One-step electrochemically co-assembled redox-active [Ru(bpy)(2)(tatp)](2+)-BSA-SWCNTs hybrid film for non-redox protein biosensors

A redox-active [Ru(bpy)(2)(tatp)](2+)-BSA-SWCNTs (bpy=2,2'-bipyridine, tatp=1,4,8,9-tetra-aza-triphenylene, BSA=bovine serum albumin, SWCNTs=single-walled carbon nanotubes) hybrid film is fabricated on an indium-tin oxide (ITO) electrode via one-step electrochemical co-assembly approach. BSA is inherently dispersive and therefore served as the linking mediator of SWCNTs, which facilitate the redox reactions of [Ru(bpy)(2)(tatp)](2+) employed as a reporter of BSA. The evidences from differential pulse voltammetry, cyclic voltammetry, scanning electron microscope, emission spectroscopy and fluorescence microscope reveal that the [Ru(bpy)(2)(tatp)](2+)-BSA-SWCNTs hybrid can be electrochemically co-assembled on the ITO electrode, showing two pairs of well-defined Ru(II)-based redox waves. Furthermore, the electrochemical co-assembly of the [Ru(bpy)(2)(tatp)](2+)-BSA-SWCNTs hybrid is found to be strongly dependent on the simultaneous presence of BSA and SWCNTs, indicating a good linear response to BSA in the range from 6 to 50mgL(-1). The results from this study provide an electrochemical co-assembly method for the development of non-redox protein biosensors.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).     

The Effects of Grafting of 2-Pyridyl to [Ru(bpy)2(Hpip)]2+ on Acid-Base and DNA-Binding Properties: Experimental and DFT Studies

Abstract

A new Ru(II) complex of [Ru(bpy)₂(Hppip)]²⁺ {bpy = 2,2′-bipyridine; Hppip = 2-(4-(pyridin- 2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} has been synthesized by grafting of 2-pyridyl to parent complex [Ru(bpy)₂(Hpip)]²⁺ {Hppip = 2-(4-phenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline}. The acid-base properties of [Ru(bpy)₂(Hppip)]²⁺ studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)₂(Hppip)]²⁺ that was driven by the protonation/deprotonation of the imidazolyl and the pyridyl moieties. The complex was demonstrated to be a DNA intercalator with an intrinsic DNA binding constant of (5.56 ± 0.2) × 10⁵ M^?1 in buffered 50 mM NaCl, as evidenced by UV-visible and luminescence titrations, reverse salt effect, DNA competitive binding with ethidium bromide, steady-state emission quenching by [Fe(CN)₆]^4-, DNA melting experiments and viscosity measurements. The density functional theory method was also used to calculate geometric/electronic structures of the complex in an effort to understand the DNA binding properties. All the studies indicated that the introduction of 2-pyridyl onto Hpip ligand is more favorable for extension of conjugate plane of the main ligand than that of phenyl, and for greatly enhanced ct-DNA binding affinity accordingly.     

Syntheses and DNA-binding studies of two ruthenium(II) complexes containing one ancillary ligand of bpy or phen: [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2

Two new ruthenium(II) complexes of [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)(2) (bpy=2,2'-bipyridine, phen=1,10-phenanthroline, pp[2,3]p=pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline) have been synthesized and characterized by elemental analysis and 1H NMR spectra. The calf thymus DNA-binding properties of the two complexes were investigated by UV-visible and emission spectroscopy, competitive binding experiments with ethidium bromide and viscosity measurements. The results indicate that the two complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA-binding constants of 3.08 x 10(6) and 6.53 x 10(6) M(-1) in buffered 50 mM NaCl, respectively, which are much larger than 6.9 x 10(5) M(-1) for [Ru(bpy)2(pp[2,3]p)](ClO4)2 containing two ancillary ligands of bpy.     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Synthesis, characterization, DNA-binding and photocleavage studies of [Ru(bpy)2(PPIP)]2+ and [Ru(phen)2(PPIP)]2+

A novel ligand 2-(4'-phenoxy-phenyl)imidazo[4,5-f][1,10]phenanthroline (PPIP) and its complexes [Ru(bpy)(2)(PPIP)](2+) (1) (bpy = 2,2'-bipyridine) and [Ru(phen)(2)(PPIP)](2+) (2) (phen = 1,10-phenanthroline) have been synthesized and characterized by mass spectroscopy, (1)H NMR and cyclic voltammetry. The interaction of two complexes with calf thymus DNA (CT-DNA) was investigated by spectroscopic and viscosity measurements. The results suggest that both complexes bind to DNA via an intercalative mode. Both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA under irradiated.     

Syntheses,characterization and DNA-binding studies of ruthenium(II) terpyridine complexes: [Ru(tpy)(PHBI)]2+ and [Ru(tpy)(PHNI)]2+

Two novel tridentate ligands, 2-(2-benzimidazole)-1,10-phenanthroline (PHBI) and 2-(2-naphthoimidazole)-1,10-phenanthroline (PHNI), and their heteroleptic complexes [Ru(tpy)(PHBI)](ClO(4))(2).2H(2)O (1) and [Ru(tpy)(PHNI)](ClO(4))(2).H(2)O (2) (tpy=2,2':6',2"-terpyridyl) have been synthesized and characterized by elemental analysis, mass spectra, 1H NMR, and electronic spectroscopy. The electrochemical behaviors of the two novel complexes were studied by cyclic voltammetry. The DNA-binding properties of the two complexes were investigated by spectroscopic methods and viscosity measurements. The results indicated that the two complexes interact with DNA in different binding modes. Complex 1 may bind to DNA via electrostatic interaction, while complex 2 binds to DNA by partial intercalation via the extended naphthyl ring into the base pairs of DNA.     

X-ray structure, redox and spectroscopic properties of ruthenium phosphine complexes [Ru(tpy)(bpy)(PPh3)] and [Ru(tpy)(bpy)(PCy3)]

The synthesis and crystal structures of two new phosphine ruthenium polypyridine complexes [Ru(tpy)(bpy)(PR₃)]²⁺ with R = Ph (1), Cy (2) are reported. Their geometrical parameters are intimately related to the electronic and steric properties of the phosphine ligand. Electrochemical and UV-Vis analyses showed the influence of the substituents of the coordinated phosphorus atom on the Ru^III/Ru^II potential and on the frontier orbitals energy gap. The results are discussed in terms of steric effects and net donor power of the phosphine ligands.     

Syntheses, characterization and DNA-binding study of chiral complexes DeltaDelta- and LambdaLambda-[Ru(bpy)2(bdptb)Ru(bpy)2]4+

A novel bridging ligand bdptb(2,2'-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4'-bipyridine) and it's chiral diruthenium(II) complex DeltaDelta- and LambdaLambda-[Ru(bpy)2(bdptb)Ru(bpy)2]4+ (Ru2) have been synthesized and characterized by electrospray mass spectra, 1H NMR, UV/visible and circular dichroism spectra. Binding behavior of these dimeric complexes with calf thymus DNA have been investigated by absorption spectra, viscosity measurements, equilibrium dialysis experiments. The electronic absorption spectra hypochromism at the metal-ligand charge transfer of the DeltaDelta- and LambdaLambda-enantiomer are 26.4%, and 40%, and bathochromism of 13.5, and 14 nm in sequence. Equilibrium dialysis experiments results show also the binding-DNA of LambdaLambda-enantiomer is stronger than DeltaDelta-enantiomer. The increasing amounts of the novel dimeric ruthenium(II) complexes on the relative viscosities of calf thymus DNA is smaller than that of the classic intercalators such as [Ru(bpy)2(dppz)]2+ and larger than that of the non-classic intercalators such as Delta-[Ru(phen)3]2+. The experiments suggest the dimeric ruthenium(II) complex may be bound to DNA by groove binder.     

Ru(bpy)(3)](2+) as a reference in transient absorption spectroscopy: differential absorption coefficients for formation of the long-lived (3)MLCT excited state

Transient absorption spectroscopy and other time-resolved methods are commonly used to study chemical reactions and biological processes induced by absorption of light. In order to scale the signal amplitude or to compare results obtained under different conditions, it is advisable to use a reference system, a standard of convenient and well-defined properties. Finding Tris(bipyridine)ruthenium(ii), [Ru(bpy)(3)](2+), a suitable candidate for a transient-absorption spectroscopy reference due to its favourable photochemical properties, we have determined accurate relative values of differential molar absorption coefficients (Δε) for light-induced formation of the metal-to-ligand charge transfer (MLCT) excited triplet state at several relevant wavelengths (wavelengths of commercially available lasers) in the UV and visible regions. We have also attempted to determine the absolute value of Δε close to the wavelength of maximum bleaching (～450 nm) and we propose to narrow down the interval of conceivable values for Δε(450) from the broad range of published values (-0.88 × 10(4) M(-1)cm(-1) to -1.36 × 10(4) M(-1)cm(-1)) to -1.1 × 10(4) M(-1)cm(-1)± 15%. Having ourselves successfully applied [Ru(bpy)(3)](2+) as a standard in a recent time-resolved study of enzymatic DNA repair, we would like to encourage other scientists to use this convenient tool as a reference in their future spectroscopic studies on time scales from picoseconds to hundreds of nanoseconds.     

Experimental and DFT studies on the DNA-binding trend and spectral properties of complexes [Ru(bpy)2L] (L = dmdpq, dpq, and dcdpq)

The trend in DNA-binding affinities and the spectral properties of a series of Ru(II) polypyridyl complexes, [Ru(bpy)₂(dmdpq)]²⁺ (1), [Ru(bpy)₂(dpq)]²⁺ (2), [Ru(bpy)₂(cndpq)]²⁺ (3) (bpy = 2,2′-bipyridine; dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline; dmdpq = di-methyl-dpq; dcdpq = di-cyano-dpq), have been experimentally and theoretically investigated. The DNA-binding constants K_b of the complexes were determined systematically with spectrophotometric titration. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out for these complexes. The experimental results show that these complexes bind to DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K_b is K_b(1) < K_b(2) ? K_b(3). The substituents on the intercalative ligands of the complexes play a very important role in the control of DNA-binding affinities of the complexes, in particular, the stronger electron-withdrawing substituent (-CN) on the intercalative ligand can greatly improve the DNA-binding property of the derivative complex. The trend in DNA-binding affinities as well as the spectral properties of metal-ligand charge-transition (¹MLCT) of this series of complexes can be reasonably explained by applying the DFT and TDDFT calculations and the frontier molecular orbital theory.     

Mechanism and biological implications of the NO release of cis-[Ru(bpy)2L(NO)](n+) complexes: a key role of physiological thiols

Nitric oxide (NO) has a critical role in several physiological and pathophysiological processes. In this paper, the reactions of the nitrosyl complexes of [Ru(bpy)₂L(NO)]ⁿ⁺ type, where L = SO₃²⁻ and imidazole and bpy = 2,2′-bipiridine, with cysteine and glutathione were studied. The reactions with cysteine and glutathione occurred through the formation of two sequential intermediates, previously described elsewhere, [Ru(bpy)₂L(NOSR)]ⁿ⁺ and [Ru(bpy)₂L(NOSR)₂] (SR = thiol) leading to the final products [Ru(bpy)₂L(H₂O)]ⁿ⁺ and free NO. The second order rate constant for the second step of this reaction was calculated for cysteine k₂(SR⁻) = (2.20 ± 0.12) × 10⁹ M^− 1 s^− 1 and k_2(RSH) = (154 ± 2) M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (1.30 ± 0.23) × 10⁹ M^− 1 s^− 1 and k₂(RSH) = (0.84 ± 0.02) M^− 1 s^− 1 for L = imidazole; while for glutathione they were k₂(SR⁻) = (6.70 ± 0.32) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 11.8 ± 0.3 M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (2.50 ± 0.36) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 0.32 ± 0.01 M^− 1 s^− 1 for L = imidazole. In all reactions it was possible to detect the release of NO from the complexes, which it is remarkably distinct from other ruthenium metallocompounds described elsewhere with just N₂O production. These results shine light on the possible key role of NO release mediated by physiological thiols in reaction with these metallonitrosyl ruthenium complexes.     

The two modes of binding of Ru(phen)(2)dppz(2+) to DNA: thermodynamic evidence and kinetic studies

The binding of Ru(phen)(2)dppz(2+) (dppz=dipyrido[3,2-a:2',3'-c]phenazine) to DNA was investigated at pH 7.0 and 25 degrees C using stopped-flow and spectrophotometric methods. Equilibrium measurements show that two modes of binding, whose characteristics depend on the polymer to dye ratio (C(P)/C(D)), are operative. The binding mode occurring for values of C(P)/C(D) higher than 3 exhibits positive cooperativity, which is confirmed by kinetic experiments. The reaction parameters are K=2 x 10(3)M(-1), omega=550, n=1, k(r)=(1.9+/-0.5) x 10(7)M(-1)s(-1) and k(d)=(9.5+/-2.5)x10(3)s(-1) at I=0.012 M. The results are discussed in terms of prevailing surface interaction with DNA grooves accompanied by partial intercalation of the dppz residue. The other binding mode becomes operative for C(P)/C(D)<3 and the equilibria analysis shows this is an ordinary intercalation mode (K=1.3 x 10(6) M(-1), n=1.5 at I=0.012 M and K=2 x 10(5) M(-1), n=1.2 at I=0.21 M). Similar behaviour is displayed by double-stranded poly(A).     

Synthesis, characterization, and DNA-binding of chiral complexes delta- and lambda-[Ru(bpy)2(pyip)]2+

New chiral Ru(II) complexes delta and lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) [(bpy = 2,2'-bipyridine; pyip = (2-(1-pyrenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline] were synthesized and characterized by elemental analysis, (1)H NMR, ESI-MS, IR, and CD spectra. Their DNA-binding properties were studied by means of UV-vis, emission spectra, CD spectra and viscosity measurements. A subtle but detectable difference was observed in the interaction of both enantiomer with CT-DNA. Spectroscopy experiments indicated that each of these complexes could interact with the DNA. The DNA-binding of the Delta-enantiomer was stronger than that of Lambda-enantiomer. DNA-viscosity experiments provided evidence that both Delta- and Lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) bound to DNA by intercalation. At the same time, the DNA-photocleavage properties of the complexes were investigated too. Under irradiation with UV light, Ru(II) complexes showed different efficiency of cleaving DNA.     

Synthesis, characterization, DNA-binding and cleavage studies of [Ru(bpy)2(actatp)]2+ and [Ru(phen)2(actatp)]2+ (actatp=acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence)

New ligand acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence (actatp) and its complexes [Ru(bpy)(2)(actatp)](ClO(4))(2).2H(2)O (1) (bpy=2,2'-bipyridine) and [Ru(phen)(2)(actatp)](ClO(4))(2).2H(2)O (2) (phen=1,10-phenanthroline) have been synthesized and characterized by UV-vis, 1H NMR, and mass spectra. The electrochemical behavior of the two complexes was studied by cyclic voltammetry. The interaction of the two complexes with calf thymus DNA has been investigated by spectrophotometric methods and viscosity measurements. The experimental results suggest that both complexes bind to DNA through an intercalative mode. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA are discussed. When irradiated at 302 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA.     

Interaction of Lambda- and Delta-[Ru(bpy)2(pbmz)](PF6)2 with the oligonucleotide duplex d(CGCGAATTCGCG)2

The interaction of the enantiomeric complexes Lambda- and Delta-[Ru(bpy)(2)(pbmz)](PF(6))(2) (bpy=2,2'-bipyridine, pbmz=2-(2'-pyridyl)benzimidazole) with the DNA duplex d(CGCGAATTCGCG)(2) was investigated by means of 2D NMR techniques. The synthesis of the enantiomers was based on the optically pure complexes Lambda- and Delta-[Ru(bpy)(2)(py)(2)](2+) and were characterized by CD and NMR spectroscopy. NMR data indicate that both enantiomers bind weakly to the oligonucleotide, approaching from the minor groove at the centre of the helix. The perturbation of the B-DNA conformation is minor with an apparent absence of enantioselectivity. Molecular modelling calculations in conjunction with the NOE data support the suggestion that more than one binding modes are present. The imidazole amine group of the pbmz ligand is probably hydrogen bonded to the DNA phosphodiesteric backbone at the AATT step, and this may provide an explanation for the diminished enantioselectivity observed.     

Visible light decomposition of ammonia to N2 with Ru(bpy)3(2+) sensitizer.

Visible light decomposition of aqueous NH3 to N2 was investigated using a photocatalyst aqueous solution based on molecular photoelectron relay systems of either sensitizer (tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+))/potassium peroxodisulfate(K(2)S(2)O(8)) or Ru(bpy)3(2+)/methylviologen dichloride(MV2+)/O2, capable of using visible light instead of UV-driven semiconductors such as TiO2. It was confirmed by using an in situ visible absorption spectral change under irradiation that the Ru(II) complex is oxidized to the Ru(III) complex by K(2)S(2)O(8), and that the Ru(III) complex formed is stable without NH3, while the added NH3 was oxidized by the Ru(III) complex to produce the Ru(II) complex. In the presence of 1 mM NH3 aqueous solution, the Ru(III) complex was the predominant species under the photostationary state, but in the presence of 100 mM NH3, Ru(II) predominated. Gas-chromatographic analysis of the gaseous phase in the presence of 8.1 M NH3 showed that the photochemical oxidation of ammonia yielded N2. It was also demonstrated by using the in situ visible absorption spectrum under irradiation of the NH3 (1 M)/Ru(bpy)3(2+) (0.1 mM)/MV2+ (10 mM) system under Ar that MV+* is accumulated, showing that NH3 works as an electron donor for MV+* accumulation with simultaneous formation of the oxidized product of ammonia ((NH3)ox) without producing N2. It was suggested that the reduced product (MV+*) and the oxidized product ((NH3)ox) are in a kind of dynamic equilibrium prohibiting further oxidation of (NH3)ox by Ru(bpy)3(3+) to N2. In the O2 atmosphere, the oxidation of MV+* to MV2+ takes place to accumulate Ru(III) complex, so that (NH3)ox was further oxidized to N2. The high activity of IrO2 as a cocatalyst in this system was demonstrated.     

Electrochemiluminescence of dipicolinic acid (DPA) and (bpy)(2)Ru(DPA)(+) (bpy = 2,2'-bipyridine).

The spectroscopic and electrochemiluminescence (ECL) properties of dipicolinic acid (DPA), (bpy)(2)Ru(2+) (bpy = 2,2'-bipyridine) and the species formed when DPA and (bpy)(2)Ru(2+) [abbreviated to (bpy)(2)Ru(DPA)(+)] are allowed to react are reported. The UV-Vis absorption maxima for (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) are 493 and 475 nm, respectively, indicating the in situ formation of a complex between DPA and (bpy)(2)Ru(2+). DPA, (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) display ECL upon oxidation in the presence of the oxidative-reductive co-reactant tri-n-propylamine (TPrA). The ECL of (bpy)(2)Ru(DPA)(+) is at least two-fold higher than either of the parent species. An ECL spectrum of (bpy)(2)Ru(DPA)(+) displays a peak maximum 40 nm red-shifted from the photoluminescence peak maximum, suggesting that the excited state formed electrochemically is different from that formed spectroscopically.     

DNA-binding and photocleavage studies of [Ru(phen)2(NMIP)]

A novel ligand 2′-(2″-nitro-3″,4″-methylenedioxyphenyl)imidazo[4′,5′-f][1,10]-phenanthroline (NMIP) and its complex [Ru(phen)₂(NMIP)]²⁺ have been synthesized and characterized by mass spectroscopy, ¹H NMR and cyclic voltammetry. Binding of the complex with calf thymus DNA (CT DNA) has been investigated by spectroscopic methods, viscosity and electrophoresis measurements. The experimental results indicate that [Ru(phen)₂(NMIP)]²⁺ binds to DNA via partial intercalative mode and the individual enantiomers of it bind to DNA in different rates. [Ru(phen)₂(NMIP)]²⁺ has also been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled Form I to the open circular Form II upon irradiation.