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Ab initio conformational analysis of nucleic acid components: Intrinsic energetic contributions to nucleic acid structure and dynamics

In recent years, the use of high‐level ab initio calculations has allowed for the intrinsic conformational properties of nucleic acid building blocks to be revisited. This has provided new insights into the intrinsic conformational energetics of these compounds and its relationship to nucleic acids structure and dynamics. In this article we review recent developments and present new results. New data include comparison of various levels of theory on conformational properties of nucleic acid building blocks, calculations on the abasic sugar, known to occur in vivo in DNA, on the TA conformation of DNA observed in the complex with the TATA box binding protein, and on inosine. Tests of the Hartree–Fock (HF), second‐order Møller–Plesset (MP2), and Density Functional Theory/Becke3, Lee, Yang and Par (DFT/B3LYP) levels of theory show the overall shape of backbone torsional energy profiles (for γ, ε, and χ) to be similar for the different levels, though some systematic differences are identified between the MP2 and DFT/B3LYP profiles. The east pseudorotation energy barrier in deoxyribonucleosides is also sensitive to the level of theory, with the HF and DFT/B3LYP east barriers being significantly lower (∼2.5 kcal/mol) than the MP2 counterpart (∼4.0 kcal/mol). Additional calculations at various levels of theory suggest that the east barrier in deoxyribonucleosides is between 3.0 and 4.0 kcal/mol. In the abasic sugar, the west pseudorotation energy barrier is found to be slightly lower than the east barrier and the south pucker is favored more than in standard nucleosides. Results on the TA conformation suggest that, at the nucleoside level, this conformation is significantly destabilized relative to the global energy minimum, or relative to the A‐ and B‐DNA conformations. Deoxyribocytosine would destabilize the TA conformation more than other bases relative to the A‐DNA conformation, but not relative to the B‐DNA conformation. © 2002 Wiley Periodicals, Inc. Biopoly (Nucleic Acid Sci) 61: 61–76, 2002; DOI 10.1002/bip.10047