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National Repository of Grey Literature 2 records found  Search took 0.01 seconds. 
Computational Study of the TiO2-Catalyzed Synthesis of Acyclonucleosides from Formamide: Implications for the Origin of Life
 Mládek, Arnošt ; Burda, Jaroslav (advisor) ; Futera, Zdeněk (referee)
The TiO2-catalyzed synthesis of nucleosides in non-aqueous formamide environ- ment via so-called acyclonucleoside intermediates represents an alternative way for the emergence of nucleic acids monomeric units, which could address the the fundamental problem associated with the formation of a --glycosidic bond between a nucleobase and a sugar moiety. In this computational contribution we present a plausible reaction route for the prebiotic TiO2-catalyzed synthesis of purine C2- and C3-acyclonucleosides in formamide, which does not require photocatalytic or radical chain mechanisms. The maximum computed activation energy along the proposed reaction channel is ≥ 32 kcal·mol≠1 , which is clearly feasible under the experimental conditions of the Saladino synthesis. We show that the rate determining step of the entire reaction path is the deprotonation of the formaldehyde hydrate methylene carbon occurring likely on defective binding sites of an anatase surface. Our calculations thus support the view of Saladino et al. about the catalytic role of the TiO2 surface in the one-pot synthesis of purine acyclonucleosides in heat formamide solution.
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Pokusy o rozlišení podjednotek trimerních a hexamerních forem purinnukleosidfosforylázy pomocí krystalové struktury komplexů purinových bází nukleosidů, acyklonukleosidů a jejich fosfonátových analogů
 Bzowska, A. ; Stepniak, K. ; Olasek, M. ; Dlugosz, M. ; Wielgus-Kutrowska, B. ; Antosiewicz, J. ; Holý, Antonín ; Koellner, G. ; Stroh, A. ; Raszewski, G. ; Steiner, T. ; Frank, J.
Attempts to demonstrate and interpret differences between subunits forming biologically active oligomers of low-(calf spleen) and high-molecular mass (E. coli) purine nucleoside phosphorylases (PNP) yielded new crystal structures of both enzymes complexed with ground-state analogue ligands in space groups and with two full trimers and one full hexamer in the asymmetric unit, respectively.
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