title: The photoinduced transformation of fluorescent DNA base analogue tC triggers DNA melting.
abstract: While fluorescent analogues of the canonical nucleobases have proven to be highly valuable in a large number of applications, up until today, fluorescent DNA base analogues remain virtually inapplicable for single-molecule fluorescence experiments which require extremely bright and photostable dyes. Insight into the photodegradation processes of these fluorophores is thus a key step in the continuous development towards dyes with improved performances. Here, we show that the commercially available fluorescent nucleobase analogue tC under intense long-term illumination and in the presence of O2 is degraded to form a single photoreaction product which we suggest to be the sulfoxide form of tC. The photoproduct is characterized by a blue-shifted absorption and a less intense fluorescence compared to that of tC. Interestingly, when tC is positioned inside double-stranded DNA this photodriven conversion of tC to its photoproduct greatly reduces the duplex stability of the overall double helix in which the probe is positioned. Since tC can be excited selectively at 400 nm, well outside the absorption band of the natural DNA bases, this observation points towards the application of tC as a general light-triggered switch of DNA duplex stability.
authors.affiliation: Department of Chemistry, University of Copenhagen, Copenhagen, DK-2100, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Preus
authors.forename: Søren
authors.initials: S
authors.lastname: Jønck
authors.forename: Michael
authors.initials: M
authors.lastname: Pittelkow
authors.forename: Anke
authors.initials: A
authors.lastname: Dierckx
authors.forename: Thitinun
authors.initials: T
authors.lastname: Karpkird
authors.forename: Bo
authors.initials: B
authors.lastname: Albinsson
authors.forename: L Marcus
authors.initials: LM
authors.lastname: Wilhelmsson
mesh_terms: D003596:Cytosine / Q000031:analogs & derivatives; D004247:DNA / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D008027:Light; D008958:Models, Molecular; D009691:Nucleic Acid Denaturation; D010640:Phenothiazines / Q000737:chemistry*; D010782:Photolysis
chemical_list: C492077:1,3-diaza-2-oxophenothiazin-3-ylacetic acid; D005456:Fluorescent Dyes; D010640:Phenothiazines; D003596:Cytosine; D004247:DNA