Browsing by Subject "Flavonoids"
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Item Characterization and isomer differentiation of glycosides and oligosaccharides using chemical derivatization with quadrupole ion trap mass spectrometry(2007-12) Pikulski, Michael, 1969-; Brodbelt, Jennifer S.Several innovative tandem mass spectrometric strategies have been developed for the structural determination and isomer differentiation of glycosides and oligosaccharides. Specifically, collisionally activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) are used in conjunction with derivatization methods designed to exploit variations in binding energies or attach chromophores. These include metal complexation incorporating modified neutral auxiliary ligands and covalent derivatization involving site-specific reactions. The elucidation of flavonoid isomers is accomplished by electrospray ionization tandem mass spectrometry (ESI-MS/MS) via formation and CAD of metal/flavonoid complexes containing an auxiliary ligand. Addition of a metal salt and a suitable neutral auxiliary ligand to flavonoids in solution results in the formation of [M(II) (flavonoid-H) ligand]⁺ complexes by ESI which, upon collisional activated dissociation, often result in more distinctive fragmentation patterns than observed for conventional protonated or deprotonated flavonoids. We compare and explore the use of alternative pyridyl ligands, with electron-releasing substituents including 4,7-diphenyl-1,10-phenanthroline. Using this technique, three groups of flavonoid glycoside isomers are differentiated, including glycosides of apigenin, quercetin and luteolin. A tunable ESI-MS/MS strategy for differentiation of flavone and flavanone diglycoside isomers based on metal complexation with auxiliary ligands that have electron-withdrawing substituents is reported. A series of auxiliary ligands with electronwithdrawing substituents was synthesized in order to tailor the relative metal binding affinities of the ligands and thus directly influence the stabilities, and consequently the dissociation pathways, of the complexes. Upon collisionally activated dissociation, the complexes yield fragmentation patterns in which the abundances of key diagnostic ions are enhanced, thus facilitating isomer differentiation. A strategy for increasing the efficiency of IRMPD in a quadrupole ion trap (QIT) based on another metal complexation strategy is described. Two IR-active ligands (IRALs) that have an IR-active phosphonate functional groups were synthesized. The IR-active groups were therefore incorporated into the analyte complexes via metal complexation. We demonstrate this new IRMPD approach for the structural characterization of flavonoids. The fragment ions obtained by IRMPD are similar to those obtained by CAD and allow facile isomer differentiation of flavonoids. Fourier transform infrared absorption attenuated total reflectance (FTIR-ATR) and energyvariable CAD experiments indicate that the high IRMPD efficiencies stem from the very large IR absorptivities of the IR-active ligands. A simplified method for determining the sequence and branching of oligosaccharides using IRMPD in a QIT is described. An IR-active boronic acid (IRABA) reagent was synthesized and subsequently used to derivatize the oligosaccharides prior to IRMPD analysis. The IRABA ligand is designed to both enhance the efficiency of the derivatization reaction and to facilitate the photon absorption process. The resulting IRMPD spectra display oligosaccharide fragments that are formed from primarily one type of diagnostic cleavage, thus making sequencing straightforward. The presence of sequential fragment ions, a phenomenon of IRMPD, permit the comprehensive sequencing of the oligosaccharides studied in a single stage of activation. The approach is demonstrated for two series of oligosaccharides, the lacto-Nfucopentaoses (LNFPs) and the lacto-N-difucohexaoses (LNDFHs).Item Citrus limonoids and flavonoids: extraction, antioxidant activity and effects on hamster plasma cholesterol distribution(Texas A&M University, 2005-11-01) Yu, JunFour in vitro models were used to measure the antioxidant activity of 11 citrus phytochemicals. The citrus limonoids and bergapten showed very weak antioxidant activity. The flavonoids demonstrated mild, to moderate, to strong antioxidant activity. In addition to some other commonly accepted structural features our data indicated that the hydroxyl group in position 6 of ring A could also increase the antioxidant activity of flavonoids. Compared with the active flavonoids, limonoids are highly oxygenated triterpenoids, with fewer hydroxyl groups to stabilize unpaired electrons (or scavenge free radicals). Bergapten lacks a hydroxyl group. This is the first report on the antioxidant activity of limonoids and neoeriocitrin. A feeding study using Syrian hamsters was followed to determine the effect of citrus limonoids and flavonoids on plasma cholesterol. Hamsters fed with limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp significantly inhibited the increase of LDL/HDL-cholesterol (36.6%, 52.9% and 57% respectively) compared with the basal control (65.8%) and the pectin control (70%). Furthermore, hamsters fed with limonin had significantly larger LDL particle size (21.21 nm) compared with the control group (19.96 nm). Further studies demonstrated that LDLs from hamsters fed with limonin and limonin 17-Beta-D-glucopyranoside were less susceptible to oxidation. These data suggest that limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp have potential inhibitory effects against atherogenesis. Supercritical CO2 (SC-CO2) was attempted to extract limonoids from grapefruit seeds and molasses. Limonin aglycone was successfully extracted with SC-CO2 directly from grapefruit seeds with the yield of 6.3 mg/g seeds at 48.3 MPa, 50˚C and 60 min with CO2 top feeding; and the limonin glucoside was extracted using SC-CO2 and ethanol as co-solvent from the defatted seeds with the yield of 0.73 mg/g seeds at 42 MPa, 52˚C, 45% ethanol (XEth=0.45) and 40 min with CO2 top feeding; and limonin glucoside also was extracted using SC-CO2 and ethanol with the yield of 0.61mg/g grapefruit molasses at 48.3 MPa, 50˚C and 10% ethanol (XEth=0.1), 40 min with CO2 top feeding. CO2 flow rate was around~5 l/min in experiments. The results demonstrated SC-CO2 extraction of limonoids from citrus juice industry byproducts has practical significance for future commercial production.Item Composition and flavonoid levels in onions (Allium cepa) grown in hydroponics in greenhouses and growth chambers(Texas Tech University, 2001-12) Morris, Jay L.One-thousand eighty long-day onions (Allium cepa L. 'Purplette') grown ' hydroponically in a greenhouse were analyzed for composition and total edible biomass to determine the amount of variability as the plant matures. Plants were harvested at 14, 21, 28, 35, 42, 49, 63, 77 and 98 d after sowing. Plant height increased as plants aged, and a significant interaction between planting date and plant age was noted. Plant weight and net number of leaves increased with age and again an interaction between age and planting date was observed. Percent N decreased from 0.55-.34% (p < 0.05) as the plants aged. Percent C (C) decreased (p < 0.05) as the plants aged but after d 77 a significant increase occurred. Ash content increased (p < 0.05) as the plant aged, with means ranging from 0.09 -1.07%. Calcium (Ca) and magnesium (Mg) concentration decreased (p < 0.05) as the plant aged with means rangmg from 128.7 - 14.2 mg/100 g and 57.1 - 22.0 mg/100 g, respectively. Potassium (K) concentrations showed an interaction (p < 0.05) between age and plant age. Total flavonol (TF) content increased (p < 0.05) from 226.1 - 554.7 mg/100g, as the plant aged from 14 d to 98 d. Dry matter (DM) content and sulfur (S)concentration was unchanged (p > 0.05) as the plant aged. Mean values ranged from 10.47-10.70% and 185.2-193.6 mg/100 g for dry matter content and S concentration, respectively. Biomass production and proximate composition of onions varied significantly as the plant ages and underwent morphological changes.Item The effect of acute consumption of a flavonol-rich cocoa drink on cerebral vasomotor reactivity in African Americans(2014-05) Ku, ByungMo; Brothers, Robert MatthewAfrican Americans (AA) are at great risk of cardiovascular diseases (CVD) which can lead to brain damage, dementia, and endothelial dysfunction. Decreased nitric oxide (NO) bioavailability contributes cardiovascular disease in AA population. Flavonols of the subclass known as flavonoids that have several beneficial effects on cerebral blood flow and cerebral vasomotor reactivity (CVMR). This study investigated the effects of the acute consumption of a flavanol-rich cocoa drink on CVMR. Ten non-smoking African American (6 males and 3 females) participants were randomly recruited. The subjects participated in two experimental sessions which were separated before and after the consumption of cocoa drink. For the pre-session, baseline CVMR was measured by the hypercapnia rebreathing (CVMR test) prior to the consumption of the cocoa drink and the again at 2h after consumption of one serving of the cocoa drink (45g of cocoa mixed with 8oz of cold water). Cerebral vascular conductance (CVC) was significantly increased in the post-study during hypercapnia rebreathing compared with the pre-study(post-study: 3.649 ± 1.833 CVC % of baseline/mmHg, pre-study: 2.483 ± 1.418 CVC % of baseline/mmHg vs. P < 0.05) Thus, CVMR was significantly increased in the post-study after the acute consumption of a flavonol-rich cocoa drink compared to the pre-study in AA.Item Flavonoid composition and antioxidant activity of pigmented sorghums of varying genotypes(2009-05-15) Dykes, LindaA wide variety of sorghum genotypes with a pigmented pericarp were grown in varying environments and were analyzed for total phenols, condensed tannins, flavan-4-ols, and in vitro antioxidant activity. In addition, sorghum flavonoids were separated, characterized, and quantified using HPLC-PDA and LC-MS. Total phenols and in vitro antioxidant activity increased when sorghums had a pigmented testa causing the presence of condensed tannins. Flavan-4-ol levels were highest in sorghums with a black pericarp (5.8-16.1 abs/mL/g), followed by those with a red pericarp (1.1-9.2 abs/mL/g). Sorghums with a black pericarp had the highest 3-deoxyanthocyanin levels (308-1885 ?g/g) and these were increased when the grain had minimal weathering and was darkest in color. Sorghums with a lemon-yellow pericarp had the highest flavanone levels (260-3586 ?g/g) with eriodictyol being the main flavanone. Flavanone levels were increased when the grain was bright yellow with minimum weathering and were high compared to those found in common sources (238-574 ?g/g, fresh wts.). No flavonoids were predominant in sorghums with a red pericarp. Flavonoid composition varied when all sorghums were grouped by secondary plant color. Sorghums with tan secondary plant color, including those with a white pericarp, had higher levels of flavones (50-932 ?g/g) than those with red/purple secondary plant color (0-172 ?g/g). On the other hand, 3-deoxyanthocyanin levels were higher in red/purple plant sorghums (14-1885 ?g/g) than in tan plant sorghums (0-24 ?g/g). Among red/purple plant sorghums, lemon-yellow pericarp sorghums had the highest levels of flavones (51-172 ?g/g). Environment and weathering had an effect on flavonoid levels. The 3-deoxyanthocyanins were reduced for sorghums grown in a dry environment (i.e. Lubbock, TX) and flavonoid levels were increased in grains with minimum weathering or molding. This study reports that all sorghums, including those with a white pericarp, have flavonoids and their levels and compositions are affected by the genotype. This information will be helpful for plant breeders, food scientists, and the pharmaceutical/nutraceutical industries in selecting sorghums with desired healthy components.Item The flavonoids and phenolic acids of the genus Silphium and their chemosystematic and medicinal value(2006) Williams, Jeffrey Douglas; Mabry, T. J. (Tom J.); Roux, Stanley J.My chemistry studies of the genus Silphium involved the flavonoids and phenolic acids among eleven species. In the course of these investigations, five new flavonol triglycosides were isolated and characterized: isorhamnetin 3-O-α-L-rhamnosyl (1'''→6'')- O-β-D-galactopyranoside 7-O-β-L-apiofuranoside (1A), quercetin 3-O-α-L-rhamnosyl (1'''→6'')-O-β-D-galactopyranoside 7-O-β-L-apiofuranoside (2A), quercetin 3-O-β-Lgalactosyl (1'''→6'')-O-β-D-rhamnopyranoside 7-O-α-L-apiofuranoside (3A), kaempferol 3-O-β-D-apiofuranoside 7-O-α-L-rhamnosyl (1''''→6''')-O-β-D-galactopyranoside (4A) and kaempferol 3-O-β-D-apiofuranoside 7-O-α-L-rhamnosyl (1''''→6''')-O-β-D (2'''-O-E- caffeoylgalactopyranoside) (5A). Many other known mono and diglycosidic flavonoids were also isolated and identified. The structures of all these compounds were established by chemical methods and spectral analyses using 1 H NMR, 13C NMR, HMQC, HMBC, ROESY, TOCSY and LC/MS techniques. The distribution of the flavonoids and phenolic acids in all eleven members were compared with Dr. Jennifer Clevinger’s DNA-based revision of the genus. In addition to the detailed chemical investigations, I present my evaluations of the chemosystematic and medicinal value of the compounds I characterized; moreover, the new flavonoids are now being made available for medicinal and pharmaceutical studies.Item Production Systems and Processing Effect on Phytochemicals in Citrus Fruits and Their Analytical and Isolation Methods(2012-12-13) Uckoo, Ram 1980-The emerging scientific evidences on the role of food components in prevention of several chronic diseases are the momentum for shifting from a traditional focus on production to enhancement of nutritional quality. To further understand the role of these phytochemicals this dissertation describes the development of rapid analytical and isolation methods, and the effect of production systems and processing techniques on the levels of phytochemicals in citrus fruits. In the first study, a simultaneous high performance liquid chromatography (HPLC) method for the rapid analysis of amines and organic acids was developed. The simultaneous extraction and analysis of samples provides an economical method for analyzing a large number of samples. In the second study, rapid separation method of potent health beneficial phytochemicals such as polymethoxyflavones from citrus peels using flash chromatography was developed. Using the developed method, five polymethoxyflavones were separated and isolated with high purity in gram level quantity. In the third study, the levels of phytochemicals in organically and conventionally grown lemons and their storage at market simulated conditions were determined. Results suggest that organically produced citrus fruits have higher content of organic acids and flavonoids than conventionally produced. The fourth and fifth study determined the influence of household processing (blending, juicing, hand squeezing techniques) and emerging processing (high pressure processing [HPP], thermal processing) on the phytochemicals content of ?Rio Red? grapefruits. Fruits processed by blending had significantly higher levels of flavonoids, furocoumarins and limonin compared to juicing and hand squeezing, while HPP enabled in extending the shelf life of the processed juice without any adverse effects. Therefore, consuming grapefruit juice processed by blending may provide higher levels of health beneficial phytochemicals. The sixth study describes a rapid flash chromatography method for isolation of PMFs and furocoumarins from citrus industrial by products such as peel oil. In the seventh study the developed method was applied to isolate 10 different phytochemicals from an unexplored citrus species, Miaray mandarin (Citrus miaray TAN.). Among them, the 5,7,8,3',4' pentamethoxyflavone was isolated for the first time from the genus Citrus.Item Species Delimitation Within the Bouteloua Gracilis-B. Hirsuta-B. Pectinata Complex(Texas Tech University, 1977-05) Finley, Willa FayeBouteloua gracilis. B. hirsuta, and B. pectinata were examined for evidence of present hybridization based on presence of "intermediate" populations occurring in the vicinity of Guadalupe Mountains National Park. To establish the nature of the relationships more clearly, flavonoid extracts of members in question were chromatographed and a series of morphological characters were measured and analyzed using multivariate techniques. No evidence for on-going hybridization was obtained; however, ancient hybridization between B. pectinata and B. gracilis may account for the morphological traits of "intermediate" populations. Commonly used dichotomous keys used to distinguish among the three species were found to be inadequate. A more workable alternative was presented.Item Structural characterization and enhanced detection of flavonoids by electrospray ionization mass spectrometry and molecular modeling(2004-08) Zhang, Junmei, 1970; Brodbelt, Jennifer S.Structural characterization and isomer differentiation of flavonoids was investigated by gas-phase hydrogen/deuterium (H/D) exchange and various metal complexation approaches using electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT-MS). Gas-phase H/D exchange was used to probe the conformations, gas-phase acidities, and sites of deprotonation of isomeric flavonoids. The structural factors that promote or prevent H/D exchange were identified and correlated with collisionally activated dissociation (CAD) patterns and/or molecular modeling data. The use of a transition metal and an auxiliary ligand to form flavonoid/transition metal/auxiliary ligand complexes was proved to be more effective than deprotonation for differentiating isomeric flavonoids using chalcones as an example (a subclass of flavonoids). The relative threshold dissociation energies of such transition metal complexes were measured by energy-variable CAD, and the structural features that influence the threshold energies were identified. The conformations, point charges, and helium (collision gas) accessible surface areas obtained by various computational means were used to rationalize the differences in threshold energies of isomeric flavonoids. Aluminum(III) was used to form strong complexes with flavonoids for more effective isomer differentiation of flavonoids. The CAD patterns of the aluminum complexes were used to differentiate flavonoids, and the structures and conformations of representative flavonoids were also identified by high level computational means. Silver complexation was used to conquer the limitation of the transition metal and aluminum complexation (flavonoids must have a 4-keto group and at least one adjacent hydroxyl group). Silver complexation could not only be used for isomer differentiation of individual flavonoids but could be adapted to characterize flavonoids in mixtures coupled with high performance liquid chromatography (HPLC). HPLC-ESI-MS was used as a sensitive method with high selectivity to detect flavonoids in kale and grapefruit juice and metabolites in urine. The major flavonoids in kale were detected and confirmed as quercetin and kaempferol by CAD and isotopic labeling. The growing conditions were found to significantly affect the flavonoid levels in kale. LC/MS and LC/MS/MS were used to identify the individual metabolites and to gain insight into the overall metabolite profiles in human urine after consumption of grapefruit juice.Item Structural characterization of isomeric flavonoid glycosides and metabolites by metal complexation and electrospray ionization tandem mass spectrometry(2007-12) Davis, Barry D., 1976-; Brodbelt, Jennifer S.Flavonoids form a vast group of natural products that occur ubiquitously throughout the plant kingdom. These compounds play a significant role in the field of phytochemistry and are of nutritional interest due to numerous reports of their benefits to human health. Structural characterization of individual flavonoid derivatives is challenging because of widespread isomerism and a lack of sensitive and specific analytical techniques. The goal of this work is to present practical tandem mass spectrometry methods for systematic isomer differentiation of flavonoid glycosides and flavonoid glucuronides. Metal complexation is used extensively as a strategy to achieve this aim. In this approach, flavonoid derivatives and metal ions are mixed in solution, resulting in the rapid self-assembly of complexes which are subsequently infused into a quadrupole ion trap mass spectrometer. Collision-induced dissociation of these flavonoid/metal complexes results in fragment ions that are highly characteristic of specific structural features of the flavonoid derivatives. These methods are adaptable to LC-MS analysis via post-column addition of the complexation reagents. Methods to differentiate the five most common glycosylation sites of monoglucosyl flavonoids are described. Based on the fragment ions yielded from magnesium or manganese complexes, specific indicators of 3-O-glucosylation, 7-O-glucosylation, 4'-O-glucosylation, 6-C-glucosylation and 8-C-glucosylation are observed. The manganese complexation method also differentiates isomeric glucose and galactose sugars at the 3 position, as well as arabinose and xylose sugars. Differentiation of isomeric flavonoid glucuronide metabolites is achieved by cobalt complexation with auxiliary ligands. The effectiveness of these methods is proven in numerous practical applications. Flavonoid glycosides are identified in extracts from apples, onions, and Silphium albiflorum. Flavonoid glucuronide metabolites are identified in urine samples and a cell culture extract. The identifications are achieved without the use of standards or additional analytical techniques. Finally, an enzymatic synthesis of flavonoid glucuronides is used to establish the regioselectivity of UGT1A1, an enzyme involved in flavonoid metabolism. The cobalt complexation method successfully identifies many hitherto uncharacterized metabolites. The significance of this work lies in its potential application to problems in botanical, agricultural, nutritional and disease-prevention studies in which precise flavonoid identification is required.