Nathalie Seurre

The role of chirality in the competition between inter and intramolecular hydrogen bonds: jet-cooled van der Waals complexes of (±)2-naphthyl-1-ethanol with (±)1-amino-2-propanol and (±)2-amino-1-butanol

The structure of jet-cooled complexes of (±) 2-naphtyl-1-ethanol with (±) 1-amino-2-propanol and (±) 2-amino-1-butanol has been studied by laser-induced fluorescence, UV and IR fluorescence dip spectroscopy, combined with DFT calculations. Chiral discrimination has been evidenced both in the electronic and vibrational spectra. The homochiral complex with 1-amino-2-propanol displays two distinct kinds of structure: an O-addition complex in which the chromophore adds to the alcohol group of 1-amino-2-propanol, and a N-addition complex in which the chromophore binds to the amino group of 1-amino-2-propanol. In contrast, the heterochiral complex with 1-amino-2-propanol, or both complexes with 2-amino-1-butanol, are of O-addition type. Deeper analysis of the O-addition structures, within the frame of the Natural Bond Orbital theory, has shown that the difference in the vibrational spectrum of the homo- and heterochiral complexes can be rationalised in terms of a different shift from linearity of the intermolecular H-bond, which results in a difference in electron density transfer along the H bond. Last, the study of the vibrational spectrum of the electronic excited state shows that the hydrogen bond network is reinforced upon electronic excitation.

Chiral recognition between lactic acid derivatives and an aromatic alcohol in a supersonic expansion: electronic and vibrational spectroscopy

Jet-cooled diastereoisomeric complexes formed between a chiral probe, (+/-)-2-naphthyl-1-ethanol, and chiral lactic acid derivatives have been characterised by laser-induced fluorescence and IR fluorescence-dip spectroscopy. Complexes with non chiral alpha-hydroxyesters and chiral beta-hydroxyesters have also been studied for the sake of comparison. DFT calculations have been performed to assist in the analysis of the vibrational spectra and the determination of the structures. The observed 1 : 1 complexes correspond to the addition of the hydroxy group of the chromophore on the oxygen atom of the hydroxy in alpha-position relative to the ester function. Moreover, (+/-)-methyl lactate and (+/-)-ethyl lactate complexes with (+/-)-2-naphthyl-1-ethanol show an enantioselectivity in the size of the formed adducts: while fluorescent 1 : 1 complexes are the most abundant species observed when mixing (S)-2-naphthyl-1-ethanol with (R)-methyl or ethyl lactate, they are absent in the case of the SS mixture, which only shows 1 : 2 adducts. This property has been related to steric hindrance brought by the methyl group on the hydroxy-bearing carbon atom.

Vibrational study of the S0 and S1 states of 2-naphthyl-1-ethanol/(water)2 and 2-naphthyl-1-ethanol/(methanol)2 complexes by IR/UV double resonance spectroscopy

2-naphthyl-1-ethanol/(water)2 and 2-naphthyl-1-ethanol/(methanol)2 complexes have been formed in a supersonic expansion and studied by laser induced fluorescence (LIF) and IR/UV double resonance spectroscopy in the region of the O–H stretch. Comparison of the measured frequencies with DFT calculations has led to the attribution of the observed 2-naphthyl-1-ethanol/(water)2 and 2-naphthyl-1-ethanol/(methanol)2 complexes to bridged structures. In these structures the solvent dimer is inserted in between the OH group of the chromophore which acts as a hydrogen bond donor, and the electron π system of the aromatic ring. Electronic excitation results in a red shift of all the νOH stretch frequencies.

Formation of hydrogen-bonded bridges in jet-cooled complexes of a chiral chromophore as studied by IR/UV double resonance spectroscopy. (±)2-Naphthyl-1-ethanol/(methanol)n=1,2 complexes

The structure of (±)2-naphthyl-1-ethanol and its 1∶1 or 1∶2 complexes with methanol has been studied by IR fluorescence dip spectroscopy, combined with DFT calculations. The bare molecule exhibits a gauche conformation of the OH group and exists as two conformers which differ by a rotation of the aromatic plane by 180° around the C2–Cα axis. When associated with methanol, both conformers form complexes which can be discriminated by the shift of their first electronic transition and which exhibit very similar structures. The 1∶1 complexes have been assigned to a structure in which methanol accepts a proton from the OH group of the chromophore and is involved in a OH⋯π interaction with the aromatic ring. A bridged structure which contains a methanol dimer inserted between the OH group of the chromophore and the aromatic ring has been proposed for the 1∶2 complexes.

Laser spectroscopy of a chiral drug in a supersonic beam: conformation and complexation of s-(+)-Naproxen

Abstract The S 0 –S 1 electronic transition of jet-cooled Naproxen has been investigated by laser-induced fluorescence excitation and emission spectroscopy. Two electronic transitions separated by 102 cm −1 have been evidenced and attributed to the presence of two conformers. With the help of DFT calculations, the structure of these conformers has been shown to correspond to a rotation by 180° of the chiral substituent with respect to the aromatic plane. When associated with alcohols, both conformers of the chromophore form complexes which give rise to different microscopic solvent shifts of the S 0 –S 1 transition. In the case of complexation with R- or S-2-butanol, the hetero- and homo-chiral pairs are characterised by different spectroscopic patterns, which allow a clear discrimination between them.

Infrared spectra of C2H4-HCl complex

We report the first rotationally resolved observation of the infrared spectrum of the molecular complex C2H4–HCl. The complex was produced by a supersonic expansion through a pulsed slit jet. By means of a high-resolution tunable diode laser spectrometer, we have recorded the spectrum of the HCl stretching vibration for the isotopes C2H4–H35Cl and C2H4–H37Cl. From the analysis of the spectra, we determined the rotational constants and vibrational frequencies of both isotopes. These experimental results have been interpreted in view of obtaining information on the intermolecular interaction. The experimental data have been complemented by standard coupled cluster singles and doubles model including connected triple excitations with a correlation consistent polarized valence triple zeta basis set ab initio followed by grid calculations, in order to study the anharmonicity, the coupling between intramolecular and intermolecular motions, and the basis set superposition error effects. The results obtained in t...

Chiral Recognition in Jet-Cooled Complexes

Jet-cooled complexes formed between a chiral probe [(±)-2-naphthyl-1-ethanol] and chiral bifunctional partners that show an intramolecular hydrogen bond have been studied by laser-induced fluorescence and IR fluorescence-dip spectroscopy as well as with DFT calculations. Chiral discrimination results in a chirality-dependent competition between the intramolecular and the intermolecular hydrogen bonds. In the case of (±)-methyl lactate, this competition manifests itself in the size of the formed adducts. In particular, while 1 : 1 complexes are the most abundant species observed when (R)-2-naphthyl-1-ethanol is mixed with (S)-methyl lactate, they are absent in the case of the SS mixture, which only forms 1 : 2 adducts.