Spectroscopie optique des paires d'ions : De la caractérisation des modèles en phase gazeuse à l'identification des paires d'ions en solution

Abstract : Ion pairs are ubiquitous in nature andwere documented in sea waters, aerosols andliving organisms, thus they play a crucial role inmany chemical and biochemical mechanisms.Although many experimental approaches aimedat identifying these ion pairs in solutions, theyfailed in characterizing their microscopicproperties, mainly due to the coexistence of manytypes of pairs in solution. This original study aimsto identify the structural properties of ion pairmodels in the gas phase that depicts theinteraction between carboxylate group and alkalication, largely present in biological media.Model systems (M+, C6H5(CH2)nCOO-, M = Li,Na, K, Rb, Cs and n ≤ 4) were the subject of thefirst studies conducted using gas phaseconformational selective IR and UV spectroscopycombined to quantum chemistry calculations.Among the identified structures, we found asecondary interaction between the cation andphenyl ring (cation-π interaction) for systems witha flexible carbon chain, which led us to study thecompetition between cation-anion and cation-πinteractions.The second study developed focused mainly oncharacterizing ion pairs (M+, CH3COO-; M = Li,Na) and free anion in solution, where the firstsolvation layer were described at the quantumlevel, followed by a solvent continuum. Thus thevibrationnal signatures proposed for theseaggregates were compared to solution spectra inlitterature, thus offering a reliable structuralassignement.This study on neutral ion pairs paves way to a betterunderstanding of ion pairing and offers a uniqueapproach to adress the structural characterization ofthese systems in solution.
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Sana Habka. Spectroscopie optique des paires d'ions : De la caractérisation des modèles en phase gazeuse à l'identification des paires d'ions en solution. Chimie théorique et/ou physique. Université Paris-Saclay, 2017. Français. ⟨NNT : 2017SACLS227⟩. ⟨tel-01618558⟩

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