Ubirajara P. Rodrigues-Filho

Efficient and clean synthesis of N-alkyl carbamates by transcarboxylation and O-alkylation coupled reactions using a DBU-CO2 zwitterionic carbamic complex in aprotic polar media

N-Alkyl carbamates were obtained with good to excellent yields by clean and mild transcarboxylation of several amines with the previously synthesized DBU–CO2 complex and subsequent O-alkylation. Transcarboxylation was found to be selective, as only carbamate was formed from 1-hydroxy-2-aminobutanol.

Contactless conductivity biosensor in microchip containing folic acid as bioreceptor

We report a glass/PDMS-based microfluidic biosensor that integrates contactless conductivity transduction and folic acid, a target for tumor biomarker, as a bioreceptor. The device presents relevant advantages such as direct determination--dismiss the use of redox mediators as in faradaic electrochemical techniques--and the absence of the known drawbacks related to the electrode-solution interface. Characterizations of the functionalization processes and chemical sensor are described in this communication.

Efficient green synthesis of bis(cyclic carbonate)poly(dimethylsiloxane) derivative using CO2 addition: a novel precursor for synthesis of urethanes

Poly(dimethyl siloxane), PDMS, with terminal cyclic carbonate groups was prepared by cycloaddition of carbon dioxide to epoxy rings using tetra alkyl-ammonium bromide as a catalyst under efficient and mild conditions. The process was carried out under a modest pressure of carbon dioxide (i.e., <2 MPa) and temperature (<200 °C). The oligomeric species was found to be a non-Newtonian fluid with low molecular weight (MW ∼ 1200 g mol−1) with n = xx − yy and thermally stable up to 200 °C. Its formation was verified by mid infrared spectroscopy (FT-MIR), Matrix-Assisted Laser Desorption Ionization Mass Spectroscopy MALDI-Tof-MS and multinuclear magnetic resonance (13C NMR, 29Si NMR, 1H NMR). The urethane synthesis was confirmed by FTIR, NMR and X-ray Photoelectron Spectroscopy (XPS) after reacting amines or diamines, in mild reactions conditions, with bis(cyclic carbonate)poly(dimethylsiloxane).

Surface structure and reactivity study of phosphotungstic acid-nitrogenated ormosils

Supramolecular interactions between nitrogenated groups in hybrid ormosils bearing phosphotungstate nanocatalyst were used to tune the photocatalytical activity of these class-II hybrid materials obtained through sol–gel chemistry. Surface chemistry and morphology of the materials was studied by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle measurements. The photocatalytic efficiency of these hybrid films, measured by the degradation of crystal violet over-layer deposited on ormosils films, is higher for ormosils bearing neutral, more polar and less H-bonding nitrile groups than those bearing alkylamine/alkylammonium functionalities, despite the lower W/Si atomic ratio on the surface and lower tungsten percentage of the pure nitrile bearing ormosils. Such higher surface reactivity of the nitrile bearing ormosils is due to weaker interaction with the phosphotungstate and the lower activity of amine bearing ormosils is attributed to the competition among reversible photochromism and photocatalysis pathways in these materials.

Microwave-assisted synthesis of NaYF4:Yb3+/Tm3+ upconversion particles with tailored morphology and phase for the design of UV/NIR-active NaYF4:Yb3+/Tm3+@TiO2 core@shell photocatalysts

Coupling of TiO2 with rare earth (RE) metal-based upconversion particles (UCPs) is a promising strategy to develop near-infrared (NIR)-driven TiO2-based photocatalysts. This, however, requires the controlled synthesis of bright NIR-to-UV UCPs with tailored morphology, size and crystalline phase. Herein, we report a rapid, efficient and reproducible co-precipitation/microwave (MW)-assisted hydrothermal method for the preparation of NaYF4:Yb3+/Tm3+ UCPs which allows tailoring the morphology (spherical nanoparticles, microrods) and crystalline phase (cubic, hexagonal) and hence the optical response of the resulting UCPs by simply varying the MW treatment time or ethylenediaminetetraacetic acid (EDTA) concentration. The EDTA concentration strongly affects the size of the primary UCPs during the co-precipitation step which plays a decisive role in dictating the final particle morphology in the subsequent MW-assisted hydrothermal step. Based on microscopic and XRD analyses, a model for the growth of UCPs with different morphologies has been proposed. Pure hexagonal microrods with strong upconversion (UC) photoluminescence (PL) in the UV (345 nm, 361 nm) and visible (450 nm, 475 nm) regions are obtained using MW treatment times of 30–60 min and EDTA/RE3+ molar ratios above 1.5. The UCPs@TiO2 core@shell composite photocatalysts prepared by coating anatase TiO2 on the surface of UCPs using a sol–gel method showed good photocatalytic activity under both ultraviolet (UV) and NIR light. This efficient and reproducible co-precipitation/MW-assisted approach may be considered as a step forward towards the efficient harvesting of sunlight for photochemical and photoelectrical applications based on TiO2.

Spectroscopic and electrochemical study of [Ru(NH3)5OH2]3+, [Ru(NH3)5Cl]2+, and [Os(NH3)5OH2]3+ immobilized on thin film of Ti(IV) oxide dispersed on the silica gel surface

Abstract [Ru(NH 3 ) 5 H 2 O] 3+ , [Ru(NH 3 ) 5 Cl] 2+ and [Os(NH 3 ) 5 H 2 O] 3+ were supported on the hydrated titanium alkoxide grafted on silica gel surface. The mononuclear complexes on the matrix surface have been characterized by specific surface area, elemental analysis, UV–Vis spectroscopy and electrochemical techniques (cyclic voltammetry, differential pulse polarography). These supported species exhibit one defined band on the visible region of the electronic spectrum: band [Ru(NH 3 ) 5 H 2 O] 3+ (668 nm), [Ru(NH 3 ) 5 Cl] 2+ (676 nm) and [Os(NH 3 ) 5 H 2 O] 3+ (825 nm), attributed to M III →Ti IV (M=Ru(III) and Os(III)) metal to metal charge transfer process. For the mononuclear anchored species [Ru(NH 3 ) 5 H 2 O] 3+ , [Ru(NH 3 ) 5 Cl] 2+ and [Os(NH 3 ) 5 H 2 O] 3+ , the ( E 1/2 ) for the M(III)/M(II) couple at 25°C are, respectively: −0.22, −0.28, and −1.15 V versus SCE. A formation of an oxo bridge TiOM(NH 3 ) 5 (M=Ru, Os) and chloro bridge TiClRu(NH 3 ) 5 was postulated for the grafted complexes on the SiO 2 /TiO 2 surface.

Surface modification by physical treatments on biomedical grade metals to improve adhesion for bonding hybrid non-isocyanate urethanes

This work aims to improve the adhesion of a hybrid non-isocyanate polydimethylsiloxane urethane (PDMSUr) coating by producing active layers on titanium alloy (Ti6Al4V) and stainless steel (SS316L) applying pulsed Nd:YAG laser and oxygen plasma. The PDMSUr is a hybrid adhesive and, when functionalized with alkoxysilane groups, can bind onto the interfacial hydroxyl groups of a (hydr)oxide/carbonate layer by sol–gel reactions. These reactions are acid catalysed and the silanol groups can bind through Si–O–metal links. The pull-off-strength of such sustainable coatings raised more than 100% for both substrates after the physical treatments, compared with the substrates etched. X-ray Photoelectron Spectroscopy (XPS) of a freshly pre-treated substrate revealed the formation of thin oxide-based reactive layers on the surface of Ti6Al4V and SS316L after the surface treatments. Both physical procedures were efficient to create oxide layers on top of metallic substrates and contributed to the improvement of adhesion strength of PDMSUr on biomedical grade metals.

Hybrid urethanesil coatings for inorganic surfaces produced by isocyanate-free and sol-gel routes: synthesis and characterization

A simple and versatile route for the preparation of self-adhesive, corrosion-resistant and photochromic hybrid coatings is presented in this paper. The coatings are based on aliphatic poly(dimethylsiloxane)-derived hydroxyurethanes (PDMSUr), produced by the isocyanate-free route for inorganic substrates such as glass and metal alloys. This route involves the ring opening polymerization of a PDMS-derived bis(cyclic carbonate) (CCPDMS) with diamines and aminosilane. The cyclic carbonate was synthesized by cycloaddition of CO2 into a PDMS diglycidyl ether. The use of aminosilanes with CCPDMS enables hybrid organic–inorganic urethanic coatings to be obtained by the sol–gel process. The crystallinity of the coating can be easily controlled through the interplay of the ratio of monoamines and diamines in the formulation. The hybrid PDMSUr materials were tested as an adhesive/coating for metallic and glazed surfaces, presenting adhesion strengths of up to 7 MPa and a maximum usage temperature of 160 °C. The incorporation of phosphotungstic acid (PWA) produced a hard material (20–60 MPa) and the elastic modulus rose by more than a hundred times as the PWA content increased. The hybrid PDMSUr 2_35% PWA presented photochromic properties and is suitable as an adhesive and impact damping layer for laminated glass used for smart window production. Furthermore, these coatings are suitable for the protection of metallic substrates against corrosion in acidic, basic and seawater media.

Poly(imide)/Organically-Modified Montmorillonite Nanocomposite as a Potential Membrane for Alkaline Fuel Cells.

In this work we evaluated the potentiality of a poly(imide) (PI)/organically-modified montmorillonite (O-MMT) nanocomposite membrane for the use in alkaline fuel cells. Both X-ray diffraction and scanning electron microscopy revealed a good dispersion of O-MMT into the PI matrix and preservation of the O-MMT layered structure. When compared to the pure PI, the addition of O-MMT improved thermal stability and markedly increased the capability of absorbing electrolyte and ionic conductivity of the composite. The results show that the PI/O-MMT nanocomposite is a promising candidate for alkaline fuel cell applications.

Quantificação de dextranas em açúcares e em cachaças

Solid dextrans are thermally stable polysaccharides losing water only at 160oC. According to IR, X-ray, DTA and DSC data no noticeable changes in dextran configuration occurs at this temperature. The total content of dextrans analyzed in 26 samples of Brazilian sugars and 57 samples of sweetened cachacas ranged from 109.5 to 1840 mg/kg and 1.6 to 11.2 mg/L with medians of 999.8 mg/kg and 5.9 mg/L respectively. Samples of sweeted cachacas have been monitored for turbidity, total soluble dextran content and weight of precipitate formed during 275 days. Precipitate formation is a kinetically controlled process which ends after 275 days when the total concentration of soluble dextrans becomes smaller than 0.25 mg/L.