Roundabout (RA) is an important indirect mechanism for gas-phase X– + CH3Y → XCH3 + Y– SN2 reactions at a high collision energy. It refers to the rotation of the CH3-group by half or multiple circles upon the collision of incoming nucleophiles before substitution takes place. The RA mechanism was first discovered in the Cl– + CH3I SN2 reaction to explain the energy transfer observed in crossed molecular beam imaging experiments in 2008. Since then, the RA mechanism and its variants have been observed not only in multiple C-centered SN2 reactions, but also in N-centered SN2 reactions, proton transfer reactions, and elimination reactions. This work reviewed recent studies on the RA mechanism and summarized the characteristics of RA mechanisms in terms of variant types, product energy partitioning, and product velocity scattering angle distribution. RA mechanisms usually happen at small impact parameters and tend to couple with other mechanisms at relatively low collision energy, and the available energy of roundabout trajectories is primarily partitioned to internal energy. Factors that affect the importance of the RA mechanism were analyzed, including the type of leaving group and nucleophile, collision energy, and microsolvation. A massive leaving group and relatively high collision energy are prerequisite for the occurrence of the roundabout mechanism. Interestingly, when reacting with CH3I, the importance of RA mechanisms follows an order of Cl– > HO– > F–, and such a nucleophile dependence was attributed to the difference in proton affinity and size of the nucleophile.
迂回（RA）是气相 X- + CH3Y → XCH3 + Y- SN2 反应在高碰撞能量下的一种重要的间接机制。它是指在发生取代反应之前，CH3-基团在进入的亲核物碰撞时旋转半圈或多圈。RA 机制最早是在 Cl- + CH3I SN2 反应中发现的，用以解释 2008 年在交叉分子束成像实验中观察到的能量转移。此后，RA 机制及其变体不仅在多个以 C 为中心的 SN2 反应中被观察到，而且在以 N 为中心的 SN2 反应、质子转移反应和消除反应中也被观察到。本研究综述了近年来关于 RA 机制的研究，并从变体类型、产物能量分配和产物速度散射角分布等方面总结了 RA 机制的特点。RA 机制通常发生在较小的撞击参数下，并倾向于在相对较低的碰撞能量下与其他机制耦合，迂回轨迹的可用能量主要被分配为内能。分析了影响 RA 机制重要性的因素，包括离去基团和亲核物的类型、碰撞能量和微溶解。大量离去基团和相对较高的碰撞能量是发生迂回机制的先决条件。有趣的是，当与 CH3I 反应时，RA 机制的重要性按照 Cl- > HO- > F- 的顺序排列，这种亲核剂依赖性被归因于质子亲和力和亲核剂大小的差异。
{"title":"Roundabout Mechanism of Ion–Molecule Nucleophilic Substitution Reactions","authors":"Xiangyu Wu, Fei Ying, Hongyi Wang, Li Yang, Jiaxu Zhang, Jing Xie","doi":"10.1021/acsphyschemau.4c00061","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00061","url":null,"abstract":"Roundabout (RA) is an important indirect mechanism for gas-phase X<sup>–</sup> + CH<sub>3</sub>Y → XCH<sub>3</sub> + Y<sup>–</sup> S<sub>N</sub>2 reactions at a high collision energy. It refers to the rotation of the CH<sub>3</sub>-group by half or multiple circles upon the collision of incoming nucleophiles before substitution takes place. The RA mechanism was first discovered in the Cl<sup>–</sup> + CH<sub>3</sub>I S<sub>N</sub>2 reaction to explain the energy transfer observed in crossed molecular beam imaging experiments in 2008. Since then, the RA mechanism and its variants have been observed not only in multiple C-centered S<sub>N</sub>2 reactions, but also in N-centered S<sub>N</sub>2 reactions, proton transfer reactions, and elimination reactions. This work reviewed recent studies on the RA mechanism and summarized the characteristics of RA mechanisms in terms of variant types, product energy partitioning, and product velocity scattering angle distribution. RA mechanisms usually happen at small impact parameters and tend to couple with other mechanisms at relatively low collision energy, and the available energy of roundabout trajectories is primarily partitioned to internal energy. Factors that affect the importance of the RA mechanism were analyzed, including the type of leaving group and nucleophile, collision energy, and microsolvation. A massive leaving group and relatively high collision energy are prerequisite for the occurrence of the roundabout mechanism. Interestingly, when reacting with CH<sub>3</sub>I, the importance of RA mechanisms follows an order of Cl<sup>–</sup> > HO<sup>–</sup> > F<sup>–</sup>, and such a nucleophile dependence was attributed to the difference in proton affinity and size of the nucleophile.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"44 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256285","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 : 2024-09-16DOI: 10.1021/acsphyschemau.4c00051
David C. Zeitz, Vivien L. Cherrette, Sarah A. Creech, Yan Li, Yuan Ping, Jin Z. Zhang
Spin relaxation of charge carriers in strongly quantum confined perovskite magic-sized clusters has been probed, for the first time, by using polarization-controlled femtosecond transient absorption (fs-TA) spectroscopy. Fs-TA measurements with a circularly polarized pump and probe allowed for the determination of the exciton spin relaxation lifetime (∼1.5 ps) at room temperature based on the dynamics of a photoinduced absorption (PIA) feature peaked at 458 nm. This spin lifetime is shorter than that of perovskite quantum dots (PQDs) with a larger size, and the results suggest that exciton confinement and defects likely play a more important role in these strongly quantum confined magic-sized clusters with a larger surface-to-volume ratio.
{"title":"Ultrafast Spin Relaxation of Charge Carriers in Strongly Quantum Confined Methylammonium Lead Bromide Perovskite Magic-Sized Clusters","authors":"David C. Zeitz, Vivien L. Cherrette, Sarah A. Creech, Yan Li, Yuan Ping, Jin Z. Zhang","doi":"10.1021/acsphyschemau.4c00051","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00051","url":null,"abstract":"Spin relaxation of charge carriers in strongly quantum confined perovskite magic-sized clusters has been probed, for the first time, by using polarization-controlled femtosecond transient absorption (fs-TA) spectroscopy. Fs-TA measurements with a circularly polarized pump and probe allowed for the determination of the exciton spin relaxation lifetime (∼1.5 ps) at room temperature based on the dynamics of a photoinduced absorption (PIA) feature peaked at 458 nm. This spin lifetime is shorter than that of perovskite quantum dots (PQDs) with a larger size, and the results suggest that exciton confinement and defects likely play a more important role in these strongly quantum confined magic-sized clusters with a larger surface-to-volume ratio.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"203 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256287","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 : 2024-09-12DOI: 10.1021/acsphyschemau.4c00029
Judith Peters, Karin Kornmueller, Rim Dannaoui, Ejona Syla, Annalisa Pastore
While exploring the behavior of lysozyme powders at different percentages of rehydration by differential scanning calorimetry, we noticed a small peak persistently on the left of the melting point of bulk water, which, when heating up the system, was always around −10 °C. The intensity of the transition was maximal at 160% rehydration and disappeared at higher values. By comparing the premelting peak properties in H2O and D2O, we attributed it to freezable water bound on the protein surface. This is the first time that such an observation has been reported.
{"title":"Direct Detection of Bound Water in Hydrated Powders of Lysozyme by Differential Scanning Calorimetry","authors":"Judith Peters, Karin Kornmueller, Rim Dannaoui, Ejona Syla, Annalisa Pastore","doi":"10.1021/acsphyschemau.4c00029","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00029","url":null,"abstract":"While exploring the behavior of lysozyme powders at different percentages of rehydration by differential scanning calorimetry, we noticed a small peak persistently on the left of the melting point of bulk water, which, when heating up the system, was always around −10 °C. The intensity of the transition was maximal at 160% rehydration and disappeared at higher values. By comparing the premelting peak properties in H<sub>2</sub>O and D<sub>2</sub>O, we attributed it to freezable water bound on the protein surface. This is the first time that such an observation has been reported.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"69 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142219238","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 : 2024-09-10DOI: 10.1021/acsphyschemau.4c00038
Pedro Hyug de Almeida da Silva, Dalete Araújo de Souza, Rubens Lucas de Freitas Filho, Ana Paula de Carvalho Teixeira, Rochel Montero Lago, Walter Ricardo Brito, Edgar Alves Araújo Junior, Litiko Lopes Takeno, Francimauro Sousa Morais, José Fábio de Lima Nascimento, Yurimiler Leyet Ruiz, Libertalamar Brilhalva Saraiva, Francisco Xavier Nobre
The combination of materials to improve properties of interest has become one of the strategies widely used for numerous applications, including new catalysts, over the last few decades. In this study, silver molybdate (β-Ag2MoO4) microcrystals were efficiently obtained by the hydrothermal method, obtaining composites with different amounts of graphene oxide (GO) (1, 2.5, 5, 7.5, and 10%, w/w) using the conventional hydrothermal method. The incorporation of GO on silver molybdate was confirmed by X-ray diffraction (XRD) and Raman spectroscopy, where the vibrational modes and crystallographic planes characteristic of the materials of interest were highlighted. The images collected by scanning electron microscopy (SEM) revealed the occurrence of plate-shaped structures (shells) anchored to the surface of the silver molybdate microcrystals (core). The optical properties showed that the materials presented Egap between 3.34 and 3.39 eV, where the sample with 7.5% of GO (GO@β-AgMo_7.5) was the one that presented energy for the conduction band, largely favorable to the formation of superoxide radicals through the photoexcitation process of electrons. The catalytic tests demonstrated that, among the samples obtained in this study, the sample with 7.5% of GO (GO@β-AgMo_7.5) exhibits superior photocatalytic performance against the dye rhodamine B (RhB) in an aqueous medium. Thus, the kinetics constant for photolysis (absence of catalysts) and for the sample β-AgMo and the sample with 7.5% of GO (GO@β-AgMo_7.5) are 0.38 × 10–3, 12 × 10–3, and 23.72 × 10–3 min–1, respectively. Therefore, it is 62.5 times more efficient in the degradation of the RhB dye, which confirms the promising photocatalytic properties of the obtained composite.
过去几十年来，通过材料组合来改善相关特性已成为广泛应用的策略之一，包括新型催化剂。在本研究中，通过水热法有效地获得了钼酸银（β-Ag2MoO4）微晶，并利用传统的水热法获得了与不同量的氧化石墨烯（GO）（1、2.5、5、7.5 和 10%，w/w）的复合材料。X 射线衍射（XRD）和拉曼光谱证实了 GO 在钼酸银上的结合，并突出显示了相关材料特有的振动模式和晶体平面。扫描电子显微镜（SEM）收集的图像显示，在钼酸银微晶（核心）表面存在板状结构（外壳）。光学特性表明，这些材料的 Egap 值在 3.34 至 3.39 eV 之间，其中含有 7.5% GO 的样品（GO@β-AgMo_7.5）具有导带能量，这在很大程度上有利于通过电子的光激发过程形成超氧自由基。催化测试表明，在本研究获得的样品中，含有 7.5% GO 的样品（GO@β-AgMo_7.5）对水介质中的染料罗丹明 B（RhB）具有优异的光催化性能。因此，在没有催化剂的情况下，β-AgMo 样品和含有 7.5% GO 的样品 (GO@β-AgMo_7.5) 的光解动力学常数分别为 0.38 × 10-3、12 × 10-3 和 23.72 × 10-3 min-1。因此，它降解 RhB 染料的效率是原来的 62.5 倍，这证实了所获得的复合材料具有良好的光催化性能。
{"title":"GO@β-Ag2MoO4 Composite: One-Step Synthesis, Characterization, and Photocatalytic Performance against RhB Dye","authors":"Pedro Hyug de Almeida da Silva, Dalete Araújo de Souza, Rubens Lucas de Freitas Filho, Ana Paula de Carvalho Teixeira, Rochel Montero Lago, Walter Ricardo Brito, Edgar Alves Araújo Junior, Litiko Lopes Takeno, Francimauro Sousa Morais, José Fábio de Lima Nascimento, Yurimiler Leyet Ruiz, Libertalamar Brilhalva Saraiva, Francisco Xavier Nobre","doi":"10.1021/acsphyschemau.4c00038","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00038","url":null,"abstract":"The combination of materials to improve properties of interest has become one of the strategies widely used for numerous applications, including new catalysts, over the last few decades. In this study, silver molybdate (β-Ag<sub>2</sub>MoO<sub>4</sub>) microcrystals were efficiently obtained by the hydrothermal method, obtaining composites with different amounts of graphene oxide (GO) (1, 2.5, 5, 7.5, and 10%, w/w) using the conventional hydrothermal method. The incorporation of GO on silver molybdate was confirmed by X-ray diffraction (XRD) and Raman spectroscopy, where the vibrational modes and crystallographic planes characteristic of the materials of interest were highlighted. The images collected by scanning electron microscopy (SEM) revealed the occurrence of plate-shaped structures (shells) anchored to the surface of the silver molybdate microcrystals (core). The optical properties showed that the materials presented <i>E</i><sub>gap</sub> between 3.34 and 3.39 eV, where the sample with 7.5% of GO (GO@β-AgMo_7.5) was the one that presented energy for the conduction band, largely favorable to the formation of superoxide radicals through the photoexcitation process of electrons. The catalytic tests demonstrated that, among the samples obtained in this study, the sample with 7.5% of GO (GO@β-AgMo_7.5) exhibits superior photocatalytic performance against the dye rhodamine B (RhB) in an aqueous medium. Thus, the kinetics constant for photolysis (absence of catalysts) and for the sample β-AgMo and the sample with 7.5% of GO (GO@β-AgMo_7.5) are 0.38 × 10<sup>–3</sup>, 12 × 10<sup>–3</sup>, and 23.72 × 10<sup>–3</sup> min<sup>–1</sup>, respectively. Therefore, it is 62.5 times more efficient in the degradation of the RhB dye, which confirms the promising photocatalytic properties of the obtained composite.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227335","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 : 2024-09-03DOI: 10.1021/acsphyschemau.4c00055
Rachel M. Sapstead, Robert M. Dalgliesh, Virginia C. Ferreira, Charlotte Beebee, Erik Watkins, A. Robert Hillman, Karl S. Ryder, Emma L. Smith, Nina-Juliane Steinke
Of the attributes that determine the performance of electroactive film-based devices, the least well quantified and understood is the spatial distribution of the component species. This is critical since it dictates the transport rates of all the mobile species (electrons, counterions, solvent, analyte, and reactant) and the film mechanical properties (as exploited in actuator devices). One of the few techniques able to provide individual species population profiles in situ is specular neutron reflectivity (NR). Historically, this information is obtained at the cost of poor time resolution (hours). Here we show how NR measurements with event mode data acquisition enable both spatial and temporal resolution; the latter can be selected postexperiment and varied during the transient. We profile individual species at “buried” interfaces under dynamic electrochemical conditions during polypyrrole electrodeposition and Cu deposition/dissolution. In the case of polypyrrole, the film is homogeneous throughout growth; there is no evidence of dendrite formation followed by solvent (water) displacement. Correlation of NR-derived film thickness and coulometric assay allows calculation of the solvent volume fraction, ϕS = 0.48. In the case of Cu in a deep eutectic solvent, the complexing nature of the medium results in time-dependent metal speciation: mechanistically, dissolution does not simply follow the deposition pathway in reverse.
在决定电活性薄膜设备性能的各种属性中，最难量化和理解的是成分物种的空间分布。这一点至关重要，因为它决定了所有移动物种（电子、反离子、溶剂、分析物和反应物）的传输速率以及薄膜的机械特性（如致动器装置中的利用）。镜面中子反射率 (NR) 是为数不多的能够在原位提供单个物种群概况的技术之一。从历史上看，获得这种信息的代价是较低的时间分辨率（小时）。在这里，我们展示了如何利用事件模式数据采集进行 NR 测量，从而实现空间和时间分辨率；后者可以在实验后进行选择，并在瞬态过程中进行改变。在聚吡咯电沉积和铜沉积/溶解过程中，我们对动态电化学条件下 "埋藏 "界面上的单个物种进行了剖析。就聚吡咯而言，薄膜在整个生长过程中都是均匀的；没有证据表明溶剂（水）置换后形成了枝晶。根据 NR 衍生的薄膜厚度和库仑测定法的相关性，可以计算出溶剂体积分数 ϕS = 0.48。就深共晶溶剂中的铜而言，介质的络合性质导致了随时间变化的金属种类：从机理上讲，溶解并不是简单地沿着沉积路径反向进行。
{"title":"Time-Resolved Spatial Distributions of Individual Components of Electroactive Films during Potentiodynamic Electrodeposition","authors":"Rachel M. Sapstead, Robert M. Dalgliesh, Virginia C. Ferreira, Charlotte Beebee, Erik Watkins, A. Robert Hillman, Karl S. Ryder, Emma L. Smith, Nina-Juliane Steinke","doi":"10.1021/acsphyschemau.4c00055","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00055","url":null,"abstract":"Of the attributes that determine the performance of electroactive film-based devices, the least well quantified and understood is the spatial distribution of the component species. This is critical since it dictates the transport rates of <i>all</i> the mobile species (electrons, counterions, solvent, analyte, and reactant) and the film mechanical properties (as exploited in actuator devices). One of the few techniques able to provide individual species population profiles <i>in situ</i> is specular neutron reflectivity (NR). Historically, this information is obtained at the cost of poor time resolution (hours). Here we show how NR measurements with <i>event mode</i> data acquisition enable both spatial <i>and</i> temporal resolution; the latter can be selected postexperiment and varied during the transient. We profile individual species at “buried” interfaces under dynamic electrochemical conditions during polypyrrole electrodeposition and Cu deposition/dissolution. In the case of polypyrrole, the film is homogeneous throughout growth; there is no evidence of dendrite formation followed by solvent (water) displacement. Correlation of NR-derived film thickness and coulometric assay allows calculation of the solvent volume fraction, ϕ<sub>S</sub> = 0.48. In the case of Cu in a deep eutectic solvent, the complexing nature of the medium results in time-dependent metal speciation: mechanistically, dissolution does not simply follow the deposition pathway in reverse.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"77 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142219240","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}
Many important processes in cells depend on the transfer of protons through water wires embedded in transmembrane proteins. Herein, we have performed more than 55 μs all-atom simulations of the light-harvesting complex of a diatom, i.e., the fucoxanthin and chlorophyll a/c binding protein (FCP) from the marine diatom Phaeodactylum tricornutum. Diatoms are unique models to study natural photosynthesis as they exert an efficient light-harvesting machinery with a robust pH-dependent photoprotective mechanism. The present study reports on the dynamics of an FCP monomer, a dimer, and a tetramer at varying pH values. Surprisingly, we have identified at low pH a water channel across FCP that selectively hydrates and protonates the acrylate of a Chl-c2 pigment located in the middle of the membrane. These results are further supported by QM/MM calculations and steered MD simulations on the proton dynamics. It is shown that proton hopping events between the lumenal and stromal sides of the membrane through the observed water channel are highly disfavored. This hindrance is due to the presence of residues Arg31 and Lys82 close to the acrylate, along with an hydronium desolvation penalty that shows close similarities to the water conductance in aquaporins. Furthermore, we provide strong evidence that this identified water channel is governing the transition between light-harvesting and photoprotective states of the major FCP complex in the diatom P. tricornutum.
{"title":"An Unexpected Water Channel in the Light-Harvesting Complex of a Diatom: Implications for the Switch between Light Harvesting and Photoprotection","authors":"Vangelis Daskalakis, Sayan Maity, Ulrich Kleinekathöfer","doi":"10.1021/acsphyschemau.4c00069","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00069","url":null,"abstract":"Many important processes in cells depend on the transfer of protons through water wires embedded in transmembrane proteins. Herein, we have performed more than 55 μs all-atom simulations of the light-harvesting complex of a diatom, i.e., the fucoxanthin and chlorophyll a/c binding protein (FCP) from the marine diatom <i>Phaeodactylum tricornutum</i>. Diatoms are unique models to study natural photosynthesis as they exert an efficient light-harvesting machinery with a robust pH-dependent photoprotective mechanism. The present study reports on the dynamics of an FCP monomer, a dimer, and a tetramer at varying pH values. Surprisingly, we have identified at low pH a water channel across FCP that selectively hydrates and protonates the acrylate of a Chl-c2 pigment located in the middle of the membrane. These results are further supported by QM/MM calculations and steered MD simulations on the proton dynamics. It is shown that proton hopping events between the lumenal and stromal sides of the membrane through the observed water channel are highly disfavored. This hindrance is due to the presence of residues Arg31 and Lys82 close to the acrylate, along with an hydronium desolvation penalty that shows close similarities to the water conductance in aquaporins. Furthermore, we provide strong evidence that this identified water channel is governing the transition between light-harvesting and photoprotective states of the major FCP complex in the diatom <i>P. tricornutum</i>.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142219241","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 : 2024-08-05DOI: 10.1021/acsphyschemau.4c0002210.1021/acsphyschemau.4c00022
Kazuhiro J. Fujimoto*, Rio Tsuji, Zheng-Yu Wang-Otomo and Takeshi Yanai*,
Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) a; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl a structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium Rhodospirillum rubrum. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl a 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl a chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.
{"title":"Prominent Role of Charge Transfer in the Spectral Tuning of Photosynthetic Light-Harvesting I Complex","authors":"Kazuhiro J. Fujimoto*, Rio Tsuji, Zheng-Yu Wang-Otomo and Takeshi Yanai*, ","doi":"10.1021/acsphyschemau.4c0002210.1021/acsphyschemau.4c00022","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00022https://doi.org/10.1021/acsphyschemau.4c00022","url":null,"abstract":"<p >Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) <i>a</i>; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl <i>a</i> structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium <i>Rhodospirillum rubrum</i>. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl <i>a</i> 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl <i>a</i> chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.</p>","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"4 5","pages":"499–509 499–509"},"PeriodicalIF":3.7,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acsphyschemau.4c00022","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142318194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-05DOI: 10.1021/acsphyschemau.4c00022
Kazuhiro J. Fujimoto, Rio Tsuji, Zheng-Yu Wang-Otomo, Takeshi Yanai
Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) a; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl a structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium Rhodospirillum rubrum. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl a 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl a chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.
{"title":"Prominent Role of Charge Transfer in the Spectral Tuning of Photosynthetic Light-Harvesting I Complex","authors":"Kazuhiro J. Fujimoto, Rio Tsuji, Zheng-Yu Wang-Otomo, Takeshi Yanai","doi":"10.1021/acsphyschemau.4c00022","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00022","url":null,"abstract":"Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) <i>a</i>; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl <i>a</i> structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium <i>Rhodospirillum rubrum</i>. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl <i>a</i> 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl <i>a</i> chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"821 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931921","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 : 2024-08-01DOI: 10.1021/acsphyschemau.4c00033
Neil C. Cole-Filipiak, Jan Troß, Paul Schrader, Laura M. McCaslin, Krupa Ramasesha
Herein, we report on the ultrafast photodissociation of nickel tetracarbonyl─a prototypical metal–ligand model system─at 197 nm. Using mid-infrared transient absorption spectroscopy to probe the bound C≡O stretching modes, we find evidence for the picosecond time scale production of highly vibronically excited nickel dicarbonyl and nickel monocarbonyl, in marked contrast with a prior investigation at 193 nm. Further spectral evolution with a 50 ps time constant suggests an additional dissociation step; the absence of any corresponding growth in signal strongly indicates the production of bare Ni, a heretofore unreported product from single-photon excitation of nickel tetracarbonyl. Thus, by probing the deep UV-induced photodynamics of a prototypical metal carbonyl, this Letter adds time-resolved spectroscopic signatures of these dynamics to the sparse literature at high excitation energies.
{"title":"Ultrafast Production of NiCO and Ni Following 197 nm Photodissociation of Nickel Tetracarbonyl","authors":"Neil C. Cole-Filipiak, Jan Troß, Paul Schrader, Laura M. McCaslin, Krupa Ramasesha","doi":"10.1021/acsphyschemau.4c00033","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00033","url":null,"abstract":"Herein, we report on the ultrafast photodissociation of nickel tetracarbonyl─a prototypical metal–ligand model system─at 197 nm. Using mid-infrared transient absorption spectroscopy to probe the bound C≡O stretching modes, we find evidence for the picosecond time scale production of highly vibronically excited nickel dicarbonyl and nickel monocarbonyl, in marked contrast with a prior investigation at 193 nm. Further spectral evolution with a 50 ps time constant suggests an additional dissociation step; the absence of any corresponding growth in signal strongly indicates the production of bare Ni, a heretofore unreported product from single-photon excitation of nickel tetracarbonyl. Thus, by probing the deep UV-induced photodynamics of a prototypical metal carbonyl, this Letter adds time-resolved spectroscopic signatures of these dynamics to the sparse literature at high excitation energies.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881714","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 : 2024-07-24DOI: 10.1021/acsphyschemau.4c0004210.1021/acsphyschemau.4c00042
Ben. J. Tickner*, Kawarpal Singh*, Vladimir V. Zhivonitko* and Ville-Veikko Telkki*,
Ultrafast nuclear magnetic resonance (NMR) uses spatial encoding to record an entire two-dimensional data set in just a single scan. The approach can be applied to either Fourier-transform or Laplace-transform NMR. In both cases, acquisition times are significantly shorter than traditional 2D/Laplace NMR experiments, which allows them to be used to monitor rapid chemical transformations. This Perspective outlines the principles of ultrafast NMR and focuses on examples of its use to detect fast molecular conversions in situ with high temporal resolution. We discuss how this valuable tool can be applied in the future to study a much wider variety of novel reactivity.
{"title":"Ultrafast Nuclear Magnetic Resonance as a Tool to Detect Rapid Chemical Change in Solution","authors":"Ben. J. Tickner*, Kawarpal Singh*, Vladimir V. Zhivonitko* and Ville-Veikko Telkki*, ","doi":"10.1021/acsphyschemau.4c0004210.1021/acsphyschemau.4c00042","DOIUrl":"https://doi.org/10.1021/acsphyschemau.4c00042https://doi.org/10.1021/acsphyschemau.4c00042","url":null,"abstract":"<p >Ultrafast nuclear magnetic resonance (NMR) uses spatial encoding to record an entire two-dimensional data set in just a single scan. The approach can be applied to either Fourier-transform or Laplace-transform NMR. In both cases, acquisition times are significantly shorter than traditional 2D/Laplace NMR experiments, which allows them to be used to monitor rapid chemical transformations. This Perspective outlines the principles of ultrafast NMR and focuses on examples of its use to detect fast molecular conversions <i>in situ</i> with high temporal resolution. We discuss how this valuable tool can be applied in the future to study a much wider variety of novel reactivity.</p>","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"4 5","pages":"453–463 453–463"},"PeriodicalIF":3.7,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acsphyschemau.4c00042","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142318357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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