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Khazaei S, Sebastiani D. Tunneling of coupled methyl quantum rotors in 4-methylpyridine: Single rotor potential versus coupling interaction. J Chem Phys 2017; 147:194303. [PMID: 29166123 DOI: 10.1063/1.5003081] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Somayeh Khazaei
- Institute of Chemistry, Martin-Luther-University Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Daniel Sebastiani
- Institute of Chemistry, Martin-Luther-University Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
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2
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Khazaei S, Sebastiani D. Methyl rotor quantum states and the effect of chemical environment in organic crystals: γ-picoline and toluene. J Chem Phys 2017; 145:234506. [PMID: 27984875 DOI: 10.1063/1.4971380] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using a set of first-principles calculations, we have studied the methyl tunnel splitting for molecular crystals of γ-picoline and toluene. The effective rotational potential energy surface of the probe methyl rotor along the tunneling path is evaluated using first-principles electronic structure calculations combined with the nudged elastic band method. The tunnel splitting is calculated by an explicit diagonalization of the one-dimensional time-independent Hamiltonian matrix. The effects of chemical environment and rotor-rotor coupling on the rotational energy barriers were investigated. It is found that more dense packing of the molecules in toluene compared to that in γ-picoline gives rise to a larger rotational barrier which in turn yields a considerably smaller tunnel splitting. Moreover, it turned out that coupled motion of the face-to-face methyl groups in γ-picoline has a significant effect on the reduction of the rotational barrier. Our results are in good agreement with the experimentally observed tunnel splitting.
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Affiliation(s)
- Somayeh Khazaei
- Institute of Chemistry, Martin-Luther-University Halle-Wittenberg, Von-Danckelmann-Platz 4, Halle (Saale) 06120, Germany
| | - Daniel Sebastiani
- Institute of Chemistry, Martin-Luther-University Halle-Wittenberg, Von-Danckelmann-Platz 4, Halle (Saale) 06120, Germany
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Tsapatsaris N, Kolesov BA, Fischer J, Boldyreva EV, Daemen L, Eckert J, Bordallo HN. Polymorphism of Paracetamol: A New Understanding of Molecular Flexibility through Local Methyl Dynamics. Mol Pharm 2014; 11:1032-41. [DOI: 10.1021/mp400707m] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
| | - Boris A. Kolesov
- Institute of Inorganic Chemistry SB RAS, Novosibirsk 630090, Russia
- REC-008 Novosibirsk State University, ul. Pirogova 2, Novosibirsk 630090, Russia
| | | | - Elena V. Boldyreva
- REC-008 Novosibirsk State University, ul. Pirogova 2, Novosibirsk 630090, Russia
- Institute of Solid-State Chemistry and Mechanochemistry SB RAS, Kutateladze 18, Novosibirsk 630128, Russia
| | - Luke Daemen
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Juergen Eckert
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Department
of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Heloisa N. Bordallo
- European Spallation Source ESS AB, P.O. Box 176, Lund 221 00, Sweden
- Niels Bohr Institute, Universitetsparken
5, Copenhagen 2100, Denmark
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4
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Tsapatsaris N, Landsgesell S, Koza MM, Frick B, Boldyreva EV, Bordallo HN. Polymorphic drugs examined with neutron spectroscopy: Is making more stable forms really that simple? Chem Phys 2013. [DOI: 10.1016/j.chemphys.2013.04.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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5
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Molecular flexibility and structural instabilities in crystalline l-methionine. Biophys Chem 2013; 180-181:76-85. [PMID: 23886538 DOI: 10.1016/j.bpc.2013.06.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 06/14/2013] [Accepted: 06/14/2013] [Indexed: 11/22/2022]
Abstract
We have investigated the dynamics in polycrystalline samples of l-methionine related to the structural transition at about 307K by incoherent inelastic and quasielastic neutron scattering, X-ray powder diffraction as well as ab-initio calculations. l-Methionine is a sulfur amino acid which can be considered a derivative of alanine with the alanine R-group CH3 exchanged by CH3S(CH2)2. Using X-ray powder diffraction we have observed at ~190K an anomalous drop of the c-lattice parameter and an abrupt change of the β-monoclinic angle that could be correlated to the anomalies observed in previous specific heat measurements. Distinct changes in the quasielastic region of the neutron spectra are interpreted as being due to the onset and slowing-down of reorientational motions of the CH3-S group, are clearly distinguished above 130K in crystalline l-methionine. Large-amplitude motions observed at low frequencies are also activated above 275K, while other well-defined vibrations are damped. The ensemble of our results suggests that the crystalline structure of l-methionine is dynamically highly disordered above 275K, and such disorder can be linked to the flexibility of the molecular thiol-ether group.
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Kearley GJ, Stare J, Kutteh R, Daemen LL, Hartl MA, Eckert J. Methyl dynamics flattens barrier to proton transfer in crystalline tetraacetylethane. J Phys Chem A 2012; 116:2283-91. [PMID: 22296223 DOI: 10.1021/jp210212q] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We analyze the interplay between proton transfer in the hydrogen-bond bridge, O···H···O, and lattice dynamics in the model system tetraacetylethane (TAE) (CH(3)CO)(2)CH═CH(COCH(3))(2) using density functional theory. Lattice dynamics calculations and molecular dynamics simulations are validated against neutron scattering data. Hindrance to the cooperative reorientation of neighboring methyl groups at low temperatures gives a preferred O atom for the bridging proton. The amplitude of methyl torsions becomes larger with increasing temperature, so that the free-energy minimum for the proton becomes flat over 0.2 Å. For the isolated molecule, however, we show an almost temperature-independent symmetric double-well potential persists. This difference arises from the much higher barriers to methyl torsion in the crystal that make the region of torsional phase space that is most crucial for symmetrization poorly accessible. Consequently, the proton-transfer potential remains asymmetric though flat at the base, even at room temperature in the solid.
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Affiliation(s)
- Gordon J Kearley
- The Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales, Australia.
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7
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Peterson VK, Shoko E, Kearley GJ. The effect of host relaxation and dynamics on guest molecule dynamics in H2/tetrahydrofuranhydrate. Faraday Discuss 2011; 151:37-46; discussion 95-115. [PMID: 22455061 DOI: 10.1039/c0fd00034e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We use ab initio molecular dynamics simulations to obtain classically the effects of H2O cage motions on the potential-energy surface (PES) of encapsulated H2 in the H2/tetrahydrofuran-hydrate system. The significant differences between the PES for the H2 in rigid and flexible cages that we find will influence calculation of the quantum dynamics of the H2. Part of these differences arises from the relaxation of the H2O cage around the classical H2, with a second part arising from the coupling of both translational and rotational motions of H2 with the H20 cage. We find that isotopic substitution of 2H for 1H of the H2O cage affects the coupling, which has implications for experiments that require the use of 2H2O, including inelastic neutron scattering that uses 2H2O cages in order to focus on the H2 guest dynamics. Overall, this work emphasizes the importance of taking into account cage dynamics in any approach used to understand the dynamics of H2 guests in porous framework materials.
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Affiliation(s)
- Vanessa K Peterson
- Australian Nuclear Science and Technology Organisation, The Bragg Institute, Lucas Heights, New South Wales, Australia.
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8
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Sobczyk L, Prager M, Sawka-Dobrowolska W, Bator G, Pawlukojć A, Grech E, van Eijck L, Ivanov A, Rols S, Wuttke J, Unruh T. The structure of diaminodurene and the dynamics of the methyl groups. J Chem Phys 2009; 130:164519. [DOI: 10.1063/1.3125629] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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9
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Pawlukojć A, Sobczyk L, Prager M, Bator G, Grech E, Nowicka-Scheibe J. DFT calculations of 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (CLA): Comparison to INS, IR and Raman vibration spectra. J Mol Struct 2008. [DOI: 10.1016/j.molstruc.2008.05.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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10
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Prager M, Pawlukojc A, Wischnewski A, Wuttke J. Inelastic neutron scattering study of methyl groups rotation in some methylxanthines. J Chem Phys 2007; 127:214509. [DOI: 10.1063/1.2803187] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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11
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Prager M, Wischnewski A, Bator G, Grech E, Pawlukojć A, Sobczyk L. INS spectroscopic study of the 1:1 tetramethylpyrazine (TMP) squaric acid (H2SQ) complex. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.02.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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12
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X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2006.10.024] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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13
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Prager M, Pietraszko A, Sobczyk L, Pawlukojć A, Grech E, Seydel T, Wischnewski A, Zamponi M. X-ray diffraction and inelastic neutron scattering study of 1:1 tetramethylpyrazine chloranilic acid complex: temperature, isotope, and pressure effects. J Chem Phys 2006; 125:194525. [PMID: 17129141 DOI: 10.1063/1.2358347] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The x-ray diffraction studies of the title complex were carried out at room temperature and 14 K for H/D (in hydrogen bridge) isotopomers. At 82 K a phase transition takes place leading to a doubling of unit cells and alternation of the hydrogen bond lengths linking tetramethylpyrazine (TMP) and chloranilic acid molecules. A marked H/D isotope effect on these lengths was found at room temperature. The elongation is much smaller at 14 K. The infrared isotopic ratio for O-H(D)...N bands equals to 1.33. The four tunnel splittings of methyl librational ground states of the protonated complex required by the structure are determined at a temperature T=4.2 K up to pressures P=4.7 kbars by high resolution neutron spectroscopy. The tunnel mode at 20.6 microeV at ambient pressure shifts smoothly to 12.2 microeV at P=3.4 kbars. This is attributed to an increase of the strength of the rotational potential proportional to r(-5.6). The three other tunnel peaks show no or weak shifts only. The increasing interaction with diminishing intermolecular distances is assumed to be compensated by a charge transfer between the constituents of deltae/e approximately 0.02 kbar(-1). The phase transition observed between 3.4 and 4.7 kbars leads to increased symmetry with only two more intense tunneling bands. In the isotopomer with deuterated hydrogen bonds and P=1 bar all tunnel intensities become equal in consistency with the low temperature crystal structure. The effect of charge transfer is confirmed by a weakening of rotational potentials for those methyl groups whose tunnel splittings were independent of pressure. Density functional theory calculations for the model TMP.(HF)2 complex and fully ionized molecule TMP+ point out that the intramolecular rotational potential of methyl groups is weaker in the charged species. They do not allow for the unequivocal conclusions about the role of the intermolecular charge transfer effect on the torsional frequencies.
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Affiliation(s)
- M Prager
- Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany.
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Tomkinson J, Telling MTF. Ammonium ions in alkali metal halide crystals: tunnelling and spin relaxation. Phys Chem Chem Phys 2006; 8:4434-40. [PMID: 17001411 DOI: 10.1039/b608590c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have used low energy inelastic neutron scattering spectroscopy to examine the tunnelling spectroscopy of the ammonium ion in the (NH4)0.02Rb(x)K(0.98-x)I system. The concentration of different species were varied as x increased, this was followed systematically and the first consistent assignment scheme for these features is given. Differences were also found for the relaxation rate of the spin temperature inversions that could be generated in these species. At a critical concentration--about x = 0.04 mole fraction--the relaxation rates of the species changed dramatically.
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Affiliation(s)
- J Tomkinson
- The ISIS Facility, The Rutherford Appleton Laboratory, CCLRC, Chilton, UK OX11 0QX.
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15
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Pawlukojć A, Natkaniec I, Bator G, Sobczyk L, Grech E, Nowicka-Scheibe J. Low frequency internal modes of 1,2,4,5-tetramethylbenzene, tetramethylpyrazine and tetramethyl-1,4-benzoquinone INS, Raman, infrared and theoretical DFT studies. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2006; 63:766-73. [PMID: 16098791 DOI: 10.1016/j.saa.2005.06.030] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 06/10/2005] [Accepted: 06/13/2005] [Indexed: 05/04/2023]
Abstract
The results of inelastic neutron scattering (INS), Raman and infrared (IR) studies on 1,2,4,5-tetramethylbenzene (durene), tetramethylpyrazine (TMP) and tetramethyl-1,4-benzoquinone (TMBQ) in the solid state are reported. The observed frequencies are analyzed on the basis of DFT calculations. The low frequency region, below 400 cm(-1), related to the torsional and bending out-of-plane vibrations of the CH(3) groups, is of particular interest. The detailed analysis is possible due to the simulation of the INS spectra by using the auntie-CLIMAX program. It is shown that the observed low frequency INS bands are dramatically shifted, compared to the calculated ones, towards higher frequencies. Although one cannot exclude deficiencies of theoretical methods as applied to low frequency modes, it seems more probable the interpretation based on an existence of non-conventional CH(...)pi, CH(...)N, CH(...)O hydrogen bonds formed by the methyl groups in crystalline phases.
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Affiliation(s)
- A Pawlukojć
- Joint Institute for Nuclear Research, 141980 Dubna, Russia
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16
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Sawka-Dobrowolska W, Bator G, Sobczyk L, Pawlukojć A, Ptasiewicz-Bak H, Rundlöf H, Krawczyk J, Nowina-Konopka M, Jagielski P, Janik JA, Prager M, Steinsvoll O, Grech E, Nowicka-Scheibe J. Elastic, quasielastic, and inelastic neutron-scattering studies on the charge-transfer hexamethylbenzene-tetracyanoquinodimethane complex. J Chem Phys 2005; 123:124305. [PMID: 16392480 DOI: 10.1063/1.2035077] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The 1:1 hexamethylbenzene (HMB)-tetracyanoquinodimethane (TCNQ) complex shows a first-order phase transition at 230/218 K (heating/cooling) with no change of the space group. The neutron-diffraction studies reveal that this transition is related to a freezing of the rotation of methyl groups. The results for 100 K enabled precise determination of configuration of HMB.TCNQ complexes. The planes of HMB and TCNQ molecules from small angle (6 degrees) so that the dicyanomethylene group approaches the HMB molecule to a distance of 3.34 angstroms. The conformation of methyl groups was exactly determined. The quasielastic neutron-scattering spectra can be interpreted in terms of 120 degrees jumps with different activation barrier in low- and high-temperature phases, equal to 3.7 and 1.8 kJ/mol, respectively. These values are lower than that for neat HMB (6 kJ/mol). The conclusion can be drawn that the methyl groups can reorient more freely in the complex. This conclusion is in agreement with the results of inelastic neutron-scattering studies of low-frequency modes assigned to torsional vibrations of methyl groups. These frequencies are lower than those for neat HMB. The analyzed increase of frequencies of these modes as compared with free molecules can be interpreted as due to formation of unconventional C-H...Y hydrogen bonds which are more pronounced in crystals of neat HMB than in those of HMB.TCNQ. The low-frequency librational modes can be treated as a sensitive measure of unconventional hydrogen bonds formed by the CH3 groups.
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17
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Prager M, Grimm H, Natkaniec I. Rotational tunneling of methyl groups in low temperature phases of mesitylene: potentials and structural implications. Phys Chem Chem Phys 2005; 7:2587-93. [PMID: 16189568 DOI: 10.1039/b503342j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Mesitylene can be stabilized at He temperature in three solid phases of so far unknown crystal structures. Rotational tunneling of methyl groups is based on rotational potentials and used to characterize structural aspects. In phase III found after the first fast cooling of the sample three nonequivalent methyl rotors with splittings of 2.7, 4.1 and 16.3 microeV are observed. Three other unresolved bands are identified by their librational modes. In the second phase II the metastability is emphasized by tunneling energies still changing at temperatures T< or = 12 K. Above this temperature tunneling bands at 6.6, 12.5, 15.0 and 18.3 microeV evolve in the manner characteristic of coupling to phonons. In the equilibrium phase I a single tunnel splitting of 10.2 microeV represents all methyl groups. A unit cell containing a single molecule at a site of threefold symmetry explains quantitatively this spectrum. Phases II and III most likely contain two nonequivalent molecules in the unit cell with no local symmetry in phase II and a mirror plane in phase III. The good moderator properties for neutrons are most likely not connected to the low energy tunneling bands but to a dense vibrational phonon density of states.
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Affiliation(s)
- M Prager
- Institut für Festkörperforschung, Forschungzzentrum Jülich, D-52425 Jülich, Germany
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18
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Birczyński A, Lalowicz Z, Łodziana Z. Rotational barriers in ammonium hexachlorometallates as studied by NMR, tunnelling spectroscopy and ab initio calculations. Chem Phys 2004. [DOI: 10.1016/j.chemphys.2003.12.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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19
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Molecular deformations of halogeno-mesitylenes in the crystal: structure, methyl group rotational tunneling, and numerical modeling. Chem Phys 2002. [DOI: 10.1016/s0301-0104(02)00817-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Johnson MR, Jones NH, Geis A, Horsewill AJ, Trommsdorff HP. Structure and dynamics of the keto and enol forms of acetylacetone in the solid state. J Chem Phys 2002. [DOI: 10.1063/1.1456032] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Ouillon R, Pinan-Lucarré JP, Ranson P, Baranovic G. Low-temperature Raman spectra of nitromethane single crystals. Lattice dynamics and Davydov splittings. J Chem Phys 2002. [DOI: 10.1063/1.1451243] [Citation(s) in RCA: 13] [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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23
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Horsewill AJ, Xue Q. Magnetic field-cycling investigations of molecular tunnelling. Phys Chem Chem Phys 2002. [DOI: 10.1039/b206263a] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kearley GJ, Johnson MR, Plazanet M, Suard E. Structure and vibrational dynamics of the strongly hydrogen-bonded model peptide: N-methyl acetamide. J Chem Phys 2001. [DOI: 10.1063/1.1385790] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Neumann M, Johnson M, Radaelli P. The low temperature phase transition in octane and its possible generalisation to other n-alkanes. Chem Phys 2001. [DOI: 10.1016/s0301-0104(01)00248-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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26
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The structure and dynamics of crystalline durene by neutron scattering and numerical modelling using density functional methods. Chem Phys 2000. [DOI: 10.1016/s0301-0104(00)00229-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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