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Andreia Leite

Bio: Andreia Leite is an academic researcher from University of Porto. The author has contributed to research in topics: Chemistry & Interferometry. The author has an hindex of 16, co-authored 53 publications receiving 651 citations.


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Journal ArticleDOI
TL;DR: Aqueous solution studies regarding the identification and characterization of complexes formed by the VIVO ion and 11 3-hydroxy-4-pyridinone derivatives have been performed using EPR and UV/vis spectroscopic techniques, and relationships between the pKa of the -OH group in position 3 of the ring are provided.
Abstract: Aqueous solution studies regarding the identification and characterization of complexes formed by the VIVO ion and 11 3-hydroxy-4-pyridinone derivatives have been performed using EPR and UV/vis spectroscopic techniques. For the three ligands (HL) adequately soluble in water (1-methyl-3-hydroxy-4-pyridinone, 1-methyl-2-ethyl-3-hydroxy-4-pyridinone, and 1,2-diethyl-3-hydroxy-4-pyridinone), potentiometric titrations were performed; the results are consistent with the formation of [V(IV)OL]+, [V(IV)OL2], [V(IV)OL2H(-1)]-, [(V(IV)O)2L2H(-2)], and [V(IV)L3]+ species. Bis chelated complexes are characterized by a cis-trans isomerism, the trans isomer being strongly favored with respect to the cis arrangement. Tris chelated non-oxo V(IV) species were prepared in CH3COOH; their spectroscopic features point to a d(z2) ground state and a geometry intermediate between an octahedron and a trigonal prism, related to the steric requirements of the substituent on the carbon atom in position 2 of the pyridinone ring. Four new solid derivatives, [V(IV)O(1,2-diethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-tolyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], [V(IV)O(1-(p-(n-butyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], and [V(IV)O(1-(p-(n-hexyl)phenyl)-2-ethyl-3-hydroxy-4-pyridinonato)2], were isolated and characterized; they exhibited a five-coordinate geometry close to square-pyramid. A criterion for establishing the degree of distortion toward the trigonal-bipyramid on the basis of the electronic absorption spectra is provided. Relationships between the pKa of the -OH group in position 3 of the ring and (i) log K of mono and bis chelated complexes, (ii) pK of the water molecule in cis-[V(IV)OL2(H2O)], (iii) log K of tris chelated species [V(IV)L3]+, and (iv) 51V hyperfine coupling constant (Az) have been established and discussed for a number of pyrone, pyridinone, and catechol ligands. The results are rationalized by assuming for pyridinones an electronic structure intermediate between that of pyrones and catechols. The relationships are valuable to the understanding of the behavior of VIVO species in aqueous solution.

70 citations

Journal ArticleDOI
TL;DR: In this paper, organic-inorganic hybrid precursors were used to obtain planar waveguides with low losses in the infrared (from 0.6-1.1 dB cm−1) and a number of propagating modes in the visible (losses from 0.4 −1.5 dB cm −1).
Abstract: Organic–inorganic hybrids were prepared using ureapropyltriethoxysilane, methacryloxypropyltrimethoxysilane and acrylic acid modified zirconium(IV) n-propoxide precursors and were characterized by small angle X-ray scattering, X-ray diffraction and photoluminescence spectroscopy. The results indicate an effective interaction between the zirconium-based nanoparticles and the siliceous nanodomains that induces changes in the hybrids' emission features. Planar waveguides were obtained by spin-coating of the prepared sols on sodalime and silica substrates. Refractive index, thickness, number of propagating modes, and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm by the prism coupling technique. The synergism between the two hybrid precursors resulted in monomode planar waveguides with low losses in the infrared (from 0.6–1.1 dB cm−1) which also support a number of propagating modes in the visible (losses from 0.4–1.5 dB cm−1). Channel waveguides were also obtained by UV photopatterning using amplitude or phase masks and propagating modes were observed at 1550 nm.

52 citations

Journal ArticleDOI
TL;DR: A fluorescent iron chelator, shown to be effective in inhibiting the growth of Mycobacterium avium in macrophages, is reported, together with the synthesis and characterization of two unsuccessful analogues selected to facilitate identification of the molecular properties responsible for the antimicrobial activity.
Abstract: We report the synthesis and characterization of a fluorescent iron chelator (4), shown to be effective in inhibiting the growth of Mycobacterium avium in macrophages, together with the synthesis and characterization of two unsuccessful analogues selected to facilitate identification of the molecular properties responsible for the antimicrobial activity. Partition of the chelators in liposomes was investigated and the compounds were assessed with respect to uptake by macrophages, responsiveness to iron overload/iron deprivation and intracellular distribution by flow cytometry and confocal microscopy. The synthesis of the hexadentate chelators is based on a tetrahedral structure to which three bidentate 3-hydroxy-4-pyridinone chelating units are linked via amide bonds. The structure is synthetically versatile, allowing further addition of functional groups such as fluorophores. Here, we analyse the non-functionalized hexadentate unit (3) and the corresponding rhodamine B (4) and fluorescein (5) labelled chelators. The iron(III) stability constant was determined for 3 and the values log beta = 34.4 and pFe(3+) = 29.8 indicate an affinity for iron of the same order of magnitude as that of mycobacteria siderophores. Fluorescence properties in the presence of liposomes show that 4 strongly interacts with the lipid phase, whereas 5 does not. Such different behaviour may explain their distinct intracellular localization as revealed by confocal microscopy. The flow cytometry and confocal microscopy studies indicate that 4 is readily engulfed by macrophages and targeted to cytosol and vesicles of the endolysosomal continuum, whereas 5 is differentially distributed and only partially colocalizes with 4 after prolonged incubation. Differential distribution of the compounds is likely to account for their different efficacy against mycobacteria.

43 citations

Journal ArticleDOI
TL;DR: In this article, a systematic investigation of erbium diffusion in LiNbO3 is presented, where depth concentration profiles are obtained by secondary ion mass spectrometry (SIMS).
Abstract: A systematic investigation of erbium diffusion in lithium niobate (LiNbO3) crystal as a function of crystal cut-direction, diffusion process parameters (temperature and time), and initial film thickness is reported. Depth concentration profiles of erbium are obtained by secondary ion mass spectrometry (SIMS). Combining experimental data with diffusion theory, the relevant diffusion parameters are derived. Diffusion from an infinite source of erbium ions is studied to evaluate the solid solubility lower limit of Er in LiNbO3. A thin film diffusion regime, with complete depletion of ion source, is also investigated. A comparison of Er diffusion with Er/Ti codiffusion in LiNbO3 crystals is reported.

40 citations

Journal ArticleDOI
TL;DR: Results from an investigation in an in vivo model of STZ-induced diabetic rats demonstrate that compound bis(1,2-dimethyl-3-hydroxy-4(1H)-pyridinonate)zinc(II), Zn(dmpp)(2), significantly lowers the blood glucose levels of individuals, thus showing evidence of glucose lowering activity.

29 citations


Cited by
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01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
TL;DR: This review shows that fluoroquinolone antibiotics have a wide spread use and that their behavior during wastewater treatment is complex with an incomplete removal, and that these biorecalcitrant compounds are present in different environmental matrices at potentially hazardous concentrations for the aquatic environment.

522 citations

Journal ArticleDOI
TL;DR: Reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed and insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.
Abstract: The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C–C and C–O bond cleavage, carbon–carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis. Additionally, insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.

273 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of the history of homogeneous catalysis and its application in alkenes, including the following: 1.1. Introduction. 2.2.
Abstract: Preface.- Acknowledgements.- 1: Introduction.- 1.1. Catalysis. 1.2. Homogeneous catalysis. 1.3. Historical notes on homogeneous catalysis. 1.4. Characterization of the catalyst. 1.5. Ligand effects. 1.6. Ligands according to donor atoms. 2: Elementary Steps.- 2.1. Creation of a 'vacant' site and co-ordination of the substrate. 2.2. Insertion versus migration. 2.3. beta-Elimination and de-insertion. 2.4. Oxidative addition. 2.5. Reductive elimination. 2.6. alpha-Elimination reactions. 2.7. Cycloaddition reactions involving a metal. 2.8. Activation of a substrate toward nucleophilic attack. 2.9. sigma-Bond metathesis. 2.10. Dihydrogen activation. 2.11. Activation by Lewis acids. 2.12. Carbon-to-phosphorus bond breaking. 2.13. Carbon-to-sulfur bond breaking. 2.14. Radical reactions. 3: Kinetics.- 3.1. Introduction. 3.2. Two-step reaction scheme. 3.3. Simplifications of the rate equation and the rete-determining step. 3.4. Determining the selectivity. 3.5. Collection of rate data. 3.6. Irregularities in catalysis. 4: Hydrogenation.- 4.1. Wilkinson's catalyst. 4.2. Asymmetric hydrogenation. 4.3. Overview of chiral bidentate ligands. 4.4. Monodentate ligands. 4.5. Non-linear effects. 4.6. Hydrogen transfer. 5: Isomerisation.- 5.1. Hydrogen shifts. 5.2. Asymmetric isomerisation. 5.3. Oxygen shifts. 6: Carbonylation of Methanol and Methyl Acetate.- 6.1. Acetic acid. 6.2. Process scheme Monsanto process. 6.3. Acetic anhydride. 6.4. Other systems. 7: Cobalt Catalysed Hydroformylation.- 7.1. Introduction. 7.2. Thermodynamics. 7.3. Cobalt catalysed processes. 7.4. Cobalt catalysed processes for higher alkenes. 7.5. Kuhlmann cobalt hydroformylation process. 7.6. Phosphine modified cobalt catalysts: the shell process. 7.7. Cobalt carbonyl phosphine complexes. 8: Rhodium Catalysed Hydroformylation.- 8.1. Introduction. 8.2. Triphenylphosphine asthe ligand. 8.3. Diphosphines as ligands. 8.4. Phosphites as ligands. 8.5. Diphosphites. 8.6. Asymmetric hydroformylation. 9: Alkene Oligomerisation.- 9.1. Introduction. 9.2. Shell-higher-olefins-process. 9.3. Ethene trimerisation. 9.4. Other alkene oligomerisation reactions. 10: Propene Polymerisation.- 10.1. Introduction to polymer chemistry. 10.2. Mechanistic investigations. 10.3. Analysis by 13CNMR spectroscopy. 10.4. The development of metallocene catalysts. 10.5. Agostic interactions. 10.6. The effect of dihydrogen. 10.7. Further work using propene and other alkenes. 10.8. Non-metallocene ETM catalysts. 10.9. Late transition metal catalysts. 11: Hydrocyanation of Alkenes.- 11.1. The adiponitrile process. 11.2. Ligand effects. 12: Palladium Catalysed Carbonylations of Alkenes.- 12.1. Introduction. 12.2. Polyketone. 12.3. Ligand effects on chain length. 12.4. Ethene/propene/CO terpolymers. 12.5. Stereoselective styrene/CO terpolymers. 13: Palladium Catalysed Cross-Coupling Reactions.- 13.1. Introduction. 13.2. Allylic reaction. 13.3. Heck reaction. 13.4. Cross-coupling reaction. 13.5. Heteroatom-carbon bond formation. 13.6. Suzuki reaction. 14: Epoxidation.- 14.1. Ethene and propene oxide. 14.2. Asymmetric epoxidation. 14.3. Asymmetric hydroxilation of alkenes with osmium tetroxide. 14.4. Jacobsen asymmetric ring-opening of epoxides. 14.5. Epoxidations with dioxygen. 15: Oxydation with Dioxygen.- 15.1. Introduction. 15.2. The Wacker reaction. 15.3. Wacker type reactions. 15.4. Terephthalic acid. 15.5. PPO. 16: Alkene Metathesis.- 16.1. Introduction. 16.2. The mechanism. 16.3. Reaction overview. 16.4. Well-characterised tungsten and molybdenum catalysts. 16.5. Ruthenium catalysts. 16.6. Stereochemistry. 16.7. Catalyst decomposition. 16.8. Alkynes. 16.9. Industrial applications. 17: Enantioselective Cyclopropanation.-

263 citations

Journal ArticleDOI
TL;DR: The acid–base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations and the determination of protonation and stability constants showed accordance with the data obtained from the different analytical techniques used.
Abstract: The acid–base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol −1 ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L−1 and T = 298.15 K was also performed for other three Zn2+/Lz− systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn2+/ligand species, while computational molecular simulations allowed information to be gained on the metal–ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye–Huckel model, the classical specific ion interaction theory, and the van’t Hoff equations, respectively.

250 citations