GLYCOSIDES IN Viola Tricolor L.

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CHAPTER 2: <strong>IN</strong>TRODUCTION groupinthe3-position. Sincemostflavonoidsareelectroactive duetothepres- ence ofphenolicgroups, electrochemical detection can alsobe used [82, 87]. 2.3.3 Identificationandstructuralcharacterization Today, LC-MS/MS is the most important technique for the identification of target flavonoids and the structural characterization of unknown members of this class of compounds. As regards target analysis, tandem-MS detection has largely replacedsingle-stage MSoperation becauseofthe much better selectivity and the wider-ranging information that can be obtained. Dependingon the nature of the application, additional information is derived from LC retention behaviour, and UV absorbance and, occasionally, FLU or ED characteristics, due comparison being made with standard injections and/or tabulated refer- ence data. In studies on the characterization of unknowns, a wide variety of LC-MS/MS techniques is usually applied next to LC-DAD UV for rapid class identification. Inaddition, LC-NMRoften turnsouttobeanindispensabletool to arrive atan unambiguous structural characterization. 2.4 LC-MSin thecharacterizationof flavonoids Structural analysis of flavonoids is essential in the search for new biologically activecompoundsandinthedevelopmentandqualitycontrol ofnaturalprod- ucts. Determination of the absolute structure of flavonoids is a complicated task, which mostly requires the combination of advanced techniques, e.g., 1 H- and 13 C-NMR-spectrometry, 1 H- 1 H-correlated spectroscopy, mass spectrometry, and/or X-ray cristallography requiring large amounts of adequately puri- fied sample[87]. Flavonoids, however, areusually presentin acomplex matrix of plant extracts, thus generally difficult to isolate in higher quantities. To alle- viate this drawback, hyphenated techniques, such as LC-MSand LC-NMR can be applied. Both techniques have advantages and disadvantages [82, 88–90]. LC-MS represents a rapid and easy-to-access methodology with high sensitiv- ity and low sample demand. LC-NMR provides more structural information (even about the stereochemistry of glycosides), but only a few laboratories are equippedwith such high endinstrumentation. Besides,due to itslow sensitiv- ity, foran LC-NMRexperimentmore sample isrequired. 17
CHAPTER 2: <strong>IN</strong>TRODUCTION 2.4.1 Instrumentation Thermospray ionization (TMS), the first soft ionization method applicable to the combination of liquid chromatography with mass spectromerty was intro- duced in the early 80’s [91] for flavonoid analysis. This technique has been in recent years gradually phased out by atmospheric pressure ionization (API), includingelectrosprayionization(ESI)andatmosphericpressure chemicalion- ization (APCI). The application of matrix-assisted laser desorption/ionization (MALDI)inflavonoidMShasalsobeenreported[92,93]. Besidestheionization sources, MS instrumentations are usually classified according to the applied mass analyzers: quadruple filters (Q), ion traps (IT), as well as time of flight (TOF) and Fourier-transform ion-cyclotron resonance (FT-ICR)devices[87]. For some years, single-stage MS operations have been replaced by tandem mass spectrometry because of the much better selectivity and wider-ranging structural information it provides. Tandem mass spectrometry is a term which coversanumberoftechniques,inwhichonestageofmassspectrometryisused to select the ion of interest and the second stage is then used to analyze it. In multi-stageMSthesestepscanberepeatedconsecutively. MS/MSexperiments can be achieved on e.g. Q-TOF or triple-quadrupole (QQQ) instruments, the application of ITanalyzers, however, allows alsoMS n analyses. 2.4.2 Nomenclatureandbasic fragmentation Fragmentionsyieldedbymassspectrometricanalysisofflavonoidsareusually designated according to a widely accepted nomenclature system for aglycones developed by Mabry [85], improved by Ma [94], and elaborated for glycocon- jugatesbyDomonandCostello[95]. TheappliedlabelsaredepictedinFig.2.5. For free aglycones labels i,j A0 and i,j B0 are used to refer to fragments con- taining intact A- and B-rings, respectively, where superscripts i and j indicate thebrokenC-ringbonds. Glycosidefragmentswithretainedchargesonthecar- bohydrate portion are designated as Ai Bi and Ci, where i represents the number of broken bond, counted from the terminal sugar unit. On the other hand, ionscontaining the aglycone are labeledasXj Yj and Zj, where jisthenumber of the cleaved interglycosidic bond, counted from the aglycone. The glycosidic bond linking to the aglycone is numbered as 0. In the case of C,O-glycosides, O-glycosylatedontheC-glycosylmoiety,thefirstglycosidicbonddoesnotcon- 18
Page 1 and 2: ANTIOXIDANT FLAVONOID GLYCOSIDES IN
Page 3 and 4: Összefoglaló Avadárvácska(Viola
Page 5 and 6: CONTENTS 3.10 Anthocyanidin and fla
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Page 33 and 34: CHAPTER 2: INTRODUCTION icant Y −
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CHAPTER 4: RESULTS AND DISCUSSION t
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CHAPTER 4: RESULTS AND DISCUSSION o
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CHAPTER 4: RESULTS AND DISCUSSION F
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76 Table 4.6: The antocyanidin and
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CHAPTER 5 Conclusion Although heart
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CHAPTER 5: CONCLUSION proposedtober
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CHAPTER 5: CONCLUSION UIBK-HorvathL
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BIBLIOGRAPHY insulinresistanceanddi
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BIBLIOGRAPHY [28] N. Saito, C. F. T
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was evaporated to dryness under red
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GLYCOSIDES IN Viola Tricolor L.

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