Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)](n+) (trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline)

Nitrosyl complexes with {Ru-NO} (6) and {Ru-NO} (7) configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] ( n+ ) [trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5- f]1,10-phenanthroline] as the perchlorate salts [ 4](ClO 4) 3 and [ 4](ClO 4) 2, respectively. Single crystals of protonated material [ 4-H (+)](ClO 4) 4.2H 2O reveal a Ru-N-O bond angle of 176.1(7) degrees and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of [ 4] (3+) in the form of [Ru(trpy)(L)(Cl)](ClO 4).4.5H 2O and [Ru(trpy)(L-H)(CH 3CN)](ClO 4) 3.H 2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from [ 4] (3+) (1953 cm (-1)) to [ 4] (2+) (1654 cm (-1)). The Ru (II)-NO* in isolated or electrogenerated [ 4] (2+) exhibits an EPR spectrum with g 1 = 2.020, g 2 = 1.995, and g 3 = 1.884 in CH 3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); (14)N (NO) hyperfine splitting ( A 2 = 30 G) was also observed. The plot of nu(NO) versus E degrees ({RuNO} (6) --> {RuNO} (7)) for 12 analogous complexes [Ru(trpy)(L')(NO)] ( n+ ) exhibits a linear trend. The electrophilic Ru-NO (+) species [ 4] (3+) is transformed to the corresponding Ru-NO 2 (-) system in the presence of OH (-) with k = 2.02 x 10 (-4) s (-1) at 303 K. In the presence of a steady flow of dioxygen gas, the Ru (II)-NO* state in [ 4] (2+) oxidizes to [ 4] (3+) through an associatively activated pathway (Delta S++ = -190.4 J K (-1) M (-1)) with a rate constant ( k [s (-1)]) of 5.33 x 10 (-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)] (2+) ([ 4] (2+)) undergoes facile photorelease of NO ( k NO = 2.0 x 10 (-1) min (-1) and t 1/2 approximately 3.5 min) with the concomitant formation of the solvate [Ru (II)(trpy)(L)(CH 3CN)] (2+) [ 2'] (2+). The photoreleased NO can be trapped as an Mb-NO adduct.     

Structural, electronic, and acid/base properties of [Ru(bpy)2(bpy(OH)2)]2+ (bpy = 2,2'-bipyridine, bpy(OH)2 = 4,4'-dihydroxy-2,2'-bipyridine)

We have synthesized the complex [Ru(bpy)(2)(bpy(OH)(2))](2+) (bpy =2,2'-bipyridine, bpy(OH)(2) = 4,4'-dihydroxy-2,2'-bipyridine). Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of the complex, with particular attention paid toward the effects of deprotonation on these properties. The most distinguishing feature observed in the X-ray structural data is a shortening of the CO bond lengths in the modified ligand upon deprotonation. Similar results are also observed in the computational studies as the CO bond becomes double bond in character after deprotonating the complex. Electrochemically, the hydroxy-modified bipyridyl ligand plays a significant role in the redox properties of the complex. When protonated, the bpy(OH)(2) ligand undergoes irreversible reduction processes; however, when deprotonated, reduction of the substituted ligand is no longer observed, and several new irreversible oxidation processes associated with the modified ligand arise. pH studies indicate [Ru(bpy)(2)(bpy(OH)(2))](2+) has two distinct deprotonations at pK(a1) = 2.7 and pK(a2) = 5.8. The protonated [Ru(bpy)(2)(bpy(OH)(2))](2+) complex has a characteristic UV/Visible absorption spectrum similar to the well-studied complex [Ru(bpy)(3)](2+) with bands arising from Metal-to-Ligand Charge Transfer (MLCT) transitions. When the complex is deprotonated, the absorption spectrum is altered significantly and becomes heavily solvent dependent. Computational methods indicate that the deprotonated bpy(O(-))(2) ligand mixes heavily with the metal d orbitals leading to a new absorption manifold. The transitions in the complex have been assigned as mixed Metal-Ligand to Ligand Charge Transfer (MLLCT).     

On the role of the bridging dicyanamidobenzene ligand in a new binuclear ruthenium complex: [{Ru(tpy)(thd)}2(mu-dicyd)][PF6] with tpy = 2,2':6',2' '-terpyridine and thd = 2,2,6,6-tetramethyl-3,5-heptanedione

The dicyanamidobenzene-bridge diruthenium complex [{Ru(tpy)(thd)}(2)(mu-dicyd)][PF(6)] ([3][PF(6)]) (dicyd = 1,4-dicyanamidobenzene, tpy = 2,2':6',2' '-terpyridine, thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and its mononuclear counterpart [Ru(tpy)(thd)(Ipcyd)] (2) [Ipcyd = 4-iodophenylcyanamide anion (Ipcyd(-))] were synthesized and fully characterized. Cyclic voltammetry of 3 showed the presence of four reversible one-electron redox couples. UV-vis-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. The stable starting dinuclear complex 3(+) is found to be a ligand-centered anion radical as shown by EPR spectroscopy, magnetic susceptibility measurements, and DFT calculations. Oxidation of 3(+) to 3(2+) led to an EPR silent system due to substantial intramolecular antiferromagnetic interaction of the electron spins carried by the low spin ruthenium(III) atom and the bridging anion radical dicyanamido (dicyd(*)(-)), an observation which was supported by UV-vis-NIR, X-ray structure, and DFT calculations. Complex 3(3+) presented an EPR spectra consistent with a total effective spin S = (1)/(2) issued from an antiferromagnetic interaction of electron spins carried by two low spin ruthenium(III) atoms and the bridging anion radical dicyd(*)(-) in accordance with UV-vis-NIR. This study shows that the dicyanamidobenzene bridging ligand has indubitably a noninnocent behavior.     

Isomeric complexes of [RuII(trpy)(L)Cl] (trpy=2,2':6',2'-terpyridine and HL=quinaldic acid): preference of isomeric structural form in catalytic chemoselective epoxidation process

The present work deals with the isomeric complexes of the molecular composition [Ru(II)(trpy)(L)Cl] in 1 and 2 (trpy = 2,2':6',2'-terpyridine, L = deprotonated form of quinaldic acid, HL). Isomeric identities of 1 and 2 have been established by their single-crystal X-ray structures, which reveal that under the meridional configuration of trpy, O(-) and N donors of the unsymmetrical L are in trans, cis and cis, trans configurations, respectively, with respect to the Ru-Cl bond. Compounds 1 and 2 exhibit appreciable differences in bond distances involving Ru-Cl and Ru-O1/Ru-N1 associated with L on the basis of their isomeric structural features. In relation to isomer 2, the isomeric complex 1 exhibits a slightly lower Ru(II)-Ru(III) oxidation potential [0.35 (1), 0.38 (2) V versus SCE in CH(3)CN] as well as lower energy MLCT transitions [559 nm and 417 nm (1) and 533 nm and 378 nm (2)]. This has also been reflected in the DFT calculation where a lower HOMO-LUMO gap of 2.59 eV in 1 compared to 2.71 eV in 2 is found. The isomeric structural effect in 1 and 2 has also been prominent in their (1)H NMR spectral profiles. The relatively longer Ru-Cl bond in 1 (2.408(2) ?) as compared to 2 (2.3813(9) ?) due to the trans effect of the anionic O(-) of coordinated L makes it labile, which in turn facilitates the transformation of [Ru(II)(trpy)(L)(Cl)] (1) to the solvate species, [Ru(II)(trpy)(L)(CH(3)CN)](Cl) (1a) while crystallizing 1 from the coordinating CH(3)CN solvent. The formation of 1a has been authenticated by its single-crystal X-ray structure. However, no such exchange of "Cl(-)" by the solvent molecule occurs in 2 during the crystallization process from the coordinating CH(3)CN solvent. The labile Ru-Cl bond in 1 makes it a much superior precatalyst for the epoxidation of alkene functionalities. Compound 1 is found to function as an excellent precatalyst for the epoxidation of a wide variety of alkene functionalities under environmentally benign conditions using H(2)O(2) as an oxidant and EtOH as a solvent, while isomer 2 remains almost ineffective under identical reaction conditions. The remarkable differences in catalytic performances of 1 and 2 based on their isomeric structural aspects have been addressed.     

Stepwise synthesis of [Ru(trpy)(L)(X)](n+) (trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; X = Cl-, H2O, NO2-, NO+, O2-). Crystal structure, spectral, electron-transfer, and photophysical aspects

Ruthenium-terpyridine complexes incorporating a 2,2'-dipyridylamine ancillary ligand [Ru(II)(trpy)(L)(X)](ClO(4))(n) [trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; and X = Cl(-), n = 1 (1); X = H(2)O, n = 2 (2); X = NO(2)(-), n = 1 (3); X = NO(+), n = 3 (4)] were synthesized in a stepwise manner starting from Ru(III)(trpy)(Cl)(3). The single-crystal X-ray structures of all of the four members (1-4) were determined. The Ru(III)/Ru(II) couple of 1 and 3 appeared at 0.64 and 0.88 V versus the saturated calomel electrode in acetonitrile. The aqua complex 2 exhibited a metal-based couple at 0.48 V in water, and the potential increased linearly with the decrease in pH. The electron-proton content of the redox process over the pH range of 6.8-1.0 was calculated to be a 2e(-)/1H(+) process. However, the chemical oxidation of 2 by an aq Ce(IV) solution in 1 N H(2)SO(4) led to the direct formation of corresponding oxo species [Ru(IV)(trpy)(L)(O)](2+) via the concerted 2e(-)/2H(+) oxidation process. The two successive reductions of the coordinated nitrosyl function of 4 appeared at +0.34 and -0.34 V corresponding to Ru(II)-NO(+) --> Ru(II)-NO* and Ru(II)-NO* --> Ru(II)-NO(-), respectively. The one-electron-reduced Ru(II)-NO* species exhibited a free-radical electron paramagnetic resonance signal at g = 1.990 with nitrogen hyperfine structures at 77 K. The NO stretching frequency of 4 (1945 cm(-1)) was shifted to 1830 cm(-1) in the case of [Ru(II)(trpy)(L)(NO*)](2+). In aqueous solution, the nitrosyl complex 4 slowly transformed to the nitro derivative 3 with the pseudo-first-order rate constant of k(298)/s(-1) = 1.7 x 10(-4). The chloro complex 1 exhibited a dual luminescence at 650 and 715 nm with excited-state lifetimes of 6 and 1 micros, respectively.     

Enantiospecific synthesis of delta and lambda [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine,ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate): (1)H and (13)C NMR studies and X-ray structure determination of rac-[Ru(bpy)(2)quo]PF(6)

In this paper, we describe the enantiospecific synthesis and the complete characterization of the two hexacoordinated ruthenium(II) monocations [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine, ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate) in their enantiomeric Delta and Lambda forms. The corresponding enantiomeric excesses (ee's) are determined by (1)H NMR using pure Delta-Trisphat (tris(tetrachlorobenzenedialato)phosphate(V) anion) as a chiral (1)H NMR shift reagent. A complete (1)H and (13)C NMR study has been carried out on rac-[Ru(bpy)(2)ppy]PF(6) and rac-[Ru(bpy)(2)quo]PF(6). Additionally, the X-ray molecular structure of rac-[Ru(bpy)(2)quo]PF(6) is reported; this latter species crystallizes in the monoclinic C2/c space group (a = 22.079 A, b = 16.874 A, c = 17.533 A, alpha = 90 degrees, beta = 109.08 degrees, gamma = 90 degrees ).     

Photobiological impact of [{(bpy)2Ru(dpp)}2RhCl2]Cl5 and [{(bpy)2Os(dpp)}2RhCl2]Cl5 [bpy=2,2'-bipyridine; dpp=2,3-Bis(2-pyridyl)pyrazine] on vero cells

The in vitro photobiology of the supramolecular complexes [{(bpy)2Ru(dpp)}2RhCl2]Cl5 and [{(bpy)2Os(dpp)}2RhCl2]Cl5 [bpy=2,2'-bipyridine; dpp=2,3-bis(2-pyridyl)pyrazine] with African green monkey kidney epithelial (Vero) cells was investigated. Previously, the complexes have been shown to photocleave DNA in the presence or absence of O2. Vero cell replication was uninhibited for cells exposed to the metal complex but protected from light. Vero cells that were exposed to metal complex, rinsed, and illuminated with >460 nm light showed a replication response that was metal complex concentration-dependent. Vero cells exposed to 3.0-120 microM [{(bpy)2Ru(dpp)}2RhCl2]Cl5 and illuminated showed inhibition of cell growth, with evidence of cell death seen for complex concentrations>or=10 microM. Cells exposed to [{(bpy)2Os(dpp)}2RhCl2]Cl5 at concentrations of 5.5-110 microM, rinsed, and illuminated showed only inhibition of cell growth. The impact of [{(bpy)2Ru(dpp)}2RhCl2]Cl5 and [{(bpy)2Os(dpp)}2RhCl2]Cl5 on cell growth following illumination shows the promise of this new structural motif as a photodynamic therapy agent.     

DNA-binding and physical studies of Pt(4'-NR2-trpy)CN+ systems (trpy = 2,2':6',2'-terpyridine)

This paper focuses on DNA-binding interactions exhibited by Pt(dma-T)CN(+), where dma-T denotes 4'-dimethylamino-2,2':6',2'-terpyridine, and includes complementary studies of the corresponding pyrr-T complex, where pyrr-T denotes 4'-(N-pyrrolidinyl)-2,2':6',2'-terpyridine. The chromophores are useful for understanding the interesting and rather intricate DNA-binding interactions exhibited by these and related systems. One reason is that the terpyridine ligands employed provide intense visible absorption and enhanced photoluminescence signals. Incorporating cyanide as a coligand further aids analysis by suppressing covalent binding. Physical methods utilized include X-ray crystallography for structures of the individual inorganic complexes. Viscometry as well as spectral studies of the absorbance, emission, and circular dichroism (CD) yield information about interactions with a variety of DNA hosts. Although there is no sign of covalent binding under the conditions used, most hosts exhibit two phases of uptake. Under conditions of high loading (low base-pair-to-platinum ratios), the dma-T complex preferentially binds externally and aggregates on the surface of the host, except for the comparatively rigid host [poly(dG-dC)]2. Characteristic signs of the aggregated form include a bisignate CD signal in the charge-transfer region of the spectrum and strongly bathochromically shifted emission. When excess DNA is present, however, the complex shifts to intercalative binding, preferentially next to G[triple bond]C base pairs if available. Once the complex internalizes into DNA it becomes virtually immune to quenching by O2 or solvent, and the emission lifetime extends to 11 micros when [poly(dI-dC)]2 is the host. On the other hand, the host itself becomes a potent quenching agent when G[triple bond]C base pairs are present because of the reducing strength of guanine residues.     

联吡啶和邻菲咯啉混配的钌配合物的核磁共振氢谱分析

合成了Ru(bpy)2(phen)(PF6)2 和Ru(bpy)(phen)2(PF6)2 (bpy和phen分别为2,2′-联吡啶和1,10 -邻菲咯啉)两种电化学发光物质,以 1HNMR谱研究这两种配合物的立体结构,利用 1H - 1HCOSY(同核相关谱)核磁共振技术详细分析并归属了它们的氢谱峰。     

Magnetic coupling through the carbon skeleton of malonate in two polymorphs of ([Cu(bpy)(H2O)][Cu(bpy)(mal)(H2O)])(ClO4)2 (H2mal = malonic acid; bpy = 2,2'-bipyridine)

Two polymorphic malonato-bridged copper(II) complexes of formula ([Cu(bpy)(H2O)][Cu(bpy)(mal)(H2O)])-(ClO4)2 (1 and 2) (bpy = 2,2'-bipyridine and mal = malonate dianion) have been prepared and their structures solved by X-ray diffraction methods. Compound 1 crystallizes in the monoclinic space group P2(1)/a, with a = 23.743(3) A, b = 9.7522(5) A, c = 27.731(2) A, beta = 114.580(10) degrees, and Z = 4. Compound 2 crystallizes in the orthorhombic space group Pbcn, with a = 23.700(5) A, b = 25.162(5) A, c = 9.693(5) A, and Z = 4. The structures of 1 and 2 are made up of uncoordinated perchlorate anions and malonate-bridged zigzag copper(II) chains grouped in an isosceles triangle running parallel to the b (1) and c (2) axes. These chains are built by a [Cu(bpy)(mal)(H2O)] unit acting as bis-monodentate ligand toward two [Cu(bpy)(H2O)] adjacent units through its OCCCO skeleton in an anti-anti conformation, whereas the OCO carboxylate bridges exhibit the anti-syn conformation. Compounds 1 and 2 contain four crystallographically independent copper(II) atoms, but the environment of all of them is distorted square pyramidal: the axial position is occupied by a water molecule, whereas the equatorial plane is formed by a chelating bpy and either a bidentate malonate or two carboxylate oxygens from two malonate groups. The equatorial Cu-O(mal) (1.911(4)-1.978(4) (1) and 1.897(5)-1.991(4) A (2)) and Cu-N(bpy) (1.983(4)-2.008(5) (1) and 1.971(6)-2.007(6) A (2)) bonds are somewhat shorter than the axial Cu-O(w) one (2.257(5)-2.524(5) (1) and 2.236(5)-2.505(6) A (2)). The angles subtended at the copper atom by the chelating bpy vary in the ranges 80.9(2)-81.8(2) degrees (1) and 80.4(2)-82.1(2) degrees (2), values which are somewhat smaller than those of the chelating malonate (80.4(2)-82.1(2) degrees (1) and 93.0(2)-93.6(2) degrees (2)). The intrachain copper-copper separations through the OCCCO fragment are 8.227(1) (1) and 8.206(2) A (2), whereas those through the OCO bridging unit are 4.579(1)-5.043(1) (1) and 4.572(2)-5.040(2) A (2). The magnetic behavior of 1 and 2 in the temperature range 2.0-290 K is very close, and it corresponds to an overall ferromagnetic coupling, the chi MT versus T curve exhibiting a maximum at 18 K. The analysis of the magnetic data through a numerical expression derived for the real topology of 1 and 2, that is, chains of isosceles triangles with two intrachain exchange pathways J1 (exchange coupling through the OCO carboxylate) and J2 (exchange coupling through the OCCCO malonate), indicates the occurrence of ferro- (J1 = +4.6 cm-1) and antiferromagnetic couplings (J2 = -4.2 cm-1). The magnetic coupling through these exchange pathways is further analyzed and substantiated by density functional theory calculations on a malonate-bridged trinuclear copper(II) model system.     

Experimental and theoretical evaluation of the charge distribution over the ruthenium and dioxolene framework of [Ru(OAc)(dioxolene)(terpy)] (terpy = 2,2':6',2' '-terpyridine) depending on the substituents

A series of ruthenium complexes [Ru(OAc)(dioxolene)(terpy)] having various substituents on the dioxolene ligand (dioxolene = 3,5-t-Bu2C6H2O2 (1), 4-t-BuC6H3O2 (2), 4-ClC6H3O2 (3), 3,5-Cl2C6H2O2 (4), Cl4C6O2 (5); terpy = 2,2':6'2' '-terpyridine) were prepared. EPR spectra of these complexes in glassy frozen solutions (CH2Cl2:MeOH = 95:5, v/v) at 20 K showed anisotropic signals with g tensor components 2.242 > g1 > 2.104, 2.097 > g2 > 2.042, and 1.951 > g3 > 1.846. An anisotropic value, Deltag = g1 - g3, and an isotropic g value, g = [(g1(2) + g2(2) + g3(2))/3]1/2, increase in the order 1 < 2 < 3 < 4 < 5. The resonance between the Ru(II)(sq) (sq = semiquinone) and Ru(III)(cat) (cat = catecholato) frameworks shifts to the latter with an increase of the number of electron-withdrawing substituents on the dioxolene ligand. DFT calculations of 1, 2, 3, and 5 also support the increase of the Ru spin density (Ru(III) character) with an increase of the number of Cl atoms on the dioxolene ligand. The singly occupied molecular orbitals (SOMOs) of 1 and 5 are very similar to each other and stretch out the Ru-dioxolene frameworks, whereas the lowest unoccupied molecular orbital (LUMO) of 5 is localized on Ru and two oxygen atoms of dioxolene in comparison with that of 1. Electron-withdrawing groups decrease the energy levels of both the SOMO and LUMO. In other words, an increase in the number of Cl atoms in the dioxolene ligand results in an increase of the positive charge on Ru. Successive shifts in the electronic structure between the Ru(II)(sq) and Ru(III)(cat) frameworks caused by the variation of the substituents are compatible with the experimental data.     

六氟磷酸二(2,2'-联吡啶)·(4,4'-二甲基-2,2'-联吡啶) 合钌(Ⅱ)的二维核磁共振谱分析

用一维NMR方法研究了电化学发光物质六氟磷酸二(2,2'-联吡啶)·(4,4'-二甲基-2,2'-联吡啶)合钌(Ⅱ)的立体结构,借助二维1H-1H COSY和1H-13C COSY实验技术对其氢谱和碳谱进行了完全的归属,并给出了其氢谱和碳谱的化学位移值.     

cis-[Ru(2,2':6',2' '-terpyridine)(DMSO)Cl(2)]: useful precursor for the synthesis of heteroleptic terpyridine complexes under mild conditions

[Ru(II)(terpy)(DMSO)Cl(2)] complexes were synthesized as a 5/1 mixture of cis and trans isomers, and their reactivities with CO and with substituted 2,2':6',2' '-terpyridine (terpy) moieties have been investigated. The structure of a trans isomer and its CO adduct have been unambiguously assigned by spectroscopy and X-ray diffraction. The [Ru(terpy)(terpy-Br)](2+) complex prepared either from the cis-[Ru(II)(terpy)(DMSO)Cl(2)] or from the cis-[Ru(II)(terpy-Br)(DMSO)Cl(2)] precursor appeared to be reactive in cross-coupling reactions promoted by low-valent palladium(0) and is an attractive target for the stepwise synthesis of polynuclear complexes bearing vacant coordination sites (terpy-Br for 4'-bromo-2,2':6',2' '-terpyridine). Several bipyridine, phenanthroline, and bipyrimidine complexes were prepared this way and their optical and redox properties determined and discussed.     

Coordination of 9-ethylguanine to the mixed-ligand compound alpha-[Ru(azpy)(bpy)Cl2] (azpy = 2-phenylazopyridine and bpy = 2,2'-bipyridine). An unprecedented ligand positional shift, correlated to the cytotoxicity of this type of [RuL2Cl2] (with L = azpy or bpy) complex

The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance.     

Excitation energy flow control in {Ru(2,2'-bipyridine)2}-{pyridylporphyrin}2 systems

The direction of excitation energy migration is reversed in a system composed of {Ru(bpy)(2)}-{pyridylporphyrin}(2) by the addition of a Zn(2+) ion. The Zn(2+) system shows an excitation-wavelength dependent emission.     

Orientational control of electronic coupling in mixed-valence, binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes

A series of binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes has been prepared around a central biphenylene unit equipped with a strap of variable length. Partial oxidation forms the mixed-valence complex that displays both ligand-to-metal, charge-transfer, and intervalence charge-transfer (IVCT) transitions in the near-IR region. On the basis of Hush theory, the electronic coupling matrix element for interaction between the metal centers decreases with increasing length of the tethering strap. This effect arises because the strap modulates the torsion angle between the phenyl rings and thereby controls the extent of through-bond electronic coupling. The coupling element favors a maximum for planar geometries and a minimum for orthogonal structures, but the full impact of the torsion angle is not realized due to thermal fluctuations.     

Total enantioselectivity in the DNA binding of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [bpm = 2,2'-bipyrimidine; Me2bpy = 4,4'-dimethyl-2,2'-bipyridine

The binding of the three stereoisomers (DeltaDelta-, LambdaLambda- and DeltaLambda-) of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; bpm = 2,2'-bipyrimidine] to a tridecanucleotide containing a single adenine bulge has been studied by 1H NMR spectroscopy. The addition of the DeltaDelta-isomer to d(CCGAGAATTCCGG)2 induced significant chemical shift changes for the base and sugar resonances of the residues at the bulge site (G3A4G5/C11C10), whereas small shifts were observed upon addition of the enantiomeric LambdaLambda-form. NOESY spectra of the tridecanucleotide bound with the DeltaDelta-isomer revealed intermolecular NOE's between the metal complex and the nucleotide residues at the bulge site, while only weak NOE's were observed to terminal residues to the LambdaLambda-form. Competitive binding studies were performed where both enantiomers were simultaneously added to the tridecanucleotide, and for all ratios of the two stereoisomers the DeltaDelta-isomer remained selectively bound at the bulge site with the LambdaLambda-enantiomer localised at the terminal regions of the tridecanucleotide. The meso-diastereoisomer (DeltaLambda) was found to bind to the tridecanucleotide with characteristics intermediate between the DeltaDelta- and LambdaLambda-enantiomers of the rac form. Two distinct sets of metal complex resonances were observed, with one set having essentially the same shift as the free metal complex, whilst the other set of resonances exhibited significant shifts. The NOE data indicated that the meso-diastereoisomer does not bind as selectively as the DeltaDelta-isomer, with NOE's observed to a greater number of nucleotide residues compared to the DeltaDelta-form. This study provides a rare example of total enantioselectivity in the binding of an inert transition metal complex to DNA, produced by the shape recognition of both ruthenium(II) centres.     

Synthesis, electrochemistry and luminescence of [Pt{4'-(R)trpy}(CN)](+) (R = Ph, o-CH(3)C(6)H(4), o-ClC(6)H(4) or o-CF(3)C(6)H(4); trpy = 2,2':6',2'-terpyridine): crystal structure of [Pt{4'-(Ph)trpy}(CN)]BF(4) x CH(3)CN

The synthesis and characterization of [Pt{4'-(R)trpy}(CN)]X (R = Ph, X = BF(4) or SbF(6); R = o-CH(3)C(6)H(4), X = SbF(6); R = o-ClC(6)H(4), X = SbF(6); or R = o-CF(3)C(6)H(4), X = SbF(6)) are described where trpy = 2,2':6',2'-terpyridine. Single crystals of [Pt{4'-(Ph)trpy}(CN)]BF(4).CH(3)CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4'-(Ph)trpy}(CN)]BF(4). An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9 degrees of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4'-(R)trpy}(CN)](+) cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E(1/2) values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4'-(Ph)trpy}(CN)](+) approximately [Pt{4'-(o-CH(3)C(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-ClC(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-CF(3)C(6)H(4))trpy}(CN)](+). All the [Pt(4'-(R)trpy}(CN)](+) cations are photoluminescent in dichloromethane. Emission by [Pt{4'-(Ph)trpy}(CN)](+) is from an excited state with largely (3)MLCT orbital parentage, but with some intraligand (3)pi-pi* character mixed-in (tau = 0.1 micros). In contrast, the other three cations display emission that appears exclusively intraligand (3)pi-pi* in origin (tau approximately 0.8 micros). Emission spectra have been recorded in a low concentration frozen DME {1 : 5 : 5 (v/v) DMF-MeOH-EtOH} glass. For the R = o-CH(3)C(6)H(4), o-ClC(6)H(4) and o-CF(3)C(6)H(4) cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4'-(Ph)trpy}(CN)](+) cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more "domed" pattern; this has been interpreted in terms of a higher percentage of intraligand (3)pi-pi* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric (3)pi-pi* and (3)MMLCT emission, respectively.