Identification of Anionic Supramolecular Complexes of Sulfonamide Receptors with Cl⁻, NO₃⁻, Br⁻, and I⁻ by APCI-MS

Abstract

As part of a mass spectrometric investigation of the binding properties of sulfonamide anion receptors, an atmospheric pressure chemical ionization mass spectrometric (APCI-MS) method involving direct infusion followed by thermal desorption was employed for identification of anionic supramolecular complexes in dichloromethane (CH 2 Cl 2 ). Specifically, the dansylamide derivative of tris(2-aminoethyl)amine (tren) (1), the chiral 1,3-benzenesulfonamide derivatives of (1R,2S)-(ϩ)-cis-1-amino-2-indanol (2), and (R)-(ϩ)-bornylamine, (3), were shown to bind halide and nitrate ions in the presence of (nϪBu) Solutions of receptors and anions in CH 2 Cl 2 were combined to form the anionic supramolecular complexes, which were subsequently introduced into the mass spectrometer via direct infusion followed by thermal desorption. The anionic supramolecular complexes Inorganic ions with small mass-to-charge ratios are typically analyzed by other techniques, such as ion chromatography and capillary electrophoresis, because under normal MS ionization conditions many compounds can produce small ions that can interfere with their detection. There are, however, some notable examples [7,8] that demonstrate the potential of soft ionization methods [9], such as atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and electrospray ionization mass spectrometry (ESI-MS)[10] for analysis of inorganic ions, and ion pairs, such as ammonium nitrate [11].Increased sensitivity for MS analysis of inorganic ions has been achieved by a relatively new and promising strategy, which bridges the fields of mass spectrometry and supramolecular chemistry [12][13][14]. This approach is based on selective host molecules for specific cationic or anionic guests, which can form ionic adducts with higher molecular mass. Most of the supramolecular complexes investigated by MS involve macrocycles, such as crown ethers and cryptands, which form cationic metal-receptor complexes detectable in positive ion mode [15][16][17][18][19]. Anion supramolecular chemistry [20] is relatively less well developed and oftentimes anion receptors are not as strong as cation receptors in terms of thermodynamic binding constants. Moreover, negative ionization is more susceptible to corona discharge [21,22]. Therefore, negative-ion mode MS detection of noncovalent anion-receptor complexes is less common than positive-ion mode, with the examples reported [23][24][25][26][27][28] for the detection of organic explosives. APCI presents some advantages compared with ESI in quantitative analysis such as higher dynamic range, and is considered rugged, easy to operate, and more tolerant of higher buffer concentrations (fewer matrix effects) [31]. Multiply charged species are typically not observed in APCI-MS spectra [1]. Even though APCI is considered a soft ionization method, it has not found the same application in anion supramolecular chemistry as ESI because the larger supramolecular ions are generally not observed. Therefore, successful identification of noncova...

Colorimetric and optical discrimination of halides by a simple chemosensor

“…Kavallieratos and coworkers used an APCI-MS (atmospheric pressure chemical ionization mass spectrometry) for the detection of halides and nitrate with sulfonamides in dichloromethane. 39 Our group recently used ESI-MS to probe a sulfate complex with a thiophene-based monocycle 40 and an octameric phosphate cluster with a tren-based amine. 41 This is a direct method to examine the stability and stoichiometry of a complex in a gaseous state.…”

Anion receptors based on organic frameworks: highlights from 2005 and 2006

“…2 ) formed by sulfonamide receptors 45a, 45b and 46 in dichloromethane. 61 This method offers the advantage that multiply charged species are not detected. Additionally, larger supramolecular ions are generally not detected meaning that species that are detected by this method are generally the more stable supramolecular complexes.…”

Experimental and Theoretical Aspects of Anion Complexes with a Thiophene-Based Cryptand

“…50 We recently used ESI-MS to probe a sulfate complex with a thiophene-based monocycle 51 and an octameric phosphate cluster with a tren-based amine. 52 This is a direct method to examine the stability and stoichiometry of a complex in a gaseous state.…”