Uracil complexes

The Mg+ complexes of cytosine, thymine and uracil are the most complex system studied via photodissociation spectroscopy to date . A complication for these systems is that these nucleobases can exist in various tautomeric forms and that complexation of a metal can change the stability order of the tautomers. DFT calculations located four tautomeric Mg(cytosine)+ complexes, and three of these (29, 30, and 31) were suggested to be responsible for the four reactive photofragment ions 32-35 observed at a wavelength of 360 nm (Scheme 4) . Related photofragmentation reactions were observed for the Mg(thymine)+" and Mg(uracil)+" complexes . ... 

Early qualitative studies already indicated that the Pt-N(3) bond in 1-subsituted thymine and uracil complexes is particularly inert toward the attack of CN, which has been attributed to the remarkable protective effect... 

Zhanpeisov, N. U. Leszczynski, J. The specific solvation effects on the structures and properties of adenine-uracil complexes A theoretical ab initio study, J. Phys. Chem. A 1998,102, 6167-6172. 

The synthesis of [Zn(OH)(Tp Bu ,pr)], which has a structure very similar to the active site of the enzyme carbonic anhydrase, was described. [Zn(L)(Tp Bu, pr)] (HL = uracil or halouracil) were also reported. The halogenated uracil complexes were injected in Dalton s lymphoma tumor system in mice and [Zn(5-fluorouracilate)-(Tp Bu ,pr)] exhibits significant antitumor activity. This complex also promotes the hydrolysis of various esters and the maximum rate of hydrolysis is found with p-nitrophenylacetate.116... 

It may be a combination of these reasons why there appears to be some uncertainty concerning metal binding sites of these ligands in studies not supported by crystal structures (13-18), Although the existence of tautomer complexes of uracil and thymine had been taken into consideration (13.), until recently, only in a single case, with uracil complexes of triammineplati-num(II), it has clearly been demonstrated by Kidani and Inagaki... 

The calculations of solvated (hydrated) complexes simulated by explicit inclusion of water molecule shows the energy loss only for the tetrahedral systems, which is due to the structural changes of the substrate induced by water adsorption [151]. It amounts to about 3 kcal/mol. In the case of octahedral systems presence of water does not increase the Ecorr value for K(3o)NaW-U but it stabilizes thymine by 1.7 kcal/mol. Isolated uracil is more stable in the water-cation environment than in the microcosmic environment with only water [157]. In all K(3o)NaW systems orientation by 02 towards Na+ remains to be the most favorable. On the other hand, in study of hydrated Li+-thymine and Li+-uracil complexes binding of (H20)Li+ to the 04 site is stabilized by 1.7- 2.9 kcal/mol over the binding to the 02 site [156],... 

We have studied the double-proton transfer reaction in the adenine-uracil complex. The calculations were performed at the HF/6-311G level, and the REF was obtained by numerical differentiation of the chemical potential defined in terms of the frontier orbital energies, as indicated in Equation 12.6. The double-proton transfer in the complex adenine-uracil is a stepwise reaction in which the two protons are transferred... 

FIGURE12.5 REF profile for the double proton transfer reaction in the adenine-uracil complex. 

The exchange on uracil and cytosine complexes has also been noted [44], and the formation of substituted uracil from the CI2 oxidation of Pt(II)—uracil complexes to Pt(IV) also reflects the increased reactivity... 

The dissociation of silver may not in some cases be a prerequisite for activity silver uracil complexes did not penetrate cells and the in vitro antibacterial action was attributed to membrane effects [25]. A survey of the in vitro antimicrobial effects of a series of metal sulfanilamides also appointed silver and gold salts as the most active, the gold sulfadiazene being as active as the silver complex [26]. The chemistry and microbiology of these species has been summarized [27]. 

Quantum-chemical analysis of the polyhydrated DNA bases species is still very scarce. The available data are following. The dihydrated complexes of 7GUA and 9GUA molecules were investigated at the MP2/6-31G(d) level [119]. The trihydrated complex of uracil and the corresponding anion radical have been calculated using the 6-31+G(d) level at the HF approximation [127]. In addition, the trihydrated uracil complexes have been the subject of experimental investigations (ID and 2G heteronuclear Overhauser spectroscopy) [128]. 

A related early study of dichloro, oxalate, malonate, methyhnalonate, and the uracil complex also showed antitumor activity. " They investigated the cis, d-trans,... 

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