Percorrer por autor "Bernardino, Raul J."
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- Bidentate Urea Derivatives of p-tert-Butyldihomooxacalix[4]arene: Neutral Receptors for Anion ComplexationPublication . Marcos, Paula M.; Teixeira, Filipa A.; Segurado, Manuel A. P.; Ascenso, José R.; Bernardino, Raul J.; Michel, Sylvia; Hubscher-Bruder, VéroniqueThree new bidentate ureidodihomooxacalix[4]- arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound ptert- butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by 1H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F- (log Kassoc = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO- and BzO-. Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.
- Preparation of Triacylglycerols Rich in Omega-3 Fatty Acids from Sardine Oil Using a Rhizomucor miehei Lipase: Focus in the EPA/DHA RatioPublication . Bispo, Paulo; Batista, Irineu; Bernardino, Raul J.; Bandarra, Narcisa MariaThe increasing evidence on the differential biochemical effects of eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) raises the need of n-3 highly unsaturated fatty acid concentrates with different amounts of these fatty acids. In the present work, physicochemical and enzymatic techniques were combined to obtain acylglycerols, mainly triacylglycerols (TAG), rich in n-3 fatty acids. Sardine oil was obtained by washing sardine (Sardina pilchardus) mince with a NaHCO3 solution, hydrolyzed in a KOH-ethanol solution, and concentrated with urea. The esterification reaction was performed in the stoichiometric proportion of substrates for re-esterification to TAG, with 10 % level of Rhizomucor miehei lipase based on the weight of substrates, without any solvent, during 48 h. This procedure led to approximately 88 % of acylglycerols, where more than 66 % were TAG and the concentration of n-3 fatty acids was higher than 60 %, the EPA and DHA ratio (EPA/DHA) was 4:1. The content of DHA in the unesterifed fraction (free fatty acids) increased from 20 to 54 %, while the EPA level in the same fraction decreased from 33 to 12.5 % (EPA/DHA ratio ≈1:4). Computational methods (density functional theory calculations) have been carried out at the B3LYP/6-31G(d,p) level to explain some of the experimental results.
- Synthesis and anion binding properties of new dihomooxacalix[4]arene diurea and dithiourea receptorsPublication . Marcos, Paula M.; Teixeira, Filipa A.; Segurado, Manuel A. P.; Ascenso, José R.; Bernardino, Raul J.; Brancatelli, Giovanna; Geremia, SilvanoFunctionalization of the lower rim of p-tert-butyldihomooxacalix[4]arene with two (thio)ureido moieties provided new diurea (n-propyl 5a, tert-butyl 5b and phenyl 5c) and dithiourea (phenyl 5d) derivatives, all in the cone conformation, as shown by NMR studies. The X-ray crystal structure of 5c is reported. The binding ability of these neutral receptors towards a large variety of anions was assessed by 1H NMR titrations. The structures and complexation energies of some complexes were also studied using DFT methods. The data showed that, in general, the association constants decrease with decrease of anion basicity and they are strongly dependent on the nature of the substituent at the urea moiety. Phenyl-(thio)urea derivatives 5c and 5d are the best anion receptors, showing the strongest complexation for F− (log Kass=2.70 and 2.75, respectively) and also for the oxoanions AcO−, BzO− and H2 PO4. These results were corroborated by DFT calculations.
- Synthesis, binding properties and theoretical studies of p-tert-butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone with alkali, alkaline earth, transition, heavy metal and lanthanide cationsPublication . Marcos, Paula M.; Ascenso, José R.; Segurado, Manuel A.P.; Bernardino, Raul J.; Cragg, Peter J.; Bernardino, Raulp-tert-Butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone (1b) was synthesized for the first time. Compound 1b was obtained in a cone conformation in solution at room temperature, as established by NMR spectroscopy (1H and 13C). The binding properties of ligand 1b for alkali, alkaline earth, transition, heavy metal and lanthanide cations have been assessed by phase transfer and proton NMR titration experiments. Molecular mechanics and ab initio techniques were also employed to complement the NMR data. The results are compared to those obtained with other closely related homooxacalixarene derivatives. Although triketone 1b is a weak extractant, it shows a strong peak selectivity for Na+ and also some preference for Ag+. Proton NMR titrations indicate the formation of 1:1 complexes between 1b and the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Although the molecular mechanics results show little correlation with the NMR data, a good agreement was obtained with the ab initio models.