Electron Affinity of the Guanine-Cytosine Base Pair and Structural Perturbations upon Anion Formation
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- 作者：Nancy A. Richardson ; Steven S. Wesolowski ; and Henry F. Schaefer ; III
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：August 28, 2002
- 年：2002
- 卷：124
- 期：34
- 页码：10163 - 10170
- 全文大小：257K
- 年卷期：v.124,no.34(August 28, 2002)
- ISSN：1520-5126
文摘
The adiabatic electron affinity (AEA) for the Watson-Crick guanine-cytosine (GC) DNA basepair is predicted using a range of density functional methods with double- and triple-
plus polarizationplus diffuse (DZP++ and TZ2P++) basis sets in an effort to bracket the true electron affinity. The methodsused have been calibrated against a comprehensive tabulation of experimental electron affinities (Chem.Rev. 2002, 102, 231). Optimized structures for GC and the GC anion are compared to the neutral andanionic forms of the individual bases as well as Rich's 1976 X-ray structure for sodium guanylyl-3',5'-cytidine nonahydrate, GpC·9H2O. Structural distortions and natural population (NPA) charge distributionsof the GC anion indicate that the unpaired electron is localized primarily on the cytosine moiety. Unliketreatments using second-order perturbation theory (MP2), density functional theory consistently predicts asubstantial positive adiabatic electron affinity for the GC pair (e.g., TZ2P++/B3LYP: +0.48 eV). Thestabilization of C- via three hydrogen bonds to guanine is sufficient to facilitate adiabatic binding of anelectron to GC and is also consistent with the positive experimental electron affinities obtained byphotoelectron spectroscopy of cytosine anions incrementally microsolvated with water molecules. The pairing(dissociation) energy for GC- (35.6 kcal/mol) is determined with inclusion of electron correlation and showsthe anion to have greater thermodynamic stability; the pairing energy for neutral GC (TZ2P++/B3LYP23.9 kcal/mol) compares favorably to previous MP2/6-31G* (23.4 kcal/mol) results and a debated experiment(21.0 kcal/mol).
plus polarizationplus diffuse (DZP++ and TZ2P++) basis sets in an effort to bracket the true electron affinity. The methodsused have been calibrated against a comprehensive tabulation of experimental electron affinities (Chem.Rev. 2002, 102, 231). Optimized structures for GC and the GC anion are compared to the neutral andanionic forms of the individual bases as well as Rich's 1976 X-ray structure for sodium guanylyl-3',5'-cytidine nonahydrate, GpC·9H2O. Structural distortions and natural population (NPA) charge distributionsof the GC anion indicate that the unpaired electron is localized primarily on the cytosine moiety. Unliketreatments using second-order perturbation theory (MP2), density functional theory consistently predicts asubstantial positive adiabatic electron affinity for the GC pair (e.g., TZ2P++/B3LYP: +0.48 eV). Thestabilization of C- via three hydrogen bonds to guanine is sufficient to facilitate adiabatic binding of anelectron to GC and is also consistent with the positive experimental electron affinities obtained byphotoelectron spectroscopy of cytosine anions incrementally microsolvated with water molecules. The pairing(dissociation) energy for GC- (35.6 kcal/mol) is determined with inclusion of electron correlation and showsthe anion to have greater thermodynamic stability; the pairing energy for neutral GC (TZ2P++/B3LYP23.9 kcal/mol) compares favorably to previous MP2/6-31G* (23.4 kcal/mol) results and a debated experiment(21.0 kcal/mol).