GLYCOSIDES IN Viola Tricolor L.

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CHAPTER 2: <strong>IN</strong>TRODUCTION bonds. Note that k,l Ai is easily confused with the aglycone fragment ( i,j A0), therefore to avoid uncertainty the subscript 0 was added to the latter [94] (for sugar fragments i > 0). For simplicity, ions formed by the direct loss of radi- cals or small neutral molecules are usually specified by reference to the parent ion (e.g. 0,2 X + –H2O). In some cases, subscripts H, D, or P was added to the labels, referring to‘hexose’, ‘deoxyhexose’, or ‘pentose’,respectively. Label‘Ei’ designates the loss of water molecules. In some instances, a number in paren- thesis was added to the label to indicate the position where the sugar unit was attached to the aglycone. 2.4.3 Structureelucidation The characterization of flavonoid glycosides by mass spectrometry comprises the determination of (i) glycosylation types (O-, C-, or mixed glycosides), (ii) types of the sugar units (hexoses, deoxyhexoses or pentoses), (iii) distribu- tion of the sugar residues, (iv) order of the glycan sequence, (v) interglycosidic linkages, (vi) glycosylation position, and (vii) nature of the aglycone. Besides summarizing papers, which reporte on the determination of the above characteristic markers, this subsection focuses on the identification options of un- known flavonoid glycosides in complex samples (e.g. plant extracts) with the emphaseson the differentiation of isomeric compounds. AlthoughMSfragmentationpatternsmaytheoreticallyvarywiththeinstru- mentation used, several authors reported that the main fragmentation paths of flavonoids are independent of the actual ionization mode (ESI, APCI, or MALDI)orthetypesofanalyzersapplied(QQQ, IT,orQTOF)[92,99–101]. On the contrary, significant differences could be observed regarding the relative abundances of fragment ions by using different instrumentation [92, 99, 100]. Therefore, methods based on the presence or absence of distinctive fragment ions are preferred to techniques, which rely only on relative intensity changes observed forisomeric compounds. Similarly,approachesnotrequiringspecialsamplepreparationmethodsare also favored. Nonetheless, methods including derivatization or complex for- mation,arealsodiscussediftheyprovidecomplementaryinformationonstruc- tural elucidation (Sec. 2.4.3.5). As the majority of the cited references report only on the study of flavones, flavonols, flavanones, and isoflavones, mass spectroscopic analysis of antho- 21
CHAPTER 2: <strong>IN</strong>TRODUCTION cyanidins will be summarized in a separate part (Sec. 2.4.3.6). On the other hand, since their unique structure allows their easy differentiation from other flavonoids, chalcones will not be discussed (for further references see [102, 103]). Inaddition,(i)ifnoparticularcommentsaregiven,considerations apply to all major flavonoid classes (except of anthocyanidins and chalcones); (ii) if their labels do not indicate charges, fragments were observed in both positive and negative ionization modes; (iii) the discussed flavonoid glycosides were namedreferring to their aglycones (Fig. 2.2a). 2.4.3.1 Characterization of glycosylation type O-, C- and C,O-glycosides can be distinguished by their positive or negative ionization spectra. As reported by many authors, for O-glycosides, the application of low or medium fragmentation energy results in heterolytic cleavage oftheirhemi-acetalO–Cbonds, yieldingdistinctiveYi fragments[98,104–110]. For C-glycosides, low fragmentation energy does not provide adequate fragmentation. At medium fragmentation energy, however, characteristic i,j X and Ei fragments result from intraglycosidic cleavages and from losses of water molecules, respectively [98, 100, 109, 111]. On the other hand, the application of higher fragmentation energy leads to intraglycosidic cleavages of the sugar units of O-glycosides and produces Yi fragments for C-glycosides, rendering the spectral interpretation difficult, sometimes misleading. In the case of C,O- glycosides, both i,j Xand Yi ions were observed [96, 98]. The characteristic positive and negative ion fragmentation of O- and C-glycosides are illustrated in Fig. 2.7 for rutin (quercetin-3-O-rhamnosylglucoside) and vitexin (apigenin-6- C-glucoside). 2.4.3.2 Natureof the glycan part As the majority of relevant papers report on the characterization of diglyco- sides, this subject is discussed primarily. Concerning the characterization of glycosides with three or more sugar residues, for the time being no sufficient information is availableto draw general conclusions. Type of the sugar unit Generally, by LC-MS n analyses no information can beobtained about the stereochemistry ofthe flavonoid glycoside’s glycan part. The sugar type can be, however, easily determined, since the Ai, Bi, and Ci 22
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
Page 7 and 8: CONTENTS R Recoveryin the fortified
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Page 17 and 18: CHAPTER 2: INTRODUCTION charides, v
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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 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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