ABSTRACT
RATIONALE: Ferrocene derivatives have become very popular molecules for biological applications. Although considerable experimental and theoretical calculation studies have demonstrated that ferrocene derivatives are easily oxidized during electrospray ionization (ESI), the details of the single electron redox reaction for protonated benzoylferrocenes in collision-induced dissociation (CID) mass spectrometry (MS) has not been obtained. Characterizing this mechanism is useful for further understanding the properties of ferrocene-containing biomaterials. METHODS: All CID MS experiments were carried out using ESI ion trap mass spectrometry in positive ion mode. In addition, the accurate mass of fragments was measured on a ESI quadrupole time-of-flight (QTOF) mass spectrometer in positive ion mode. Theoretical calculations were carried out by the density functional theory (DFT) method with a hybrid basis set consisting of 6-31G (d) and ECP LanL2DZ in the Gaussian 03 program. RESULTS: In the fragmentation of protonated benzoylferrocenes, the characterized ferrocinium cation was observed, which was proposed from the cleavage of the bond between the ipso-carbon atom and the carbonyl carbon followed by a single electron redox in [substituted benzoyl/ferrocene] complexes. Moreover, when the complex contained an oxidant (substituted benzoyl cation) with higher electron affinity, the single electron redox reaction was more efficient. A correlation was established between the intensities of the two competitive product ions and the electron affinities of substituted benzoyl cations. CONCLUSIONS: The single electron redox reaction by the [substituted benzoyl/ferrocene] complexes was proposed by CID MS and theoretical calculations, which provided potential evidence to further understand the reversible reduction characteristics of ferrocene-containing biomaterials.
Subject(s)
Ferrous Compounds/chemistry , Spectrometry, Mass, Electrospray Ionization/methods , Electrons , Ions , Models, Molecular , Oxidation-Reduction , Protons , ThermodynamicsABSTRACT
A powerful ionic liquid-based ultrasonic-assisted extraction (ILUAE) method combined with ultra-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC/ESI-QTOFMS(n) ) was employed in the rapid simultaneous screening of iridoid glycosides, phenylethanoid glycosides, and cucurbitacin glycosides from P. scrophulariiflora. The ILUAE procedure was optimized over several ultrasonic parameters, including the ultrasonic power, concentration of the ionic liquid, and solid-liquid ratio. A comparison with conventional heat-reflux extraction and regular UAE demonstrated that the optimized approach yielded a high extraction efficiency (Picroside I, 2.84%; Picroside II, 3.57%; 6-O-E-feruloyl catalpol, 2.20%) within a short extraction time of 30 min. Negative ion mode ESI-QTOFMS(2) analysis of the fragmentation reactions of the [M-H](-) ions was conducted to characterize the diagnostic ions related to the glycosyl moieties, aglycone units, and the type and substituted position of the ester groups. Interestingly, the positional isomers of the iridoid glycosides could be easily discriminated based on the characteristic ions. A total of 15 glycosides, including three groups of iridoid glycoside isomers and two groups of phenylethanoid glycoside isomers, were conveniently identified within 13.5 min. Moreover, 6'-O-vanilloyl catalpol was identified in P. scrophulariiflora for the first time. The method developed here was further validated by measuring the recovery, correlation coefficient (R(2) ), and reproducibility (RSD, n = 5) of three iridoid glycosides: 89.60%-109.02%, 0.9991-0.9998, and 0.93%-1.44%, respectively. This study demonstrated the capabilities of ILUAE combined with UPLC/ESI-QTOFMS(n) for the rapid screening of glycosides in P. scrophulariiflora. This method offers an approach to similar studies on other natural plants.
