Redox chemistry and electronic properties of 2,3,5,6-tetrakis(2-pyridyl)pyrazine-bridged diruthenium complexes controlled by N,C,N '-biscyclometalated ligands

To investigate the consequences of cyclometalation for electronic communication in dinuclear ruthenium complexes, a series of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) bridged diruthenium complexes was prepared and studied. These complexes have a central tppz ligand bridging via nitrogen-to-ruthenium coordination bonds, while each ruthenium atom also binds either a monoanionic, N,C,N'-terdentate 2,6-bis(2'-pyridyl)phenyl (R-N boolean AND C boolean AND N) ligand or a 2,2':6',2 ''-terpyridine (tpy) ligand. The N,C,N'-, that is, biscyclometalation, instead of the latter N,N', N ''-bonding motif significantly changes the electronic properties of the resulting complexes. Starting from well-known [{Ru(tpy)}(2)(mu-tppz)](4+) (tpy = 2,2':2 '',6-terpyridine) ([3](4+)) as a model compound, the complexes [{Ru(R-N boolean AND C boolean AND N)}(mu-tppz){Ru(tpy)}](3+) (R-N boolean AND C(H)boolean AND N = 4-R-1,3-dipyridylbenzene, R = H ([4a](3+)), CO2Me ([4b](3+))), and [{Ru(R-N boolean AND C boolean AND N)}(2)(mu-tppz)](2+), (R = H ([5a](2+)), CO2Me ([5b](2+))) were prepared with one or two N,C,N'-cyclometalated terminal ligands. The oxidation and reduction potentials of cyclometalated [4](3+) and [5](2+) are shifted negatively compared to non-cyclometalated [3](4+), the oxidation processes being affected more significantly. Compared to [3](4+), the electronic spectra of [5](2+) display large bathochromic shifts of the main MLCT transitions in the visible spectral region with low-energy absorptions tailing down to the NIR region. One-electron oxidation of [3](4+) and [5](2+) gives rise to low-energy absorption bands. The comproportionation constants and NIR band shape correspond to delocalized Robin-Day class III compounds. Complexes [4a](3+) (R = H) and [4b](3+) (R = CO2Me) also exhibit strong electronic communication, and notwithstanding the large redox-asymmetry the visible metal-to-ligand charge-transfer absorption is assigned to originate from both metal centers. The potential of the first, ruthenium-based, reversible oxidation process is strongly negatively shifted. On the contrary, the second oxidation is irreversible and cyclometalated ligand-based. Upon one-electron oxidation, a weak and low-energy absorption arises.

Steric stabilisation of the P_P bond in a bulky tetraorganodiphosphine: synthesis, characterisation and X-ray structure determination of tetrakis(2,4,6-triisopropylphenyl)diphosphine

We report the synthesis and characterisation of tetrakis(2,4,6-triisopropylphenyl)diphosphine. Synthesis is effected by the treatment of PCl3 with an excess of 2,4,6-triisopropylphenyllithium (or the equivalent Grignard reagent) in 70% yield. While under normal circumstances the triarylphosphine would be expected, excessive bulk prevents this, and the resulting diphosphine is, unusually, stable to PP cleavage by further organolithium moieties. The compound is stable, both thermally (m.p. 185°C) and to air and water in the solid state, although conversion to the equivalent diorganophosphinate ester is effected by boiling ethanolic solutions in air. Crystallisation from hexane/ethanol afforded pale yellow crystals of X-ray quality. The molecule is characterised by m.p., IR, NMR, elemental analysis (C, H, P) and MS. The X-ray structure shows an antiperiplanar conformation with a PP separation of 2.2461(16) Å. Comparisons are made with other diphosphines, the title compound being only the fourth simple diphosphine to be structurally characterised.

Divinyldisiloxane and divinylsilane complexes of rhodium(I)

Reaction of the tetrakis(cyclooctene)rhodium(I) complex [{Rh(C8H14-c)2(μ-Cl)}2] with the appropriate divinyldisiloxane molecules (ViSiR2)2O (R=Me or Ph) yields, by displacement of the cycloctene ligands, the complexes [{Rh(ViSiR2)2O(μ-Cl)}2] (R=Me (1) or Ph (2)). These react further with a tertiary phosphine PR3 to give cis-[Rh{(ViSiR2)2O}(PR′3)Cl] (R′=Ph or C6H4Me-p). The complex cis-[{Rh(Vi2SiMe2)(μ-Cl)}2] (7) was similarly prepared by the displacement of ethylene from [{Rh(C2H4)2(μ-Cl)}2] by the divinyldimethylsilane Vi2SiMe2. X-ray molecular structures of the crystalline complexes 1, 2 and 7 show a distorted square planar Rh(I) environment, the CH2CH groups being orthogonal to this plane; 1 and 2 have the Rh–(ViSiR2)2O metallacycle in the chair conformation, but differ in the nature of the central Rh(Cl)RhCl core, which is planar for 1 and puckered for 2, but each of 1 and 2 is the rac-diastereoisomer, whereas 7 has the meso-configuration. In solution 1 and 2 exist as a mixture of isomers, probably the rac- and meso-pairs as established by multinuclear NMR spectral studies. A series of saturation transfer NMR spectroscopic experiments showed that the divinyldisiloxane ligands in [{Rh(ViSiPh2)2O(μ-Cl)}2] underwent a dynamic process involving the dissociation, rotation and then reassociation of the vinyl groups.

Synthesis and X-ray crystal and molecular structure of tetrakis(2,2-dimethyl-1-phenylethenyl)chromium(IV), the first structurally-characterised homoleptic alkenyl compound of a transition metal

The title compound, the first homoleptic Group 6A metal alkenyl, has been prepared from CrCl3·3(thf), and its properties, including X-ray crystal structure determination, are reported.

Multistep π dimerization of tetrakis(n-decyl)heptathienoacene radical cations: a combined experimental and theoretical study

Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C+) form exceptionally stable p-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary p-dimerization process is investigated here with a focus on the ultimate[D4T7C+]2 p-dimer dication and yet-unreported transitoryspecies formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the p-dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one-electron oxidation: 1) a different transient conformation of the ultimate [D4T7C+]2 p-dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]2C+ p-dimer radical cations formed prior to the fully oxidized [D4T7]2C+ p-dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems.

Expression Patterns of Cell Adhesion Molecules in Mice`s Lung After Administration of Meso-2,3-Dimercaptosuccinic Acid-Coated Maghemite Nanoparticles

We studied the expression pattern of cell adhesion molecules associated to transendothelial migration of leukocytes in different lung`s vascular compartments after administration of a magnetic fluid sample containing maghemite nanoparticles surface-coated with meso-2,3-dimercaptosuccinic acid. The analyses were conducted in mice 4 and 12 h after endovenous administration of the magnetic fluid in control mice. Firstly, the migratory activity of leukocytes after magnetic fluid surface-coated with meso-2,3-dimercaptosuccinic acid administration was confirmed using broncho-alveolar lavage and light microscopy. Then, the expression of cell adhesion molecules in the lung`s vascular compartments was investigated by immunofluorescence microscopy of frozen sections, using antibodies against L-selectin, P-selectin, E-selectin, macrophage antigen-1, and leukocyte function associated antigen-1. L- and P-selectin showed similar pattern of expression in the pulmonary vasculature in animals treated with magnetic fluid and in the control group. In contrast, macrophage antigen-1 and leukocyte function associated antigen-1 were found in capillary only in animals treated with magnetic fluid surface-coated with meso-2,3-dimercaptosuccinic acid administration. In addition, after magnetic fluid administration E-selectin was found in post-capillary sites. Our findings demonstrated that magnetic fluid surface-coated with meso-2,3-dimercaptosuccinic acid administration exhibits modulation effects on expression patterns of E-selectin, macrophage antigen-1, and leukocyte function associated antigen-1 in the lung`s vascular compartments. These findings are very important in a strategy to reduce the potential toxicity of magnetic fluid surface-coated with meso-2,3-dimercaptosuccinic acid administration for medical applications.

On an Electrode Modified by a Supramolecular Ruthenium Mixed Valence (Ru(II)/Ru(III)) Diphosphine-Porphyrin Assembly

Three novel polymetallic ruthenium (III) meso-tetra(4-pyridyl)porphyrins containing peripheral ""RuCl(3)(dppb)"" moieties have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCl(3)(dppb)](4)} porphyrin complex crystallizes in the triclinic space group FT. This structure is discussed and compared with the crystal data for the mer-[RuCl(3)(dppb)(py)]. The {TPyP[RuCl(3)(dppb)](4)} and {CoTPyP[RuCl(3)(dppb)](4)} porphyrins were used to obtain electrogenerated films on ITO and glass carbon electrode surfaces, respectively. Such tetraruthenated porphyrins form films of a mixed-valence species {TPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2)(4n2+) and {CoTPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2n)(4n2+) on the electrode surface. The modified electrode with {CoTPyP[RuCl(3)(dppb)](4)} is very stable and can be used to detect organic substrates such as catechol.

Synthesis and structure of the dimeric copper(II) complex tetrakis[N-thiazol-2-yl-(4-methylphenyl)sulfonamidate]dicopper(II)

The coordination chemistry of the ligand N-thiazol-2-yl-toluenesulfonamidate towards the copper(II) ion has been investigated using an electrochemical synthesis method. The X-ray structure of this complex was elucidated and is discussed. The compound crystallised in the monoclinic crystal system, P2(1)/c space group with a = 17.3888(9), b = 16.3003(9), c = 18.3679(9) angstrom and beta = 114.3640(10)degrees. Four bidentate sulfathiazolato anions bridge two metal centers in a paddle-wheel fashion, with the nitrogen atoms as donors to give a dimeric species with a Cu center dot center dot center dot Cu distance of 2.7859(5) angstrom.

Relationship between structure and photoactivity of porphyrins derived from protoporphyrin IX

Protoporphyrin (Pp IX) derivatives were prepared to study the relationship between photosensitizer structure and photoactivity, with an emphasis on understanding the role of membrane interactions in the efficiency of photosensitizers used in photodynamic therapy (PDT). The synthetic strategies described here aimed at changing protoporphyrin periferic groups, varying overall charge and oil/water partition, while maintaining their photochemical properties. Three synthetic routes were used: (1) modification of Pp IX at positions 3(1) and 8(1) by addition of alkyl amine groups of different lengths (compounds 2-5), (2) change of Pp IX at positions 13(3) and 17(3), generating alkyl amines (compounds 6 and 7), a phosphate amine (compound 8), and quarternary ammonium compounds (compounds 9 and 10), and (3) amine-alkylation of Hematoporphyrin IX (Hp IX) at positions 3(1), 8(1), 13(3) and 17(3) (compound 12). Strategy 1 leads to hydrophobic compounds with low photocytotoxicity. Strategy 2 leads to compounds 6-10 that have high levels of binding/incorporation in vesicles, mitochondria and cells, which are indicative of high bioavailability. Addition of the phosphate group (compound 8), generates an anionic compound that has low liposome and cell incorporation, plus low photocytotoxicity. Compound 12 has intermediate incorporation and photocytotoxic properties. Compound modification is also associated with changes in their sub-cellular localization: 30% of 8 (anionic) is found in mitochondria as compared to 95% of compound 10 (cationic). Photocytotoxicity was shown to be highly correlated with membrane affinity, which depends on the asymmetrical and amphiphilic characters of sens, as well as with sub-cellular localization.

Supramolecular assemblies of a new class of nonplanar cationic metalloporphyrins and anionic metallophthalocyanines

The heteroaggregation behavior between a new class of nonplanar cationic beta-octabrominated meso-alkylpyridinium zinc(II)-porphyrins (beta-Br(8)(ZnP)) and anionic tetrasulfonated metallophthalocyanines (MTSPc, M = Ni(II) and Cu(II)) has been studied by UV-Vis electronic spectroscopy, in dimethylsulfoxide (DMSO) solution. The heteroaggregate stoichiometry and the association constants were determined by means of Job plots. Dimers and unexpected trimers, taking into account the existence of axially coordinated DMSO molecules to the central metal in both beta-Br(8)(ZnP) and MTSPc complexes, are formed in solution. The spectroscopic properties of the heteroaggregates are markedly different from those observed in the correspondent planar cationic derivatives, the heteroaggregates showing major changes predominantly in the beta-Br(8)(ZnP) Soret band region and minor effects in the MTSPc Q bands. The observed changes in the Soret band region (red/blue shifts, decrease in the absorption intensities) depend on the nature of the alkyl substituent attached to the meso-pyridinium group. The greater versatility of the nonplanar porphyrins accommodating the meso-substituents in out-of-plane and in-plane conformations is proposed to explain the observed stoichiometries and the differences on the heteroaggregates spectroscopic properties for each beta-Br(8)(ZnP) compound. The likely conformations assumed by the meso-substituents in these beta-Br(8)(ZnP) compounds and its spectroscopic characteristics are in accordance with the participation of the substituents as the main factor on the extent of the observed red-shifted spectra in nonplanar porphyrins. The obtained association constants (K(IP)) for the dimers and trimers are lower than those previously found for the similar planar cationic porphyrin systems, due to the lack of extensive pi-pi interactions and to the less effective approximation between the ionic groups, resulting in loosened heteroaggregates, particularly for the trimeric systems. Furthermore, the experimental results suggest that the NiTSPc is more distorted in DMSO solution than the CuTSPc derivative, favoring the interaction with the nonplanar beta-Br(8)(ZnP) compounds. (C) 2007 Elsevier B.V. All rights reserved.

Electroluminescent devices based on rare-earth tetrakis beta-diketonate complexes

In this paper the synthesis, photo luminescence and electroluminescence investigation of the novel tetrakis beta-diketonate of rare-earth complexes such as M[Eu(dbM)(4)] and M[Tb(acac)(4)] with a variety of cationic ligands, M=Li(+), Na(+) and K(+) have been investigated. The emission spectra of the Eu(3+) and Tb(3+) complexes displayed characteristic narrow bands arising from intraconfigurational transitions of trivalent rare-earth ions and exhibited red color emission for the Eu(3+) ion ((5)D(0) -> F(J), J=0-6) and green for the Tb(3+) ion ((5)D(4) -> (7)F(J), J = 6-0). The lack of the broaden emission bands arising from the ligands suggests the efficient intramolecular energy transfer from the dbm and acac ligands to Eu(3+) and Tb(3+) ions, respectively. In accordance to the expected, the values of PL quantum efficiency (eta) of the emitting (5)D(0) state of the tetrakis(beta-diketonate) complexes of Eu(3+) were higher compared with those tris-complexes. Therefore, organic electroluminescent (EL) devices were fabricated with the structure as follows: indium tin oxide (ITO)/hole transport layer (HTL) NPB or MTCD/emitter layer M[RE(beta-diketonate)(4)] complexes)/Aluminum (Al). All the films were deposited by thermal evaporation carried out in a high vacuum environment system. The OLED light emission was independent of driving voltage, indicating that the combination of charge carriers generates excitons within the M[RE(beta-diketonate)(4)] layers, and the energy is efficiently transferred to RE(3+) ion. As a best result, a pure red and green electroluminescent emission was observed from the Eu(3+) and Tb(3+) devices, confirmed by (X,Y) color coordinates. (C) 2008 Elsevier B.V. All rights reserved.

New hydrazine sensors based on electropolymerized meso-tetra (4-sulphonatephenyl)porphyrinate manganese (III)/silver nanomaterial

A new electrocatalytic active porphyrin nanocomposite material was obtained by electropolymerization of meso-tetra(4-sulphonatephenyl) porphyrinate manganese(III) complex (MnTPPS) in alkaline solutions containing sub-micromolar concentrations of silver chloride. The modified glassy carbon electrodes efficiently oxidize hydrazine at 10 mV versus Ag/AgCl, dramatically decreasing the overpotential of conventional carbon electrodes. The analytical characteristics of this amperometric sensor coupled with batch injection analysis (BIA) technique were explored. Wide linear dynamic range (2.5 x 10(-7) to 2.5 x 10(-4) mol L-1), good repeatability (R.S.D. = 0.84%, n = 30) and low detection (3.1 x 10(-8) mol L-1) and quantification (1.0 x 10(-7) mol L-1) limits, as well as very fast sampling frequency (60 determinations per hour) were achieved. (c) 2007 Elsevier B.V. All rights reserved.

Synthesis, characterization and spectroscopic investigation of new tetrakis(acetylacetonato)thulate(III) complexes containing alkaline metals as countercations

In this work a series of tetrakis complexes C[Tm(acac)(4)] where C(+) = Li(+) Na(+) and K(+) countercations and acac = acetylacetonate ligand were synthesized and characterized for photoluminescence investigation The relevant aspect is that these complexes are water-free in the first coordination sphere The emission spectra of the tetrakis Tm(3+)-complexes present narrow bands characteristic of the (1)G(4)->(3)H(6) (479 nm) (1)G(4)->(3)F(4) (650 nm) and (1)G(4) ->(3)H(5) (779 nm) transitions of the Tm(3+) ion with the blue emission color at 479 nm as the most prominent one The lifetime values (tau) of the emitting (1)G(4) level of the C[Tm(acac)(4)] complexes were 344 360 and 400 ns for the Li(+) Na(+) and K(+) countercations respectively showing an increasing linear behavior versus the ionic radius of the alkaline ion An efficient intramolecular energy transfer process from the triplet state (T) of the ligands to the emitting (1)G(4) state of the Tm(3+) ion is observed This fact together with the absence of water molecules in first coordination sphere allows these tetrakis Tm(3+)-complexes to act as efficient blue light conversion molecular devices (c) 2010 Elsevier B V All rights reserved

Descrição osteológica de materiais pós-cranianos de dois cinodontes não-mamalianos do meso/neotriássico (formação santa maria, bacia do paraná) do Rio Grande do Sul, Brasil

Na presente dissertação, foram descritos materiais pós-cranianos de dois cinodontes não-mamalianos (Therapsida, Cynodontia) do Triássico sul-rio-grandense (Bacia do Paraná, Formação Santa Maria). Os espécimes descritos (UFRGS PV-0146-T, um chiniquodontídeo, e UFRGS PV-0715-T, um traversodontídeo) representam ramos distintos na evolução dos cinodontes (Probainognathia e Cynognathia, com os chiniquodontídeos pertencendo ao primeiro grupo e estando mais intimamente relacionados ao surgimento dos mamíferos). A comparação entre estes dois espécimes e os cinodontes já descritos na literatura não mostrou a presença de nenhum padrão que pudesse ser aplicado ao esqueleto pós-craniano das duas linhagens por eles representadas. Por vezes, o chiniquodontídeo mostrou similaridades anatômicas com táxons de Cynognathia e o traversodontídeo apresentou aspectos mais similares aos Probainognathia. O fato de os dois espécimes estudados apresentarem semelhanças morfológicas com táxons filogeneticamente não muito próximos e diferenças em relação à táxons mais estreitamente vinculados indica a ocorrência de inúmeras homoplasias na evolução dos cinodontes e mostra que a interpretação das relações filogenéticas entre estes animais (e sua implicação mais significativa, a que diz respeito ao surgimento e à evolução dos mamíferos) deve ser tratada com extremo cuidado, uma vez que homoplasias certamente ocorrem também no esqueleto sincraniano e na dentição, nos quais estão baseadas as hipóteses filogenéticas mais usuais.

Análise descritiva dos sistemas convectivos de escala meso-(alpha) através das imagens de satélite GOES-8

Na América do Sul há uma forte incidência de Sistemas Convectivos de Mesoescala (SCM), que na maioria das vezes, estão associados a desastres naturais. Estes causam impactos não só do ponto de vista meteorológico, mas também social e econômico. Neste trabalho analisa-se 49 Sistemas Convectivos de Meso-α, que atuam na América do Sul, durante os anos de 1999, 2000 e 2001. Com o auxílio de imagens do satélite GOES-8(canal IR, 10,4μm), identifica-se padrões comportamentais ao longo da vida dos SCM. Para a caracterização da evolução temporal e espacial, faz-se uma divisão da análise em duas partes: temporal e espacial. Na análise temporal, observam-se as variações rítmicas na intensificação da atividade convectiva. Na análise espacial, são observadas características como: tamanho e tempo de vida dos SCM e de seus respectivos núcleos distâncias entre os núcleos, trajetórias dos SCM entre outras características comportamentais dos núcleos convectivos que constituem o sistema. A análise dos dados mostra que mais da metade dos casos analisados sofrem dois tipos de variações na atividade convectiva, uma com período de 12 horas, e outra com menor periodicidade, 5,1 horas. Mostra-se que a evolução espacial dos SCM dá-se em média na direção das latitudes mais baixas, de forma discreta com o aparecimento de novos núcleos, na direção noroeste em relação ao núcleo antigo.