André Luiz Barboza Formiga

Photocytotoxic activity of a nitrosyl phthalocyanine ruthenium complex--a system capable of producing nitric oxide and singlet oxygen.

The synthesis, structural aspects, pharmacological assays, and in vitro photoinduced cytotoxic properties of [Ru(NO)(ONO)(pc)] (pc=phthalocyanine) are described. Its biological effect on the B16F10 cell line was studied in the presence and absence of visible light irradiation. At comparable irradiation levels, [Ru(NO)(ONO)(pc)] was more effective than [Ru(pc)] at inhibiting cell growth, suggesting that occurrence of nitric oxide release following singlet oxygen production upon light irradiation may be an important mechanism by which the nitrosyl ruthenium complex exhibits enhanced biological activity in cells. Following visible light activation, the [Ru(NO)(ONO)(pc)] complex displayed increased potency in B16F10 cells upon modifications to the photoinduced dose; indeed, enhanced potency was detected when the nitrosyl ruthenium complex was encapsulated in a drug delivery system. The liposome containing the [Ru(NO)(ONO)(pc)] complex was over 25% more active than the corresponding ruthenium complex in phosphate buffer solution. The activity of the complex was directly proportional to the ruthenium amount present inside the cell, as determined by inductively coupled plasma mass spectroscopy. Flow cytometry analysis revealed that the photocytotoxic activity was mainly due to apoptosis. Furthermore, the vasorelaxation induced by [Ru(NO)(ONO)(pc)], proposed as NO carrier, was studied in rat isolated aorta. The observed vasodilation was concentration-dependent. Taken together, the present findings demonstrate that the [Ru(NO)(ONO)(pc)] complex induces vascular relaxation and could be a potent anti-tumor agent. Nitric oxide release following singlet oxygen production upon visible light irradiation on a nitrosyl ruthenium complex produces two radicals and may elicit phototoxic responses that may find useful applications in photodynamic therapy.

A highly efficient redox chromophore for simultaneous application in a photoelectrochemical dye sensitized solar cell and electrochromic devices

We synthesized a novel series of compounds based on a ruthenium(II) dicarboxybipyridine (dcbpy) complex containing chloro and trans-1,4-bis[2-(4-pyridyl)ethenyl]benzene (BPEB) ligands. The binuclear species Na6[{[RuII(dcbpy)2Cl}2(BPEB)] exhibits an electrochromic effect when reduced, which is assigned to the radical BPEB0/˙, similarly as in viologen-based compounds. The carboxylate groups on the 4,4′ positions of bipyridine allow a strong attachment to the TiO2 surface, contributing to an efficient and reversible electron transfer from the oxide to the chromophoric ligand, coloring the oxide film blue. The coloration efficiency CE(λ) at 633 nm was 109 cm2 C−1, which is high compared to TiO2 itself. The complex also exhibits a high photon-to-electron conversion efficiency (IPCE > 70%) when applied as a photoanode in a dye sensitized solar cell (DSSC).

Conduction and photoelectrochemical properties of monomeric and electropolymerized tetraruthenated porphyrin films

The influence of the preparation method on the structure, conduction and photoelectrochemical properties of monomeric and polymeric tetraruthenated porphyrin films on ITO glass and nanocrystalline TiO2 has been investigated. The films were characterized by STM, MAC mode SFM, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and combined electro-/photoelectrochemical techniques. The electronic diffusion coefficient D(e)C(m)2 of the films differed by three to four orders of magnitude depending on the procedure employed for the deposition process. The photoelectrochemical properties were evaluated either: by depositing the films directly on transparent ITO electrodes, under an applied bias potential and presence of O2 as electron acceptor; or by depositing the porphyrin material on nanocrystalline TiO2 in a Grätzel-type cell. In the first case the porphyrin films exhibited a typical p-type semiconductor behavior described by a Schottky junction model, while in the second the films behaved as a sensitizer of an n-type semiconductor. The photoelectrochemical properties of the porphyrin films and their performance as sensitizer in Grätzel-type cells were found to be strongly dependent on the conductivity and packing characteristics of the material. Semi-empirical calculations were performed by modified MM2 and ZINDO/S methods, in order to simulate the packing and electronic structures of the tetraruthenated porphyrin.

Synthesis, spectroscopic characterization, DFT studies, and initial antibacterial assays in vitro of a new palladium(II) complex with tryptophan

A new palladium(II) complex with the amino acid L-tryptophan (Pd-TRP) was synthesized in aqueous solution and characterized by chemical and spectroscopic methods. Elemental, ESI-QTOF mass spectrometric, and thermal analyses of the solid compound permitted proposing the [Pd(C11H11N2O2)2] · 2H2O composition. Infrared, Raman, and UV-Vis spectroscopic data indicate the coordination of the ligand to Pd(II) through monodentate oxygen of carboxylate and through nitrogen of the amino group. The 1H and 13C NMR spectroscopic data confirm coordination through the carboxylate, while 15N NMR data confirm coordination of nitrogen of NH2. Density functional theory studies confirmed nitrogen and oxygen coordination to palladium(II) as a minimum of the potential energy surface with calculations of the hessians showing no imaginary frequencies. Biological studies were performed to provide information concerning the antibacterial activities of the compound. The Pd-TRP complex was shown to be active against Gram-positive and Gram-negative pathogenic bacterial strains.

Synthesis of amine-tagged metal–organic frameworks isostructural to MIL-101(Cr)

Materials that are isostructural to MIL-101(Cr) were obtained from partial replacement of terephthalic acid to 2-aminoterephthalic acid, a linker containing amine functionalities in the synthesis media. The produced materials were characterized by different techniques, confirming the formation of the structure, their porosity and its functionalization. These results support that our simplified method to insert controllable amounts of amine functionalities on MIL-101(Cr) surface was employed successfully to produce materials that can present different surface character and reactivity.

Palladium(II) complex with S-allyl-L-cysteine: new solid-state NMR spectroscopic measurements, molecular modeling and antibacterial assays.

Nuclear magnetic resonance studies, molecular modeling and antibacterial assays of the palladium(II) complex with S-allyl-L-cysteine (deoxyalliin) are presented. Studies based on solid and solution 13C and 15N nuclear magnetic resonance (NMR) spectroscopy confirmed that the palladium(II) complex preserved the same structural arrangement in both states, with no modifications on coordination sphere when dissolved in water. Density functional theory (DFT) studies stated that the trans isomer is the most stable one. Antibacterial activities of S-allyl-L-cysteine and its palladium(II) complex were evaluated by antibiogram assays using the disc diffusion method. The palladium(II) complex showed an effective antibacterial activity against Staphylococcus aureus (Gram-positive), Escherichia coli and Pseudomonas aeruginosa (Gram-negative) bacterial cells.

Electronic Spectra of N-Heterocyclic Pentacyanoferrate(II) Complexes in Different Solvents, Studied by Multiconfigurational Perturbation Theory

Ligand-field and charge-transfer spectra of N-heterocyclic pentacyanoferrate(II) complexes [Fe(CN)5L]n− were investigated using multiconfigurational perturbation theory. The spectrum of [Fe(CN)5(py)]3– was studied in detail under vacuum and in the following polarizable continuum model (PCM) simulated solvents: acetone, acetonitrile, dimethylsulfoxide (DMSO), ethanol, methanol, and water. The ligand-field states proved to be rather insensitive to the solvent environment, whereas much stronger solvent effects were observed for the charge-transfer (CT) transitions. The nature of the intense band was confirmed as a metal-to-ligand charge transfer originating from a 3d(xz) → π(b1)* (L)-orbital transition. The difference between the calculated and experimental transition energy of this CT transition is minimal for aprotic solvents, but increases strongly with the solvent proton donor ability in the protic solvents. In an attempt to improve the description of this CT state, up to 14 solvent molecules were explicitly included in the quantum model. In DMSO, the spectra of complexes with ligands L (where L is pyridine, 4-picoline, 4-acetylpyridine, 4-cyanopyridine, pyrazine, and N-methylpyrazinium) correlate very well with the experiment.

Spin State Energetics and Oxyl Character of Mn-Oxo Porphyrins by Multiconfigurational ab Initio Calculations: Implications on Reactivity

Important electromeric states in manganese-oxo porphyrins MnO(P)(+) and MnO(PF4)(+) (porphyrinato or meso-tetrafluoroporphyrinato) have been investigated with correlated ab initio methods (CASPT2, RASPT2), focusing on their possible role in multistate reactivity patterns in oxygen transfer (OAT) reactions. Due to the lack of oxyl character, the Mn(V) singlet ground state is kinetically inert. OAT reactions should therefore rather proceed through thermally accessible triplet and quintet states that have a more pronounced oxyl character. Two states have been identified as possible candidates: a Mn(V) triplet state and a Mn(IV)O(L(•)a2u)(+) quintet state. The latter state is high-lying in MnO(P)(+) but is stabilized by the substitutions of H by F at the meso carbons (where the a2u orbital has a significant amplitude). Oxyl character and Mn-O bond weakening in these two states stems from the fact that the Mn-O π* orbitals become singly (triplet) or doubly occupied (quintet). Moreover, an important role for the reactivity of the triplet state is also likely to be played by the π bond that has an empty π* orbital, because of the manifest diradical character of this π bond, revealed by the CASSCF wave function. Interestingly, the diradical character of this bond increases when the Mn-O bond is stretched, while the singly occupied π* orbital looses its oxygen radical contribution. The RASPT2 results were also used as a benchmark for the description of excited state energetics and Mn-O oxyl character with a wide range of pure and hybrid density functionals. With the latter functionals both the Mn(V) → Mn(IV) promotion energy and the diradical character of the π bond (with empty π*) are found to be extremely dependent on the contribution of exact exchange. For this reason, pure functionals are to be preferred.

Supramolecular Interactions between Inorganic and Organic Blocks of Pentacyanoferrate/Poly(4-vinylpyridine) Hybrid Metallopolymer

The combination of organic and inorganic molecular building blocks gives rise to hybrid supramolecular materials showing properties from both chemical domains. This work presents the synthesis of metallopolymers made from poly(4-vinylpyridine) (P4VP) and pentacyanoferrate(II) at various polymer repeating unit/[Fe(CN)(5)](3-) ratios (py/Fe) and focuses on the influence of each block on the properties of the other. The solvatochromic shift of the [Fe(CN)(5)](3-) moiety was investigated as a function of the py/Fe ratio and the water molar fraction (X(H(2)O)) of the ethanol/water medium. Asymmetric solvation favoring ethanol was enhanced as the py/Fe ratio increased. The results lead to a modification of the well-established thermodynamical model for asymmetrical solvation and suggest the formation of water-rich domains within the polymer coils with a large number of [Fe(CN)(5)](3-) units. From the macromolecular perspective, the increase of [Fe(CN)(5)](3-) units resulted in higher values of intrinsic viscosity, which is rationalized by the increase of the polymer coil charge density and therefore the increase in hydrodynamic volume due to repulsive electrical forces. Evaluating the intrinsic viscosity of a sample with py/Fe = 25 in solvent mixtures with different water molar fractions, it was found that the hydrodynamic volume is maximized at intermediate X(H(2)O) values, where both the ethanol-soluble uncomplexed polymer block and the water-soluble [Fe(CN)(5)](3-)-pendant units can be suitably solvated, preventing coil shrinkage.

A-βcyclodextrin/siloxane hybrid polymer: synthesis, characterization and inclusion complexes

A hybrid polymer derived from siloxane and β-cyclodextrin (β-CD) was obtained by reaction of β-CD with g-isocyanatopropyltriethoxysilane (IPTS), followed by hydrolysis/condensation reactions, generating a β-CD-modified polysilsesquioxane resin (PSS-β-CD). PSS-β-CD hybrid was characterized by infrared spectroscopy and 13C and 29Si nuclear magnetic resonance. This hybrid was typically amorphous and thermally stable up to 180 oC. PSS-β-CD was able to form films and its morphology was evaluated by scanning electron microscopy. The capability of β-CD grafted in the hybrid polymer to form inclusion complex was evaluated by the formation of a β-CD-phenolphthalein complex using UV-Vis spectroscopy. Even without changes in pH, the red form of phenolphthalein converts to the colorless one when PSS-β-CD is immersed in the solution. Theoretical calculations (AM1 and DFT methods) show that the complex is formed through the inclusion of the phenolate ring into β-CD cavity, favoring the colorless form of phenolphthalein by more than 15 kcal mol-1.