the association of the reacting species. These proof-of-concept results demonstrate the significant influence of solvent (water) coordination on acid-catalyzed bimolecular reactions, such as hydrolysis, within confined spaces.
{"title":"Confined hot-pressurized water in Brønsted-acidic Beta zeolite speeds up the O-demethylation of guaiacol","authors":"Massimo, Bocus, Elias, Van Den Broeck, Xian, Wu, Mathias, Bal, Jeroen, Bomon, Louis, Vanduyfhuys, Bert F., Sels, Bert U. W., Maes, Veronique, Van Speybroeck","doi":"10.26434/chemrxiv-2024-ll505","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-ll505","url":null,"abstract":"New lignocellulose biorefinery technologies that enable the conversion of lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In this study, we investigate the Brønsted acid-catalyzed O-demethylation of guaiacol in hot-pressurized water (HPW) as a model reaction for transforming lignin-derived phenolic substrates featuring ortho methoxy groups. We compare the effects of Brønsted mineral acid (HCl) and microporous solid acid (H-BEA zeolite) in water to elucidate the hydrolysis mechanism and the impact of zeolite microporosity on reaction rates. Operando molecular modeling combined with experimental kinetic studies reveals that, regardless of the catalyst type, O-demethylation follows a concerted, one-step O-activated SN2 mechanism. This mechanism involves a strong hydrogen bond between guaiacol and a hydronium ion as an ionic contact pair. Protons confined within the zeolite form more active undercoordinated hydronium ions, which are associated with lower enthalpic requirements and thus accelerate the hydrolysis. The molecular organization of solvent and reactants around the confined catalytic active site plays a crucial role in modulating the association of the reacting species. These proof-of-concept results demonstrate the significant influence of solvent (water) coordination on acid-catalyzed bimolecular reactions, such as hydrolysis, within confined spaces.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dual catalytic reactions may be made more effective through an improved integration of the catalytic cycles achieved using bifunctional catalysts. Herein we describe new bifunctional photocatalysts consisting of a photoactive donor-acceptor cyanoarene unit linked to a bipyridine ligand moiety that can bind transition metals. The bifunctional photocatalysts were synthesized in 3-5 steps form commercially available compounds and fully characterized in terms of photophysical properties, which are strongly affected by the type of linkage used (C vs. O) to connect the cyanoarene core to the ligand. Catalytic tests carried out in the Nicatalyzed C-O cross-coupling of alcohols to aryl bromides promoted by visible light have shown that the bifunctional systems are more active than the corresponding ‘dual catalytic systems’ (i.e., not covalently bound), taking advantage of the proximity between the two catalytic moieties (Ni-complex and photocatalyst). The best bifunctional dyes were tested with several alcohols and aryl halides, giving good yields at low catalytic loading (0.5-2 mol%).
{"title":"Bifunctional photocatalysts display proximity-enhanced catalytic activity in metallaphotoredox C–O coupling","authors":"Luca, Pignataro, Luigi, Dolcini, Andrea, Solida, Daniele, Lavelli, Andrés Mauricio, Hidalgo-Núñez, Tommaso, Gandini, Matthieu, Fornara, Alessandro, Colella, Alberto, Bossi, Marta, Penconi, Daniele, Fiorito, Cesare, Gennari, Alberto, Dal Corso","doi":"10.26434/chemrxiv-2024-qgsl2","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-qgsl2","url":null,"abstract":"Dual catalytic reactions may be made more effective through an improved integration of the catalytic cycles achieved using bifunctional catalysts. Herein we describe new bifunctional photocatalysts consisting of a photoactive donor-acceptor cyanoarene unit linked to a bipyridine ligand moiety that can bind transition metals. The bifunctional photocatalysts were synthesized in 3-5 steps form commercially available compounds and fully characterized in terms of photophysical properties, which are strongly affected by the type of linkage used (C vs. O) to connect the cyanoarene core to the ligand. Catalytic tests carried out in the Nicatalyzed C-O cross-coupling of alcohols to aryl bromides promoted by visible light have shown that the bifunctional systems are more active than the corresponding ‘dual catalytic systems’ (i.e., not covalently bound), taking advantage of the proximity between the two catalytic moieties (Ni-complex and photocatalyst). The best bifunctional dyes were tested with several alcohols and aryl halides, giving good yields at low catalytic loading (0.5-2 mol%).","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.26434/chemrxiv-2024-xdl01
Vanessa J., Bukas, Alexandra M., Dudzinski, Elias, Diesen, Karsten, Reuter
Reaction mechanisms in heterogeneous electrocatalysis have been known to change through the local field that arises at the electrified metal/liquid interface. First-principles simulations specifically predict that such a field can significantly modify the surface binding of dipolar or polarizable intermediates along a catalytic reaction path. This dependence can then lead to a corresponding dependence upon applied potential even for so-called ‘chemical’ reaction steps that do not involve an explicit proton-coupled-electron-transfer such as, e.g., O2 adsorption during the oxygen reduction reaction (ORR). And yet, such effects are only now starting to be systematically explored at the atomic level. In this study, we directly compare the potential dependence of O2 adsorption as the first ORR step on Au(111) vs Pt(111). Using ab initio molecular dynamics and free energy sampling, we find that the strong dependence previously predicted at Au(111) is specifically lost at Pt(111). By decoupling the O2 potential response into contributions of different physical origin, we explain this contrast through the inherently different reactivity of the two metals. We finally discuss an indirect effect of potential through the surface coverage that can promote a dissociative-type mechanism at Pt(111) by breaking the O-O bond already during the first step of the ORR mechanism. Our results thus overall suggest a more complex mechanistic picture than hitherto anticipated; one where the local field may manifest in different, yet potentially equally important, ways over different systems.
{"title":"Oxygen Adsorption at the Electrochemical Metal/Water Interface: Au(111) vs Pt(111)","authors":"Vanessa J., Bukas, Alexandra M., Dudzinski, Elias, Diesen, Karsten, Reuter","doi":"10.26434/chemrxiv-2024-xdl01","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-xdl01","url":null,"abstract":"Reaction mechanisms in heterogeneous electrocatalysis have been known to change through the local field that arises at the electrified metal/liquid interface. First-principles simulations specifically predict that such a field can significantly modify the surface binding of dipolar or polarizable intermediates along a catalytic reaction path. This dependence can then lead to a corresponding dependence upon applied potential even for so-called ‘chemical’ reaction steps that do not involve an explicit proton-coupled-electron-transfer such as, e.g., O2 adsorption during the oxygen reduction reaction (ORR). And yet, such effects are only now starting to be systematically explored at the atomic level. In this study, we directly compare the potential dependence of O2 adsorption as the first ORR step on Au(111) vs Pt(111). Using ab initio molecular dynamics and free energy sampling, we find that the strong dependence previously predicted at Au(111) is specifically lost at Pt(111). By decoupling the O2 potential response into contributions of different physical origin, we explain this contrast through the inherently different reactivity of the two metals. We finally discuss an indirect effect of potential through the surface coverage that can promote a dissociative-type mechanism at Pt(111) by breaking the O-O bond already during the first step of the ORR mechanism. Our results thus overall suggest a more complex mechanistic picture than hitherto anticipated; one where the local field may manifest in different, yet potentially equally important, ways over different systems.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants of increasing concern due to their persistence and potential health impacts. New guidelines with exceedingly low detection limits necessitate the development of promising materials for preconcentration. Six different metal-organic frameworks were evaluated for their potential as dispersive solid-phase extraction (dSPE) sorbents for PFAS quantitation by quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS). UiO-66 demonstrated the highest combined average adsorption (87%) and recovery (85%) across 33 PFAS spiked in water at 2 ppb, and 75% recovery for 50 PFAS at 200 ppq. The developed dSPE workflow using UiO-66 resulted in limit of detections (LODs) as low as 4 ppq with average LODs of 108 ppq across 50 PFAS by testing at concentrations of 200 to 800 ppq. UiO-66 retained its crystalline structure post-PFAS adsorption, indicating stability for dSPE. Nearly 100% average recovery across all 50 PFAS was observed for UiO-66 using a 20 ppt spike, whereas ZIF-8 resulted in lower recovery. The efficacy of using UiO-66 as a dSPE material was assessed using six environmental water samples from different locations in Sydney, Australia, with all samples having quantifiable levels of PFAS. In water collected from Sydney Airport, 22 PFAS were detected above the limit of quantification (LOQ). Across all environmental water samples, a total of 25 PFAS were quantified above LOQs, with internal standard recoveries between 70-120%. In addition, the presence of multiply charged counterions decreased short-chained PFAS adsorption, while chloride had no impact. While polymeric resins have been used for screening ~50 PFAS with limits of detection ranging from 1 to 80 ppt, UiO-66 can be used to detect 50 PFAS at concentrations as low as 200 ppq. The high performance of UiO-66 in terms of recovery and detection limits underscores its potential for practical analytical applications in PFAS detection.
{"title":"Metal-Organic Frameworks for the Trace Multiplexed Quantitation of 50 PFAS by Liquid Chromatography Mass Spectrometry","authors":"William, Donald, Lisa, Hua, Marcello, Solomon, Deanna, D'Alessandro","doi":"10.26434/chemrxiv-2024-qkvkd","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-qkvkd","url":null,"abstract":"Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants of increasing concern due to their persistence and potential health impacts. New guidelines with exceedingly low detection limits necessitate the development of promising materials for preconcentration. Six different metal-organic frameworks were evaluated for their potential as dispersive solid-phase extraction (dSPE) sorbents for PFAS quantitation by quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS). UiO-66 demonstrated the highest combined average adsorption (87%) and recovery (85%) across 33 PFAS spiked in water at 2 ppb, and 75% recovery for 50 PFAS at 200 ppq. The developed dSPE workflow using UiO-66 resulted in limit of detections (LODs) as low as 4 ppq with average LODs of 108 ppq across 50 PFAS by testing at concentrations of 200 to 800 ppq. UiO-66 retained its crystalline structure post-PFAS adsorption, indicating stability for dSPE. Nearly 100% average recovery across all 50 PFAS was observed for UiO-66 using a 20 ppt spike, whereas ZIF-8 resulted in lower recovery. The efficacy of using UiO-66 as a dSPE material was assessed using six environmental water samples from different locations in Sydney, Australia, with all samples having quantifiable levels of PFAS. In water collected from Sydney Airport, 22 PFAS were detected above the limit of quantification (LOQ). Across all environmental water samples, a total of 25 PFAS were quantified above LOQs, with internal standard recoveries between 70-120%. In addition, the presence of multiply charged counterions decreased short-chained PFAS adsorption, while chloride had no impact. While polymeric resins have been used for screening ~50 PFAS with limits of detection ranging from 1 to 80 ppt, UiO-66 can be used to detect 50 PFAS at concentrations as low as 200 ppq. The high performance of UiO-66 in terms of recovery and detection limits underscores its potential for practical analytical applications in PFAS detection.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A series of base-free Pd-catalyzed borylation procedures are reported for a number of alkenyl carboxylates. High-throughput experimentation was used to discover and optimize these reactions using in situ generated catalyst systems. With lactone or lactam substrates, the resulting alkenyl pinacol boronates are hydrolytically unstable, undergoing protodeboronation under even mildly basic aqueous conditions. Optimization of this protodeboronation resulted in a mild, two-step reduction of the C–O bond, achieving net-deoxygenation while leaving the alkene intact. In contrast, use of an alternative tetraalkoxydiboron source – B2EPin2 – was successful in catalysis, and offered improved stability of the resulting organoboron species. This enables further reactivity, such as cross-coupling, while suppressing protodeboronation.
{"title":"Base-free palladium-catalyzed borylation of enol carboxylates and further reactivity toward deboronation and cross-coupling","authors":"David, Leitch, Gregory, Gaube, Douglas, Miller, Rowan, McCallum, Nahiane, Pipaon Fernandez","doi":"10.26434/chemrxiv-2024-5mlml","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-5mlml","url":null,"abstract":"A series of base-free Pd-catalyzed borylation procedures are reported for a number of alkenyl carboxylates. High-throughput experimentation was used to discover and optimize these reactions using in situ generated catalyst systems. With lactone or lactam substrates, the resulting alkenyl pinacol boronates are hydrolytically unstable, undergoing protodeboronation under even mildly basic aqueous conditions. Optimization of this protodeboronation resulted in a mild, two-step reduction of the C–O bond, achieving net-deoxygenation while leaving the alkene intact. In contrast, use of an alternative tetraalkoxydiboron source – B2EPin2 – was successful in catalysis, and offered improved stability of the resulting organoboron species. This enables further reactivity, such as cross-coupling, while suppressing protodeboronation.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the classic view, spin pairing occurs between two electrons in a chemical bond where the bonding interaction compensates for the penalty of electrostatic repulsion. It is a mystery whether spin pairing can occur between two non-bonded electrons within a molecular entity. Unveiling this elusive spin entanglement (i.e., pairing between two spatially segregated spins) at the molecular scale, is a long-standing challenge. Clar’s goblet proposed by Erich Clar in 1972, provides an ideal model to verify this unusual property. Here, we report the solution-phase synthesis of Clar’s goblet and experimental elucidation of its spin properties. Magnetic studies reveal that the two spins are spatially segregated with an average distance of 8.7 Å, and antiferromagnetically coupled in the ground state with an ES-T of –0.29 kcal/mol. Our results provide direct evidence of spin entanglement in the Clar’s goblet and may inspire the design of correlated molecular spins for quantum information technologies.
{"title":"Unveiling the mysterious hydrocarbon – Clar’s goblet","authors":"Jishan, Wu, Tianyu, Jiao, Cong-Hui, Wu, Yu-Shuang, Zhang, Xiaohe, Miao, Shaofei, Wu, Shang-Da, Jiang","doi":"10.26434/chemrxiv-2024-ks6xm","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-ks6xm","url":null,"abstract":"In the classic view, spin pairing occurs between two electrons in a chemical bond where the bonding interaction compensates for the penalty of electrostatic repulsion. It is a mystery whether spin pairing can occur between two non-bonded electrons within a molecular entity. Unveiling this elusive spin entanglement (i.e., pairing between two spatially segregated spins) at the molecular scale, is a long-standing challenge. Clar’s goblet proposed by Erich Clar in 1972, provides an ideal model to verify this unusual property. Here, we report the solution-phase synthesis of Clar’s goblet and experimental elucidation of its spin properties. Magnetic studies reveal that the two spins are spatially segregated with an average distance of 8.7 Å, and antiferromagnetically coupled in the ground state with an ES-T of –0.29 kcal/mol. Our results provide direct evidence of spin entanglement in the Clar’s goblet and may inspire the design of correlated molecular spins for quantum information technologies.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.26434/chemrxiv-2024-3q21n
Shannon, Stahl, Zhi-Ming, Su, Darren L., Poole, Mohammad, Rafiee, Robert S., Paton, Daniel J., Weix
Nickel-catalyzed cross-electrophile coupling (XEC) reactions of (hetero)aryl electrophiles represent appealing alternatives to palladium-catalyzed methods for biaryl synthesis, but they often generate significant quantities of homocoupling and/or proto-dehalogenation side products. In this study, an informer library of heteroaryl chloride and aryl bromide coupling partners is used to identify Ni-catalyzed XEC conditions that access high selectivity for the cross-product when using equimolar quantities of the two substrates. Two different catalyst systems are identified that show complementary scope and broad functional-group tolerance, and time-course data suggest the two methods follow different mechanisms. A NiBr2/terpyridine catalyst system with Zn as the reductant converts the aryl bromide into an aryl-zinc intermediate that undergoes in situ coupling with 2-chloropyridines, while a NiBr2/bipyridine catalyst system with tetrakis(dimethylamino)ethylene as the reductant uses FeBr2 and NaI as additives to achieve selective cross-coupling.
{"title":"Selective Ni-Catalyzed Cross-Electrophile Coupling of Heteroaryl Chlorides and Aryl Bromides at 1:1 Substrate Ratio","authors":"Shannon, Stahl, Zhi-Ming, Su, Darren L., Poole, Mohammad, Rafiee, Robert S., Paton, Daniel J., Weix","doi":"10.26434/chemrxiv-2024-3q21n","DOIUrl":"https://doi.org/10.26434/chemrxiv-2024-3q21n","url":null,"abstract":"Nickel-catalyzed cross-electrophile coupling (XEC) reactions of (hetero)aryl electrophiles represent appealing alternatives to palladium-catalyzed methods for biaryl synthesis, but they often generate significant quantities of homocoupling and/or proto-dehalogenation side products. In this study, an informer library of heteroaryl chloride and aryl bromide coupling partners is used to identify Ni-catalyzed XEC conditions that access high selectivity for the cross-product when using equimolar quantities of the two substrates. Two different catalyst systems are identified that show complementary scope and broad functional-group tolerance, and time-course data suggest the two methods follow different mechanisms. A NiBr2/terpyridine catalyst system with Zn as the reductant converts the aryl bromide into an aryl-zinc intermediate that undergoes in situ coupling with 2-chloropyridines, while a NiBr2/bipyridine catalyst system with tetrakis(dimethylamino)ethylene as the reductant uses FeBr2 and NaI as additives to achieve selective cross-coupling.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.26434/chemrxiv-2024-h1x6w
Steven William, Rutherford
Water molecules in hydrophobic micropores of Metal Organic Framework (MOF) materials show disparate behavior in adsorption equilibrium. Ranging from behavior indicative of large, Type V uptakes occurring at low relative pressure, to Type III equilibrium where little water is adsorbed, this phenomenon provides a challenge for a priori prediction. In an effort to elucidate adsorption mechanisms, this study advances a quantitative description of hydrophobicity through novel application of Ising model analysis (IMA). It is applied to scrutinize hydrophobicity indicated by Type III adsorption and displayed by micropores that are too large to induce a Type V water adsorption equilibrium. Two types of hydrophobicity are identified and partitioned into structural hydrophobicity and surface hydrophobicity. Additionally, through analysis of a data set for 25 materials, the utility of the concepts of nanocapillarity and nanowetting in a modified Kelvin analysis (MKA) are established for water in MOF systems. The method and analysis are applied to these phenomena in MOF micropores and could foreseeably aid in screening studies, be used to assess the presence of cooperative, wetting, and condensation-like mechanisms and be further employed to assess hydrophobicity in other microporous materials.
金属有机框架（MOF）材料疏水微孔中的水分子在吸附平衡中表现出不同的行为。从在低相对压力下发生的大量 V 型吸附行为，到几乎不吸附水的 III 型平衡，这种现象给先验预测带来了挑战。为了阐明吸附机制，本研究通过伊辛模型分析（IMA）的新颖应用，推进了对疏水性的定量描述。它被用于仔细研究由 III 型吸附所显示的疏水性，以及因微孔过大而导致 V 型水吸附平衡所显示的疏水性。确定了两类疏水性，并将其分为结构疏水性和表面疏水性。此外，通过分析 25 种材料的数据集，确定了纳米毛细管和纳米润湿概念在改良开尔文分析 (MKA) 中对 MOF 系统中水的实用性。该方法和分析适用于 MOF 微孔中的这些现象，可帮助进行筛选研究，用于评估合作、润湿和类似凝结机制的存在，并可进一步用于评估其他微孔材料的疏水性。
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Organic acids play an important role in atmospheric chemistry, particularly in the formation of aerosol particles. They are often detected with hydronium, ammonium, or nitrate chemical ionization sources, which are generally soft ionization sources but may cause fragmentation. Here we explore the reactivity of adipic acid, an analogue to the alpha-pinene oxidation product pinic acid, upon complexation with ammonium. Mass spectra and mass-selective vibrational spectra show that even mild activation, consistent with normal operation of an electrospray ionization source, yields (adipic acid)H+ and neutral ammonia. This is traced to a specific structural motif in which both protonated carboxylic acid carbonyl groups combine to form a site that is locally more basic than ammonia. Further mild collisional activation yields sequential loss of two water molecules, the known behavior of carboxylic acids in superacids, necessitating abstraction of at least one hydrogen from a CH group. Deuterium labeling experiments confirm that the second step indeed involves CH hydrogen atoms. Comparison of vibrational spectra and quantum chemical calculations allows us to assign structures for each step, identifying several ring structures but notably not forming the minimum energy structure upon the first loss of water. ESI of a range of linear dicarboxylic acids shows this to be a common feature of this class of organic acids. We propose a mechanism that explains this reactivity and discuss possible atmospheric implications of these observations.
有机酸在大气化学，特别是气溶胶粒子的形成中发挥着重要作用。它们通常用氢离子、铵或硝酸盐化学电离源进行检测，这些化学电离源通常是软电离源，但可能会导致碎裂。在此，我们探讨了己二酸（α-蒎烯氧化产物蒎酸的类似物）与铵络合后的反应性。质谱和质量选择性振动光谱显示，即使是与电喷雾电离源正常操作相一致的轻度活化，也会产生（己二酸）H+ 和中性氨。这可追溯到一种特殊的结构模式，其中质子化的两个羧酸羰基结合形成一个局部碱性高于氨的位点。进一步的温和碰撞活化产生了两个水分子的连续损失，这是已知的羧酸在超酸中的行为，需要从 CH 基团中抽取至少一个氢。氘标记实验证实，第二步确实涉及 CH 氢原子。通过比较振动光谱和量子化学计算，我们可以为每一步分配结构，确定几个环状结构，但值得注意的是，在第一次失水时没有形成最小能量结构。一系列线性二羧酸的 ESI 显示，这是这类有机酸的共同特征。我们提出了一种机制来解释这种反应性，并讨论了这些观察结果可能对大气产生的影响。
{"title":"Unusual Confinement-Induced Basicity and Proton-Mediated CH Activity of an Adipic Acid-Ammonium Cluster","authors":"Christopher, Johnson, John, Kreinbihl, Nicoline, Frederiks, Kathleen, Nickson, Emily, Racow, Melanie, Chiu, Annapoorani, Hariharan","doi":"10.26434/chemrxiv-2022-xqj08-v3","DOIUrl":"https://doi.org/10.26434/chemrxiv-2022-xqj08-v3","url":null,"abstract":"Organic acids play an important role in atmospheric chemistry, particularly in the formation of aerosol particles. They are often detected with hydronium, ammonium, or nitrate chemical ionization sources, which are generally soft ionization sources but may cause fragmentation. Here we explore the reactivity of adipic acid, an analogue to the alpha-pinene oxidation product pinic acid, upon complexation with ammonium. Mass spectra and mass-selective vibrational spectra show that even mild activation, consistent with normal operation of an electrospray ionization source, yields (adipic acid)H+ and neutral ammonia. This is traced to a specific structural motif in which both protonated carboxylic acid carbonyl groups combine to form a site that is locally more basic than ammonia. Further mild collisional activation yields sequential loss of two water molecules, the known behavior of carboxylic acids in superacids, necessitating abstraction of at least one hydrogen from a CH group. Deuterium labeling experiments confirm that the second step indeed involves CH hydrogen atoms. Comparison of vibrational spectra and quantum chemical calculations allows us to assign structures for each step, identifying several ring structures but notably not forming the minimum energy structure upon the first loss of water. ESI of a range of linear dicarboxylic acids shows this to be a common feature of this class of organic acids. We propose a mechanism that explains this reactivity and discuss possible atmospheric implications of these observations.","PeriodicalId":9813,"journal":{"name":"ChemRxiv","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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