Study of the spectroscopic and electrochemical properties of tetraruthenated porphyrins by theoretical-experimental approach

The spectroscopic and electrochemical properties of two isomeric forms of the supramolecular species [μ-(H₂TPyP){Ru(bpy)₂Cl}₄]⁴⁺ (H₂TPyP = 5,10,15,20-tetra(3- or 4-pyridyl)porphyrin, bpy = 2,2′-bipyridine) have been compared and consistently interpreted with the aid of molecular orbital calculations. In these complexes, the HOMO and LUMO levels are predominantly localized in the ruthenium complexes and porphyrin ring, respectively. There is an extensive mixing of the wave functions of both components in other MOs, however, and their contributions are reflected in the spectroelectrochemical and spectroscopic behavior. For example, the electronic mixing is enough to allow the energy-transfer from the peripheral complexes to the porphyrin ring, as well as the appearance of a Ru^II(dπ) → H₄P(pπ*) charge-transfer band at 700 nm in the bis-protonated [μ-(H₄TPyP){Ru(bpy)₂Cl}₄]⁴⁺ species, showing the strong stabilization of the porphyrin LUMO levels.     

Synthesis,Structure, DNA‐Binding Properties,and Cytotoxicity of Ruthenium(II) Polypyridyl Complexes

Many ruthenium(II) complexes show high antitumor activities, and the in vitro antitumor activities are usually related to DNA binding. We designed and synthesized two Ru^II polypyridyl complexes, [Ru(dmp)₂(fpp)]²⁺ (dmp=2,9‐dimethyl‐1,10‐phenanthroline; fpp=2‐[3,4‐(difluoromethylenedioxy)phenyl]imidazo[4,5‐f] [1,10]phenanthroline and [Ru(phen)₂(fpp)]²⁺ (phen=1,10‐phenanthroline). The DNA‐binding properties of these complexes have been investigated by spectroscopic titration, DNA melting experiments, viscosity measurements, and photoactivated cleavage. The mechanism studies of photocleavage revealed that singlet oxygen (¹O₂) and superoxide anion radical (O$\rm{{_{2}^{{^\cdot} -}}}$ ) may play an important role in the photocleavage. The cytotoxicity of complexes 1 and 2 have been evaluated by MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) method; complex 2 shows slightly higher anticancer potency than 1 does against all the cell lines screened.     

Synthesis and structural characterisation of new cationic dinuclear ruthenium(II) thiolato complexes of the type [Ru2(η-arene)2(μ-p-S-C6H4-Br)3]

Dinuclear dichloro complexes [Ru(C₆H₆)Cl₂]₂, [Ru(p-MeC₆H₄ ⁱPr)Cl₂]₂, [Ru(1,2,4,5-C₆H₂Me₄)Cl₂]₂, and [Ru(C₆Me₆)Cl₂]₂ react in ethanol with p-bromothiophenol to give the corresponding cationic complexes [Ru₂(C₆H₆)₂(p-S-C₆H₄-Br)₃]⁺ (1), [Ru₂(p-MeC₆H₄ ⁱPr)₂(p-S-C₆H₄-Br)₃]⁺ (2), [Ru₂(1,2,4,5-C₆H₂Me₄)₂(p-S-C₆H₄-Br)₃]⁺ (3), and [Ru₂(C₆Me₆)₂(p-S-C₆H₄-Br)₃]⁺ (4), which can be isolated in quantitative yield as their chloride salts. X-ray structure analysis of these complexes shows that the nature of the arene ligand influences the folding of the p-S-C₆H₄-Br units. In 1, where the less hindered arene ligand is present, the three phenyl rings of the thiolato units are not constrained to a coplanar arrangement, whereas in 4 the C₆Me₆ forces the three phenyl rings to be in perfect planarity. Complexes 2 and 3 show an intermediary arrangement.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Electronic Effect of Substituents on the DNA Intercalation of Ruthenium(II)?Polypyridyl Complexes

Five ruthenium(II) complexes, i.e., [Ru(bpy)₂(TIP)]²⁺ (bpy=2,2′‐bipyridine; TIP=2‐thiophenimidazo[4,5‐f] [1,10]phenanthroline; 1 ), [Ru(bpy)₂(5‐NTIP)]²⁺ (5‐NTIP=2‐(5‐nitrothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 2 ), [Ru(bpy)₂(5‐MOTIP)]²⁺ (5‐MOTIP=2‐(5‐methoxythiophen)imidazo[4,5‐f] [1,10]phenanthroline; 3 ), [Ru(bpy)₂(5‐BTIP)]²⁺ (5‐BTIP=2‐(5‐bromothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 4 ), and [Ru(bpy)₂(4‐BTIP)]²⁺ (4‐BTIP=2‐(4‐bromothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 5 ), were synthesized and characterized by elemental analysis and UV/VIS, IR, and ¹H‐NMR spectroscopic methods. The photophysical and DNA‐binding properties were investigated by means of UV and fluorescence spectroscopic methods and viscosity measurements, respectively. The results suggest that all five complexes can bind to CT‐DNA with various binding strength. Complexes 2 and 3 showed the strongest and the weakest binding affinity, respectively, among these five complexes. Due to the substituent position of the Br‐atom in the ligand, complex 5 interacted stronger with CT‐DNA than complex 4 . The binding affinities of the complexes decreased in the order 2, 5, 4, 1 , and 3 .     

Electrochromic properties of mixed valence binuclear ruthenium complexes adsorbed on nanocrystalline SnO2 films

The electrochromic properties of two new mixed valence ruthenium complexes: K[(NC₅H₄CH₂PO₃H₂)Ru^III(NH₃)₄(NC)Ru^II(CN)₅] and K[(NC₅H₄PO₃H₂)Ru^III(NH₃)₄(NC)Ru^II(CN)₅], where phosphonic acid groups have been introduced at the pyridine ligand, have been studied in homogeneous solution and adsorbed on transparent nanocrystalline SnO₂ electrodes. These species exhibit a superior stability with respect to the previously studied, K[(NC₅H₄CO₂H)Ru^III(NH₃)₄NCRu^II(CN)₅] complex, showing negligible optical density changes after cycling 20 000 times the electrodes between −0.5 and 0.5 V versus SCE.     

Interactions of bis-[μ-chloro-chlorotricarbonylruthenium(II)] and poly-[μ-dichloro-dicarbonylruthenium(II)] with nucleosides

The interactions of dimeric complex bis-[μ-chloro-chlorotricarbonylruthenium(II)], [Ru(CO)₃Cl₂]₂, and the polymeric complex poly-[μ-dichlorodicarbonylruthenium(II)], [Ru(CO)₂Cl₂]_x, with nucleosides (Nucl) in a 1:1 Ru:Nucl molar ratio for the dimer and 1:2 Ru:Nucl for the polymer, resulted in formation of the monomeric mononucleoside [Ru(CO)₃(Nucl)Cl₂] and bis-nucleoside [Ru(CO)₂(Nucl)₂Cl₂] complexes, respectively. The dimer [Ru(CO)₃Cl₂]₂ also gave the ionic bis-nucleoside complexes [Ru(CO)₃(Nucl)₂Cl]Cl in the molar ratio 1:2 Ru:Nucl. The mononucleoside complexes are stable in solution while the bis-nucleoside complexes tend to lose one nucleoside in strong complexing solvents, probably by solvent substitution. The complexes [Ru(CO)₃(Nucl)Cl₂] and [Ru(CO)₂(Nucl)₂Cl₂] with one N(1)H ionizable imino proton undergo ionization in alkaline solution and the complexes [Ru(CO)₃(NuclH⁺)Cl] and [Ru(CO)₂(NuclH⁺)₂], respectively, were isolated. In these deprotonated complexes the nucleosides behave as bidentate ligands, while in the protonated ones they act as monodentate. All Complexes were characterized by elemental analyses and various spectroscopic methods.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.     

Diastereomeric bactericidal effect of Ru(phenanthroline)2dipyridophenazine

Metal susceptibility assays and spot plating were used to investigate the antimicrobial activity of enantiopure [Ru(phen)₂dppz]²⁺ (phen =1,10‐phenanthroline and dppz = dipyrido[3,2‐a:2´,3´‐c]phenazine) and [μ‐bidppz(phen)₄Ru₂]⁴⁺ (bidppz =11,11´‐bis(dipyrido[3,2‐a:2´,3´‐c]phenazinyl)), on Gram‐negative Escherichia coli and Gram‐positive Bacillus subtilis as bacterial models. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined for both complexes: while [μ‐bidppz(phen)₄Ru₂]⁴⁺ only showed a bactericidal effect at the highest concentrations tested, the antimicrobial activity of [Ru(phen)₂dppz]²⁺ against B. subtilis was comparable to that of tetracyline. In addition, the Δ‐enantiomer of [Ru(phen)₂dppz]²⁺ showed a 2‐fold higher bacteriostatic and bactericidal effect compared to the Λ‐enantiomer. This was in accordance with the enantiomers relative binding affinity for DNA, thus strongly indicating DNA binding as the mode of action.     

Syntheses and properties of new metal-carbon bonded heteroleptic complexes of ruthenium(II) containing terpyridine coligand

Reactions of 2-(arylazo)aniline, HL [H represents the dissociable protons upon orthometallation and HL is p-RC₆H₄N = NC₆H₄-NH₂; R = H for HL¹; CH₃ for HL² and Cl for HL³] with Ru(R₁-tpy)Cl₃ (where R₁-tpy is 4′-(R₁)-2,2′,6′′,2′′-terpyridine and R₁ = H or 4-N,N-dimethylaminophenyl or 4-methylphenyl) afford a group of complexes of type [Ru(L)(R₁-tpy)]·ClO₄ each of which contains C,N,N coordinated L⁻ as a tridentate ligand along with a terpyridine. Structure of one such complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, display characteristic ¹H NMR signals and intense dπ(Ru^II) → π∗(tpy) MLCT transitions in the visible region. Cyclic voltammetric studies on [Ru(L)(R₁-tpy)]·ClO₄ complexes show Ru(II)-Ru(III) oxidation within 0.63-0.67 V versus SCE.     

Spectroscopic and Structural Characterization,Enzyme Inhibitions,and Antioxidant Effects of New Ru(II) and Ni(II) Complexes of Schiff Base

The new complex compounds [RuLCl(p‐cymene)] ? 3H₂O and [NiL₂(H₂O)₂] ? 3H₂O (L: 1‐{4‐[(2‐hydroxy‐3‐methoxybenzylidene)amino]phenyl}ethanone) were prepared and characterized using FT‐IR, ¹H‐ and ¹³C‐NMR, mass spectroscopy, TGA, elemental analysis, X‐ray powder diffraction and magnetic moment techniques. Octahedral geometry for new Ni(II) and Ru(II) complexes was proposed. Thermal decomposition confirmed the existence of lattice and coordinated water molecule in the complexes. To determine the antioxidant properties of Schiff base ligand and its Ni(II), Ru(II) metal complexes, FRAP, CUPRAC, ABTS and DPPH methods of antioxidant assays were used. Moreover, enzyme inhibition of complexes was evaluated against carbonic anhydrase I and II isoenzymes (CA I and CA II) and acetylcholinesterase (AChE). For CA I and CA II, the best inhibition enzymes, was the Ni(II) complex with 62.98±18.41, 86.17±23.62 Ki values, whereas this inhibition effect showed ligand with 24.53±2.66 Ki value for the AChE enzyme.     

Synthesis and characterization of Ru(II) and Ru(III) complexes of diphenylphosphinoacetic acid and their interaction with small molecules

Complexes of Ru(II) and Ru(III) with the bidentate ligand diphenylphosphinoacetic acid (POH) are reported. The ligand POH reacts with RuCl₂(PPh₃)₃ in a 1:3 ratio to give a five-coordinate complex of composition Ru(PO)₂(POH) with complete displacement of PPh₃. In a 1:2 ratio however the complex Ru(PO)₂(PPh₃) is formed. The reaction of POH with RuCl₂(DMSO)₄ in a 2:1 ratio afforded a yellow complex of composition HRu(PO)₂Cl(DMSO). In a 3:1 ratio of POH to RuCl₂(DMSO)₄ however, the complex HRu(PO)₃ was obtained. Neutral complexes of the composition Ru(PO)₂Cl(AsPh₃) and Ru(PO)₃ were obtained by the reaction of RuCl₃(AsPh₃)₂·MeOH with POH in 1:2 and 1:3 mole ratios in acetone solution, respectively. A dimeric chloro bridged complex of composition [Ru(PO)₂Cl]₂ was obtained on reaction of RuCl₃3H₂O with POH in methanol. The complexes have been characterized on the basis of elemental analysis ¹H, ¹³C{¹H} and ³¹P{¹H} NMR, EPR and electrochemical studies.The square pyramidal complexes 1 and 2 undergo facile addition reactions with CO, H₂, PPh₃ and DMSO to form octahedral species. The redox potentials Ru^III/Ru^II of the complexes become more positive with an increase in the π-acidity of the ligand coordinated to the metal ion.     

DNA binding and bending by dinuclear complexes comprising ruthenium polypyridyl centres linked by a bis(pyridylimine) ligand

The interaction of enantiomerically pure dinuclear complexes of the form [Ru₂(L-L)₄L¹]⁴⁺ (where L-L = 2,2^′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L¹ = bis(pyridylimine) ligand ((C₅H₄N)CN(C₆H₄))₂CH₂)) with ct-DNA have been investigated by absorbance, circular dichroism, fluorescence displacement assays, thermal analysis, linear dichroism and gel electrophoresis. The complexes all bind more strongly to DNA than ethidium bromide, stabilise DNA and have a significant bending effect on DNA. The data for Δ,Δ-[Ru₂(bpy)₄L¹]⁴⁺ are consistent with it binding to DNA outside the grooves wrapping the DNA about it. By way of contrast the other complexes are groove-binders. The phen complexes provide a chemically and enantiomerically stable alternative to the DNA-coiling di-iron triple-helical cylinder previously studied. In contrast to the di-iron helicates, the phen complexes show DNA sequence effects with Δ,Δ-[Ru₂(phen)₄L¹]⁴⁺ binding preferentially to GC and Λ,Λ-[Ru₂(phen)₄L¹]⁴⁺ to AT.     

The synthesis and characterization of mixed ligand Ru(II) complexes with dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) and 2,3,5,6-tetra(2-pyridyl)-pyrazine (tppz)

The synthesis of the mixed ligand mono metallic [Ru(dpop′)(tppz)]²⁺ and bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ (dpop′ = dipyrido(2,3-a:3′,2′-j)phenazine; tppz = 2,3,5,6 tetra-(2-pyridyl)pyrazine) complexes is described. The [Ru(dpop′)(tppz)]²⁺ complex display an intense absorption at 518 nm which is assigned to a Ru(dπ) → dpop′ (π∗) MLCT transition, and at 447 nm which is assigned to a Ru(dπ) → tppz(π∗) MLCT transition. It undergoes emission at RT in CH₃CN with λ_em = 722 nm. The bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ complex shows a low energy absorption shoulder near 635 nm assigned to a Ru(dπ) → tppz(π∗) MLCT transition and an intense peak at 542 nm due to Ru(dπ) → dpop′ (π∗) MLCT transition. The bimetallic complex also emits at RT in CH₃CN with λ_em = 785 nm. Cyclic voltammetry shows reversible Ru^+2/+3 oxidations at 1.68 V for the monometallic complex and Ru^+2/+3 oxidation couples at +1.94 and +1.70 V for the bimetallic complex.     

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2′-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)₂(mppne)]²⁺ (bpy is 2, 2′–bipyridyl), [Ru(bpy)₂(mppae)]²⁺, [Ru(bpy)₂(mpppe)]²⁺, [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, ¹H NMR, fast-atom bombardment or electron-impact mass, UV–vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d _Ru→π*_sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d _Ru→π*_bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the ¹H NMR method. [Ru(bpy)₂(mppne)]²⁺, [Ru(bpy)₂(mppae)]²⁺ and [Ru(bpy)₂(mpppe)]²⁺ exhibit redox waves corresponding to the Ru^III/Ru^II couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH₃CN, 0.1 M tetrabutylammonium hexafluorophosphate)—corresponding voltammograms of [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)₂(mppne)]²⁺ and [Ru(bpy)₂(mppae)]²⁺ are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10⁵ to 10⁶ M⁻¹. Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)₂(mppne)]²⁺>[Ru(bpy)₂(mppae)]²⁺, although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)₂(sq)]⁺-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.Electronic Supplementary Material Supplementary material is available for this article at .     

Luminescent α-diimine complexes of ruthenium(II) containing scorpionate ligands

We describe the synthesis, characterization, and reactivity of several Ru(II) complexes of the type cis-L₂Ru(Z)ⁿ⁺, where L is an α-diimine [e.g. 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)] ligand and Z is a bis-coordinated scorpionate ligand such as tris-(1-pyrazolyl)methane (HC(pz)₃, PZ=1-pyrazolyl; n=2) or tetrakis-(1-pyrazolyl)borate anion (B(pz)₄ ⁻; n=1). The complexes each exhibit strong visible absorption assigned as a π*(L)←dπ(Ru) metal-to-ligand charge-transfer (MLCT) transition characteristic of the cis-L₂Ru²⁺ kernel. A corresponding MLCT excited state emission is observed in room temperature CH₃CN solution, although emission energies, lifetimes, and quantum yields are reduced relative to Ru(bpy)₃ ²⁺. Electronic spectra and cyclic voltammetry measurements indicate that the relative π-acceptor abilities of the coordinated Z are: Z=(1H-pyrazolyl)₂(pz)₂B(pz)₂<(pyridine)₂<(pz)₂CH(pz). Uncoordinated pz groups of cis-(bpy)₂Ru(pz)₂B(pz)₂ ⁺ can be reacted to form a sterically hindered, localized-valence (K_com33 l mol⁻¹) cis,cis-(bpy)₂Ru^II(pz)₂B(pz)₂Ru^II(bpy)₂ ³⁺ dimer. The dimer properties are interpreted by comparison to the known cis-(bpy)₂Ru^II(pz)₂Ru^II(bpy)₂ ²⁺ analog. The dimer is photoreactive and undergoes an asymmetrical photocleavage in CH₃CN (yielding cis-(bpy)₂Ru^III(pz)₂B(pz)₂ ²⁺ and cis-(bpy)₂Ru^II(CH₃CN)₂ ²⁺), similar to the corresponding thermal reaction observed for the mixed-valence cis-(bpy)₂Ru^II(pz)₂Ru^III(bpy)₂ ³⁺ system.     

Structure?Activity Relationship of Polypyridyl Ruthenium(II) Complexes as DNA Intercalators,DNA Photocleavage Reagents,and DNA Topoisomerase and RNA Polymerase Inhibitors

To investigate the relationship between the molecular structure and biological activity of polypyridyl Ru^II complexes, such as DNA binding, photocleavage ability, and DNA topoisomerase and RNA polymerase inhibition, six new [Ru(bpy)₂(dppz)]²⁺ (bpy=2,2′‐bipyridine; dppz=dipyrido[3,2‐a:2,′,3′‐c]phenazine) analogs have been synthesized and characterized by means of ¹H‐NMR spectroscopy, mass spectrometry, and elemental analysis. Interestingly, the biological properties of these complexes have been identified to be quite different via a series of experimental methods, such as spectral titration, DNA thermal denaturation, viscosity, and gel electrophoresis. To explain the experimental regularity and reveal the underlying mechanism of biological activity, the properties of energy levels and population of frontier molecular orbitals and excited‐state transitions of these complexes have been studied by density‐functional theory (DFT) and time‐depended DFT (TDDFT) calculations. The results suggest that DNA intercalative ligands with better planarity, greater hydrophobicity, and less steric hindrance are beneficial to the DNA intercalation and enzymatic inhibition of their complexes.     

New ruthenium complexes from Ru3(CO)12 and 6-Alkyl- or 6-Phenyl-2-hydroxypyridines

Trirutheniumdodecacarbonyl (Ru₃(CO)₁₂) reacts with 2-hydroxy-6-methylpyridine and with 2-hydroxy-5,6,7,8-tetrahydroquinoline in toluene to form centrosymmetric tetranuclear complexes of the type [Ru(η², μ-L)(CO)₂(μ₃-L)Ru(CO)₂]₂, where L is the respective (N,O)-pyridonate ligand (2 and 3). The structures of these complexes, which are almost insoluble in all common solvents, could be determined by single-crystal X-ray diffraction. Reaction of Ru₃(CO)₁₂ with 2-hydroxy-4,6-diphenylpyridine in methanol includes ortho-metallation at the phenyl ring, furnishing the dinuclear complex [Ru(κ²N,C-L)(CO)₂(μ-OCH₃)₂Ru(CO)₂ (κ²N,C-L)] (4), where L = (2-(6-hydroxy-4-phenylpyridin-2-yl)phenyl), according to an X-ray crystal structure determination.     

Synthesis and characterization of Pt(II) and Pt(II)/Ru(II) complexes with the bidentate bridging ligand dipyrido(2,3-a:3′,2′-h)phenazine (dpop)

Three new complexes [Pt(dpop)(Cl)₂], [(Cl)₂Pt(dpop)Pt(Cl)₂] and [(bpy)₂Ru(dpop)Pt(Cl)₂](PF₆)₂ (dpop = dipyrido(2,3-a:3′,2′-h)phenazine) were prepared and studied. The electronic absorption spectra of the complexes display Pt dπ → dpop π* and Ru dπ → dpop π* MLCT transitions at longer wavelengths than for previously reported similar complexes. Results of cyclic voltammograms show reversible dpop centered reductions while for the mixed metal [(bpy)₂Ru(dpop)Pt(Cl)₂]²⁺ an irreversible Pt(II) oxidative wave precedes the Ru(II) oxidation/reduction couple. Spectroelectrochemical results show that all oxidative and reductive processes are completely reversible. The [(Cl)₂Pt(dpop)Pt(Cl)₂] complex cleaves in solution with pseudo-first order kinetics resulting in loss of the Pt dπ → dpop π* MLCT transition at 545 nm.     

Combined arene ruthenium porphyrins as chemotherapeutics and photosensitizers for cancer therapy

Mononuclear 5-(4-pyridyl)-10,15,20-triphenylporphyrin and 5-(3-pyridyl)-10,15,20-triphenylporphyrin as well as tetranuclear 5,10,15,20-tetra(4-pyridyl)porphyrin (tetra-4-pp) and 5,10,15,20-tetra(3-pyridyl)porphyrin) (tetra-3-pp) arene ruthenium(II) derivatives (arene is C₆H₅Me or p-Pr ⁱ C₆H₄Me) were prepared and evaluated as potential dual photosensitizers and chemotherapeutics in human Me300 melanoma cells. In the absence of light, all tetranuclear complexes were cytotoxic (IC₅₀ ≤ 20 μM), while the mononuclear derivatives were not (IC₅₀ ≥ 100 μM). Kinetic studies of tritiated thymidine and tritiated leucine incorporations in cells exposed to a low concentration (5 μM) of tetranuclear p-cymene derivatives demonstrated a rapid inhibition of DNA synthesis, while protein synthesis was inhibited only later, suggesting arene ruthenium–DNA interactions as the initial cytotoxic process. All complexes exhibited phototoxicities toward melanoma cells when exposed to laser light of 652 nm. At low concentration (5 μM), LD₅₀ of the mononuclear derivatives was between 5 and 10 J/cm², while for the tetranuclear derivatives LD₅₀ was approximately 2.5 J/cm² for the [Ru₄(η⁶-arene)₄(tetra-4-pp)Cl₈] complexes and less than 0.5 J/cm² for the [Ru₄(η⁶-arene)₄(tetra-3-pp)Cl₈] complexes. Examination of cells under a fluorescence microscope revealed the [Ru₄(η⁶-arene)₄(tetra-4-pp)Cl₈] complexes as cytoplasmic aggregates, whereas the [Ru₄(η⁶-arene)₄(tetra-3-pp)Cl₈] complexes were homogenously dispersed in the cytoplasm. Thus, these complexes present a dual synergistic effect with good properties of both the arene ruthenium chemotherapeutics and the porphyrin photosensitizer.