Preparation, characterization and structure of ruthenium phosphine complexes containing non-innocent ligands

Phosphine ruthenate complexes containing the non-innocent ligands 4-chloro-1,2-phenylenediamine (opda-CI) and 3,3',4,4'-tetraamminebiphenyl (diopda) were synthesized and characterized by means of X-ray diffraction, electrochemistry, P-31{H-1} NMR and electronic spectroscopies. Crystals of cis-[RuCl2 (dppb)(bqdi-CI)] complex were isolated as a mixture of two conformational isomers due to different positions of the chlorine atoms of the o-phenylene ligand in relation to the P1 atom of the phosphine moiety. (C) 2011 Elsevier Ltd. All rights reserved.

Long-term rabbits bone response to titanium implants in the presence of inorganic bovine-derived graft

This study evaluated bone responses to titanium implants in the presence of an inorganic graft material. The bilateral mandible incisors of 24 rabbits were surgically extracted and one of the exposed sockets, chosen at random, was filled with an inorganic xenogenic bone graft (Gen-ox (R)), whereas the remaining socket was left to heal naturally and served as a control. After 60 days, titanium implants were inserted in the specific areas, and on days 0, 30, 60, and 180 after the implant insertions, six animals of each group were killed. Digital periapical radiography of implant region was obtained and vertical bone height (VBH) and bone density (BD) were evaluated by digital analysis system. In the undecalcified tissue cuts, bone-to-implant contact (BIC) and bone area (BA) within the limits of the implant threads were evaluated and compared statistically by means of two-way ANOVA and Tukey's test (rho < 0.05). No significant differences were detected in VBH and BA, either between groups or between different experimental intervals. The BD was significantly higher in the experimental group than in the control group in all the intervals tested, but there were no significant differences by interval. The BIC was statistically lower in the control group on day 0; however, a significant increase was observed on days 60 and 180 (rho < 0.05). The use of an inorganic xenograft prior to insertion of a titanium implant did not interfere with the course of osseointegration.

Adding value to the Brazilian sisal: acid hydrolysis of its pulp seeking production of sugars and materials

The present work is inserted into the broad context of the upgrading of lignocellulosic fibers. Sisal was chosen in the present study because more than 50% of the world's sisal is cultivated in Brazil, it has a short life cycle and its fiber has a high cellulose content. Specifically, in the present study, the subject addressed was the hydrolysis of the sisal pulp, using sulfuric acid as the catalyst. To assess the influence of parameters such as the concentration of the sulfuric acid and the temperature during this process, the pulp was hydrolyzed with various concentrations of sulfuric acid (30-50%) at 70 A degrees C and with 30% acid (v/v) at various temperatures (60-100 A degrees C). During hydrolysis, aliquots were withdrawn from the reaction media, and the solid (non-hydrolyzed pulp) was separated from the liquid (liquor) by filtering each aliquot. The sugar composition of the liquor was analyzed by HPLC, and the non-hydrolyzed pulps were characterized by viscometry (average molar mass), and X-ray diffraction (crystallinity). The results support the following conclusions: acid hydrolysis using 30% H2SO4 at 100 A degrees C can produce sisal microcrystalline cellulose and the conditions that led to the largest glucose yield and lowest decomposition rate were 50% H2SO4 at 70 A degrees C. In summary, the study of sisal pulp hydrolysis using concentrated acid showed that certain conditions are suitable for high recovery of xylose and good yield of glucose. Moreover, the unreacted cellulose can be targeted for different applications in bio-based materials. A kinetic study based on the glucose yield was performed for all reaction conditions using the kinetic model proposed by Saeman. The results showed that the model adjusted to all 30-35% H2SO4 reactions but not to greater concentrations of sulfuric acid. The present study is part of an ongoing research program, and the results reported here will be used as a comparison against the results obtained when using treated sisal pulp as the starting material.

Field dependent transition to the non-linear regime in magnetic hyperthermia experiments: Comparison between maghemite, copper, zinc, nickel and cobalt ferrite nanoparticles of similar sizes

Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patient's body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and saturation magnetization, but strikingly different magnetic anisotropies. From magnetic hyperthermia experiments we found that, while at low fields maghemite is the best nanomaterial for hyperthermia applications, above a critical field, close to the transition from the linear to the non-linear regime, cobalt ferrite becomes more efficient. The results were also analyzed with respect to the energy conversion efficiency and compared with dynamic hysteresis simulations. Additional analysis with nickel, zinc and copper-ferrite nanoparticles of similar sizes confirmed the importance of the magnetic anisotropy and the damping factor. Further, the analysis of the characterization parameters suggested core-shell nanostructures, probably due to a surface passivation process during the nanoparticle synthesis. Finally, we discussed the effect of particle-particle interactions and its consequences, in particular regarding discrepancies between estimated parameters and expected theoretical predictions. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi. org/10.1063/1.4739533]

Self-supported bacterial cellulose/boehmite organic-inorganic hybrid films

Self-supported organic-inorganic hybrid transparent films have been prepared from bacterial cellulose and boehmite. SEM results indicate that the BC membranes are covered by Boehmite and XRD patterns suggest structural changes on cellulose due to Boehmite addition. Thermal stability is accessed through TG curves and is dependent on Boehmite content. Transparency, as evaluated by UV-Vis absorption, increases with increasing content of boehmite suggesting application of these materials as transparent substrates for opto-electronic devices.

Structural Refinement and Photoluminescence Properties of MnWO4 Nanorods Obtained by Microwave-Hydrothermal Synthesis

Manganese tungstate (MnWO4) nanorods were prepared at room temperature by the co-precipitation method and synthesized after processing in a microwave-hydrothermal (MH) system at 140 degrees C for 6-96 min. These nanorods were structurally characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform (FT)-Raman spectroscopy. The growth direction, shape and average size distribution of nanorods were observed by means of transmission electron microscopy (TEM) and high resolution TEM (HR-TEM). The optical properties of the nanorods were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. XRD patterns, Rietveld refinement data and FT-Raman spectroscopy indicate that the MnWO4 precipitate is not a single phase structure while the nanorods synthesized by MH processing have a wolframite-type monoclinic structure without deleterious phases. FT-Raman spectra exhibited the presence of 17 Raman-active modes from 50 to 1,000 cm(-1). TEM and HR-TEM micrographs indicated that the nanorods are aggregated due to surface energy by Van der Waals forces and grow along the [100] direction. UV-vis absorption measurements confirmed non-linear values for the optical band gap (from 3.2 to 2.72 eV), which increased as the MH processing time increased. The structural characterizations indicated that the presence of defects in the MnWO4 precipitate promotes a significant contribution to maximum PL emission, while MnWO4 nanorods obtained by MH processing decrease the PL emission due to the reduction of defects in the lattice.

Clinical evaluation of the failure rate of metallic brackets bonded with orthodontic composites

The purpose of the present study was to evaluate in vivo the failure rate of metallic brackets bonded with two orthodontic composites. Nineteen patients with ages ranging from 10.5 to 38.7 years needing corrective orthodontic treatment were selected for study. The enamel surfaces from second premolars to second premolars were treated with Transbond Plus-Self Etching Primer (3M Unitek). Next, 380 orthodontic brackets were bonded on maxillary and mandibular teeth, as follows: 190 with Transbond XT composite (3M Unitek) (control) and 190 with Transbond Plus Color Change (3M Unitek) (experimental) in contralateral quadrants. The bonded brackets were light cured for 40 s, and initial alignment archwires were inserted. Bond failure rates were recorded over a six-month period. At the end of the evaluation, six bond failures occurred, three for each composite. Kaplan-Meyer method and log-rank test (Mantel-Cox) was used for statistical analysis, and no statistically significant difference was found between the materials (p=0.999). Both Transbond XT and Transbond Plus Color Change composites had low debonding rates over the study period.

Effective properties evaluation for smart composite materials

The purpose of this article is to present a method which consists in the development of unit cell numerical models for smart composite materials with piezoelectric fibers made of PZT embedded in a non-piezoelectric matrix (epoxy resin). This method evaluates a globally homogeneous medium equivalent to the original composite, using a representative volume element (RVE). The suitable boundary conditions allow the simulation of all modes of the overall deformation arising from any arbitrary combination of mechanical and electrical loading. In the first instance, the unit cell is applied to predict the effective material coefficients of the transversely isotropic piezoelectric composite with circular cross section fibers. The numerical results are compared to other methods reported in the literature and also to results previously published, in order to evaluate the method proposal. In the second step, the method is applied to calculate the equivalent properties for smart composite materials with square cross section fibers. Results of comparison between different combinations of circular and square fiber geometries, observing the influence of the boundary conditions and arrangements are presented.

Clinical evaluation of the failure rates of metallic brackets

OBJECTIVES: The aim of this study was to evaluate in vivo the bonding of metallic orthodontic brackets with different adhesive systems. MATERIAL AND METHODS: Twenty patients (10.5-15.1 years old) who had sought corrective orthodontic treatment at a University Orthodontic Clinic were evaluated. Brackets were bonded from the right second premolar to the left second premolar in the upper and lower arches using: Orthodontic Concise, conventional Transbond XT, Transbond XT without primer, and Transbond XT associated with Transbond Plus Self-etching Primer (TPSEP). The 4 adhesive systems were used in all patients using a split-mouth design; each adhesive system was used in one quadrant of each dental arch, so that each group of 5 patients received the same bonding sequence. Initial archwires were inserted 1 week after bracket bonding. The number of bracket failures for each adhesive system was quantified over a 6-month period. RESULTS: The number of debonded brackets was: 8- Orthodontic Concise, 2- conventional Transbond XT, 9- Transbond XT without primer, and 1- Transbond XT + TPSEP. By using the Kaplan-Meier methods, statistically significant differences were found between the materials (p=0.0198), and the Logrank test identified these differences. Conventional Transbond XT and Transbond XT + TPSEP adhesive systems were statistically superior to Orthodontic Concise and Transbond XT without primer (p<0.05). There was no statistically significant difference between the dental arches (upper and lower), between the dental arch sides (right and left), and among the quadrants. CONCLUSIONS: The largest number of bracket failures occurred with Orthodontic Concise and Transbond XT without primer systems and few bracket failures occurred with conventional Transbond XT and Transbond XT+TPSEP. More bracket failures were observed in the posterior region compared with the anterior region.

Surface modification by metal ion implantation forming metallic nanoparticles in insulating matrix.

There is special interest in the incorporation of metallic nanoparticles in a surrounding dielectric matrix for obtaining composites with desirable characteristics such as for surface plasmon resonance, which can be used in photonics and sensing, and controlled surface electrical conductivity. We investigated nanocomposites produced through metallic ion implantation in insulating substrate, where the implanted metal self-assembles into nanoparticles. During the implantation, the excess of metal atom concentration above the solubility limit leads to nucleation and growth of metal nanoparticles, driven by the temperature and temperature gradients within the implanted sample including the beam-induced thermal characteristics. The nanoparticles nucleate near the maximum of the implantation depth profile (projected range), that can be estimated by computer simulation using the TRIDYN. This is a Monte Carlo simulation program based on the TRIM (Transport and Range of Ions in Matter) code that takes into account compositional changes in the substrate due to two factors: previously implanted dopant atoms, and sputtering of the substrate surface. Our study suggests that the nanoparticles form a bidimentional array buried few nanometers below the substrate surface. More specifically we have studied Au/PMMA (polymethylmethacrylate), Pt/PMMA, Ti/alumina and Au/alumina systems. Transmission electron microscopy of the implanted samples showed the metallic nanoparticles formed in the insulating matrix. The nanocomposites were characterized by measuring the resistivity of the composite layer as function of the dose implanted. These experimental results were compared with a model based on percolation theory, in which electron transport through the composite is explained by conduction through a random resistor network formed by the metallic nanoparticles. Excellent agreement was found between the experimental results and the predictions of the theory. It was possible to conclude, in all cases, that the conductivity process is due only to percolation (when the conducting elements are in geometric contact) and that the contribution from tunneling conduction is negligible.

Femtosecond laser processing of glassy and polymeric matrices containing metals and semiconductor nanostructures

Tailoring properties of materials by femtosecond laser processing has been proposed in the last decade as a powerful approach for technological applications, ranging from optics to biology. Although most of the research output in this field is related to femtosecond laser processing of single either organic or inorganic materials, more recently a similar approach has been proposed to develop advanced hybrid nanomaterials. Here, we report results on the use of femtosecond lasers to process hybrid nanomaterials, composed of polymeric and glassy matrices containing metal or semiconductor nanostructures. We present results on the use of femtosecond pulses to induce Cu and Ag nanoparticles in the bulk of borate and borosilicate glasses, which can be applied for a new generation of waveguides. We also report on 3D polymeric structures, fabricated by two-photon polymerization, containing Au and ZnO nanostructures, with intense two-photon fluorescent properties. The approach based on femtosecond laser processing to fabricate hybrid materials containing metal or semiconductor nanostructures is promising to be exploited for optical sensors and photonics devices.

ScPdZn and ScPtZn with YAlGe type structure: group-subgroup relation and 45Sc solid state NMR spectroscopy

The intermetallic compounds ScPdZn and ScPtZn were prepared from the elements by high-frequency melting in sealed tantalum ampoules. Both structures were refined from single crystal X-ray diffractometer data: YAlGe type, Cmcm, a = 429.53(8), b = 907.7(1), c = 527.86(1) pm, wR2 = 0.0375, 231 F2 values, for ScPdZn and a = 425.3(1), b = 918.4(2), c = 523.3(1) pm, wR2 = 0.0399, 213 F2 values for ScPtZn with 14 variables per refinement. The structures are orthorhombically distorted variants of the AlB2 type. The scandium and palladium (platinum atoms) build up ordered networks Sc3Pd3 and Sc3Pt3 (boron networks) which are slightly shifted with respect to each other. These networks are penetrated by chains of zinc atoms (262 pm in ScPtZn) which correspond to the aluminum positions, i.e. Zn(ScPd) and Zn(ScPt). The corresponding group-subgroup scheme and the differences in chemical bonding with respect to other AlB2-derived REPdZn and REPtZn compounds are discussed. 45Sc solid state NMR spectra confirm the single crystallographic scandium sites. From electronic band structure calculations the two compounds are found metallic with free electron like behavior at the Fermi level. A larger cohesive energy for ScPtZn suggests a more strongly bonded intermetallic than ScPdZn. Electron localization and overlap population analyses identify the largest bonding for scandium with the transition metal (Pd, Pt).

Studies of Inorganic Layer and Framework Structures Using Time-, Temperature- and Pressure-Resolved Powder Diffraction Techniques

This thesis is concerned with in-situ time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition MIV(HPO4)2·nH2O (MIV = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition MIVX2O7 (MIV = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo2O8. The results are compiled in seven published papers and two manuscripts. Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO4)2·H2O and intercalation of alkane diamines in α-Zr(HPO4)2·H2O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO4)(H2PO4)·2H2O to TiP2O7 three intermediate phases, γ'-Ti(PO4)(H2PO4)·(2-x)H2O, β-Ti(PO4)(H2PO4) and Ti(PO4)(H2P2O7)0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO4)2 was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO4)2 to cubic α-ZrP2O7 two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO4)2, forms at 598 K, and the second phase, β-ZrP2O7, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. In-situ high-pressure studies of τ-Zr(HPO4)2 revealed two new phases, tetragonal ν-Zr(HPO4)2 and orthorhombic ω-Zr(HPO4)2 that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO4)2 was solved and refined using the Rietveld method. The high-pressure properties of the pyrophosphates ZrP2O7 and TiP2O7, and the pyrovanadate ZrV2O7 were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV2O7 has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV2O7 and becomes X-ray amorphous at pressures above 4 GPa. In-situ high-pressure studies of trigonal α-ZrMo2O8 revealed the existence of two new phases, monoclinic δ-ZrMo2O8 and triclinic ε-ZrMo2O8 that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo2O8 was solved by direct methods and refined using the Rietveld method.

Synthesis and properties of substituted Hg-based superconductors

This thesis is focused on studies of substituted Hg-based superconducting copper oxides ((Hg1-xMx)Ba2Can-1CunO2n+2+δ). These compounds are promising objects of investigation, not only from a fundamental point of view but also because of their high values of superconducting transition temperature (Tc) and irreversibility field (Hirr). The first part of the thesis is devoted to optimization of the synthesis procedure for Hg-based cuprates. The influence of different parameters (T, t, p(Hg), p(O2)) on the synthesis of these compounds in sealed silica tubes was studied. Optimal conditions yielded samples containing up to 95% of HgBa2Ca2Cu3O8+δ (Hg-1223). The formation of solid solutions with the formula (Hg1-xCux)Ba2Ca2Cu3O8+δ (where x <= 0.5) was also established. Another technique was developed, using LiF as a flux, for synthesis of samples containing up to 90% of the HgBa2CaCu2O6+δ (Hg-1212) phase. The second part concerns synthesis and studies of oxyfluorides using Hg-1212 and Hg-1223 as starting materials together with XeF2 as a fluorinating agent. It was found that oxyfluorides of both phases have a parabolic dependence of Tc vs. a parameter as well as enhanced Tc values (ΔT ≈ 3-4 K) in comparison with optimally doped non-fluorinated analogues. The crystal structure of Hg-1223 oxyfluoride was studied by X-ray powder and neutron diffraction methods. It is suggested that chemical modification of the crystal structure leads to a decrease in Cu-O distance without noticeable change in Cu-O-Cu angle (in the (CuO2) layers), which may be the significant factors influencing this Tc increase. Hg-1223 oxyfluoride was also studied under high pressure for first time. It was found that this compound has a record-high Tc value (≈ 166 K) at P ≈ 23 GPa. The last part describes the investigation of substituted Hg-based superconductors in the series (Hg0.9M0.1)Ba2CuO4+δ {(Hg,M)-1201}, where M = Tl, Pb, W, Mo, Nb and V. A comprehensive study of these compounds by various methods (X-ray powder diffraction, EDX, IR-, EXAFS- and XANES -spectroscopy) indicated that the change of charge carrier doping level is a crucial factor determining the irreversibility line. (Hg0.9Mo0.1)Ba2CuO4+δ showed the most improved irreversibility line position among the (Hg,M)-1201 compounds studied in this series.

Significance of non‐sinking particulate organic carbon and dark CO2 fixation to heterotrophic carbon demand in the mesopelagic northeast Atlantic

[EN] It is generally assumed that sinking particulate organic carbon (POC) constitutes the main source of organic carbon supply to the deep ocean's food webs. However, a major discrepancy between the rates of sinking POC supply (collected with sediment traps) and the prokaryotic organic carbon demand (the total amount of carbon required to sustain the heterotrophic metabolism of the prokaryotes; i.e., production plus respiration, PCD) of deep-water communities has been consistently reported for the dark realm of the global ocean. While the amount of sinking POC flux declines exponentially with depth, the concentration of suspended, buoyant non-sinking POC (nsPOC; obtained with oceanographic bottles) exhibits only small variations with depth in the (sub)tropical Northeast Atlantic. Based on available data for the North Atlantic we show here that the sinking POC flux would contribute only 4–12% of the PCD in the mesopelagic realm (depending on the primary production rate in surface waters). The amount of nsPOC potentially available to heterotrophic prokaryotes in the mesopelagic realm can be partly replenished by dark dissolved inorganic carbon fixation contributing between 12% to 72% to the PCD daily. Taken together, there is evidence that the mesopelagic microheterotrophic biota is more dependent on the nsPOC pool than on the sinking POC supply. Hence, the enigmatic major mismatch between the organic carbon demand of the deep-water heterotrophic microbiota and the POC supply rates might be substantially smaller by including the potentially available nsPOC and its autochthonous production in oceanic carbon cycling models.