Spectro-electrochemical Studies on [Ru(TAP)2(dppz)]2+—Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides (original) (raw)
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Journal of inorganic …, 2010
The structural and spectroscopic properties of [Ru(phen) 2 (dppz)] 2+ and [Ru(tap) 2 (dppz)] 2+ (phen = 1,10phenanthroline; tap= 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine ) have been investigated by means of density functional theory (DFT), time-dependent DFT (TD-DFT) within the polarized continuum model (IEF-PCM) and quantum mechanics/molecular mechanics (QM/MM) calculations. The model of the Δ and Λ enantiomers of Ru(II) intercalated in DNA in the minor and major grooves is limited to the metal complexes intercalated in two guanine-cytosine base pairs. The main experimental spectral features of these complexes reported in DNA or synthetic polynucleotides are better reproduced by the theoretical absorption spectra of the Δ enantiomers regardless of intercalation mode (major or minor groove). This is especially true for [Ru(phen) 2 (dppz)] 2+ . The visible absorption of [Ru(tap) 2 (dppz)] 2+ is governed by the MLCT tap transitions regardless of the environment (water, acetonitrile or bases pair), the visible absorption of [Ru(phen) 2 (dppz)] 2+ is characterized by transitions to metal-to-ligand-charge-transfer MLCT dppz in water and acetonitrile and to MLCT phen when intercalated in DNA. The response of the IL dppz state to the environment is very sensitive. In vacuum, water and acetonitrile these transitions are characterized by significant oscillator strengths and their positions depend significantly on the medium with blue shifts of about 80 nm when going from vacuum to solvent. When the complex is intercalated in the guanine-cytosine base pairs the 1 IL dppz transition contributes mainly to the band at 370 nm observed in the spectrum of [Ru(phen) 2 (dppz)] 2+ and to the band at 362 nm observed in the spectrum of [Ru(tap) 2 (dppz)] 2+ .
Photochemical & Photobiological Sciences, 2011
The transient species formed following excitation of fac-[Re(CO) 3 (F 2 dppz)(py)] + (F 2 dppz = 11,12-difluorodipyrido[3,2-a:2¢,3¢-c]phenazine) bound to double-stranded polynucleotides [poly(dA-dT)] 2 or [poly(dG-dC)] 2 have been studied by transient visible and infra-red spectroscopy in both the picosecond and nanosecond time domains. The latter technique has been used to monitor both the metal complex and the DNA by monitoring the regions 1900-2100 and 1500-1750 cm -1 respectively. These data provide direct evidence for electron transfer from guanine to the excited state of the metal complex, which proceeds both on a sub-picosecond time scale and with a lifetime of 35 ps, possibly due to the involvement of two excited states. No electron transfer is found for the [poly(dA-dT)] 2 complex, although characteristic changes are seen in the DNA-region TRIR consistent with changes in the binding of the bases in the intercalation site upon excitation of the dppz-complex. ; Fax: +353 1 671 2826; Tel: +353 1 896 1947 † Electronic supplementary information (ESI) available: UV/vis absorption spectra and emission ([poly(dA-dT)] 2 ] only) of fac-[Re(CO) 3 (F 2 dppz)(py)] + recorded in buffered D 2 O solution in the presence of increasing concentrations of [poly(dA-dT)] 2 ] or [poly(dG-dC)] 2 ]. See
Faraday Discuss., 2015
The intercalating [Ru(TAP)2(dppz)]2+ complex can photo-oxidise guanine in DNA, although in mixed-sequence DNA it can be difficult to understand the precise mechanism due to uncertainties in where and how the complex is bound. Replacement of guanine with the less oxidisable inosine (I) base can be used to understand the mechanism of electron transfer (ET). Here the ET has been compared for both Λ- and Δ-enantiomers of [Ru(TAP)2(dppz)]2+ in a set of sequences where guanines in the readily oxidisable GG step in {TCGGCGCCGA}2 have been replaced with I. The ET has been monitored using picosecond and nanosecond transient absorption and picosecond time-resolved IR spectroscopy. In both cases inosine replacement leads to a diminished yield, but the trends are strikingly different for Λ- and Δ-complexes.
Journal of Molecular Modeling, 2014
The synthesis of a new Ru(II) complex is reported. Its absorption spectrum when interacting with DNA in water was calculated at the hybrid quantum mechanics molecular mechanics level of theory and compared with experimental data. The vertical transitions were computed using timedependent density functional theory in the linear response approximation. The complex and its environment were treated at the quantum mechanical and molecular mechanical levels, respectively. The effects of the environment were investigated in detail and conveniently classified into electrostatic and polarization effects. The latter were modeled using the computationally inexpensive "electronic response of the surroundings" method. It was found that the main features of the experimental spectrum are nicely reproduced by the theoretical calculations. Moreover, analysis of the most intense transitions utilizing the natural transition orbital formalism revealed important insights into their nature and their potential role in the irreversible oxidation of DNA, a phenomenon that could be relevant in the field of cancer therapy.
Journal of Photochemistry and Photobiology A: Chemistry, 2007
The absorption spectroscopy of [Ru(phen) 2 dppz] 2+ and [Ru(tap) 2 dppz] 2+ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen) 2 dppz] 2+ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT (d Ru → * dppz ) absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap) 2 dppz] 2+ between 522 nm and 400 nm is the presence of various excited states such as MLCT (d Ru → * TAP ), ligand-to-ligand-charge-transfer LLCT ( dppz → * TAP ) or intra-ligand IL ( dppz → * dppz ) states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H 2 O, CH 3 CN) the absorption spectrum of [Ru(tap) 2 dppz] 2+ is dominated by a strong absorption at 388 nm (CH 3 CN) or 390 nm (H 2 O) assigned to a 1 IL ( dppz → * dppz ) corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the 1 IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA.
DNA Photocleavage by a Supramolecular Ru(II)−Viologen Complex
Inorganic Chemistry, 2002
A novel Ru(II) complex possessing two sequentially linked viologen units, Ru−V 1 −V 2 6+ , was synthesized and characterized. Upon excitation of the Ru(II) unit (λ exc ) 532 nm, fwhm ∼ 10 ns), a long-lived charge-separated (CS) state is observed (τ ) 1.7 µs) by transient absorption spectroscopy. Unlike Ru(bpy) 3 2+ , which cleaves DNA upon photolysis through the formation of reactive oxygen species, such as 1 O 2 and O 2 -, the photocleavage of plasmid DNA by Ru−V 1 −V 2 6+ is observed both in air and under N 2 atmosphere (λ irr > 395 nm).
Journal of Molecular Structure, 2001
Nanosecond transient resonance Raman and picosecond transient absorption spectroscopic investigations of the two structurally analogous Ru-polypyridyl complexes, Ruphen 2 dppz 21 (1) and Rutap 2 dppz 21 (2), are presented (phen 1,10phenanthroline, dppz dipyrido [3,2-a:2 0 ,3 0 -c] phenazine; tap 1,4,5,8 tetraazaphenanthrene). The ®ndings offer insight into the differing nature of the lowest excited states of the two complexes, and describe the role of these states within the very distinct photophysical behaviour of each, both in relation to solvent response and their interaction with DNA (facilitated in each case through the intercalating dppz ligand). The active, solvent-sensitive, dppz-based 3 MLCT states involved in the`lightswitch' behaviour of (1) are probed, alongside evidence of a progression through a precursor transient state when the complex is in non-aqueous environment. Evidence has been provided of a photophysical pathway for (2), involving formation of a tapbased lowest 3 MLCT state. When (2) is bound to DNA through the dppz ligand, a photo-driven electron transfer process ensues between the guanine base of DNA and the lowest 3 MLCT state. q
Photoinduced electron transfer between ruthenium complexes and nucleotides or DNA
Pure and Applied Chemistry, 1997
The quenching of the luminescence of Ru(TAP)++, Ru(HAT)z(bpyp+ (TAP = 1,4,5$-tetraazaphenanthrene; HAT = 1,4,5,8,9,12-hexaazatphenylene; bpy = 2,2'bipyridyl) and related oxidising complexes by DNA, polynucleotides, and purine nucleotides occurs by reductive electron transfer. Laser flash photolysis provides evidence for the formation of the reduced metal complex and the deprotonated nucleotide radical cation. This photo-oxidation leads to DNA strand-breaks and to the formation of covalent adducts with GMP or DNA. The adducts with RU(TAP)~~+ or Ru(HAT),(bpy)2+ are formed via a covalent bond between the C atom p to the coordinating N in the TAP or HAT ligand and the N2 of guanine.
Journal of the American Chemical Society, 2013
Visible light irradiation of a ruthenium(II) quinone-containing complex, [(phen) 2 Ru(phendione)] 2+ (1 2+), where phendione = 1,10-phenanthroline-5,6-dione, leads to DNA cleavage in an oxygen independent manner. A combination of NMR analyses, transient absorption spectroscopy, and fluorescence measurements in water and acetonitrile reveal that complex 1 2+ must be hydrated at the quinone functionality, giving [(phen) 2 Ru-(phenH 2 O)] 2+ (1H 2 O 2+ , where phenH 2 O = 1,10-phenanthroline-6-one-5-diol), in order to access a long-lived 3 MLCT hydrate state (τ ∼ 360 ns in H 2 O) which is responsible for DNA cleavage. In effect, hydration at one of the carbonyl functions effectively eliminates the lowenergy 3 MLCT SQ state (Ru III phen-semiquinone radical anion) as the predominant nonradiative decay pathway. This 3 MLCT SQ state is very short-lived (<1 ns) as expected from the energy gap law for nonradiative decay, 1 and too short-lived to be the photoactive species. The resulting excited state in 1H 2 O 2+ * has photophysical properties similar to the 3 MLCT state in [Ru(phen) 3 ] 2+ * with the added functionality of basic sites at the ligand periphery. Whereas [Ru(phen) 3 ] 2+ * does not show direct DNA cleavage, the deprotonated form of 1H 2 O 2+ * does via a proton-coupled electron transfer (PCET) mechanism where the peripheral basic oxygen sites act as the proton acceptor. Analysis of the small molecule byproducts of DNA scission supports the conclusion that cleavage occurs via H-atom abstraction from the sugar moieties, consistent with a PCET mechanism. Complex 1 2+ is a rare example of a ruthenium complex which 'turns on' both reactivity and luminescence upon switching to a hydrated state.