title: Analysis of the major chiral compounds of Artemisia herba-alba essential oils (EOs) using reconstructed vibrational circular dichroism (VCD) spectra: En route to a VCD chiral signature of EOs.
abstract: An unprecedented methodology was developed to simultaneously assign the relative percentages of the major chiral compounds and their prevailing enantiomeric form in crude essential oils (EOs). In a first step the infrared (IR) and vibrational circular dichroism (VCD) spectra of the crude essential oils were recorded and in a second step they were modelized as a linear weighted combination of the IR and VCD spectra of the individual spectra of pure enantiomer of the major chiral compounds present in the EOs. The VCD spectra of enantiomer of known enantiomeric excess shall be recorded if they are not yet available in a library of VCD spectra. For IR, the spectra of pure enantiomer or racemic mixture can be used. The full spectra modelizations were performed using a well known and powerful mathematical model (least square estimation: LSE) which resulted in a weighting of each contributing compound. For VCD modelization, the absolute value of each weighting represented the percentage of the associate compound while the attached sign addressed the correctness of the enantiomeric form used to build the model. As an example, a model built with the non-prevailing enantiomer will show a negative sign of the weighting value. For IR spectra modelization, the absolute value of each weighting represented the percentage of the compounds without of course accounting for the chirality of the prevailing enantiomers. Comparison of the weighting values issuing from IR and VCD spectra modelizations is a valuable source of information: if they are identical, the EOs are composed of nearly pure enantiomers, if they are different the chiral compounds of the EOs are not in an optically pure form. The method was applied on four samples of essential oil of Artemisia herba-alba in which the three major compounds namely (-)-α-thujone, (+)-β-thujone and (-)-camphor were found in different proportions as determined by GC-MS and chiral HPLC using polarimetric detector. In order to validate the methodology, the modelization of the VCD spectra was performed on purpose using the individual VCD spectra of (-)-α-thujone, (+)-β-thujone and (+)-camphor instead of (-)-camphor. During this work, the absolute configurations of (-)-α-thujone and (+)-β-thujone were confirmed by comparison of experimental and calculated VCD spectra as being (1S,4R,5R) and (1S,4S,5R) respectively.
authors.affiliation: Aix-Marseille Université, EA4672 LISA Equipe METICA, Case 451, Av. Escadrille Normandie Niémen, 13397 Marseille Cedex 20, France.
authors.forename: Mohammed El-Amin
authors.initials: Mel-A
authors.lastname: Said
authors.affiliation: Aix-Marseille Université, EA4672 LISA Equipe METICA, Case 451, Av. Escadrille Normandie Niémen, 13397 Marseille Cedex 20, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Vanloot
authors.affiliation: Aix-Marseille Université, EA4672 LISA Equipe METICA, Case 451, Av. Escadrille Normandie Niémen, 13397 Marseille Cedex 20, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bombarda
authors.affiliation: Aix-Marseille Université, Spectropole, Service 511, F-13397 Marseille, France.
authors.forename: Jean-Valère
authors.initials: JV
authors.lastname: Naubron
authors.affiliation: MSISM Research Team Faculte Polydisciplinaire, Cadi Ayyad University, Safi, Morocco.
authors.forename: El Montassir
authors.initials: el M
authors.lastname: Dahmane
authors.affiliation: MSISM Research Team Faculte Polydisciplinaire, Cadi Ayyad University, Safi, Morocco.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Aamouche
authors.affiliation: Aix-Marseille Université, Centrale Marseille, CNRS, ISM2 UMR 7313, Marseille, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Jean
authors.affiliation: Aix-Marseille Université, Centrale Marseille, CNRS, ISM2 UMR 7313, Marseille, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vanthuyne
authors.affiliation: Aix-Marseille Université, EA4672 LISA Equipe METICA, Case 451, Av. Escadrille Normandie Niémen, 13397 Marseille Cedex 20, France. Electronic address: nathalie.dupuy@univ-amu.fr.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Dupuy
authors.affiliation: Aix-Marseille Université, Centrale Marseille, CNRS, ISM2 UMR 7313, Marseille, France. Electronic address: christian.roussel@univ-amu.fr.
authors.forename: Christian
authors.initials: C
authors.lastname: Roussel
mesh_terms: D019306:Artemisia / Q000737:chemistry*; D002942:Circular Dichroism / Q000379:methods*; D008401:Gas Chromatography-Mass Spectrometry; D009822:Oils, Volatile / Q000032:analysis*; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism
chemical_list: D009822:Oils, Volatile
keywords: Artemisia herba-alba; Chiral signature; Diastereomers; Essential oil; Vibrational circular dichroism