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Abstract The helical structures of DNA and RNA were originally revealed by experimental data. Likewise, the development of programs for modeling these natural polymers was guided by known structures. These nucleic acid polymers represent only two members of a potentially vast class of polymers with similar structural features, but that differ from DNA and RNA in the backbone or nucleobases. Xeno nucleic acids (XNAs) incorporate alternative backbones that affect the conformational, chemical, and thermodynamic properties of XNAs. Given the vast chemical space of possible XNAs, computational modeling of alternative nucleic acids can accelerate the search for plausible nucleic acid analogs and guide their rational design. Additionally, a tool for the modeling of nucleic acids could help reveal what nucleic acid polymers may have existed before RNA in the early evolution of life. To aid the development of novel XNA polymers and the search for possible pre-RNA candidates, this article presents the proto-Nucleic Acid Builder (https://github.com/GT-NucleicAcids/pnab), an open-source program for modeling nucleic acid analogs with alternative backbones and nucleobases. The torsion-driven conformation search procedure implemented here predicts structures with good accuracy compared to experimental structures, and correctly demonstrates the correlation between the helical structure and the backbone conformation in DNA and RNA. 

The restrained electrostatic potential (RESP) charge model is widely used in molecular dynamics simulations, especially for the AMBER and GAFF force fields. We have implemented the RESP scheme using the accessible and widely used Python language and the NumPy numerical library. This article provides a programming‐oriented introduction to the RESP scheme and highlights some of the features of NumPy that are useful in scientific computing.

 

Cyanuric acid (CA), a triazine heterocycle, is extensively utilized for noncovalent self‐assembly. The association between poly(adenine) and CA into micron‐length fibers was a remarkable observation made by Sleiman and co‐workers, who proposed that adenine and CA adopt a hexameric rosette configuration in analogy with previously reported structures for CA assemblies. However, recent experimental observations from the Krishnamurthy group led to a reevaluation of the hexameric rosette model, wherein they have proposed a hydrogen‐bonded helicene model as an alternative. Our molecular dynamics simulations show that the hexad model is indeed unlikely and that this novel noncovalent helicene geometry, where the adenine and CA bases form an extended helical hydrogen‐bond network across the system, is a more probable structural motif. The existence of noncovalent helicene compounds may have wide‐ranging applications in DNA nanotechnology and helicene chemistry.