Preferential Ion Microsolvation in Mixed-Modifier Environments Observed Using Differential Mobility Spectrometry
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J. Am. Soc. Mass Spectrom. (2019) DOI: 10.1007/s13361-019-02332-1
RESEARCH ARTICLE
Preferential Ion Microsolvation in Mixed-Modifier Environments Observed Using Differential Mobility Spectrometry Neville J. A. Coughlan,1 Chang Liu,2 Michael J. Lecours,1 J. Larry Campbell,1,2 W. Scott Hopkins1 1
Department of Chemistry, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada SCIEX, Four Valley Dr., Concord, ON L4K 4V8, Canada
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Abstract. The preferential solvation behavior for eight different derivatives of protonated quinoline was measured in a tandem differential mobility spectrometer mass spectrometer (DMS-MS). Ion-solvent cluster formation was induced in the DMS by the addition of chemical modifiers (i.e., solvent vapors) to the N2 buffer gas. To determine the effect of more than one modifier in the DMS environment, we performed DMS experiments with varying mixtures of water, acetonitrile, and isopropyl alcohol solvent vapors. The results show that doping the buffer gas with a binary mixture of modifiers leads to the ions binding preferentially to one modifier over another. We used density functional theory to calculate the ion-solvent binding energies, and in all cases, calculations show that the quinolinium ions bind most strongly with acetonitrile, then isopropyl alcohol, and most weakly with water. Computational results support the hypothesis that the quinolinium ions bind exclusively to whichever solvent they have the strongest interaction with, regardless of the presence of other modifier gases. Keywords: Differential ion mobility, DMS, Ion mobility, Modifiers, Preferential solvation, Gas-phase solvation, DFT, Ion-solvent clustering Received: 12 June 2019/Revised: 20 August 2019/Accepted: 27 August 2019
Introduction
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referential solvation is a phenomenon whereby a solute that is solvated in a binary (or higher order) solvent system interacts preferentially with one solvent over another [1]. More specifically, the solute’s inner solvation shell does not resemble the bulk composition of the solvent medium, but rather is composed predominantly of the more strongly interacting species. From a chemical perspective, the nature of solvation is of obvious importance, since most chemical reactions take place
Electronic supplementary material The online version of this article (https:// doi.org/10.1007/s13361-019-02332-1) contains supplementary material, which is available to authorized users. Correspondence to: J. Campbell; e-mail: [email protected], W. Hopkins; e-mail: [email protected]
in some solvated phase. The specific choice of solvent, mixed or otherwise, can drastically alter key reaction parameters for a given chemical reaction—for a review on the subject, see ref. [2]. Because it is difficult to directly interrogate the solvent shell in condensed phase experiments, properties of the solvated molecule are often targeted as a proxy to observe preferential solvation. For example, it has been shown that the infrared (IR) absorption characteristics [3], solvatochromic
