Mohamed MH, Wilson LD, Headley JV, Peru KM. Electrospray ionization mass spectrometry studies of cyclodextrin-carboxylate ion inclusion complexes.
RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2009;
23:3703-3712. [PMID:
19899185 DOI:
10.1002/rcm.4302]
[Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Aqueous solutions containing simple model aliphatic and alicyclic carboxylic acids (surrogates 1-4) were studied using negative ion electrospray mass spectrometry (ESI-MS) in the presence and absence of alpha-, beta-, and gamma-cyclodextrin. Molecular ions were detected corresponding to the parent carboxylic acids and complexed forms of the carboxylic acids; the latter corresponding to non-covalent inclusion complexes formed between carboxylic acid and cyclodextrin compounds (e.g., beta-CD, alpha-CD, and gamma-CD). The formation of 1:1 non-covalent inclusion cyclodextrin-carboxylic complexes and non-inclusion forms of the cellobiose-carboxylic acid compounds was also observed.Aqueous solutions of Syncrude-derived mixtures of aliphatic and alicyclic carboxylic acids (i.e. naphthenic acids; NAs) were similarly studied using ESI-MS, as outlined above. Molecular ions corresponding to the formation of CD-NAs inclusion complexes were observed whereas 1:1 non-inclusion forms of the cellobiose-NAs complexes were not detected. The ESI-MS results provide evidence for some measure of inclusion selectivity according to the 'size-fit' of the host and guest molecules (according to carbon number) and the hydrogen deficiency (z-series) of the naphthenic acid compounds. The relative abundances of the molecular ions of the CD-carboxylate anion adducts provide strong support for differing complex stability in aqueous solution. In general, the 1:1 complex stability according to hydrogen deficiency (z-series) of naphthenic acids may be attributed to the nature of the cavity size of the cyclodextrin host compounds and the relative lipophilicity of the guest.
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