Browsing by Subject "METAL"

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  • Eder, Franz R.; Kotakoski, Jani; Kaiser, Ute; Meyer, Jannik C. (2014)
  • Enders, Lukas; Casadio, David S.; Aikonen, Santeri; Lenarda, Anna; Wirtanen, Tom; Hu, Tao; Hietala, Sami; Ribeiro, Lucilia S.; Pereira, Manuel Fernando R.; Helaja, Juho (2021)
    A simple "reagent-free" thermal air treatment turns active carbon into a mildly oxidized material with increased quinoidic content that catalytically dehydrogenates saturated N-heterocycles to the corresponding aromatic compounds. Thermal decarboxylation improves the activity of the catalyst further, making it overall more efficient compared to other widely used carbocatalysts such as oxidized carbon nanotubes, graphene oxide and untreated active carbons. The substrate scope covers 1,2,3,4-tetrahydroquinolines (THQ), 1,2,3,4-tetrahydro-beta-carbolines and related N-heterocyclic structures. The developed protocol also successfully dehydrogenates 3-(cyclohexenyl)indoles to 3-aryl indoles, opening a concise transition metal-free approach to (hetero)biaryls as exemplified with the synthesis of the core structure of progesterone receptor antagonist. Hammett plots, deuterium KIE measurements and computations at DFT level suggest that bimolecular hydride transfer mechanism is more likely to operate between THQs and the o-quinoidic sites of the catalyst, than the addition-elimination hemiaminal route. Comparison of structural parameters and catalytic performance of various oxidized carbon materials, prepared by different oxidative and optional post treatments, revealed that quinoidic content and surface area correlate with the obtained yields, while carboxylic acid content has a clear inhibiting effect for the studied oxidative dehydrogenations (ODHs). The carbocatalyst itself can be prepared from inexpensive and environmentally benign starting materials and its catalytic activity can be enhanced by a simple thermal oxidation in air that produces no reagent waste. Furthermore, oxygen is used as terminal oxidant, and the carbocatalyst is recyclable at least six times without a notable loss of activity.
  • Gupta, Govind; Gliga, Anda; Hedberg, Jonas; Serra, Angela; Greco, Dario; Odnevall Wallinder, Inger; Fadeel, Bengt (2020)
    Abstract The neurotoxicity of hard metal-based nanoparticles (NPs) remains poorly understood. Here, we deployed the human neuroblastoma cell line SH-SY5Y differentiated or not into dopaminergic- and cholinergic-like neurons to study the impact of tungsten carbide (WC) NPs, WC NPs sintered with cobalt (Co), or Co NPs versus soluble CoCl2. Co NPs and Co salt triggered a dose-dependent cytotoxicity with an increase in cytosolic calcium, lipid peroxidation, and depletion of glutathione (GSH). Co NPs and Co salt also suppressed glutathione peroxidase 4 (GPX4) mRNA and protein expression. Co-exposed cells were rescued by N-acetylcysteine (NAC), a precursor of GSH, and partially by liproxstatin-1, an inhibitor of lipid peroxidation. Furthermore, in silico analyses predicted a significant correlation, based on similarities in gene expression profiles, between Co-containing NPs and Parkinson's disease, and changes in the expression of selected genes were validated by RT-PCR. Finally, experiments using primary human dopaminergic neurons demonstrated cytotoxicity and GSH depletion in response to Co NPs and CoCl2 with loss of axonal integrity. Overall, these data point to a marked neurotoxic potential of Co-based but not WC NPs and show that neuronal cell death may occur through a ferroptosis-like mechanism.
  • Trochowski, Mateusz; Kobielusz, Marcin; Mroz, Krystian; Surowka, Marcin Karol; Hämäläinen, Jani; Iivonen, Tomi; Leskelä, Markku; Macyk, Wojciech (2019)
    Synthetic procedures, including doping, sintering and surface coating, can noticeably affect the physicochemical properties of semiconductors. Introduced changes very often translate into photocatalytic and photoelectrochemical activity alterations. However, in this work we have focused on more subtle treatments, which result in lack of changes observed using XRD, UV-vis, porosimetry, TEM or SEM. We have subjected titanium dioxide (P25, UV100) to a treatment with reducing agents used in procedures of noble metal deposition (citrate, borohydride, and photoreduction), or surface decoration with small amounts of TiO2 by atomic layer deposition (ALD; 10 to 200 deposition cycles), which presumably should be neutral to its activity. Although the "classical" characterization methods did not show any differences between the original and treated samples, spectroelectrochemical (SE-DRS) determination of the density of states (DOS) and catechol adsorption tests revealed a significant influence of such treatments on the photocatalytic activity (photogeneration of HO radicals, water reduction, and herbicide degradation) and photoelectrochemical behaviour of the studied samples. We have shown that the applied slight surface modifications of titanium dioxide ("insignificant" at the first glance) may strongly affect the activity of this material. Such often overlooked effects must be taken into account during a comparative photoactivity analysis of various semiconductors, since an insignificant surface treatment may noticeably influence surface chemistry. We have also demonstrated that SE-DRS can be considered as a useful tool to study these effects, although it can be difficult to correlate a particular treatment with recorded changes in the density of states.
  • Saressalo, Anton; Kilpeläinen, Aarre; Mizohata, Kenichiro; Profatilova, Iaroslava; Nolvi, Anton; Kassamakov, Ivan; Tikkanen, Pertti O.; Calatroni, Sergio; Wuensch, Walter; Djurabekova, Flyura (2021)
    High electric fields are present in a rapidly growing number of applications, which include elementary particle accelerators, vacuum interrupters, miniature x-ray sources, and satellites. Many of these applications are limited by the breakdown strength of the materials exposed to electric fields. Different methods have been developed to improve the quality of metal electrode surfaces, aiming to increase their breakdown strength. Not many systematical studies have been performed to provide a proper understanding of what contributes to the correlation between the breakdown strength and the quality of the surface. In this work, we apply a novel method for reducing vacuum arc breakdowns by cleaning the electrode surfaces with O and Ar plasma. The method can be used to alter the surfaces of the Cu electrodes in situ, i.e., without exposing them to air between the measurements. This plasma cleaning treatment is shown to reduce the number of surface impurities and to speed up the conditioning process of the samples under high-voltage pulses. Specifically, the first breakdown field was observed to increase by more than 90% after the plasma cleaning.
  • Ribeiro de Barros, Heloise; Garcia, Isabel; Kuttner, Christian; Zeballos, Nicoll; Camargo, Pedro H. C.; Cordoba de Torresi, Susana Ines; Lopez-Gallego, Fernando; Liz-Marzan, Luis M. (2021)
    The use of light as an external stimulus to control the enzyme activity is an emerging strategy that enables accurate, remote, and noninvasive biotransformations. In this context, immobilization of enzymes on plasmonic nanoparticles offers an opportunity to create light-responsive biocatalytic materials. Nevertheless, a fundamental and mechanistic understanding of the effects of localized surface plasmon resonance (LSPR) excitation on enzyme regulation remains elusive. We herein investigate the plasmonic effects on biocatalysis using Au nanospheres (AuNSp) and nanostars (AuNSt) as model plasmonic nanoparticles, lipase from Candida antarctica fraction B (CALB) as a proof-of-concept enzyme, and 808 nm as near-infrared light excitation. Our data show that LSPR excitation enables an enhancement of 58% in the enzyme activity for CALB adsorbed on AuNSt, compared with the dark conditions. This work shows how photothermal heating over the LSPR excitation enhances the CALB activity through favoring product release in the last step of the enzyme mechanism. We propose that the results reported herein shed important mechanistic and kinetic insights into the field of plasmonic biocatalysis and may inspire the rational development of plasmonic nanomaterial-enzyme hybrids with tailored activities under external light irradiation.
  • Poon, Wing-Lam; Lee, Jetty Chung-Yung; Leung, Kin Sum; Alenius, Harri; El-Nezami, Hani; Karisola, Piia (2020)
    Bioactive, oxygenated metabolites of polyunsaturated fatty acids (PUFAs) are important indicators of inflammation and oxidative stress but almost nothing is known about their interactions with nanomaterials (NMs). To investigate the effects of nano-sized materials (n-TiO2, n-ZnO, n-Ag) and their bulk-sized or ionic (b-TiO2, b-ZnO, i-Ag) counterpart, we studied the status of oxidative stress and PUFA metabolism in THP-1 cells at low-toxic concentrations (
  • Lopez-de-Luzuriaga, Jose M.; Monge, Miguel; Elena Olmos, M.; Rodriguez-Castillo, Maria; Soldevilla, Ines; Sundholm, Dage; Valiev, Rashid R. (2020)
    We report the synthesis of novel perhalophenyl three- coordinated gold( I) complexes using 1,2- bis-(diphenylphosphino)benzene (dppBz) as the chelating ligand and [AuR(tht)] (R = C6F5, C6Cl2F3, C6Cl5) as the perhalophenyl-gold(I) source, leading to [AuR(dppBz)] (R = C6F5 (1), C6Cl2F3 (2), C6Cl5 (3)) complexes. The solid-state structures of compounds 2 and 3 consist of discrete three-coordinated Au(I) complexes, which show a distorted trigonal planar geometry for the gold center with dissimilar Au-P distances. The distorted structural arrangement is closely related to its photophysical properties. The studied complexes display very intense emissions at room temperature (RT) and at 77 K in the solid state. Studies of the emissive properties of the complexes at different temperatures suggest that the emissions are phosphorescent at 77 K and exhibit thermally activated delayed fluorescence (TADF) at RT. First-principle calculations of the photophysical processes yielded rate constants for intersystem crossing and reverse intersystem crossing that are in excellent agreement with experimental data.
  • Seppanen, Matti; Karvonen, Mikko; Virolainen, Petri; Remes, Ville; Pulkkinen, Pekka; Eskelinen, Antti; Liukas, Antti; Makela, Keijo T. (2016)
    Background and purpose In a previous registry report, short-term implant survival of hip resurfacing arthroplasty (HRA) in Finland was found to be comparable to that of total hip arthroplasty (THA). Since then, it has become evident that adverse reactions to metal debris (ARMDs) may also be associated with HRA, not only with large-diameter head metal-on-metal THA. The aim of the study was to assess medium- to long-term survivorship of HRA based on the Finnish Arthroplasty Register (FAR).Patients and methods 5,068 HRAs performed during the period 2001-2013 in Finland were included. Kaplan-Meier survival analysis was used to calculate survival probabilities and their 95% confidence intervals (CIs). Cox multiple regression, with adjustment for age, sex, diagnosis, femoral head size, and hospital volume was used to analyze implant survival of HRA devices with revision for any reason as endpoint. The reference group consisted of 6,485 uncemented Vision/Bimetric and ABG II THAs performed in Finland over the same time period.Results The 8-year survival, with any revision as an endpoint, was 93% (CI: 92-94) for Birmingham Hip Resurfacing (BHR), 86% (CI: 78-94) for Corin, 91% (CI: 89-94) for ReCap, 92% (CI: 89-96) for Durom, and was 72% (CI: 69-76) for the Articular Surface Replacement (ASR). The 10-year survival, with any revision as an endpoint, for reference THAs was 92% (CI: 91-92) and for all HRAs it was 86% (CI: 84-87%). Female HRA patients had about twice the revision risk of male patients. ASR had an inferior outcome: the revision risk was 4-fold higher than for BHR, the reference implant.Interpretation The 10-year implant survival of HRAs is 86% in Finland. According to new recommendations from NICE (The National Institute for Health and Care Excellence), an HRA/THA should have a revision rate of 5% or less at 10 years. None of the HRAs studied achieved this goal.
  • Moreau, Juulia-Gabrielle; Kohout, Tomas; Wünnemann, Kai; Halodova, Patricie; Haloda, Jakub (2019)
    Shock-darkening, the melting of metals and iron sulfides into a network of veins within silicate grains, altering reflectance spectra of meteorites, was previously studied using shock physics mesoscale modeling. Melting of iron sulfides embedded in olivine was observed at pressures of 40-50 GPa. This pressure range is at the transition between shock stage 5 (C-S5) and 6 (C-S6) of the shock metamorphism classification in ordinary and enstatite chondrites. To better characterize C-S5 and C-S6 with a mesoscale modeling approach and assess post-shock heating and melting, we used multi-phase (i.e. olivine/enstatite, troilite, iron, pores, and plagioclase) meshes with realistic configurations of grains. We carried out a systematic study of shock compression in ordinary and enstatite chondrites at pressures between 30 and 70 GPa. To setup mesoscale sample meshes with realistic silicate, metal, iron sulfide, and open pore shapes, we converted backscattered electron microscope images of three chondrites. The resolved macroporosity in meshes was 3-6%. Transition from shock C-S5 to C-S6 was observed through (1) the melting of troilite above 40 GPa with melt fractions of similar to 0.7-0.9 at 70 GPa, (2) the melting of olivine and iron above 50 GPa with melt fraction of similar to 0.001 and 0.012, respectively, at 70 GPa, and (3) the melting of plagioclase above 30 GPa (melt fraction of 1, at 55 GPa). Post-shock temperatures varied from similar to 540 K at 30 GPa to similar to 1300 K at 70 GPa. We also constructed models with increased porosity up to 15% porosity, producing higher post-shock temperatures (similar to 800 K increase) and melt fractions (similar to 0.12 increase) in olivine. Additionally we constructed a pre-heated model to observe post-shock heating and melting during thermal metamorphism. This model presented similar results (melting) at pressures 10-15 GPa lower compared to the room temperature models. Finally, we demonstrated dependence of post-shock heating and melting on the orientation of open cracks relative to the shock wave front. In conclusion, the modeled melting and post-shock heating of individual phases were mostly consistent with the current shock classification scheme (Stoffler et al., 1991, 2018).