Artículos de revistas: "Chromace"

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Bastit-Kalinowska, Agnès. "Aquileienses clerici quasi chorus beatorum habentur (Hieronim, Kronika, rok 374). Przykład życia religijnego duchownych pod koniec IV wieku". Vox Patrum 70 (12 de diciembre de 2018): 205–15. http://dx.doi.org/10.31743/vp.3205.

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The end of the fourth century sees the emergence, in the West, of several experiences of monastic life in the city for the bishop and a part of his presbyterium (Eusèbe of Vercelli, Martin of Tours, Paulin of Nola, Augustin of Hippo). A similar attempt, around the priest Chromace of Aquileia (before his episcopate, and maybe even later), is documented by some testimonies of Jerome from Stridon and Rufin from Aquileia for the years 370s. These testimonies are the object of the present study.

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Escudero-Castejon, Lidia, Sergio Sanchez-Segado, Stephen Parirenyatwa y Animesh Jha. "Formation of Chromium-Containing Molten Salt Phase during Roasting of Chromite Ore with Sodium and Potassium Hydroxides". Journal for Manufacturing Science and Production 16, n.º 4 (1 de diciembre de 2016): 215–25. http://dx.doi.org/10.1515/jmsp-2016-0023.

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AbstractChromium has a wide range of applications including metals and alloys manufacturing, pigments, corrosion resistance coatings and leather tanning. The production of chromium chemicals is based on the oxidative alkali roasting of chromite ores, which leads to the formation of water-soluble alkali chromates. Previous investigations reported that when chromite is roasted with soda-ash, a molten salt containing chromium, which is mainly composed of sodium carbonate and sodium chromate (Na2CO3-Na2CrO4 binary mixture), forms under typical roasting conditions. The physical properties of the liquid phase, which are dependent on the temperature, charge and gangue compositions, play an important role on the oxidation reaction and may limit the chromate recovery by hindering the oxygen transport to the reaction interface. This investigation focuses on the alkali roasting of chromite ore at 1,000 oC using NaOH and KOH, followed by water leaching. The influence of the alkali ratio on the chromium extraction yield is analysed, and the results obtained with both hydroxides are compared. Sample characterisation and thermodynamic analysis, including phase diagrams, equilibrium calculations and computation of liquidus curves, are combined with the purpose of studying the formation of the molten salt phase under different roasting conditions and its effect on the final chromium recovery.

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Bockmair, Georg. "Non-Chromate Surface Protection for Aircraft Maintenance". Advanced Materials Research 38 (marzo de 2008): 7–13. http://dx.doi.org/10.4028/www.scientific.net/amr.38.7.

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While chromates as anti-corrosion pigments in primers and wash primers have disappeared in most industries, there are still quite a lot of chromated paints used in the aircraft industry. Intensive efforts to develop alternative pre-treatments to chromate conversion coatings and to chromic acid anodization have begun. The intention of this report is to give an overview of the state-of-the-art techniques about such pre-treatment/coating systems of aluminium for aircraft maintenance, which are in accordance with the latest environmental policies. The objective is to evaluate the combination of surface pre-treatment and paint as a whole.

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Ayinla, Kuranga I., Alafara A. Baba, Bankim C. Tripathy y Ranjan K. Dwari. "Production of Industrial-Grade Monoclinic Lead Chromate (PbCrO4) from Indigenous Chromite ore for Paint Pigment Utilization". Journal of Nepal Chemical Society 44, n.º 2 (6 de agosto de 2024): 101–9. http://dx.doi.org/10.3126/jncs.v44i2.68321.

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Decades of use have proven that lead chromate (PbCrO4) powder is an excellent paint pigment material. Unfortunately, practically this entire superb chromate compound used for decorative systems, protective systems, and mass dyeing of paper and polymer materials is conventionally made using inorganic synthetic chromium salts. In this study, we reported a promising simple, low-cost lead chromate production route derived from chromite ore from Nigeria. The Nigerian chromite ore was roasted in a 1:1 NaOH salt and then leached with water at 60°C. Lead nitrate was added to the leached liquor to further co-precipitate it. The resulting precipitate was then cleaned in ethanol and oven dried for ten hours at 80°C. The experimental results showed that lead ion concentration, temperature and flow rate have large influence on lead chromate precipitation, and the precipitation data fit a diffusion model. The activation energy of lead precipitation obtained was 4.76 kJ/mol, and the reaction order was 0.873 nearly one in relation to the concentration of lead ion. Additionally, XRD, FT-IR, and SEM/EDS comparative investigation of the properties established which favourable paint pigment performance similar to that of commercial industrial lead chromate powder in a range of all established physicochemical properties clarified the developing direction of research on lead chromate synthesis from Chromite leached liquor.

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5

Wunsch, Friederike M., Bernhard Wünsch, Freddy A. Bernal y Thomas J. Schmidt. "Quantitative Structure–Activity Relationships of Natural-Product-Inspired, Aminoalkyl-Substituted 1-Benzopyrans as Novel Antiplasmodial Agents". Molecules 26, n.º 17 (30 de agosto de 2021): 5249. http://dx.doi.org/10.3390/molecules26175249.

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On the basis of the finding that various aminoalkyl-substituted chromene and chromane derivatives possess strong and highly selective in vitro bioactivity against Plasmodium falciparum, the pathogen responsible for tropical malaria, we performed a structure–activity relationship study for such compounds. With structures and activity data of 52 congeneric compounds from our recent studies, we performed a three-dimensional quantitative structure–activity relationship (3D-QSAR) study using the comparative molecular field analysis (CoMFA) approach as implemented in the Open3DQSAR software. The resulting model displayed excellent internal and good external predictive power as well as good robustness. Besides insights into the molecular interactions and structural features influencing the antiplasmodial activity, this model now provides the possibility to predict the activity of further untested compounds to guide our further synthetic efforts to develop even more potent antiplasmodial chromenes/chromanes.

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6

Equeenuddin, Sk Md y B. C. Raymahashay. "Retention of Anionic Pollutants by Overburden Material at Chromite Mines: An Experimental Investigation". Asian Journal of Water, Environment and Pollution 5, n.º 4 (enero de 2008): 109–13. http://dx.doi.org/10.3233/ajw-2008-5_4_12.

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The goethite-rich overburden material at chromite mines is an efficient sink for the chromate anion. Leaching experiments using a saline solution showed that the material at the Sukinda mine of Orissa had retained a higher amount of chromate compared with the material at the nearby Boula mine. This difference can be attributed to the mineralogy at the two sites. For example, the proportion of poorly crystalline goethite is higher in the Sukinda material compared with Boula. Experiments on further adsorption of arsenate and phosphate indicated that the Boula sample had higher uptake capacity for both anions. This is obviously because the Sukinda sample had initially adsorbed more chromate. These results can be useful in evaluating natural attenuation of fertilizer-derived pollutants in the agricultural land near chromite mines.

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7

Cagide, F., T. Silva, J. Reis, A. Gaspar, F. Borges, L. R. Gomes y J. N. Low. "Discovery of two new classes of potent monoamine oxidase-B inhibitors by tricky chemistry". Chemical Communications 51, n.º 14 (2015): 2832–35. http://dx.doi.org/10.1039/c4cc08798d.

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8

Lemarié, Joseph. "Le sermon 34 de Chromace d'Aquilée pour I'Épiphanie. Nouvelle attestation dans I'homéliaire carolingien du Pseudo-Bède". Sacris Erudiri 33 (enero de 1992): 121–24. http://dx.doi.org/10.1484/j.se.2.303777.

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9

Tapia, I., V. Alcázar y J. R. Morán. "Synthesis of chromanes using pyruvic acid dimethylhydrazone dianion". Canadian Journal of Chemistry 68, n.º 12 (1 de diciembre de 1990): 2190–91. http://dx.doi.org/10.1139/v90-335.

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10

Petit, François, Henri Debontride, Michel Lenglet, Gérard Juhel y Didier Verchere. "Contribution of Spectrometric Methods to the Study of the Constituents of Chromating Layers". Applied Spectroscopy 49, n.º 2 (febrero de 1995): 207–10. http://dx.doi.org/10.1366/0003702953963733.

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The amorphous constituents of a chromating layer may be defined by the simultaneous use of diffuse reflection spectrometry in the ultraviolet and visible, and of Fourier transform infrared spectrometry. The PO4 group is characterized in the infrared reflection spectrum by bands located near 1070, 1030, and 900 cm−1 for chromium phosphate. The CrO4 group induces bands at 960, 860, and 820 cm−1 for zinc chromate and at about 980, 950, and 860 cm−1 for chromium chromates. The ligandmetal charge transfer bands (LMCT) characteristic of the chromates are situated in the region 3.35 to 4.20 eV. The study of the thermal behavior of chromium phosphate CrPO4 and zinc chromate ZnCrO4 shows that these compounds are stable up to 300°C. Complex chromates of Cr(III) may be observed in the range 150 to 300°C. These analytical data show the contribution of these methods which, used in the reflection mode, are demonstrably the best suited to the analysis of chromating layers on coated steel, of which the primary constituents are chromium phosphate and complex Cr(III) chromates. These results allow the interpretation of the thermal behavior of chromating layers.

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11

Alawadhi, Khaled, Richard Brown y Jalal Alsarraf. "A replacement of chromate coating for adhesive bonding of stainless steel in a corrosive environment". International Journal of Engineering & Technology 3, n.º 3 (6 de septiembre de 2014): 396. http://dx.doi.org/10.14419/ijet.v3i3.3041.

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For adhesive bonding of stainless steel to itself, a surface treatment involving chromates is used. However, chromates are environmentally unfriendly so a replacement is being sought. In this paper, an alternative to chromate was investigated. The standard test method, ASTM D 1002, was used to measure the failure load of adhesively bonded stainless steel samples. A general-purpose epoxy adhesive was used. To simulate marine exposure, adhesively bonded samples were placed in a 5% salt spray for extended periods of time, up to five weeks. Results indicated that the initial shear strength of adhesive joints prepared with a traditional chromate preparation was 25% greater than the new, alternative coating. However, more importantly, the rate of decrease in strength with salt spray exposure was greater for the chromate than for the alternative. After 21 days, both bonding surface treatments had the same strength. However, after this period of time, the alternative was stronger than the chromate treatment, indicating that the alternative was a more durable coating. An adhesive/adherent coated system was investigated using a finite element method in order to investigate the influence of adhesive thickness between the adhesive and the adherent, and the residual stress in the adhesive layer. Keywords: Adhesive, Alternative Coating, Crevice Corrosion, Potentio-Dynamic, Salt Spray.

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12

Henry, Karen S., John C. Petura, Steven Brooks, Steven Dentico, Stephen A. Kessel y Mark Harris. "Preventing surface deposition of chromium with asphalt caps at chromite ore processing residue sites: a case study". Canadian Geotechnical Journal 44, n.º 7 (1 de julio de 2007): 814–39. http://dx.doi.org/10.1139/t07-029.

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Caps were constructed on chromite ore processing residue (COPR) sites in the Kearny, New Jersey, area between 1989 and 1994 to prevent human exposure to hexavalent chromium (Cr(VI)). The caps comprise geotextile overlain by 100 mm of dense graded aggregate (DGA) and 100 mm of hot mix asphalt (HMA). Prior to constructing these "composite asphalt caps" (CACs), Cr(VI) was sometimes deposited on surface soils as chromate (salts) during evaporative periods. We initially thought the geotextile and DGA acted as a capillary barrier, stopping capillary water rise, but site inspection revealed that the DGA and geotextile were too moist to perform this function. Further study included a literature review, DGA capillary rise estimates, in situ measurement of soil-water content over 7 months at a representative COPR site, and numerical modeling of matric suction gradients induced by evaporation. The collective results reveal that the CACs eliminate upward matric suction gradients from the COPR–soil through the DGA, thereby precluding surface chromate deposition. Even during evaporative periods, the low unsaturated hydraulic conductivity of the HMA restricts upward movement of moisture and soluble chromate from underlying COPR–soil. In contrast, there are almost always upward matric suction gradients in uncapped COPR–soil.Key words: capillary rise, chromite ore processing residue, chromate, hexavalent chromium, composite asphalt cap, evaporation.

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13

Voevodin, N., D. Buhrmaster, V. Balbyshev, A. Khramov, J. Johnson y R. Mantz. "Nonchromated Coating Systems for Corrosion Protection of Aircraft Aluminum Alloys". Materials Performance 45, n.º 11 (1 de noviembre de 2006): 48–51. https://doi.org/10.5006/mp2006_45_11-48.

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The U.S. Air Force requires the development of an environmentally compliant, chromate-free aircraft coating system that meets or exceeds current corrosion protection capabilities. A number of nonchromated pretreatments and primers have been independently developed over the past years. This report compares the corrosion resistance performance of selected fully nonchromate systems to the standard chromate-containing coating system. The data identified two nonchromated systems that performed comparably to the standard chromated aircraft coating system.

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14

Sharma, Sangita, Kinnari H. Parikh, Mahesh V. Kadia, Falguni D. Thakkar y Dhara D. Patel. "Polarization Studies on Inhibitory Effect of Chromates and Dichromates on Corrosion of Tin Coated Steel in 0.5M Monochloroacetic Acid". E-Journal of Chemistry 5, n.º 2 (2008): 302–8. http://dx.doi.org/10.1155/2008/658706.

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Chromates and Dichromates have been tested for its inhibitory effects towards tin coated steel in 0.5M monochloroacetic acid. The corrosion behaviour of potassium chromate, sodium chromate, potassium dichromate, sodium dichromate and ammonium dichromate was studied by polarization curves, Tafel parameters like Tafel slopes, extrapolation of cathodic Tafel line and intersection of cathodic and anodic line at open circuit potential in presence of inhibitors have been tabulated along with other electrochemical parameters and corrosion current have been calculated from Tafel lines. The efficiencies are calculated and compared reasonably well with those obtained from loss in weight data. All the inhibitors induce a significant increase of potential positive and direction accounts for cathodic polarization. The Icorrhas also been calculated and that accounts well for cathodic reactions in presence of chromates and dichromates as inhibitors.

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15

Gomes, Ligia R., John Nicolson Low, Fernando Cagide, Daniel Chavarria y Fernanda Borges. "New insights in the discovery of novelh-MAO-B inhibitors: structural characterization of a series ofN-phenyl-4-oxo-4H-chromene-3-carboxamide derivatives". Acta Crystallographica Section E Crystallographic Communications 71, n.º 5 (25 de abril de 2015): 547–54. http://dx.doi.org/10.1107/s2056989015007859.

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SixN-substituted-phenyl 4-oxo-4H-chromene-3-carboxamides, namelyN-(2-nitrophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10N2O5(2b),N-(3-methoxyphenyl)-4-oxo-4H-chromene-3-carboxamide, C17H13NO4, (3a),N-(3-bromophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10BrNO3, (3b),N-(4-methoxyphenyl)-4-oxo-4H-chromene-3-carboxamide, C17H13NO4, (4a),N-(4-methylphenyl)-4-oxo-4H-chromene-3-carboxamide, C17H13NO3, (4d), andN-(4-hydroxyphenyl)-4-oxo-4H-chromene-3-carboxamide, C16H11NO4, (4e), have been structurally characterized. All compounds exhibit ananticonformation with respect to the C—N rotamer of the amide and atrans-related conformation with the carbonyl groups of the chromone ring of the amide. These structures present an intramolecular hydrogen-bonded network comprising an N—H...O hydrogen bond between the amide N atom and the O atom of the carbonyl group of the pyrone ring, forming anS(6) ring, and a weak Car—H...O hydrogen bond in which the carbonyl group of the amide acts as acceptor for the H atom of anortho-C atom of the exocyclic phenyl ring, which results in anotherS(6) ring. The N—H...O intramolecular hydrogen bond constrains the carboxamide moiety such that it is virtually coplanar with the chromone ring.

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Pokorný, Petr y David Čítek. "Effect of Addition of Chromate to Concrete on the Bond Strength of Hot-Dip Galvanized Ribbed Rebar at Ambient Temperature". Key Engineering Materials 868 (octubre de 2020): 10–14. http://dx.doi.org/10.4028/www.scientific.net/kem.868.10.

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This article studies the effect of chromate (CrO42-) addition to concrete mix on the corrosion behavior of hot-dip galvanized reinforcement and primarily on the bond strength of this reinforcement with concrete. According to the original literature, the addition of chromates should prevent corrosion of the coating in fresh concrete with the evolution of hydrogen. The results show that this is indeed the case, but the need for a greater amount of added chromates also reduces the mechanical properties of the concrete. This ultimately affects the bond strength of the hot-dip galvanized reinforcement with concrete. Due to legislation, it is totally unacceptable to add any amount of chromates to the concrete mix (CrVI - toxic substance).

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Verner, Petr y V. Chrást. "Behavior of conversion layers in the laboratory test conditions". Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis 53, n.º 2 (2005): 127–32. http://dx.doi.org/10.11118/actaun200553020127.

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Toxicity of CrVI is a basic problem of chromate conversion layers. This paper refers to regulation EU, which limit occurrence CrVI. Purpose of experiment is alert to alternative anticorrosive inhibitors without CrVI. Alternative inhibitors are on the base CrIII. These inhibitors protect probably similar mechanism as chromans with CrVI.

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Vacek, Václav y Vladimír Rod. "Diffusion coefficients of potassium chromate and dichromate in water at 25 °C". Collection of Czechoslovak Chemical Communications 51, n.º 7 (1986): 1403–6. http://dx.doi.org/10.1135/cccc19861403.

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The concentration dependences of diffusion coefficients of potassium chromate and dichromate in water at 25 °C were measured by using the Taylor technique of the concentration pulse dispersion in laminar flow of liquid. The results were compared with hitherto published mutually inconsistent data for potassium and sodium chromates and dichromates.

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Gomes, Ligia R., John Nicolson Low, Carlos Fernandes, Alexandra Gaspar y Fernanda Borges. "Crystal structures of ethyl 6-(4-methylphenyl)-4-oxo-4H-chromene-2-carboxylate and ethyl 6-(4-fluorophenyl)-4-oxo-4H-chromene-2-carboxylate". Acta Crystallographica Section E Crystallographic Communications 72, n.º 1 (1 de enero de 2016): 8–13. http://dx.doi.org/10.1107/s2056989015022781.

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The crystal structures of two chromone derivatives,viz.ethyl 6-(4-methylphenyl)-4-oxo-4H-chromene-2-carboxylate, C19H16O4, (1), and ethyl 6-(4-fluorophenyl)-4-oxo-4H-chromene-2-carboxylate C18H13FO4, (2), have been determined: (1) crystallizes with two molecules in the asymmetric unit. A comparison of the dihedral angles beween the mean planes of the central chromone core with those of the substituents, an ethyl ester moiety at the 2-position and apara-substituted phenyl ring at the 6-position shows that each molecule differs significantly from the others, even the two independent molecules (aandb) of (1). In all three molecules, the carbonyl groups of the chromone and the carboxylate aretrans-related. The supramolecular structure of (1) involves only weak C—H...π interactions between H atoms of the substituent phenyl group and the phenyl group, which link molecules into a chain of alternating moleculesaandb, and weak π–π stacking interactions between the chromone units. The packing in (2) involves C—H...O interactions, which form a network of two intersecting ladders involving the carbonyl atom of the carboxylate group as the acceptor for H atoms at the 7-position of the chromone ring and from anortho-H atom of the exocyclic benzene ring. The carbonyl atom of the chromone acts as an acceptor from ameta-H atom of the exocyclic benzene ring. π–π interactions stack the molecules by unit translation along theaaxis.

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Zhou, Yong, Pei Zhang, Jinping Xiong y Fuan Yan. "The corrosion behavior of chromated AA2024 aluminum alloy in 3.5% NaCl solution". Anti-Corrosion Methods and Materials 66, n.º 6 (4 de noviembre de 2019): 879–87. http://dx.doi.org/10.1108/acmm-01-2019-2070.

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Purpose A chromate conversion coating was prepared on the surface of bare AA2024 aluminum alloy by direct immersion in the chromating treatment bath, and the corrosion behavior of chromated AA2024 aluminum alloy in 3.5 per cent NaCl solution was studied by electrochemical measurement and microstructural observation. Design/methodology/approach According to the polarization curve test and the scanning electron microscope observation, the corrosion evolution of chromated AA2024 in 3.5 per cent NaCl solution was divided into the following three stages: coating failure, pitting corrosion and intergranular corrosion (IGC). Findings In the first stage, the chromate coating degraded gradually due to the combined action of chloride anions and water molecules, resulting in the complete exposure of AA2024 substrate to 3.5 per cent NaCl solution. Subsequently, in the second stage, chloride anions adsorbed at the sites of θ phase (Al2Cu) and S phase (Al2CuMg) on the AA2024 surface preferentially, and some corrosion pits initiated at the above two sites and propagated towards the deep of crystal grains. However, the propagation of a pit terminated when the pit front arrived at the adjacent grain boundary, where the initiation of IGC occurred. Originality/value Finally, in the third stage, the corrosion proceeded along the continuous grain boundary net and penetrated the internal of AA2024 substrate, resulting in the propagation of IGC. The related corrosion mechanisms for the bare and the chromated AA2024 were also discussed.

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Dey, Satarupa, Baishali Pandit y A. K. Paul. "Reduction of Hexavalent Chromium by Viable Cells of Chromium Resistant Bacteria Isolated from Chromite Mining Environment". Journal of Mining 2014 (10 de agosto de 2014): 1–8. http://dx.doi.org/10.1155/2014/941341.

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Environmental contamination of hexavalent chromium [Cr(VI)] is of serious concern for its toxicity as well as mutagenic and carcinogenic effects. Bacterial chromate reduction is a cost-effective technology for detoxification as well as removal of Cr(VI) from polluted environment. Chromium resistant and reducing bacteria, belonging to Arthrobacter, Pseudomonas, and Corynebacterium isolated from chromite mine overburden and seepage samples of Orissa, India, were found to tolerate 12–18 mM Cr(VI) during growth. Viable cells of these isolates were also capable of growing and reducing 100 μM Cr(VI) quite efficiently in Vogel Bonner (V.B.) broth under batch cultivation. Freshly grown cells of the most potent isolate, Arthrobacter SUK 1201, reduced 100 μM Cr(VI) in 48 h. Reduction potential of SUK 1201 cells decreased with increase in Cr(VI) concentration but increased with increase in cell density and attained its maximum at 1010 cells/mL. Chromate reducing efficiency of SUK 1201 was promoted in the presence of glucose and glycerol while the highest reduction was at pH 7.0 and 25°C. The reduction process was inhibited by divalent cations Ni, Co, and Cd, but not by Cu. Similarly, carbonyl cyanide m-chlorophenylhydrazone, N,N,-Di cyclohexyl carbodiimide, sodium azide, and sodium fluoride were inhibitory to chromate reduction, while 2,4 dinitrophenol promoted the process. Cells permeabilized by toluene increased the efficiency of Cr(VI) reduction and, thereby, indicate that Arthrobacter sp. SUK 1201, indigenous to chromite mining environment, could be used as an ideal tool for chromium bioremediation.

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Li, Zeng Xin, Guo Ming Wang y Qiang Liang. "The Comparison of Three Recycling Processes of Copper Chromite Spent Catalysts". Advanced Materials Research 599 (noviembre de 2012): 566–69. http://dx.doi.org/10.4028/www.scientific.net/amr.599.566.

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Three technologies of recycling copper chromite spent catalysts from furfuryl production by furfural hydrogenization were developed. After the organic species was removed from the solid waste by vacuum pressure distillation at 130°C, the resultant solid waste catalyst was mixed with soda ash, followed by roasting, leaching and removing silicon in a reverberating furnace to obtain sodium chromate. Dissolving the cupric oxide in soda ash solution to remove chrome and then dissolving it in nitric acid, cupric nitrate can be obtained. A certain proportion of such sodium chromate and cupric nitrate were mixed and treated by ammonia solution to give precipitate, which was roasted and granulated to get new catalyst used in furfuryl production. Three processes features and their respective advantages and disadvantages were discussed.

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Starks, Courtney M., Russell B. Williams, Vanessa L. Norman, Stephanie M. Rice, Mark O’Neil-Johnson, Julie A. Lawrence y Gary R. Eldridge. "Antibacterial chromene and chromane stilbenoids from Hymenocardia acida". Phytochemistry 98 (febrero de 2014): 216–22. http://dx.doi.org/10.1016/j.phytochem.2013.11.012.

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Andersson, Petter y Mats Norell. "Scale Growth on Austenitic Alloys under KCl Deposits at 500°C". Materials Science Forum 595-598 (septiembre de 2008): 333–42. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.333.

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The scale growth on two austenitic alloys, Alloy 310 and Sanicro 28, under KCl deposits was examined. This is relevant to the long term corrosion of superheater tubes in biofuel combustion. Coupons were encapsulated in tablets so that 1 mm of KCl with a relative density of 91% covered the metal. Samples were tested at 500°C in 5%O2-10%H2O-N2 for 24, 168 and 672 h. After exposure the salt was broken off and the scale was characterised by using SEM-EDX and AES. After 24 h a 50 nm thick oxide surrounded 500 nm thick chromates on the surface. No oxide layer was detected under the chromates and no Cl was found under either layer. The chromate growth requires lateral transportation of Cr along the surface. This reduces the protectiveness of the oxide and accelerates the formation of less protective Fe rich oxides. The formation of chromates also releases HCl inside the KCl tablet. The chromates did not grow significantly between 24 and 168 h, but the oxide grew equally thick beneath and between them and Cl was enriched around the metal oxide interface. After 672 h the oxides were about 5 μm thick and only few chromates were seen. Crystals of KCl formed in areas with thick porous and Fe rich oxides on both alloys.

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Gomes, Ligia R., John Nicolson Low, Fernando Cagide y Fernanda Borges. "The crystal structures of fourN-(4-halophenyl)-4-oxo-4H-chromene-3-carboxamides". Acta Crystallographica Section E Crystallographic Communications 71, n.º 1 (1 de enero de 2015): 88–93. http://dx.doi.org/10.1107/s2056989014027054.

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FourN-(4-halophenyl)-4-oxo-4H-chromene-3-carboxamides (halo = F, Cl, Br and I),N-(4-fluorophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10FNO3,N-(4-chlorophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10ClNO3,N-(4-bromophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10BrNO3,N-(4-iodophenyl)-4-oxo-4H-chromene-3-carboxamide, C16H10INO3, have been structurally characterized. The molecules are essentially planar and each exhibits ananticonformation with respect to the C—N rotamer of the amide and acisgeometry with respect to the relative positions of the Carom—Carombond of the chromone ring and the carbonyl group of the amide. The structures each exhibit an intramolecular hydrogen-bonding network comprising an N—H...O hydrogen bond between the amide N atom and the O atom of the carbonyl group of the pyrone ring, forming anS(6) ring, and a weak Carom—H...O interaction with the O atom of the carbonyl group of the amide as acceptor, which forms anotherS(6) ring. All four compounds have the same supramolecular structure, consisting ofR22(13) rings that are propagated along thea-axis direction by unit translation. There is π–π stacking involving inversion-related molecules in each structure.

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Pettersson, J., C. Pettersson, Nicklas Folkeson, Lars Gunnar Johansson, Erik Skog y Jan Erik Svensson. "The Influence of Sulfur Additions on the Corrosive Environments in a Waste-Fired CFB Boiler". Materials Science Forum 522-523 (agosto de 2006): 563–70. http://dx.doi.org/10.4028/www.scientific.net/msf.522-523.563.

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Corrosion/deposition field tests have been carried out in the superheater region of a commercial waste-fired 75MW CFBC boiler using air cooled probes. The influence of material temperature (450-500°C), flue gas temperature, temperature variations (i.e. thermal cycling) and additives to the fuel (elemental sulphur and dolomite) on deposition and corrosion was studied. The results presented here mainly consider the influence of sulphur additions to the fuel. The fuel was a mixture of 50% household waste and 50% industrial waste. After exposure the samples were analyzed by ESEM/EDX, XRD, AAS, FIB and IC. With no additional sulphur, alkali chlorides made up a large part of the deposit/corrosion product layer and in some cases chromate (VI) was detected. It is suggested that the chromate (VI) has formed by reaction of the protective oxide with alkali chlorides in the deposit. Adding sulphur to the fuel changed the composition of the deposits, alkali chlorides being largely replaced by alkali sulphates. No chromates(VI) were detected in the sulphur-added runs. It is suggested that adding sulphur to the fuel may decrease fireside corrosion because it changes the composition of the deposit. Alkali sulphates are much less corrosive than alkali chlorides partly because they do not form chromate(VI).

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Stoulil, Jan, Martina Anisová, Eva Mistova y Jaroslav Fojt. "Zr-based coating for the prevention of silver tarnishing". Anti-Corrosion Methods and Materials 61, n.º 1 (20 de diciembre de 2013): 38–43. http://dx.doi.org/10.1108/acmm-01-2013-1230.

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Purpose – This work aims to focus on evaluation of the ability of cathodically deposited ZrO2-based coatings to stabilise the surface of silver against tarnishing caused by S2−-based species and comparison of these coatings with Cr oxide-based coating. Design/methodology/approach – The coatings were evaluated using inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), impedance spectroscopy (EIS) and galvanostatic reduction of specimens exposed to H2S vapours. Findings – The kinetics of deposition were studied and optimum conditions for coating formation were determined. The options of manual application suitable for practical use were studied also. Zr specimens showed better barrier properties than did a chromated specimen. The best properties were observed on a specimen with a manually fast-applied coating. However, Zr coating does not provide as good protection from tarnishing as chromate. The structure of the Cr coating contains species of chromate that oxidize species of S2−. Originality/value – The paper provides new information regarding the anticorrosive properties of cathodically deposited ZrO2 coating as an alternative to Cr coating for the preservation of silver surfaces.

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28

Gomes, Ligia R., John Nicolson Low, Fernando Cagide, Alexandra Gaspar y Fernanda Borges. "A comparison of the structures of some 2- and 3-substituted chromone derivatives: a structural study on the importance of the secondary carboxamide backbone for the inhibitory activity of MAO-B". Acta Crystallographica Section E Crystallographic Communications 71, n.º 11 (3 de octubre de 2015): 1270–77. http://dx.doi.org/10.1107/s2056989015017958.

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The crystal structures of the 3-substituted tertiary chromone carboxamide derivative, C17H13NO3,N-methyl-4-oxo-N-phenyl-4H-chromene-3-carboxamide (1), and the chromone carbonyl pyrrolidine derivatives, C14H13NO3, 3-(pyrrolidine-1-carbonyl)-4H-chromen-4-one (3) and 2-(pyrrolidine-1-carbonyl)-4H-chromen-4-one (4) have been determined. Their structural features are discussed and compared with similar compounds namely with respect to their MAO-B inhibitory activities. The chromone carboxamide presents a –synconformation with the aromatic rings twisted with respect to each other [the dihedral angle between the mean planes of the chromone system and the exocyclic phenyl ring is 58.48 (8)°]. The pyrrolidine derivatives also display a significant twist: the dihedral angles between the chromone system and the best plane formed by the pyrrolidine atoms are 48.9 (2) and 23.97 (12)° in (3) and (4), respectively. Compound (3) shows a short C—H...O intramolecular contact forming anS(7) ring. The supramolecular structures for each compound are defined by weak C—H...O hydrogen bonds, which link the molecules into chains and sheets. The Cambridge Structural Database gave 45 hits for compounds with a pyrrolidinecarbonyl group. A simple statistical analysis of their geometric parameters is made in order to compare them with those of the molecules determined in the present work.

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29

Kendig, M. W. y R. G. Buchheit. "Corrosion Inhibition of Aluminum and Aluminum Alloys by Soluble Chromates, Chromate Coatings, and Chromate-Free Coatings". CORROSION 59, n.º 5 (mayo de 2003): 379–400. http://dx.doi.org/10.5006/1.3277570.

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30

Liu, Cheng Jun, Jie Qi y Mao Fa Jiang. "Experimental Study on Sulfuric Acid Leaching Behavior of Chromite with Different Temperature". Advanced Materials Research 361-363 (octubre de 2011): 628–31. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.628.

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Utilizing Pakistan chromite as raw material, the rapid leaching of chromium and iron could be realized by the sulfuric acid leaching process on the condition of atmospheric pressure and the addition of oxidant A. And the leaching rate of chromium and iron would be 98.5% and 71.9%, respectively. The sulfuric acid leaching processes with different temperature were systematically studied by chemical analysis and phase analysis. The results showed that, with the increase of reaction temperature, the leaching rate of chromium would increase gradually, but the leaching rate of iron increased at first and then decreases and reached its maximum at 140°C. When the temperature > 160°C, the phases of the leaching residue were magnesium iron silicate and a few of silica, no chromohercynite, chrompicotite and magnesioferrite existed in the chromite. The leaching solution of sulfuric acid leaching process could be used for preparing the basic chrome sulfate, and there is no Cr6+ in the leaching residue and solution. The results would provide theoretical guidance for solving environmental pollution problem of Cr6+ in traditional chromate production process.

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31

Iwata, Naoki y Susumu Kitanaka. "New Cannabinoid-Like Chromane and Chromene Derivatives from Rhododendron anthopogonoides". CHEMICAL & PHARMACEUTICAL BULLETIN 59, n.º 11 (2011): 1409–12. http://dx.doi.org/10.1248/cpb.59.1409.

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32

Osyanin, Vitaly A., Dmitry V. Osipov, Irina V. Melnikova, Kirill S. Korzhenko, Irina A. Semenova y Yuri N. Klimochkin. "Catalyst-Free Synthesis of Chromane-Type N,O-Acetals via Intramolecular Addition of Phenols to Enamines". Synthesis 52, n.º 23 (27 de julio de 2020): 3604–21. http://dx.doi.org/10.1055/s-0040-1707209.

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A new strategy to 2-aminochromanes through catalyst-free cascade reaction of 3-trifluoroacetyl-4H-chromenes and 4H-chromene-3-carbaldehydes with cyclic secondary amines is presented. The reaction proceeds through subsequent 1,4- and 1,2-additions of amine, bimolecular elimination of trifluoroacetamide or formamide, and 6-exo-trig cyclization. The latter stage is a very rare example of addition of phenols to enamines. The obtained semicyclic N,O-acetals were applied as useful precursors for the synthesis of other chromanes.

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33

Hall, J. B. y J. K. Kouba. "Electron Microscopy of Barium-Promoted Copper Chromite". Proceedings, annual meeting, Electron Microscopy Society of America 43 (agosto de 1985): 390–91. http://dx.doi.org/10.1017/s0424820100118825.

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Copper chromite was reported as an effective catalyst for the hydrogenation of esters to alcohols by Homer Adkins in 1931, and it still remains the catalyst of choice for this reaction. Its most common commercial application is in the hydrogenation of fatty esters to detergent range linear alcohols. Typical reaction conditions are relatively severe: 200-250°C and 2000-4000 psig hydrogen. Barium is often used as a promoter and such a catalyst is prepared by codeposition of barium and copper chromates followed by calcination to the mixed chromite. The catalyst is usually activated by reduction with hydrogen which is believed to generate highly dispersed copper metal. The barium supposedly retards overreduction of the catalyst and ameliorates sulfate poisoning.Knowledge of the distribution and association of the Ba, Cu, and Cr catalyst components is important in understanding its function and in the design of better catalysts.

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34

Matern, K. y T. Mansfeldt. "Chromate adsorption from chromite ore processing residue eluates by three Indian soils". Environmental Chemistry 13, n.º 4 (2016): 674. http://dx.doi.org/10.1071/en15147.

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Environmental context Chromate (CrO42–)-containing waste is illegally dumped in some places in the state of Uttar Pradesh, north India, although CrO42– is known to be toxic and carcinogenic. Because CrO42– is leached from the landfills, this study investigated the adsorption of CrO42– by soils. The results indicated that CrO42– is highly leachable and adsorption is inhibited, which leads to contamination of the groundwater and drinking water in this area. Abstract Chromite ore processing residue (COPR) is a harmful waste of the chromate (CrO42–) extraction roasting process. Nevertheless, deposition of COPR in uncontrolled surface landfills is still common practice in some countries. Leaching of carcinogenic CrO42– and contamination of groundwater is a key environmental risk arising from COPR sites. The objective of this study was to evaluate the adsorption behaviour of CrO42– from COPR eluates by soils. Prior to the adsorption experiments, batch studies at varying solid-to-liquid ratios were performed to evaluate the solubility of CrO42– from COPR. Chromate adsorption experiments were carried out in a batch system with eluates obtained from two different Indian COPRs to assess potential groundwater contamination by CrO42–. Three soils that originate from the surroundings of COPR dumping sites were chosen in order to provide realistic adsorption conditions. The data were evaluated with the Freundlich and Langmuir equation. Chromate adsorption was inhibited because of the high pH of both of the soils (pH 6.7 to 7.2) and the eluates (pH 12.3) as well as the high carbonate concentration of the eluates. The extent and behaviour of CrO42– adsorption from both eluates was similar. The main difference between the eluates was the solubility of CrO42– from COPR and thus the initial CrO42– concentration. The results presented in this study provide an improved understanding of the mobility of CrO42– in the affected area, which is important because the local population uses the groundwater not only for the needs of livestock but also as drinking water.

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35

Kumla, Decha, José Pereira, Tida Dethoup, Luis Gales, Joana Freitas-Silva, Paulo Costa, Michael Lee et al. "Chromone Derivatives and Other Constituents from Cultures of the Marine Sponge-Associated Fungus Penicillium erubescens KUFA0220 and Their Antibacterial Activity". Marine Drugs 16, n.º 8 (20 de agosto de 2018): 289. http://dx.doi.org/10.3390/md16080289.

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A previously unreported chromene derivative, 1-hydroxy-12-methoxycitromycin (1c), and four previously undescribed chromone derivatives, including pyanochromone (3b), spirofuranochromone (4), 7-hydroxy-6-methoxy-4-oxo-3-[(1E)-3-oxobut-1-en-1-yl]-4H-chromene-5-carboxylic acid (5), a pyranochromone dimer (6) were isolated, together with thirteen known compounds: β-sitostenone, ergosterol 5,8-endoperoxide, citromycin (1a), 12-methoxycitromycin (1b), myxotrichin D (1d), 12-methoxycitromycetin (1e), anhydrofulvic acid (2a), myxotrichin C (2b), penialidin D (2c), penialidin F (3a), SPF-3059-30 (7), GKK1032B (8) and secalonic acid A (9), from cultures of the marine sponge- associated fungus Penicillium erubescens KUFA0220. Compounds 1a–e, 2a, 3a, 4, 7–9, were tested for their antibacterial activity against Gram-positive and Gram-negative reference and multidrug-resistant strains isolated from the environment. Only 8 exhibited an in vitro growth inhibition of all Gram-positive bacteria whereas 9 showed growth inhibition of methicillin-resistant Staphyllococus aureus (MRSA). None of the compounds were active against Gram-negative bacteria tested.

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36

Xu, Yuan-Ze, Jia-Wei Tian, Feng Sha, Qiong Li y Xin-Yan Wu. "Concise Synthesis of Chromene/Chromane-Type Aryne Precursors and Their Applications". Journal of Organic Chemistry 86, n.º 9 (14 de abril de 2021): 6765–79. http://dx.doi.org/10.1021/acs.joc.1c00493.

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37

Geier, Johannes, Holger Lessmann, Brigitte Hellweg, Uta Jappe, Petra Spornraft-Ragaller, Thomas Fuchs, Werner Aberer et al. "Chromated metal products may be hazardous to patients with chromate allergy". Contact Dermatitis 60, n.º 4 (abril de 2009): 199–202. http://dx.doi.org/10.1111/j.1600-0536.2008.01476.x.

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38

Guliev, I. S., O. P. Maksakova, F. R. Babaev, R. G. Nanajanova, A. S. Javadova y G. S. Martynova. "Adamantans in the oils as the indexes of presence of oil source rocks in deep depths (Absheron archipelago, South Caspian depression)". Azerbaijan Oil Industry, n.º 2 (15 de febrero de 2020): 4–9. http://dx.doi.org/10.37474/0365-8554/2020-2-4-9.

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The distribution features of adamantans of С10-С14 composition and their role in petroleum genesis has been studied, the biomarkers, adamantine and its homologs identified in Absheron archipelago oils via the method of chromate-mass-spectrometry. The calculations by the chromato-mass-spectrometry data justified that the adamantine and its methyl-substituted compounds are located in the order of increase of their thermo-dynamic steadiness in the following way: 2-Mad > 1-Mad > 3-Mad > Ad, which, in its turn, justifies the genesis of adamantine in the oils via thermic transition of normal alkanes. A complex interpretation of geological-geochemical data allows to make conclusions on a probable bedding of oil sources rocks in deep depths (approximately 13 km or deeper) of South Caspian depression.

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39

Nastasă, Cristina Mariana, Mihaela Duma, Adrian Pîrnău, Laurian Vlase, Brîndușa Tiperciuc y Ovidiu Oniga. "Development of new 5-chromenyl-2,4-thiazolidinediones as antimicrobial agents". Medicine and Pharmacy Reports 89, n.º 1 (20 de septiembre de 2015): 122–27. http://dx.doi.org/10.15386/cjmed-509.

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Background and aims. In the context of the increasing phenomenon of microbial resistance to usual drugs, the development of new treatment strategies and new therapeutic protocols is a constant need. Thiazolidinedione and chromone represent two important scaffolds in medicinal chemistry due to their large pharmacological applicability.Methods. We synthesized a new 5-(chromene-3-yl)methylene-2,4-thiazolidinedione starting from 6,8-dichloro-4-oxo-4H-chromene-3-carbaldehyde. Then, by treating with different α-bromoalkylarylketones, we obtained N-substituted derivatives. All new compounds were investigated for their antimicrobial potential, using the diffusion method, against Listeria monocytogenes ATCC 13932, Staphylococcus aureus ATCC 49444, Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 14028 and Candida albicans ATCC 10231. Three concentrations, 10 mg/ml, 5 mg/ml and 1 mg/ml of compounds were used. The results were evaluated by the measurement of the inhibition zone diameters and compared to those of gentamicin and fluconazole respectively, as reference drugs.Results. All new synthesized compounds were characterized using physico-chemical and spectrometric methods. They displayed modest to good antimicrobial activity. New molecules 8, 9 and 10 may represent promising candidates, showing zone inhibition diameters superior to those of reference drugs.Conclusions. This work presents chemical synthesis, characterization and investigation of the antibacterial and antifungal potential of 5-(chromene-3-yl)methylene-2,4-thiazolidinedione derivatives, which may be worthy of future research for designing new chemical entities.

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40

Iwata, Naoki y Susumu Kitanaka. "ChemInform Abstract: New Cannabinoid-Like Chromane and Chromene Derivatives from Rhododendron anthopogonoides." ChemInform 43, n.º 16 (22 de marzo de 2012): no. http://dx.doi.org/10.1002/chin.201216194.

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Kochnev, Ivan A., Alexey Y. Barkov, Nikita S. Simonov, Maria V. Ulitko, Nikolay S. Zimnitskiy, Vladislav Y. Korotaev y Vyacheslav Y. Sosnovskikh. "Different Behavior of 2-Substituted 3-Nitro-2H-chromenes in the Reaction with Stabilized Azomethine Ylides Generated from α-Iminoesters". Molecules 27, n.º 24 (16 de diciembre de 2022): 8983. http://dx.doi.org/10.3390/molecules27248983.

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The AgOAc-catalysed reaction of 3-nitro-2-phenyl-2H-chromenes with stabilized azomethine ylides generated from the imines based on methyl glycinate and arylaldehydes leads to a mixture of endo and endo’ isomers of the corresponding chromeno[3,4-c]pyrrolidines in a ratio of 2.0–2.3:1 in 85–93% total yields as a result of a Michael addition/Mannich reaction sequence. In a similar reaction involving 2-trifluoromethyl-3-nitro-2H-chromenes, only endo chromeno[3,4-c]pyrrolidines are formed in 85–94% yields. 3-Nitro-2-(trichloromethyl)-2H-chromenes under the same conditions react with these azomethine ylides to give the corresponding Michael adducts as individual anti-isomers with the cis,trans-configuration of the chromane ring in 40–67% yields. Some 4-CF3-substituted chromano[3,4-c]pyrrolidines exhibited high cytotoxic activity against HeLa human cervical carcinoma cells.

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42

Filippidis, A. "Chemical variation of chromite in the central sector of Xerolivado chrome mine of Vourinos, Western Macedonia, Greece". Neues Jahrbuch für Mineralogie - Monatshefte 1997, n.º 8 (11 de octubre de 1997): 354–70. http://dx.doi.org/10.1127/njmm/1997/1997/354.

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43

Yang, Yong-xun, Jin-xin Wang, Qun Wang, Hui-liang Li, Ming Tao, Qian Luo y Hong Liu. "New chromane and chromene meroterpenoids from flowers of Rhododendron rubiginosum Franch. var. rubiginosum". Fitoterapia 127 (junio de 2018): 396–401. http://dx.doi.org/10.1016/j.fitote.2018.03.017.

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Saeed, Muhammad, Malika Rani, Kiran Batool, Hafiza Batool, Aisha Younus, Sikander Azam, Arshad Mehmood et al. "Synthesis and Fabrication of Co1−xNixCr2O4 Chromate Nanoparticles and the Effect of Ni Concentration on Their Bandgap, Structure, and Optical Properties". Journal of Composites Science 5, n.º 9 (14 de septiembre de 2021): 247. http://dx.doi.org/10.3390/jcs5090247.

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In the present work, cobalt-chromite-based pigment Co1-xNixCr2O4 chromate powder and nanoparticles with various transition metal concentrations (x = 0.2, 0.4, 0.6, and 0.8) were manufactured by applying aqueous synthesis approaches and sol–gel synthesis routes. XRD analysis of the powder shows that all samples formulated by the sol–gel method were crystalline with a spinel structure. Chromites show green color with a higher nickel concentration, while Co-substituent shows blackish pigments. Samples were annealed at distinct temperatures ranging from 600 °C to 750 °C. The nanoparticles obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RS), photoluminescence (PL), and energy-dispersive X-ray spectroscopy (EDS). The particle size of the parent compound (CoCr2O4) ranges from 100 nm to 500 nm, as measured by SEM. The tendency of particles to form aggregates with increasing annealing temperature was observed. These compounds may be successfully used as an effective doped nickel-cobalt ceramic pigment.

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45

Alvarez, Angel H., Rafael Moreno-Sánchez y Carlos Cervantes. "Chromate Efflux by Means of the ChrA Chromate Resistance Protein from Pseudomonas aeruginosa". Journal of Bacteriology 181, n.º 23 (1 de diciembre de 1999): 7398–400. http://dx.doi.org/10.1128/jb.181.23.7398-7400.1999.

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ABSTRACT Everted membrane vesicles of Pseudomonas aeruginosaPAO1 harboring plasmid pCRO616, expressing the ChrA chromate resistance protein, accumulated four times more51CrO4 2− than vesicles from plasmidless cells, indicating that a chromate efflux system functions in the resistant strain. Chromate uptake showed saturation kinetics with an apparent Km of 0.12 mM chromate and aV max of 0.5 nmol of chromate/min per mg of protein. Uptake of chromate by vesicles was dependent on NADH oxidation and was abolished by energy inhibitors and by the chromate analog sulfate. The mechanism of resistance to chromate determined by ChrA appears to be based on the active efflux of chromate driven by the membrane potential.

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46

Abdolmohammadi, Shahrzad, Seyed Reza Rasouli Nasrabadi, Ahmad Seif y Narges Elmi Fard. "Ag/CdS Nanocomposite: An Efficient Recyclable Catalyst for the Synthesis of Novel 8-Aryl-8H-[1,3]dioxolo[4,5-g]chromene-6-carboxylic Acids under Mild Reaction Conditions". Combinatorial Chemistry & High Throughput Screening 21, n.º 5 (20 de julio de 2018): 323–28. http://dx.doi.org/10.2174/1386207321666180604104456.

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Aim and Objective: Chromene derivatives are privileged heterocyclic systems that exhibit various types of biological properties such as antioxidant, anticancer, antimicrobial, hypotensive, and local anesthetic. Cadmium sulfide nanoparticles (CdS NPs) as an efficient heterogeneous catalyst is used in various organic transformations because of its certain unique and unusual physico-chemical properties. The effectiveness of catalytic activity of CdS NPs can be improved due to the combined effect of Ag particles. Results: Ag/CdS nanocomposite is a readily available, recyclable, and non-toxic catalyst used for the highly efficient synthesis of novel 8-aryl-8H-[1,3]dioxolo[4,5-g]chromrne-6-carboxylic acids. This reaction is conveniently performed under mild reaction conditions. All synthesized compounds were well characterized by their satisfactory elemental analyses, IR, 1H and 13C NMR spectroscopy. The synthesized catalyst was fully characterized by XRD, SEM, and EDX techniques. Materials and Methods: The present methodology focuses on the condensation reaction of arylmethylidenepyruvic acids with 3,4-methylenedioxyphenol, using a catalytic amount of Ag/CdS nanocomposite (15 mol%) in aqueous media at room temperature to afford 8-aryl-8H-[1,3]dioxolo [4,5-g]chromrne-6-carboxylic acids in high yields (90-97%) within short reaction times (2-4 h). The Ag/CdS nanocomposite was also prepared by an ultrasonic-assisted sol-gel method. Conclusion: In conclusion, we have successfully synthesized novel 8-aryl-8H-[1,3]dioxolo[4,5- g]chromrne-6-carboxylic acid derivatives by the Ag/CdS nanocomposite catalyzed cyclocondensation reaction of arylmethylidenepyruvic acids with 3,4-methylenedioxyphenol under mild reaction conditions. Environmentally benign procedure, high to excellent yields of products, simplicity of operation, and use of readily available and recyclable catalyst are the advantages of this new practical reaction.

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47

McLean, Jeff y Terry J. Beveridge. "Chromate Reduction by a Pseudomonad Isolated from a Site Contaminated with Chromated Copper Arsenate". Applied and Environmental Microbiology 67, n.º 3 (1 de marzo de 2001): 1076–84. http://dx.doi.org/10.1128/aem.67.3.1076-1084.2001.

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ABSTRACT A pseudomonad (CRB5) isolated from a decommissioned wood preservation site reduced toxic chromate [Cr(VI)] to an insoluble Cr(III) precipitate under aerobic and anaerobic conditions. CRB5 tolerated up to 520 mg of Cr(VI) liter−1 and reduced chromate in the presence of copper and arsenate. Under anaerobic conditions it also reduced Co(III) and U(VI), partially internalizing each metal. Metal precipitates were also found on the surface of the outer membrane and (sometimes) on a capsule. The results showed that chromate reduction by CRB5 was mediated by a soluble enzyme that was largely contained in the cytoplasm but also found outside of the cells. The crude reductase activity in the soluble fraction showed aKm of 23 mg liter−1 (437 μM) and a V max of 0.98 mg of Cr h−1 mg of protein−1 (317 nmol min−1 mg of protein−1). Minor membrane-associated Cr(VI) reduction under anaerobiosis may account for anaerobic reduction of chromate under nongrowth conditions with an organic electron donor present. Chromate reduction under both aerobic and anaerobic conditions may be a detoxification strategy for the bacterium which could be exploited to bioremediate chromate-contaminated or other toxic heavy metal-contaminated environments.

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48

Ribeiro Laia, Fernanda M., Maria I. L. Soares, Clara S. B. Gomes y Teresa M. V. D. Pinho e Melo. "Pericyclic Reactions of Azafulvenium Methides Bearing Internal Dipolarophiles - Synthesis of Chromene and Chromane Derivatives". European Journal of Organic Chemistry 2015, n.º 6 (15 de enero de 2015): 1341–54. http://dx.doi.org/10.1002/ejoc.201403407.

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49

Acosta-Navarrete, Yaned M., Yhoana L. León-Márquez, Karina Salinas-Herrera, Irvin E. Jácome-Galarza, Víctor Meza-Carmen, Martha I. Ramírez-Díaz y Carlos Cervantes. "Expression of the six chromate ion transporter homologues of Burkholderia xenovorans LB400". Microbiology 160, n.º 2 (1 de febrero de 2014): 287–95. http://dx.doi.org/10.1099/mic.0.073783-0.

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The chromate ion transporter (CHR) superfamily comprises transporters that confer chromate resistance by extruding toxic chromate ions from cytoplasm. Burkholderia xenovorans strain LB400 has been reported to encode six CHR homologues in its multireplicon genome. We found that strain LB400 displays chromate-inducible resistance to chromate. Susceptibility tests of Escherichia coli strains transformed with cloned B. xenovorans chr genes indicated that the six genes confer chromate resistance, although under different growth conditions, and suggested that expression of chr genes is regulated by sulfate. Expression of chr genes was measured by quantitative reverse transcription-PCR (RT-qPCR) from total RNA of B. xenovorans LB400 grown under different concentrations of sulfate and exposed or not to chromate. The chr homologues displayed distinct expression levels, but showed no significant differences in transcription under the various sulfate concentrations tested, indicating that sulfate does not regulate chr gene expression in B. xenovorans. The chrA2 gene, encoded in the megaplasmid, was the only chr gene whose expression was induced by chromate and it was shown to constitute the chromate-responsive chrBACF operon. These data suggest that this determinant is mainly responsible for the B. xenovorans LB400 chromate resistance phenotype.

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50

Ackerley, D. F., C. F. Gonzalez, C. H. Park, R. Blake, M. Keyhan y A. Matin. "Chromate-Reducing Properties of Soluble Flavoproteins from Pseudomonas putida and Escherichia coli". Applied and Environmental Microbiology 70, n.º 2 (febrero de 2004): 873–82. http://dx.doi.org/10.1128/aem.70.2.873-882.2004.

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ABSTRACT Cr(VI) (chromate) is a toxic, soluble environmental contaminant. Bacteria can reduce chromate to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of interest. Genetic and protein engineering of suitable enzymes can improve bacterial bioremediation. Many bacterial enzymes catalyze one-electron reduction of chromate, generating Cr(V), which redox cycles, generating excessive reactive oxygen species (ROS). Such enzymes are not appropriate for bioremediation, as they harm the bacteria and their primary end product is not Cr(III). In this work, the chromate reductase activities of two electrophoretically pure soluble bacterial flavoproteins—ChrR (from Pseudomonas putida) and YieF (from Escherichia coli)—were examined. Both are dimers and reduce chromate efficiently to Cr(III) (k cat/Km = ∼2 × 104 M−1 · s−1). The ChrR dimer generated a flavin semiquinone during chromate reduction and transferred >25% of the NADH electrons to ROS. However, the semiquinone was formed transiently and ROS diminished with time. Thus, ChrR probably generates Cr(V), but only transiently. Studies with mutants showed that ChrR protects against chromate toxicity; this is possibly because it preempts chromate reduction by the cellular one-electron reducers, thereby minimizing ROS generation. ChrR is thus a suitable enzyme for further studies. During chromate reduction by YieF, no flavin semiquinone was generated and only 25% of the NADH electrons were transferred to ROS. The YieF dimer may therefore be an obligatory four-electron chromate reducer which in one step transfers three electrons to chromate and one to molecular oxygen. As a mutant lacking this enzyme could not be obtained, the role of YieF in chromate protection could not be directly explored. The results nevertheless suggest that YieF may be an even more suitable candidate for further studies than ChrR.

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