Uracil anions, structure

The optimized structure of the ODCase complex with the uracil anion (3) was used to argue for the importance of dynamic effects in transition state stabilization. When the C6-CO2 distance constraint was removed, CO2 was released and drifted away from the Asp-Lys-Asp-Lys tetrad, and at the same time, C6 of the resulting uracil anion moved towards Lys73. The Asp-Lys-Asp-Lys tetrad appeared to be... 

O. Dolgounitcheva, V. G. Zakrzewski, and J. V. Ortiz, Chem. Phys. Lett., 307, 220-226 (1999). Structures and Electron Detachment Energies of Uracil Anions. 

Further STM and SXS smdies [Wu et al., 1998] concerning this phenomenon indicated that the presence of specifically and nonspecifically adsorbing anions as well as organic molecules (e.g., pyridine, bipyridine, and uracil) may also lift the reconstructed surface by exhibiting a structural transition, and it has been extensively studied and reviewed in [Kolb, 1996]. 

An ab initio study on the structure and splitting of the uracil dimer anion-radical (see Scheme 3.72, R = H) gives preference to the one-step mechanism (Voityuk and Roesch 1997). Anion-radical anions of the pyrimidine dimers cleave with rate constants in excess of 10 s ... 

A comparison of these nucleobase-derived metallacalixarenes with natural nucleobase-derived tetrands may be advisable. In the non-natural quartets formed by interconnection of uracil, purine or its derived nucleobases with coordinative metals, the cationic character lies on the metals in the periphery and anions are bound in the cavity. In natural tetrands of these nucleobases, the hydrogen bonds interconnect the bases and the structures are stabilized by a cation located in the centre whereas phosphate groups located in the periphery carry negative charge (2005AGE668). As against the existence of only natural... 

An ab initio study on the structure and splitting of the uracil dimer anion radical (see Scheme 3-66 and keep R = H) gives preference to the one-step mechanism (Voityuk Roesch 1997). Anion radical anions of the pyrimidine dimers cleave with rate constants in excess of 106 sec 1 (Yeh Falvey 1991). However, the cyclobutyl dimer of a quinone, dithymoquinone, also cleaves upon single-electron reduction but much more slowly than the pyrimidine dimers (Robbins Falvey 1993). It is truly an unresolved issue as to why the anion radical cleavage depicted in Scheme 3-66 is so facile. Water participation can probably decrease the barrier of the cycloreversion on physiological conditions (Saettel Wiest 2001). 

Moorthy PN, Hayon E (1975) Free-radical intermediates produced from the one-electron reduction of purine, adenine and guanine derivatives in water. J Am Chem Soc 97 3345-3350 Mori M, Teshima S-l, Yoshimoto H, Fujita S-l, Taniguchi R, Hatta H, Nishimoto S-l (2001) OH Radical reaction of 5-substituted uracils pulse radiolysis and product studies of a common redox-ambivalent radical produced by elimination of the 5-substituents. J Phys Chem B 105 2070-2078 Morin B, Cadet J (1995) Chemical aspects of the benzophenone-photosensitized formation of two lysine - 2 -deoxyguanosine cross-links. J Am Chem Soc 117 12408-12415 Morita H, Kwiatkowski JS,TempczykA(1981) Electronic structures of uracil and its anions. Bull Chem Soc Jpn 54 1797-1801... 

Fig. 2. Tautomers of uracil (R = H, X = O), thymine (R = Me, X = O), cytosine (R = H, X = NH) and their N(1 )-alkylated derivatives in neutral and in the most common anionic species. Only one of the resonance structures is shown.

The relationships between the deprotonation energy of proton donor and complex stability as well as its VDE were characterized in our work devoted to complexes between uracil and a series of alcohols with deprotonation enthalpy (HDP) varied in a systematic manner [48], We found out that a H p smaller than 14.3 eV is required for BFPT with the product being UH OR. Two minima coexist on the anionic energy surface for 14.8 eV < HDP < 14.3 eV. These minima correspond to the UH OR and 1 HOR structures. For ROH s with deprotonation enthalpies above 14.8 eV only the U HOR minimum exists on the potential energy surface. 

The energy of stabilization of the anionic complex increases when acidity of alcohols increases (Figure 21-17). For anionic complexes for which we identified two minima corresponding to U HOR and UH OR structures, the structure with protonated uracil is more stable. The vertical detachment energy of anionic complex systematically increases when deprotonation energy of alcohol decreases. There is a discontinuity in VDE of ca. 0.5 eV, which is a manifestation of intermolecular proton transfer (Figure 21-18). 

Platinum-acetamide-blue and platinum-uracil-blue compounds have been reported. The tetranuclear uracil blue [Pt4(l-MeU)4(NH3)g](N03)5-H20, where 1-MeU is the mono-anion of 1-methyluracil, has structure and properties resembling 2-pyridone-blues. Platinum blue compounds with uridine, isonicotinamide, malonamide, and biuret have been described. ... 

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