Processing and Physicochemical Properties of Magnetite Nanoparticles Coated with Curcuma longa L. Extract.

In this work, Curcuma longa L. extract has been used in the synthesis and direct coating of magnetite (Fe3O4) nanoparticles ~12 nm, providing a surface layer of polyphenol groups (-OH and -COOH). This contributes to the development of nanocarriers and triggers different bio-applications. Curcuma longa L. is part of the ginger family (Zingiberaceae); the extracts of this plant contain a polyphenol structure compound, and it has an affinity to be linked to Fe ions. The nanoparticles' magnetization obtained corresponded to close hysteresis loop Ms = 8.81 emu/g, coercive field Hc = 26.67 Oe, and low remanence energy as iron oxide superparamagnetic nanoparticles (SPIONs). Furthermore, the synthesized nanoparticles (G-M@T) showed tunable single magnetic domain interactions with uniaxial anisotropy as addressable cores at 90-180°. Surface analysis revealed characteristic peaks of Fe 2p, O 1s, and C 1s. From the last one, it was possible to obtain the C-O, C=O, -OH bonds, achieving an acceptable connection with the HepG2 cell line. The G-M@T nanoparticles do not induce cell toxicity in human peripheral blood mononuclear cells or HepG2 cells in vitro, but they can increase the mitochondrial and lysosomal activity in HepG2 cells, probably related to an apoptotic cell death induction or to a stress response due to the high concentration of iron within the cell.

Reductive Oligomerization of Nitroaniline Catalyzed by Fe3O4 Spheres Decorated with Group 11 Metal Nanoparticles.

The present work demonstrates a simple and sustainable method for forming azo oligomers from low-value compounds such as nitroaniline. The reductive oligomerization of 4-nitroaniline was achieved via azo bonding using nanometric Fe3O4 spheres doped with metallic nanoparticles (Cu NPs, Ag NPs, and Au NPs), which were characterized by different analytical methods. The magnetic saturation (M s) of the samples showed that they are magnetically recoverable from aqueous environments. The effective reduction of nitroaniline followed pseudo-first-order kinetics, reaching a maximum conversion of about 97%. Fe3O4-Au is the best catalyst, its a reaction rate (k Fe3O4-Au = 0.416 mM L-1 min-1) is about 20 times higher than that of bare Fe3O4 (k Fe3O4 = 0.018 mM L-1 min-1). The formation of the two main products was determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS), evidencing the effective oligomerization of NA through N = N azo linkage. It is consistent with the total carbon balance and the structural analysis by density functional theory (DFT)-based total energy. The first product, a six-unit azo oligomer, was formed at the beginning of the reaction through a shorter, two-unit molecule. The nitroaniline reduction is controllable and thermodynamically viable, as shown in the computational studies.

Physical properties, marginal adaptation and bioactivity of an experimental mineral trioxide aggregate-like cement modified with bioactive materials.

PURPOSE: To evaluate the effect of adding wollastonite and bioactive glass to an experimental mineral trioxide aggregate-like cement (MTA) on the dimensional stability, compressive strength, solubility, bioactivity, and marginal adaptation by scanning electron microscopy (SEM) and X-ray diffraction (XRD). METHODS: Four groups were evaluated at 7, 14, and 21 days: MTA Angelus, experimental MTA-like cement (MTA Exp), BG10 (MTA Exp+10 wt% bioactive glass), and WO20 (MTA Exp+20 wt% wollastonite). To evaluate marginal adaptation, extracted teeth were endodontically obturated and root-end cavities were prepared and filled with the tested materials. RESULTS: Cements with bioactive materials showed minimal dimensional changes. Adding wollastonite or bioactive glass to MTA Exp reduces the compressive strength but does not affect solubility. Bismite (Bi2O3), larnite (Ca2SiO4), calcite (CaCO3) and carbonated hydroxyapatite (Ca5[PO4,CO3]3[OH]) were identified in the four cements; ettringite (Ca6Al2[SO4]3[OH]12·26H2O) and bismutite ([BiO]2CO3) were only observed in MTA Exp, BG10, and WO20. Cement-dentin interfaces were not observed after 14 days on the BG10 and WO20 cement composites due to the ettringite formation. CONCLUSION: Acicular growing crystals typical of hydroxyapatite were found on the surfaces of all cements. An improved marginal adaptation was observed with the addition of wollastonite or bioactive glass.

Cell viability and physicochemical effects of different concentrations of bismuth trioxide in a mineral trioxide aggregate cement.

PURPOSE: To evaluate the effect of three concentrations of bismuth trioxide (Bi2O3) on the biological and physicochemical properties of an experimental mineral trioxide aggregate-type (MTA-type) cement at different time points. METHODS: Three experimental groups with white Portland cement containing 15, 20, or 25 wt% of Bi2O3 were assessed. Cellular proliferation in human periodontal ligament fibroblasts was evaluated with an MTT assay. Radiopacity, dimensional stability, pH, and compressive strength were evaluated at different time points. RESULTS: Bismuth trioxide induced cell proliferation in the Bi15 and Bi25 groups in a time-dependent manner; pH was similar in all groups. Compressive strength was associated with time and bismuth concentration. Bi25 had significantly contracted at day 7 and expanded at day 14 (ANOVA P < 0.05, post hoc Tukey test P < 0.05). CONCLUSION: A higher Bi2O3 concentration had a negative effect on the physical properties of the cement at all time points.

Effect of Surface Roughness of Deciduous and Permanent Tooth Enamel on Bacterial Adhesion.

The adhesion of some bacteria has been attributed to critical levels of roughness in hard tissues, which increases the risk of developing caries. The objective of this work was to assess the effect of deciduous and permanent tooth enamel surface roughness on bacterial adhesion. One hundred and eight samples of deciduous and permanent enamel were divided into two groups (n = 54). G1_DE deciduous enamel and G2_PE permanent enamel. The surface roughness was measured by profilometry and atomic force microscopy (AFM). Subsequently, the evaluation of bacterial adherence was carried out in triplicate by means of the XTT cell viability test. Additionally, bacterial adhesion was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The average values of the micrometric roughness in both groups were similar; however, in the nanometric scale they presented significant differences. Additionally, the G1_DE group showed the highest amount of adhered S. mutans and S. sanguinis compared to the G2_EP group. Although the roughness of deciduous and permanent enamel showed contrasting results according to the evaluation technique (area and scale of analysis), bacterial adhesion was greater in deciduous enamel; hence, enamel roughness may not be a determining factor in the bacterial adhesion phenomenon.

Experimental Study of the Influence of CH4 and H2 on the Conformation, Chemical Composition, and Luminescence of Silicon Quantum Dots Inlaid in Silicon Carbide Thin Films Grown by Remote Plasma-Enhanced Chemical Vapor Deposition.

Silicon carbide (SiC) has become an extraordinary photonic material. Achieving reproducible self-formation of silicon quantum dots (SiQDs) within SiC matrices could be beneficial for producing electroluminescent devices operating at high power, high temperatures, or high voltages. In this work, we use a remote plasma-enhanced chemical vapor deposition system to grow SiC thin films. We identified that a particular combination of 20 sccm of CH4 and a range of 58-100 sccm of H2 mass flow with 600 °C annealing allows the abundant and reproducible self-formation of SiQDs within the SiC films. These SiQDs dramatically increase the photoluminescence-integrated intensity of our SiC films. The photoluminescence of our SiQDs shows a normal distribution with positive skewness and well-defined intensity maxima in blue regions of the electromagnetic spectrum (439-465 nm) and is clearly perceptible to the naked eye.

Correlation between dental enamel chemical composition and bracket debonding, comparing adhesive systems through a scanning electron microscope.

Literature reports indicate that during bracket removal there can be enamel damage. We compare the shear bond strength (SBS) and tooth enamel loss of four adhesive systems and identify the Ca/P ratio. Then a total of 20 premolars were divided into four groups of five each. After prophylaxis, photographs were taken at 35× with a scanning electron microscope (SEM) and analyzed with X-ray spectroscopy (EDS) at 250×. Brackets were bonded with Transbond™ MIP(G1), Transbond™ PLUS SEP(G2), Enlight(G3) and Stylus®(G4) adhesives, 24 h after were debonded with a Instron universal testing machine at 1 mm/min. All the brackets were photographed with the SEM. The amount of lost enamel was measured with AutoCad. All the results were measured with a significance level p < .05. The SBS general average at debonding was 7.94 ± 2.26 MPa, meanwhile the SBS for G1, G2, G3 and G4 was 9.38 ± 1.46, 6.28 ± 0.69, 9.08 ± 2.45 and 7.04 ± 2.64 MPa respectively. 90% of the samples had no enamel loss, 10% had enamel loss. Only two samples in G1 presented an enamel loss area of 0.34mm2 and 0.80mm2 respectively. From EDS analysis, the Ca/P ratio was 1.6 ± 0.05, 1.61 ± 0.03, 1.64 ± 0.83 and 1.59 ± 0.07 for G1, G2, G3 and G4 respectively; no statistically significant differences were found. We conclude that no association was found between the Ca/P ratio and enamel damage when brackets are removed. HIGHLIGHTS: Where enamel is lost, we observe fractures, steps, horizontal and vertical enamel loss. There is a loss of tooth enamel from 0.34 to 0.80 mm2 with Transbond PLUS SEP. Structural loss of enamel is almost inevitable during the separation of the bracket.

Three-Dimensional Porous Scaffolds Derived from Bovine Cancellous Bone Matrix Promote Osteoinduction, Osteoconduction, and Osteogenesis.

The use of three-dimensional porous scaffolds derived from decellularized extracellular matrix (ECM) is increasing for functional repair and regeneration of injured bone tissue. Because these scaffolds retain their native structures and bioactive molecules, in addition to showing low immunogenicity and good biodegradability, they can promote tissue repair and regeneration. Nonetheless, imitating these features in synthetic materials represents a challenging task. Furthermore, due to the complexity of bone tissue, different processes are necessary to maintain these characteristics. We present a novel approach using decellularized ECM material derived from bovine cancellous bone by demineralization, decellularization, and hydrolysis of collagen to obtain a three-dimensional porous scaffold. This study demonstrates that the three-dimensional porous scaffold obtained from bovine bone retained its osteoconductive and osteoinductive properties and presented osteogenic potential when seeded with human Wharton's jelly mesenchymal stromal cells (hWJ-MSCs). Based on its characteristics, the scaffold described in this work potentially represents a therapeutic strategy for bone repair.

Rapid electrochemical recognition of trimethoprim in human urine samples using new modified electrodes (CPE/Ag/Au NPs) analysing tunable electrode properties: experimental and theoretical studies.

Pharmaceutical effluents are a serious environmental issue, which require to be treated by a suitable technique; thus, the electrochemical process is actively considered as a viable method for the treatment. In this work, new carbon paste electrodes (CPEs) were fabricated by compressing gold and silver nanoparticles (NPs), namely, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs and then completely characterized by different analytical methods. The performance of the electrodes was studied after determining their surface area (×10-6 cm2) as 4.17, 5.05, 5.27, and 5.12, producing high anodic currents for K4[Fe(CN)6] compared to the commercial electrode. This agrees with the results of impedance study, where the electron transfer rate constants (kapp, ×10-3 cm s-1) were determined to be 28.7, 42.6, 41.0, and 101.4 for CPE, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively, through the Bode plot-phase shifts. This is consistent with the charge transfer resistance (RCT, Ω), resulting as 171 for CPE/Ag/Au NPs < 395 for CPE/Ag NPs < 427 for CPE/Au NPs and < 742 for CPE. Therefore, these electrodes were employed to detect trimethoprim (TMP) since metallic NPs contribute good crystallinity, stability, conduciveness, and surface plasmon resonance to the CPE, convalescing the sensitivity; comprehensively, they were applied for its detection in real water and human urine samples, and the limit of detection (LOD) was as low as 0.026, 0.032, and 0.026 µmol L-1 for CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively. In contrast, unmodified CPE was unable to detect TMP due to the lack of efficiency. The developed technique shows excellent electrochemical recovery of 92.3 and 97.1% in the urine sample. Density functional theory (DFT) was used to explain the impact of the metallic center in graphite through density of states (DOS).

Evaluation of enamel loss by scanning electron microscopy after debonding brackets place with four different adhesives.

The clinically adequate shear bond strengths (SBS) should be from 2.8 to 10 MPa. The aim of this research is to observe tooth enamel loss through a scanning electron microscope (SEM) during the debonding of braces of four adhesive systems. Then, 100 premolars were used in 4 groups of 25 specimens each, for Transbond MIP (G1), Enlight (G2), Stylus (G3), and Transbond Plus SEP (G4). The research was done under the NOM ISO/TS 11405:2015. Gemini 3M were placed under the manufacturer's recommendations. The SBS test was done at 24 hr in an Instron electromechanical universal testing machine at 1 mm/1 min. Adhesive remnant index (ARI) was measured, all of the brackets where examined in the SEM. For the shear bonding strength G1 = 10.09 ± 2.73 MPa, G2 = 9.27 ± 3.99 MPa, G3 = 7.83 ± 4.46 MPa, and G4 = 6.40 ± 2.85 MPa statistically significant differences were found when comparing the four groups (p = .002). In the Tukey post hoc test, G1 versus G4 and G2 versus G4, statistically significant differences were found. For the ARI a value of 1 in 46%, followed by a value of 2 in 38%, a value of 3 in 13% and a value of 0 in 3% of the total samples, finding statistically significant differences (p < .001). In relation to the tooth enamel loss due to SBS, statistically significant differences were found (p = .326). G1 and G4 had not statistically significant differences. Even though our results concur with the appropriate clinical values, we observed tooth enamel loss with Transbond Plus SEP and Stylus.

Green synthesis of ZnO nanoparticles using a Dysphania ambrosioides extract. Structural characterization and antibacterial properties.

The Structural properties of Zinc oxide nanoparticles (ZnO-NPs) as well as their antibacterial properties against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa; as well as bacteria that are usually found in the mouth of humans and are related to dental conditions, such as Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Streptococcus mutans and Streptococcus sanguinis, are presented in this report. ZnO-NPs were grown by green synthesis, using the Mexican plant Dysphania ambrosioides known in Mexico as "epazote", which was used by native populations of Mexico as a dewormer, is currently used widely in traditional Mexican cuisine and is rich in organic compounds as flavonoids and terpenes which may favor the synthesis of nanoparticles (NPs). ZnO-NPs were synthesized by the mentioned technology and were compared with commercial ZnO-NPs as a reference. Synthesized and commercial ZnO-NPs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG). Antibacterial properties were evaluated using a disc diffusion test (Kirby-Bauer method). The results indicate that ZnO-NPs were synthesized in the size range of 5-30 nm. The presence of the ZnO crystalline phase was identified by high resolution transmission electron microscopy (HRTEM) and XRD analysis. The commercial ZnO-NPs were in the size range of 15-35 nm. The antibacterial test indicates that most of the bacterial strains used in this study were sensitive to synthesized and commercial NPs, with Prevotella intermedia being the most sensitive to ZnO-NPs.

Adhesion of Streptococcus mutans and Streptococcus sanguinis on Er:YAG Laser-Irradiated Dental Enamel: Effect of Surface Roughness.

Objective: To determine surface roughness caused by Er:YAG laser irradiation and its effect on the increase in bacterial adhesion. Background: Er:YAG laser was proposed as a strategic device to reduce caries by its ability to generate chemical and structural changes in tooth enamel; in turn, it produces undesirable effects on the tooth surface that could increase its roughness and allow a greater accumulation of microorganisms. Methods: Eighty-four samples of human enamel were divided into seven groups (n = 12): G1_control (no laser irradiation); G2_100/H2O, G3_200/H2O, and G4_300/H2O were irradiated with Er:YAG laser (12.7, 25.5, and 38.2 J/cm2, respectively) under water irrigation. In addition, G5_100, G6_200, and G7_300 were irradiated with the energy densities described above and no water irrigation. Surface roughness measurements were recorded before and after treatment using a profilometer. Afterward, three samples per group were incubated in a microorganism suspension for the tetrazolium salt (XTT) assay. Biofilm morphology was observed using scanning electron microscopy and confocal laser scanning microscope. One-way analysis of variance and t-tests were performed for statistical analysis (p < 0.05). Results: There were no statistically significant differences in roughness values in the G5_100 group before and after treatment, but there were statistically significant differences observed in the other groups evaluated (p < 0.05). No significant differences in adhesion of both strains were detected in irradiated groups compared with G1_control. Conclusions: The increase in roughness on dental enamel surfaces was proportional to the irradiation conditions. However, the increase in surface roughness caused by Er:YAG laser irradiation did not affect Streptococcus mutans and S. sanguinis adhesion.

Comparative study of dental enamel loss after debonding braces by analytical scanning electron microscopy (SEM).

Clinical procedures when shear forces are applied to brackets suggest adhesion forces between 2.8 and 10.0 MPa as appropriate. In this study dental enamel was evaluated by scanning electron microscopy (SEM) before and after removing the brackets. Thirty bicuspids (previous prophylaxis) with metallic brackets (Roth Inovation 0.022 GAC), Transbond Plus SEP 3M Unitek adhesive and Transbond XT 3M resin were used. The samples were preserved to 37°C during 24 hr and submited to tangential forces with the Instron Universal machine 1.0 mm/min speed load strength resistance debonding. Also the Adhesive Remanent Index (ARI) test was made, evaluating the bracket base and the bicuspid surface. All the bracket SEM images were processed with AutoCAD to determine the enamel detached area. The average value was 6.86 MPa (SD ± 3.2 MPa). ARI value 1= 63.3%, value 2= 20%, value 3= 13.3% and 33% presented value 0. All those samples with dental enamel loss, presented different situations as fractures, ledges, horizontal, and vertical loss in some cases, and some scratch lines. There is no association between the debonding resistance and enamel presence. Less than half of the remanent adhesive on the dental enamel was present in most of the samples when the ARI test was applied. When the resin area increases, the debonding resistance also increases, and when the enamel loss increases, the resin free metallic area of the bracket base decreases in the debonding.

Análisis químico elemental y de fases por medio de PIXE, DSC, TGA y DRX en MTA Angelus® y un cemento Portland blanco / Elemental chemical composition and phase analysis by means of PIXE, DSC, TGA, and DRX of MTA Angelus® and a white Portland cement

Resumen: El mineral trióxido agregado (MTA) es un cemento usado principalmente para sellar perforaciones en órganos dentales debido a que endurece en presencia de humedad, está compuesto por cemento Portland y trióxido de bismuto. Objetivo: Analizar y comparar por medio de PIXE, DSC, TGA y DRX la composición química elemental y de fases del cemento MTA Angelus® y de un cemento Portland blanco (CPB-CA). Material y métodos: MTA Angelus® blanco y un cemento Portland blanco fueron analizados con PIXE en un acelerador de partículas; el análisis de fases cristalinas se realizó por medio de DRX y contrastado los picos con los de base de datos del ICDD, el DSC se realizó en un calorímetro hasta 900 °C. Resultados: PIXE detectó como elementos de mayor porcentaje fueron aluminio, silicio y calcio para ambos cementos; habiendo diferencias en los porcentajes de azufre; el bismuto sólo se detectó en MTA Angelus®. Se detectaron como elementos traza cobre y estroncio en el MTA Angelus®, además de zirconio en CPB-CA. La relación entre silicio-calcio y silicio-aluminio en los dos cementos es similar. Se identificaron tres fases cristalinas en ambos cementos, silicato dicálcico, silicato tricálcico y aluminato tricálcico; sin embargo, se identificó Bismita en el MTA Angelus® y sulfato de calcio en forma de yeso en CPB-CA, que se logró corroborar con la ayuda de la técnica DSC. Conclusiones: Se logró observar la baja cantidad de yeso en MTA Angelus® por medio de la calorimetría. Tanto las fases cristalinas como la composición química elemental son similares en ambos cementos.

Abstract: Mineral trioxide aggregate (MTA) is a cement mainly used to seal tooth perforations; this is due to the fact that it hardens when in presence of humidity. It is composed of Portland cement and Bismuth trioxide. Objective: To analyze and compare with PIXE, DSC, TGA and DRX elementary chemical and phase composition of MTA Angelus® cement with a white Portland cement (WPC). Material and methods: MTA Angelus® white and a white Portland cement were analyzed with PIXE in a particle accelerator, phase analyses were conducted with XRD contrasting peaks with those in the ICDD database. DSC was conducted in a calorimeter up to 900 oC. Results: PIXE detected the following as greater percentage elements: aluminum, silica and calcium for both cements. Differences were found with sulfur percentages; Bismuth was only detected in MTA Angelus®. Trace elements of copper and strontium were detected in MTA Angelus® and zirconium in WPC. Relationship between silica-calcium and silica-aluminum was similar in both cements. In both cements, three crystalline phases were detected: dicalcium silicate, tricalcium silicate and tricalcium aluminate. Nevertheless, Bismite was identified in MTA Angelus® and calcium sulfate in the form of gypsum in WPC, this was corroborated with DSC technique. Conclusions: In MTA Angelus®, low gypsum amounts were observed by means of calorimetry. In both cements, crystalline phases and elemental chemical composition were similar.

Optical Absorption and Visible Photoluminescence from Thin Films of Silicon Phthalocyanine Derivatives.

The interest of microelectronics industry in new organic compounds for the manufacture of luminescent devices has increased substantially in the last decade. In this paper, we carried out a study of the usage feasibility of three organic bidentate ligands (2,6-dihydroxyanthraquinone, anthraflavic acid and potassium derivative salt of anthraflavic acid) for the synthesis of an organic semiconductor based in silicon phthalocyanines (SiPcs). We report the visible photoluminescence (PL) at room temperature obtained from thermal-evaporated thin films of these new materials. The surface morphology of these films was analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM indicated that the thermal evaporation technique is an excellent resource in order to obtain low thin film roughness when depositing these kinds of compounds. Fourier transform infrared spectroscopy (FTIR) spectroscopy was employed to investigate possible changes in the intra-molecular bonds and to identify any evidence of crystallinity in the powder compounds and in the thin films after their deposition. FTIR showed that there was not any important change in the samples after the thermal deposition. The absorption coefficient (α) in the absorption region reveals non-direct transitions. Furthermore, the PL of all the investigated samples were observed with the naked eye in a bright background and also measured by a spectrofluorometer. The normalized PL spectra showed a Stokes shift ≈ 0.6 eV in two of our three samples, and no PL emission in the last one. Those results indicate that the Vis PL comes from a recombination of charge carriers between conduction band and valence band preceded by a non-radiative relaxation in the conduction band tails.

The cis-bis(decanoate)tin phthalocyanine/DPPC film at the air/water interface.

Films made of cis-bis-decanoate-tin(IV) phthalocyanine (PcSn10) and racemic dipalmitoylphosphatidylcholine (DPPC) are studied with compression isotherms and Brewster angle microscopy (BAM) at the air/water interface. Films enriched in PcSn10 present phase separation elliptical-shaped domains. These domains present optical anisotropy and molecular order. They are enriched in PcSn10, and the film outside these domains is enriched in DPPC, as shown in by high-angle annular dark-field transmission electron microscopy on Langmuir-Blodgett (LB) transferred films. Film collapse area and atomic force microscopy images of LB transferred films on mica indicate that the films are actually multilayers. A computational survey was performed to determine how the PcSn10 molecules prefer to self-assemble, in films basically made of PcSn10. The relative energetic stability for several dimeric assemblies was obtained, and a crystal model of the film was developed through packing and repeating the PcSn10 molecules, along the crystallographic directions of the unit cell. Our results contribute to understanding the strong interaction between PcSn10 and DPPC at the air/water interface, where even small quantities of DPPC (~1-2%) can modify the film in an important way.

Determination of the size distribution of metallic nanoparticles by optical extinction spectroscopy.

A method is proposed to estimate the size distribution of nearly spherical metallic nanoparticles (NPs) from optical extinction spectroscopy (OES) measurements based on Mie's theory and an optimization algorithm. The described method is compared against two of the most widely used techniques for the task: transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). The size distribution of Au and Cu NPs, obtained by ion implantation in silica and a subsequent thermal annealing in air, was determined by TEM, grazing-incidence SAXS (GISAXS) geometry, and our method, and the average radius obtained by all the three techniques was almost the same for the two studied metals. Concerning the radius dispersion (RD), OES and GISAXS give very similar results, while TEM considerably underestimates the RD of the distribution.

Surface properties of Ni-Pt/SiO2 catalysts for N2O decomposition and reduction by H2.

The surface properties of bimetallic Ni-Pt/SiO2 catalysts with variable Ni/Ni + Pt atomic ratio (0.75, 0.50, and 0.25) were studied using N2O decomposition and N2O reduction by hydrogen reactions as probes. Catalysts were prepared by incipient wetness impregnation of the silica support with aqueous solutions of the metal precursors to a total metal loading of 2 wt %. For both model reactions, Pt/SiO2 catalyst was substantially more active than Ni/SiO2 catalyst. Mean particle size by TEM was about the same (in the range 6-8 nm) for all catalysts and truly bimetallic particles (more than 95%) were evidenced by EDS in the Ni-Pt/SiO2 catalysts. CO adsorption on the bimetallic catalysts showed differences in the linear CO absorption band as a function of the Ni/Pt atomic ratio. Bimetallic Ni-Pt/SiO2 catalysts showed, for the N2O decomposition, a catalytic behavior that points out an ensemble-size sensitive behavior for Ni-rich compositions. For the N2O + H2 reaction, the bimetallic catalysts were very active at low temperature. The following activity order at 300 K was observed: Ni75Pt25 > Ni25Pt75 approximately Ni50Pt50 > Pt. TOF values for these catalysts increased 2-5 times compared to the most active reference catalyst (Pt/SiO2). The enhancement of the activity in the Ni75Pt25 bimetallic catalysts is explained in terms of the presence of mixed Ni-Pt ensembles.

Valoración de las propiedades físicas de tres resinas duales como agentes cementantes / Evaluation of physical properties of three dual resins as cementing agents

Se compararon tres materiales dentales de resina dual utilizados como agentes cementantes y dos como grupo control a base de resina fotopolimerizable y autopolimerizable; se frabricaron muestras las cuales fueron sometidas a fuerzas compresivas y flexionales empleando la Máquina de Pruebas Universales (INSTRON) para comparar su resistencia de acuerdo con los parámetros que marca la Norma número 27 de la Asociación Dental Americana. Se encontró que la resina dual presenta mayor resistencia ante estas fuerzas, corroborando esto, con los mismos fragmentos que fueron sometidos a la pruebas mediante el empleo de la Microscopía electrónica de Barrido que se usa para observar la ultraestructura de las mismas resinas