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M. B. Thomas

Bio: M. B. Thomas is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Fluorine-19 NMR & Flavones. The author has an hindex of 9, co-authored 11 publications receiving 379 citations.

Papers
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Book ChapterDOI
01 Jan 1970
TL;DR: The methanol spectra of flavones and flavonols exhibit two major absorption peaks in the region 240 - 400 nm1 as discussed by the authors, and these two peaks are commonly referred to as Band I (usually 300 − 380 nm, Table V-1 records the λmaxvalues for Band I for all flavones examined in the present investigation), and Band II (usually 240 - 280 nm).
Abstract: The methanol spectra of flavones and flavonols exhibit two major absorption peaks in the region 240 – 400 nm1. These two peaks are commonly referred to as Band I (usually 300 – 380 nm, Table V-1 records the λmaxvalues for Band I for all flavones and flavonols examined in the present investigation), and Band II (usually 240 – 280 nm). Band I is considered to be associated with absorption due to the B-ring cinnamoyl system, and Band II with absorption involving the A-ring benzoyl system (see III) [1].

208 citations

Book ChapterDOI
01 Jan 1970
TL;DR: In this paper, fresh cut metallic sodium (2.5 g) was added cautiously in small portions to dry spectroscopic methanol (100 ml), stored in a glass container with a tightly fitting plastic stopper.
Abstract: Sodium methoxide (NaOMe). Freshly cut metallic sodium (2.5 g) was added cautiously in small portions to dry spectroscopic methanol (100 ml). The solution was stored in a glass container with a tightly fitting plastic stopper.

69 citations

Book ChapterDOI
01 Jan 1970
TL;DR: Isoflavones, flavanones and dihydroflavonols all give similar UV spectra as a result of their having little or no conjugation between the A- and B-rings.
Abstract: Isoflavones, flavanones and dihydroflavonols all give similar UV spectra as a result of their having little or no conjugation between the A- and B-rings. They are all readily distinguished from flavones and flavonols by their UV spectra, which typically exhibit an intense Band II absorption with only a shoulder or low intensity peak representing Band I.

40 citations

Book ChapterDOI
01 Jan 1970
TL;DR: Two-dimensional paper chromatography represents one of the best methods for the rapid separation of mixtures of flavonoids from crude methanol or methanoline-water extracts of dried plant material.
Abstract: Two-dimensional paper chromatography represents one of the best methods for the rapid separation of mixtures of flavonoids from crude methanol or methanol-water extracts of dried plant material. Furthermore, sufficient quantities of the separated compound for both hydrolytic and ultraviolet spectral analyses often can be isolated from about 30 chromatograms. The present discussion will emphasize the chromatographic techniques routinely employed in this laboratory for the analysis of flavonoids; however, a number of other procedures and variations have been published elsewhere [1, 2]

19 citations

Journal ArticleDOI
TL;DR: A new flavone, scaposin, has been isolated from Hymenoxys scaposa (Compositae) and its structure established as 5,5',7-trihydroxy-3,4,6,8-tetramethoxyflavone by synthesis as discussed by the authors.

15 citations


Cited by
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Journal ArticleDOI
TL;DR: Analytical techniques for the characterization of juices from different Citrus fruits regarding their flavonoid content (even if present in only trace amounts), concentrating on the most widely used methods (LC-MS and LC-MS-MS).
Abstract: In the early nineties the presence of flavonoids in Citrus juices began to attract the attention of a number of researchers, as a result of their biological and physiological importance. This short review will explore two different aspects. The first part will focus on analytical techniques for the characterization of juices from different Citrus fruits regarding their flavonoid content (even if present in only trace amounts), concentrating on the most widely used methods (LC-MS and LC-MS-MS). The second part analyzes data reported in the literature regarding the composition of Citrus juices. The main components that have been detected so far are flavanone-O-glycosides and flavone-O- or -C-glycosides. The presence of such derivatives in various hand-squeezed and industrial juices is discussed, with special emphasis on their correlation to different species.

584 citations

Journal ArticleDOI
TL;DR: It is shown that quercetin glucosides are not present in plasma of human subjects 1.5 h after consumption of onions (a rich source of flavonoid glucoside), and the existence of substitutions in the B and/or C ring of plasma quercets suggests that these conjugates will each have very different biological activities.
Abstract: The position of conjugation of the flavonoid quercetin dramatically affects biological activity in vitro, therefore it is important to determine the exact nature of the plasma metabolites. In the present study, we have used various methods (HPLC with diode array detection, LCMS, chemical and enzymic synthesis of authentic conjugates and specific enzymic hydrolysis) to show that quercetin glucosides are not present in plasma of human subjects 1.5 h after consumption of onions (a rich source of flavonoid glucosides). All four individuals had similar qualitative profiles of metabolites. The major circulating compounds in the plasma after 1.5 h are identified as quercetin-3-glucuronide, 3'-methylquercetin-3-glucuronide and quercetin-3'-sulfate. The existence of substitutions in the B and/or C ring of plasma quercetin metabolites suggests that these conjugates will each have very different biological activities.

443 citations

Journal ArticleDOI
TL;DR: The distribution of six compounds with three different polyphenol skeletons in Rosmarinus officinalis suggests that rosemary extracts are excellent antioxidants in both aqueous and lipid systems.
Abstract: The distribution of six compounds with three different polyphenol skeletons have been studied in Rosmarinus officinalis: phenolic diterpenes (carnosic acid, carnosol, and 12-O-methylcarnosic acid), caffeoyl derivatives (rosmarinic acid), and flavones (isoscutellarein 7-O-glucoside and genkwanin), each showing a characteristic behavior and distribution during the vegetative cycle. Only in leaves were all six compounds present, and the highest accumulation rate was related with the young stages of development. Rosmarinic acid showed the highest concentrations of all the polyphenols in all organs. The distribution of this acid in leaves, flowers, and stems suggests that in the first stages of flower growth, levels were due to in situ biosynthesis, and in the last stages, the contribution of transport phenomena was increased. The antioxidant activity of six extracts with different polyphenolic composition was evaluated in aqueous and lipid systems. The results clearly suggest that rosemary extracts are excellent antioxidants in both aqueous and lipid systems.

346 citations

Journal ArticleDOI
TL;DR: Evaluation of data reveals a correlation in most cases between the occurrence of flavonoid aglycones, the presence of secretory structures and the production of other lipophilic plant products.

319 citations

Journal ArticleDOI
TL;DR: The overall regulation role of these compounds in compatible and incompatible host‐microbe interactions is discussed in this review.
Abstract: Numerous reports have been published on the occurrence, isolation, and characterization of phenolic compounds in plant‐soil systems. The low molecular weight phenolics are of great interest because of their effects as allelopathic compounds and plant growth regulators, and they have traditionally been considered as defense molecules in plant‐pathogen interactions. More recently, their role as signal molecules in plant‐microbe systems has become evident. Specific molecules can act either as inducers for virulent genes in plant‐pathogen systems, such as Agrobacterium, or as inducers and “repressors”; in Rhizobium‐legumc and probably other symbiosis. The overall regulation role of these compounds in compatible and incompatible host‐microbe interactions is discussed in this review.

286 citations