Paula M. Marcos
University of Lisbon
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Featured researches published by Paula M. Marcos.
Beilstein Journal of Organic Chemistry | 2012
Kevin Cottet; Paula M. Marcos; Peter J. Cragg
Summary Hexahomotrioxacalix[3]arenes, commonly called oxacalix[3]arenes, were first reported in 1962. Since then, their chemistry has been expanded to include numerous derivatives and complexes. This review describes the syntheses of the parent compounds, their derivatives, and their complexation behaviour towards cations. Extraction data are presented, as are crystal structures of the macrocycles and their complexes with guest species. Applications in fields as diverse as ion selective electrode modifiers, fluorescence sensors, fullerene separations and biomimetic chemistry are described.
Journal of Inclusion Phenomena and Macrocyclic Chemistry | 2002
Paula M. Marcos; José R. Ascenso; Manuel A. P. Segurado; J. L. C. Pereira
The binding properties of two phenylketones (2a and 3a) and two ethylesters (2b and {3b) derived from p-tert-butyldihomooxacalix[4]arene or from p-tert-butylcalix[4]arene, in the cone conformation, towards transition (Ag+, Ni2+, Cu2+, Co2+, Zn2+, Fe2+ and Mn2+) and heavy (Cd2+, Hg2+ and Pb2+) metal cations have been determined by extraction studies with metal picrates and liquid membrane transport experiments with the same salts. The affinity of these ligands for Ag+ has also been investigated by 1H NMR spectroscopy. Both ketones are better extractants than the esters, and show a strong preference for Ag+, while Cu2+ is the most extracted cation with the esters. 1H NMR titrations with AgSO3CF3 indicate 1 : 1 complexes for all ligands, those with ketones are more stable, on the NMR time scale, than those with esters. Both esters are good carriers for Ag+, and 2b exhibits the highest transport rate (4.7 μmol h-1) found until now with dihomooxacalix[4]arene derivatives.
New Journal of Chemistry | 2004
Paula M. Marcos; Sandra Félix; José R. Ascenso; Manuel A. P. Segurado; J. L. C. Pereira; Poupak Khazaeli-Parsa; Véronique Hubscher-Bruder; Françoise Arnaud-Neu
The binding properties of the tetra(diethyl)amide (2) derived from p-tert-butyldihomooxacalix[4]arene, in the cone conformation, towards alkali, alkaline earth, transition (Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and heavy (Ag+, Cd2+, Hg2+ and Pb2+) metal cations have been established by extraction studies of metal picrates from an aqueous solution into dichloromethane, transport experiments with the same salts through a dichloromethane membrane and stability constant measurements in methanol. Results concerning the calorimetric study of Na+ and K+ complexes in methanol are presented. The affinity of 2 for some cations (Na+, K+, Ba2+, Ag+ and Zn2+) has been investigated by 1H NMR spectrometry, as well. The results are compared to those obtained with the analogous calix[4]arene tetraamide derivative 3. Amide 2 displays a preference for the alkali cations (mainly Na+ and K+) in contrast to amide 3 that prefers the alkaline earth cations. Ag+ and Cd2+ soft Lewis acids are also strongly bound by both amides. 1H NMR titrations confirm the formation of 1∶1 complexes between 2 and all cations studied, also suggesting that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. 2 shows transport rates that do not follow the same trends as the stability constants or extraction percentages; it can therefore be characterized as a selective receptor.
Tetrahedron | 1997
Paula M. Marcos; JoséR. Ascenso; Roger Lamartine; J. L. C. Pereira
Abstract Four tetraethers (methyl, ethyl, allyl and benzyl) of p - tert -butyldihomooxacalix[4]arene were synthesized and their conformational behaviour studied by means of variable temperature 1 H NMR, including the determination of coalescence temperatures and ΔG + . It was shown that the methyl ether still has some conformational monility at −100 °C, the ethyl ether displays a fixed conformation at −20 °C and the other two derivatives are conformationally rigid at room temperature. The conformations obtained are the 1,2-alternate B and cone, depending on the derivative formed.
Journal of Physical Organic Chemistry | 1999
Paula M. Marcos; José R. Ascenso; Manuel A. P. Segurado; J. L. C. Pereira
The tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene (2) was synthesized for the first time. This derivative possesses the cone conformation in solution at room temperature, which was confirmed by NMR measurements (1H, 13C and NOE 1D). Extraction studies with metal picrates from neutral aqueous solution into dichloromethane, transport experiments with metal picrates through a dichloromethane membrane and stability constant measurements by UV absorption spectroscopy in methanol and acetonitrile were performed to evaluate the binding ability of ketone 2 towards alkali and alkaline earth metal cations. The tetraphenylketone of p-tert-butylcalix[4]arene (3) was also studied, and the results for the two derivatives were compared. Compound 2 shows a preference for K+ and Ba2+ cations, being selective only in the alkaline earth metal cation series. Compound 3 is a stronger binder than 2, but is a weaker extractant. Both show transport rates that are not proportional to complex stability or to extraction efficiency. Ketone 2 can be characterized as a selective receptor. Copyright
Tetrahedron | 2001
Paula M. Marcos; José R. Ascenso; Manuel A. P. Segurado; J. L. C. Pereira
Abstract The synthesis of the inherently chiral triethyl ester monomethyl ether of p-tert-butyldihomooxacalix[4]arene (3) is reported. A distorted cone conformation in solution at room temperature has been established for triester 3 by NMR measurements (1H, 13C, NOE 1D and 2D). The extracting and complexing properties of 3 towards the entire alkali and alkaline earth cation series have been assessed by picrate extraction and stability constant determinations. Transport experiments with metal picrates through a CH2Cl2 membrane have also been performed. Comparison is made with tetraethyl ester of p-tert-butylcalix[4]arene (4) described in literature and also studied by us. 3 is a poor phase transfer agent and binder. In contrast, it is a good carrier, mainly for the alkali cations and displays a selective transport for Ba2+.
Journal of Organic Chemistry | 2014
Paula M. Marcos; Filipa A. Teixeira; Manuel A. P. Segurado; José R. Ascenso; Raul J. Bernardino; Sylvia Michel; Véronique Hubscher-Bruder
Three new bidentate ureidodihomooxacalix[4]arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound p-tert-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 (1)H 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 K(assoc) = 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.
Supramolecular Chemistry | 2007
Paula M. Marcos; José R. Ascenso; Peter J. Cragg
The binding of alkali, alkaline earth, transition (Mn2 + , Fe2 + , Co2 + , Ni2 + , Cu2 + and Zn2 + ) and heavy metal (Ag+, Cd2 + , Hg2 + and Pb2 + ) cations by cone p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide (1b) has been assessed by extraction studies of metal picrates from water to dichloromethane and proton NMR titration experiments. Molecular modelling techniques were also employed to complement the NMR data. The results are compared to those obtained with the dihomooxacalix[4]arene (2b) and calix[4]arene (3b) derivative analogues. Triamide 1b displays a high extracting ability towards Na+, Ba2 + , Ni2 + , Co2 + , Ag+ and mainly Pb2 + (80% E). However, these values are lower than those obtained with tetraamides 2b and 3b, presumably due to the higher conformational flexibility of 1b. 1H NMR titrations indicate the formation of 1:1 complexes between 1b and all the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms.
Supramolecular Chemistry | 2006
Paula M. Marcos; S Felix; Ascenso; Map Segurado; B Mellah; R Abidi; Hubscher-Bruder; F Arnaud-Neu
The binding properties of three p-tert-butyldihomooxacalix[4]arene tetraketone derivatives (tert-butyl 2b, adamantyl 2c and phenyl 2d) in the cone conformation and one derivative (methyl 2a) in a partial cone conformation, towards alkali and alkaline earth metal cations have been established by extraction studies of metal picrates from water into dichloromethane, stability constant measurements in methanol and acetonitrile, and by 1H NMR spectrometry. Transport experiments of metal picrates through a dichloromethane membrane were also performed. The results are compared to those obtained with closely-related calix[n]arene derivatives (n = 4 and 5) and discussed in terms of the substituents, size and conformational effects. Methylketone 2a is a poor binder for all the cations studied, due to its partial cone conformation. Ketones 2b, 2c and 2d show high extraction and complexation levels for the alkali cations, with similar profiles and preference for K+ and Na+ (plateau selectivity). Towards alkaline earth cations, these ketones show a strong peak selectivity for Ba2+ in extraction, but a plateau selectivity for Ca2+, Sr2+ and Ba2+ in complexation. The nature of the substituent attached to the ketone function has some influence on their binding properties, with phenylketone 2d being a slightly weaker binder than ketones 2b and 2c. 1H NMR titrations confirm the formation of 1:1 complexes between the ketones and the cations studied, also indicating that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Ketones 2b, 2c and 2d show transport rates that do not follow, in general, the same trends observed in extraction and complexation.
New Journal of Chemistry | 2015
Giuseppe Gattuso; Anna Notti; Melchiorre F. Parisi; Paula M. Marcos; José R. Ascenso; Giovanna Brancatelli; Silvano Geremia
Ion-pair recognition–complexation of monoamine neurotransmitters and trace amine hydrochlorides takes place – with outstanding efficiency and selectivity – within the π-rich cavity and the pocket formed at the lower rim by the two ureido moieties of the tailor-made dihomooxacalixarene receptors 1 and 2. The solid-state structure of 1 is also reported.