Thiolate coordination to Fe(II)-porphyrin NO centers

The interaction of the Fe(II)-porphyrin NO model complex [Fe(TPP)(NO)] (1, TPP=tetraphenylporphyrin) with thiophenolate ligands and tetrahydrothiophene is explored both computationally and experimentally. Complex 1 is reacted with substituted thiophenolates and the obtained six-coordinate adducts of type [Fe(TPP)(SR)(NO)](-) are investigated in solution using electron paramagnetic resonance (EPR) spectroscopy. From the obtained g values and (14)N hyperfine pattern of the NO ligand it is concluded that the interaction of the thiophenolates with the Fe(II) center is weak in comparison to the corresponding 1-methylimidazole adduct. The strength of the Fe-S bond is increased when alkylthiolates are used as evidenced by comparison with the published EPR spectra of ferrous NO adducts in cytochromes P450 and P450nor, which have an axial cysteinate ligand. These results are further evaluated by density functional (DFT) calculations. The six-coordinate model complex [Fe(P)(SMe)(NO)](-) (1-SMe; P=porphine ligand used for the calculations) has an interesting electronic structure where NO acts as a medium strong sigma donor and pi acceptor ligand. Compared to the N-donor adducts with 1-methylimidazole (1-MeIm), etc., donation from the pi(h)( *) orbital of NO to Fe(II) is reduced due to the stronger trans effect of the alkylthiolate ligand. This is reflected by the predicted longer Fe-NO bond length and smaller Fe-NO force constant for 1-SMe compared to the 1-MeIm adduct. Therefore, the Fe(II)-porphyrin NO adducts with trans alkylthiolate coordination have to be described as Fe(II)-NO(radical) systems. The N-O stretching frequency of these complexes is predicted below 1600cm(-1) in agreement with the available experimental data. In addition, 1-SMe has a unique spin density distribution where Fe has a negative spin density of -0.26 from the calculations. The implications of this unusual electronic structure for the reactivity of the Fe(II)-NO alkylthiolate adducts as they occur in cytochrome P450nor are discussed.     

Enantioselective binding of lambda- and delta-[Ru(bpy)(2)(HPIP)]Cl2 (HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline) to the hexanucleotide [d(5'-GTCGAC-3')2

Multidimensional NMR techniques (1D (1)HNMR, 2D DQF (1)H(1)H COSY and 2D (1)H(1)H NOESY), electrospray ionization mass spectrometry (ESI-MS) and electronic spectroscopy, were performed to study the interactions of the enantiomers lambda- and delta-[Ru(bpy)(2)(HPIP)]Cl(2), (HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthro-line) with the self complementary hexanucleotide duplex d(5'-GTCGAC-3')(2). The results show that the delta-[Ru(bpy)(2)(HPIP)]Cl(2) binds tightly to the oligonucleotide, by intercalation of the ligand HPIP, between the A5 and C6 base sequence of the same strand, probably through the minor groove. Lambda-enantiomer binds weakly, suggesting groove interactions with the hexanucleotide duplex. ESI-MS spectrometry and UV-vis spectroscopy also confirmed these observations.     

On the lability of dimethylsulfoxide (DMSO) coordinated to the [Ru(II)-NO(+)] species: X-ray structures of mer-[RuCl(3)(DMSO)(2)(NO)] and mer-[RuCl(3)(CD(3)CN)(DMSO)(NO)

The syntheses of nitrosyl–dimethylsulfoxide–ruthenium(II) complexes with general formula mer-[RuCl₃(L)(DMSO)(NO)] (L=DMSO or CD₃CN) is reported. The mer-[RuCl₃(DMSO)₂(NO)] (1) complex was obtained from the reaction of [RuCl₃(NO)] with the sulfoxide ligand in acetone. The mer-[RuCl₃(CD₃CN)(DMSO)(NO)] (2) compound was obtained from mer-[RuCl₃(DMSO)₂(NO)] maintained in deuterated acetonitrile. These data suggest a slow kinetic reaction due the low lability of the DMSO ligand coordinated to the {Ru^II–NO⁺} species. The crystal and molecular structures of (1) and (2) have been determined from X-ray studies. Crystal data: for (1), monoclinic, P2₁/c, a=8.8340(2) Å, b=12.0230(3) Å, c=13.7064(4) Å, β=114.546(2)°, Z=4, R1=0.0429; for (2), monoclinic, P21/n, a=10.0180(7) Å, b=9.5070(7) Å, c=13.3340(9) Å, β=102.264(4)°, Z=4, R1=0.0472. The spectroscopic characterization of (1), in solid state (infrared spectrum) and in solution (nuclear magnetic resonance and cyclic voltammetry) is also described.     

Photoirradiation reactions and crystal structures of two geometrical isomers of [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol)

The photoirradiation reactions of two geometrical isomers (cis-1 and cis-2) of [Ru(OAc)(2cqn)₂NO] (H2cqn=2-chloro-8-quinolinol) were studied. Cis-2 [Ru(OAc)(2cqn)₂NO] (2) photochemically isomerized to cis-1 [Ru(OAc)(2cqn)₂NO] (1) in CH₂Cl₂ or DMSO using an Xe lamp as a light source and the reaction was irreversible. The 2 to 1 isomerization coexisting with ¹⁵NO gas and its evolution of the ¹H NMR spectra showed that the dissociation and recombination of both the NO and the acetate ion involve in the isomerization. On the other hand, 1 did not isomerize but the NO ligand exchanged with ¹⁵NO. The crystal structures of 1 and 2 were determined by X-ray diffraction.     

Release of NO by a nitrosyl complex upon activation by the mitochondrial reducing power

The reaction of trans-[Ru(NH(3))(4)P(OEt)(3)NO](3+) and mitochondria was investigated through differential pulse polarography and fluorimetry. The nitrosyl complex undergoes one-electron reduction centered on the NO ligand site. The reaction between the mitochondrial reductor and trans-[Ru(NH(3))(4)P(OEt)(3)NO](3+) exhibits a second order specific rate constant calculated as k=2 x 10(1) M(-1) s(-1). The reduced species, trans-[Ru(NH(3))(4)P(OEt)(3)NO](2+), quickly releases NO, yielding trans-[Ru(NH(3))(4)P(OEt)(3)H(2)O](2+). The low toxicities of both trans-[Ru(NH(3))(4)P(OEt)(3)(NO)](2+) and trans-[Ru(NH(3))(4)P(OEt)(3)H(2)O](2+) and its ability to release NO after reductive activation in a biological medium make the nitrosyl compound a useful model of a hypotensive drug.     

The effects of ruthenium tetraammine compounds on vascular smooth muscle.

The time course of the relaxation effect induced by a single dose (3 x 10(-6) mol/L) of trans-[Ru(NH3)4L(NO)]3+ (L=nic, 4-pic, py, imN, P(OEt)3, SO(3)(2-), NH3, and pz) species and sodium nitroprusside (4 x 10(-9) mol/L) was studied in aortic rings without endothelium and pre-contracted with noradrenaline (1 x 10(-6) mol/L). All the compounds induced a relaxing effect in the aortic rings, but the intensity and time of relaxation were different. Only the species where L=py, 4-pic, and P(OEt)3 were able to induce 100% (99-100%) of the relaxing effect during the assay. trans-[Ru(NH3)4(L)(NO)]3+ (L=SO(3)(2-) and NH3) showed the lowest relaxing effect (36 and 37%, respectively) when compared with the other compounds. Relationship was observed between the time corresponding to half of the maximum relaxation intensity observed and, respectively, k-NO, E0'[Ru(NO)]3+/[Ru(NO)]2+ in trans-[Ru(NH3)4(L)(NO)]3+ species and E0'Ru(III)/Ru(II) in trans-[Ru(NH3)4(L)(H2O)]3+ ions. These relationships strongly suggested that the NO liberation from the reduced nitrosyl complexes was responsible for the observed relaxation.     

Picosecond Kerr-gated time-resolved resonance Raman spectroscopy of the [Ru(phen)(2)dppz](2+) interaction with DNA

To investigate the basis of the 'light-switch' effect, the solvent dependence of the Kerr-gated picosecond-time resolved resonance Raman (TR(3)) spectra of [Ru(bpy)(2)dppz](2+), [Ru(phen)(2)dppz](2+), and the modified complex [Ru(phen)(2)cpdppzOMe](2+) and a dimer [mu-C4(cpdppz)(2)-(phen)(4)Ru(2)](4+) were studied. The investigation focussed on comparing the behaviour of [Ru(phen)(2)dppz](2+) in acetonitrile, ethanol, H(2)O, D(2)O, and DNA. The data are consistent with a model wherein excitation induces metal-to-ligand charge transfer (MLCT) to any of the ligands (termed the 'precursor' state) which, by interligand electron transfer (ILET), produces an excited state localised on the dppz ligand, MLCT(1). In water this state relaxes with a characteristic time of approximately 6 ps to a non-emissive state (MLCT(2)). The TR(3) spectra in water, acetonitrile and DNA are all distinctly different. However, the early (4 ps) water spectrum resembles the spectrum in DNA. This interesting observation suggests that the DNA-bound excited state of the complex can be thought of as a model for the initial, poorly solvated state in water.     

The photorelease of nitrogen monoxide (NO) from pentacyanonitrosyl coordination compounds of group 8 metals.

The photodetachment of NO from [M(II)(CN)5NO]2- with M = Fe, Ru, and Os, upon laser excitation at various wavelengths (355, 420, and 480 nm) was followed by various techniques. The three complexes showed a wavelength-dependent quantum yield of NO production Phi(NO), as measured with an NO-sensitive electrode, the highest values corresponding to the larger photon energies. For the same excitation wavelength the decrease of Phi(NO) at 20 degrees C in the order Fe > Ru > Os, is explained by the increasing M-N bond strength and inertness of the heavier metals. Transient absorption data at 420 nm indicate the formation of the [M(III)(CN)5H2O]2- species in less than ca. 1 micros for M = Fe and Ru. The enthalpy content of [Fe(III)(CN)5H2O]2- with respect to the parent [Fe(II)(CN)5NO]2- state is (190 +/- 20) kJ mol(-1), as measured by laser-induced optoacoustic spectroscopy (LIOAS) upon excitation at 480 nm. The production of [Fe(III)(CN)5H2O]2- is concomitant with an expansion of (8 +/- 3) ml mol(-1) consistent with an expansion of the water bound through hydrogen bonds to the CN ligands plus the difference between NO release into the bulk and water entrance into the first coordination sphere. The activated process, as indicated by the relatively strong temperature dependence of the Phi(NO) values and by the temperature dependence of the appearance of the [Fe(III)(CN)5H2O]2- species, as determined by LIOAS, is attributed to NO detachment in less than ca. 100 ns from the isonitrosyl (ON) ligand (MS1 state).     

Syntheses,characterization and X-ray structures of the fac-[RuCl3(NO)(dppe)] and the trans-[RuCl(NO)(dppe)2]2+ species

Trans-[RuCl(NO)(dppe)2]2+ species were prepared. The complexes have been characterized by microanalysis, IR and 31P[1H] NMR spectroscopy and cyclic voltammetry. The trans-[RuCl(NO)(dppe)2](ClO4)2 complex shows a reversible one-electron-reduction process at E(1/2) = 0.200 V and another one-electron-reduction irreversible process at -0.620 V, both centered at the NO+ group. The dissociation of the NO group from the trans-[RuCl(NO)(dppe)2]2+ after two one-electron reductions results in the formation of the trans- and cis-[RuCl2(dppe)2] isomers. The product of an electrolyzed solution of the same complex at -0.300 V shows an EPR signal consistent with the presence of the [RuCl(NO(0))(dppe)2]+ complex. Crystal data for trans-[RuCl(NO)(dppe)2]2+*[RuCl4(NO)(H2O)]*1/2[RuCl6]4-*2[H2O] (I) and trans-[RuCl(NO)(dppe)(2)]2+*2[RuCl4(NO)(CH3O)]-*3[CH3OH] (II) are as follow: (I) Space group P-1, a=10.4040(3) A, b=12.3470(4) A, c=23.5620(8) A, alpha=95.885(2) degrees, beta=99.608(2) degrees, gamma=104.378(2) degrees, R=0.0521; (II) space group P-1, a=10.9769(2) A, b=13.2753(3) A, c=24.0287(4) A, alpha=99.743(1) degrees, beta=95.847(1) degrees, gamma=97.549(1) degrees; R=0.0496. The fac-[RuCl3(NO)(dppe)] (III) complex has been also prepared; its crystal data are: space group P2(1)/n (No. 14), a=11.841(2) A, b=13.775(2) A, c=16.295(4) A, beta=92.81(2) degrees; R1=0.0395.     

Synthesis, characterization and DNA binding studies of two mixed ligand complexes of ruthenium(II)

Two mixed ligand complexes [Ru(bpy)(2)(DMHBT)]Cl(2)(1) and [Ru(phen)(2)(DMHBT)]Cl(2) (2) (where DMHBT is 11,13-dimethyl-13H-4,5,9,11,14-hexaaza-benzo[b]triphenylene-10,12-dione) have been synthesized and characterized by electrospray ionization (ESI) mass, (1)H-(1)H correlation spectroscopy (COSY), electronic spectroscopy, fluorescence spectroscopy and cyclic voltammetry. Spectroscopic titration and viscosity changes of calf thymus (CT)-DNA in the presence of incremental amount of complexes 1 and 2 clearly demonstrate that both these complexes bind intercalatively to DNA, with binding constant 2.87+/-0.20 x 10(4)M(-1) and 1.01+/-0.20 x 10(5)M(-1) for complexes 1 and 2, respectively. All the experimental evidences suggest that the ancillary ligand 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) influences the intercalative binding of these complexes to DNA.     

trans-[Ru(NO)(NH3)4(py)](BF4)3.H2O encapsulated in PLGA microparticles for delivery of nitric oxide to B16-F10 cells: Cytotoxicity and phototoxicity

The NO donor trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O (py=pyridine) was loaded into poly-lactic-co-glycolic acid (PLGA) microparticles using the double emulsification technique. Scanning electron microscopy (SEM) and dynamic light scattering revealed that the particles are spherical in shape, have a diameter of 1600nm, and have low tendency to aggregate. The entrapment efficiency was 25%. SEM analysis of the melanoma cell B16-F10 in the presence of the microparticles containing the complex trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O (pyMP) showed that the microparticles were adhered to the cell surface after 2h of incubation. The complex with concentrations lower than 1x10(-4)M did not show toxicity in B16-F10 murine cells. The complex in solution is toxic at higher concentrations (>1x10(-3)M), with cell death attributed to NO release following the reduction of the complex. pyMP is not cytotoxic due to the lower bioavailability and availability of the entrapped complex to the medium and its reducing agents. However, pyMP is phototoxic upon light irradiation. The phototoxicity strongly suggests that cell death is due to NO release from trans-[Ru(NO)(NH(3))(4)(py)](3+). This work shows that pyMP can serve as a model for a drug delivery system carrying the NO donor trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O, which can release NO locally at the tumor cell by irradiation with light only.     

Synthesis, crystal structures, and anti-convulsant activities of ternary [Zn(II)(3,5-diisopropylsalicylate)(2)], [Zn(II)(salicylate)(2)] and [Zn(II)(aspirinate)(2)] complexes

Following observations that bis(3,5-diisopropylsalicylato)diaquazinc(II), [Zn(II)(3,5-DIPS)(2)(H(2)O)(2)], had anti-convulsant activity, bis(acetylsalicylate)diaquazinc(II), [Zn(II)(aspirinate)(2)(H(2)O)(2)], and the Zn(II) ternary 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neocuproine, NC) or dimethyl sulfoxide (DMSO) complexes of Zn(II)3,5-diisopropylsalicylate, salicylate, and acetylsalicylate were synthesized and spectroscopically characterized. Anti-convulsant and Rotorod toxicity activities of these complexes were determined to examine their anti-convulsant and undesirable central nervous stimulant or depressant activities of these Zn(II) non-steroidal anti-inflammatory agent complexes. Bis(3,5-diisopropylsalicylato)-1,10-phenanthorlinezinc(II), [Zn(II)(3,5-DIPS)(2)(phen)], (1) has one bidentate phen ligand and two mono-deprotonated 3,5-DIPS ligands. One of the carboxylates bonds in an asymmetric chelating mode. The Zn(II) atom exhibits a distorted bicapped rectangular pyramidal environment N(2)O(2)OO (4+1+1 *). In the neocuproine complex, bis(3,5-diisopropylsalicylato)-2,9-dimethyl-1,10-phenanthorlinezinc(II), [Zn(II)(3,5-DIPS)(2)(NC)] (2), the Zn(II) atom has a much more distorted bicapped rectangular pyramidal environment, N(2)O(2)O(2) (4+2 *), compared to 1. The two carboxylate ligands exhibit the same asymmetric coordinating mode with longer metalloelement-oxygen bond distances compared to 1. The space group of [Zn(II)(aspirinate)(2)(H(2)O)(2)] (3), which has been reported as Cc is corrected to C2/c. The zinc atom exhibits a (4+2 *) bicapped square pyramidal environment. While the two ternary phenanthroline-containing complexes, 1 and 2, evidenced weak protection against maximal electroshock (MES)- and subcutaneous Metrazol (scMET) induced seizures, [Zn(II)(3,5-DIPS)(2)(DMSO)(2)], [Zn(II)(aspirinate)(2)(H(2)O)(2)], and bis(salicylato)-1,10-phenanthorlinezinc(II), [Zn(II)(salicylate)(2)(phen)], were found to be particularly useful in protecting against MES and scMET seizures and [Zn(II)(aspirinate)(2)(H(2)O)(2)] and [Zn(II)(salicylate)(2)(phen)] were found to have activity in protecting against Psychomotor seizures, without causing Rotorod toxicity. Activities of these and other Zn(II) complexes of non-steroidal anti-inflammatory agents are consistent with the well-known anti-inflammatory responses of Zn(II)-dependent enzymes. There was also some evidence of Rotorod toxicity consistent with a mechanism of action involving sedative-hypnotic activity of recognized anti-epilepticdrugs.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

DNA binding of lambda- and delta-cis-beta-[Ru(RR-picchxn)(phen)](2)+ studied by NMR and flow linear dichroism spectroscopy

Two novel substitutionally-inert diastereomeric ruthenium(II) cations of the form lambda- and delta-cis-beta-[Ru(RR-picchxn)(phen)]2+, where RR-picchxn is N,N'-dimethyl-N,N'-di(2-picolyl)-1R,2R-diaminocyclohexane and phen is 1,10-phenanthroline, have been studied with respect to their interactions with duplex DNA. NMR investigations show that both diastereomers bind to the oligonucleotide [d(CGCGATCGCG)]2 in the fast exchange regime and that binding predominantly takes place in the minor groove of the oligonucleotide, but that the governing interactions are significantly different for the two delta and lambda forms. Linear dichroism data support the latter interpretation, in that the relative orientations of cis-beta-[Ru(RR-picchxn)(phen)]2+ to calf thymus DNA also are observed to differ for the delta and lambda diastereomers. Interpretation of these data indicates the lambda form to be bound with the planar phen ligand closely parallel to the DNA base-pairs, but the average orientation of the phen ligand in the delta form deviates significantly from a parallel alignment.     

The effects of grafting of 2-pyridyl to [Ru(bpy)(2)(Hpip)](2+) on acid-base and DNA-binding properties: experimental and DFT studies

A new Ru(II) complex of [Ru(bpy)(2)(Hpip)](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)(Hpip)](2+) studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)(2)(Hpip)](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) x 10(5) 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.     

Complexes trans-[RuCl(2)(nic)(4)] and trans-[RuCl(2)(i-nic)(4)] as free radical scavengers

This study evaluates the action of the new ruthenium complexes trans-RuCl(2)(nic)(4)] (I) and trans-[RuCl(2)(i-nic)(4)] (II) as free radical scavengers. In our experiments, both compounds acted as scavengers of superoxide anion (O(2)*(-)), hydroxyl radicals (HO*) and nitrogen monoxide (formally known as 'nitric oxide'; NO*). In addition, complexes I and II potentiated the release of NO* from S-nitroso-N-acetyl-DL-penicilamine (SNAP), a NO* donor. Complex II, but not I, also decreased the nitrite levels in culture media of activated macrophages. A hypsochromic shift of lambda(max) and a significant change in half-wave potential (E(1/2)) was observed when NO* was added to the Complex II. Thiobarbituric reactive substance (TBARS) levels were significantly reduced in rats treated for 1 week with Complex II plus tert-butylhydroperoxide, when compared to rats treated only with tert-butylhydroperoxide. None of the complexes showed cytotoxicity. These findings support the suggestion that the new ruthenium complexes, especially trans-[RuCl(2)(i-nic)(4)] or its derivatives, might provide potential therapeutic benefits in disorders where reactive nitrogen (RNS) or oxygen (ROS) species are involved.     

The [Ru(Hedta)NO](0.1-) system: structure, chemical reactivity and biological assays

The [Ru(II)(Hedta)NO(+)] complex is a diamagnetic species crystallizing in a distorted octahedral geometry, with the Ru-N(O) length 1.756(4) A and the RuNO angle 172.3(4) degrees . The complex contains one protonated carboxylate (pK(a)=2.7+/-0.1). The [Ru(II)(Hedta)NO(+)] complex undergoes a nitrosyl-centered one-electron reduction (chemical or electrochemical), with E(NO+/NO)=-0.31 V vs SCE (I=0.2 M, pH 1), yielding [Ru(II)(Hedta)NO](-), which aquates slowly: k(-NO)=2.1+/-0.4x10(-3) s(-1) (pH 1.0, I=0.2 M, CF(3)COOH/NaCF(3)COO, 25 degrees C). At pHs>12, the predominant species, [Ru(II)(edta)NO](-), reacts according to [Ru(II)(edta)NO](-)+2OH(-)-->[Ru(II)(edta)NO(2)](3-), with K(eq)=1.0+/-0.4 x 10(3) M(-2) (I=1.0 M, NaCl; T=25.0+/-0.1 degrees C). The rate-law is first order in each of the reactants for most reaction conditions, with k(OH(-))=4.35+/-0.02 M(-1)s(-1) (25.0 degrees C), assignable mechanistically to the elementary step comprising the attack of one OH(-) on [Ru(II)(edta)NO](-), with subsequent fast deprotonation of the [Ru(II)(edta)NO(2)H](2-) intermediate. The activation parameters were DeltaH(#)=60+/-1 kJ/mol, DeltaS(#)=-31+/-3 J/Kmol, consistent with a nucleophilic addition process between likely charged ions. In the toxicity up-and-down tests performed with Swiss mice, no death was observed in all the doses administered (3-9.08 x 10(-5) mol/kg). The biodistribution tests performed with Wistar male rats showed metal in the liver, kidney, urine and plasma. Eight hours after the injection no metal was detected in the samples. The vasodilator effect of [Ru(II)(edta)NO](-) was studied in aortic rings without endothelium, and was compared with sodium nitroprusside (SNP). The times of maximal effects of [Ru(II)(edta)NO](-) and SNP were 2 h and 12 min, respectively, suggesting that [Ru(II)(edta)NO](-) releases NO slowly to the medium in comparison with SNP.     

Spectroscopic and electrochemical properties of a new nitrosyl-complex of Ru(II): trans-[Ru(NO){(CH3CH2)2PCH2CH2P(CH2CH3)2}2Cl](PF6)2

A new ruthenium nitric oxide complex with the bidentate phosphine, 1,2-bis(diethylphosphino)ethane (depe), has been synthesized and characterized by UV-Vis, infrared, EPR, NMR, electrochemical techniques and X-ray structure determination. The electronic spectrum showed a typical band of dπ→pπ* charge-transfer (CT) transition, assigned to Ru(II)NO transition, and the vibrational spectrum exhibited a peak of nitrosyl ligand at (ν_NO=1851 cm⁻¹). A model structure for this complex has been proposed based on ¹H, ¹H{³¹P}, ³¹P{¹H}, ¹³C{¹H}, COSY ¹H¹H{³¹P}, J-Resolved, HSQC, HMBC, HSQC ¹H¹³C{³¹P} and ¹H¹³C HSQC/¹H¹H TOCSY spectral data, and confirmed by X-ray diffraction. The nitrosonium character for the NO ligand become evident through both electron paramagnetic resonance and X-ray data (angle RuNO=177.4(3)°). The reversible monoeletronic process at E_1/2=0.040 V versus SHE was assigned to the ligand NO⁺/NO redox couple. Under treatment with Cd(Hg) solutions containing the [Ru(NO)(depe)₂Cl](PF₆)₂ yields a signal in the EPR spectrum (g_⊥=1.99 and g_//=1.88) which fitted quite well with the simulated spectra of coordinated NO species.     

Reactivity pathways for nitric oxide and nitrosonium with iron complexes in biologically relevant sulfur coordination spheres

The interaction of nitric oxide (NO) with iron-sulfur cluster proteins results in the formation of dinitrosyl iron complexes (DNICs) coordinated by cysteine residues from the peptide backbone or with low molecular weight sulfur-containing molecules like glutathione. Such DNICs are among the modes available in biology to store, transport, and deliver NO to its relevant targets. In order to elucidate the fundamental chemistry underlying the formation of DNICs and to characterize possible intermediates in the process, we have investigated the interaction of NO (g) and NO(+) with iron-sulfur complexes having the formula [Fe(SR)(4)](2-), where R=(t)Bu, Ph, or benzyl, chosen to mimic sulfur-rich iron sites in biology. The reaction of NO (g) with [Fe(S(t)Bu)(4)](2-) or [Fe(SBz)(4)](2-) cleanly affords the mononitrosyl complexes (MNICs), [Fe(S(t)Bu)(3)(NO)](-) (1) and [Fe(SBz)(3)(NO)](-) (3), respectively, by ligand displacement. Mononitrosyl species of this kind were previously unknown. These complexes further react with NO (g) to generate the corresponding DNICs, [Fe(SPh)(2)(NO)(2)](-) (4) and [Fe(SBz)(2)(NO)(2)](-) (5), with concomitant reductive elimination of the coordinated thiolate donors. Reaction of [Fe(SR)(4)](2-) complexes with NO(+) proceeds by a different pathway to yield the corresponding dinitrosyl S-bridged Roussin red ester complexes, [Fe(2)(mu-S(t)Bu)(2)(NO)(4)] (2), [Fe(2)(mu-SPh)(2)(NO)(4)] (7) and [Fe(2)(mu-SBz)(2)(NO)(4)] (8). The NO/NO(+) reactivity of an Fe(II) complex with a mixed nitrogen/sulfur coordination sphere was also investigated. The DNIC and red ester species, [Fe(S-o-NH(2)C(6)H(4))(2)(NO)(2)](-) (6) and [Fe(2)(mu-S-o-NH(2)C(6)H(4))(2)(NO)(4)] (9), were generated. The structures of 8 and 9 were verified by X-ray crystallography. The MNIC complex 1 can efficiently deliver NO to iron-porphyrin complexes like [Fe(TPP)Cl], a reaction that is aided by light. Removal of the coordinated NO ligand of 1 by photolysis and addition of elemental sulfur generates higher nuclearity Fe/S clusters.     

Chemical and biological characterization of technetium(I) and Rhenium(I) tricarbonyl complexes with dithioether ligands serving as linkers for coupling the Tc(CO)(3) and Re(CO)(3) moieties to biologically active molecules

The organometallic precursor (NEt(4))(2)[ReBr(3)(CO)(3)] was reacted with bidendate dithioethers (L) of the general formula H(3)C-S-CH(2)CH(2)-S-R (R = -CH(2)CH(2)COOH, CH(2)-C&tbd1;CH) and R'-S-CH(2)CH(2)-S-R' (R' = CH(3)CH(2)-, CH(3)CH(2)-OH, and CH(2)COOH) in methanol to form stable rhenium(I) tricarbonyl complexes of the general composition [ReBr(CO)(3)L]. Under these conditions, the functional groups do not participate in the coordination. As a prototypic representative of this type of Re compounds, the propargylic group bearing complex [ReBr(CO(3))(H(3)C-S-CH(2)CH(2)-S-CH(2)C&tbd1;CH)] Re2 was studied by X-ray diffraction analysis. Its molecular structure exhibits a slightly distorted octahedron with facial coordination of the carbonyl ligands. The potentially tetradentate ligand HO-CH(2)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(2)-OH was reacted with the trinitrato precursor [Re(NO(3))(3)(CO)(3)](2-) to yield a cationic complex [Re(CO)(3)(HO-CH(2)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(2)-OH)]NO(3) Re8 which shows the coordination of one hydroxy group. Re8 has been characterized by correct elemental analysis, infrared spectroscopy, capillary electrophoresis, and X-ray diffraction analysis. Ligand exchange reaction of the carboxylic group bearing ligands H(3)C-S-CH(2)CH(2)-S-CH(2)CH(2)-COOH and HOOC-CH(2)-S-CH(2)CH(2)-S-CH(2)-COOH with (NEt(4))(2)[ReBr(3)(CO)(3)] in water and with equimolar amounts of NaOH led to complexes in which the bromide is replaced by the carboxylic group. The X-ray structure analysis of the complex [Re(CO)(3)(OOC-CH(2)-S-CH(2)CH(2)-S-CH(2)-COOH)] Re6 shows the second carboxylic group noncoordinated offering an ideal site for functionalization or coupling a biomolecule. The no-carrier-added preparation of the analogous (99m)Tc(I) carbonyl thioether complexes could be performed using the precursor fac-[(99m)Tc(H(2)O)(3)(CO)(3)](+), with yields up to 90%. The behavior of the chlorine containing (99m)Tc complex [(99m)TcCl(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))] Tc1 in aqueous solution at physiological pH value was investigated. In saline, the chromatographically separated compound was stable for at least 120 min. However, in chloride-free aqueous solution, a water-coordinated cationic species Tc1a of the proposed composition [(99m)Tc(H(2)O)(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))](+) occurred. The cationic charge of the conversion product was confirmed by capillary electrophoresis. By the introduction of a carboxylic group into the thioether ligand as a third donor group, the conversion could be suppressed and thus the neutrality of the complex preserved. Biodistribution studies in the rat demonstrated for the neutral complexes [(99m)TcCl(CO)(3)(CH(3)CH(2)-S-CH(2)CH(2)-S-CH(2)CH(3))] Tc1 and [(99m)TcCl(CO)(3)(CH(2)-S-CH(2)CH(2)-S-CH(2)-C&tbd1;CH)] Tc2 a significant initial brain uptake (1.03 +/- 0.25% and 0.78 +/- 0.08% ID/organ at 5 min. p.i.). Challenge experiments with glutathione clearly indicated that no transchelation reaction occurs in vivo.