Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision‐induced dissociation spectra

Reductions involving more than one electron with formation of the M ϩ and [Mϩ2H] ϩ ions were observed for electrosprayed meso-tris (N-methylpyridinium-4-yl)porphyrin iodides, MI 3 . These reductions were studied by using different solvents and flow rates. Formation of the [Mϩ2H] ϩ ions occurred only for protic solvents and to a larger extent at lower flow rates. The type of the fourth substituent does not seem to affect the reduction processes. , it is generally accepted that redox reactions do occur in the capillary sprayers and that they are responsible for charge balance [1,2]. Redox processes in electrospray mass spectrometry were comprehensively investigated by and, more recently, electrochemical aspects and applications of electrospray ionization were the focus of reviews [9,10].Ions formed by one electron reduction from nonmetallated dicationic species in solution were previously observed in positive-mode electrospray mass spectrometry for ionic compounds such as diquaternary pyridinium salts [11-13] and free-base N-alkylpyridiniumyl porphyrin salts [14]. One-and two-electron reductions of the cations of metallated N-alkylpyridiniumyl porphyrin salts were also reported, when electrospray was used in the positive mode [15][16][17].When acquiring the electrospray mass spectra of 5,10,15-tris(N-methyl-pyridinium-4-yl)-20-phenylporphyrin iodide, MI 3 , we observed, besides the expected M 3ϩ ion, ions such as M 2ϩ , M ϩ , and [Mϩ2H] ϩ , which may be the result of reductive processes. Reductions involving more than one electron were never reported before for electrosprayed free-base cationic porphyrins and, although formation of [MϩnH] ϩ ions (n Ͼ 1) in desorption ionization (fast atom or ion bombardment) [18 -20] and matrix assisted laser desorption (MALDI) [21] has been described, it was never reported as occurring in electrospray mass spectrometry (ESI-MS) until now. These facts prompted us to use ESI-MS to investigate a group of meso-tris(N-methylpyridinium-4-yl)porphyrin iodides, MI 3 , with a different fourth meso substituent (see Scheme 1) to gather more information on the species formed with respect to their formation reactions and to their relation with the ionization processes occurring in the electrospray interface. ExperimentalThe key neutral porphyrin derivatives were obtained from crossed-Rothemund reactions using the appropriate benzaldehydes and pyrrole in refluxing acetic acid and nitrobenzene [22][23][24]. The alkylation with methyl

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confidence: 86%

Section: Esi Mass Spectra and Product Ion Spectra In Other Solventsmentioning

confidence: 99%

Section: Esi Mass Spectra and Product Ion Spectra In Other Solventsmentioning

confidence: 99%

See 1 more Smart Citation

Reduction of cationic free-base meso-tris-N-methylpyridinium-4-yl porphyrins in positive mode electrospray ionization mass spectrometry

Ramos

Marques

Correia

et al. 2007

“…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.…”

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confidence: 99%

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

Kavallieratos

Sabucedo

Pau

et al. 2005

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...

“…Quats exist endogenously within various tissues of the body (such as the central nervous system) and play a vital role in numerous biochemical pathways [1,2]. Additionally, they are frequently synthesized and routinely utilized in a variety of industries, with their uses ranging from personal care items such as antimicrobials [3][4][5] and antistatic agents [6,7] to herbicides [8][9][10][11] and pharmaceuticals [12,13].…”

Section: Introductionmentioning

confidence: 99%

A Novel Route to Recognizing Quaternary Ammonium Cations Using Electrospray Mass Spectrometry

Shackman

Ding

Bolgar

2014

Abstract. Characterizing and elucidating structures is a commonplace and necessary activity in the pharmaceutical industry with mass spectrometry and NMR being the primary tools for analysis. Although many functional groups are readily identifiable, quaternary ammonium cations have proven to be difficult to unequivocally identify using these techniques. Due to the lack of an N-H bond, quaternary ammonium groups can only be detected in the 1 H NMR spectra by weak signals generated from long-range 14 N-H coupling, which by themselves are inconclusive evidence of a quaternary ammonium functional group. Due to their low intensity, these signals are frequently not detected. Additionally, ions cannot be differentiated in a mass spectrum as an M + or [M + H] + ion without prior knowledge of the compound's structure. In order to utilize mass spectrometry as a tool for determining this functionality, ion cluster formation of quaternary ammonium cations and non-quaternary amines was studied using electrospray ionization. Several mobile phase modifiers were compared; however, the addition of small amounts of trifluoroacetic acid proved superior in producing characteristic and intense [M +2TFA] -clusters for compounds containing quaternary ammonium cations when using negative electrospray. By fragmenting this characteristic ion using CID, nearly all compounds studied could be unambiguously identified as containing a quaternary ammonium cation or a non-quaternary amine attributable to the presence (non-quaternary amine) or absence (quaternary ammonium cation) of the resulting [2TFA + H] -ion in the product spectra. This method of analysis provides a rapid, novel, and reliable technique for indicating the presence of quaternary ammonium cations in order to aid in structural elucidation.