Montserrat Vallejo-López

Probing the CH⋅⋅⋅π Weak Hydrogen Bond in Anesthetic Binding: The Sevoflurane–Benzene Cluster

Cooperativity between weak hydrogen bonds can be revealed in molecular clusters isolated in the gas phase. Here we examine the structure, internal dynamics, and origin of the weak intermolecular forces between sevoflurane and a benzene molecule, using multi-isotopic broadband rotational spectra. This heterodimer is held together by a primary C-H⋅⋅⋅π hydrogen bond, assisted by multiple weak C-H⋅⋅⋅F interactions. The multiple nonbonding forces hinder the internal rotation of benzene around the isopropyl C-H bond in sevoflurane, producing detectable quantum tunneling effects in the rotational spectrum.

Interactions between alkanes and aromatic molecules: a rotational study of pyridine–methane

The rotational spectrum of the adduct pyridine-methane shows that methane links to an aromatic molecule apparently through a C-H···π weak hydrogen bond. The shape and the internal dynamics behaviour of this complex are very similar to that of the van der Waals complexes involving aromatic molecules with rare gases.

How Water Interacts with Halogenated Anesthetics: The Rotational Spectrum of Isoflurane–Water

The rotational spectra of several isotopologues of the 1:1 complex between the inhaled anesthetic isoflurane and water have been recorded and analyzed by using Fourier transform microwave spectroscopy. The rotational spectrum showed a single rotamer, corresponding to the configuration in which the most stable conformer of isolated isoflurane is linked to the water molecule through an almost linear C-H⋅⋅⋅O weak hydrogen bond. All transitions display a hyperfine structure due to the (35)Cl (or (37)Cl) nuclear quadrupole effects.

OH⋅⋅⋅N and CH⋅⋅⋅O Hydrogen Bonds Control Hydration of Pivotal Tropane Alkaloids: Tropinone⋅⋅⋅H2O Complex

The effect of monohydration in equatorial/axial isomerism of the common motif of tropane alkaloids is investigated in a supersonic expansion by using Fourier-transform microwave spectroscopy. The rotational spectrum reveals the equatorial isomer as the dominant species in the tropinone⋅⋅⋅H2 O complex. The monohydrated complex is stabilized primarily by a moderate OH⋅⋅⋅N hydrogen bond. In addition, two CH⋅⋅⋅O weak hydrogen bonds also support this structure, blocking the water molecule and avoiding any molecular dynamics in the complex. The water molecule acts as proton donor and chooses the ternary amine group over the carbonyl group as a proton acceptor. The experimental work is supported by theoretical calculations; the accuracy of the B3LYP, M06-2X, and MP2 methods is also discussed.

Fluorination Effects on the Shapes of Complexes of Water with Ethers: A Rotational Study of Trifluoroanisole–Water

The rotational spectra of five isotopologues of the 1:1 complex trifluoroanisole-water have been investigated with pulsed jet Fourier transform microwave spectroscopy. The triple fluorination of the methyl group greatly affects the features of the rotational spectrum of the complex with water, with respect to those of the related complex anisole-water. The shape, the internal dynamics, and the isotopic effects turned out to be quite different from those of the anisole-water adduct ( Giuliano , B. M. ; Caminati , W. Angew. Chem., Int. Ed. 2005 , 44 , 603 - 606 ). However, as in anisole-water, water has the double role as a proton donor and proton acceptor, and it is linked to trifluoroanisole through two, O-H···O and C-H···O hydrogen bonds.

Rotational spectra of bicyclic decanes: the trans conformation of (-)-lupinine.

The conformational and structural properties of the bicyclic quinolizidine alkaloid (-)-lupinine have been investigated in a supersonic jet expansion using microwave spectroscopy. The rotational spectrum is consistent with a single dominant trans conformation within a double-chair skeleton, which is stabilized by more than 10.4 kJ mol(-1) with respect to other conformations. In the isolated conditions of the jet, the hydroxy methyl side chain of the molecule locks in to form an intramolecular O-H···N hydrogen bond to the electron lone pair at the nitrogen atom. Accurate rotational constants, centrifugal distortion corrections, and (14)N nuclear quadrupole coupling parameters are reported and compared to ab initio (MP2) and DFT (M06-2X) calculations. The stability of lupinine is further compared computationally with epilupinine and decaline in order to gauge the influence of intramolecular hydrogen bonding, absent in these molecules.

Scopine Isolated in the Gas Phase.

The rotational spectrum of the tropane alkaloid scopine is detected by Fourier transform microwave spectroscopy in a pulsed supersonic jet. A nonconventional method for bringing the molecules intact into the gas phase is used in which scopine syrup is mixed with glycine powder and the solid mixture is vaporized with an ultrafast UV laser beam. Laser vaporization prevents the easy isomerization to scopoline previously observed with conventional heating methods. A single conformer is unambiguously observed in the supersonic jet and corresponds to the energetically most stable species according to quantum chemical calculations. Rotational and centrifugal distortion constants are accurately determined. The spectrum shows fine and hyperfine structure due to the hindered rotation of the methyl group and the presence of a quadrupolar nucleus (14 N), respectively. This additional information allows the angle of N-methyl inversion between the N-CH3 bond and the bicyclic C-N-C plane to be determined (131.8-137.8°), as well as the internal rotation barrier of the methyl group (6.235(1) kJ mol-1 ).

Pseudorotational Landscape of Seven-Membered Rings: The Most Stable Chair and Twist-Boat Conformers of ε-Caprolactone

The conformational landscape and ring-puckering properties of ε-caprolactone have been analyzed by using microwave spectroscopy and quantum chemical calculations. Two conformers were detected in a supersonic jet expansion, the most stable form being a chair containing the ester group in its rectangular flap. This conformation benefits from reduced CH2 bond eclipsing and angle strain, while π-electron delocalization in the ester group is increased. The derived effective structure of the chair form satisfactorily agrees with the calculated near-equilibrium structure. A twist-boat conformer was also identified (9.4 kJ mol(-1) higher in energy at CCSD(T)/aug-cc-pVTZ level), and was located in the boat-twist-boat pseudorotation cycle of the seven-membered ring. Three other low-energy conformers were investigated and characterized in terms of the four puckering coordinates of the seven-membered ring. Potential interconversions in the four-dimensional conformation space are also discussed.

Local anesthetics in the gas-phase: The rotational spectrum of butamben and isobutamben

MONTSERRAT VALLEJO-LÓPEZ, Physical Chemistry, University of the Basque Country, Leioa Bilbao, Spain; PATRICIA ECIJA, Physical Chemistry Department, Universidad del Paı́s Vasco, Bilbao, Spain; WALTHER CAMINATI, Dep. Chemistry ’Giacomo Ciamician’, University of Bologna, Bologna, Italy; JENS-UWE GRABOW, Institut für Physikalische Chemie und Elektrochemie, Gottfried-Wilhelm-LeibnizUniversität, Hannover, Germany; ALBERTO LESARRI, Departamento de Quı́mica Fı́sica y Quı́mica Inorgánica, Universidad de Valladolid, Valladolid, Spain; EMILIO J. COCINERO, Physical Chemistry Department, Universidad del Paı́s Vasco, Bilbao, Spain.