Rincón Elizabeth, Yáñez Manuel, Toro-Labbé Alejandro, Mó Otilia
Laboratorio de Química Teórica Computacional (QTC), Pontificia Universidad Católica de Chile, Santiago, Chile.
Phys Chem Chem Phys. 2007 May 28;9(20):2531-7. doi: 10.1039/b618050g. Epub 2007 Mar 29.
The effect of Ni(II), Cu(II) and Zn(II) association on the diketo/keto-enol tautomerism of thymine has been investigated through the use of B3LYP density functional theory calculations. Final energies were obtained at the B3LYP/6-311+G(2df,2p)//B3LYP/6-311+G(d,p) level of theory. Ni(II) and Cu(II) lead to an oxidation of thymine which for Zn(ii) is only partial and catalyze the tautomerization process, this catalytic effect being much larger for Ni(2+) and Zn(2+) than for Cu(2+). One of the most significant consequences of the oxidation of the base is that the calculated BDE's are primarily dictated by the value of the second ionization potential of the metal, and therefore follow the sequence Cu(2+) > Ni(2+) > Zn(2+). Also importantly, metal dication association leads to a stabilization of the keto-enol tautomer, which becomes the most stable form upon interaction with Ni(2+) and Zn(2+). This stabilization enhancement is the consequence of three concomitant factors, namely, (i) a stronger interaction of the metal cation with the carbonyl oxygen, (ii) the interaction of the metal with the dehydrogenated ring nitrogen, (iii) an aromatization of the six-membered ring.
通过使用B3LYP密度泛函理论计算，研究了镍（II）、铜（II）和锌（II）缔合对胸腺嘧啶二酮/酮-烯醇互变异构的影响。最终能量在B3LYP/6-311+G(2df,2p)//B3LYP/6-311+G(d,p)理论水平上获得。镍（II）和铜（II）导致胸腺嘧啶氧化，而锌（II）的氧化只是部分氧化，并催化互变异构过程，这种催化作用对于镍（2+）和锌（2+）比对于铜（2+）要大得多。碱基氧化的最显著后果之一是，计算得到的键解离能（BDE）主要由金属的第二电离势的值决定，因此遵循铜（2+）>镍（2+）>锌（2+）的顺序。同样重要的是，金属二价阳离子缔合导致酮-烯醇互变异构体稳定，在与镍（2+）和锌（2+）相互作用时，它成为最稳定的形式。这种稳定性增强是三个伴随因素的结果，即：（i）金属阳离子与羰基氧的更强相互作用；（ii）金属与脱氢环氮的相互作用；（iii）六元环的芳构化。
