Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 18, Issue 27, Pages 18045-18053Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6cp03268k
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Funding
- King Abdullah University of Science and Technology (KAUST)
- King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia [K1017]
- Spanish MINECO [CTQ2014-59832-JIN]
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We present theoretical characterization of fluorescent non-natural nucleobases, (tz)A, (tz)G, C-tz, and U-tz, 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.
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