974 resultados para Ion Implantation effects


Relevância:

30.00% 30.00%

Publicador:

Resumo:

We report the synthesis and application of some ion-tagged catalysts in organometallic catalysis and organocatalysis. With the installation of an ionic group on the backbone of a known catalyst, two main effects are generally obtained. i) a modification of the solubility of the catalyst: if judicious choice of the ion pair is made, the ion-tag can confer to the catalyst a solubility profile suitable for catalyst recycling. ii) the ionic group can play a non-innocent role in the process considered: if stabilizing interaction between the ionic group and the developing charges in the transition state are established, the reaction can speed up. We describe the use of ion-tagged diphenylprolinol as Zn ligand. The chiral ligand grafted onto an ionic liquid (IL) was recycled 10 times with no loss of reactivity and selectivity, when it was employed in the first example of enantioselective addition of ZnEt2 to aldehydes in ILs. An ammonium-tagged phosphine displayed the capability to stabilize Pd catalysts for the Suzuki reaction in ILs. The ionic phase was recycled 6 times with no detectable loss of activity and very low Pd leaching in the organic phase. This catalytic system was also employed for the functionalization of the challenging substrate 5,11-dibromotetracene. In the field of organocatalysis, we prepared two ion-tagged derivatives of the McMillan imidazolidinone. The results of the asymmetric Diels-Alder reaction between trans-cinnamaldehyde and cyclopentadiene exhibited great dependence on the position and nature of the ionic group. Finally, when O-TMS-diphenylprolinol was tagged with an imidazolium ion, exploiting a silyl ether linker, an efficient catalyst for the asymmetric addition of aldehydes to nitroolefins was achieved. The catalyst displayed enhanced reactivity and the same high level of selectivity of the untagged parent catalyst and it could be employed in a wide range of reaction conditions, included use of water as solvent.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Throughout the world, pressures on water resources are increasing, mainly as a result of human activity. Because of their accessibility, groundwater and surface water are the most used reservoirs. The evaluation of the water quality requires the identification of the interconnections among the water reservoirs, natural landscape features, human activities and aquatic health. This study focuses on the estimation of the water pollution linked to two different environmental issues: salt water intrusion and acid mine drainage related to the exploitation of natural resources. Effects of salt water intrusion occurring in the shallow aquifer north of Ravenna (Italy) was analysed through the study of ion- exchange occurring in the area and its variance throughout the year, applying a depth-specific sampling method. In the study area were identified ion exchange, calcite and dolomite precipitation, and gypsum dissolution and sulphate reduction as the main processes controlling the groundwater composition. High concentrations of arsenic detected only at specific depth indicate its connexion with the organic matter. Acid mine drainage effects related to the tin extraction in the Bolivian Altiplano was studied, on water and sediment matrix. Water contamination results strictly dependent on the seasonal variation, on pH and redox conditions. During the dry season the strong evaporation and scarce water flow lead to low pH values, high concentrations of heavy metals in surface waters and precipitation of secondary minerals along the river, which could be released in oxidizing conditions as demonstrated through the sequential extraction analysis. The increase of the water flow during the wet season lead to an increase of pH values and a decrease in heavy metal concentrations, due to dilution effect and, as e.g. for the iron, to precipitation.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Aseptic loosening of metal implants is mainly attributed to the formation of metal degradation products. These include particulate debris and corrosion products, such as metal ions (anodic half-reaction) and ROS (cathodic half-reaction). While numerous clinical studies describe various adverse effects of metal degradation products, detailed knowledge of metal-induced cellular reactions, which might be important for possible therapeutic intervention, is not comprehensive. Since endothelial cells are involved in inflammation and angiogenesis, two processes which are critical for wound healing and integration of metal implants, the effects of different metal alloys and their degradation products on these cells were investigated. Endothelial cells on Ti6Al4V alloy showed signs of oxidative stress, which was similar to the response of endothelial cells to cathodic partial reaction of corrosion induced directly on Ti6Al4V surfaces. Furthermore, oxidative stress on Ti6Al4V alloy reduced the pro-inflammatory stimulation of endothelial cells by TNF-α and LPS. Oxidative stress and other stress-related responses were observed in endothelial cells in contact with Co28Cr6Mo alloy. Importantly, these features could be reduced by coating Co28Cr6Mo with a TiO2 layer, thus favouring the use of such surface modification in the development of medical devices for orthopaedic surgery. The reaction of endothelial cells to Co28Cr6Mo alloy was partially similar to the effects exerted by Co2+, which is known to be released from metal implants. Co2+ also induced ROS formation and DNA damage in endothelial cells. This correlated with p53 and p21 up-regulation, indicating the possibility of cell cycle arrest. Since CoCl2 is used as an hypoxia-mimicking agent, HIF-1α-dependence of cellular responses to Co2+ was studied in comparison to anoxia-induced effects. Although important HIF-1α-dependent genes were identified, a more detailed analysis of microarray data will be required to provide additional information about the mechanisms of Co2+ action. All these reactions of endothelial cells to metal degradation products might play their role in the complex processes taking place in the body following metal device implantation. In the worst case this can lead to aseptic loosening of the implant and requirement for revision surgery. Knowledge of molecular mechanisms of metal-induced responses will hopefully provide the possibility to interfere with undesirable processes at the implant/tissue interface, thus extending the life-time of the implant and the overall success of metal implant applications.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The effect of acetyl-L-carnitine (ALCAR) supplementation to 3-month-old rats in normal-loading and unloading conditions has been here investigated by a combined morphological, biochemical and transcriptional approach to test whether ALCAR might cause a remodeling of the metabolic/contractile phenotype of soleus muscle. Morphological assessment demonstrated an increase of type I oxidative fiber content and cross-sectional area in ALCAR-treated animals both in normal-loading and in unloading conditions. ALCAR prevented loss of mitochondrial mass in unloaded animals whereas no ALCAR-dependent increase of mitochondrial mass occurred in normal-loaded muscle. Validated microarray analysis delineated an ALCAR-induced maintenance of a slow-oxidative expression program only in unloaded soleus muscle. Indeed, the muscle adjustment of the expression profile of factors underlying mitochondrial oxidative metabolism, protein turnover, fiber type differentiation and an adaptation of voltage-gated ion channel expression was distinguishable with respect to the loading status. This selectivity may suggest a key role of muscle loading status in the manifestation of ALCAR effects. The results extend to a broader level of biological informations the previous notion on ALCAR positive effect in rat soleus muscle during unloading and point to a role of ALCAR for the maintenance of its slow-oxidative fiber character.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Sorafenib targets the Raf/mitogen-activated protein kinase, VEGF, and platelet-derived growth factor pathways and prolongs survival patients in advanced hepatocellular carcinoma (HCC). Everolimus inhibits the mammalian target of rapamycin, a kinase overactive in HCC. To investigate whether the antitumor effects of these agents are additive, we compared a combined and sequential treatment regimen of everolimus and sorafenib with monotherapy. After hepatic implantation of Morris Hepatoma (MH) cells, rats were randomly allocated to everolimus (5 mg/kg, 2×/week), sorafenib (7.5 mg/kg/d), combined everolimus and sorafenib, sequential sorafenib (2 weeks) then everolimus (3 weeks), or control groups. MRI quantified tumor volumes. Erk1/2, 4E-BP1, and their phosphorylated forms were quantified by immunoblotting. Angiogenesis was assessed in vitro by aortic ring and tube formation assays, and in vivo with Vegf-a mRNA and vascular casts. After 35 days, tumor volumes were reduced by 60%, 85%, and 55%, relative to controls, in everolimus, the combination, and sequential groups, respectively (P < 0.01). Survival was longest in the combination group (P < 0.001). Phosphorylation of 4E-BP1 and Erk1/2 decreased after everolimus and sorafenib, respectively. Angiogenesis decreased after all treatments (P < 0.05), although sorafenib increased Vegf-a mRNA in liver tumors. Vessel sprouting was abundant in control tumors, lower after sorafenib, and absent after the combination. Intussusceptive angiogenic transluminal pillars failed to coalesce after the combination. Combined treatment with everolimus and sorafenib exerts a stronger antitumoral effect on MH tumors than monotherapy. Everolimus retains antitumoral properties when administered sequentially after sorafenib. This supports the clinical use of everolimus in HCC, both in combination with sorafenib or after sorafenib.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The H(+) -coupled divalent metal-ion transporter DMT1 serves as both the primary entry point for iron into the body (intestinal brush-border uptake) and the route by which transferrin-associated iron is mobilized from endosomes to cytosol in erythroid precursors and other cells. Elucidating the molecular mechanisms of DMT1 will therefore increase our understanding of iron metabolism and the etiology of iron overload disorders. We expressed wild type and mutant DMT1 in Xenopus oocytes and monitored metal-ion uptake, currents and intracellular pH. DMT1 was activated in the presence of an inwardly directed H(+) electrochemical gradient. At low extracellular pH (pH(o)), H(+) binding preceded binding of Fe(2+) and its simultaneous translocation. However, DMT1 did not behave like a typical ion-coupled transporter at higher pH(o), and at pH(o) 7.4 we observed Fe(2+) transport that was not associated with H(+) influx. His(272) --> Ala substitution uncoupled the Fe(2+) and H(+) fluxes. At low pH(o), H272A mediated H(+) uniport that was inhibited by Fe(2+). Meanwhile H272A-mediated Fe(2+) transport was independent of pH(o). Our data indicate (i) that H(+) coupling in DMT1 serves to increase affinity for Fe(2+) and provide a thermodynamic driving force for Fe(2+) transport and (ii) that His-272 is critical in transducing the effects of H(+) coupling. Notably, our data also indicate that DMT1 can mediate facilitative Fe(2+) transport in the absence of a H(+) gradient. Since plasma membrane expression of DMT1 is upregulated in liver of hemochromatosis patients, this H(+) -uncoupled facilitative Fe(2+) transport via DMT1 can account for the uptake of nontransferrin-bound plasma iron characteristic of iron overload disorders.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

BACKGROUND: Paclitaxel-eluting stents (PES) have been shown to reduce the rate of restenosis and the need for repeated revascularization procedures compared with bare metal stents. However, long-term effects of paclitaxel on vascular function are unknown. The purpose of the present study was to assess coronary vasomotor response to exercise after paclitaxel-eluting stent implantation. METHODS: Coronary vasomotion was evaluated by biplane quantitative coronary angiography at rest and during supine bicycle exercise in 27 patients with coronary artery disease. Twelve patients were treated with a bare metal stent (controls), and fifteen patients with a paclitaxel-eluting stent. All patients were restudied 6+/-2 (range 2-12) months after stent implantation. Minimal luminal diameter, stent diameter, proximal, distal and a reference vessel diameter were determined. RESULTS: Reference vessels showed exercise-induced vasodilation in both groups (+20+/-5% controls; +26+/-3% PES group). Vasomotion within the stented vessel segments was abolished. In the controls, the adjacent segments proximal and distal to the stent showed exercise-induced vasodilation (+17+/-3% and +24+/-4%). In contrast, there was exercise-induced vasoconstriction of the proximal and distal vessel segments adjacent to the paclitaxel-eluting stent (-13+/-6% and -18+/-4%; p<0.005). After sublingual nitroglycerin, the proximal and distal vessel segments dilated in both groups. Exercise-induced vasoconstriction adjacent to paclitaxel-eluting stent correlated inversely with the time interval after stent implantation. CONCLUSIONS: Paclitaxel-eluting stent implantation is associated with exercise-induced vasoconstriction in the persistent region suggesting endothelial dysfunction as the underlying mechanism. Improvement of vascular function occurs over time, indicating delayed vascular healing.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The single electron transistor (SET) is a Coulomb blockade device, whose operation is based on the controlled manipulation of individual electrons. Single electron transistors show immense potential to be used in future ultra lowpower devices, high density memory and also in high precision electrometry. Most SET devices operate at cryogenic temperatures, because the charging energy is much smaller than the thermal oscillations. The room temperature operation of these devices is possible with sub- 10nm nano-islands due to the inverse dependance of charging energy on the radius of the conducting nano-island. The fabrication of sub-10nm features with existing lithographic techniques is a technological challenge. Here we present the results for the first room temperature operating SET device fabricated using Focused Ion Beam deposition technology. The SET device, incorporates an array of tungsten nano-islands with an average diameter of 8nm. The SET devices shows clear Coulomb blockade for different gate voltages at room temperature. The charging energy of the device was calculated to be 160.0 meV; the capacitance per junction was found to be 0.94 atto F; and the tunnel resistance per junction was calculated to be 1.26 G Ω. The tunnel resistance is five orders of magnitude larger than the quantum of resistance (26 k Ω) and allows for the localization of electrons on the tungsten nano-island. The lower capacitance of the device combined with the high tunnel resistance, allows for the Coulomb blockade effects observed at room temperature. Different device configurations, minimizing the total capacitance of the device have been explored. The effect of the geometry of the nano electrodes on the device characteristics has been presented. Simulated device characteristics, based on the soliton model have been discussed. The first application of SET device as a gas sensor has been demonstrated.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Roads and highways present a unique challenge to wildlife as they exhibit substantial impacts on the surrounding ecosystem through the interruption of a number of ecological processes. With new roads added to the national highway system every year, an understanding of these impacts is required for effective mitigation of potential environmental impacts. A major contributor to these negative effects is the deposition of chemicals used in winter deicing activities to nearby surface waters. These chemicals often vary in composition and may affect freshwater species differently. The negative impacts of widespread deposition of sodium chloride (NaCl) have prompted a search for an `environmentally friendly' alternative. However, little research has investigated the potential environmental effects of widespread use of these alternatives. Herein, I detail the results of laboratory tests and field surveys designed to determine the impacts of road salt (NaCl) and other chemical deicers on amphibian communities in Michigan's Upper Peninsula. Using larval amphibians I demonstrate the lethal impacts of a suite of chemical deicers on this sensitive, freshwater species. Larval wood frogs (Lithobates sylvatica) were tolerant of short-term (96 hours) exposure to urea (CH4N2O), sodium chloride (NaCl), and magnesium chloride (MgCl2). However, these larvae were very sensitive to acetate products (C8H12CaMgO8, CH3COOK) and calcium chloride (CaCl2). These differences in tolerance suggest that certain deicers may be more harmful to amphibians than others. Secondly, I expanded this analysis to include an experiment designed to determine the sublethal effects of chronic exposure to environmentally realistic concentrations of NaCl on two unique amphibian species, L. sylvatica and green frogs (L. clamitans). L. sylvatica tend to breed in small, ephemeral wetlands and metamorphose within a single season. However, L. clamitans breed primarily in more permanent wetlands and often remain as tadpoles for one year or more. These species employ different life history strategies in this region which may influence their response to chronic NaCl exposure. Both species demonstrated potentially harmful effects on individual fitness. L. sylvatica larvae had a high incidence of edema suggesting the NaCl exposure was a significant physiologic stressor to these larvae. L. clamitans larvae reduced tail length during their exposure which may affect adult fitness of these individuals. In order to determine the risk local amphibians face when using these roadside pools, I conducted a survey of the spatial distribution of chloride in the three northernmost counties of Michigan. This area receives a relatively low amount of NaCl which is confined to state and federal highways. The chloride concentrations in this region were much lower than those in urban systems; however, amphibians breeding in the local area may encounter harmful chloride levels arising from temporal variations in hydroperiods. Spatial variation of chloride levels suggests the road-effect zone for amphibians may be as large as 1000 m from a salt-treated highway. Lastly, I performed an analysis of the use of specific conductance to predict chloride concentrations in natural surface water bodies. A number of studies have used this regression to predict chloride concentrations from measurements of specific conductance. This method is often chosen in the place of ion chromatography due to budget and time constraints. However, using a regression method to characterize this relationship does not result in accurate chloride ion concentration estimates.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In patients with drug-resistant hypertension, chronic electric stimulation of the carotid baroreflex is an investigational therapy for blood pressure reduction. We hypothesized that changes in cardiac autonomic regulation can be demonstrated in response to chronic baroreceptor stimulation, and we analyzed the correlation with blood pressure changes. Twenty-one patients with drug-resistant hypertension were prospectively included in a substudy of the Device Based Therapy in Hypertension Trial. Heart rate variability and heart rate turbulence were analyzed using 24-hour ECG. Recordings were obtained 1 month after device implantation with the stimulator off and after 3 months of chronic electric stimulation (stimulator on). Chronic baroreceptor stimulation decreased office blood pressure from 185+/-31/109+/-24 mm Hg to 154+/-23/95+/-16 mm Hg (P<0.0001/P=0.002). Mean heart rate decreased from 81+/-11 to 76+/-10 beats per minute(-1) (P=0.001). Heart rate variability frequency-domain parameters assessed using fast Fourier transformation (FFT; ratio of low frequency:high frequency: 2.78 versus 2.24 for off versus on; P<0.001) were significantly changed during stimulation of the carotid baroreceptor, and heart rate turbulence onset was significantly decreased (turbulence onset: -0.002 versus -0.015 for off versus on; P=0.004). In conclusion, chronic baroreceptor stimulation causes sustained changes in heart rate variability and heart rate turbulence that are consistent with inhibition of sympathetic activity and increase of parasympathetic activity in patients with drug-resistant systemic hypertension; these changes correlate with blood pressure reduction. Whether the autonomic modulation has favorable cardiovascular effects beyond blood pressure control should be investigated in further studies.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

BACKGROUND: Although considerable bone fill may occur following treatment of peri-implantitis, re-osseointegration appears to be limited and unpredictable. Objectives: To evaluate the effects of various decontamination techniques and implant surface configurations on re-osseointegration of contaminated dental implants. MATERIAL AND METHODS: Three months after tooth extraction, implants consisting of a basal part and an exchangeable intraosseous implant cylinder (EIIC) were placed in the mandibles of dogs. The EIIC was machined (M), sandblasted and acid-etched (SLA), or titanium plasma sprayed (TPS). Ligature-induced peri-implantitis was initiated 8 weeks post-implantation and lasted until bone loss reached the junction of the two implant parts. Three treatment modalities were applied: (T1) the EIIC was exchanged for a pristine EIIC; (T2) the EIIC was sprayed in situ with saline; and (T3) the EIIC was removed, cleansed outside the mouth by spraying with saline, steam-sterilized, and remounted. A collagen barrier was placed over each fixture, and 3 months later, samples were processed for histology and histomorphometry. RESULTS: T2 revealed the highest bone-to-implant contact (BIC) level (significantly better than T1 and T3). T2 also yielded the highest bone crest level (significantly better than T1), followed by T3 (significantly better than T1). SLA showed the highest BIC level (significantly better than M), followed by TPS. There were no statistically significant differences in bone crest height between implant types. CONCLUSIONS: Both SLA implants and in situ cleansing resulted in the best re-osseointegration and bone fill of previously contaminated implants.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The endometrium contains a distinct population of immune cells that undergo cyclic changes during the menstrual cycle and implantation. The majority of these leucocytes are uterine NK (uNK) cells, however how these cells interact with uterine stromal fibroblasts remains unclear. We therefore investigated the paracrine effect of medium conditioned by uterine decidual leucocytes (which are enriched for uNK cells) on the gene expression profile of endometrial stromal fibroblasts in vitro using a cDNA microarray. Our results, verified by real-time PCR, ELISA and FACS analysis, reveal that soluble factors from uterine leucocytes substantially alter endometrial stromal fibroblast gene expression. The largest group of up-regulated genes found was chemokines and cytokines. These include IL-8, CCL8 and CXCL1, which have also been shown to be stimulated by contact of stromal fibroblasts with trophoblast, suggesting that uNK cells work synergistically to support trophoblast migration during implantation. The decidual leucocytes also up-regulated IL-15 and IL-15Ralpha in stromal fibroblasts which could produce a niche for uNK cells allowing proliferation within and recruitment into the uterus, as seen in bone marrow. Overall this study demonstrates, for the first time, the paracrine communication between uterine leucocytes and uterine stromal fibroblasts, and adds to the understanding of how the uterine immune system contributes to the changes seen within the cycling endometrium.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

BACKGROUND/AIMS ATP-gated P2X4 purinergic receptors (P2X4Rs) are cation channels with important roles in diverse cell types. To date, lack of specific inhibitors has hampered investigations on P2X4Rs. Recently, the benzodiazepine derivative, 5-BDBD has been proposed to selectively inhibit P2X4Rs. However, limited evidences are currently available on its inhibitory properties. Thus, we aimed to characterize the inhibitory effects of 5-BDBD on recombinant human P2X4Rs. METHODS We investigated ATP-induced intracellular Ca(2+) signals and whole cell ion currents in HEK 293 cells that were either transiently or stably transfected with hP2X4Rs. RESULTS Our data show that ATP (< 1 μM) stimulates P2X4R-mediated Ca(2+) influx while endogenously expressed P2Y receptors are not activated to any significant extent. Both 5-BDBD and TNP-ATP inhibit ATP-induced Ca(2+) signals and inward ion currents in a concentration-dependent manner. Application of two different concentrations of 5-BDBD causes a rightward shift in ATP dose-response curve. Since the magnitude of maximal stimulation does not change, these data suggest that 5-BDBD may competitively inhibit the P2X4Rs. CONCLUSIONS Our results demonstrate that application of submicromolar ATP concentrations allows reliable assessment of recombinant P2XR functions in HEK 293 cells. Furthermore, 5-BDBD and TNP-ATP have similar inhibitory potencies on the P2X4Rs although their mechanisms of actions are different.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

BACKGROUND Pathology studies have shown delayed arterial healing in culprit lesions of patients with acute coronary syndrome (ACS) compared with stable coronary artery disease (CAD) after placement of drug-eluting stents (DES). It is unknown whether similar differences exist in-vivo during long-term follow-up. Using optical coherence tomography (OCT), we assessed differences in arterial healing between patients with ACS and stable CAD five years after DES implantation. METHODS AND RESULTS A total of 88 patients comprised of 53 ACS lesions with 7864 struts and 35 stable lesions with 5298 struts were suitable for final OCT analysis five years after DES implantation. The analytical approach was based on a hierarchical Bayesian random-effects model. OCT endpoints were strut coverage, malapposition, protrusion, evaginations and cluster formation. Uncovered (1.7% vs. 0.7%, adjusted p=0.041) or protruding struts (0.50% vs. 0.13%, adjusted p=0.038) were more frequent among ACS compared with stable CAD lesions. A similar trend was observed for malapposed struts (1.33% vs. 0.45%, adj. p=0.072). Clusters of uncovered or malapposed/protruding struts were present in 34.0% of ACS and 14.1% of stable patients (adj. p=0.041). Coronary evaginations were more frequent in patients with ST-elevation myocardial infarction compared with stable CAD patients (0.16 vs. 0.13 per cross section, p=0.027). CONCLUSION Uncovered, malapposed, and protruding stent struts as well as clusters of delayed healing may be more frequent in culprit lesions of ACS compared with stable CAD patients late after DES implantation. Our observational findings suggest a differential healing response attributable to lesion characteristics of patients with ACS compared with stable CAD in-vivo.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Mass spectrometric analysis of elemental and isotopic compositions of several NIST standards is performed by a miniature laser ablation/ionisation reflectron-type time-of-flight mass spectrometer (LMS) using a fs-laser ablation ion source (775 nm, 190 fs, 1 kHz). The results of the mass spectrometric studies indicate that in a defined range of laser irradiance (fluence) and for a certain number of accumulations of single laser shot spectra, the measurements of isotope abundances can be conducted with a measurement accuracy at the per mill level and at the per cent level for isotope concentrations higher and lower than 100 ppm, respectively. Also the elemental analysis can be performed with a good accuracy. The LMS instrument combined with a fs-laser ablation ion source exhibits similar detection efficiency for both metallic and non-metallic elements. Relative sensitivity coefficients were determined and found to be close to one, which is of considerable importance for the development of standard-less instruments. Negligible thermal effects, sample damage and excellent characteristics of the fs-laser beam are thought to be the main reason for substantial improvement of the instrumental performance compared to other laser ablation mass spectrometers.