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Ke Z, Weng J, Xu X. Calculating 13 C NMR chemical shifts of large molecules using the eXtended ONIOM method at high accuracy with a low cost. J Comput Chem 2023; 44:2347-2357. [PMID: 37572044 DOI: 10.1002/jcc.27201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 07/15/2023] [Accepted: 07/24/2023] [Indexed: 08/14/2023]
Abstract
Fragmentation-based methods for nuclear magnetic resonance (NMR) chemical shift calculations have become more and more popular in first-principles calculations of large molecules. However, there are many options for a fragmentation-based method to select, such as theoretical methods, fragmentation schemes, the number of levels of theory, etc. It is important to study the optimal combination of the options to achieve a good balance between accuracy and efficiency. Here we investigate different combinations of options used by a fragmentation-based method, the eXtended ONIOM (XO) method, for 13 C chemical shift calculations on a set of organic and biological molecules. We found that: (1) introducing Hartree-Fock exchange into density functional theory (DFT) could reduce the calculation error due to fragmentation in contrast to pure DFT functionals, while a hybrid functional, xOPBE, is generally recommended; (2) fragmentation schemes generated from the molecular tailoring approach (MTA) with small level parameter n, for example, n = 2 and the degree-based fragmentation method (DBFM) with n = 1, are sufficient to achieve satisfactory accuracy; (3) the two-level XO (XO2) NMR calculation is superior to the calculation with only one level of theory, as the second level (i.e., low level) of theory provides a way to well describe the long-range effect. These findings are beneficial to practical applications of fragmentation-based methods for NMR chemical shift calculations of large molecules.
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Affiliation(s)
- Zhipeng Ke
- Institute of Photochemistry and Photofunctional Materials, University of Shanghai for Science and Technology, Shanghai, China
- Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Ministry of Education Key Laboratory of Computational Physical Sciences, Department of Chemistry, Fudan University, Shanghai, China
| | - Jingwei Weng
- Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Ministry of Education Key Laboratory of Computational Physical Sciences, Department of Chemistry, Fudan University, Shanghai, China
| | - Xin Xu
- Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Ministry of Education Key Laboratory of Computational Physical Sciences, Department of Chemistry, Fudan University, Shanghai, China
- Hefei National Laboratory, Hefei, China
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Li H, Wang X, Yuan K, Lv L, Liu K, Wang C, Pan S, Wang P, Li Z. The luminescent and reaction mechanisms of a fluorescent probe for the detection of hypochlorous acid: Insights from theory. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 294:122572. [PMID: 36889138 DOI: 10.1016/j.saa.2023.122572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 02/26/2023] [Accepted: 02/27/2023] [Indexed: 06/18/2023]
Abstract
We have designed and synthesized a novel fluorescent probe BMH for detection of hypochlorous acid (HClO), which can increase dramatically the fluorescence intensity and had ultrafast response, a low detection limit and a wide pH range of application. In this paper, we further studied its fluorescence quantum yield and photoluminescence mechanism theoretically. The calculated results indicated the first excited states of BMH and BM (it was the oxidized product by HClO) were bright states with large oscillator strengths, however, due to more larger reorganization energy of BMH, the predicted internal conversion rate kIC of BMH was four orders of magnitude larger than that of BM; moreover, owing to the effect of heavy atom from sulfur atom in BMH, the predicted intersystem crossing rate kisc of BMH was five orders of magnitude larger than that of BM; meanwhile there was no significant difference found between both the predicted radiative rates kr, thus the calculated fluorescence quantum yield of BMH was nearly zero and that of BM was more than 90%, the data showed the BMH had no fluorescence but its oxidated produce BM possessed strong fluorescence. In addition, the reaction mechanism of BMH transforming into BM has been investigated too, according to the potential energy profile, we found that the course of BMH converting into BM consisted of three elementary reactions. The research results revealed the solvent effect can decreased the activation energy, which was more favorable for these elementary reactions.
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Affiliation(s)
- Huixue Li
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Xiaofeng Wang
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Kun Yuan
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Lingling Lv
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Kui Liu
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Changqing Wang
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Sujuan Pan
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Peng Wang
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China
| | - Zhifeng Li
- School of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China.
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Kolganov AA, Gabrienko AA, Stepanov AG. Reaction of Methane with Benzene and CO on Cu-Modified ZSM-5 Zeolite Investigated by 13C MAS NMR Spectroscopy. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.140188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Kolganov AA, Gabrienko A, Stepanov AG. DFT approach to predict 13C NMR chemical shifts of hydrocarbon species adsorbed on Zn-modified zeolite. Phys Chem Chem Phys 2022; 24:22241-22249. [DOI: 10.1039/d2cp02468c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
13C MAS NMR spectroscopy is a powerful technique to study the mechanisms of hydrocarbon transformations on heterogeneous catalysts. It can reliably identify the surface intermediates and the adsorbed products based...
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Panthi D, Adeyiga O, Odoh SO. DFT Analysis of Methane C-H Activation and Over-Oxidation by [Cu 2 O] 2+ and [Cu 2 O 2 ] 2+ Sites in Zeolite Mordenite: Intra- versus Inter-site Over-Oxidation. Chemphyschem 2021; 22:2517-2525. [PMID: 34519406 DOI: 10.1002/cphc.202100580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 09/09/2021] [Indexed: 11/06/2022]
Abstract
Methane over-oxidation by copper-exchanged zeolites prevents realization of high-yield catalytic conversion. However, there has been little description of the mechanism for methane over-oxidation at the copper active sites of these zeolites. Using density functional theory (DFT) computations, we reported that tricopper [Cu3 O3 ]2+ active sites can over-oxidize methane. However, the role of [Cu3 O3 ]2+ sites in methane-to-methanol conversion remains under debate. Here, we examine methane over-oxidation by dicopper [Cu2 O]2+ and [Cu2 O2 ]2+ sites using DFT in zeolite mordenite (MOR). For [Cu2 O2 ]2+ , we considered the μ-(η2 :η2 ) peroxo-, and bis(μ-oxo) motifs. These sites were considered in the eight-membered (8MR) ring of MOR. μ-(η2 :η2 ) peroxo sites are unstable relative to the bis(μ-oxo) motif with a small interconversion barrier. Unlike [Cu2 O]2+ which is active for methane C-H activation, [Cu2 O2 ]2+ has a very large methane C-H activation barrier in the 8MR. Stabilization of methanol and methyl at unreacted dicopper sites however leads to over-oxidation via sequential hydrogen atom abstraction steps. For methanol, these are initiated by abstraction of the CH3 group, followed by OH and can proceed near 200 °C. Thus, for [Cu2 O]2+ and [Cu2 O2 ]2+ species, over-oxidation is an inter-site process. We discuss the implications of these findings for methanol selectivity, especially in comparison to the intra-site process for [Cu3 O3 ]2+ sites and the role of Brønsted acid sites.
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Affiliation(s)
- Dipak Panthi
- Department of Chemistry, University of Nevada Reno, 1664N. Virginia Street, Reno, NV 89557-0216, USA
| | - Olajumoke Adeyiga
- Department of Chemistry, University of Nevada Reno, 1664N. Virginia Street, Reno, NV 89557-0216, USA
| | - Samuel O Odoh
- Department of Chemistry, University of Nevada Reno, 1664N. Virginia Street, Reno, NV 89557-0216, USA
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Adeyiga O, Odoh SO. Methane Over-Oxidation by Extra-Framework Copper-Oxo Active Sites of Copper-Exchanged Zeolites: Crucial Role of Traps for the Separated Methyl Group. Chemphyschem 2021; 22:1101-1109. [PMID: 33786957 DOI: 10.1002/cphc.202100103] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 03/30/2021] [Indexed: 11/07/2022]
Abstract
Copper-exchanged zeolites are useful for stepwise conversion of methane to methanol at moderate temperatures. This process also generates some over-oxidation products like CO and CO2 . However, mechanistic pathways for methane over-oxidation by copper-oxo active sites in these zeolites have not been previously described. Adequate understanding of methane over-oxidation is useful for developing systems with higher methanol yields and selectivities. Here, we use density functional theory (DFT) to examine methane over-oxidation by [Cu3 O3 ]2+ active sites in zeolite mordenite MOR. The methyl group formed after activation of a methane C-H bond can be stabilized at a μ-oxo atom of the active site. This μ-(O-CH3 ) intermediate can undergo sequential hydrogen atom abstractions till eventual formation of a copper-monocarbonyl species. Adsorbed formaldehyde, water and formates are also formed during this process. The overall mechanistic path is exothermic, and all intermediate steps are facile at 200 °C. Release of CO from the copper-monocarbonyl costs only 3.4 kcal/mol. Thus, for high methanol selectivities, the methyl group from the first hydrogen atom abstraction step must be stabilized away from copper-oxo active sites. Indeed, it must be quickly trapped at an unreactive site (short diffusion lengths) while avoiding copper-oxo species (large paths between active sites). This stabilization of the methyl group away from the active sites is central to the high methanol selectivities obtained with stepwise methane-to-methanol conversion.
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Affiliation(s)
- Olajumoke Adeyiga
- Department of Chemistry, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV 89557-0216, USA
| | - Samuel O Odoh
- Department of Chemistry, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV 89557-0216, USA
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