Nickel, copper, and zinc centered ruthenium-substituted porphyrins: effect of transition metals on photoinduced DNA cleavage and photoinduced melanoma cell toxicity

Coordination of two [Ru(bipy)(2)Cl](+) moieties (where bipy = 2,2'-bipyridine) to the pyridyl nitrogens in the 5,10-positions of meso-5,10,15-(4-pyridyl)-20-(pentafluorophenyl)porphyrin gives the diruthenium porphyrin complex I. Insertion of nickel(II), copper(II), and zinc(II) into the porphyrin center gives the complexes II-IV, respectively. Electronic transitions associated with the ruthenium porphyrin include an intense Soret band and four less intense Q-bands in the visible region of the spectrum. An intense π-π* transition in the UV region associated with the bipyridyl groups and a metal-to-ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are also observed. A shift of the Soret band and collapse of the Q-bands into one band is observed upon insertion of the metal ions into the porphyrin center. Electrochemical properties associated with the complexes include a redox couple in the cathodic region attributed to the porphyrin and a redox couple in the anodic region due to the Ru(III/II) couple. DNA titrations of the complexes indicate that they interact strongly with DNA potentially through an intercalation mechanism. Irradiation of aqueous solutions of the complexes and supercoiled DNA at a 5:1 base pair to complex ratio with visible light above 400 nm shows nicking of DNA for the nickel(II) and copper(II) complexes and photocleavage of DNA for the zinc(II) complex. Cell studies with dermal skin (normal) fibroblast and melanoma cells indicate that the free base porphyrin(I) is toxic to both normal and melanoma cells, while the nickel(II) and copper(II) complexes, II and III, are non-toxic to both cell lines when irradiated with a tungsten lamp. The zinc(II) complex, IV, is non-toxic to normal cells but toxic to melanoma cells when irradiated under the same conditions.     

A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent: synthesis, characterization, DNA binding, and melanoma cell studies

When the new porphyrin 5,10-(4-pyridyl)-15,20-(pentafluorophenyl)porphyrin is reacted with 2 equiv of Ru(bipy)(2)Cl(2) (where bipy = 2,2'-bipyridine) formation of the target ruthenated porphyrin is achieved with 40% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrin Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dpi) to bipy(pi*) metal to ligand charge transfer (MLCT) band. The bipyridyl pi to pi* transition occurs at 295 nm. Cyclic voltammetry experiments reveal two single-electron redox couples in the cathodic region at E(1/2) = -0.80 and -1.18 V vs Ag/AgCl associated with the porphyrin. Two overlapping redox couples at E(1/2) = 0.83 V vs Ag/AgCl due to the Ru(III/II) centers is also observed. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give a K(b) = 7.6 x 10(5) M(-1) indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 400 nm), complete nicking of the DNA is observed. Cell studies show that the ruthenated porphyrin is more toxic to melanoma skin cells than to normal fibroblast cells. When irradiated with a 60 W tungsten lamp, the ruthenium porphyrin preferentially leads to apoptosis of the melanoma cells over the normal skin cells.     

Theoretical study on the electronic excitations of a porphyrin-polypyridyl ruthenium(II) photosensitizer

In this work, we investigated the UV-vis spectra of the [Ru(bipy)(2)(MPyTPP)Cl](+) (MPyTPP = 5-pyridyl-15,20,25-triphenylporphyrin) complex and its related species [Ru(bipy)(2)(py)Cl](+) and MPyTPP, by using time-dependent density functional theory and a set of functionals (B3LYP, M05, MPWB1K, and PBE0) in chloroform with the basis set 6-31++G(d,p) for nonmetal atoms and the pseudopotential LANL2DZ for Ru. Practically no geometrical changes are observed in the Ru environment when py ligand is replaced by MPyTPP. This replacement favors the electronic redistribution from bipy ligands to Ru, and from the metal to MPyTPP ligand, as indicated by NBO analysis. We found that M05 functional predicts very well the UV-vis spectra, as it shows a low deviation with respect to the experimental data, with a maximum error of 0.19 eV (11 nm). M05 theoretical electronic spectrum of [Ru(bipy)(2)(MPyTPP)Cl](+) complex indicates that the presence of the Ru complex does not alter Q porphyrin bands, while charge transfer bands from Ru to bipy and porphyrin ligands mixes up in the region close to the porphyrin Soret band. Theoretical analysis allows the decomposition of this broad experimental band into specific ones identifying the Soret band and new metal to ligand charge transfers toward porphyrin at 425 and 478 nm, which were not possible in none of the moieties MPyTPP and [Ru(bipy)(2)(Py)Cl](+) complex. In the UV region, the most intense intraligand band of bipy ligands becomes slightly blue-shifted both in the experimental and in the theoretical spectrum of [Ru(bipy)(2)(MPyTPP)Cl](+) complex compared to that in [Ru(bipy)(2)(py)Cl](+) complex. Some of the bands of [Ru(bipy)(2)(MPyTPP)Cl](+) showed in this theoretical study may have practical applications. That is the case for the band at 478 nm, with potential use in PDT, and those more energetic at 348 and 329 nm, which could help in the cleavage mechanism of DNA performed by this ruthenium complex.     

Preparation, characterization, and photophysical properties of Pt-M (M = Ru, Re) heteronuclear complexes with 1,10-phenanthrolineethynyl ligands

When 3-ethynyl-1,10-phenanthroline (HCCphen) or 3,8-diethynyl-1,10-phenanthroline (HCCphenCCH) is utilized as a bifunctional bridging ligand via stepwise molecular fabrication, a series of Pt-Ru and Pt-Re heteronuclear complexes composed of both platinum(II) terpyridyl acetylide chromophores and a Ru(phen)(bpy)2/Re(phen)(CO)3Cl subunit were prepared by complexation of one or two Pt((t)Bu3tpy)(2+) units to the mononuclear Ru(II) or Re(I) precursor through platinum acetylide sigma coordination. These Pt-Ru and Pt-Re complexes exhibit intense low-energy absorptions originating from both Pt- and Ru (Re)-based metal-to-ligand charge-transfer (MLCT) states in the near-visible region. They are strongly luminescent in both solid states and fluid solutions with a submicrosecond range of lifetimes and 0.27-6.58% of quantum yields in degassed acetonitrile. For the Pt-Ru heteronuclear complexes, effective intercomponent Pt --> Ru energy transfer takes place from the platinum(II) terpyridyl acetylide chromophores to the ruthenium(II) tris(diimine)-based emitters. In contrast, dual emission from both Pt- and Re-based (3)MLCT excited states occurs because of less efficient intercomponent Pt --> Re energy transfer in the Pt-Re heteronuclear complexes.     

Electrochemical oxidation of methanol using dppm-bridged Ru/Pd, Ru/Pt and Ru/Au catalysts

The electrochemical oxidation of methanol was carried out using a series of dppm-bridged Ru/Pd, Ru/Pt and Ru/Au heterobimetallic complexes as catalysts. The major oxidation products were formaldehyde dimethyl acetal (dimethoxymethane, DMM) and methyl formate (MF). The Ru/Pd and Ru/Pt bimetallic catalysts generally afforded lower product ratios of DMM/MF and higher current efficiencies than the Ru/Au catalysts. The Ru/Au bimetallics exhibited product ratios and current efficiencies similar to those obtained from the Ru mononuclear compound CpRu(PPh(3))(2)Cl. Increasing the methanol concentration afforded higher current efficiencies, while the addition of water to the samples shifted the product distribution toward the more highly oxidized product, MF.     

Isomeric [RuCl2(dmso)2(indazole)2] complexes: ruthenium(II)-mediated coupling reaction of acetonitrile with 1H-indazole

Reaction of the antitumor complex trans-[Ru(III)Cl4(Hind)2]- (Hind = indazole) with an excess of dimethyl sulfoxide (dmso) in acetone afforded the complex trans,trans,trans-[Ru(II)Cl2(dmso)2(Hind)2] (1). Two other isomeric compounds trans,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (2) and cis,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (3) have been obtained on refluxing cis-[Ru(II)Cl(2)(dmso)(4)] with 2 equiv. of indazole in ethanol and methanol, respectively. Isomers 1 and 2 react with acetonitrile yielding the complexes trans-[Ru(II)Cl2(dmso)(Hind){HN=C(Me)ind}].CH3CN (4.CH3CN) and trans,cis-[Ru(II)Cl2(dmso)2{HN=C(Me)ind}].H2O (5.H2O), respectively, containing a cyclic amidine ligand resulting from insertion of the acetonitrile C triple bond N group in the N1-H bond of the N2-coordinated indazole ligand in the nomenclature used for 1H-indazole. These are the first examples of the metal-assisted iminoacylation of indazole. The products isolated have been characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, electrospray mass-spectrometry, thermogravimetry, differential scanning calorimetry, 1H NMR spectroscopy, and solid-state 13C CP MAS NMR spectroscopy. The isomeric structures of 1-3 and the presence of a chelating amidine ligand in 4 and 5 have been confirmed by X-ray crystallography. The electrochemical behavior of 1-5 and the formation of 5 have been studied by cyclic voltammetry.     

Mixed-metal supramolecular complexes coupling phosphine-containing Ru(II) light absorbers to a reactive Pt(II) through polyazine bridging ligands

Supramolecular bimetallic Ru(II)/Pt(II) complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) and their synthons [(tpy)Ru(L)(BL)](n)()(+) (where L = Cl(-), CH(3)CN, or PEt(2)Ph; tpy = 2,2':6',2'-terpyridine; and BL = 2,2'-bipyrimidine (bpm) or 2,3-bis(2-pyridyl)pyrazine (dpp)) have been synthesized and studied by cyclic voltammetry, electronic absorption spectroscopy, mass spectral analysis, and (31)P NMR. The mixed-metal bimetallic complexes couple phosphine-containing Ru chromophores to a reactive Pt site. These complexes show how substitution of the monodentate ligand on the [(tpy)RuCl(BL)](+) synthons can tune the properties of these light absorbers (LA) and incorporate a (31)P NMR tag by addition of the PEt(2)Ph ligand. The redox potentials for the Ru(III/II) couples occur at values greater than 1.00 V versus the Ag/AgCl reference electrode and can be tuned to more positive potentials on going from Cl(-) to CH(3)CN or PEt(2)Ph (E(1/2) = 1.01, 1.55, and 1.56 V, respectively, for BL = bpm). The BL(0/-) couple at -1.03 (bpm) and -1.05 V (dpp) for [(tpy)Ru(PEt(2)Ph)(BL)](2+) shifts dramatically to more positive potentials upon the addition of the PtCl(2) moiety to -0.34 (bpm) and -0.50 V (dpp) for the [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) bridged complex. The lowest energy electronic absorption for these complexes is assigned as the Ru(d pi) --> BL(pi*) metal-to-ligand charge transfer (MLCT) transition. These MLCT transitions are tuned to higher energy in the monometallic synthons when Cl(-) is replaced by CH(3)CN or PEt(2)Ph (516, 452, and 450 nm, for BL = bpm, respectively) and to lower energy when Pt(II)Cl(2) is coordinated to the bridging ligand (560 and 506 nm for BL = bpm or dpp). This MLCT state displays a broad emission at room temperature for all the dpp systems with the [(tpy)Ru(PEt(2)Ph)(dpp)PtCl(2)](2+) system exhibiting an emission centered at 750 nm with a lifetime of 56 ns. These supramolecular complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) represent the covalent linkage of TAG-LA-BL-RM assembly (TAG = NMR active tag, RM = Pt(II) reactive metal).     

The synthesis of covalently linked tetraarylporphyrin dimers

A new and general synthesis of porphyrin dimers is described. The synthesis involves the reaction of dibromoalkanes with phenolic porphyrins, such as 5(4-hydroxyphenyl)-10,15,20-tritolylporphyrin, to form σ-bromoalkyl porphyrin ethers. The latter compounds are then reacted with a second phenolic porphyrin to give porphyrin dimers. A mixed metalloporphyrin dimer has been prepared which contains both V(IV) and Cu(II). The compounds have been examined spectroscopically. The free-base porphyrin dimers show a splitting of the intense Soret band. This is interpreted as indicative of weak singlet energy transfer between the covalently linked porphyrins.     

Comparative Study of Ru(bpz)32+Ru(bipy)32+and Ru(bpz)2CI2 as Photosensitizers of DNA Cleavage and Adduct Formation

Abstract— The efficiency of ruthenium complexes for photosensitizing DNA damage depends on the oxidizing character of their ligands. Here we report on the difference in behavior of tris(2.2'-bipyrazyl)ruthenium(II) (Ru[bpz]₃²+), tris(2,2′-bipyridyl)ruthenium(II) (Ru[bipy]₃²+) and cis-dichlorobis(2,2′-bipyrazyl)ruthenium(II) (Ru[bpz]₂Cl₂). Upon irradiation at 436 nm, Ru(bpz)₃²+was far less stable than Ru(bipy)₃²+. Ru(bpz)₃²+in phosphate buffer containing NaCl undergoes a photoanation reaction leading to the formation of Ru(bpz)₂Cl₂, as previously reported also in organic media. In the presence of phage φX174 DNA, Ru(bpz)₃²+photosensitized the formation of single strand breaks with an efficiency that was, at the beginning of irradiation, similar to that of Ru(bipy)₃²+. After 8 min of irradiation, the cleavage efficiency of Ru(bpz)₃²+reached a plateau that may correspond to its photode-composition. For the same conditions, Ru(bpz)₂Cl₂ did not induce DNA breakage. Scavenging experiments showed that, in the presence of oxygen, DNA cleavage induced by Ru(bpz)₃²+partly resulted from the formation of singlet oxygen and hydroxyl radical while in the absence of oxygen an additionnal mechanism involving electron transfer between the excited state of the ruthenium complex and DNA is proposed. The ICP measurement showed that Ru(bpz)₃²+and Ru(bpz)₂Cl₂ gave rise to covalent binding onto DNA in contrast with Ru(bipy)₃²+, which did not bind to DNA under the experimental conditions. The results are discussed with regard to the potential use of these photosensitizers in phototherapy.     

Physicochemical and photophysical studies on porphyrin-based donor-acceptor systems: effect of redox potentials on ultrafast electron-transfer dynamics

We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.     

Photophysical properties of long rodlike meso-meso-linked zinc(II) porphyrins investigated by time-resolved laser spectroscopic methods

The molecular design of directly meso-meso-linked porphyrin arrays as a new model of light-harvesting antenna as well as a molecular photonic wire was envisaged to bring the porphyrin units closer for rapid energy transfer. For this purpose, zinc(II) 5,15-bis(3,5-bis(octyloxy)phenyl)porphyrin (Z1) and its directly meso-meso-linked porphyrin arrays up to Z128 (Zn, n represents the number of porphyrins) were synthesized. The absorption spectra of these porphyrin arrays change in a systematic manner with an increase in the number of porphyrins; the high-energy Soret bands remain at nearly the same wavelength (413-414 nm), while the low-energy exciton split Soret bands are gradually red-shifted, resulting in a progressive increase in the exciton splitting energy. The exciton splitting is nicely correlated with the values of cos[pi/(N + 1)] according to Kasha's exciton coupling theory, providing a value of 4250 cm(-1) for the exciton coupling energy in the S(2) state. The increasing red-shifts for the Q-bands are rather modest. The fluorescence excitation anisotropy spectra of the porphyrin arrays show that the photoexcitation of the high-energy Soret bands exhibits a large angle difference between absorption and emission dipoles in contrast with the photoexcitation of the low-energy exciton split Soret and Q-bands. This result indicates that the high-energy Soret bands are characteristic of the summation of the individual monomeric transitions with its overall dipole moment deviated from the array chain direction, while the low-energy Soret bands result from the exciton splitting between the monomeric transition dipoles in line with the array chain direction. From the fluorescence quantum yields and fluorescence lifetime measurements, the radiative coherent length was estimated to be 6-8 porphyrin units in the porphyrin arrays. Ultrafast fluorescence decay measurements show that the S(2) --> S(1) internal conversion process occurs in less than 1 ps in the porphyrin arrays due to the existence of exciton split band as a ladder-type deactivation channel, while this process is relatively slow in Z1 (approximately 1.6 ps). The rate of this process seems to follow the energy gap law, which is mainly determined by the energy gap between the two Soret bands of the porphyrin arrays.     

Synthesis,structure, and spectroscopic,photochemical, redox,and catalytic properties of ruthenium(II) isomeric complexes containing dimethyl sulfoxide,chloro, and the dinucleating bis(2-pyridyl)pyrazole ligands

Two isomeric Ru(II) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2a, and cis(out),cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru(II)Cl(2)(Hbpp)(MeCN)(dmso)], 4. While the 1 e(-) oxidation of 2b or cis(out),cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3b, generates a stable product, the same process for 2a or trans,cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K(III)(O)(-->)(S) = 0.25 +/- 0.025, k(III)(O)(-->)(S) = 0.017 s(-1), and k(III)(S)(-->)(O) = 0.065 s(-1); K(II)(O)(-->)(S) = 6.45 x 10(9), k(II)(O)(-->)(S) = 0.132 s(-1), k(II)(S)(-->)(O) = 2.1 x 10(-11) s(-1)). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.     

Luminescent complexes of Re(I) and Ru(II) with appended macrocycle groups derived from 5,6-dihydroxyphenanthroline: cation and anion binding

A range of ligands in which a macrocyclic unit is fused to a 1,10-phenanthroline unit has been prepared starting from 5,6-dihydroxyphenanthroline. The ligands are L1 in which the pendant ligand is 18-crown-6; L2, in which the pendant ligand is benzo-24-crown-8; and L(3), in which the macrocycle contains two carboxamide units. Ligands L1 and L2 can bind Group 1 and 2 metal cations in their crown-ether cavities; L3 contains two H-bond (amide) donors and is suitable for anion-binding. Luminescent complexes of the form [Ru(bipy)2L]2+, [ReL(CO)3Cl] and [RuL(CN)4]2- were prepared and some were structurally characterised; their interactions with various guest species were investigated by luminescence and NMR spectroscopy. For complexes with the crown ethers (L1 and L2), binding of K+ was rather weak, but the electrostatic effect due to the charge on the host complex was clear with [RuL1(CN)4]2- binding K+ more strongly than [Ru(bipy)2L1]2+. Binding to the pendant crown ethers was much stronger with Ba2+, and both [ReL1(CO)3Cl] and [ReL2(CO)3Cl] showed substantial luminescence quenching in MeCN on addition of Ba2+ ions, with binding constants of 4.5 x 10(4) M(-1) for [ReL1(CO)3Cl]/Ba2+ and 1.3 x 10(5) M(-1) for [ReL2(CO)3Cl]/Ba2+. Complexes [Ru(bipy)2L3]2+ and [ReL3(CO)3Cl], due to their H-bond donor sites, showed binding of dihydrogenphosphate to the macrocycle. Whereas [ReL3(CO)3Cl] showed 1 : 1 binding with (H2PO4)- in dmso with a binding constant of 65 M(-1), [Ru(bipy)2L3]2+ showed 1 : 2 binding, with microscopic association constants of ca. 1 x 10(6) and 1.6 x 10(6) M(-1) in MeCN. The fact that K2 > K1 suggests a cooperative interaction whereby binding of the first anion makes binding of the second one easier to an extent which overcomes electrostatic effects, and a model for this is proposed which also accounts for the substantial increase in luminescence from [Ru(bipy)2L3]2+ (5-fold enhancement) when the second (H2PO4)- anion binds. Both [Ru(bipy)2L3]2+ and [ReL3(CO)3Cl] undergo complete luminescence quenching and a change in colour to near-black in the presence of (anhydrous) fluoride in MeCN, probably due to deprotonation of the carboxamide group. These changes are however irreversible on a long timescale and lead to slow decomposition.     

A trinuclear heterobimetallic Ru(II)/Pt(II) complex as a chemodosimeter selective for sulfhydryl-containing amino acids and peptides

A trinuclear heterobimetallic Ru(II)/Pt(II) complex, cis-{Ru(phen)2[CN-Pt(DMSO)Cl2]2} (phen = 1,10-phenanthroline), is able to function as a "switch-on" luminescent chemodosimeter for sulfhydryl-containing amino acids and peptides via specific binding of the amino acids/peptides with the Pt(II) centers and the subsequent cleavage of the Ru(II)-Pt(II) cyano-bridge.     

Reaction mechanism of Ru(II) piano‐stool complexes: Umbrella sampling QM/MM MD study

Biologically relevant interactions of piano‐stool ruthenium(II) complexes with ds‐DNA are studied in this article by hybrid quantum mechanics—molecular mechanics (QM/MM) computational technique. The whole reaction mechanism is divided into three phases: (i) hydration of the [Ru^II(η⁶‐benzene)(en)Cl]⁺ complex, (ii) monoadduct formation between the resulting aqua‐Ru(II) complex and N7 position of one of the guanines in the ds‐DNA oligomer, and (iii) formation of the intrastrand Ru(II) bridge (cross‐link) between two adjacent guanines. Free energy profiles of all the reactions are explored by QM/MM MD umbrella sampling approach where the Ru(II) complex and two guanines represent a quantum core, which is described by density functional theory methods. The combined QM/MM scheme is realized by our own software, which was developed to couple several quantum chemical programs (in this study Gaussian 09) and Amber 11 package. Calculated free energy barriers of the both ruthenium hydration and Ru(II)‐N7(G) DNA binding process are in good agreement with experimentally measured rate constants. Then, this method was used to study the possibility of cross‐link formation. One feasible pathway leading to Ru(II) guanine‐guanine cross‐link with synchronous releasing of the benzene ligand is predicted. The cross‐linking is an exergonic process with the energy barrier lower than for the monoadduct reaction of Ru(II) complex with ds‐DNA. © 2014 Wiley Periodicals, Inc.     

Synthesis, structure, and electrochemical properties of a family of 2-(arylazo)phenolate complexes of ruthenium with unusual C-C coupling and N=N cleavage

Reaction of 2-(4'-R-phenylazo)-4-methylphenols (R = OCH3, CH3, H, Cl, and NO2) with [Ru(dmso)(4)Cl2]affords a family of five ruthenium(III) complexes, containing a 2-(arylazo)phenolate ligand forming a six-membered chelate ring and a tetradentate ligand formed from two 2-(arylazo)phenols via an unusual C-C coupling linking the two ortho carbons of the phenyl rings in the arylazo fragment. A similar reaction with 2-(2'-methylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a similar complex, in which one 2-(2'-methylphenylazo)-4-methylphenolate ligand is coordinated forming a six-membered chelate ring, and the other two ligands have undergone the C-C coupling reaction, and the coupled species is coordinated as a tetradentate ligand forming a five-membered N,O-chelate ring, a nine-membered N,N-chelate ring, and another five-membered chelate ring. Reaction of 2-(2',6'-dimethylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl2] has afforded a complex in which two 2-(2',6'-dimethylphenylazo)-4-methylphenols are coordinated as bidentate N,O-donors forming five- and six-membered chelate rings, while the third one has undergone cleavage across the N=N bond, and the phenolate fragment, thus generated, remains coordinated to the metal center in the iminosemiquinonate form. Structures of four selected complexes have been determined by X-ray crystallography. The first six complexes are one-electron paramagnetic and show rhombic ESR spectra. The last complex is diamagnetic and shows characteristic 1H NMR signals. All the complexes show intense charge-transfer transitions in the visible region and a Ru(III)-Ru(IV) oxidation on the positive side of SCE and a Ru(III)-Ru(II) reduction on the negative side.     

2,2'-Dipyridylketone (dpk) as ancillary acceptor and reporter ligand in complexes [(dpk)(Cl)Ru(mu-tppz)Ru(Cl)(dpk)]n+ where tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine

The tppz-bridged diruthenium(II) complex [(dpk)(Cl)Ru(II)(mu-tppz)Ru(II)(Cl)(dpk)](ClO4)2, [2](ClO4)2, and mononuclear [(dpk)(Cl)Ru(II)(tppz)](ClO4), [1](ClO4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, dpk = 2,2'-dipyridylketone], have been synthesized. The 260 mV separation between successive one-electron oxidation couples in [2]2+ translates to a relatively small comproportionation constant, Kc, of 2.5 x 10(4) for the intermediate. It is shown how electrochemical data (E(ox), E(red), Kc) reflect the donor/acceptor effects of ancillary ligands L in a series of systems [(L)ClRu(mu-tppz)RuCl(L)]n, particularly the competition between L and tppz for electron density from the metal. According to EPR (g1 = 2.470, g2 = 2.195, and g3 = 1.873 at 4 K) the intermediate [2]3+ is a mixed-valent Ru(II)Ru(III) species which shows a rather narrow intervalence charge transfer (IVCT) band at 1800 nm (epsilon = 1500 M(-1) cm(-1)). The width at half-height (Deltanu(1/2)) of 700 cm(-1) of the IVCT band is much smaller than the calculated value of 3584 cm(-1), obtained by using the Hush formula Deltanu(1/2) = (2310E(op))(1/2) (E(op) = 5556 cm(-1), energy of the IVCT transition) which would be applicable to localized (Class II) mixed-valent Ru(II)Ru(III) systems. Valence delocalization in [2]3+ is supported by the uniform shift of the nu(C=O) band of the N,N'-coordinated dpk ligands from 1676 cm(-1) in the Ru(II)Ru(II) precursor to 1690 cm(-1) in the Ru(2.5)Ru(2.5) form, illustrating the use of the dpk acceptor to act as reporter ligand via the free but pi-conjugated organic carbonyl group. The apparent contradiction between the moderate value of Kc and the narrow IVCT band is being discussed considering "borderline" or "hybrid" "Class II-III" concepts of mixed-valency, as well as coordination aspects, i.e., the bis-tridentate nature of the pi-acceptor bridging ligand. Altogether, the complex ions [1]+ and [2]2+ display four and five successive reduction processes, respectively, involving both tppz- and dpk-based unoccupied pi orbitals. The one-electron reduced form [2]+ has been assigned as a tppz*- radical-anion-containing species which exhibits a free-radical-type EPR signal at 4K (g(parallel) = 2.002, g(perpendicular) = 1.994) and one moderately intense ligand-based low-energy band at 965 nm (epsilon = 1100 M(-1) cm(-1)).     

Cu、Ni、Ru、Pt对费托合成Fe催化剂的助剂作用研究

考察了Cu、Ni、Ru、Pt对费托合成Fe催化剂的助剂作用。XRD结果表明,加入Cu、Ni助剂对催化剂有一定的分散作用,而Ru、Pt影响不大。XPS结果表明,所有添加的助剂在催化剂表面均有一定程度的富集,且4种过渡金属助剂与Fe存在不同程度的电荷相互作用。H₂-TPR表明,Cu、Pt、Ru在催化剂还原过程中首先还原为金属态,进而能够明显促进催化剂的还原。CO-TPD表明,加入Cu、Pt、Ni助剂对CO的吸附活化有明显的促进作用。用固定床反应器对催化剂的费托反应性能进行了评价,反应结果表明,加入Ru、Ni、Pt、Cu会依次提高催化剂的反应活性,Pt、Cu、Ru、Ni助剂会依次使催化剂的CH₄选择性增加,并降低C₅₊的选择性。     

Electrochemical, spectroscopic, and photophysical properties of structurally diverse polyazine-bridged Ru(II),Pt(II) and Os(II),Ru(II),Pt(II) supramolecular motifs

Five new tetrametallic supramolecules of the motif [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) and three new trimetallic light absorbers [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) (TL = bpy = 2,2'-bipyridine or phen = 1,10-phenanthroline; M = Ru(II) or Os(II); BL = dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline, or bpm = 2,2'-bipyrimidine) were synthesized and their redox, spectroscopic, and photophysical properties investigated. The tetrametallic complexes couple a Pt(II)-based reactive metal center to Ru and/or Os light absorbers through two different polyazine BL to provide structural diversity and interesting resultant properties. The redox potential of the M(II/III) couple is modulated by M variation, with the terminal Ru(II/III) occurring at 1.58-1.61 V and terminal Os(II/III) couples at 1.07-1.18 V versus Ag/AgCl. [{(TL)(2)M(dpp)}(2)Ru(BL)](PF(6))(6) display terminal M(dπ)-based highest occupied molecular orbitals (HOMOs) with the dpp(π*)-based lowest unoccupied molecular orbital (LUMO) energy relatively unaffected by the nature of BL. The coupling of Pt to the BL results in orbital inversion with localization of the LUMO on the remote BL in the tetrametallic complexes, providing a lowest energy charge separated (CS) state with an oxidized terminal Ru or Os and spatially separated reduced BL. The complexes [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) and [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) efficiently absorb light throughout the UV and visible regions with intense metal-to-ligand charge transfer (MLCT) transitions in the visible at about 540 nm (M = Ru) and 560 nm (M = Os) (ε ≈ 33,000-42,000 M(-1) cm(-1)) and direct excitation to the spin-forbidden (3)MLCT excited state in the Os complexes about 720 nm. All the trimetallic and tetrametallic Ru-based supramolecular systems emit from the terminal Ru(dπ)→dpp(π*) (3)MLCT state, λ(max)(em) ≈ 750 nm. The tetrametallic systems display complex excited state dynamics with quenching of the (3)MLCT emission at room temperature to populate the lowest-lying (3)CS state population of the emissive (3)MLCT state.     

Irreversible and reversible formation of a [2]rotaxane containing platinum(II) complex with an N-alkyl bipyridinium ligand as the axis component

An N-Alkyl bipyridinium having a polymethylene chain and a bulky aryl group at the end, [4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2]Cl (Cl), reacts with K[PtCl3(dmso)] to produce the Pt complex with the N-alkyl bipyridinium ligand [Cl2(dmso)Pt{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}][PtCl3(dmso)] as a 6:1 mixture of trans and cis isomers ([trans-][PtCl3(dmso)] and [cis-][PtCl3(dmso)]). Addition of alpha-cyclodextrin (alpha-CD) to a solution of Cl in dmso-d6/D2O (3:1) forms [2]pseudorotaxane [{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}.(alpha-CD)]Cl (Cl) which is equilibrated with Cl and alpha-CD in solution. The reaction of K[PtCl3(dmso)] with Cl affords the [2]rotaxane [trans-Cl2(dmso)Pt{4,4'-bpy-N-(CH2)10OC6H(3)-3,5-tBu2}.(alpha-CD)][PtCl3(dmso)] ([trans-][PtCl3(dmso)]) which contains alpha-CD and [trans-][PtCl3(dmso)] as the cyclic and axis components, respectively. Dissolution of a mixture of [trans-][PtCl3(dmso)], [cis-][PtCl3(dmso)] and alpha-CD in dmso-d6/D2O (3:1) forms a mixture of the rotaxanes containing [trans--d6][PtCl3(dmso)] and [cis--d6][PtCl3(dmso)]. The reaction involves partial dissociation of the bipyridinium from Pt of [trans-][PtCl3(dmso)] or [cis-][PtCl3(dmso)] to yield [PtCl3(dmso)] and formation of pseudorotaxane with alpha-CD, followed by recoordination of the bipyridinium to the Pt. The reversible formation of the Pt-N coordination bond is studied in a dmso solution of the N-butyl compounds [trans-Cl2(dmso)Pt{4,4'-bpy-N-nBu}][PtCl3(dmso)] ([trans-][PtCl3(dmso)]).