Intermolecular vs. intramolecular photoinduced electron transfer from nucleotides in DNA to acridinium ion derivatives in relation with DNA cleavage

Selective fluorescence sensors for Cu2+ and Hg2+ ions using acridinium-polymer complexes

The photophysical properties of two acridinium derivatives, 9-phenyl-10-methylacridinium (Ph-Arc+) and 9-mesityl-10-methyl acridinium (Mes-Acr+) were investigated in aqueous solutions of poly(methacrylic acids) (PMAA) at various pH values with various polymer to dye (R/D) ratios. In acidic conditions, PMAA effectively turned on the emission of both acridinium derivatives. Micromolar concentrations of copper (II) ions can selectively turn off the emission of dye/PMAA mixtures with a linear response range from 0.50 to 10.0 µM and a detection limit as low as 0.38 µM. In near neutral conditions, Mes-Acr+ in PMAA solutions displayed extremely weak emission. However, trace amounts of Hg2+ ions can instantly turn on the emission with a low detection limit of 43.6 nM and a linear range between 1.0 to 10.0 µM. This analytical method is fast, cost-effective, and environmentally friendly, as it is conducted in 100 % aqueous solution with commercial acridinium derivatives and a biocompatible polymer.

Photoinduced Electron Transfer between DNA and Water-Soluble Porphyrins

Photophysical properties of five kinds of porphyrins (H₂TMPyP, ZnTMPyP, PdTMPyP, H₂TPPS, and ZnTPPS) complexed with model DNAs (ctDNA and dGMP) have been investigated using steady-state absorption, circular dichroism (CD), and femtosecond transient absorption spectroscopy. Upon addition of ctDNA (or dGMP), larger hypochromism and red shifts are observed for H₂TMPyP and PdTMPyP compared to the other samples. The steady-state measurements have suggested that the binding modes of H₂TMPyP-ctDNA and PdTMPyP-ctDNA are partial intercalation and full intercalation, respectively, while ZnTMPyP-ctDNA shows outside groove binding. No significant interaction was observed between both H₂TPPS and ZnTPPS with two kinds of DNA. Upon excitation of the porphyrins into the higher excited state S₂ (Soret band), the appearance of the transient absorption from ∼500 to ∼620 nm at about 0.05 ps in H₂TMPyP-ctDNA, H₂TMPyP-dGMP, and PdTMPyP-dGMP indicates the occurrence of the electron transfer (ET) from guanine to H₂TMPyP and PdTMPyP. The forward ET are extremely fast (k_f ≥ 1.0 × 10¹³ s^-1), and the backward ET rates are ∼5.6 × 10¹² and ∼4.0 × 10¹² s^-1, respectively. The complexation with DNA may lead to the shorter lifetime of the fluorescence of H₂TMPyP and PdTMPyP.

DNA-Targeted NO Release Photoregulated by Green Light

A novel molecular hybrid has been designed and synthesized in which acridine orange (AO) is covalently linked to an N-nitrosoaniline derivative through an alkyl spacer. Photoexcitation of the AO antenna with the highly biocompatible green light results in intense fluorescence emission and triggers NO detachment from the N-nitroso appendage via an intramolecular electron transfer. The presence of the AO moiety encourages the binding with DNA through both external and partially intercalative fashions, depending on the DNA:molecular hybrid molar ratio. Importantly, this dual-mode binding interaction with the biopolymer does not preclude the NO photoreleasing performances of the molecular hybrid, permitting NO to be photogenerated nearby DNA with an efficiency similar to that of the free molecule. These properties make the presented compound an intriguing candidate for fundamental and potential applicative research studies where NO delivery in the DNA proximity precisely regulated by harmless green light is required.

Attenuation of guanine oxidation via DNA-mediated electron transfer in a crowded environment using small cosolutes

Guanine oxidation induced by photoirradiation on a pyrene-modified oligonucleotide was investigated under molecular crowding using small cosolutes such as glycerol.

Photoinduced Electron Transfer between Anionic Corrole and DNA

The interaction between a water-soluble anionic Ga(III) corrole [Ga(tpfc)(SO3Na)2] and calf thymus DNA (ct-DNA) has been investigated by using femtosecond transient absorption spectroscopy. A significant broadening from 570 to 585 nm of positive absorption band of the blend of Ga(tpfc)(SO3Na)2 and ct-DNA (Ga(tpfc)(SO3Na)2-ctDNA) has been observed from 0.15 to 0.50 ps after photoexcitation of Ga(tpfc)(SO3Na)2 into the Soret band. The control experiment has been performed on the model DNA ([poly(dG-dC)]2) rich in guanine bases, which exhibits a similar spectral broadening, whereas it is absent for [poly(dA-dT)]2 without guanine bases. The molecular orbital calculation shows that HOMO of Ga(tpfc)(SO3Na)2 is lower than that of guanine bases. The results of the electrochemical experiment show the reversible electron transfer (ET) between Ga(tpfc)(SO3Na)2 and guanine bases of ct-DNA is thermodynamically favorable. The dynamical analysis of the transient absorption spectra reveals that an ultrafast forward ET from the guanine bases to Ga(tpfc)(SO3Na)2 occurs within the pulse duration (156 fs), leading to the formation of an intermediate state. The following back ET to the ground state of Ga(tpfc)(SO3Na)2 may be accomplished in 520 fs.

Radiolysis and photolysis studies on active transient species of berberine

In this paper, the photochemical and photobiological characters of the active radicals of berberine (BBR) was investigated for finding an efficient and safe photosensitizer with highly active transient products using in Photodynamic therapy (PDT) study. The active species of BBR was generated and identified by using pulse radiolysis method. In neutral aqueous solution, BBR react with hydrated electron and hydroxyl radical, forming the radical anion and neutral radical of BBR, and the related reaction rates were determined as 3.5×10(10) and 6.7×10(9) M(-1) s(-1), respectively. Further, the capability of BBR to photosensitize DNA cleavage was testified by laser flash photolysis (LFP) method, the results demonstrated that BBR neutral radical could react with guanine mononucleotide (K=1.9×10(9) M(-1) s(-1)) via electron transfer to give the guanine neutral radical. Additionally BBR selective cleavage single and double strand DNA at guanine moiety was observed. Finally, combining with the thermodynamic calculation, the possible photodamage mechanism of dGMP and DNA induced by BBR was clarified.