Abstract

Background: The computation of DNA is a field of growing interest, primarily focused on studying its individual constituents, but a few authors have gone further by analyzing standard microhelices with DFT methods. Objective: Because these studies did not consider that, at the atomic level, other possible DNA and RNA helices with the WC-type arrangement are also stable, this is the main objective here. Methods: Therefore, forty microhelices were optimized in a simple model with three WC base pairs composed of nucleosides using the M06-2X DFT method. Results: Based on the spatial arrangement of the intramolecular H-bond with the 2′-OH group, five types of RNA:RNA double microhelices were obtained; by this arrangement, they were related to the corresponding DNA:DNA ones. In addition to A-type and B-type microhelices, two new types were found, conveniently named B1-type and C-type. The structural geometric parameters of all these optimized microhelices in an isolated state were compared and analyzed in detail. The total counterpoise-corrected interaction energies were determined in these microhelices. RNA microhelices with different types of intramolecular H-bond arrangements involving the 2′-OH group in each single strand were also optimized, as well as their corresponding DNA helices having the same spatial arrangement. Different DNA:RNA hybrid microhelices were also considered, and their structural geometric parameters were compared to those of other microhelices. Conclusions: the identification and detailed characterization, for the first time, of ten main stable spatial geometric shapes with different exocyclic and endocyclic torsional angles. Several relationships among the structural geometric parameters of these microhelices were also established. Although the new DNA/RNA helix types containing theoretically obtained WC pairs have not been found in biological helices, they could be synthesized and they may open the possibility of being used for other purposes.

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