Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Reva, Igor; Jesus, A. J. Lopes; Rosado, Mário T. S.; Fausto, Rui; Eusébio, M. Ermelinda S.; Redinha, J.S.

doi:10.1039/b610962d

Cited by 69 publications

(76 citation statements)

References 39 publications

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“…37 Based on these predictions, the two conformers should be present in the gaseous sample of 6MOI before the matrix deposition. Since they are separated by a medium-high energy barrier (∼9 kJ mol −1 in the anti → syn direction, see Figure 1), no conformational cooling 5,6,38,39 is expected to occur during the deposition, and therefore both of them should be preserved in both matrices immediately after the deposition, as it has already been confirmed in our previous experiments. Figure 2 shows the mid-infrared spectra of 6MOI isolated in an argon ( Fig.…”

Section: A Gas Phase Conformational Equilibriummentioning

confidence: 76%

“…[1][2][3][4] Two methodologies are commonly employed to alter the relative abundance of the trapped conformers: annealing of the sample 5,6 or subjecting it to narrowband or broadband radiation of the IR or UV spectral regions. 2,[7][8][9][10][11][12][13][14] In the first case, the population of less stable forms is reduced in favour of the most stable ones, providing that the energy barriers for the isomerizations can be surmounted.…”

Section: Introductionmentioning

confidence: 99%

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Conformational changes in matrix-isolated 6-methoxyindole: Effects of the thermal and infrared light excitations

Jesus

Reva

Araujo-Andrade

et al. 2016

The Journal of Chemical Physics

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Conformational changes induced thermally or upon infrared excitation of matrix-isolated 6-methoxyindole were investigated. Narrowband near-infrared excitation of the first overtone of the N-H stretching vibration of each one of the two identified conformers is found to induce a selective large-scale conversion of the pumped conformer into the other one. This easily controllable bidirectional process consists in the intramolecular reorientation of the methoxy group and allowed a full assignment of the infrared spectra of the two conformers. Matrices with different conformational compositions prepared by narrow-band irradiations were subsequently used to investigate the effects of both thermal and broadband infrared excitations on the conformational mixtures. Particular attention is given to the influence of the matrix medium (Ar vs. Xe) and conformational effects of exposition of the sample to the spectrometer light source during the measurements. C 2016 AIP Publishing LLC. [http://dx

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Section: A Gas Phase Conformational Equilibriummentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Conformational changes in matrix-isolated 6-methoxyindole: Effects of the thermal and infrared light excitations

Jesus

Reva

Araujo-Andrade

et al. 2016

The Journal of Chemical Physics

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“…This behavior has been observed in our previous studies of the other butanediol isomers. 7,8,12 The conformational distribution of these molecules after deposition in the matrix was skewed toward the most stable species of each conformer family, whose members share a common heavy atom backbone. This process is generally described as conformational cooling.…”

Section: -Butanediol Molecule (M) the Intramolecular H-bond Energy mentioning

confidence: 99%

“…This was achieved by the experimental identification of the most abundant conformers present in the low-temperature matrixes, conformational cooling effects taking place during deposition of these matrixes, 12,13 and observation of rotamerization reactions upon matrix annealing, rationalizing these experimental results on the basis of the theoretically obtained potential energy surface of the molecule.…”

Section: Introductionmentioning

confidence: 99%

“…An analogous phenomenon can also occur during deposition of the matrixes, due to the local heating of the matrix upon landing on the matrix surface of the molecules being deposited. 12,13 Due to the importance of the intramolecular H-bonding in the studied molecule, [9][10][11] a detailed analysis of this interaction was also undertaken on the basis of various theoretical and experimental approaches. Hence, both the natural bond orbital (NBO) 14,15 and atoms in molecules (AIM) 16 theories were used in the present study.…”

Section: Introductionmentioning

confidence: 99%

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Conformational Cooling Dynamics in Matrix-Isolated 1,3-Butanediol

et al. 2009

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The complete conformational space of monomeric 1,3-butanediol has been characterized theoretically, and 73 unique stable conformers were found at the MP2/6-311++G(d,p) level. These were classified into nine families whose members share the same heavy atom backbone configurations and differ in the hydrogen atom orientations. The first and third most populated backbone families are governed by the formation of an intramolecular hydrogen bond; however, the second precludes this type of interaction and was frequently overlooked in previous studies. Its stability is determined by the relatively high entropy of its main conformers. The hydrogen bonding of four of the most important conformers was characterized by means of atoms in molecules (AIM, also known as QTAIM) and natural bond orbital (NBO) analyses. Using appropriate isodesmic reactions, hydrogen bonding energy stabilizations of 12-14 kJ mol(-1) have been found. Experimentally, monomeric molecules of 1,3-butanediol were isolated in low-temperature inert matrixes, and their infrared spectra were analyzed from the viewpoint of the conformational distribution. All the relevant transition states for the conformational interconversion reaction paths were characterized at the same level of theory to interpret the conformational cooling dynamics observed in the low-temperature matrixes. The energy barriers for rotation of the OH groups were calculated to be very low (<3 kJ mol(-1)). These barriers were overcome in the experiments at 10 K (Ar matrix), in the process of matrix deposition, and population within each family was reduced to the most stable conformers. Further increase in the substrate temperature (up to 40 K, Xe matrix) resulted in conformational cooling where the medium-height barriers (approximately 13 kJ mol(-1)) could be surmounted and all conformational population converted to the ground conformational state. Remarkably, this state turned to consist of two forms of the most stable hydrogen bonded family, which were predicted by calculations to be accidentally degenerated and were found in the annealed matrix in equal amounts. All of these experimentally observed conformational cooling processes were analyzed and supported by full agreement with the theoretical calculations.

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Direct Time‐Domain Observation of Conformational Relaxation in Gas‐Phase Cold Collisions

et al. 2016

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Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics,a nd physical chemistry.M easurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flowwithin amolecule.However,gas-phase conformational cooling has not been previously observed directly.Inthis work, we directly observe conformational dynamics of 1,2propanediol in cold (6 K) collisions with atomic helium using microwave spectroscopya nd buffer-gas cooling. Precise knowledge and control of the collisional environment in the buffer-gas allows us to measure the absolute collision crosssection for conformational relaxation. Several conformers of 1,2-propanediol are investigated and found to have relaxation cross-sections with He ranging from s = 4.7(3.0) 10 À18 cm 2 to s > 510 À16 cm 2 .Our method is applicable to abroad class of molecules and could be used to provideinformation about the potential energy surfaces of previously uninvestigated molecules.The structure of organic molecules is critical to molecular function in biology and chemistry.I np articular,u nderstanding the properties of conformers,which are isomers differing by rotation about one or more chemical bonds,p rovides insight relevant to diverse phenomena such as chemical and catalytic activity, [1,2] thef olding of proteins, [3][4][5][6] behavior of DNA, [1,7] metabolism of sugar, [8,9] and reactions of organic molecules with trapped ions. [10] Conformers may be observed in many environments,u sing ad iverse set of spectroscopic methods.F or example,m olecular beam microwave spectroscopy can provide detailed information about structure and indirect measurement of conformer energies. [11][12][13] Cryogenic matrix isolation spectroscopy can measure dynamics in asolid state environment [14] and ultrafast spectroscopy can measure both structure and reaction dynamics. [15] Each method provides aw indow into certain conformational properties and provides data that can test quantum-chemistry theory calculations.Much of our understanding of gas-phase conformers comes from jet cooled molecular beam spectroscopy and cryogenic matrix isolation spectroscopy experiments.The low ro-vibrational and moving-frame temperature of molecules in as upersonic jet allows for precise,c onformer specific spectroscopy. [16] Although such experiments typically realize arotational and translational temperature of afew Kelvin, in many cases excited conformers with energies of hundreds of Kelvin remain in the sample.T he relaxation (cooling) of conformational degrees of freedom is the conversion of ahigh energy conformer into al ower energy conformer. It can be induced by gas-phase collisions or by couplings to asolid state environment, and typically happens substantially slower than rotational and translational cooling. Quantitative study of relaxation provides key information about conformational interconversion barriers.I nj et cooled molecular beam spectroscopy,c onclusions about the interconversion barriers separating co...

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Stepwise conformational cooling towards a single isomeric state in the four internal rotors system 1,2-butanediol

Cited by 69 publications

References 39 publications

Conformational changes in matrix-isolated 6-methoxyindole: Effects of the thermal and infrared light excitations

Conformational changes in matrix-isolated 6-methoxyindole: Effects of the thermal and infrared light excitations

Conformational Cooling Dynamics in Matrix-Isolated 1,3-Butanediol

Direct Time‐Domain Observation of Conformational Relaxation in Gas‐Phase Cold Collisions

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