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Chen D, Khetan A, Lei H, Rizzotto V, Yang JY, Jiang J, Sun Q, Peng B, Chen P, Palkovits R, Ye D, Simon U. Copper Site Motion Promotes Catalytic NO x Reduction under Zeolite Confinement. Environ Sci Technol 2023; 57:16121-16130. [PMID: 37842921 DOI: 10.1021/acs.est.3c03422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2023]
Abstract
Ammonia-mediated selective catalytic reduction (NH3-SCR) is currently the key approach to abate nitrogen oxides (NOx) emitted from heavy-duty lean-burn vehicles. The state-of-art NH3-SCR catalysts, namely, copper ion-exchanged chabazite (Cu-CHA) zeolites, perform rather poorly at low temperatures (below 200 °C) and are thus incapable of eliminating effectively NOx emissions under cold-start conditions. Here, we demonstrate a significant promotion of low-temperature NOx reduction by reinforcing the dynamic motion of zeolite-confined Cu sites during NH3-SCR. Combining complex impedance-based in situ spectroscopy (IS) and extended density-functional tight-binding molecular dynamics simulation, we revealed an environment- and temperature-dependent nature of the dynamic Cu motion within the zeolite lattice. Further coupling in situ IS with infrared spectroscopy allows us to unravel the critical role of monovalent Cu in the overall Cu mobility at a molecular level. Based on these mechanistic understandings, we elicit a boost of NOx reduction below 200 °C by reinforcing the dynamic Cu motion in various Cu-zeolites (Cu-CHA, Cu-ZSM-5, Cu-Beta, etc.) via facile postsynthesis treatments, either in a reductive mixture at low temperatures (below 250 °C) or in a nonoxidative atmosphere at high temperatures (above 450 °C).
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Affiliation(s)
- Dongdong Chen
- National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
| | - Abhishek Khetan
- Multiscale Modelling of Heterogeneous Catalysis in Energy Systems, RWTH Aachen University, Schinkelstrasse 8, 52062 Aachen, Germany
| | - Huarong Lei
- National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
- Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen Germany
| | - Valentina Rizzotto
- Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen Germany
| | - Jia-Yue Yang
- Optics & Thermal Radiation Research Center, Shandong University, 266237 Qingdao, China
| | - Jiuxing Jiang
- MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry, Sun Yat-Sen University, 510275 Guangzhou, China
| | - Qiming Sun
- Innovation Center for Chemical Sciences, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 215123 Suzhou, China
| | - Baoxiang Peng
- Laboratory of Industrial Chemistry, Ruhr University Bochum, 44780 Bochum, Germany
| | - Peirong Chen
- National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
| | - Regina Palkovits
- Chair of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany
| | - Daiqi Ye
- National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
| | - Ulrich Simon
- Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen Germany
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Lei H, Chen D, Yang JY, Khetan A, Jiang J, Peng B, Simon U, Ye D, Chen P. Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NO x Reduction over Cu-SSZ-13 Zeolites by In Situ UV-Vis Spectroscopy and Time-Dependent DFT Calculation. Environ Sci Technol 2023; 57:12465-12475. [PMID: 37556316 DOI: 10.1021/acs.est.3c00458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/11/2023]
Abstract
The low-temperature mechanism of chabazite-type small-pore Cu-SSZ-13 zeolite, a state-of-the-art catalyst for ammonia-assisted selective reduction (NH3-SCR) of toxic NOx pollutants from heavy-duty vehicles, remains a debate and needs to be clarified for further improvement of NH3-SCR performance. In this study, we established experimental protocols to follow the dynamic redox cycling (i.e., CuII ↔ CuI) of Cu sites in Cu-SSZ-13 during low-temperature NH3-SCR catalysis by in situ ultraviolet-visible spectroscopy and in situ infrared spectroscopy. Further integrating the in situ spectroscopic observations with time-dependent density functional theory calculations allows us to identify two cage-confined transient states, namely, the O2-bridged Cu dimers (i.e., μ-η2:η2-peroxodiamino dicopper) and the proximately paired, chemically nonbonded CuI(NH3)2 sites, and to confirm the CuI(NH3)2 pair as a precursor to the O2-bridged Cu dimer. Comparative transient experiments reveal a particularly high reactivity of the CuI(NH3)2 pairs for NO-to-N2 reduction at low temperatures. Our study demonstrates direct experimental evidence for the transient formation and high reactivity of proximately paired CuI sites under zeolite confinement and provides new insights into the monomeric-to-dimeric Cu transformation for completing the Cu redox cycle in low-temperature NH3-SCR catalysis over Cu-SSZ-13.
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Affiliation(s)
- Huarong Lei
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
- Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Dongdong Chen
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
| | - Jia-Yue Yang
- Optics & Thermal Radiation Research Center, Shandong University, Qingdao 266237 China
| | - Abhishek Khetan
- Fuel Science Center, RWTH Aachen University, Schinkelstr. 8, 52074 Aachen, Germany
| | - Jiuxing Jiang
- MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275 China
| | - Baoxiang Peng
- Laboratory of Industrial Chemistry, Ruhr-University Bochum, Universitätsstr. 150, Bochum 44780 Germany
| | - Ulrich Simon
- Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
- Fuel Science Center, RWTH Aachen University, Schinkelstr. 8, 52074 Aachen, Germany
| | - Daiqi Ye
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
| | - Peirong Chen
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, School of Environment and Energy, South China University of Technology, 510006 Guangzhou, China
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Zhou X, Khetan A, Zheng J, Huijben M, Janssen RAJ, Er S. Discovery of lead quinone cathode materials for Li-ion batteries. Digit Discov 2023; 2:1016-1025. [PMID: 38013813 PMCID: PMC10408572 DOI: 10.1039/d2dd00112h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Accepted: 05/30/2023] [Indexed: 11/29/2023]
Abstract
Organic cathode materials are attractive candidates for the development of high-performance Li-ion batteries (LIBs). The chemical space of candidate molecules is too vast to be explored solely by experiments; however, it can be systematically explored by a high-throughput computational search that incorporates a spectrum of screening techniques. Here, we present a time- and resource-efficient computational scheme that incorporates machine learning and semi-empirical quantum mechanical methods to study the chemical space of approximately 200 000 quinone-based molecules for use as cathode materials in LIBs. By performing an automated search on a commercial vendor database, computing battery-relevant properties such as redox potential, gravimetric charge capacity, gravimetric energy density, and synthetic complexity score, and evaluating the structural integrity upon the lithiation process, a total of 349 molecules were identified as potentially high-performing cathode materials for LIBs. The chemical space of the screened candidates was visualized using dimensionality reduction methods with the aim of further downselecting the best candidates for experimental validation. One such directly purchasable candidate, 1,4,9,10-anthracenetetraone, was analyzed through cyclic voltammetry experiments. The measured redox potentials of the two lithiation steps, , of 3.3 and 2.4 V, were in good agreement with the predicted redox potentials, , of 3.2 and 2.3 V vs. Li/Li+, respectively. Lastly, to lay out the principles for rational design of quinone-based cathode materials beyond the current work, we constructed and discussed the quantitative structure property relationships of quinones based on the data generated from the calculations.
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Affiliation(s)
- Xuan Zhou
- DIFFER - Dutch Institute for Fundamental Energy Research De Zaale 20 5612 AJ Eindhoven the Netherlands
- Department of Applied Physics, Eindhoven University of Technology Eindhoven 5600 MB the Netherlands
| | - Abhishek Khetan
- DIFFER - Dutch Institute for Fundamental Energy Research De Zaale 20 5612 AJ Eindhoven the Netherlands
- Multiscale Modeling of Heterogeneous Catalysis in Energy Systems, RWTH Aachen University Aachen 52062 Germany
| | - Jie Zheng
- MESA+ Institute for Nanotechnology, University of Twente Enschede 7500 AE the Netherlands
| | - Mark Huijben
- MESA+ Institute for Nanotechnology, University of Twente Enschede 7500 AE the Netherlands
| | - René A J Janssen
- DIFFER - Dutch Institute for Fundamental Energy Research De Zaale 20 5612 AJ Eindhoven the Netherlands
- Molecular Materials and Nanosystems, Institute for Complex Molecular System, Eindhoven University of Technology Eindhoven 5600 MB the Netherlands
| | - Süleyman Er
- DIFFER - Dutch Institute for Fundamental Energy Research De Zaale 20 5612 AJ Eindhoven the Netherlands
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Sorkun E, Zhang Q, Khetan A, Sorkun MC, Er S. RedDB, a computational database of electroactive molecules for aqueous redox flow batteries. Sci Data 2022; 9:718. [PMID: 36443329 PMCID: PMC9705518 DOI: 10.1038/s41597-022-01832-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 11/04/2022] [Indexed: 11/29/2022] Open
Abstract
An increasing number of electroactive compounds have recently been explored for their use in high-performance redox flow batteries for grid-scale energy storage. Given the vast and highly diverse chemical space of the candidate compounds, it is alluring to access their physicochemical properties in a speedy way. High-throughput virtual screening approaches, which use powerful combinatorial techniques for systematic enumerations of large virtual chemical libraries and respective property evaluations, are indispensable tools for an agile exploration of the designated chemical space. Herein, RedDB: a computational database that contains 31,618 molecules from two prominent classes of organic electroactive compounds, quinones and aza-aromatics, has been presented. RedDB incorporates miscellaneous physicochemical property information of the compounds that can potentially be employed as battery performance descriptors. RedDB’s development steps, including: (i) chemical library generation, (ii) molecular property prediction based on quantum chemical calculations, (iii) aqueous solubility prediction using machine learning, and (iv) data processing and database creation, have been described. Measurement(s) | Clean Database • Physicochemical properties of redox active molecules • aqueous solubility | Technology Type(s) | Calculation • Physics • machine learning |
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Zhang Q, Khetan A, Er S. Comparison of computational chemistry methods for the discovery of quinone-based electroactive compounds for energy storage. Sci Rep 2020; 10:22149. [PMID: 33335155 PMCID: PMC7746720 DOI: 10.1038/s41598-020-79153-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 12/02/2020] [Indexed: 11/09/2022] Open
Abstract
High-throughput computational screening (HTCS) is a powerful approach for the rational and time-efficient design of electroactive compounds. The effectiveness of HTCS is dependent on accuracy and speed at which the performance descriptors can be estimated for possibly millions of candidate compounds. Here, a systematic evaluation of computational methods, including force field (FF), semi-empirical quantum mechanics (SEQM), density functional based tight binding (DFTB), and density functional theory (DFT), is performed on the basis of their accuracy in predicting the redox potentials of redox-active organic compounds. Geometry optimizations at low-level theories followed by single point energy (SPE) DFT calculations that include an implicit solvation model are found to offer equipollent accuracy as the high-level DFT methods, albeit at significantly lower computational costs. Effects of implicit solvation on molecular geometries and SPEs, and their overall effects on the prediction accuracy of redox potentials are analyzed in view of computational cost versus prediction accuracy, which outlines the best choice of methods corresponding to a desired level of accuracy. The modular computational approach is applicable for accelerating the virtual studies on functional quinones and the respective discovery of candidate compounds for energy storage.
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Affiliation(s)
- Qi Zhang
- DIFFER-Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.,CCER-Center for Computational Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.,Department of Applied Physics, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands
| | - Abhishek Khetan
- DIFFER-Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.,CCER-Center for Computational Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands
| | - Süleyman Er
- DIFFER-Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands. .,CCER-Center for Computational Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.
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Sorkun MC, Khetan A, Er S. AqSolDB, a curated reference set of aqueous solubility and 2D descriptors for a diverse set of compounds. Sci Data 2019; 6:143. [PMID: 31395888 PMCID: PMC6687799 DOI: 10.1038/s41597-019-0151-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 07/12/2019] [Indexed: 11/09/2022] Open
Abstract
Water is a ubiquitous solvent in chemistry and life. It is therefore no surprise that the aqueous solubility of compounds has a key role in various domains, including but not limited to drug discovery, paint, coating, and battery materials design. Measurement and prediction of aqueous solubility is a complex and prevailing challenge in chemistry. For the latter, different data-driven prediction models have recently been developed to augment the physics-based modeling approaches. To construct accurate data-driven estimation models, it is essential that the underlying experimental calibration data used by these models is of high fidelity and quality. Existing solubility datasets show variance in the chemical space of compounds covered, measurement methods, experimental conditions, but also in the non-standard representations, size, and accessibility of data. To address this problem, we generated a new database of compounds, AqSolDB, by merging a total of nine different aqueous solubility datasets, curating the merged data, standardizing and validating the compound representation formats, marking with reliability labels, and providing 2D descriptors of compounds as a Supplementary Resource.
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Affiliation(s)
- Murat Cihan Sorkun
- DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.,Center for Computational Energy Research, DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands
| | - Abhishek Khetan
- DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.,Center for Computational Energy Research, DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands
| | - Süleyman Er
- DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands. .,Center for Computational Energy Research, DIFFER - Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands.
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Chen P, Rizzotto V, Khetan A, Xie K, Moos R, Pitsch H, Ye D, Simon U. Mechanistic Understanding of Cu-CHA Catalyst as Sensor for Direct NH 3-SCR Monitoring: The Role of Cu Mobility. ACS Appl Mater Interfaces 2019; 11:8097-8105. [PMID: 30706712 DOI: 10.1021/acsami.8b22104] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The concept to utilize a catalyst directly as a sensor is fundamentally and technically attractive for a number of catalytic applications, in particular, for the catalytic abatement of automotive emission. Here, we explore the potential of microporous copper-exchanged chabazite (Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) zeolite catalysts, which are used commercially in the selective catalytic reduction of automotive nitrogen oxide emission by NH3 (NH3-SCR), as impedance sensor elements to monitor directly the NH3-SCR process. The NH3-SCR sensing behavior of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts at typical reaction temperatures (i.e., 200 and 350 °C) was evaluated according to the change of ionic conductivity and was mechanistically investigated by complex impedance-based in situ modulus spectroscopy. Short-range (local) movement of Cu ions within the zeolite structure was found to determine largely the NH3-SCR sensing behavior of both catalysts. Formation of NH3-solvated, highly mobile CuI species showed a predominant influence on the ionic conductivity of both catalysts and, consequently, hindered NH3-SCR sensing at 200 °C. Density functional theory calculations over a model Cu-SAPO-34 system revealed that CuII reduction to CuI by coadsorbed NH3 and NO weakened significantly the coordination of the Cu site to the CHA framework, enabling high mobility of CuI species that influences substantially the NH3-SCR sensing. The in situ spectroscopic and theoretical investigations not only unveil the mechanisms of Cu-CHA catalyst as sensor elements for direct NH3-SCR monitoring but also allow us to get insights into the speciation of active Cu sites in NH3-SCR under different reaction conditions with varied temperatures and gas compositions.
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Affiliation(s)
- Peirong Chen
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy , South China University of Technology , Guangzhou 510006 , China
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Valentina Rizzotto
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Abhishek Khetan
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
- Institute for Combustion Technology , RWTH Aachen University , Templergraben 64 , Aachen 52056 , Germany
- Department of Mechanical Engineering , Carnegie Mellon University , 5000 Forbes Avenue , Pittsburgh , Pennsylvania 15213 , United States
| | - Kunpeng Xie
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Ralf Moos
- Department of Functional Materials and Bayreuth Engine Research Center (BERC) , University of Bayreuth , Bayreuth 95440 , Germany
| | - Heinz Pitsch
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
- Institute for Combustion Technology , RWTH Aachen University , Templergraben 64 , Aachen 52056 , Germany
| | - Daiqi Ye
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy , South China University of Technology , Guangzhou 510006 , China
| | - Ulrich Simon
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
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Yang S, Schmidt DO, Khetan A, Schrader F, Jakobi S, Homberger M, Noyong M, Paulus A, Kungl H, Eichel RA, Pitsch H, Simon U. Electrochemical and Electronic Charge Transport Properties of Ni-Doped LiMn₂O₄ Spinel Obtained from Polyol-Mediated Synthesis. Materials (Basel) 2018; 11:ma11050806. [PMID: 29772663 PMCID: PMC5978183 DOI: 10.3390/ma11050806] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 05/09/2018] [Accepted: 05/14/2018] [Indexed: 12/26/2022]
Abstract
LiNi0.5Mn1.5O4 (LNMO) spinel has been extensively investigated as one of the most promising high-voltage cathode candidates for lithium-ion batteries. The electrochemical performance of LNMO, especially its rate performance, seems to be governed by its crystallographic structure, which is strongly influenced by the preparation methods. Conventionally, LNMO materials are prepared via solid-state reactions, which typically lead to microscaled particles with only limited control over the particle size and morphology. In this work, we prepared Ni-doped LiMn2O4 (LMO) spinel via the polyol method. The cycling stability and rate capability of the synthesized material are found to be comparable to the ones reported in literature. Furthermore, its electronic charge transport properties were investigated by local electrical transport measurements on individual particles by means of a nanorobotics setup in a scanning electron microscope, as well as by performing DFT calculations. We found that the scarcity of Mn3+ in the LNMO leads to a significant decrease in electronic conductivity as compared to undoped LMO, which had no obvious effect on the rate capability of the two materials. Our results suggest that the rate capability of LNMO and LMO materials is not limited by the electronic conductivity of the fully lithiated materials.
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Affiliation(s)
- Shuo Yang
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Dirk Oliver Schmidt
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Abhishek Khetan
- Institute for Combustion Technology, RWTH Aachen University, 52056 Aachen, Germany.
| | - Felix Schrader
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Simon Jakobi
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Melanie Homberger
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Michael Noyong
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
| | - Anja Paulus
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
- Institute of Energy and Climate Research IEK-9: Fundamental Electrochemistry, Forschungszentrum Jülich, 52425 Jülich, Germany.
| | - Hans Kungl
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
- Institute of Energy and Climate Research IEK-9: Fundamental Electrochemistry, Forschungszentrum Jülich, 52425 Jülich, Germany.
| | - Rüdiger-Albert Eichel
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
- Institute of Energy and Climate Research IEK-9: Fundamental Electrochemistry, Forschungszentrum Jülich, 52425 Jülich, Germany.
- Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
| | - Heinz Pitsch
- Institute for Combustion Technology, RWTH Aachen University, 52056 Aachen, Germany.
| | - Ulrich Simon
- Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany.
- Jülich Aachen Research Alliance-JARA, 52428 Jülich, Germany.
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Khetan A, Krishnamurthy D, Viswanathan V. Towards Synergistic Electrode-Electrolyte Design Principles for Nonaqueous Li-O[Formula: see text] batteries. Top Curr Chem (Cham) 2018; 376:11. [PMID: 29557503 DOI: 10.1007/s41061-018-0188-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 01/26/2018] [Indexed: 11/26/2022]
Abstract
One route toward sustainable land and aerial transportation is based on electrified vehicles. To enable electrification in transportation, there is a need for high-energy-density batteries, and this has led to an enormous interest in lithium-oxygen batteries. Several critical challenges remain with respect to realizing a practical lithium-oxygen battery. In this article, we present a detailed overview of theoretical efforts to formulate design principles for identifying stable electrolytes and electrodes with the desired functionality and stability. We discuss design principles relating to electrolytes and the additional stability challenges that arise at the cathode-electrolyte interface. Based on a thermodynamic analysis, we discuss two important requirements for the cathode: the ability to nucleate the desired discharge product, Li[Formula: see text]O[Formula: see text], and the ability to selectively activate only this discharge product while suppressing lithium oxide, the undesired secondary discharge product. We propose preliminary guidelines for determining the chemical stability of the electrode and illustrate the challenge associated with electrode selection using the examples of carbon cathodes and transition metals. We believe that a synergistic design framework for identifying electrolyte-electrode formulations is needed to realize a practical Li-O[Formula: see text] battery.
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Affiliation(s)
- Abhishek Khetan
- Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA, 15213, USA
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Iliksu M, Khetan A, Yang S, Simon U, Pitsch H, Sauer DU. Elucidation and Comparison of the Effect of LiTFSI and LiNO 3 Salts on Discharge Chemistry in Nonaqueous Li-O 2 Batteries. ACS Appl Mater Interfaces 2017; 9:19319-19325. [PMID: 28485949 DOI: 10.1021/acsami.7b03592] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The role of lithium salts in determining the discharge capacity of Li-O2 batteries has been highlighted in several recent studies; however, questions pertaining to their effect on the cathode surface and in the solution phase still remain unanswered. We conducted galvanostatic discharge experiments with different compositions of a binary mixture of 1 M of LiNO3 and LiTFSI in tetraglyme (TEGDME) as the electrolyte and analyzed the discharge products using techniques such as FT-IR, Raman spectroscopy, and SEM. It was observed that there is a nonlinear correlation between the electrolyte composition and the first discharge capacity, with the highest discharge capacity achieved with the electrolyte composition as 0.75 M LiNO3 and 0.25 M LiTFSI. The ID/IG values obtained from Raman spectroscopy, which represent the degree of order in the carbon cathode surface, were found to be correlated to the measured capacity. Our results indicate that at concentrations of LiNO3 higher than 0.75 M in the electrolyte, nitrogen doping of the carbon surface reaches a critical limit, beyond which it becomes unfavorable for the discharge process. On the other hand, decomposition of the electrolyte and formation of an amorphous layer on the cathode surface was found to intensify with increasing LiTFSI concentration. Our results show that the maximum discharge capacity of the cells is strongly dependent on the surface structure of the carbon cathode, which in turn is heavily influenced by the electrolyte composition. Classical molecular dynamics simulations of the same system indicated no such nonlinearity in the co-ordination of Li+ ions with respect to electrolyte composition, indicating that the ionic association strength of the anion may have only a limited effect.
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Affiliation(s)
- Merve Iliksu
- Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University , Aachen, 52066, Germany
- Juelich Aachen Research Alliance-JARA , Juelich, 52428, Germany
| | - Abhishek Khetan
- Institute for Combustion Technology, RWTH Aachen University , Aachen, 52056, Germany
| | - Shuo Yang
- Juelich Aachen Research Alliance-JARA , Juelich, 52428, Germany
- Institute of Inorganic Chemistry, RWTH Aachen University , Aachen, 52074, Germany
| | - Ulrich Simon
- Juelich Aachen Research Alliance-JARA , Juelich, 52428, Germany
- Institute of Inorganic Chemistry, RWTH Aachen University , Aachen, 52074, Germany
| | - Heinz Pitsch
- Institute for Combustion Technology, RWTH Aachen University , Aachen, 52056, Germany
| | - Dirk Uwe Sauer
- Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University , Aachen, 52066, Germany
- Juelich Aachen Research Alliance-JARA , Juelich, 52428, Germany
- Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University , Aachen, 52074, Germany
- Helmholtz Institute Muenster, IEK-12, Forschungszentrum Juelich GmbH, Muenster, 48149, Germany
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11
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Chen P, Khetan A, Yang F, Migunov V, Weide P, Stürmer SP, Guo P, Kähler K, Xia W, Mayer J, Pitsch H, Simon U, Muhler M. Experimental and Theoretical Understanding of Nitrogen-Doping-Induced Strong Metal–Support Interactions in Pd/TiO2 Catalysts for Nitrobenzene Hydrogenation. ACS Catal 2017. [DOI: 10.1021/acscatal.6b02963] [Citation(s) in RCA: 110] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Peirong Chen
- Institute
of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
| | - Abhishek Khetan
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Institute
for Combustion Technology, RWTH Aachen University, Templergraben 64, 52056 Aachen, Germany
| | - Fengkai Yang
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Vadim Migunov
- Ernst
Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
| | - Philipp Weide
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Sascha P. Stürmer
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Penghu Guo
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Kevin Kähler
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Wei Xia
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Joachim Mayer
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Ernst
Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
| | - Heinz Pitsch
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Institute
for Combustion Technology, RWTH Aachen University, Templergraben 64, 52056 Aachen, Germany
| | - Ulrich Simon
- Institute
of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
| | - Martin Muhler
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
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12
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Kim YJ, Khetan A, Wu W, Chun SE, Viswanathan V, Whitacre JF, Bettinger CJ. Evidence of Porphyrin-Like Structures in Natural Melanin Pigments Using Electrochemical Fingerprinting. Adv Mater 2016; 28:3173-3180. [PMID: 26924536 DOI: 10.1002/adma.201504650] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 01/13/2016] [Indexed: 06/05/2023]
Abstract
Eumelanins are extended heterogeneous biopolymers composed of molecular subunits with ambiguous macromolecular topology. Here, an electrochemical fingerprinting technique is described, which suggests that natural eumelanin pigments contain indole-based tetramers that are arranged into porphyrin-like domains. Spectroscopy and density functional theory calculations suggest that sodium ions undergo occupancy-dependent stepwise insertion into the core of porphyrin-like tetramers in natural eumelanins at discrete potentials.
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Affiliation(s)
- Young Jo Kim
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Abhishek Khetan
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
- Institute for Combustion Technology, RWTH, Aachen, 52062, Germany
| | - Wei Wu
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Sang-Eun Chun
- Department of Chemistry, University of Oregon, Eugene, OR, 97403, USA
| | | | - Jay F Whitacre
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Christopher J Bettinger
- Department of Materials Science and Engineering, Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
- McGowan Institute of Regenerative Medicine, 450 Technology Drive, Suite 300, Pittsburgh, PA, 15219, USA
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13
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14
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Khetan A, Luntz A, Viswanathan V. Trade-Offs in Capacity and Rechargeability in Nonaqueous Li-O2 Batteries: Solution-Driven Growth versus Nucleophilic Stability. J Phys Chem Lett 2015; 6:1254-1259. [PMID: 26262983 DOI: 10.1021/acs.jpclett.5b00324] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The development of high-capacity rechargeable Li-O2 batteries requires the identification of stable solvents that can promote a solution-based discharge mechanism, which has been shown to result in higher discharge capacities. Solution-driven discharge product growth requires dissolution of the adsorbed intermediate LiO2*, thus generating solvated Li+ and O2(-) ions. Such a mechanism is possible in solvents with high Gutmann donor or acceptor numbers. However, O2(-) is a strong nucleophile and is known to attack solvents via proton/hydrogen abstraction or substitution. This kind of a parasitic process is extremely detrimental to the battery's rechargeability. In this work, we develop a thermodynamic model to describe these two effects and demonstrate an anticorrelation between solvents’ stability and their ability to enhance capacity via solution-mediated discharge product growth. We analyze the commonly used solvents in the same framework and describe why solvents that can promote higher discharge capacity are also prone to degradation. Solvating additives for practical Li-O2 batteries will have to be outliers to this observed anticorrelation.
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Affiliation(s)
- Abhishek Khetan
- †Institute for Combustion Technology, RWTH, Templergraben 64, Aachen 52056, Germany
- §Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States
| | - Alan Luntz
- ‡SUNCAT, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025-7015, United States
| | - Venkatasubramanian Viswanathan
- §Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States
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15
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Narayan P, Khetan A. Dramatic regression of coronary artery stenosis three years after diagnosis. Perfusion 2015; 30:587-9. [PMID: 25575704 DOI: 10.1177/0267659114567934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
While strategies for the prevention of the progression of coronary artery lesions have been proposed, documentation of the regression of significant coronary artery lesions is rare. Lifestyle modifications and exercise have been reported to influence the regression of coronary disease, but a dramatic disappearance of coronary artery lesions demonstrated angiographically has been rarely reported. We describe a case where diet and lifestyle modifications, along with lipid-lowering therapy, led to the significant regression of coronary artery stenosis.
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Affiliation(s)
- P Narayan
- Department of Cardiac Surgery, NH Rabindranath Tagore International Institute of Cardiac Sciences, Mukundapur, Kolkata, India
| | - A Khetan
- Department of Cardiology, NH Rabindranath Tagore International Institute of Cardiac Sciences, Mukundapur, Kolkata, India
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16
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Kwak D, Khetan A, Noh S, Pitsch H, Han B. First Principles Study of Morphology, Doping Level, and Water Solvation Effects on the Catalytic Mechanism of Nitrogen-Doped Graphene in the Oxygen Reduction Reaction. ChemCatChem 2014. [DOI: 10.1002/cctc.201402248] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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17
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Abstract
Developing rechargeable Li-O2 batteries hinges on identifying stable solvents resistant to decomposition. Here, we focus on solvent stability against adsorption-induced H-abstraction during discharge. Using a detailed thermodynamic analysis, we show that a solvent's propensity to resist H-abstraction is determined by its acid dissociation constant, pKa, in its own environment. Upon surveying hundreds of solvents for their pKa values in different media, we find linear correlations between the pKa values across various classes of solvents in any two given media. Utilizing these correlations, we choose DMSO as the common standard to compare the relative stability trends. We construct a stability plot based on the solvent's HOMO level and its pKa in DMSO, which reveals that most solvents obey a correlation where solvents with lower HOMO levels tend to have lower pKa values in DMSO. However, this is at odds with the stability requirement that demands deep HOMO levels and high pKa values. Thus, stable solvents need to be outliers to this observed correlation.
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Affiliation(s)
- Abhishek Khetan
- †Institute for Combustion Technology, RWTH Aachen University, Aachen 52056, Germany
| | - Heinz Pitsch
- †Institute for Combustion Technology, RWTH Aachen University, Aachen 52056, Germany
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18
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Abstract
One crucial challenge in developing rechargeable Li-O2 batteries is to identify a stable solvent that is resistant to decomposition in the electrochemical environment of Li2O2. We attempt to identify descriptors that could be used to test for solvent stability. We build on the recent quantitative experimental results on oxygen consumption and release during discharge and charge respectively. We limit our focus to understanding trends in oxidative stability of solvents and based on a systematic treatment of the electrochemical environment of Li2O2, we propose that, to a first approximation, the highest occupied molecular orbital (HOMO) level could be a good descriptor. We demonstrate that this descriptor correlates well with the experimentally measured degree of rechargeability. We utilize this descriptor to screen a large number of solvents and identify several solvents that could enhance the rechargeability of nonaqueous Li-O2 batteries. We provide a comprehensive compilation of available computational and experimental data of several key solvent parameters that we believe will be the genesis for an 'electrolyte genome'.
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Affiliation(s)
- Abhishek Khetan
- †Institute for Combustion Technology, RWTH, Aachen, Germany, 52056
| | - Heinz Pitsch
- †Institute for Combustion Technology, RWTH, Aachen, Germany, 52056
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19
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Affiliation(s)
- M. Aryanpour
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305
- Institut für Technische
Verbrennung, RWTH Aachen University, Templergraben
64, 52056 Aachen, Germany
| | - A. Khetan
- Institut für Technische
Verbrennung, RWTH Aachen University, Templergraben
64, 52056 Aachen, Germany
| | - H. Pitsch
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305
- Institut für Technische
Verbrennung, RWTH Aachen University, Templergraben
64, 52056 Aachen, Germany
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20
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Han L, Khetan A, Hu WS, Sherman DH. Time-lapsed confocal microscopy reveals temporal and spatial expression of the lysine epsilon-aminotransferase gene in Streptomyces clavuligerus. Mol Microbiol 1999; 34:878-86. [PMID: 10594815 DOI: 10.1046/j.1365-2958.1999.01638.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To investigate the temporal and spatial expression patterns of the gene (lat ) encoding lysine epsilon-aminotransferase (LAT) for cephamycin C biosynthesis, a mutant form of green fluorescent protein (mut1GFP) was integrated into the Streptomyces clavuligerus chromosome (strain LH369), resulting in a translational fusion with lat. LAT activity and fluorescence profiles of the recombinant protein paralleled the native LAT enzyme activity profile in wild-type S. clavuligerus, which peaked during exponential growth phase and decreased slowly towards stationary phase. These results indicate that the LAT-Mut1GFP fusion protein retains both LAT and GFP functionality in S. clavuligerus LH369. LH369 produced wild-type levels of cephamycin C in minimal medium culture conditions supplemented with lysine. Time-lapsed confocal microscopy of the S. clavuligerus LH369 strain revealed the temporal and spatial characteristics of lat gene expression and demonstrated that physiological development of S. clavuligerus colonies leading to cephamycin C biosynthesis is limited to the substrate mycelia.
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Affiliation(s)
- L Han
- Department of Microbiology and Biological Process Technology Institute, University of Minnesota, Minneapolis 55455, USA
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21
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Khetan A, Malmberg LH, Kyung YS, Sherman DH, Hu WS. Precursor and cofactor as a check valve for cephamycin biosynthesis in Streptomyces clavuligerus. Biotechnol Prog 1999; 15:1020-7. [PMID: 10585184 DOI: 10.1021/bp990090f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The biosynthesis of secondary metabolites is closely linked to primary metabolism via the supply of precursors, cofactors, and cellular energy. The availability of these precursors and cofactors can potentially be rate-limiting for secondary metabolism. A combined experimental and kinetic modeling approach was used to examine the regulation of flux in the cephamycin biosynthetic pathway in Streptomyces clavuligerus. The kinetic parameters of lysine 6-aminotransferase (LAT), the first enzyme leading to cephamycin biosynthesis and one which was previously identified as being a rate-limiting enzyme, were characterized. LAT converts lysine to alpha-aminoadipic acid using alpha-ketoglutarate as a cosubstrate. The K(m) values for lysine and alpha-ketoglutarate were substantially higher than those for their intracellular concentrations, suggesting that lysine and alpha-ketoglutarate may play a key role in regulating the flux of cephamycin biosynthesis. The important role of this precursor/cosubstrate was supported by simulated results using a kinetic model. When the intracellular concentrations and high K(m) values were taken into account, the predicted intermediate concentration was similar to the experimental measurements. The results demonstrate the controlling roles that precursors and cofactors may play in the biosynthesis of secondary metabolites.
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Affiliation(s)
- A Khetan
- Department of Chemical Engineering, Biological Process Technology Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Abstract
The biosynthesis of beta-lactams is one of the most thoroughly studied antibiotic pathways. The availability of the characteristics and the time profiles of activities of enzymes involved in the biosynthesis allows one to critically evaluate the potential rate-limiting steps in its production. Our approach to understanding the control of beta-lactam biosynthesis has been pursued using a two-stage strategy: (1) to predict the rate-limiting steps using a kinetic model and (2) to relax the rate-limiting steps by engineering the biosynthetic pathway or by altering the kinetic parameters of the predicted key rate-limiting enzyme. Kinetic analysis of the pathway dynamics of cephamycin C production in Streptomyces clavuligerus was performed using data obtained from wild type. Sensitivity analysis revealed that the availability of precursor alpha-aminoadipic acid and activity of ACV synthetase were the potential rate-limiting steps. Relaxation of the precursor limitation was accomplished by integration of an additional copy of the gene encoding lysine-epsilon-aminotransferase (lat) into the chromosome. The recombinant strain showed an increased level of cephamycin C production as expected. The intracellular levels of different intermediates in the pathway in batch cultures were analyzed.
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Affiliation(s)
- A Khetan
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis 55455, USA
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