Browsing by Author "Rodrigues, Maria A. A."
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- ESI-MS of Cucurbituril Complexes Under Negative PolarityPublication . Rodrigues, Maria A. A.; Mendes, Debora C.; Ramamurthy, Vaidhyanathan; Da Silva, José PauloElectrospray ionization mass spectrometry (ESI-MS) is a powerful tool to study host-guest supramolecular interactions. ESI-MS can be used for detailed gas-phase reactivity studies, to clarify the structure, or simply to verify the formation of complexes. Depending on the structure of the host and of the guest, negative and/or positive ESI are used. Here we report the unexpected formation of host-guest complexes between cucurbit[n]urils (n = 7, 8, CB[n]) and amine, styryl pyridine, and styryl pyridine dimer cations, under negative ESI. Non-complexed CB[n] form double charged halide (Br-, Cl-, F-) adducts. Under negative ESI, halide ions interact with CB[n] outer surface hydrogen atoms. One to one host-guest complexes (1:1) of CB[n] with positive charged guests were also observed as single and double charged ions under negative ESI. The positive charge of guests is neutralized by ion-pairing with halide anions. Depending on the number of positive charges guests retain in the gas phase, one or two additional halide ions are required for neutralization. Complexes 1:2 of CB[8] with styryl pyridines retain two halide ions in the gas phase, one per guest. Styryl pyridine dimers form 1:1 complexes possessing a single extra halide ion and therefore a single positive charge. Negative ESI is sensitive to small structural differences between complexes, distinguishing between 1:2 complexes of styryl pyridine-CB[8] and corresponding 1:1 complexes with the dimer. Negative ESI gives simpler spectra than positive ESI and allows the determination of guest charge state of CB[n] complexes in the gas phase.
- Quantitative analysis of biogenic polyamines in distilled drinks by direct electrospray ionization tandem mass spectrometry using a nanocontainerPublication . Galego, Ludovina; Rodrigues, Maria A. A.; Mendes, Débora C.; Jockusch, Steffen; Silva, José P. daRATIONALE: Biogenic polyamines in drinks have been implicated in undesirable physiological effects. Methods for their detection and quantification usually involve derivatization, pre-concentration and clean-up. To assist the evaluation of the potential risk of distillates, it was important to develop a simple and fast analytical method, which is described in this study.METHODS: Biogenic polyamines were selectively encapsulated after addition of a nanocontainer, cucurbit[7] uril (50 mu M), to the distilled drink samples, which were acidified with HCl (pH 3) prior addition of the nanocontainer. The quantification of polyamines was achieved by direct infusion electrospray ionization quadrupole ion trap mass spectrometry in the multiple reaction monitoring mode, using encapsulated amantadine as internal standard, and by monitoring signals originating from their host-guest complexes.RESULTS: Six point calibration curves, ranging from 0.5 mu M to 20 mu M of polyamines in water and ethanol/water (50: 50), were used to establish instrument response. The method was validated by analysis of fortified Arbutus spirits. Samples of Arbutus and grape pomace spirits were also analyzed. Linear responses were observed for all polyamines and were similar in water, hydro-alcoholic solutions and fortified Arbutus spirits. Putrescine the simple polyamine was detected only in grape pomace distillate samples.CONCLUSIONS: A quantitative method was developed for rapid and simple analysis of biogenic polyamines in distilled drinks. The detection limits depend on the ionization properties of the samples. Encapsulated amantadine can be used to probe these properties and method application. Copyright (C) 2016 John Wiley & Sons, Ltd.