Thermal and structural properties of commercial dental resins light-cured with blue emitting diodes (LEDs)

We have investigated the thermal and structural properties of different commercial dental resins: Filtek(TM) Z-350, Grandio(A (R)), Tetric Ceram(A (R)), and TPH Spectrum(A (R)). The purpose of the present study was to evaluate quantitatively the photo-polymerization behavior and the effect of filler contents on the kinetic cures of the dental resins by using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. We have successfully obtained the low and high glass transition T (g) values of the dental composite resins from DSC curves. It was also observed a good agreement between the both T (g) values, activation energies from thermal degradation, and the degree of conversion obtained for all samples. The results have shown that Tetric Ceram(A (R)) dental resin presented the higher T (g) values, activation energy of 215 +/- A 6 KJ mol(-1), and the higher degree of conversion (63%) when compared to the other resins studied herein.

Enzyme immobilization on Ag nanoparticles/polyaniline nanocomposites

We show a simple strategy to obtain all efficient enzymatic broelectrochemical device, in which urease was immobilized oil electroactive nanostructured membranes (ENMs) made with polyaniline and silver nanoparticles (AgNP) stabilized in polyvinyl alcohol (PAni/PVA-AgNP). Fabrication of the modified electrodes comprised the chemical deposition of polyaniline followed by drop-coating of PVA-AgNP and urease, resulting in a final ITO/PAni/PVA-AgNP/urease electrode Configuration. For comparison. the electrochemical performance of ITO/PAni/urease electrodes (without Ag nanoparticles) was also studied. The performance of the modified electrodes toward Urea hydrolysis was investigated via amperometric measurements, revealing a fast increase in cathodic current with a well-defined peak upon addition of urea to the electrolytic solution. The cathodic currents for the ITO/PAni/PVA-AgNP urease electrodes were significantly higher than for the ITO/PAni/urease electrodes. The friendly environment provided by the ITO/PAni/PVA-AgNP electrode to the immobilized enzyme promoted efficient catalytic conversion of urea into ammonium and bicarbonate tons. Using the Michaelis-Menten kinetics equation, a K(M)(aPP) of 2.7 mmol L(-1) was obtained. indicating that the electrode architecture employed may be advantageous for fabrication of enzymatic devices with improved biocatalytic properties. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Controlled fabrication of gold nanoparticles biomediated by glucose oxidase immobilized on chitosan layer-by-layer films

The control of size and shape of metallic nanoparticles is a fundamental goal in nanochemistry, and crucial for applications exploiting nanoscale properties of materials. We present here an approach to the synthesis of gold nanoparticles mediated by glucose oxidase (GOD) immobilized on solid substrates using the Layer-by-Layer (LbL) technique. The LbL films contained four alternated layers of chitosan and poly(styrene sulfonate) (PSS), with GOD in the uppermost bilayer adsorbed on a fifth chitosan layer: (chitosan/PSS)(4)/(chitosan/GOD). The films were inserted into a solution containing gold salt and glucose, at various pHs. Optimum conditions were achieved at pH 9, producing gold nanoparticles of ca. 30 nm according to transmission electron microscopy. A comparative study with the enzyme in solution demonstrated that the synthesis of gold nanoparticles is more efficient using immobilized GOD. (C) 2009 Elsevier B.V. All rights reserved.

Influence of different solvents on the structural, optical and morphological properties of CdS nanoparticles

CdS is one of the most important II-VI semiconductors, with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized via microwave-assisted solvothermal technique. Structural and morphological characterization revealed the presence of crystalline structures presenting single phase with different morphologies such as ""nanoflowers"" and nanoplates depending on the solvent used. Optical characterization was made by diffuse reflectance and photoluminescence spectroscopy, revealing the influence of the different solvents on the optical properties due to structural defects generated during synthesis. It is proposed that these defects are related to sulfur vacancies, with higher concentration of defects for the sample synthesized in ethylene glycol in comparison with the one synthesized in ethylene diamine. (C) 2011 Elsevier B.V. All rights reserved.

Changes on degree of conversion of dual-cure luting light-cured with blue LED

The indirect adhesive procedures constitute recently a substantial portion of contemporary esthetic restorative treatments. The resin cements have been used to bond tooth substrate and restorative materials. Due to recently introduction of the self-bonding resin luting cement based on a new monomer, filler and initiation technology has become important to study the degree of conversion of these new materials. In the present work the polymerization reaction and the filler content of dual-cured dental resin cements were studied by means of infra-red spectroscopy (FT-IR) and thermogravimetry (TG). Twenty specimens were made in a metallic mold (8 mm diameter x 1 mm thick) from each of 2 cements, PanaviaA (R) F2.0 (Kuraray) and RelyX (TM) Unicem Applicap (3M/ESPE). Each specimen was cured with blue LED with power density of 500 mW/cm(2) for 30 s. Immediately after curing, 24 and 48 h, and 7 days DC was determined. For each time interval 5 specimens were pulverized, pressed with KBr and analyzed with FT-IR. The TG measurements were performed in Netzsch TG 209 under oxygen atmosphere and heating rate of 10A degrees C/min from 25 to 700A degrees C. A two-way ANOVA showed DC (%) mean values statistically significance differences between two cements (p < 0.05). The Tukey`s test showed no significant difference only for the 24 and 48 h after light irradiation for both resin cements (p > 0.05). The Relx-Y (TM) Unicem mean values were significantly higher than PanaviaA (R) F 2.0. The degree of conversion means values increasing with the storage time and the filler content showed similar for both resin cements.

Morphology and Blue Photoluminescence Emission of PbMoO(4) Processed in Conventional Hydrothermal

PbMoO(4) micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120 degrees C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO(4) micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points, out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO(4)] and [PbO(8)] clusters into the lattice.

Joint Experimental and Theoretical Analysis of Order Disorder Effects in Cubic BaZrO(3) Assembled Nanoparticles under Decaoctahedral Shape

Periodic first-principles calculations based on density functional theory at the B3LYP level has been carried out to investigate the photoluminescence (PL) emission of BaZrO(3) assembled nanoparticles at room temperature. The defect created in the nanocrystals and their resultant electronic features lead to a diversification of electronic recombination within the BaZrO(3) band gap. Its optical phenomena are discussed in the light of photoluminescence emission at the green-yellow region around 570 nm. The theoretical model for displaced atoms and/or angular changes leads to the breaking of the local symmetry, which is based on the refined structure provided by Rietveld methodology. For each situation a band structure, charge mapping, and density of states were built and analyzed. X-ray diffraction (XRD) patterns, UV-vis measurements, and field emission scanning electron microscopy (FE-SEM) images are essential for a full evaluation of the crystal structure and morphology.

Effect of pH on the production of dispersed Bi4Ge3O12 nanoparticles by combustion synthesis

This paper reports the production of bismuth germanate ceramic scintillator (Bi4Ge3O12) by combustion synthesis (SHS) method, focusing on the influence of the synthesis parameters on the crystalline phases and agglomeration of the nanoparticles. The synthesis and sintering conditions were investigated through thermal analysis, X-ray diffraction as function of temperature, dilatometry and scanning electron microscopy. Well-dispersed Bi4Ge3O12 powder was accomplished by the combustion of the initial solution at pH 9, followed by low temperature calcination and milling. Sintered ceramics presented relative density of 98% and single crystalline Bi4Ge3O12 phase. The luminescent properties of the ceramics were investigated by photo- and radio- luminescence measurements and reproduced the typical Bi4Ge3O12 single-crystal spectra when excited with UV, beta and X-rays. The sintered ceramics presented light output of 4.4 x 10(3) photons/McV. (c) 2008 Published by Elsevier Ltd.

Degree of Conversion and Temperature Increase of a Composite Resin Light Cured with an Argon Laser and Blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature ( T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (degrees C) of the microhybrid composite resin (Filtek (TM) Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm(2) for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen ( model MB 102, Quebec, Canada). Spectroscopy ( FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm(-1) resolution, 300 to 4000-cm(-1) wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1638 cm(-1)) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm(-1)). For T (degrees C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (degrees C) were submitted to ANOVA and Tukey`s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% ( 100 to 1000 mW/cm(2)) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm(2)) for an LED. The temperature change values varied from 1.1 to 13.1 degrees C (100 to 1000 mW/cm(2)) for an argon laser and from 1.9 to 15.0 degrees C (100 to 1000 mW/cm(2)) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both light-curing units.

Er : YAB nanoparticles and vitreous thin films by the polymeric precursor method

The synthesis of Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystalline powders and vitreous thin films were studied. Precursor solutions were obtained using a modified polymeric precursor method using D-sorbitol as complexant agent. The chemical reactions were described. Y(0.)9Er(0.1)Al(3)(BO(3))(4) composition presents good thermal stability with regard to crystallization. The Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystallized phase can be obtained at 1,150 degrees C, in agreement with other authors. Crack- and porosity-free films were obtained with very small grain size and low RMS roughness. The films thickness revealed to be linearly dependent on precursor solution viscosity, being the value of 25 mPa s useful to prepare high-quality amorphous multi-layers (up to similar to 800 nm) at 740 degrees C during 2 h onto silica substrates by spin coating with a gyrset technology.

Intense violet-blue photoluminescence in BaZrO3 powders: A theoretical and experimental investigation of structural order-disorder

Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO3 (BZO) powders with structural order-disorder. Ab-initio calculations, ultraviolet-visible absorption spectroscopy and PL were performed. Theoretical results showed that the local disorder in the network-formed Zr clusters present an important role in the formation of hole-electron pair. The experimental data and theoretical results are in agreement, indicating that the PL emission in BZO powders can be related to the structural order-disorder degree in the lattice. (C) 2008 Elsevier B.V. All rights reserved.

Effect of Different Solvent Ratios (Water/Ethylene Glycol) on the Growth Process of CaMoO(4) Crystals and Their Optical Properties

In this paper, calcium molybdate (CaMoO(4)) crystals (meso- and nanoscale) were synthesized by the coprecipitation method using different solvent volume ratios (water/ethylene glycol). Subsequently, the obtained suspensions were processed in microwave-assisted hydrothermal/solvothermal systems at 140 degrees C for 1 h. These meso- and nanocrystals processed were characterized by X-ray diffraction (X R I)), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR). ultraviolet visible (UV-vis) absorption spectroscopies, held-emission gun scanning electron microscopy (FEG-SEM). transmission electron microscopy (TEM). and photoluminescence (PL) measurements. X RI) patterns and FT-Raman spectra showed that these meso- and nanocrystals have a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 827 cm(-1), which is associated with the Mo-O anti-symmetric stretching vibrations into the [MoO(4)] clusters. FEG-SEM micrographs indicated that the ethylene glycol concentration in the aqueous solution plays an important role in the morphological evolution of CaMoO(4) crystals. High-resolution TEM micrographs demonstrated that the mesocrystals consist of several aggregated nanoparticles with electron diffraction patterns of monocrystal. In addition, the differences observed in the selected area electron diffraction patterns of CaMoO(4) crystals proved the coexistence of both nano- and mesostructures, First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level were employed in order to understand the band structure find density of states For the CaMoO(4). UV-vis absorption measurements evidenced a variation in optical band gap values (from 3.42 to 3.72 cV) for the distinct morphologies. The blue and green PI. emissions observed in these crystals were ascribed to the intermediary energy levels arising from the distortions on the [MoO(4)] clusters clue to intrinsic defects in the lattice of anisotropic/isotropic crystals.

Photodynamic therapy associating Photogem (R) and blue LED on L929 and MDPC-23 cell culture

To evaluate the cytotoxicity of PDT (photodynamic therapy) with Photogem (R) associated to blue LED (light-emitting diode) on L929 and MDPC-23 cell cultures, 30000 cells/cm(2) were seeded in 24-well plates for 48 h, incubated with Photogem (R) (10, 25 or 50 mg/l) and irradiated with an LED source (460 +/- 3 nm; 22 mW/cm(2)) at two energy densities (25.5 or 37.5 J/cm(2)). Cell metabolism was evaluated by the MTT (methyltetrazolium) assay (Dunnet`s post hoc tests) and cell morphology by SEM (scanning electron microscopy). Flow cytometry analysed the type of PDT-induced cell death as well and estimated intracellular production of ROS (reactive oxygen species). There was a statistically significant decrease of mitochondrial activity (90% to 97%) for all Photogem (R) concentrations associated to blue LED, regardless of irradiation time. It was also demonstrated that the mitochondrial activity was not recovered after 12 or 24 h, characterizing irreversible cell damage. PDT-treated cells presented an altered morphology with ill-defined limits. In both cell lines, there was a predominance of necrotic cell death and the presence of Photogem (R) or irradiation increased the intracellular levels of ROS. PDT caused severe toxic effects in normal cell culture, characterized by the reduction of the mitochondrial activity, morphological alterations and induction of necrotic cell death.

Highly Stable, Edible Cellulose Films Incorporating Chitosan Nanoparticles

The need for biodegradable polymers for packaging has fostered the development of novel, biodegradable polymeric materials from natural sources, as an alternative to reduce amount of waste and environmental impacts. The present investigation involves the synthesis of chitosan nanoparticles-carboxymethylcellulose films, in view of their increasing areas of application in packaging industry. The entire process consists of 2-steps including chitosan nanoparticles preparation and their incorporation in carboxymethylcellulose films. Uniform and stable particles were obtained with 3 different chitosan concentrations. The morphology of chitosan nanoparticles was tested by transmission electron microscopy, revealing the nanoparticles size in the range of 80 to 110 nm. The developed film chitosan nanoparticles-carboxymethylcellulose films were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis, solubility tests, and mechanical analysis. Improvement of thermal and mechanical properties were observed in films containing nanoparticles, with the best results occurring upon addition of nanoparticles with 110 nm size in carboxymethylcellulose films. Practical Application Carboxymethylcellulose films containing chitosan nanoparticles synthesized and characterized in this article could be a potential material for food and beverage packaging applications products due to the increase mechanical properties and high stability. The potential application of the nanocomposites prepared would be in packaging industry to extend the shelf life of products.

Pt(II) and Ag(I) complexes with acesulfame: Crystal structure and a study of their antitumoral, antimicrobial and antiviral activities

Two new complexes of platinum(II) and silver(I) with acesulfame were synthesized. Acesulfame is in the anionic form acesulfamate (ace). The structures of both complexes were determined by X-ray crystallography. For K(2)[PtCl(2)(ace)(2)] the platinum atom is coordinated to two Cl(-) and two N-acesulfamate atoms forming a trans-square planar geometry. Each K(+) ion interacts with two oxygen atoms of the S(=O)(2) group of each acesulfamate. For the polymeric complex [Ag(ace)](n) the water molecule bridges between two crystallographic equivalent Agl atoms which are related each other by a twofold symmetry axis. Two Agl atoms, related to each other by a symmetry centre, make bond contact with two equivalent oxygen atoms. These bonds give rise to infinite chains along the unit cell diagonal in the ac plane. The in vitro cytotoxic analyses for the platinum complex using HeLa (human cervix cancer) cells show its low activity when compared to the vehicle-treated cells. The Ag(I) complex submitted to in vitro antimycobacterial tests, using the Microplate Alamar Blue (MABA) method, showed a good activity against Mycobacterium tuberculosis, responsible for tuberculosis, with a minimal inhibitory concentration (MIC) value of 11.6 mu M. The Ag(I) complex also presented a promising activity against Gram negative (Escherichia colt and Pseudomonas aeruginosa) and Gram positive (Enterococcus faecalis) microorganisms. The complex K(2)[PtCl(2)(ace)(2)] was also evaluated for antiviral properties against dengue virus type 2 (New Guinea C strain) in Vero cells and showed a good inhibition of dengue virus type 2 (New Guinea G strain) replication at 200 mu M, when compared to vehicle-treated cells. (C) 2010 Elsevier Inc. All rights reserved.