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Jacovella U, da Silva G, Bieske EJ. Unveiling New Isomers and Rearrangement Routes on the C 7H 8+ Potential Energy Surface. J Phys Chem A 2019; 123:823-830. [PMID: 30608153 DOI: 10.1021/acs.jpca.8b10642] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The unimolecular reactions of C7H8+ radical cations are among those most studied by mass spectrometry, especially the rearrangement of toluene and cycloheptatriene molecular ions, which are directly connected to the formation of benzylium and tropylium cations. This study reveals important new isomers and isomerization pathways on the C7H8+ potential energy surface, through the application of gas-phase electronic photodissociation spectroscopy in conjunction with ab initio calculations. Presented are the first gas-phase vibrationally resolved electronic spectra of the o-isotoluene, norcaradiene, bicyclo[3.2.0]hepta-2,6-diene radical cations, and ring-opened products from cyclic C7H8+ species. The isomerization route from the norbornadiene radical cation to the toluene radical cation, which competes with isomerization to the bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation, is identified. Further, this work expands understanding of the C7H8+ potential energy surface by connecting spiro[2.4]hepta-4,6-diene and acyclic 1,2,4,6-heptatetraene radical cations, and confirms the important role of the o-isotoluene radical cation in the interconversion pathways of C7H8+ species.
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Jacovella U, Muller G, Catani KJ, Bartlett NI, Bieske EJ. Electronic Spectra of the Triacetylene Cation (HC6H+) and Protonated Triacetylene (HC6H2+) Tagged with Ar. Aust J Chem 2019. [DOI: 10.1071/ch18508] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Polyacetylene cations (HC2nH+) play important roles in combustion processes and in the chemistry of planetary atmospheres and interstellar clouds. Here we report the electronic spectrum for the triacetylene cation (HC6H+) recorded over the 300–610nm range by photodissociating mass-selected ions tagged with argon atoms in a tandem mass spectrometer. The spectrum shows three band systems that are assigned to (origin transition 16665cm−1), (origin transition 23916cm−1), and (origin transition 29920cm−1). Although the band system is well known, the and band systems are observed for the first time in the gas phase. In addition, the electronic spectrum of the protonated triacteylene cation tagged with an argon atom (HC6-Ar) is reported, providing the first gas-phase spectrum for this species.
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Bull JN, Buntine JT, Scholz MS, Carrascosa E, Giacomozzi L, Stockett MH, Bieske EJ. Photodetachment and photoreactions of substituted naphthalene anions in a tandem ion mobility spectrometer. Faraday Discuss 2019; 217:34-46. [DOI: 10.1039/c8fd00217g] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Tandem IMS-laser-IMS is used to probe the intrinsic electronic absorptions of deprotonated substituted naphthalene anions.
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Bull JN, Carrascosa E, Giacomozzi L, Bieske EJ, Stockett MH. Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry. Phys Chem Chem Phys 2018; 20:19672-19681. [PMID: 30014081 PMCID: PMC6063075 DOI: 10.1039/c8cp03244k] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Photo-induced proton transfer, deprotomer-dependent photochemistry, and intramolecular charge transfer in flavin anions are investigated using action spectroscopy.
The intrinsic optical properties and photochemistry of flavin adenine dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other on the two phosphates (PO4,PO4 deprotomer). Ion mobility data and electronic action spectra suggest that photo-induced proton transfer occurs from the isoalloxazine group to a phosphate group, converting the PO4,PO4 deprotomer to the N-3,PO4 deprotomer. Comparisons of the isomer selective action spectra of FAD dianions and flavin monoanions with solution spectra and gas-phase photodissociation action spectra suggests that solvation shifts the electronic absorption of the deprotonated isoalloxazine group to higher energy. This is interpreted as evidence for significant charge transfer in the lowest optical transition of deprotonated isoalloxazine. Overall, this work demonstrates that the site of deprotonation of flavin anions strongly affects their electronic absorptions and photochemistry.
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Bull JN, Scholz MS, Carrascosa E, da Silva G, Bieske EJ. Double Molecular Photoswitch Driven by Light and Collisions. PHYSICAL REVIEW LETTERS 2018; 120:223002. [PMID: 29906145 DOI: 10.1103/physrevlett.120.223002] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2017] [Indexed: 06/08/2023]
Abstract
The shapes of many molecules can be transformed by light or heat. Here we investigate collision- and photon-induced interconversions of EE, EZ, and ZZ isomers of the isolated Congo red (CR) dianion, a double molecular switch containing two ─N═N─ azo groups, each of which can have the E or Z configuration. We find that collisional activation of CR dianions drives a one-way ZZ→EZ→EE cascade towards the lowest-energy isomer, whereas the absorption of a single photon over the 270-600 nm range can switch either azo group from E to Z or Z to E, driving the CR dianion to lower- or higher-energy forms. The experimental results, which are interpreted with the aid of calculated statistical isomerization rates, indicate that photoisomerization of CR in the gas phase involves a passage through conical intersection seams linking the excited and ground state potential energy surfaces rather than through isomerization on the ground state potential energy surface following internal conversion.
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Carrascosa E, Bull JN, Scholz MS, Coughlan NJA, Olsen S, Wille U, Bieske EJ. Reversible Photoisomerization of the Isolated Green Fluorescent Protein Chromophore. J Phys Chem Lett 2018; 9:2647-2651. [PMID: 29724104 DOI: 10.1021/acs.jpclett.8b01201] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Fluorescent proteins have revolutionized the visualization of biological processes, prompting efforts to understand and control their intrinsic photophysics. Here we investigate the photoisomerization of deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone anion (HBDI-), the chromophore in green fluorescent protein and in Dronpa protein, where it plays a role in switching between fluorescent and nonfluorescent states. In the present work, isolated HBDI- molecules are switched between the Z and E forms in the gas phase in a tandem ion mobility mass spectrometer outfitted for selecting the initial and final isomers. Excitation of the S1 ← S0 transition provokes both Z → E and E → Z photoisomerization, with a maximum response for both processes at 480 nm. Photodetachment is a minor channel at low light intensity. At higher light intensities, absorption of several photons in the drift region drives photofragmentation, through channels involving CH3 loss and concerted CO and CH3CN loss, although isomerization remains the dominant process.
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Scholz MS, Bull JN, Carrascosa E, Adamson BD, Kosgei GK, Rack JJ, Bieske EJ. Linkage Photoisomerization of an Isolated Ruthenium Sulfoxide Complex: Sequential versus Concerted Rearrangement. Inorg Chem 2018; 57:5701-5706. [PMID: 29663799 DOI: 10.1021/acs.inorgchem.8b00871] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ruthenium sulfoxide complexes undergo thermally reversible linkage isomerization of sulfoxide ligands from S- to O-bound in response to light. Here, we report photoisomerization action spectra for a ruthenium bis-sulfoxide molecular photoswitch, [Ru(bpy)2(bpSO)]2+, providing the first direct evidence for photoisomerization of a transition metal complex in the gas phase. The linkage isomers are separated and isolated in a tandem drift tube ion mobility spectrometer and exposed to tunable laser radiation provoking photoisomerization. Direct switching of the S,S-isomer to the O,O-isomer following absorption of a single photon is the predominant isomerization pathway in the gas phase, unlike in solution, where stepwise isomerization is observed with each sulfoxide ligand switching in turn. The change in isomerization dynamics is attributed to rapid vibrational quenching that suppresses isomerization in solution. Supporting electronic structure calculations predict the wavelengths and intensities of the peaks in the photoisomerization action spectra of the S,S- and S,O-isomers, indicating that they correspond to metal-to-ligand charge transfer (MLCT) and ligand-centered ππ* transitions.
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Poad BLJ, Maccarone AT, Yu H, Mitchell TW, Saied EM, Arenz C, Hornemann T, Bull JN, Bieske EJ, Blanksby SJ. Differential-Mobility Spectrometry of 1-Deoxysphingosine Isomers: New Insights into the Gas Phase Structures of Ionized Lipids. Anal Chem 2018; 90:5343-5351. [PMID: 29608293 DOI: 10.1021/acs.analchem.8b00469] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Separation and structural identification of lipids remain a major challenge for contemporary lipidomics. Regioisomeric lipids differing only in position(s) of unsaturation are often not differentiated by conventional liquid chromatography-mass spectrometry approaches leading to the incomplete, or sometimes incorrect, assignation of molecular structure. Here we describe an investigation of the gas phase separations by differential-mobility spectrometry (DMS) of a series of synthetic analogues of the recently described 1-deoxysphingosine. The dependence of the DMS behavior on the position of the carbon-carbon double bond within the ionized lipid is systematically explored and compared to trends from complementary investigations, including collision cross-sections measured by drift tube ion mobility, reaction efficiency with ozone, and molecular dynamics simulations. Consistent trends across these modes of interrogation point to the importance of direct, through-space interactions between the charge site and the carbon-carbon double bond. Differences in the geometry and energetics of this intramolecular interaction underpin DMS separations and influence reactivity trends between regioisomers. Importantly, the disruption and reformation of these intramolecular solvation interactions during DMS are proposed to be the causative factor in the observed separations of ionized lipids which are shown to have otherwise identical collision cross-sections. These findings provide key insights into the strengths and limitations of current ion-mobility technologies for lipid isomer separations and can thus guide a more systematic approach to improved analytical separations in lipidomics.
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Bull JN, Carrascosa E, Mallo N, Scholz MS, da Silva G, Beves JE, Bieske EJ. Photoswitching an Isolated Donor-Acceptor Stenhouse Adduct. J Phys Chem Lett 2018; 9:665-671. [PMID: 29356541 DOI: 10.1021/acs.jpclett.7b03402] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Donor-acceptor Stenhouse adducts (DASAs) are a new class of photoswitching molecules with excellent fatigue resistance and synthetic tunability. Here, tandem ion mobility mass spectrometry coupled with laser excitation is used to characterize the photocyclization reaction of isolated, charge-tagged DASA molecules over the 450-580 nm range. The experimental maximum response at 530 nm agrees with multireference perturbation theory calculations for the S1 ← S0 transition maximum at 533 nm. Photocyclization in the gas phase involves absorption of at least two photons; the first photon induces Z-E isomerization from the linear isomer to metastable intermediate isomers, while the second photon drives another E-Z isomerization and 4π-electrocyclization reaction. Cyclization is thermally reversible in the gas phase with collisional excitation.
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Bull JN, Scholz MS, Carrascosa E, Bieske EJ. FromEtoZand back again: reversible photoisomerisation of an isolated charge-tagged azobenzene. Phys Chem Chem Phys 2018; 20:509-513. [DOI: 10.1039/c7cp07278c] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Substituted azobenzenes serve as chromophores and actuators in a wide range of molecular photoswitches.
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Catani KJ, Muller G, Jusko P, Theulé P, Bieske EJ, Jouvet C. Electronic spectrum of the protonated diacetylene cation (H2C4H+). J Chem Phys 2017; 147:084302. [DOI: 10.1063/1.4990572] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Scholz MS, Bull JN, Coughlan NJA, Carrascosa E, Adamson BD, Bieske EJ. Photoisomerization of Protonated Azobenzenes in the Gas Phase. J Phys Chem A 2017; 121:6413-6419. [DOI: 10.1021/acs.jpca.7b05902] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Bull JN, Coughlan NJA, Bieske EJ. Protomer-Specific Photochemistry Investigated Using Ion Mobility Mass Spectrometry. J Phys Chem A 2017; 121:6021-6027. [DOI: 10.1021/acs.jpca.7b05800] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Ritchie C, Vamvounis G, Soleimaninejad H, Smith TA, Bieske EJ, Dryza V. Photochrome-doped organic films for photonic keypad locks and multi-state fluorescence. Phys Chem Chem Phys 2017; 19:19984-19991. [PMID: 28722049 DOI: 10.1039/c7cp02818k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The spectroscopic properties of poly(methyl methacrylate) polymer films doped with two kinds of photochromic molecular switches are investigated. A green-fluorescent sulfonyl diarylethene (P1) is combined with either a non-fluorescent diarylethene (P2) or red-fluorescent spiropyran (P3). Photoswitching between the colorless and colored isomers (P1: o-BTFO4 ↔ c-BTFO4, P2: o-DTE ↔ c-DTE, P3: SP ↔ MC) enables the P1 + P2 and P1 + P3 films to be cycled through three distinct states. From the initial state (o-BTFO4 + o-DTE/SP), irradiation with UV light generates the second state (c-BTFO4 + c-DTE/MC), where c-BTFO4 → c-DTE/MC energy transfer is established. Irradiation with green light then generates the third state (c-BTFO4 + o-DTE/SP), where the energy transfer acceptor is no longer present. Finally, irradiation with blue light regenerates the initial state. For the P1 + P2 film, only one state is fluorescent, with the irradiation inputs required to be entered in the correct order to access this state, acting as a keypad lock. For the P1 + P3 film, the states emit either no fluorescence, red fluorescence, or green fluorescence, all using a common excitation wavelength. Additionally, once the fluorescence is activated with UV light, it undergoes a time-dependent color transition from red to green, due to the pairing of P-type and T-type photochromes. These multi-photochromic systems may be useful for security ink or imaging applications.
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Georgiou DC, Haghighatbin MA, Hogan CF, Scholz MS, Bull JN, Bieske EJ, Wilson DJD, Dutton JL. A Strong
cis
‐Effect in an Imidazole‐Imidazolium‐Substituted Alkene. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201702287] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Lim SF, Harris BL, Khairallah GN, Bieske EJ, Maître P, da Silva G, Adamson BD, Scholz MS, Coughlan NJA, O'Hair RAJ, Rathjen M, Stares D, White JM. Seleniranium Ions Undergo π-Ligand Exchange via an Associative Mechanism in the Gas Phase. J Org Chem 2017; 82:6289-6297. [PMID: 28530810 DOI: 10.1021/acs.joc.7b00877] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Collision-induced dissociation mass spectrometry of the ammonium ions 4a and 4b results in the formation of the seleniranium ion 5, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion-molecule reactions between the ion 5 (m/z = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions 7 (m/z = 225), 6 (m/z = 239), 8 (m/z = 253), and 9 (m/z = 267), respectively. Further reaction of seleniranium 6 with cyclopentene resulted in further π-ligand exchange giving seleniranium ion 7, confirming that direct π-ligand exchange between seleniranium ion 5 and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion 5 with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively.
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Georgiou DC, Haghighatbin MA, Hogan CF, Scholz MS, Bull JN, Bieske EJ, Wilson DJD, Dutton JL. A Strong
cis
‐Effect in an Imidazole‐Imidazolium‐Substituted Alkene. Angew Chem Int Ed Engl 2017; 56:8473-8480. [DOI: 10.1002/anie.201702287] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Indexed: 01/02/2023]
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O'Connor GD, Chan B, Sanelli JA, Cergol KM, Dryza V, Payne RJ, Bieske EJ, Radom L, Schmidt TW. Hydrogen-adduction to open-shell graphene fragments: spectroscopy, thermochemistry and astrochemistry. Chem Sci 2017; 8:1186-1194. [PMID: 28451259 PMCID: PMC5369534 DOI: 10.1039/c6sc03787a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 09/24/2016] [Indexed: 11/25/2022] Open
Abstract
We apply a combination of state-of-the-art experimental and quantum-chemical methods to elucidate the electronic and chemical energetics of hydrogen adduction to a model open-shell graphene fragment. The lowest-energy adduct, 1H-phenalene, is determined to have a bond dissociation energy of 258.1 kJ mol-1, while other isomers exhibit reduced or in some cases negative bond dissociation energies, the metastable species being bound by the emergence of a conical intersection along the high-symmetry dissociation coordinate. The gas-phase excitation spectrum of 1H-phenalene and its radical cation are recorded using laser spectroscopy coupled to mass-spectrometry. Several electronically excited states of both species are observed, allowing the determination of the excited-state bond dissociation energy. The ionization energy of 1H-phenalene is determined to be 7.449(17) eV, consistent with high-level W1X-2 calculations.
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Catani KJ, Muller G, da Silva G, Bieske EJ. Electronic spectrum and photodissociation chemistry of the linear methyl propargyl cation H2C4H3+. J Chem Phys 2017; 146:044307. [DOI: 10.1063/1.4974338] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Bull JN, Carrascosa E, Scholz MS, Coughlan NJA, Bieske EJ. Online measurement of photoisomerisation efficiency in solution using ion mobility mass spectrometry. Analyst 2017; 142:2100-2103. [DOI: 10.1039/c7an00398f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A new method for probing the photoisomerisation of molecules in solution using ion mobility mass spectrometry is described and demonstrated with a azoheteroarene photoswitch.
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Bull JN, Scholz MS, Coughlan NJA, Bieske EJ. Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole). Phys Chem Chem Phys 2017; 19:12776-12783. [DOI: 10.1039/c7cp01733b] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Reversible E–Z photoswitching of a protonated azoheteroarene is demonstrated using ion mobility mass spectrometry.
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Bull JN, Scholz MS, Coughlan NJA, Kawai A, Bieske EJ. Monitoring Isomerization of Molecules in Solution Using Ion Mobility Mass Spectrometry. Anal Chem 2016; 88:11978-11981. [DOI: 10.1021/acs.analchem.6b04000] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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48
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Coughlan NJA, Scholz MS, Hansen CS, Trevitt AJ, Adamson BD, Bieske EJ. Photo and Collision Induced Isomerization of a Cyclic Retinal Derivative: An Ion Mobility Study. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:1483-1490. [PMID: 27278825 DOI: 10.1007/s13361-016-1427-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 05/10/2016] [Accepted: 05/20/2016] [Indexed: 06/06/2023]
Abstract
A cationic degradation product, formed in solution from retinal Schiff base (RSB), is examined in the gas phase using ion mobility spectrometry, photoisomerization action spectroscopy, and collision induced dissociation (CID). The degradation product is found to be N-n-butyl-2-(β-ionylidene)-4-methylpyridinium (BIP) produced through 6π electrocyclization of RSB followed by protonation and loss of dihydrogen. Ion mobility measurements show that BIP exists as trans and cis isomers that can be interconverted through buffer gas collisions and by exposure to light, with a maximum response at λ = 420 nm.Graphical Abstract.
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Coughlan NJA, Wallace CM, Adamson BD, Bieske EJ. Photoisomerization of β-Ionone Protonated Schiff Base in the Gas Phase. J Phys Chem A 2016; 120:6557-62. [PMID: 27483192 DOI: 10.1021/acs.jpca.6b05645] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The photoisomerization of β-ionone protonated Schiff base (BIPSB) is investigated in the gas phase by irradiating mobility-selected ions in a tandem ion mobility spectrometer with tunable radiation. Four distinguishable isomers are produced by electrospray ionization whose structures are deduced from their collision cross sections and photoisomerization behavior along with density functional theory calculations. They include two geometric isomers of BIPSB with trans or cis configurations about the polyene chain's terminal C═N double bond, a bicyclic structure formed through electrocyclization of the polyene chain, and a Z-retro-γ-ionone isomer. Although trans-BIPSB and 9-cis-BIPSB have similar photoisomerization action spectra, with a maximum response at 375 nm, they photoconvert to different isomers. The trans-BIPSB isomer transforms to the bicyclic form upon exposure to light over the 320-400 nm range, whereas the cis-BIPSB isomer is prevented by steric hindrance from forming the bicyclic BIPSB isomer following irradiation and is proposed instead to form the 7,9-di-cis isomer. Neither the bicyclic isomer nor the Z-retro-γ-ionone isomer respond strongly to near-UV light.
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Artiukhin DG, Bieske EJ, Buchachenko AA. Ab Initio Characterization of the Electrostatic Complexes Formed by H2 Molecule and Cr(+), Mn(+), Cu(+), and Zn(+) Cations. J Phys Chem A 2016; 120:5006-15. [PMID: 26914616 DOI: 10.1021/acs.jpca.5b12700] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Equilibrium structures, dissociation energies, and rovibrational energy levels of the electrostatic complexes formed by molecular hydrogen and first-row S-state transition metal cations Cr(+), Mn(+), Cu(+), and Zn(+) are investigated ab initio. Extensive testing of the CCSD(T)-based approaches for equilibrium structures provides an optimal scheme for the potential energy surface calculations. These surfaces are calculated in two dimensions by keeping the H-H internuclear distance fixed at its equilibrium value in the complex. Subsequent variational calculations of the rovibrational energy levels permits direct comparison with data obtained from equilibrium thermochemical and spectroscopic measurements. Overall accuracy within 2-3% is achieved. Theoretical results are used to examine trends in hydrogen activation, vibrational anharmonicity, and rotational structure along the sequence of four electrostatic complexes covering the range from a relatively floppy van der Waals system (Mn(+)···H2) to an almost a rigid molecular ion (Cu(+)···H2).
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