K. R. Markham

Bio: K. R. Markham is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Baptisia & Glucoside. The author has an hindex of 14, co-authored 20 publications receiving 777 citations.

The Ultraviolet Spectra of Flavones and Flavonols

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].

Ultraviolet-Visible and Proton Magnetic Resonance Spectroscopy of Flavonoids

Abstract: A number of reviews of ultraviolet and visible absorption spectroscopy have appeared in the past (Jurd, 1962; Mabry et al., 1970; Swain, 1965; Mabry, 1969; Harborne, 1963) the most comprehensive being those of Jurd (1962) and Mabry et al., (1970). The article by Jurd summarizes the work in this field up to about 1960 and gives detailed references to the original spectroscopic work carried out with flavonoids. The book by Mabry et al (1970) updates Jurd’s chapter and in addition provides a detailed catalogue of the ultraviolet (UV) spectra of 175 flavonoids together with comprehensive data on reagent induced shifts for each flavonoid. The present article includes some of the more significant aspects of the earlier reviews and in addition brings them up to date.

Reagents and Procedures for the Ultraviolet Spectral Analysis of Flavonoids

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.

Flavonoid composition of Citrus juices.

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.

Human metabolism of dietary flavonoids: Identification of plasma metabolites of quercetin

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.

Phenolic diterpenes, flavones, and rosmarinic acid distribution during the development of leaves, flowers, stems, and roots of Rosmarinus officinalis. Antioxidant activity.

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.