Nucleotides. Part XXVIII. Chemical syntheses of the 2′-5′-cordycepin-trimer core

The chemical synthesis of 3′-deoxyadenyly-(2′-5′)-3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenosine ( 30 ; trimeric cordycepin) is described by three different routes using various protecting groups and applying the phosphotriester approach. The intermediates have been isolated and characterized by elemental analyses and spectroscopic means. High yields of 30 have been obtained on deprotection making this biologically very active compound available in preparative scale.     

Few-electron corrections of statistical exchange potential in low-energy electron scattering

In order to allow for the relative increase of self-interaction in few-electron systems, a reduction factor is introduced into the statistical free-electron exchange potential. This net-exchange potential has been used in the calculation of elastic electron scattering by rare-gas atoms in the low-energy region from 0 to 10 eV. Whereas former attempts to treat these phenomena as simple potential scattering have failed, in this work at least a crude qualitative agreement with experimental data has been achieved in most cases.     

Practical aspects of the uncertainty and traceability of spectrochemical measurement results by electrothermal atomic absorption spectrometry

The determination of trace elements concentration in water by electrothermal atomic absorption spectrometry (ETAAS) is a common and well established technique in many chemical testing laboratories. However, the evaluation of measurement uncertainty results is not systematically implemented. The paper presents an easy step-by-step example leading to the evaluation of the combined standard uncertainty of copper determination in water using ETAAS. The major contributors to the overall measurement uncertainty are identified due to amount of copper in water sample that mainly depends on the absorbance measurements, due to certified reference material and due to auto-sampler volume measurements. The practical aspects how the traceability of copper concentration in water can be established and demonstrated are also pointed out.     

Reglucosylation of the Benzoxazinoid DIMBOA with Inversion of Stereochemical Configuration is a Detoxification Strategy in Lepidopteran Herbivores

Benzoxazinoids are chemical defenses against herbivores and are produced by many members of the grass family. These compounds are stored as stable glucosides in plant cells and require the activity of glucosidases to release the corresponding toxic aglucones. In maize leaves, the most abundant benzoxazinoid is (2R)‐DIMBOA‐Glc, which is converted into the toxic DIMBOA upon herbivory. The ways in which three Spodoptera species metabolize this toxin were investigated. (2S)‐DIMBOA‐Glc, an epimer of the initial plant compound, was observed in the insect frass, and the associated glucosyltransferase activity was detected in the insect gut tissue. The epimeric glucoside produced by the insect was found to be no longer reactive towards plant glucosidases and thus cannot be converted into a toxin. Stereoselective reglucosylation thus represents a detoxification strategy in Spodoptera species that might help to explain their success as agricultural pests on benzoxazinoid‐containing crops.     

Reactions in Nitroimidazole Triggered by Low‐Energy (0–2 eV) Electrons: Methylation at N1‐H Completely Blocks Reactivity

Low‐energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4‐nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA. The remarkably rich chemistry of 4NI is completely blocked in 1‐methyl‐4‐nitroimidazole (Me4NI), that is, upon methylation of 4NI at the N1 site. These remarkable results have also implications for the development of nitroimidazole based radiosensitizers in tumor radiation therapy.     

Semilinear integro-differential equations in Hilbert space

Existence, uniqueness and asymptotic behavior of solutions to integro-differential equations involving monotone operators are discussed.