Mass Spectrometry Study and Infrared Spectroscopy of the Complex Between Camphor and the Two Enantiomers of Protonated Alanine: The Role of Higher‐Energy Conformers in the Enantioselectivity of the Dissociation Rate Constants. Issue 8 (6th June 2013)

• Record Type: Journal Article
• Authors: Sen, Ananya; Le Barbu‐Debus, Katia; Scuderi, Debora; Zehnacker‐Rentien, Anne
• Is Part Of: Chirality. Volume 25:Issue 8(2013:Aug.)
• Page Start: 436
• Page End: 443
• Publication Date: 2013-06-06
• Subjects: Chirality -- Periodicals; Pharmaceutical chemistry -- Periodicals; 541.22
• DOI: 10.1002/chir.22164
• Languages: English
• ISSNs: 0899-0042

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>The properties of the protonated complexes built from <italic>S</italic> camphor and <italic>R</italic> or <italic>S</italic> alanine were studied in a Paul ion trap at room temperature by collision‐induced dissociation (CID) and infrared multiple‐photon dissociation spectroscopy (IRMPD), as well as molecular dynamics and ab initio calculations. While the two diastereomer complexes display very similar vibrational spectra in the fingerprint region, in line with similar structures, and almost identical calculated binding energies, their collision‐induced dissociation rates are different. Comparison of the IRMPD results to computed spectra shows that the <italic>SS</italic> and <italic>SR</italic> complexes both contain protonated alanine strongly hydrogen‐bonded to the keto group of camphor. The floppiness of this structure around the NH<sup>+</sup>…O = C hydrogen bond results in a complex potential energy surface showing multiple minima. Calculating the dissociation rate constant within the frame of the transition state theory shows that the <named-content id="d14e412" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">fragmentation</named-content> rate larger for the heterochiral <italic>SR</italic> complex than the homochiral <italic>SS</italic> complex can be explained in terms of two almost isoenergetic low‐energy conformers in the latter that are not present for the former. Chirality 25:436‐443, 2013. © 2013 Wiley Periodicals, Inc.</p> </abstract>