C-Glycosylflavonoids. The chemistry of aspalathin

1. The isolation of aspalathin, the principal phenolic constituent in the leaves of Aspalathus linearis, is described and its properties are discussed. 2. The compound has been identified as 3'-C-beta-d-glucopyranosyl-2',3,4,4',6'-pentahydroxydihydrochalcone by the preparation and analysis of various derivatives, by photochemical oxidation to 2,3-dihydroiso-orientin and by nuclear-magnetic-resonance studies.     

C-Glycosylflavonoids. The chemistry of orientin and iso-orientin

1. The structures of orientin and iso-orientin have been investigated by periodic acid and ferric chloride oxidation of the tetra-O-methyl derivatives and by identification of the products of oxidation. 2. The preparation and properties of the 3',4',7-trimethyl ethers of orientin and iso-orientin are described, and the nuclear-magnetic-resonance spectra of orientin, iso-orientin and their tri- and tetra-O-methyl derivatives are discussed. 3. Orientin and iso-orientin are formulated as 8- and 6-C-beta-d-glucopyranosyl-luteolin respectively.     

The chemistry of flavins and flavoproteins. Aerobic photochemistry

1. When a mixture of FMN and a reducing substrate (e.g. unprotonated amine) is illuminated oxygen is consumed. 2. The rate of oxygen uptake increases as oxygen concentration falls with some substrates (type I reaction), but with other substrates (typically aromatic compounds) the rate falls as the oxygen concentration falls (type II reaction). 3. The kinetics of type I reactions with EDTA, dl-alpha-phenylglycine and diethanolamine are all consistent with a mechanism in which the rate-determining step, hydrogen abstraction by the FMN triplet, is followed by rapid reoxidation of reduced FMN by oxygen. The reaction is faster at low oxygen concentrations because oxygen quenches the triplet. 4. The sensitivity of reaction rates to substituents in dl-alpha-phenylglycine can be described by a Hammett rho value of -0.6. 5. Individual rate constants for quenching and reaction of the FMN triplet with substrate were calculated (2.4x10(8) and 2.1x10(7)m(-1)s(-1) respectively for EDTA) on the assumption that oxygen quenches the triplet in a diffusion-controlled reaction. 6. The pH-dependences of oxygen uptake rates with six natural amino acids as substrates were measured. 7. Photoinactivations of l-glutamate dehydrogenase and d-amino acid oxidase by FMN were demonstrated.     

The chemistry of insect hemolymph. III. Glycerol

Free glycerol has been identified as a major solute in plasma of pupae of the silk moth, Hyalophora cecropia. Glycerol is not found in the blood of larvae; it appears about the time of pupation, and then gradually accumulates during diapause to reach after 6 months a level of about 0.3 M. When diapause is broken and the adult develops, glycerol rapidly disappears. In diapausing pupae of the related species, Telea polyphemus, about 0.05 M glycerol was found; in 3 other saturniid species, there was little or none. It is suggested that glycerol may be a product of a modified glycolytic pathway.     

The inter-relationship between triplet energies and spin chemistry.

Triplet energies play a considerable role in optical spectroscopy, and can be determined from phosphorescence or the quenching thereof. Their role in spin chemistry may not be as obvious, but the triplet state has always had an important function or utility, namely of reaction intermediates such as radical pairs, their precursors, of carbenes, and of the final products. In situ NMR spectroscopy represents a useful tool to explore certain properties of the triplet state, especially in cases with no phosphorescence. The 'phase' of CIDNP resonances, i.e., emission or enhanced absorption, reflects the spin selectivity of electron transfer reactions. In radical ion pairs the spin selectivity is determined by the relation between the change of the standard free enthalpy DeltaG degrees during the electron back transfer and the triplet energies (E(T)) of the products. If triplet recombination is energetically feasible (DeltaG degrees > E(T)), it is typically the more efficient process in agreement with the Marcus theory.     

The chemistry of insect hemolymph. II. Trehalose and other carbohydrates

α,α-Trehalose, a sugar previously regarded as a product characteristic of certain lower plants, has been identified as a major blood sugar of insects. Trehalose has been isolated in pure form from the blood of pupae of the silk moth, Telea polyphemus, and has been recognized chromatographically in all the insects examined, which comprise 10 species belonging to 5 different orders. Trehalose has been determined quantitatively with anthrone after either chromatographic separation or chemical degradation of other sugars. In larvae and pupae of 4 species of Lepidoptera it ranges from 0.2 to 1.5 gm. per 100 ml. of blood and makes up over 90 per cent of the blood sugar; in larvae of a sawfly, about 80 per cent of the blood sugar is trehalose. In Bombyx mori and Platysamia cecropia, the pupal blood trehalose level is about half that in the mature larva, suggesting utilization of trehalose for glycogen synthesis during pupation. Small amounts of glucose and apparent glycogen are also present in the plasma of these insects. In Bombyx larval plasma there is also 0.04 to 0.12 gm. per 100 ml. of glucose-6-phosphate and smaller amounts of an apparent ketose phosphate.