Influence of base stacking and hydrogen bonding on the fluorescence of 2-aminopurine and pyrrolocytosine in nucleic acids

Samantha J O Hardman, Katherine C Thompson

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Fluorescent nucleobase analogues are used extensively to probe the structure and dynamics of nucleic acids. The fluorescence of the adenine analogue 2-aminopurine and the cytosine analogue pyrrolocytosine is significantly quenched when the bases are located in regions of double-stranded nucleic acids. To allow more detailed structural information to be obtained from fluorescence studies using these bases, we have studied the excited-state properties of the bases at the CIS and TDB3LYP level in hydrogen-bonded and base-stacked complexes. The results reveal that the first excited state (the fluorescent state) of a hydrogen-bonded complex containing 2-aminopurine and thymine is just the first excited state of 2-aminopurine alone. However, the same cannot be said for structures in which 2-aminopurine is base stacked with other nucleobases. Stacking causes the molecular orbitals involved in the fluorescence transition to spread over more than one base. The predicted rate for the fluorescence transition is reduced, thus reducing the fluorescence quantum yield. The decrease in radiative rate varies with the stacking arrangement (e.g., A- or B-form DNA) and with the identity of the nucleobase with which 2-aminopurine is stacked. Stacking 2-aminopurine between two guanine moieties is shown to significantly decrease the energy gap between the first and second excited states. We do not find reliable evidence for a low-energy charge-transfer state in any of the systems that were studied. In the case of pyrrolocytosine, base stacking was found to reduce the oscillator strength for the fluorescence transition, but very little spreading of molecular orbitals across more than one base was observed.

    Original languageEnglish
    Pages (from-to)9145-55
    Number of pages11
    JournalBiochemistry
    Volume45
    Issue number30
    DOIs
    Publication statusPublished - 1 Aug 2006

    Keywords

    • 2-Aminopurine
    • Base Pairing
    • Computational Biology
    • Cytosine
    • Hydrogen Bonding
    • Nucleic Acid Probes
    • Spectrometry, Fluorescence

    Research Beacons, Institutes and Platforms

    • Manchester Institute of Biotechnology

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