Structural and energetic characterization of the emissive RNA alphabet based on the isothiazolo[4,3-d]pyrimidine heterocycle core

Mohit Chawla, Albert Poater, Romina Oliva, Luigi Cavallo

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16 Scopus citations

Abstract

We present theoretical characterization of fluorescent non-natural nucleobases, tzA, tzG, tzC, and tzU, derived from the isothiazolo[4,3-d]pyrimidine heterocycle. Consistent with the experimental evidence, our calculations show that the non-natural bases have minimal impact on the geometry and stability of the classical Watson-Crick base pairs, allowing them to accurately mimic natural bases in a RNA duplex, in terms of H-bonding. In contrast, our calculations indicate that H-bonded base pairs involving the Hoogsteen edge are destabilized relative to their natural counterparts. Analysis of the photophysical properties of the non-natural bases allowed us to correlate their absorption/emission peaks to the strong impact of the modification on the energy of the lowest unoccupied molecular orbital, LUMO, which is stabilized by roughly 1.0-1.2 eV relative to the natural analogues, while the highest occupied molecular orbital, HOMO, is not substantially affected. As a result, the HOMO-LUMO gap is reduced from 5.3-5.5 eV in the natural bases to 4.0-4.4 eV in the modified ones, with a consequent bathochromic shift in the absorption and emission spectra. © 2016 the Owner Societies.
Original languageEnglish (US)
Pages (from-to)18045-18053
Number of pages9
JournalPhys. Chem. Chem. Phys.
Volume18
Issue number27
DOIs
StatePublished - 2016

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