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Issue 40, 2011
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The role of weak hydrogen bonds in chiral recognition

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Abstract

Chiral recognition has been studied in neutral or ionic weakly bound complexes isolated in the gas phase by combining laser spectroscopy and quantum chemical calculations. Neutral complexes of the two enantiomers of lactic ester derivatives with chiral chromophores have been formed in a supersonic expansion. Their structure has been elucidated by means of IR-UV double resonance spectroscopy in the 3 μm region. In both systems described here, the main interaction ensuring the cohesion of the complex is a strong hydrogen bond between the chromophore and methyl-lactate. However, an additional hydrogen bond of much weaker strength plays a discriminative role between the two enantiomers. For example, the 1 : 1 heterochiral complex between R-(+)-2-naphthyl-ethanol and S-(+) methyl-lactate is observed, in contrast with the 1 : 1 homochiral complex which lacks this additional hydrogen bond. On the other hand, the same kind of insertion structures is formed for the complex between S-(±)-cis-1-amino-indan-2-ol and the two enantiomers of methyl-lactate, but an additional addition complex is formed for R-methyl-lactate only. This selectivity rests on the formation of a weak CH⋯π interaction which is not possible for the other enantiomer. The protonated dimers of Cinchona alkaloids, namely quinine, quinidine, cinchonine and cinchonidine, have been isolated in an ion trap and studied by IRMPD spectroscopy in the region of the ν(OH) and ν(NH) stretch modes. The protonation site is located on the alkaloid nitrogen which acts as a strong hydrogen bond donor in all the dimers studied. While the nature of the intermolecular hydrogen bond is similar in the homochiral and heterochiral complexes, the heterochiral complex displays an additional weak CH⋯O hydrogen bond located on its neutral part, which results in slightly different spectroscopic fingerprints in the ν(OH) stretch region. This first spectroscopic evidence of chiral recognition in protonated dimers opens the way to the study of the complexes of Cinchona alkaloids involved in enantioselective catalysis. These examples show how secondary hydrogen bonds controlled by stereochemical factors govern molecular recognition processes.

Graphical abstract: The role of weak hydrogen bonds in chiral recognition

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Publication details

The article was received on 31 Mar 2011, accepted on 19 Aug 2011 and first published on 19 Sep 2011


Article type: Perspective
DOI: 10.1039/C1CP20987F
Citation: Phys. Chem. Chem. Phys., 2011,13, 17916-17929
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    The role of weak hydrogen bonds in chiral recognition

    D. Scuderi, K. Le Barbu-Debus and A. Zehnacker, Phys. Chem. Chem. Phys., 2011, 13, 17916
    DOI: 10.1039/C1CP20987F

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