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Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol. MOLECULES (BASEL, SWITZERLAND) 2021; 27:molecules27010101. [PMID: 35011331 PMCID: PMC8746872 DOI: 10.3390/molecules27010101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/11/2021] [Accepted: 12/15/2021] [Indexed: 12/31/2022]
Abstract
Rotational microwave jet spectroscopy studies of the monoterpenol α-fenchol have so far failed to identify its second most stable torsional conformer, despite computational predictions that it is only very slightly higher in energy than the global minimum. Vibrational FTIR and Raman jet spectroscopy investigations reveal unusually complex OH and OD stretching spectra compared to other alcohols. Via modeling of the torsional states, observed spectral splittings are explained by delocalization of the hydroxy hydrogen atom through quantum tunneling between the two non-equivalent but accidentally near-degenerate conformers separated by a low and narrow barrier. The energy differences between the torsional states are determined to be only 16(1) and 7(1) cm-1hc for the protiated and deuterated alcohol, respectively, which further shrink to 9(1) and 3(1) cm-1hc upon OH or OD stretch excitation. Comparisons are made with the more strongly asymmetric monoterpenols borneol and isopinocampheol as well as with the symmetric, rapidly tunneling propargyl alcohol. In addition, the third-in contrast localized-torsional conformer and the most stable dimer are assigned for α-fenchol, as well as the two most stable dimers for propargyl alcohol.
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Medel R, Camiruaga A, Saragi RT, Pinacho P, Pérez C, Schnell M, Lesarri A, Suhm MA, Fernández JA. Rovibronic signatures of molecular aggregation in the gas phase: subtle homochirality trends in the dimer, trimer and tetramer of benzyl alcohol. Phys Chem Chem Phys 2021; 23:23610-23624. [PMID: 34661223 DOI: 10.1039/d1cp03508h] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular aggregation is of paramount importance in many chemical processes, including those in living beings. Thus, characterization of the intermolecular interactions is an important step in its understanding. We describe here the aggregation of benzyl alcohol at the molecular level, a process governed by a delicate equilibrium between OH⋯O and OH⋯π hydrogen bonds and dispersive interactions. Using microwave, FTIR, Raman and mass-resolved double-resonance IR/UV spectroscopic techniques, we explored the cluster growth up to the tetramer and found a complex landscape, partly due to the appearance of multiple stereoisomers of very similar stability. Interestingly, a consistently homochiral synchronization of transiently chiral monomer conformers was observed during cluster growth to converge in the tetramer, where the fully homochiral species dominates the potential energy surface. The data on the aggregation of benzyl alcohol also constitute an excellent playground to fine-tune the parameters of the most advanced functionals.
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Affiliation(s)
- Robert Medel
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
| | - Ander Camiruaga
- Department of Physical Chemistry, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Barrio Sarriena S/N, 4894 Leioa, Spain.
| | - Rizalina Tama Saragi
- Departamento de Química Física y Química Inorgánica, Facultad de Ciencias - I.U. CINQUIMA, Universidad de Valladolid, Paseo de Belén, 7, 47011 Valladolid, Spain
| | - Pablo Pinacho
- Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany.,Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118 Kiel, Germany
| | - Cristóbal Pérez
- Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany.,Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118 Kiel, Germany
| | - Melanie Schnell
- Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany.,Institute of Physical Chemistry, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118 Kiel, Germany
| | - Alberto Lesarri
- Departamento de Química Física y Química Inorgánica, Facultad de Ciencias - I.U. CINQUIMA, Universidad de Valladolid, Paseo de Belén, 7, 47011 Valladolid, Spain
| | - Martin A Suhm
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
| | - José A Fernández
- Department of Physical Chemistry, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Barrio Sarriena S/N, 4894 Leioa, Spain.
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Medel R, Suhm MA. Predicting OH stretching fundamental wavenumbers of alcohols for conformational assignment: different correction patterns for density functional and wave-function-based methods. Phys Chem Chem Phys 2021; 23:5629-5643. [PMID: 33656038 DOI: 10.1039/d1cp00342a] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A model is presented for the prediction of OH stretching fundamental wavenumbers of alcohol conformers in the gas phase by application of a small set of empirical anharmonicity corrections to calculations in the harmonic approximation. In contrast to the popular application of a uniform scaling factor, the local chemical structure of the alcohol is taken into account to greatly improve accuracy. Interestingly, different correction patterns emerge for results of hybrid density functional (B3LYP-D3 and PBE0-D3) and wave-function-based methods (SCS-LMP2, LCCSD(T*)-F12a and CCSD(T)-F12a 1D). This raises questions about electronic structure deficiencies in these methods and differences in anharmonicity between alcohols. After its initial construction on the basis of literature assignments the model is tested with Raman jet spectroscopy of propargyl alcohol, cyclohexanol, borneol, isopinocampheol and 2-methylbutan-2-ol. For propargyl alcohol a spectral splitting attributed to tunneling is resolved. PBE0-D3 is identified as a well performing and broadly affordable electronic structure method for this model. A mean absolute error of 1.3 cm-1 and a maximum absolute error of 3 cm-1 result for 46 conformers of 24 alcohols in a 60 cm-1 range, when a single parameter is adjusted separately for each alcohol substitution class (methanol, primary, secondary, tertiary).
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Affiliation(s)
- Robert Medel
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
| | - Martin A Suhm
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
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Medel R, Suhm MA. Understanding benzyl alcohol aggregation by chiral modification: the pairing step. Phys Chem Chem Phys 2020; 22:25538-25551. [PMID: 33169124 DOI: 10.1039/d0cp04825a] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A combination of linear infrared and Raman spectroscopy in supersonic slit jet expansions is used to clarify the conformational preferences in the dimer of the transiently chiral benzyl alcohol (phenylmethanol) under vacuum isolation. By experimentally exploring close analogies with the permanently chiral 1-phenylethanol, which is conformationally locked in the jet through intramolecular chirality induction, and by computational analysis of their conformational energy landscapes, several conclusions are drawn. The lowest energy dimer is confirmed to be cooperatively OHOHπ-bonded and shown to be homochiral. Its heterochiral counterpart is slightly higher in energy and can be spectrally assigned as a minor constituent. A metastable heterochiral OHπ/OHπ structure with weakly coupled hydrogen bonds is efficiently trapped behind a Ci symmetry-enhanced barrier and can be assigned by IR/Raman mutual exclusion. Its homochiral counterpart is kinetically less stable but might be addressed by rotational spectroscopy. Ratings of standard density functionals with a standard basis set in terms of reproducing these experimental chirality synchronization benchmarks are presented.
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Affiliation(s)
- Robert Medel
- Institute of Physical Chemistry, University of Goettingen, Tammannstr. 6, 37077 Goettingen, Germany.
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Hudson RL, Ferrante RF. Mid-infrared spectra of dipropargyl ether ices revisited. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 233:118206. [PMID: 32146427 PMCID: PMC7523429 DOI: 10.1016/j.saa.2020.118206] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 02/16/2020] [Accepted: 02/26/2020] [Indexed: 06/10/2023]
Abstract
The infrared (IR) spectrum of dipropargyl ether, (HC≡C-CH2)2O, has been reinvestigated for the compound's liquid, amorphous, and crystalline forms. The IR baseline changes and bandshape distortions seen in literature spectra have been considerably reduced by a different choice of conditions for preparing the crystalline solid, leading to the discovery of two crystalline phases of the ether. A spectrum of the liquid phase has been recorded and compared to that of the amorphous ether to check for possible procedural artifacts. To facilitate cross-laboratory comparisons, estimates are made for absorption coefficients of three IR peaks of the amorphous solid's spectrum. An interpretation is discussed for changes reported in spectral baselines and bandshapes on warming amorphous dipropargyl ether, and tests and predictions are described. The suggestion that the results from dipropargyl ether warming experiments might pose problems in applying Beer's Law to astronomical observations is addressed.
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Affiliation(s)
- Reggie L Hudson
- Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
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Rahul KK, Meka JK, Pavithraa S, Gorai P, Das A, Lo JI, Sekhar BNR, Cheng BM, Janardhan P, Bhardwaj A, Mason NJ, Sivaraman B. Infrared attenuation due to phase change from amorphous to crystalline observed in astrochemical propargyl ether ices. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 224:117393. [PMID: 31398696 DOI: 10.1016/j.saa.2019.117393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 07/15/2019] [Accepted: 07/15/2019] [Indexed: 06/10/2023]
Abstract
Astrochemical ices are known to undergo morphological changes, from amorphous to crystalline, upon warming the ice from lower (10 K) to higher temperatures. Phase changes are mostly identified by the observation of significant changes in the InfraRed (IR) spectrum, where the IR bands that are broad in the amorphous phase are narrower and split when the ice turns crystalline. To-date all the molecules that are studied under astrochemical conditions are observed to follow such a behaviour without significant attenuation in the IR wavelength. However, in this paper we report a new observation when propargyl ether (C3H3OC3H3) is warmed from the amorphous phase, at 10 K, through the phase transition temperature of 170 K, the crystalline ice being found to strongly attenuate IR photons at the mid-IR wavelengths.
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Affiliation(s)
- K K Rahul
- Physical Research Laboratory, Ahmedabad, India
| | - J K Meka
- Physical Research Laboratory, Ahmedabad, India
| | - S Pavithraa
- Physical Research Laboratory, Ahmedabad, India
| | - P Gorai
- Indian Centre for Space Physics, Kolkata, India
| | - A Das
- Indian Centre for Space Physics, Kolkata, India
| | - J-I Lo
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan
| | | | - B-M Cheng
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan
| | - P Janardhan
- Physical Research Laboratory, Ahmedabad, India
| | - A Bhardwaj
- Physical Research Laboratory, Ahmedabad, India
| | | | - B Sivaraman
- Physical Research Laboratory, Ahmedabad, India.
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Saini J, Dubey P, Verma K, Karir G, Viswanathan KS. Intermolecular Complexes and Molecular Conformations Directed by Hydrogen Bonds: Matrix Isolation and Ab Initio Studies. J Indian Inst Sci 2019. [DOI: 10.1007/s41745-019-00152-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Dubey P, Mukhopadhyay A, Viswanathan K. Do amino acids prefer only certain backbone structures? Steering through the conformational maze of l-threonine using matrix isolation infrared spectroscopy and ab initio studies. J Mol Struct 2019. [DOI: 10.1016/j.molstruc.2018.07.066] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Saini J, Viswanathan KS. From the propargyl alcohol–water complex to the propargyl alcohol dimer: where does the propargyl alcohol–methanol complex fit in? NEW J CHEM 2019. [DOI: 10.1039/c8nj06051g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A correlation was recognized between the structures of PA–H2O, PA–MeOH and PA dimer complexes that could help predict the structures of larger systems in a systematic way.
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Affiliation(s)
- Jyoti Saini
- Department of Chemical Sciences
- Indian Institute of Science Education and Research
- Mohali
- India
| | - K. S. Viswanathan
- Department of Chemical Sciences
- Indian Institute of Science Education and Research
- Mohali
- India
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Samanta AK, Banerjee P, Bandyopadhyay B, Pandey P, Chakraborty T. Antagonistic Interplay Between an Intermolecular CH···O and an Intramolecular OH···O Hydrogen Bond in a 1:1 Complex Between 1,2-Cyclohexanedione and Chloroform: A Combined Matrix Isolation Infrared and Quantum Chemistry Study. J Phys Chem A 2017; 121:6012-6020. [PMID: 28737917 DOI: 10.1021/acs.jpca.7b05615] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Matrix isolation infrared spectra of a weak C-H···O hydrogen-bonded complex between the keto-enol form of 1,2-cyclohexanedione (HCHD) and chloroform have been measured. The spectra reveal that the intramolecular O-H···O H-bond of HCHD is weakened as a result of complex formation, manifesting in prominent blue shift (∼23 cm-1) of the νO-H band and red shifts (∼7 cm-1) of νC═O bands of the acceptor (HCHD). The νC-H band of donor CHCl3 undergoes a large red shift of ∼33 cm-1. Very similar spectral effects are also observed for formation of the complex in CCl4 solution at room temperature. Our analysis reveals that out of several possible iso-energetic conformational forms of the complex, the one involving antagonistic interplay between the two hydrogen bonds (intermolecular C-H···O and intramolecular O-H···O) is preferred. The combined experimental and calculated data presented here suggest that in condensed media, conformational preferences are guided by directional hyperconjugative charge transfer interactions at the C-H···O hydrogen bonding site of the complex.
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Affiliation(s)
- Amit Kumar Samanta
- Center for Free-Electron Laser Science (CFEL) , Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
| | - Pujarini Banerjee
- Department of Physical Chemistry, Indian Association for the Cultivation of Science , Kolkata, India
| | - Biman Bandyopadhyay
- Department of Chemistry, Malaviya National Institute of Technology Jaipur, J. L. N. Marg , Jaipur, India
| | | | - Tapas Chakraborty
- Department of Physical Chemistry, Indian Association for the Cultivation of Science , Kolkata, India
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