Correlation of Solution and Gas Phase Complexation Assessed by Electrospray Ionization Mass Spectrometry:  Application to One-, Two-, and Three-Ring Macrocycles

Abstract

Electrospray ionization mass spectrometry (ESI-MS) was used to probe multiple cation complexation by C(12)H(25)<N18N>(CH(2))(12)<N18N>(CH(2))(12)<N18N>C(12)H(25), 2, and <18N>CH(2)C(6)H(4)CH(2)<N18>, 3. Complexation of two cations (2Na(+), 2 K(+), or Na(+) and K(+)) by 3 and three cations by 2 (3 Na(+), 3 K(+), and mixtures) as well as mixed proton-metallic cation complexes of both were observed. The K(+)/Na(+) cation-binding selectivity of 18-crown-6 was studied by ESI-MS of a methanol solution, and the selectivity profile was favorably compared with data obtained previously by ion-selective electrode techniques in the same solvent.

Molecular recognition and supramolecular chemistry in the gas phase

“…Development of the electrospray ionization method has provided the basis for the study of crown ether-alkali metal ion-binding properties. A large variety of crowns have been studied, from the simplest representatives, including their aza-and thia-analogs (Takahashi et al, 1992;Colton et al, 1995a), to bis- (Beer, 1985) and triscrowned structures (Wang et al, 1995a;Wang & Gokel, 1996;also, see: Wang et al, 1995b), cleft-like (Blair et al, 1998a), caged (Blair et al, 2000;Reyzer et al, 2001), and acetal crown ethers (Oshima, 1998). Also, the binding ability to alkaline earth Shen et al, 2000) and heavy metal ions was examined (Blades et al, 1990;Colton et al, 1995a;Blair et al, 2000).…”

Synthesis, alkali metal picrate extraction, and alkali metal cation binding selectivities of some new cage‐annulated polyoxamacrocyclic crown ethers

“…ESI-MS has proven to be a versatile method for analysis of supramolecular complexes formed in solution and transported into the gas phase for detection [6][7][8][9][10][11][12][13][14][15][16][17][18]. Based upon the intensities of complexes in the resulting mass spectra, it is possible to estimate the relative binding selectivities of different hosts toward different guests.…”

Metal-complex formation in continuous-flow ligand-exchange reactors studied by electrospray mass spectrometry

“…Good correlation between the theoretical plot and the experimental data is achieved. Although a close relationship between the observed intensity of the mass spectrum and the calculated concentration of the formed complex was reported for 1:1 complexes of crown ethers with Na ϩ and°K ϩ° [ 18],°in°the°present°case°it°is°more°difficult°to correlate intensities to concentrations of metal complexes because various complexes are formed (see below) and these complexes appear to have different ionization efficiencies. Despite this limitation, the measured optimum total ligand concentration for the maximum concentration of MeL (Ϸ23 M) and MeL 2 (Ϸ50 M) are in good agreement with the values predicted from the theoretical plot, 25 M and 53 M, respectively.…”

“…FAB-MS and ESI-MS have been used in the past to evaluate binding selectivities of various compounds, e.g., caged crown ethers to metal-ions [16]. An excellent correlation between obtained ESI mass spectral data and expected binding selectivities has been reported in several papers [13,17,18], although several parameters should be kept in mind. For a good correlation between complex formation in solution and what is observed in the mass spectrum [14], particularly the competing effect of the solvent, the conditions and ionization efficiencies of the different complexes, and molecules have to be taken into account.…”