Solvation in aqueous binary mixtures: consequences of the hydrophobic character of the ionic liquids and the solvatochromic probes

Information on the solvation in mixtures of water, W, and the ionic liquids, ILs, 1-allyl-3-R-imidazolium chlorides; R = methyl, 1-butyl, and 1-hexyl, has been obtained from the responses of the following solvatochromic probes: 2,6-dibromo-4-[(E)-2-(1-R-pyridinium-4-yl)ethenyl] phenolate, R = methyl, MePMBr2; 1-octyl, OcPMBr(2), and the corresponding quinolinium derivative, MeQMBr(2). A model developed for solvation in binary mixtures of W and molecular solvents has been extended to the present mixtures. Our objective is to assess the relevance to solvation of hydrogen-bonding and the hydrophobic character of the IL and the solvatochromic probe. Plots of the medium empirical polarity, E-T(probe) versus its composition revealed non-ideal behavior, attributed to preferential solvation by the IL and, more efficiently, by the IL-W hydrogen-bonded complex. The deviation from linearity increases as a function of increasing number of carbon atoms in the alkyl group of the IL, and is larger than that observed for solvation by W plus molecular solvents (1-propanol and 2-(1-butoxy)ethanol) that are more hydrophobic than the ILs investigated. This enhanced deviation is attributed to the more organized structure of the ILs proper, which persists in their aqueous solutions. MeQMBr(2) is more susceptible to solvent lipophilicity than OcPMBr(2), although the former probe is less lipophilic. This enhanced susceptibility agrees with the important effect of annelation on the contributions of the quinonoid and zwitterionic limiting structures to the ground and excited states of the probe, hence on its response to both medium composition and lipophilicity of the IL.

Thermo and mechanical cycling and veneering method do not influence Y-TZP core/veneer interface bond strength

Objectives: The purpose of this study was to evaluate the influence of thermal and mechanical cycling and veneering technique on the shear bond strength of Y-TZP (yttrium oxide partially stabilized tetragonal zirconia polycrystal) core–veneer interfaces. Materials and methods: Cylindrical Y-TZP specimens were veneered either by layering (n = 20) or by pressing technique (n = 20). A metal ceramic group (CoCr) was used as control (n = 20). Ten specimens for each group were thermal and mechanical cycled and then all samples were subjected to shear bond strength in a universal testing machine with a 0.5 mm/min crosshead speed. Mean shear bond strength (MPa) was analysed with a 2-way analysis of variance and Tukey’s test ( p < 0.05). Failure mode was determined using stereomicroscopy and scanning electron microscopy (SEM). Results: Thermal and mechanical cycling had no influence on the shear bond strength for all groups. The CoCr group presented the highest bond strength value ( p < 0.05) (34.72 7.05 MPa). There was no significant difference between Y-TZP veneered by layering (22.46 2.08 MPa) or pressing (23.58 2.1 MPa) technique. Failure modes were predominantly adhesive for CoCr group, and cohesive within veneer for Y-TZP groups. Conclusions: Thermal and mechanical cycling, as well as the veneering technique does not affect Y-TZP core–veneer bond strength. Clinical significance: Different methods of veneering Y-TZP restorations would not influence the clinical performance of the core/veneer interfaces.

Comparative degradation of ZnO- and SnO(2)-based polycrystalline non-ohmic devices by current pulse stress

The degradation behaviour of SnO(2)-based varistors (SCNCr) due to current pulses (8/20 mu s) is reported here for the first time in comparison with the ZnO-based commercial varistors (ZnO). Puncturing and/or cracking failures were observed in ZnO-based varistors possessing inferior thermo-mechanical properties in comparison with that found in a SCNCr system free of failures. Both systems presented electric degradation related to the increase in the leakage current and decrease in the electric breakdown field, non-linear coefficient and average value of the potential barrier height. However, it was found that a more severe degradation occurred in the ZnO-based varistors concerning their non-ohmic behaviour, while in the SCNCr system, a strong non-ohmic behaviour remained after the degradation. These results indicate that the degradation in the metal oxide varistors is controlled by a defect diffusion process whose rate depends on the mobility, the concentration of meta-stable defects and the amount of electrically active interfaces. The improved behaviour of the SCNCr system is then inferred to be associated with the higher amount of electrically active interfaces (85%) and to a higher energy necessary to activate the diffusion of the specific defects.

Percolated non-Newtonian flow for silicone obtained from exfoliated bioinorganic layered double hydroxide intercalated with amino acid

A simple and scalable procedure was used to obtain thin, stable, homogeneous, and easy-to-handle films composed of silicone derived from dimethicones containing dispersed hydrotalcite-type materials previously organo-modified with amino acids. The absence of the typical X-ray pattern of the bioinorganic LDH filler suggested an exfoliation process that was further indirectly evidenced by a drastic change in the rheological behavior, which turned from a quasi-Newtonian behavior for the silicone free of LDH filler to an extensive developed gel-like structure for the nanocomposite derivatives. Visualized by the shear-thinning exponent of the complex viscosity in the low-frequency range, the percolation threshold was evident for filler loading as low as <5 w/W%, suggesting the presence of a largely developed interface between the filler and the polymer. The increase of more than one order of magnitude in viscosity was explained by the rather strong attrition phenomenon between the tethered amino acid anions and the silicone chains. UVB radiation absorption profiles make such bioinorganic polymer nanocomposites potentially applicable in skin protection. Thermo-gravimetric analysis revealed significant improvement in the thermal stability, especially in the final step of the polymer combustion, thus underlining the role of the hybrid material as a thermal retardant agent. (C) 2011 Elsevier B.V. All rights reserved.

Degree of conversion of nanofilled and microhybrid composite resins photo-activated by different generations of LEDs

Objective: This study aimed at evaluating the degree of conversion (DC) of four composite resins, being one nanofilled and 3 microhybrid resins, photo-activated with second- and third-generation light-emitting diodes (LEDs). Material and methods: Filtek (TM) Z350 nanofilled composite resins and Amelogen (R) Plus, Vit-l-escence (TM) and Opallis microhybrid resins were photo-activated with two second-generation LEDs (Radii-cal and Elipar Free Light (TM) 2) and one third-generation LED (Ultra-Lume LED 5) by continuous light mode, and a quartz halogen-tungsten bulb (QHT, control). After 24 h of storage, the samples were pulverized into fine powder and 5 mg of each material were mixed with 100 mg of potassium bromide (KBr). After homogenization, they were pressed, which resulted in a pellet that was evaluated using an infrared spectromer (Nexus 470, Thermo Nicolet) equipped with TGS detector using diffuse reflectance (32 scans, resolution of 4 cm(-1)) coupled to a computer. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1). Results: The ANOVA showed a significant effect on the interaction between the light-curing units (LCUs) and the composite resins (p<0.001). The Tukey's test showed that the nanofilled resin (Filtek (TM) Z350) and Opallis when photo-activated by the halogen lamp (QTH) had the lowest DC compared with the other microhybrid composite resins. The DC of the nanofilled resin (Filtek (TM) Z350) was also lower using LEDs. The highest degrees of conversion were obtained using the third-generation LED and one of second-generation LEDs (Elipar Free Light (TM) 2). Conclusions: The nanofilled resin showed the lowest DC, and the Vit-l-escence (TM) microhybrid composite resin showed the highest DC. Among the LCUs, it was not possible to establish an order, even though the second-generation LED Radii-cal provided the lowest DC.

Optical and thermal investigation of GeO2-PbO thin films doped with Au and Ag nanoparticles

The present work reports on the thermo-optical study of germanate thin films doped with Au and Ag nanoparticles. Transmission Electron Microscopy images, UV-visible absorption and Micro-Raman scattering evidenced the presence of nanoparticles and the formation of collective excitations, the so called surface plasmons. Moreover, the effects of the metallic nanoparticles in the thermal properties of the films were observed. The thermal lens technique was proposed to evaluate the Thermal Diffusivity (D) of the samples. It furnishes superficial spatial resolution of about 100 mu m, so it is appropriate to study inhomogeneous samples. It is shown that D may change up to a factor 3 over the surface of a film because of the differences in the nanoparticles concentration distribution. (C) 2011 Elsevier B.V. All rights reserved.

Light scattering on the structural characterization of DMPG vesicles along the bilayer anomalous phase transition

Highly charged vesicles of the saturated anionic lipid dimyristoyl phosphatidylglycerol (DMPG) in low ionic strength medium exhibit a very peculiar thermo-structural behavior. Along a wide gel-fluid transition region, DMPG dispersions display several anomalous characteristics, like low turbidity, high electrical conductivity and viscosity. Here, static and dynamic light scattering (SLS and DLS) were used to characterize DMPG vesicles at different temperatures. Similar experiments were performed with the largely studied zwitterionic lipid dimyristoyl phosphatidylcholine (DMPC). SLS and DLS data yielded similar dimensions for DMPC vesicles at all studied temperatures. However, for DMPG, along the gel-fluid transition region, SLS indicated a threefold increase in the vesicle radius of gyration, whereas the hydrodynamic radius, as obtained from DLS, increased 30% only. Despite the anomalous increase in the radius of gyration, DMPG lipid vesicles maintain isotropy, since no light depolarization was detected. Hence, SLS data are interpreted regarding the presence of isotropic vesicles within the DMPG anomalous transition, but highly perforated vesicles, with large holes. DLS/SLS discrepancy along the DMPG transition region is discussed in terms of the interpretation of the Einstein-Stokes relation for porous vesicles. Therefore, SLS data are shown to be much more appropriate for measuring porous vesicle dimensions than the vesicle diffusion coefficient. The underlying nanoscopic process which leads to the opening of pores in charged DMPG bilayer is very intriguing and deserves further investigation. One could envisage biotechnological applications, with vesicles being produced to enlarge and perforate in a chosen temperature and/or pH value. (C) 2012 Elsevier Ireland Ltd. All rights reserved.

Elaboration and Characterization of Nano-Biocomposites Based on Plasticized Poly(Hydroxybutyrate-Co-Hydroxyvalerate) with Organo-Modified Montmorillonite

Nano-biocomposites based on a biodegradable bacterial copolyester, poly(hydroxybutyrate-co-hydroxyvalerate), have been elaborated with an organo-modified montmorillonite (OMMT) clay as nanofiller, and acetyl tributyl citrate as plasticizer. The corresponding (nano)structures, thermal and mechanical properties, permeability, and biodegradability have been determined. Polyhydroxyalkanoates are very thermal sensitive then to follow the degradation the corresponding matrices have been analyzed by size exclusion chromatography. The results indicate that the addition of the plasticizer decreases the thermo-mechanical degradation, during the extrusion. These nano-biocomposites show an intercalated/exfoliated structure with good mechanical and barrier properties, and an appropriated biodegradation kinetic. Intending to understand the changes in the thermal properties, the nano-biocomposites were characterized by thermal gravimetric analysis and differential scanning calorimetry. The presence of the OMMT clay did not influence significantly the transition temperatures. However, the filler not only acted as a nucleating agent which enhanced the crystallization, but also as a thermal barrier, improving the thermal stability of the biopolymer. The results indicated that the addition of the plasticizer reduces the glass transition temperature and the crystalline melting temperature. The plasticizer acts as a processing aid and increases the processing temperature range (lower melting temperature).

Natural Membranes for Application in Biomedical Devices

Polymers from natural sources are particularly useful as biomaterials for medical devices applications. In this study, the results of characterization of a gelatin network electrolyte doped with europium triflate (Eu(CF3SO3)(3)) are described. The unusual electronic properties of the trivalent lanthanide ions make them well suited as luminescent reporter groups, with many applications in biotechnology. Samples of solvent-free electrolytes were prepared with a range of guest salt concentration. Materials based on Eu(CF3SO3)(3) were obtained as mechanically robust, flexible, transparent, and completely amorphous films. Samples were characterized by thermal analysis (thermo-gravimetry analysis (TGA) and differential scanning calorimetry (DSC), electrochemical stability, scanning electronmicroscopy (SEM), and photoluminescence spectroscopy.

Central poststroke pain: somatosensory abnormalities and the presence of associated myofascial pain syndrome

Background: Central post-stroke pain (CPSP) is a neuropathic pain syndrome associated with somatosensory abnormalities due to central nervous system lesion following a cerebrovascular insult. Post-stroke pain (PSP) refers to a broader range of clinical conditions leading to pain after stroke, but not restricted to CPSP, including other types of pain such as myofascial pain syndrome (MPS), painful shoulder, lumbar and dorsal pain, complex regional pain syndrome, and spasticity-related pain. Despite its recognition as part of the general PSP diagnostic possibilities, the prevalence of MPS has never been characterized in patients with CPSP patients. We performed a cross-sectional standardized clinical and radiological evaluation of patients with definite CPSP in order to assess the presence of other non-neuropathic pain syndromes, and in particular, the role of myofascial pain syndrome in these patients. Methods: CPSP patients underwent a standardized sensory and motor neurological evaluation, and were classified according to stroke mechanism, neurological deficits, presence and profile of MPS. The Visual Analogic Scale (VAS), McGill Pain Questionnaire (MPQ), and Beck Depression Scale (BDS) were filled out by all participants. Results: Forty CPSP patients were included. Thirty-six (90.0%) had one single ischemic stroke. Pain presented during the first three months after stroke in 75.0%. Median pain intensity was 10 (5 to 10). There was no difference in pain intensity among the different lesion site groups. Neuropathic pain was continuous-ongoing in 34 (85.0%) patients and intermittent in the remainder. Burning was the most common descriptor (70%). Main aggravating factors were contact to cold (62.5%). Thermo-sensory abnormalities were universal. MPS was diagnosed in 27 (67.5%) patients and was more common in the supratentorial extra-thalamic group (P <0.001). No significant differences were observed among the different stroke location groups and pain questionnaires and scales scores. Importantly, CPSP patients with and without MPS did not differ in pain intensity (VAS), MPQ or BDS scores. Conclusions: The presence of MPS is not an exception after stroke and may present in association with CPSP as a common comorbid condition. Further studies are necessary to clarify the role of MPS in CPSP.

Microclimate under different shading screens in greenhouses cultivated with bromeliads

This study had as its objective the evaluation of the influence of shading screens of different colors on the different microclimate variables in a greenhouse covered with transparent low-density polyethylene (LDPE). The experiment was conducted with five treatments: thermo-reflective screen (T1); a control - without screen (T2); red screen (T3); blue screen (T4); and black screen (T5), all of them with 70% of shading. An automatic micrometeorological station was installed in each treatment, measuring air temperature (T), relative humidity (RH), incoming solar radiation (Rg), photosynthetically active radiation (PAR) and net radiation (Rn) continuously. The control (T2) and red screen (T3) treatments promoted the highest solar radiation transmissivity, respectively 56.3 and 27%. The black screen (T5) had the lowest solar radiation transmissivity (10.4%). For PAR and Rn the same tendency was observed. The highest temperature was observed under blue screen (T4) treatment, which was 1.3 °C higher than external condition. Blue screen (T4) treatment also presented the highest relative humidity difference between inside and outside conditions.

Her2p molecular modeling, mutant analysis and intramitochondrial localization

Bacterial GatCAB amidotransferases are responsible for the transamidation of mischarged glutamyl-tRNA(Gln) into glutaminyl-tRNA(Gln). Mitochondria matrix also has a multienzymatic complex necessary for the transamidation of glutamyl-tRNA(Gln). Gtf1p, Her2p and Pet112p are the constituents of mitochondrial GatFAB amidotransferase complex. Her2p is subunit A of GatFAB complex, while Gtf1p is subunit F, a connector protein between Pet112p (subunit B) and Her2p. Here we evaluate through molecular modeling and amino acid correlation analysis the HER2 protein family. Localization studies indicated that Her2p is predominantly localized in the mitochondrial outer membrane, but it is also located in the mitochondrial matrix where together with Pet112p and Gtf1p constitutes the GatFAB complex. Finally, HER2 random mutagenesis unveiled important residues that provide thermo stability for the complex and are differently suppressed by overexpression of GTF1 or PET112. For instance, her2/ts11 mutant showed its fermentative growth impaired, and poorly rescued by GTF1 indicating that Her2p unknown function in the mitochondria outer membrane affects cell viability.