1
|
Ma X, Anyaeche RO, Feng E, Johnson E, Roller E, Rumley DJ, Nash JJ, Kenttämaa HI. Gas-Phase Reactivity of Quinoline-Based Singlet Oxenium Cations. J Org Chem 2024; 89:5458-5468. [PMID: 38554096 DOI: 10.1021/acs.joc.3c02895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/01/2024]
Abstract
Isomeric quinolyloxenium cations were generated in the gas phase in an ion trap mass spectrometer to explore their reactions. The structures of some products were identified via collision-activated dissociation experiments involving model compounds to demonstrate that they have the expected heavy atom connectivity. The lack of radical reactions suggests that the cations have closed-shell singlet electronic ground states. Calculations (CASPT2/CASSCF(16,14)/cc-pVTZ//CASSCF(16,14)/cc-pVTZ) predict that their closed-shell singlet (1A') ground states are lower in energy by ca. 25 kcal mol-1 than their lowest-lying excited states. All cations are reactive toward dimethyl disulfide, dimethyl sulfide, and allyl iodide and most toward water and moderately reactive toward cyclohexane, reflecting their strongly electrophilic nature. They form adducts with nucleophiles in exothermic reactions (ca. 50 kcal mol-1 for dimethyl sulfide) that can fragment or be stabilized via IR emission. Most water adducts spontaneously isomerize to lower-energy tautomers. The nucleophiles preferentially add to those carbon atoms in the benzene ring that have the greatest positive charge (but not the carbonyl carbon). The cations react with cyclohexane via hydride abstraction by the oxygen atom. This is the only reaction that initially involves the oxygen atom and hence reflects the formally positively charged, monovalent oxygen atom in these cations.
Collapse
Affiliation(s)
- Xin Ma
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Ruth O Anyaeche
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Erlu Feng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Erynn Johnson
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Ethan Roller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Daniel J Rumley
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47906, United States
| |
Collapse
|
2
|
Juneau A, Lepage I, Sabbah SG, Winter AH, Frenette M. Mechanistic Insight into Phenol Dearomatization by Hypervalent Iodine: Direct Detection of a Phenoxenium Cation. J Org Chem 2022; 87:14274-14283. [PMID: 36215691 DOI: 10.1021/acs.joc.2c01765] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Phenol dearomatization is one of several oxidation reactions enabled by hypervalent iodine reagents. However, the presence of a proposed free phenoxenium intermediate in phenol dearomatization is a matter of debate in the literature. Here, we report the unambiguous detection of a free phenoxenium intermediate in the reaction of an electron-rich phenol, 2,4,6-trimethoxyphenol, and (diacetoxyiodo)benzene using UV-vis and resonance Raman spectroscopies. In contrast, we predominantly detect single electron oxidation products of less electron-rich phenols or alkoxy-substituted aromatics in their reaction with (diacetoxyiodo)benzene using UV-vis and electron paramagnetic resonance (EPR) spectroscopies. We conclude that the often-postulated free phenoxenium intermediate, while possible with highly stabilizing substituents, is unlikely to be a general mechanistic pathway in the reaction of typical phenols with hypervalent iodine reagents. The polar solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or the use of more strongly oxidizing hypervalent iodine reagents, such as [bis(trifluoroacetoxy)iodo]benzene (PIFA) or [hydroxy(tosyloxy)iodo]benzene (HTIB), can help reduce the formation of radical byproducts and favors the formation of phenoxenium intermediates.
Collapse
Affiliation(s)
- Antoine Juneau
- Department of Chemistry, Quebec Centre for Advanced Materials and NanoQAM, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada
| | - Iannick Lepage
- Department of Chemistry, Quebec Centre for Advanced Materials and NanoQAM, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada
| | - Sami G Sabbah
- Department of Chemistry, Quebec Centre for Advanced Materials and NanoQAM, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada
| | - Arthur H Winter
- Department of Chemistry, Iowa State University, 1605 Gilman Hall, Ames, Iowa 50010, United States
| | - Mathieu Frenette
- Department of Chemistry, Quebec Centre for Advanced Materials and NanoQAM, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada
| |
Collapse
|
3
|
Du L, Wang J, Qiu Y, Liang R, Lu P, Chen X, Phillips DL, Winter AH. Generation and direct observation of a triplet arylnitrenium ion. Nat Commun 2022; 13:3458. [PMID: 35710806 PMCID: PMC9203820 DOI: 10.1038/s41467-022-31091-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 05/31/2022] [Indexed: 11/22/2022] Open
Abstract
Nitrenium ions are important reactive intermediates in both chemistry and biology. Although singlet nitrenium ions are well-characterized by direct methods, the triplet states of nitrenium ions have never been directly detected. Here, we find that the excited state of the photoprecursor partitions between heterolysis to generate the singlet nitrenium ion and intersystem crossing (ISC) followed by a spontaneous heterolysis process to generate the triplet p-iodophenylnitrenium ion (np). The triplet nitrenium ion undergoes ISC to generate the ground singlet state, which ultimately undergoes proton and electron transfer to generate a long-lived radical cation that further generates the reduced p-iodoaniline. Ab Initio calculations were performed to map out the potential energy surfaces to better understand the excited state reactivity channels show that an energetically-accessible singlet-triplet crossing lies along the N-N stretch coordinate and that the excited triplet state is unbound and spontaneously eliminates ammonia to generate the triplet nitrenium ion. These results give a clearer picture of the photophysical properties and reactivity of two different spin states of a phenylnitrenium ion and provide the first direct glimpse of a triplet nitrenium ion. Nitrenium ions are highly electrophilic reactive intermediates of formula R−N−R+, nitrogen analogue of carbenes. Here the authors report the detection of a triplet nitrenium ion using time-resolved spectroscopic methods and ab initio computations, allowing a glimpse at the properties and behavior of this important class of intermediates.
Collapse
Affiliation(s)
- Lili Du
- School of Life Sciences, Jiangsu University, 212013, Zhenjiang, P.R. China.,Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
| | - Juanjuan Wang
- Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Department of Chemistry, Beijing Normal University, 100875, Beijing, P.R. China
| | - Yunfan Qiu
- Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, IA, 50011, USA
| | - Runhui Liang
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
| | - Penglin Lu
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
| | - Xuebo Chen
- Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Department of Chemistry, Beijing Normal University, 100875, Beijing, P.R. China.
| | - David Lee Phillips
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China. .,Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, IA, 50011, USA.
| | - Arthur H Winter
- Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, IA, 50011, USA.
| |
Collapse
|
4
|
Mark A, Feinberg EC, Dinnocenzo JP. Direct Experimental Evidence for Alkoxyl Radicals Reacting as Hydrogen Atom Donors toward Pyridines. J Org Chem 2021; 86:7508-7514. [PMID: 34033720 DOI: 10.1021/acs.joc.1c00504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nanosecond transient absorption spectroscopy was used to generate ethoxyl radicals and demonstrate that they react with 2,6-lutidine and 4-phenylpyridine to give the corresponding N-hydropyridinyl radicals-products of a novel hydrogen atom transfer from the alkoxyl radical to the nitrogen atom of the substituted pyridines. Nanosecond kinetics show that both reactions are rapid (k ∼ 107 M-1 s-1) in acetonitrile at room temperature. Rate constants measured for reaction of the ethoxyl vs. d5-ethoxyl radical with 2,6-lutidine and 4-phenylpyridine show that both reactions exhibit primary H/D kinetic isotope effects for the hydrogen (deuterium) atom transfer reactions.
Collapse
Affiliation(s)
- Analuz Mark
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Elizabeth C Feinberg
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Joseph P Dinnocenzo
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| |
Collapse
|
5
|
Yang S, Cao C, Islam A, Sun S, Deng Z, Li J, Ni S, Tong QX, Li MD. Disentangling Multiple Effects on Excited-State Intramolecular Charge Transfer among Asymmetrical Tripartite PPI-TPA/PCz Triads. Chemistry 2021; 27:1337-1345. [PMID: 32776379 DOI: 10.1002/chem.202002862] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 07/25/2020] [Indexed: 11/07/2022]
Abstract
By utilizing the bipolarity of 1,2-diphenylphenanthroimidazole (PPI), two types of asymmetrical tripartite triads (PPI-TPA and PPI-PCz) were designed with triphenylamine (TPA) and 9-phenylcarbazole (PCz). These triads are deep-blue luminescent materials with a high fluorescence quantum yield of nearly 100 %. To trace the photophysical behaviors of these triads, their excited-state evolution channels and interchromophoric interactions were investigated by ultrafast time-resolved transient absorption and excited-state theoretical calculations. The results suggest that the electronic nature, asymmetrical tripartite structure, and electron-hole distance of these triads, as well as solvent polarity, determine the lifetime of intramolecular charge transfer (ICT). Interestingly, PPI-PCz triads show anti-Kasha ICT, and the charge-transfer direction among the triads is adjustable. For the PPI-TPA triad, the electron is transferred from TPA to PPI, whereas for the PPI-PCz triad the electron is pushed from PPI to PCz. Exploration of the excited-state ICT in these triads may pave the way to design better luminescent materials in the future.
Collapse
Affiliation(s)
- Sirui Yang
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Chen Cao
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China.,Center of Super-Diamond and Advanced Films (COSDAF), Department of Chemistry, City University of Hong Kong, Hong Kong SAR, 999077, P. R. China
| | - Amjad Islam
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Shanshan Sun
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Ziqi Deng
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Jiayu Li
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Shaofei Ni
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Qing-Xiao Tong
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| | - Ming-De Li
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou, 515063, P. R. China
| |
Collapse
|
6
|
Pang J, Deng Z, Sun S, Huang G, Zhang G, Islam A, Dang L, Phillips DL, Li MD. Unprecedentedly Ultrafast Dynamics of Excited States of C═C Photoswitching Molecules in Nanocrystals and Microcrystals. J Phys Chem Lett 2021; 12:41-48. [PMID: 33296591 DOI: 10.1021/acs.jpclett.0c03232] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The C═C photoswitching molecules [1,2-di(4-pyridyl)ethylene (DPE), 4-styrylpyridine (SP), and trans-1,2-stilbene (TS)] show favorable photoisomerization characteristics. Although the solid states of photoswitching molecules are usually used in optical devices, their excited state's evolution has been little explored. Here, the excited state's relaxation of DPE, SP, and TS in nanocrystal/microcrystal suspensions as well as in solution phase was studied to uncover the early events of their excited states. The dynamics of nanocrystal/microcrystal suspensions was tremendously accelerated in comparison to the kinetics obtained in the solution for these molecules under excitation. DPE exhibits the slowest decay rate, while SP shows the fastest decay rate in nanocrystal suspensions or solution, suggesting SP may be the best candidate for the photoswitching device. The intermolecular interactions and space restriction of the crystal lead to the acceleration of the excited state's evolution for DPE, SP, and TS. This provides new insight into the design of optical materials.
Collapse
Affiliation(s)
- Junhong Pang
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Ziqi Deng
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Shanshan Sun
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Guanheng Huang
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Guohui Zhang
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Amjad Islam
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Li Dang
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - David Lee Phillips
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Ming-De Li
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Province, Shantou University, Shantou 515063, China
| |
Collapse
|
7
|
Zhao J, Zhang X, Zhu R, Su T, Phillips DL. Photophysical Properties Controlled by Substituents with Lone-Pair Electrons at the Ortho- or Para-Positions of Fluoroquinolone Antibiotics. J Phys Chem B 2019; 123:3156-3162. [PMID: 30900898 DOI: 10.1021/acs.jpcb.8b10859] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ortho- or para-substituents of NH2 or N-alkyl-containing lone-pair electrons were found to change the energy levels and transition configurations of the highest occupied molecular orbital for some fluoroquinolone-based antibiotics (FQs) and can significantly influence the electronic structure, intermolecular hydrogen bonding, internal conversion, and fluorescence and intersystem crossing efficiencies of FQs in acetonitrile or aqueous solution after photoexcitation. These findings provide new insights that can help in the molecular design strategies to regulate the photophysical properties of photosensitive medicines, photodynamic therapy reagents, and energy conversion materials that contain similar aromatic carbonyl structures.
Collapse
Affiliation(s)
- Jianfeng Zhao
- Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong 11111 , P. R. China
| | - Xiting Zhang
- Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong 11111 , P. R. China
| | - Ruixue Zhu
- Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong 11111 , P. R. China.,School of Physical Science and Technology , Shanghai Tech University , Shanghai 201210 , P. R. China
| | - Tao Su
- Department of Molten Salt Chemistry and Engineering, Shanghai Institute of Applied Physics , Chinese Academy of Sciences , 2019, Jia Luo Road , Jiading District, Shanghai 201800 , P. R. China
| | - David Lee Phillips
- Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong 11111 , P. R. China
| |
Collapse
|
8
|
Li MD, Yan Z, Zhu R, Phillips DL, Aparici-Espert I, Lhiaubet-Vallet V, Miranda MA. Enhanced Drug Photosafety by Interchromophoric Interaction Owing to Intramolecular Charge Separation. Chemistry 2018; 24:6654-6659. [DOI: 10.1002/chem.201800716] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2018] [Indexed: 01/07/2023]
Affiliation(s)
- Ming-De Li
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province; Shantou University; Guangdong 515063 P. R. China
| | - Zhiping Yan
- Department of Chemistry; The University of Hong Kong, Pokfulam Road; Hong Kong S. A. R. P. R. China
| | - Ruixue Zhu
- Department of Chemistry; The University of Hong Kong, Pokfulam Road; Hong Kong S. A. R. P. R. China
| | - David Lee Phillips
- Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province; Shantou University; Guangdong 515063 P. R. China
- Department of Chemistry; The University of Hong Kong, Pokfulam Road; Hong Kong S. A. R. P. R. China
| | - Isabel Aparici-Espert
- Instituto de Tecnología Química UPV-CSIC; Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas; Avda de los Naranjos s/n 46022 Valencia Spain
| | - Virginie Lhiaubet-Vallet
- Instituto de Tecnología Química UPV-CSIC; Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas; Avda de los Naranjos s/n 46022 Valencia Spain
| | - Miguel A. Miranda
- Instituto de Tecnología Química UPV-CSIC; Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas; Avda de los Naranjos s/n 46022 Valencia Spain
| |
Collapse
|
9
|
Yang Y, Fang W, Chen X. Mechanistic insights into the formation of oxenium ions and radical intermediates through the photolysis of phenylhydroxylamine and its derivatives. Phys Chem Chem Phys 2018; 20:2220-2229. [PMID: 29303190 DOI: 10.1039/c7cp07071c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photolysis of photoprecursors to produce oxenium ions has been the subject of extensive experimental studies from femtosecond to microsecond time scales. However, mechanistic insights into the generation of activated intermediate species remain elusive. Herein, we present a theoretical investigation to comprehensively elucidate the possible reaction channels for the formation of oxenium ions and radical intermediates at the multi-configuration perturbation level of theory. Computational results show that photo-initiated electron donation from the phenyl moiety to the repulsive N-O σ* orbital leads to the formation of a diradical intermediate in ground state, and further triggers intramolecular electron transfer from the phenyl moiety to the ammonia radical cation (˙NH3+). This affords closed-shell singlet oxenium ions and neutral :NH3 as the major products. However, the generation of open-shell triplet outcomes is shown to rely on the energetically accessible single-triplet crossings and spin-orbital interaction among the involved electronic states. Taken together, these data can be used to determine the electronic structures and related properties, as well as reactivities, of oxenium ions and radicals generated by the photolysis of phenylhydroxylamine and its derivatives.
Collapse
Affiliation(s)
- Yumei Yang
- Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Department of Chemistry, Beijing Normal University, Xin-wai-da-jie 19, Beijing 100875, P. R. China.
| | | | | |
Collapse
|
10
|
Du L, Qiu Y, Lan X, Zhu R, Phillips DL, Li MD, Dutton AS, Winter AH. Direct Detection of the Open-Shell Singlet Phenyloxenium Ion: An Atom-Centered Diradical Reacts as an Electrophile. J Am Chem Soc 2017; 139:15054-15059. [PMID: 28945081 DOI: 10.1021/jacs.7b07512] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A new photoprecursor to the phenyloxenium ion, 4-methoxyphenoxypyridinium tetrafluoroborate, was investigated using trapping studies, product analysis, computational investigations, and laser flash photolysis experiments ranging from the femtosecond to the millisecond time scale. These experiments allowed us to trace the complete arc of the photophysics and photochemistry of this photoprecursor beginning with the initially populated excited states to its sequential formation of transient intermediates and ultimate formation of stable photoproducts. We find that the excited state of the photoprecursor undergoes heterolysis to generate the phenyloxenium ion in ∼2 ps but surprisingly generates the ion in its open-shell singlet diradical configuration (1A2), permitting an unexpected look at the reactivity of an atom-centered open-shell singlet diradical. The open-shell phenyloxenium ion (1A2) has a much shorter lifetime (τ ∼ 0.2 ns) in acetonitrile than the previously observed closed-shell singlet (1A1) phenyloxenium ion (τ ∼ 5 ns). Remarkably, despite possessing no empty valence orbitals, this open-shell singlet oxenium ion behaves as an even more powerful electrophile than the closed-shell singlet oxenium ion, undergoing solvent trapping by weakly nucleophilic solvents such as water and acetonitrile or externally added nucleophiles (e.g., azide) rather than engaging in typical diradical chemistry, such as H atom abstraction, which we have previously observed for a triplet oxenium ion. In acetonitrile, the open-shell singlet oxenium ion is trapped to generate ortho and para Ritter intermediates, one of which (para) is directly observed as a longer-lived species (τ ∼ 0.1 ms) in time-resolved resonance Raman experiments. The Ritter intermediates are ultimately trapped by either the 4-methoxypyridine leaving group (in the case of para addition) or trapped internally via an essentially barrierless rearrangement (in the case of ortho addition) to generate a cyclized product. The expectation that singlet diradicals react similarly to triplet or uncoupled diradicals needs to be reconsidered, as a recent study by Perrin and Reyes-Rodríguez (J. Am. Chem. Soc. 2014, 136, 15263) suggested the unsettling possibility that singlet p-benzyne could suffer nucleophilic attack to generate a naked phenyl anion. Now, this study provides direct spectroscopic observation of this phenomenon, with an atom-centered open-shell singlet diradical reacting as a powerful electrophile. To the question of whether a nucleophile can attack a singly occupied molecular orbital, the answer is apparently yes, at least if another partially occupied orbital is available to avoid violation of the rules of valence.
Collapse
Affiliation(s)
- Lili Du
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, People's Republic of China
| | - Yunfan Qiu
- Department of Chemistry, Iowa State University , 2101d Hach Hall, Ames, Iowa 50011, United States
| | - Xin Lan
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, People's Republic of China
| | - Ruixue Zhu
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, People's Republic of China
| | - David Lee Phillips
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, People's Republic of China
| | - Ming-De Li
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, People's Republic of China.,Department of Chemistry, Shantou University , Guangdong 515063, P. R. China.,Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University , Shantou 515063, P. R. China
| | - Andrew S Dutton
- Department of Chemistry, Iowa State University , 2101d Hach Hall, Ames, Iowa 50011, United States
| | - Arthur H Winter
- Department of Chemistry, Iowa State University , 2101d Hach Hall, Ames, Iowa 50011, United States
| |
Collapse
|
11
|
Kobayashi Y, Okajima H, Sotome H, Yanai T, Mutoh K, Yoneda Y, Shigeta Y, Sakamoto A, Miyasaka H, Abe J. Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer. J Am Chem Soc 2017; 139:6382-6389. [DOI: 10.1021/jacs.7b01598] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yoichi Kobayashi
- Department
of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Hajime Okajima
- Department
of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Hikaru Sotome
- Division
of Frontier Materials Science and Center for Promotion of Advanced
Interdisciplinary Research, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Takeshi Yanai
- Department
of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan
| | - Katsuya Mutoh
- Department
of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Yusuke Yoneda
- Division
of Frontier Materials Science and Center for Promotion of Advanced
Interdisciplinary Research, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Yasuteru Shigeta
- Department
of Physics, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8577, Japan
| | - Akira Sakamoto
- Department
of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| | - Hiroshi Miyasaka
- Division
of Frontier Materials Science and Center for Promotion of Advanced
Interdisciplinary Research, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Jiro Abe
- Department
of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
| |
Collapse
|
12
|
Zhu R, Li MD, Du L, Phillips DL. Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions. J Phys Chem B 2017; 121:2712-2720. [PMID: 28281345 DOI: 10.1021/acs.jpcb.6b11934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light. This photoexcitation is followed by a fast carbon-halogen bond cleavage that leads to the generation of radical intermediates via either triplet and/or singlet excited states. It is found that the singlet excited state-mediated carbon-halogen cleavage is the predominant dehalogenation process in ACN solvent, whereas a triplet state-mediated carbon-halogen cleavage prefers to occur in the ACN/water mixed solutions. The singlet-to-triplet energy gap is decreased in the ACN/water mixed solvents and this helps facilitate an intersystem crossing process, and thus, the carbon-halogen bond cleavage happens mostly through an excited triplet state in the aqueous solutions examined. The ns-TA and ns-TR3 results also provide some evidence that radical intermediates are generated through a homolytic carbon-halogen bond cleavage via predominantly the singlet excited state pathway in ACN but via mainly the triplet state pathway in the aqueous solutions. In strong acidic solutions, protonation at the oxygen and/or nitrogen atoms of the 1,2,4-triazole-3-one group appears to hinder the dehalogenation reactions. This may offer the possibility that the phototoxicity of ITR due to the generation of aryl or halogen radicals can be reduced by protonation of certain moieties in suitably designed ITR halogen-containing derivatives.
Collapse
Affiliation(s)
- Ruixue Zhu
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Pokfulam, Hong Kong S.A.R., P. R. China
| | - Ming-de Li
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Pokfulam, Hong Kong S.A.R., P. R. China.,Department of Chemistry, Shantou University , Shantou 515063, China
| | - Lili Du
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Pokfulam, Hong Kong S.A.R., P. R. China
| | - David Lee Phillips
- Department of Chemistry, The University of Hong Kong , Pokfulam Road, Pokfulam, Hong Kong S.A.R., P. R. China
| |
Collapse
|
13
|
Qiu Y, Winter AH. New photoheterolysis precursors to study oxenium ions: combining experiment and theory. Org Biomol Chem 2017; 15:2666-2671. [DOI: 10.1039/c7ob00180k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The combination of theoretical calculations and laser flash photolysis experiments has aided in understanding the reactivity and properties of oxenium ions.
Collapse
Affiliation(s)
- Yunfan Qiu
- Department of Chemistry
- Iowa State University
- Ames
- USA
| | | |
Collapse
|
14
|
Du L, Zhang X, Xue J, Tang W, Li MD, Lan X, Zhu J, Zhu R, Weng Y, Li YL, Phillips DL. Influence of Water in the Photogeneration and Properties of a Bifunctional Quinone Methide. J Phys Chem B 2016; 120:11132-11141. [PMID: 27723330 DOI: 10.1021/acs.jpcb.6b08705] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Quinone methides (QM) are crucial reactive species in molecular biology and organic chemistry, with little known regarding the mechanism(s) for the generation of short-lived reactive QM intermediates from relevant precursors in aqueous solutions. In this study, several time-resolved spectroscopy methods were used to directly examine the photophysics and photochemical pathways of 1,1'-(2,2'-dihydroxy-1,1'-binaphthyl-6,6'-diyl)bis(N,N,N-trimethylmethanaminium) bromide (BQMP-b) from initial photoexcitation to the generation of the key reactive binol QM intermediate (BQM) in aqueous solution. The fluorescence of BQMP-b is effectively quenched with a small amount of water, which suggests an excited state intramolecular proton transfer (ESIPT) occurs. The kinetics isotope effects observed in femtosecond and nanosecond time-resolved transient absorption experiments provide evidence for the participation of water molecules in the BQMP-b singlet excited state ESIPT process and in the subsequent -HNMe3+ group release and ground state intramolecular proton transfer that give rise to production of the reactive BQM intermediate. Nanosecond time-resolved resonance Raman (ns-TR3) measurements were also employed to investigate the structure and properties of several intermediates, including the key reactive BQM in aqueous solution. The ns-TR3 and density functional theory (DFT) computational results were compared, and this indicates the binol moiety and water molecules both have important roles in the characteristics and structure of the key reactive BQM intermediate produced from BQMP-b. The results presented here also provide new benchmark characterization of bifunctional quinone methide intermediates that can be utilized to guide direct time-resolved spectroscopic study of the alkylation and interstrand cross-linking reactions of quinone methides with DNA in the future.
Collapse
Affiliation(s)
- Lili Du
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| | - Xiting Zhang
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| | - Jiadan Xue
- Department of Chemistry, Zhejiang Sci-Tech University , Hangzhou 310018, P. R. China
| | - WenJian Tang
- School of Pharmacy, Anhui Medical University , Meishan Road 81, Hefei 230032, P.R. China
| | - Ming-De Li
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| | - Xin Lan
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| | - Jiangrui Zhu
- Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, P. R. China
| | - Ruixue Zhu
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| | - Yuxiang Weng
- Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, P. R. China
| | - Yun-Liang Li
- Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, P. R. China
| | - David Lee Phillips
- Department of Chemistry, University of Hong Kong , Pokfulam Road, Hong Kong S.A.R., P. R. China
| |
Collapse
|
15
|
Liu M, Li MD, Huang J, Li T, Liu H, Li X, Phillips DL. Substituent Effects on the Photodeprotection Reactions of Selected Ketoprofen Derivatives in Phosphate Buffered Aqueous Solutions. Sci Rep 2016; 6:21606. [PMID: 26899243 PMCID: PMC4761923 DOI: 10.1038/srep21606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 01/27/2016] [Indexed: 11/15/2022] Open
Abstract
Photodeprotection is an important reaction that has been attracting broad interest for use in a variety of applications. Recent advances in ultrafast and vibrational time-resolved spectroscopies can facilitate obtaining data to help unravel the reaction mechanisms involving in the photochemical reactions of interest. The kinetics and reaction mechanisms for the photodeprotection reactions of ketoprofen derivatives containing three different substituents (ibuprofen, Br and I) were investigated by femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy methods in phosphate buffered solutions (PBS). Fs-TA allows us to detect the decay kinetics of the triplet species as the key precursor for formation of a carbanion species for three different substituents attached to ketoprofen. To characterize the structural and electronic properties of the corresponding carbanion and triplet intermediates, TR3 spectroscopic experiments were conducted. The transient spectroscopy work reveals that the different substituents affect the photodecarboxylation reaction to produce carbon dioxide which in turn influences the generation of the carbanion species which determines the rate of the photorelease of the functional groups attached on the ketoprofen parent molecule. The fingerprint TR3 spectroscopy results suggest that ketoprofen derivatives may be deactivated to produce a triplet carbanion when increasing the atom mass of the halogen atoms.
Collapse
Affiliation(s)
- Mingyue Liu
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - Ming-De Li
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - Jinqing Huang
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - Tianlu Li
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - Han Liu
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - Xuechen Li
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| | - David Lee Phillips
- Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong
| |
Collapse
|
16
|
Tojo S, Fujitsuka M, Majima T. Structures of 4-substituted thioanisole radical cations studied by time-resolved resonance Raman spectroscopy during pulse radiolysis and theoretical calculations. RSC Adv 2016. [DOI: 10.1039/c6ra21460f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The structures of 4-substituted thioanisole radical cations were studied by time-resolved resonance Raman spectroscopy during pulse radiolysis and DFT calculation, indicating importance of charge and spin distributions toward the dimerization.
Collapse
Affiliation(s)
- Sachiko Tojo
- The Institute of Scientific and Industrial Research (SANKEN)
- Osaka University
- Ibaraki
- Japan
| | - Mamoru Fujitsuka
- The Institute of Scientific and Industrial Research (SANKEN)
- Osaka University
- Ibaraki
- Japan
| | - Tetsuro Majima
- The Institute of Scientific and Industrial Research (SANKEN)
- Osaka University
- Ibaraki
- Japan
| |
Collapse
|
17
|
Yue Y, Novianti ML, Tessensohn ME, Hirao H, Webster RD. Optimizing the lifetimes of phenoxonium cations derived from vitamin E via structural modifications. Org Biomol Chem 2015; 13:11732-9. [PMID: 26480893 DOI: 10.1039/c5ob01868d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Systematic synthesis of a number of new phenolic compounds with structures similar to vitamin E led to the identification of several sterically hindered compounds that when electrochemically oxidised in acetonitrile in a -2e(-)/-H(+) process formed phenoxonium diamagnetic cations that were resistant to hydrolysis reactions. The reactivity of the phenoxonium ions was ascertained by performing cyclic voltammetric scans during the addition of carefully controlled quantities of water into acetonitrile solutions, with the data modelled using digital simulation techniques.
Collapse
Affiliation(s)
- Yanni Yue
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
| | | | | | | | | |
Collapse
|
18
|
Li MD, Albright TR, Hanway PJ, Liu M, Lan X, Li S, Peterson J, Winter AH, Phillips DL. Direct Spectroscopic Detection and EPR Investigation of a Ground State Triplet Phenyl Oxenium Ion. J Am Chem Soc 2015. [PMID: 26198984 DOI: 10.1021/jacs.5b06302] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Oxenium ions are important reactive intermediates in synthetic chemistry and enzymology, but little is known of the reactivity, lifetimes, spectroscopic signatures, and electronic configurations of these unstable species. Recent advances have allowed these short-lived ions to be directly detected in solution from laser flash photolysis of suitable photochemical precursors, but all of the studies to date have focused on aryloxenium ions having closed-shell singlet ground state configurations. To study alternative spin configurations, we synthesized a photoprecursor to the m-dimethylamino phenyloxenium ion, which is predicted by both density functional theory and MRMP2 computations to have a triplet ground state electronic configuration. A combination of femtosecond and nanosecond transient absorption spectroscopy, nanosecond time-resolved Resonance Raman spectroscopy (ns-TR(3)), cryogenic matrix EPR spectroscopy, computational analysis, and photoproduct studies allowed us to trace essentially the complete arc of the photophysics and photochemistry of this photoprecursor and permitted a first look at a triplet oxenium ion. Ultraviolet photoexcitation of this precursor populates higher singlet excited states, which after internal conversion to S1 over 800 fs are followed by bond heterolysis in ∼1 ps, generating a hot closed-shell singlet oxenium ion that undergoes vibrational cooling in ∼50 ps followed by intersystem crossing in ∼300 ps to generate the triplet ground state oxenium ion. In contrast to the rapid trapping of singlet phenyloxenium ions by nucleophiles seen in prior studies, the triplet oxenium ion reacts via sequential H atom abstractions on the microsecond time domain to ultimately yield the reduced m-dimethylaminophenol as the only detectable stable photoproduct. Band assignments were made by comparisons to computed spectra of candidate intermediates and comparisons to related known species. The triplet oxenium ion was also detected in the ns-TR(3) experiments, permitting a more clear assignment and identifying the triplet state as the π,π* triplet configuration. The triplet ground state of this ion was further supported by photolysis of the photoprecursor in an ethanol glass at ∼4 K and observing a triplet species by cryogenic EPR spectroscopy.
Collapse
Affiliation(s)
- Ming-De Li
- †Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, S.A.R., P. R. China
| | - Toshia R Albright
- ‡Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, Iowa 50011, United States
| | - Patrick J Hanway
- ‡Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, Iowa 50011, United States
| | - Mingyue Liu
- †Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, S.A.R., P. R. China
| | - Xin Lan
- †Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, S.A.R., P. R. China
| | - Songbo Li
- †Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, S.A.R., P. R. China
| | - Julie Peterson
- ‡Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, Iowa 50011, United States
| | - Arthur H Winter
- ‡Department of Chemistry, Iowa State University, 2101d Hach Hall, Ames, Iowa 50011, United States
| | - David Lee Phillips
- †Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, S.A.R., P. R. China
| |
Collapse
|
19
|
Su Y, Wang X, Li Y, Song Y, Sui Y, Wang X. Nitrogen Analogues of Thiele’s Hydrocarbon. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201410256] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
20
|
Su Y, Wang X, Li Y, Song Y, Sui Y, Wang X. Nitrogen Analogues of Thiele’s Hydrocarbon. Angew Chem Int Ed Engl 2014; 54:1634-7. [DOI: 10.1002/anie.201410256] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Indexed: 11/12/2022]
|