Since the publications of Wolfe-Simon et al. reporting the replacement of phosphorus by arsenic in bio-molecules of a bacterium, strain GFAJ-1, numerous comments have claimed that such a substitution cannot be possible. The present report is a prospective study aimed at identifying if arsenic can substitute for the lighter element of the same column without structural damage in key biological molecules. Arsenic indeed is a chemical analog of phosphorus with a similar atomic radius, as well as near identical electronegativity. To this end, systematic computational experiments using Density Functional Theory (DFT) were carried out on arsenic analogs of selected systems representing the DNA helix and of the energetic chain ATP, ADP and AMP .To assess the plausibility of the As to P substitution in a DNA architecture, a comparative study of the Dimethylphosphate (DMP) and Dimethyl-arsenate (DMA) anions was carried out. It was found that the gauche-gauche arrangement that mimics the helix structure is the most stable one in both model molecules. In the same way, apart from a lengthening of the bonds around the As atoms, the structures of the anionic analogs, ATAs, ADAs and AMAs reproduce those of the biological systems, showing that there is no structural evidence to discard the hypothesis of the possible inclusion of As in place of P in both types of architecture. However, the topological analysis of the Electron Localization Function shows a 50% weakening of As-O covalent bonds in all systems, which may be why Nature chose P instead of As for building biological compounds.

Structural and energetic aspects of the replacement of phosphorus by arsenic in DNA and ATP: A quantum chemical view

248th National Meeting (2014)

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