Electrospray ionization mass spectrometry studies of cyclodextrin‐carboxylate ion inclusion complexes

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.

Investigation of the sorption properties of β-cyclodextrin-based polyurethanes with phenolic dyes and naphthenates

“…The role of the porogen was further tested using a CL-CDI (1:3) (cellobiose:CDI (1:3)) copolymer. CL is amphiphilic in nature due to its concave shape and may form complexes with apolar organic molecules, as concluded previously [39]. The isotherm generated from the sorption of PNP with CL-CDI (1:3) is shown in Fig.…”

“…The equilibrium concentrations of NAs were determined using negative ion electrospray ionization mass spectrometry (ESI-MS). The instrumental conditions for the analyses of NAs have been described previously [39].…”

“…The phenolic dyes reported herein are p-nitrophenol (PNP) and phenolphthalein (phth) which have been used previously for the estimation of the surface area of sorbent materials [34,35] and an understanding of the molecular recognition by b-CD domains [31,[36][37][38], respectively. NAs have been extensively described in previous work [29,39,40]. The copolymer materials are comprised of b-CD and diisocyanate co-monomers with variable aliphatic and aromatic molecular structure features according to their relative molecular size and conformational motility (cf.…”

Novel materials for environmental remediation of oil sands contaminants

“…In a follow-up study, Mohamed et al (9) reported the occurrence of molecular selectivity among congeners of NAs in aqueous solutions containing CDs, based on low-resolution mass spectrometry. The observed change in relative concentrations of oil sands acids is evident in Figure 3 by a comparison of the extract of NAs before and after equilibration with CD.…”

“…The expanded definition includes oil sands acid-extractable organics with aromatic functional groups, nitrogen and sulfur atoms, along with unsaturated groups (15,16). For example, oil sands acids are known to fluoresce and evidently contain unsaturated and aromatic functionality that can be exploited using synchronous fluorescence spectroscopy and UV detection (9). OSPW contains thousands of oil Brought to you by | Western University Authenticated Download Date | 6/9/15 8:16 PM sands acids, many of which are only resolved using ultrahigh-resolution mass spectrometry.…”