Nitroxyl as a ligand in ruthenium tetraammine systems: a density functional theory study.

The properties of the free nitroxyl molecule and the nitroxyl ligand in Ru(ii) tetraammines (trans-[Ru(NH3)4(nitroxyl)(n)(L)](2+n) (n = nitroxyl charge; L = NH3, py, P(OEt)3, H2O, Cl(-) and Br(-))) were studied using density functional theory. According to the calculated conformational energies, HNO complexes are more stable than their deprotonated analogues, and the singlet configuration (trans-(1)[Ru(NH3)4(L)HNO](2+)) is lower in energy than the corresponding triplet (trans-(3)[Ru(NH3)4(L)HNO](2+)). An evaluation of the σ and π components of the L-Ru-HNO bond suggest that the increased stability of these orbitals and the enhanced contributions from the HNO orbitals correlate to shorter Ru-N(H)O distances and higher νRu-HNO stretching frequencies. The stability of the Ru-HNO bond was also evaluated through a theoretical kinetic study of HNO dissociation from trans-(1)[Ru(NH3)4(L)HNO](2+). The order of the Ru-HNO bonding stability in trans-(1)[Ru(NH3)4(L)HNO](2+) as a function of L was found to be as follows: H2O > Cl(-)∼ Br(-) > NH3 > py > P(OEt)3. This order parallels the order of the trans-effect and trans-influence series experimentally measured for L in octahedral complexes. The same trend was also observed using an explicit solvent model, considering the presence of both HNO and H2O molecules in the transition state. For this series, the calculated bond dissociation enthalpies for the Ru-HNO bonds are in the range 23.8 to 45.7 kcal mol(-1). A good agreement was observed between the calculated ΔG(‡) values for the displacement of HNO by H2O in trans-(1)[Ru(NH3)4(P(OEt)3HNO](2+) (23.4 kcal mol(-1)) and the available experimental data for the substitution reactions of trans[Ru(NH3)4(POEt)3(Lx)](2+) (19.4 to 24.0 kcal mol(-1) for Lx = isn and P(OET)3, respectively).

Cyanate as an Active Precursor of Ethyl Carbamate Formation in Sugar Cane Spirit.

The thermodynamic and kinetic aspects of ethyl carbamate (EC) formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10(-5) and (8.9 ± 0.4) × 10(-5) s(-1), respectively, at 25 °C in 48% aqueous ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases (ΔH1(⧧) = 19.4 ± 1 kcal/mol, ΔS1(⧧) = −12.1 ± 1 cal/K, and ΔG1(⧧) = 23.0 ± 1 kcal/mol) and decrease as the solution pH increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, the isocyanic acid (HNCO) is the active EC precursor. The calculated ΔG1(⧧), ΔH1(⧧), and ΔS1(⧧) values are in very good agreement with the experimental ones.

Anti-inflammatory and Anti-nociceptive Activity of Ruthenium Complexes with Isonicotinic and Nicotinic Acids (Niacin) as Ligands.

This work evaluated the analgesic and anti-inflammatory activity of ruthenium(II) complexes trans-[Ru(NO(+))(NH3)4(L)](BF4)3 and [Ru(NH3)5(L)](BF4)3 containing the nonsteroidal anti-inflammatory drugs nicotinic acid (Hnic) and its isomer isonicotinic acid (ina) as ligands (L). The anti-nociceptive potential of these complexes and the free ligands (noncoordinated to ruthenium) was tested in different models with doses ranging from 1 to 100 µmol/kg. The ligands themselves were inactive; however, the ruthenium complexes containing Hnic and ina inhibited mechanical hyperalgesia induced by prostaglandin E2, carrageenan-induced hyperalgesia, and antigen-induced arthritis. Moreover, the ruthenium complexes inhibited overt nociception induced by formalin, acetic acid, capsaicin, and cinnamaldehyde. The mechanism involved in the anti-nociceptive effects of the ruthenium complexes suggested that ATP-sensitive K(+) channel pathways were not involved because glibenclamide did not affect their anti-nociceptive activities. However, the anti-nociceptive effect appears to be a consequence of the reduction in neutrophil migration and inhibition of the protein kinase C pathway.

Antitubercular activity of Ru (II) isoniazid complexes.

Despite the resistance developed by the Mycobacterium tuberculosis (MTb) strains, isoniazid (INH) has been recognized as one of the best drug for treatment of Tuberculosis (Tb). The coordination of INH to ruthenium metal centers was investigated as a strategy to enhance the activity of this drug against the sensitive and resistant strains of MTb. The complexes trans-[Ru(NH3)4(L)(INH)](2+) (L=SO2 or NH3) were isolated and their chemical and antituberculosis properties studied. The minimal inhibitory concentration (MIC) data show that [Ru(NH3)5(INH)](2+) was active in both resistant and sensitive strains, whereas free INH (non-coordinated) showed to be active only against the sensitive strain. The coordination of INH to the metal center in both [Ru(NH3)5(INH)](2+) and trans-[Ru(NH3)4(SO2)(INH)](2+) complexes led to a shift in the INH oxidation potential to less positive values compared to free INH. Despite, the ease of oxidation of INH did not lead to an increase in the in vitro INH activity against MTb, it might have provided sensitivity toward resistant strains. Furthermore, ruthenium complexes with chemical structures analogous to those described above were synthesized using the oxidation products of INH as ligands (namely, isonicotinic acid and isonicotinamide). These last compounds were not active against any strains of MTb. Moreover, according to DFT calculations the formation of the acyl radical, a proposed intermediate in the INH oxidation, is favored in the [Ru(NH3)5(INH)](2+) complex by 50.7kcalmol(-1) with respect to the free INH. This result suggests that the stabilization of the acyl radical promoted by the metal center would be a more important feature than the oxidation potential of the INH for the antituberculosis activity against resistant strains.

Secondary coordination sphere effects in ruthenium(III) tetraammine complexes: role of the coordinated water molecule.

The complexes trans-[Ru(III)(NH3)4(4-pic)(H2O)](CF3SO3)3 (1) and [Ru(III)(NH3)5(4-pic)](CF3SO3)3 (2) were isolated and studied experimentally by electron paramagnetic resonance (EPR) and UV-vis spectroscopies, cyclic voltammetry, and X-ray crystallography and theoretically by ligand-field theory (LFT) and density functional theory (DFT) calculations. Complex 1 is reported in two different crystal forms, 1a (100 K) and 1b (room temperature). EPR and UV-vis spectroscopies suggest that aqua ligand interaction in this low-spin ruthenium(III) complex changes as a function of hydrogen bonding with solvent molecules. This explicit water solvent effect was explained theoretically by DFT calculations, which demonstrated the effect of rotation of the aqua ligand about the Npic-Ru-Oaq axis. The UV-vis spectrum of 1 shows in an aqueous acid solution a broad- and low-intensity absorption band around 28,500 cm(-1) (ε ≈ 500 M(-1) cm(-1)) that is assigned mainly to a charge-transfer (CT) transition from the equatorial ligands to the Ru ß-4dxy orbital (ß-LUMO) using DFT calculations. The electronic reflectance spectrum of 1 shows a broad and intense absorption band around 25,500 cm(-1) that is assigned to a CT transition from 4-picoline to the Ru ß-4dxz orbital (ß-LUMO) using DFT calculations. The t2g(5) set of orbitals had its energy splitting investigated by LFT. LFT analysis shows that a rhombic component arises from C2v symmetry by a simple π-bonding ligand (H2O in our case) twisting about the trans (C2) axis. This twist was manifested in the EPR spectra, which were recorded for 1 as a function of the solvent in comparison with [Ru(NH3)5(4-pic)](3+) and [Ru(NH3)5(H2O)](3+). Only 1 shows an evident change in the g-tensor values, wherein an increased rhombic component is correlated with a higher nucleophilicity (donor) solvent feature, as parametrized by the Abraham system.

Unexpected NO transfer reaction between trans-[Ru(II)(NO+)(NH3)4(L)]3+ and Fe(III) species: observation of a heterobimetallic NO-bridged intermediate.

The reaction between trans-[Ru(II)(NO(+))(NH3)4(L)](3+), L = ImN, IsN, Nic, P(OMe)3, P(OEt)3, and P(OH)(OEt)2, and the Fe(III) species [Fe(III)(TPPS)], metmyoglobin, and hemoglobin was monitored by UV-vis, EPR, and electrochemical techniques (DPV, CV). No reaction was observed when L = ImN, IsN, Nic, and P(OH)(OEt)2. However, when L = P(OMe)3 and P(OEt)3, the reaction was quantitative and the products were trans-[Ru(III)(H2O)(NH3)4(P(OR)3)](3+) and [Fe(II)(NO(+))] species. Reaction kinetics data and DFT calculations suggest a two-step reaction mechanism with the initial formation of a bridged [Ru-(µNO)-Fe] intermediate, which was confirmed through electrochemical techniques (E(0)' = -0.47 V vs NHE). The calculated specific rate constant values for the reaction were in the ranges k1 = 1.1 to 7.7 L mol(-1) s(-1) and k2 = 2.4 × 10(-3) to 11.4 × 10(-3) s(-1) for L = P(OMe)3 and P(OEt)3. The oxidation of the ruthenium center (Ru(II) to Ru(III)) containing the nitrosonium ligand suggests that NO can act as an electron transfer bridge between the two metal centers.

Experimental chemotherapy against Trypanosoma cruzi infection using ruthenium nitric oxide donors.

The ruthenium NO donors of the group trans-[Ru(NO)(NH3)4L]n+, where the ligand (L) is N-heterocyclic H2O, SO(3)(2-), or triethyl phosphite, are able to lyse Trypanosoma cruzi in vitro and in vivo. Using half-maximal (50%) inhibitory concentrations against bloodstream trypomastigotes (IC50try) and cytotoxicity data on mammalian V-79 cells (IC50V79), the in vitro therapeutic indices (TIs) (IC50V79/IC50try) for these compounds were calculated. Compounds that exhibited an in vitro TI of > or = 10 and trypanocidal activity against both epimastigotes and trypomastigotes with an IC50(try/epi) of < or = 100 microM were assayed in a mouse model for acute Chagas' disease, using two different routes (intraperitoneal and oral) for drug administration. A dose-effect relationship was observed, and from that, the ideal dose of 400 nmol/kg of body weight for both trans-[Ru(NO)(NH3)4isn](BF4)3 (isn, isonicotinamide) and trans-[Ru(NO)(NH3)4imN](BF4)3 (imN, imidazole) and median (50%) effective doses (ED50) of 86 and 190 nmol/kg, respectively, were then calculated. Since the 50% lethal doses (LD50) for both compounds are higher than 125 micromol/kg, the in vivo TIs (LD50/ED50) of the compounds are 1,453 for trans-[Ru(NO)(NH3)4isn](BF4)3 and 658 for trans-[Ru(NO)(NH3)4imN](BF4)3. Although these compounds exhibit a marked trypanocidal activity and are able to react with cysteine, they exhibit very low activity in T. cruzi-glycosomal glyceraldehyde-3-phosphate dehydrogenase tests, suggesting that this enzyme is not their target. The trans-[Ru(NO)(NH3)4isn](BF4)3 and trans-[Ru(NO)(NH3)4imN](BF4)3 compounds are able to eliminate amastigote nests in myocardium tissue at 400-nmol/kg doses and ensure the survival of all infected mice, thus opening a novel set of therapies to try against trypanosomatids.

Quantitative ester analysis in cachaca and distilled spirits by gas chromatography-mass spectrometry (GC-MS).

An analytical procedure for the separation and quantification of ethyl acetate, ethyl butyrate, ethyl hexanoate, ethyl lactate, ethyl octanoate, ethyl nonanoate, ethyl decanoate, isoamyl octanoate, and ethyl laurate in cachaca, rum, and whisky by direct injection gas chromatography-mass spectrometry was developed. The analytical method is simple, selective, and appropriated for the determination of esters in distilled spirits. The limit of detection ranged from 29 (ethyl hexanoate) to 530 (ethyl acetate) microg L(-1), whereas the standard deviation for repeatability was between 0.774% (ethyl hexanoate) and 5.05% (isoamyl octanoate). Relative standard deviation values for accuracy vary from 90.3 to 98.5% for ethyl butyrate and ethyl acetate, respectively. Ethyl acetate was shown to be the major ester in cachaca (median content of 22.6 mg 100 mL(-1) anhydrous alcohol), followed by ethyl lactate (median content of 8.32 mg 100 mL(-1) anhydrous alcohol). Cachaca produced in copper and hybrid alembic present a higher content of ethyl acetate and ethyl lactate than those produced in a stainless-steel column, whereas cachaca produced by distillation in a stainless-steel column present a higher content of ethyl octanoate, ethyl decanoate, and ethyl laurate. As expected, ethyl acetate is the major ester in whiskey and rum, followed by ethyl lactate for samples of rum. Nevertheless, whiskey samples exhibit ethyl lactate at contents lower or at the same order of magnitude of the fatty esters.

Amino acids profile of sugar cane spirit (cachaça), rum, and whisky.

An analytical procedure for the separation and quantification of 20 amino acids in cachaças has been developed involving C18 solid phase cleanup, derivatization with o-phthalaldehyde/2-mercaptoethanol, and reverse phase liquid chromatography with fluorescence detection. The detection limit was between 0.0050 (Cys) and 0.25 (Ser)mgL(-1), whereas the recovery index varies from 69.5 (Lys) to 100 (Tyr)%. Relative standard deviations vary from 1.39 (Trp) to 13.4 (Glu)% and from 3.08 (Glu) to 13.5 (His) for the repeatability and intermediate precision, respectively. From the quantitative profile of amino acids in 41 cachaças, 5 rums, and 12 whisky samples, the following order of amino acids in significant quantities is observed: Gly=Ser

Profiles of polycyclic aromatic hydrocarbons in Brazilian sugar cane spirits: discrimination between Cachaças produced from nonburned and burned sugar cane crops.

Cachaça may be contaminated by a remarkable presence of polycyclic aromatic hydrocarbons (PAHs) when the sugar cane crop used for its production is burned before harvesting. The analysis of 15 PAHs by liquid chromatography coupled to a fluorescence detector in 131 cachaça samples from burned and nonburned sugar cane crops is reported. Average contents of 21.1 and 1.91 microg L(-1) for total PAHs were observed for cachaças originating from burned and nonburned sugar cane plantations, respectively. The main difference between these two classes of cachaças is in the quantitative profile of the most potent carcinogenic PAH, benzo[a]pyrene, which is more abundant in cachaça produced from burned sugar cane crops (4.54 x 10(-2) microg L(-1)) than in cachaça produced from nonburned crops (9.02 x 10(-3) microg L(-1)). The contents of benzo[a]pyrene in both classes of cachaça are lower than the legal limit established by the European Union (EU) at 2.00 microg L(-1) for food products. In relation to the total PAH content suggested by the German Society for Fat Science, both cachaças from burned (21.1 microg L(-1)) and nonburned crops (1.91 microg L(-1)) are below the limit (25 microg L(-1)) for total PAH content. The analytical data for PAHs, when treated through the multivariate statistical methods principal component analysis and canonical discriminant analysis, provide a very good distinction between samples produced from burned and nonburned sugar cane crops with a certainty of 98.1%.

Immobilization of the [RuII(edta)NO+] Ion on the surface of functionalized silica gel.

The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates.

Deactivation of triplet-excited riboflavin by purine derivatives: important role of uric acid in light-induced oxidation of milk sensitized by riboflavin.

The reactivity of purine derivatives (uric acid, xanthine, hypoxanthine, and purine) toward triplet-excited riboflavin in aqueous solution at pH 6.4 is described on the basis of kinetic (laser flash photolysis), electrochemical (square-wave voltammetry), and theoretical data (density functional theory, DFT). Direct deactivation of triplet-excited riboflavin in aqueous solution, pH 6.4 at 24 degrees C, in the presence of uric acid, xanthine, and hypoxanthine strongly suggests a direct electron transfer from the purine to the triplet-excited riboflavin with k = 2.9 x 10(9) M(-1) s(-1) (DeltaH(++) = 14.7 kJ mol(-1), DeltaS(++) = -15.6 J mol(-1) K(-1)), 1.2 x 10(9) M(-1) s(-1) (DeltaH(++) = 34.3 kJ mol(-1), DeltaS(++) = +45.3 J mol(-1) K(-1)), and 1.7 x10(8) M(-1) s(-1) (DeltaH(++) = 122 kJ mol(-1), DeltaS(++) = +319 J mol(-1) K(-1)), respectively. From the respective one-electron oxidation potentials collected in aqueous solution at pH 6.4 for uric acid (E = +0.686 vs normal hydrogen electrode, NHE), xanthine (E = +1.106 vs NHE), and hypoxanthine (E = +1.654 vs NHE), the overall free energy changes for electron transfer from the quencher to the triplet-excited riboflavin are as follows: uric acid (DeltaG(o) = -114 kJ mol(-1)), xanthine (DeltaG(o) = -73.5 kJ mol(-1)), hypoxanthine (DeltaG(o) = -20.6 kJ mol(-1)), and purine (DeltaG(o) > 0). The inertness observed for purine toward triplet-excited riboflavin corroborates with its electrochemical inactivity in the potential range from 0 up to 2 V vs NHE. These data are in agreement with the DFT results, which show that the energy of the purine highest occupied molecular orbital (HOMO) (-0.2685 arbitrary unit) is lower than the energy of the semioccupied molecular orbital (SOMO) (-0.2557 a.u.) of triplet-excited riboflavin, indicating an endergonic process for the electron-transfer process. The rate-determining step for deactivation by purine derivatives can be assigned to an electron transfer from the purine derivative to the SOMO orbital of the triplet-excited riboflavin. The results show that uric acid may compete with oxygen and other antioxidants to deactivate triplet-excited riboflavin in milk serum and other biological fluids leading to a free radical process.

Activation of carbon dioxide by bicyclic amidines.

Activation of the carbon dioxide molecule was achieved using bicyclic amidines (DBU, PMDBD, and DBN). The solution reaction of CO(2) with amidines yielded the corresponding zwitterionic complexes through the formation of a N-CO(2) bond. (13)C NMR data confirmed the carbamic nature of the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2). However, when these adducts were crystallized, the X-ray analyses of the single crystals were in agreement with bisamidinium bicarbonate salt structures, indicating that structural changes occurred in the crystallization process. The elemental and thermogravimetric analysis data for the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2), initially obtained by the direct reaction of amidines with CO(2), suggest that these molecules are probably associated with one molecule of water by hydrogen-bond formation (amidinium(+)-COO(-)...H(2)O). A correlation was observed between the thermal stability and the transcarboxylating activity for the amidine-CO(2) complexes. Theoretical calculations of hardness were performed at the B3LYP/cc-pVTZ level of theory and showed concordance with the experimental reactivity of DBU and PMDBD toward CO(2).

Reactivity of bovine whey proteins, peptides, and amino acids toward triplet riboflavin as studied by laser flash photolysis.

The reaction between the triplet excited state of riboflavin and amino acids, peptides, and bovine whey proteins was investigated in aqueous solution in the pH range from 4 to 9 at 24 degrees C using nanosecond laser flash photolysis. Only tyrosine and tryptophan (and their peptides) were found to compete with oxygen in quenching the triplet state of riboflavin in aqueous solution, with second-order rate constants close to the diffusion limit, 1.75 x 10(9) and 1.40 x 10(9) L mol(-1) s(-1) for tyrosine and tryptophan, respectively, with beta-lactoglobulin and bovine serum albumin having comparable rate constants of 3.62 x 10(8) and 2.25 x 10(8) L mol(-1) s(-1), respectively. Tyrosine, tryptophan, and their peptides react with the photoexcited triplet state of riboflavin by electron transfer from the tyrosine and tryptophan moieties followed by a fast protonation of the resulting riboflavin anion rather than by direct H-atom abstraction, which could be monitored by time-resolved transient absorption spectroscopy as a decay of triplet riboflavin followed by a rise in riboflavin anion radical absorption. For cysteine- and thiol-containing peptides, second-order rate constants depend strongly on pH, for cysteine corresponding to pKaRSH = 8.35. H-atom abstraction seems to operate at low pH, which with rising pH gradually is replaced by electron transfer from the thiol anion. From the pH dependence of the second-order rate constant, the respective values for the H-atom abstraction (k = 1.64 x 10(6) L mol(-1) s(-1)) and for the electron transfer (k = 1.20 x 10(9) L mol(-1) s(-1)) were determined.

Comparison between cachaça and rum using pattern recognition methods.

The differentiation between cachaça and rum using analytical data referred to alcohols (methanol, propanol, isobutanol, and isopentanol), acetaldehyde, ethyl acetate, organic acids (octanoic acid, decanoic acid, and dodecanoic acid), metals (Al, Ca, Co, Cu, Cr, Fe, Mg, Mn, Ni, Na, and Zn), and polyphenols (protocatechuic acid, sinapaldehyde, syringaldehyde, ellagic acid, syringic acid, gallic acid, (-)-epicatechin, vanillic acid, vanillin, p-coumaric acid, coniferaldehyde, coniferyl alcohol, kaempferol, and quercetin) is described. The organic and metal analyte contents were determined in 18 cachaça and 21 rum samples using chromatographic methods (GC-MS, GC-FID, and HPLC-UV-vis) and inductively coupled plasma atomic emission spectrometry, respectively. The analytical data of the above compounds, when treated by principal component analysis, hierarchical cluster analysis, discriminant analysis, and K-nearest neighbor analysis, provide a very good discrimination between the two classes of beverages.

4,4'-dithiodipyridine as a bridging ligand in osmium and ruthenium complexes: the electron conductor ability of the -S-S- bridge.

The compounds [Ru(NH(3))(5)(dtdp)](TFMS)(3), [Os(NH(3))(5)(dtdp)](TFMS)(3), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](TFMS)(6), [(NH(3))(5)Os(dtdp)Ru(NH(3))(5)](TFMS)(3)(PF(6))(2), and [(NH(3))(5)Os(dtdp)Fe(CN)(5)] (dtdp = 4,4'-dithiodipyridine, TFMS = trifluoromethanesulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and (1)H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH(3))(5)(dtdp)](3+) as a function of the solution pH enable us to calculate the pK(a) for the [Os(NH(3))(5)(dtdpH)](4+) and [Os(NH(3))(5)(dtdpH)](3+) acids as 3.5 and 5.5, respectively. The comparison of the above pK(a) data with that for the free ligand (pK(1) = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](6+), is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the pi orbitals of the dttp ligand relative to that found in [Os(NH(3))(5)(dtdp)](3+). The comproportionation constant, K(c) = 2.0 x 10(5), for the equilibrium equation [Os(II)Os(II)] + [Os(III)Os(III)] right harpoon over left harpoon 2[Os(II)Os(III)] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH(3))(5)Os(dtdp)Os(NH(3))(5)](5+) (lambda(MMCT) = 1665 nm, epsilon = 3.5 x 10(3) M(-)(1) cm(-)(1), deltanu(1/2) = 3.7 x 10(3) cm(-)(1), alpha = 0.13, and H(AB) = 7.8 x 10(2) cm(-)(1)), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH(3))(5)Os(III)(dtdp)Ru(II)(NH(3))(5)](5+) (lambda(MMCT) = 965 nm, epsilon = 2.2 x 10(2) M(-)(1) cm(-)(1), deltanu(1/2) = 3.0 x 10(3) cm(-)(1), and H(AB) = 2.2 x 10(2) cm(-)(1)) and [(NH(3))(5)Os(III)(dtdp)Fe(II)(CN)(5)] (lambda(MMCT) = 790 nm, epsilon = 7.5 x 10 M(-)(1) cm(-)(1), deltanu(1/2) = 5.4 x 10(3) cm(-)(1), and H(AB) = 2.0 x 10(2) cm(-)(1)) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K(c) and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.

Kinetic, mechanistic, and DFT study of the electrophilic reactions of nitrosyl complexes with hydroxide.

We present a kinetic study of OH(-) additions to several nitrosyl complexes containing mainly ruthenium and different coligands (polypyridines, amines, pyridines, cyanides). According to a first-order rate law in each reactant, we propose a fast ion pair formation equilibrium, followed by addition of OH(-) to the [MX(5)NO](n) moieties, with formation of the [MX(5)NO(2)H](n(-1)) intermediates. Additional attack by a second OH(-) gives the final products, [MX(5)NO(2)]((n-2)). A linear plot was found for ln k(4) (the addition rate constant) against the redox potential for nitrosyl reduction, E(NO+/-NO), showing a free-energy relationship with a slope close to 20 V(-1), consistent with an associative mechanism. Theoretical DFT calculated descriptors, as the charge density in the [MNO] moieties and the LUMO energies, qualitatively correlate with the rate constants. A linear to bent transformation was calculated for the nitrosyl complexes, as they evolve to the angular MNO(2)H and MNO(2) complexes. The geometries were optimized for the different complexes and adduct-intermediates, showing significant changes in the relevant distances and angles upon OH(-) addition. IR vibrations and electronic transitions were also calculated. The complete reaction profile was studied for the nitroprusside ion, including the description of the transition state structure. Experimental activation parameters revealed that both the activation enthalpies and entropies increase when going from the negatively charged to the positively charged complexes. As the rate constants increase in the same direction, we conclude that the reactions are entropically driven, compensating, this function, the increase in the activation enthalpies. The latter trend can be explained by the energies involved in angular reorganization after OH(-) coordination, which are larger as the positive charge in the nitrosyl moiety becomes larger. The use of E(NO+/-NO) as a predictive tool for electrophilic reactivity could be extended to similar reactions implying other nucleophiles, such as amines and thiolates.

In vivo effects of the controlled NO donor/scavenger ruthenium cyclam complexes on blood pressure.

Ruthenium(II/III) complexes able to bind and release NO* were tested in vivo, in conscious Wistar rats instrumented for continuous blood pressure (BP) measurement and administration of in bolus injections (5 to 100 nmol/Kg i.v.) of trans-[Ru(II)Cl(NO+)(cyclam)](PF6)2 (cyclam-NO) or sodium nitroprusside (SNP). For normotensive rats, cyclam-NO produced a sustained 10% BP reduction of basal MAP during 7 +/- 0.4 to 11 +/- 0.3 min. In acute hypertensive rats, cyclam-NO produced BP reduction 3-fold larger than in normotensive rats and similar to that of SNP (maximal effect: 41 +/- 1.3 vs. 45 +/- 2.2 mmHg, respectively). However, the duration of the effect of cyclam-NO was 13 to 21-fold longer than that of SNP. The hypotensive effect of cyclam-NO was fully blocked in presence of continuous infusion of a NO* scavenger, carboxy-PTIO (6 mmol/Kg/min), or of the inhibitor of cGMP activation, methylene blue (83 nmol/Kg/min), or of the cyclam-NO precursor, trans-[RuCl(tfins)(cyclam)](tfms) (cyclam-tfms) (500 mmol/Kg/min). The long lasting BP reduction of cyclam-NO can be interpreted in terms of a slower rate of NO* release (k-NO = 2.2 x 10(-3) S(-1) at 35 degrees C) following chemical reduction (E(0') = 0.10 V vs NHE). In summary, cyclam-NO showed an hypotensive effect around 20 times longer than SNP in either normotensive or hypertensive rats, which was completely inhibited by methylene blue or carboxy-PTIO. Continuous infusion of cyclam-tfms completely blocked the hypotensive effect of cyclam-NO by scavenging the NO* released by the reduced cyclam-NO.

Spectrophotometric determination of caramel content in spirits aged in oak casks.

A new methodology was developed for determination of caramel in spirits aged in oak casks. The method is based on differences between the electronic spectra of oak aqueous alcoholic extracts and caramel solutions in the same solvent. The data were treated by 2 different approaches: the simplest one was based on the plot of caramel concentration versus the ratio of absorbance at 210 and 282 nm; the other was based on a partial least squares (PLS) calibration model using the first derivative of the spectral data. Both methodologies were applied to analysis of 159 aged spirit samples. The mean caramel content of several Brazilian sugar cane spirits (cachaça) and all United States whiskies was smaller than that of Scottish whiskies and other brandies from several countries. Correlation was good between caramel concentrations for the same sample calculated by the 2 methods. The uncertainties following PLS and the absorbance ratio method were 0.01 and 0.03 g/L, respectively, for a sample containing 0.45 g/L caramel. Treatment of UV-VIS spectra by pattern recognition using hierarchical clustering analysis and principal components analysis allowed discrimination of the samples as a function of their caramel content. It was possible to distinguish U.S. whiskies from other whiskies, but a clear differentiation among Brazilian cachaças as a function of their geographic origin was not feasible. Small caramel quantities as low as 0.08 g/L were clearly detected by these methodologies.

Ruthenium Nitrosyl Complexes with N-Heterocyclic Ligands.

A new route was developed for preparing a series of trans nitrosyl complexes of general formula trans-[Ru(NH(3))(4)L(NO)](BF(4))(3), where L = imidazole, L-histidine, pyridine, or nicotinamide. The complexes have been characterized by elemental analysis, molar conductance measurements, UV-visible, infrared, proton nuclear magnetic, and electron paramagnetic resonance spectroscopies, and electrochemical techniques. The compounds possess relatively high nu(NO) stretching frequencies indicating that a high degree of positive charge resides on the coordinated nitrosyl group. The nitrosyl complexes react with OH(-) according to the equation trans-[Ru(NH(3))(4)L(NO)](3+) + 2OH(-) right arrow over left arrow trans-[Ru(NH(3))(4)L(NO(2))](+) + H(2)O, with a K(eq) (at 25.0 degrees C in 1.0 mol/L NaCl) of 2.2 x 10(5), 5.9 x 10(7), 9.7 x 10(10), and 4.6 x 10(13) L(2) mol(-)(2) for the py, nic, imN, and L-hist complexes, respectively. Only one redox process attributed to the reaction [Ru(II)(NH(3))(4)L(NO(+))](3+) + e(-) right arrow over left arrow trans-[Ru(II)(NH(3))(4)L(NO(0))](2+) was observed in the range -0.45 to 1.20 V for all the nitrosyl complexes. Linear correlations are observed in plots of nu(NO) versus E(1/2) and of E(1/2) versus summation operatorE(L) showing that the oxidizing strength of the coordinated NO increases with increase in L pi-acidity. The crystal structure analysis of trans-[Ru(NH(3))(4)nicNO](2)(SiF(6))(3) shows that the mean Ru-N-O angle is very close to 180 degrees (177 +/- 1 degrees ) and the mean N-O distance is 1.17 +/- 0.02 Å, thus confirming the presence of the Ru(II)-NO(+) moiety in the nitrosyl complexes studied.