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91.
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Hidenori Okamura Antony Crisp Sarah Hübner Sidney Becker Petra Rov Thomas Carell 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18864-18869
The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information‐carrying RNA oligomers able to self‐replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto‐RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis‐urea (biuret) and tris‐urea (triuret) are able to directly react with ribose. The urea‐ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides’ base‐pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea‐containing RNA bases are good candidates for a proto‐RNA world. 相似文献
93.
E. Niecke P. Becker A. Fuchs M. Nieger T. Schiffer W.W. Schoeller 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):613-616
Abstract The synthesis and x-ray structure analysis of a novel type of carbenoids, aryl-P(=E)=C(Cl)Li(thf)3 (E=N-aryl, C(SiMe3)2), as well as the first example of a 1,3-diphosphetane-2,4-diyl, (aryl-PCCl)2, is reported and on the basis of quantum chemical calculations its bonding situation is discussed. Furthermore, selected examples for the varying reaction behavior of both types of compounds are presented. 相似文献
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Manfred Scheer Uta Becker 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):391-392
Abstract Studies of the reaction pathway of tetrahedral P4 with cobalt- and molybdenum coordination compounds lead to novel complexes containing PX-ligands (x = 2,4) in unusual binding modes. 相似文献
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Thermal conformations of semiflexible macromolecules are generically described by the worm-like chain model. The end-to-end
distance distribution, a fundamental quantity of the model, is not yet known in closed form. We provide a solution to the
practical problem of choosing an appropriate approximation. First, a comprehensive review of existing approximations and exact
limiting results is given. We then propose an explicit expression which interpolates between all relevant limiting cases.
We show that it accurately reproduces, at no computational cost, high-precision Monte Carlo data, covering a wide range from
stiff to flexible chains and from looped to fully stretched configurations. Using this result we quantify the enhancement
of short worm-like loop formation by (protein) bridges. 相似文献