Issue 6, 2010

Microhydration of 9-methylguanine:1-methylcytosinebase pair and its radical anion: a density functional theory study

Abstract

In this study, we present density functional theory calculations on the properties of proton transfer and electron binding in isolated, mono-, di-, and pentahydrated 9-methylguanine:1-methylcytosine (mG:mC) base pair radical anions. It was found that the proton transfer in mG:mC˙ is coupled to the interbase propeller-twisting and stretching motions, which cooperatively shorten the proton-transfer distance. Without the propeller-twisting motion, the interbase stretching will be hindered and the proton-transfer distance will become somewhat longer, which in turn, results in rising of the kinetic barrier for proton transfer. The monohydration can assist or resist the proton-transfer reaction, depending on the hydration sites. Inclusion of five water molecules in the first hydration shell around mG:mC˙ only moderately lowers the proton-transfer barrier from 3.80 to 3.01 kcal mol−1 and the reaction energy from −3.16 to −6.40 kcal mol−1 due to the cancellation between opposite influences of H2O molecules. A further consideration of bulk hydration using a polarizable continuum model does not affect the proton-transfer energetics. In contrast, both the first hydration shell and bulk hydration were found to play important roles in stabilizing the excess electron in mG:mC; the adiabatic electron affinity of mG:mC increases from 0.302 to 0.645 eV upon inclusion of five water molecules in the first hydration shell, and further increases to 1.813 eV when the bulk hydration is considered. We noticed that the water molecule can enhance electron binding by direct interaction with the nucleobase that accommodates excess electron or through the indirect effect of tuning interbase hydrogen bonds. In addition, the microhydration effects on proton transfer and electron binding were found to be approximately additive.

Graphical abstract: Microhydration of 9-methylguanine:1-methylcytosine base pair and its radical anion: a density functional theory study

Article information

Article type
Paper
Submitted
02 Oct 2009
Accepted
18 Nov 2009
First published
23 Dec 2009

Phys. Chem. Chem. Phys., 2010,12, 1253-1263

Microhydration of 9-methylguanine:1-methylcytosine base pair and its radical anion: a density functional theory study

H. Chen, S. C. N. Hsu and C. Kao, Phys. Chem. Chem. Phys., 2010, 12, 1253 DOI: 10.1039/B920603E

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