The use of a graphite-castor oil polyurethane composite electrode for the determination of hydroquinone in photographic developers

The performance of a new graphite-castor oil polyurethane composite electrode in the determination of hydroquinone in photographic developers in a differential pulse voltammetric (DPV) procedure is described. The 60% (graphite, w/w) composite electrode presented good stability, repeatability and accurate response. Limit of detection of 934 nmol L⁻¹ was observed for hydroquinone within a linear dynamic range from 66 to 530 nmol L⁻¹. The determination of hydroquinone in a photographic developer sample showed agreement with the label values in a 95% confidence level with maximum 2% relative error and recoveries between 100.1 and 100.4%. No need of sample preparation was required since the p-methylaminophenolsulfate (metol) present in the developer formulation did not interfered in the measurements.     

Multicomponent synthesis of dihydrobenzoxazepinones by coupling Ugi and Mitsunobu reactions

Various dihydrobenzo[f][1,4]oxazepin-5-ones have been convergently prepared in 2-3 steps by coupling Ugi and Mitsunobu reactions. Two alternative methodologies were used: in the first one the Ugi condensation was followed by a Mitsunobu cyclization (2 steps); in the second one an intermolecular Mitsunobu reaction was followed by a deprotection step and then by an intramolecular Ugi reaction. Also a "convertible" isocyanide was used.     

Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.     

Isocorannulenofuran: a versatile building block for the synthesis of large buckybowls

Isocorannulenofuran, synthesized in two steps from accessible bromocorannulene, gives Diels-Alder adducts with benzynes which can be deoxygenated to produce large polycyclic aromatic hydrocarbons (PAHs) combining the bowl-shaped corannulene subunit with planar fragments. [reaction: see text]     

Computational insights into the mechanism of radical generation in B12-dependent methylmalonyl-CoA mutase

ONIOM calculations have provided novel insights into the mechanism of homolytic Co-C5' bond cleavage in the 5'-deoxyadenosylcobalamin cofactor catalyzed by methylmalonyl-CoA mutase. We have shown that it is a stepwise process in which conformational changes in the 5'-deoxyadenosine moiety precede the actual homolysis step. In the transition state structure for homolysis, the Co-C5' bond elongates by approximately 0.5 Angstroms from the value found in the substrate-bound reactant complex. The overall barrier to homolysis is approximately 10 kcal/mol, and the radical products are approximately 2.5 kcal/mol less stable than the initial ternary complex of enzyme, substrate, and cofactor. The movement of the deoxyadenosine moiety during the homolysis step positions the resulting 5'-deoxyadenosyl radical for the subsequent hydrogen atom transfer from the substrate, methylmalonyl-CoA.     

Effects of HeNe laser irradiation on experimental paracoccidioidomycotic lesions

Paracoccidioidomycosis (PCM) is the most prevalent human mycosis in Latin America. The infection is thought to take place firstly in the lungs and then may disseminate to other organs and tissues. Treatment by currently available antifungals is lengthy, the drugs may have undesirable side effects, and some are costly. Occasional resistant strains of Paracoccidioides brasiliensis, the causative agent of PCM, have been reported. So, the search for more efficient treatments or adjuvant therapies has to be continued. In this work, we evaluated the effects of HeNe laser irradiation on cutaneous inflammatory lesions caused by the inoculation of 5 x 10(6)/0.1ml yeasts cells into the back footpad of Balb/c mice. HeNe irradiation (lambda=632.8nm, 3mW, incident energy of 3J/cm(2)) was applied at days 7, 8 and 9 post-infection and histological and immunohistochemical analysis were done. Unirradiated animals were used as controls. The results showed that laser-treated mice presented reduction of footpad edema, faster cutaneous wound healing, confluent granuloma, diffuse- and more loosely distributed immunolabeling for TNF-alpha, enhanced labeling of IFN-gamma and any P. brasiliensis form detected, whereas multiple viable fungi were seen in diffuse widespread granulomas obtained from non-treated mice foot-pad. Fungi that were harvested from laser-treated animals presented no capability of growth in vitro as compared to those obtained from non-treated mice. We conclude that HeNe laser irradiation was able to inhibit the progress of inflammatory local reaction produced by P. brasiliensis infection and influence local cytokines production. We suggest that this treatment modality can be a useful coadjuvant tool to be combined with antifungal agents in the treatment of PCM ulcerations. The mechanisms involved in laser therapy of PCM lesions need further investigation.     

Synthesis, cytotoxic effect, and structure-activity relationship of Pd(II) complexes with coumarin derivatives

We report the influence of the substituent at the N atom of the ligands on the synthesis, biological activity, and stability of Pd(II) complexes of the general formula PdL(2). The compounds adopt a cis or trans configuration with respect to the substituent at the nitrogen atom. Sterically hindered substituents promote the formation of trans isomers, whereas when the nitrogen atom is unsubstituted, cis isomers are formed. The compounds were characterized by elemental analysis, infrared and 1H NMR spectroscopies, and electrospray mass spectrometry. The complexes were also studied using X-ray diffraction and computational DFT methods. Both complexes cis-3a and trans-3c exhibit square-planar geometries around the Pd(II) atom. The cytotoxic effects of these complexes were examined on two human leukemia cell lines, HL-60 and NALM-6. Pd complex cis-3a showed significant cytotoxic activity. The effects exhibited by this complex were comparable to those reported for carboplatin. Loigand 2a was not cytotoxic. Computational analysis carried out at the PB/B3LYP/LACVP**//mPW1PW91/LanL2DZ level showed excellent correlation between the energy difference of the cis and trans isomers and the cytotoxic activity, rendering computations a useful predictive tool for the design of new drugs.     

Stability and Coordination Mode of Complexes of Polyphosphates and Polymetaphosphates with Copper(II) Ions in Aqueous Solution—Potentiometric,Spectral and Theoretical Studies

Complexes of copper(II) with a number of polyphosphate and polymetaphosphate anions have been studied in aqueous solutions by potentiometric, spectroscopic and theoretical methods. Stability constants of the complexes have been determined as well as their coordination modes. Results of the equilibrium studies provided evidence for the formation of ML, MHL and ML(OH) _x type complexes with the ligands studied. The length of the polyphosphate chain was found to affect the oxygen atom charge that is reflected in the stability constants of the ML type complexes. Moreover, the stability of the complex is also influenced by the spatial arrangement of the phosphate groups in phosphates and metaphosphates. The spectral parameters observed for certain complexes have permitted us to deduce the inner coordination sphere of the studied complexes.     

High dimensional coordination polymers based on transition metals, 1,2,4,5-benzenetetracarboxylate anion and 1,3-bis(4-pyridyl)propane nitrogen ligand

The reaction between 1,2,4,5-benzenetetracarboxylic acid (H₄BT) and transition metal ions Mn⁺², Co⁺² and Cu⁺² in the presence of the N-donor co-ligand 1,3-bis(4-pyridyl) propane (BPP) has afforded three new coordination polymers named, {[Mn₄(BT)₂(BPP)₆(H₂O)₆]·4H₂O}_nMnBTBPP, {[Co₂(BT)(BPP)₂(H₂O)₆]·2H₂O}_nCoBTBPP and {[Cu₂(BT)(BPP)₂(H₂O)]·6H₂O}_nCuBTBPP. They were characterized by a combination of analytical, spectroscopic and crystallographic methods. According to the thermal analysis results all the compounds present coordinated and lattice water molecules in the structures. In compounds MnBTBPP and CoBTBPP, the metal centers exhibit octahedral geometry while in compound CuBTBPP, the Cu⁺² ions adopt square-planar and square-pyramidal geometries. In all cases, both BPP and BT ligands are coordinated to the metal sites in the bridging mode extending the polymeric networks. The BT ligand carboxylate groups act in a monodentate coordination mode as indicated by the Raman spectra data through the Δν [ν_asym(COO) − ν_sym(COO)] value.     

Differentiability of the isoperimetric profile and topology of analytic Riemannian manifolds

We show that smooth isoperimetric profiles are exceptional for real analytic Riemannian manifolds. For instance, under some extra assumptions, this can happen only on topological spheres. To cite this article: R. Grimaldi et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).