Fast Back Electron Transfer Prevents Guanine Damage by Photoexcited Thionine Bound to DNA

Abstract

The phenothiazinium dye thionine has a high excited state reduction potential and is quenched by guanine on the femtosecond time scale. Here, we show by gel electrophoresis that irradiation of thionine with 599 nm light in the presence of an oligonucleotide duplex does not produce permanent DNA damage. Upon photoexcitation of thionine weakly associated with guanosine-5'-monophosphate, the reduced protonated thionine radical and neutral guanine radical are detected by transient absorption spectroscopy, indicating that the quenching of thionine by guanine occurs via an electron-transfer mechanism. The observation of radical formation without permanent guanine damage indicates that fast back electron transfer plays a critical role in governing the yield of damage by DNA-binding molecules.

Biophysical studies on the base specificity and energetics of the DNA interaction of photoactive dye thionine: Spectroscopic and calorimetric approach

“…1A), a tricyclic heteroaromatic molecule, has been studied for its intercalative interaction, photoinduced mutagenic actions on binding to DNA, photoinduced inactivation of viruses and as impedance based DNA biosensor [11][12][13][14]. Tuite and Kelly [15] suggested that thionine intercalated and also bound to the outside of linear duplex DNA.…”

Photosensitized one-electron oxidation of DNA

“…However, once a hole escapes from the Coulombic interaction, it efficiently migrates through DNA by the A-hopping [18]. Insertion of a single G in the A n sequence between NDI and Gs significantly diminished the transient absorption of NDI ؒ-(NDG), since the inserted G serves as a hole trap on the hole shift process causing inhibition of consecutive A-hopping in which a hole migrates to Gs [40,41]. c ODNs were photoirradiated with 355-nm laser (1.6 mJ pulse −1 , 1500 pulses, total irradiated energy of 2.4 J), digested with snake venom phosphodiesterase/nuclease P1/alkaline phosphatase to 2'-deoxyribonucleosides.…”

“…Excitation of DNA-bound Sens produces the Sens ؒ− /DNA ؒ+ (ultimately yielding G ؒ+ by hole transfer) charge-separated state through photoinduced electron transfer. However, the efficiency of producing photosensitized DNA damage is low because of the charge recombination [10,29,37,40]. Thus, the absorption of a photon by Sens occasionally leads to DNA damage, but only with the aid of hole transfer, which provides time for DNA ؒ+ and Sens ؒ− to react with water or O 2 [14,33,[41][42][43][44]47].…”

Highly sensitive voltammetric detection of DNA hybridization in sandwich format using thionine-capped gold nanoparticle/reporter DNA conjugates as signal tags

“…Thionine is a small electroactive molecule [15] that is usually used as an electrochemical indicator for DNA hybridization because it possesses strong interaction with DNA [16]. Nitrogen atoms of the NH 2 moieties of thionine bind strongly to AuNP surfaces.…”