81,521 research outputs found
Formation of Carbon−Carbon-Bonded Dimers in the Reduction of [CoIIsalophen] [salophen =N,N‘-o-Phenylenebis(salicylideneaminato)]: Their Reactivity with Electrophiles To Form Co−C Bonds
No full textThe reduction of cobalt-Schiff base complexes has been explored as a function of the nature of the ligand. In the case of substituted salen complexes, reduction occurred at the metal with the formation of bifunctional Co(I)-Na complexes, while for salophen derivatives the reductive coupling of imino groups was observed. Such C-C bonds function as electron shuttles in chemical reductions. Reduction of [Co(MeOsalen)] (1) with Na metal in THF led to a monomeric [Co(MeOsalen)Na(THF)(2)] (2A) and a dimeric [{Co(MeOsalen)Na(THF)}(2)] (2B) compound. Compounds 2A and 2B exemplify a bifunctional acid-base system with both centers in close proximity. The analogous reduction of [Co(salophen)] (3) and [Co(MeOsalophen)] (5) led to dimeric cobalt(II) derivatives containing a bridging C-C bond across two units in [Co-2(salophen)(2)Na-2(THF)(6)] (4) and [Co-2(MeOsalophen)(2)Na-2(THF)(4)] (6), respectively. However, such cobalt(II) centers behave as cobalt(I), since the C-C bond provides a pair of electrons to the metal couple during the chemical reaction. Alkylation at the cobalt has been observed in complexes 4 and 6 with the concomitant formation of a Co(III)-C bond in [Co(salophen)(Me)] (9), [Co(salophen)(COOMe)(THF)] (10), [Co(MeOsalophen)(Me)(H2O)] (11), and [Co(MeOsalophen)(COOMe)(H2O)] (12). The cleavage and formation of the C-C bond linking the two salophen units have been observed in the reversible reactions of 4 and 6 with carbon dioxide leading to the CO2 adducts [Co(salophen)NaCO2(THF)] (13) and [Co(MeOsalophen)NaCO2(THF)] (14). Crystallographic data: 2 is triclinic, space group P (1) over bar, a = 14.651(1) Angstrom, b = 15.355(1) Angstrom, c = 11.671(11), alpha = 105.70(1)degrees, beta = 102.66(1)degrees, gamma = 97.65(1)degrees, Z = 2, and R = 0.044; 4 is monoclinic, space group P2(1)/c, a = 11.270(2) Angstrom, b = 17.594(3) Angstrom, c = 16.606(3) Angstrom, alpha = gamma = 90 degrees, beta = 90.45(2)degrees, Z = 2, and R = 0.053; 6 is triclinic, space group P (1) over bar, a = 11.857(4)Angstrom, b = 12.639(4) Angstrom, c = 10.553(5), alpha = 106.28(3)degrees, beta = 101.17(3)degrees, gamma = 103.04(3)degrees, Z = 1, and R = 0.057
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Use of Industrial Food Waste for Chromium Removal from Tannery Wastewater
No full textTannery wastewater requires an adequate treatment for chromium removal before discharge, to prevent environmental pollution. Chromium sulphate, in fact, is the most used compound to stabilise animal hides, and therefore high concentrations of Cr(III) are found in spent tanning baths. To front the problem precipitation processes, based on lime addition, are frequently adopted, because of their low cost. Nonetheless, due to the colloidal form of precipitates, these processes have to be carried out with great attention to reach required performances. An interesting alternative to precipitation processes is represented by adsorption of chromium on low cost-materials, especially if chromium can be recovered from produced sludges, regenerating the adsorbent, and reducing sludge toxicity. Among others, chitosan, a carbohydrate obtained from deacetilation of chitin, the second polysaccharide for diffusion in the environment, seems to be very attractive. Previous studies, in fact, have shown that it has a good sequestrating ability towards many heavy metals, including chromium, and can be added during treatment as component of seafood shells, instead of being dosed as pure chemical product. Starting from these considerations it is presented an experimental study, whose aim is to better understand the advantages of chitosan use for tannery wastewater treatment. The study includes a preliminary investigation on the main mechanisms responsible for chromium removal in presence of chitosan, discerning between adsorption on polymeric groups of this polysaccharide, and formation of insoluble chromium hydroxide, caused by pH increase induced by chitosan addition. Process efficiency is also quantified, and treatment optimisation is proposed. This part of the study, carried out with synthetic wastewater to exclude any effects related to compounds other than chromium, allows to recognize adsorption as the main process causing chromium removal, and to assess the good performances related to chitosan as sequestrating agent. Successive investigations, carried out using real wastewater, concern, instead, the possibility of chromium recovery from produced sludge, and the possibility of process development using seafood shells instead of commercial chitosan. Obtained results, illustrated and discussed in the paper, show that chromium recovery from sludge is possible at very low pH values, and that shrimp shells use increases chromium removal efficiency, due to the development of precipitation processes together with adsorption ones
The Catalytic efficiency of Free-Base Porphyrins in promoting the N-Aryl oxazolidinones synthesis
No full textBetween other applications oxazolidinones are largely used as intermediates as well as chiral auxiliaries in organic synthesis1 and constitute a class of new antibacterial and antibiotics,2-7 the best pharmaceutical performances are usually observed for N-aryl oxazolidin-2-ones (NAOs), such as Linezolid,8 Tedizolid9 and Toloxatone,10 that are FDA-approved drugs. One of the most interesting methodologies for the synthesis of NAOs is the CO2 cycloaddition to aziridines in order to use this greenhouse gas as a renewable C1 synthetic building block. Recently, we have reported a ruthenium porphyrin-based catalytic procedure for synthesising N alkyl oxazolidin-2-ones11,12 and, during our efforts to extend the same procedure to the synthesis of NAOs, we discovered that this reaction was efficiently promoted by the very convenient TPPH2/TBACl catalytic system (TPPH2=tetraphenyl porphyrin; TBACl=tetrabutyl ammonium chloride). Here, we report the optimization and study scope of the synthesis of N aryl oxazolidin-2-ones, which were obtained either by reacting CO2 with purified N aryl aziridines or by applying a two-steps procedure. The latter methodology consists in the Ru(TPP)CO-catalysed synthesis of N-aryl aziridines that were converted into corresponding NAOs by the TPPH2/TBACl-catalysed cycloaddition of CO2.
1. Z. Vahideh and M. H. Majid, Current Organic Synthesis, 2018, 15, 3-20.
2. F. H. Malik Nasibullah, Naseem Ahmad, Abdul Rahman Khan, and Masihur Rahman, Adv. Sci. Eng. Med., 2015, 7, 91-111.
3. S. J. Pradeep, D. V. Maulikkumar, M. D. Tejas and K. C. Asit, Current Medicinal Chemistry, 2015, 22, 4379-4397.
4. A. Bhushan, N. J. Martucci, O. B. Usta and M. L. Yarmush, Expert Opinion on Drug Metabolism & Toxicology, 2016, 12, 475-477.
5. C. Roger, J. A. Roberts and L. Muller, Clinical Pharmacokinetics, 2018, 57, 559-575.
6. M. Nasibullah, F. Hassan, N. Ahmad, A. R. Khan and M. Rahman, Advanced Science, Engineering and Medicine, 2015, 7, 91-111.
7. K. Michalska, I. Karpiuk, M. Król and S. Tyski, Bioorg. Med. Chem., 2013, 21, 577-591.
8. A. Zahedi Bialvaei, M. Rahbar, M. Yousefi, M. Asgharzadeh and H. Samadi Kafil, J. Antimicrob. Chemother., 2017, 72, 354-364.
9. D. McBride, T. Krekel, K. Hsueh and M. J. Durkin, Expert Opinion on Drug Metabolism & Toxicology, 2017, 13, 331-337.
10. F. Moureau, J. Wouters, D. P. Vercauteren, S. Collin, G. Evrard, F. Durant, F. Ducrey, J. J. Koenig and F. X. Jarreau, European Journal of Medicinal Chemistry, 1992, 27, 939-948.
11. D. Carminati, E. Gallo, C. Damiano, A. Caselli and D. Intrieri, Eur. J. Inorg. Chem., 2018, 2018, 5258-5262.
12. D. Intrieri, C. Damiano, P. Sonzini and E. Gallo, J. Porphyrins Phthalocyanines, 2019, 23, 305-328
Self-consistent surface-temperature boundary condition for iquefying-fuel-based hybrid rockets internal-ballistics simulation
No full textA novel methodology for the calculation of the surface temperature of liquefying fuels typically burned in hybrid rockets is proposed. This procedure stems from the formulation of a fuel in-depth pyrolysis model coupled with the resolution of the thermo-fluid-dynamic field in the rocket combustion chamber, which allows for the characterization of the unstable liquid layer formed on top of the fuel surface. The aim is the simulation of the internal ballistics of hybrid rocket engines fed by paraffin-based fuels without the need for parametrically assigning the surface temperature to match the experimental data as, indeed, required in the authors’ previous work. With the presented technique, surface temperature and fuel vaporization rate are calculated locally along the wall, and, with the integration of a liquid fuel entrainment model, which requires the tuning of just one parameter (i.e. the so-called entrainment factor), the fuel regression rate is determined. The overall numerical approach, upon the assumption that the liquid fuel is in the supercritical pressure regime, is based on the solution of the Reynolds-averaged Navier–Stokes equations for single-phase multicomponent turbulent reacting flow. A series of numerical simulations are carried out to unveil the effect of the oxygen mass flux, which allowed deriving an approximate analytical equation for the regression rate prediction. A set of hot fires of a laboratory-scale hybrid rocket are reproduced through single numerical simulations carried out on the fuel port average geometry in the burn to validate the computational model, showing deviations between the measured and predicted average regression rate less than 4.5%. In order to fairly match also the fuel consumption axial profile, transient numerical simulations over the entire engine firing are conducted with which the post-burn port shape is captured with maximum error of 8%
Urban environments regeneration. Technological issues for adaptive re-use
No full textThe technological approach to the regeneration project of urban contexts is strongly oriented to the quality of living and implies approaches that pursue, on the one hand, environmental and energy objectives, and on the other, conservation and enhancement of the existing heritage according to the inseparable combination of "environment and innovation".
In this transformative scenario the public space and, in general, the open spaces, play a strategic role, already covered traditionally within the city system as nodal elements not only in relation to usability and comfort but also to cultural identity, thus giving an added value to the urban fabric itself.
In relation to the different functions attributed to the urban open space, an application case study is presented that focuses attention on climate-adaptive design approach, based on microclimate simulation for urban modelling
Análisis, parametrización y formación para el módulo comercial (SD) de SAP R/3 en una empresa valenciana del sector textil
No full textConsulta en la Biblioteca ETSI Industriales (5775)[ES] El presente documento representa una cuarta parte de un estudio cuyo objeto es,
como bien se indica en el título, el análisis y la parametrización de SAP R/3 para una
empresa valenciana del sector textil. Posteriormente a este paso, se procede a la
formación de los futuros usuarios del ERP con el fin de facilitar que la implantación de
SAP R/3 sea todo un éxito.Gil Gallo, C. (2006). Análisis, parametrización y formación para el módulo comercial (SD) de SAP R/3 en una empresa valenciana del sector textil. https://riunet.upv.es/handle/10251/37071.Archivo delegad
Straightforward heterogeneization of Cu(I) complexes of chiral pyridine containing macrocyclic ligands (Pc-L*) and their applications to cyclopropanation reactions
No full textWe have recently reported that copper(I) complexes of the new C1-symmetric pyridine-based 12 membered tetraaza macrocyclic (Pc-L*) ligands are competent catalysts in the enantioselective cyclopropanation of olefins employing ethyl diazoacetate (EDA) as carbene precursor.1 Heterogeneous single site catalysts in many cases show superior performances in terms of activity, selectivity and reciclability coupling together the advantages of heterogeneous and homogeneous systems.2 We report here preliminary results on the heterogeneization of our system. Cu(I) complexes (see fig), based on functionalised pyridine-containing macrocyclic chiral ligands were heterogeneized on mesoporous ordered and non-ordered silicas (Davisil, MCM-41, etc.) by the SHB method.2 Materials obtained were fully characterized for metal content, textural properties, hydrogen bonds between Cu complex and surface silanols by a pool of techniques. Catalysts were tested in enantioselective cyclopropanation of olefins and they showed performances at least comparable to those obtained with the homogeneous counterpart. Tests using both basic and ordered silicas with the aim of exploiting the confinement effect on stereoselectivity are currently in progress.
References
[1] Caselli, A.; Cesana, F.; Gallo, E.; Casati, N.; Macchi, P.; Sisti, M.; Celentano, G.; Cenini, S.. Dalton Trans. 2008, 4202. [2] C. Bianchini, P. Barbaro, V. Dal Santo, R. Gobetto, A. Meli, W. Oberhauser, R. Psaro, F. Vizza, Adv. Synth. Catal., 2001, 343, 41-45
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