Recursos de colección

Estudo Geral - Universidade de Coimbra (19.630 recursos)

ESTUDO GERAL é a designação do repositório digital da produção científica da Universidade de Coimbra, com o objectivo de divulgar conteúdos digitais de natureza científica de autores ligados à Universidade de Coimbra. A sua criação insere-se no movimento de Acesso Livre à Literatura científica (Open Access), ao qual o Conselho de Reitores das Universidades Portuguesas aderiu em 2006 e que a Universidade de Coimbra subscreveu. À semelhança de outras grandes universidades nacionais e internacionais, a UC tem o maior interesse em aumentar a sua presença na rede informática mundial, sendo cada vez mais - e também por essa via - um emissor de conhecimento e cultura.

FCTUC Bioquímica - Artigos em Revistas Internacionais

Mostrando recursos 1 - 20 de 155

  1. Fluoxetine and Norfluoxetine Revisited: New Insights into the Electrochemical and Spectroscopic Properties

    Garrido, E. Manuela; Garrido, Jorge; Calheiros, Rita; Borges, Fernanda
    The extent to which humans and wildlife are exposed to the vast array of anthropogenic chemicals and their degradation products, along with related naturally occurring compounds, is nowadays an important issue. The study of the physical-chemical properties of the compounds and/or degradation products is an important subject because some of them are intrinsically related to its resistance to degradation and/or bioaccumulation. Accordingly, the study of the electrochemical behavior of the selective serotonin reuptake inhibitor fluoxetine and its main metabolite norfluoxetine was investigated. The identification of the oxidation processes was done via two fluoxetine analogues, 1-(benzyloxy)-4-(trifluoromethyl)benzene and N-methyl-3-phenylpropan-1-amine hydrochloride. The oxidative...

  2. Conformational Studies of Poly(9,9-dialkylfluorene)s in Solution Using NMR Spectroscopy and Density Functional Theory Calculations

    Justino, Licínia L. G.; Ramos, M. Luísa; Abreu, Paulo E.; Carvalho, Rui A.; Sobral, Abilio J. F. N.; Scherf, Ullrich; Burrows, Hugh D.
    Relationships have been obtained between intermonomer torsional angle and NMR chemical shifts (1H and 13C) for isolated chains of two of the most important poly(9,9-dialkylfluorenes), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and the copolymer poly(9,9-dioctylfluorene-co-[2,1,3]benzothiadiazole-4,7-diyl) (F8BT), using DFT calculations. The correlations provide a model for NMR spectral data interpretation and the basis for analysis of conformational changes in poly(9,9-dialkylfluorene-2,7-diyl)s. The correlations obtained for PF2/6 indicate that the 13C chemical shifts of the aromatic carbons close to the intermonomer connection (C1, C2, and C3) have minimum values at planar conformations (0° and 180°) and maximum values at 90° conformations. In contrast, the 1H chemical shifts...

  3. Oxygen-by-sulfur substitutions in glycine: conformational and vibrational effects

    Carvalho, Luís A. E. Batista de; Marques, M. Paula M.; Teixeira-Dias, José J. C.
    Molecular geometries, energies, dipole moments and atomic charges of several conformations of glycine (NH2CH2C(O)OH) and its oxygen-by-sulfur substituted analogues (NH2CH2C(O)SH, NH2CH2C(S)OH and NH2CH2C(S)SH) were determined by ab initio MO calculations at the MP2/6-31G** level, and vibrational frequencies, infrared and Raman intensities were evaluated within the harmonic approximation, at the HF/6-31G** level. Profiles for the potential energy and several geometric parameters as a function of the NC–C(X) (X = O, S) dihedral angle (C–C internal rotation) were obtained using the 3-21G(N*) basis set. Conformational and vibrational effects of oxygen-by-sulfur substitutions are discussed. In particular, the occurrence of intramolecular close contacts between...

  4. Synthesis of novel -functionalized phosphinic acid derivatives of thiophene and the first crystal structure of an -hydroxyalkylphosphinate

    Bligh, S. W. Annie; McPartlin, Mary; Sanganee, Mahesh J.; Woodroffe, Thomas M.; Geraldes, Carlos F. G. C.
    Reaction of 2,5-diformylthiophene with Ph2CHNH2 and hypophosphorus acid yields novel -hydroxy- or -amino-methylphosphinic acid derivatives depending on reaction conditions; the X-ray structure analysis of diphenylmethylammonium 5-formyl-2-thienyl(hydroxy)methylphosphinate provides the first direct structural information on the -hydroxyalkylphosphinate class of compounds.

  5. Evolution of Photoluminescence across Dimensionality in Lanthanide Silicates

    Kostova, Mariya H.; Ananias, Duarte; Paz, Filipe A. Almeida; Ferreira, Artur; Rocha, João; Carlos, Luís D.
    The dehydratation process of layered lanthanide silicates K3[LnSi3O8(OH)2], Ln = Y, Eu, Tb, and Er, and the structural characterization of the obtained small-pore framework K3LnSi3O9, Ln = Y, Eu, Tb, and Er solids, named AV-23, have been reported. The structure of AV-23 has been solved by single-crystal X-ray diffraction (XRD) methods and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, and 29Si MAS NMR. The photoluminescence (PL), radiance, and lifetime values of AV-23 have been studied and compared with those of AV-22. Both materials have a similar chemical makeup and structures sharing analogous building blocks, hence providing a unique...

  6. Energy Transfer and Emission Decay Kinetics in Mixed Microporous Lanthanide Silicates with Unusual Dimensionality

    Evans, Rachel C.; Ananias, Duarte; Douglas, Alastair; Douglas, Peter; Carlos, Luis D.; Rocha, João
    We have investigated the energy transfer dynamics in mixed lanthanide open-framework silicates, known as Ln-AV-20 materials, with the stoichiometric formula Na1.08K0.5Ln1.14Si3O8.5·1.78H2O (Ln = Gd3+, Tb3+, Eu3+), using steady-state and time-resolved luminescence spectroscopy. Energy transfer between donor and acceptor Ln3+ ions is extremely efficient, even at low molar ratios of the acceptor Ln3+ (<5%). The presence of two different Ln3+ environments makes the Ln-AV-20 intralayer structure intermediate between purely one-dimensional (1D) and two-dimensional (2D). The unusual dimensionality of the Ln-AV-20 layers prevents modeling of energy transfer kinetics by conventional kinetic models. We have developed a computer modeling program for the analysis...

  7. Cytotoxic Activity of Metal Complexes of Biogenic Polyamines: Polynuclear Platinum(II) Chelates

    Teixeira, Luísa J.; Seabra, Marta; Reis, Elisa; Cruz, M. Teresa Girão da; Lima, M. Conceição Pedroso de; Pereira, Eulália; Miranda, M. Adelaide; Marques, M. Paula M.
    Several polynuclear Pt(II) chelates with biogenic polyamines were synthesized and screened for their potential antiproliferative and cytotoxic activity in different human cancer cell lines. To gather information regarding the structure−activity relationships underlying their biological activity, the complexes studied were designed to differ in geometrical parameters such as the nature of the ligand and the number and chemical environment of the metal centers. Distinct effects were found for different cell lines and different structural characteristics of the complexes; chelates II, III, and IV displayed specificity toward the HeLa and HSC-3 epithelial-type cells, while V, VI, and VII were clearly more effective...

  8. Complex Formation between Heptakis(2,6-di-O-methyl)-β-cyclodextrin and Cyclopentadienyl Molybdenum(II) Dicarbonyl Complexes: Structural Studies and Cytotoxicity Evaluations

    Pereira, Cláudia C. L.; Diogo, Cátia V.; Burgeiro, Ana; Oliveira, Paulo J.; Marques, Maria Paula M.; Braga, Susana S.; Paz, Filipe A. Almeida; Pillinger, Martyn; Gonçalves, Isabel S.
    The inclusion compounds isolated from nonaqueous solutions of heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and the complexes [CpMoL2(CO)2](BF4) (L = MeCN, L2 = 2,2′-biimidazole) were characterized in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), 13C{1H} CP/MAS NMR, and FTIR spectroscopy. Powder XRD showed that the compound with [CpMo(MeCN)2(CO)2](BF4) was amorphous, while that with [CpMo(H2biim)(CO)2](BF4) was microcrystalline. The powder XRD pattern of the microcrystalline product could be satisfactorily indexed in the orthorhombic crystal system with space group P212121 and final unit cell parameters of a = 28.489(3) Å, b = 19.198(2) Å, and c = 16.042(2) Å. A hypothetical structural model...

  9. Evaluation of [Co(gly)3]- as a 35Cl- NMR Shift Reagent for Cellular Studies

    Diven, Conrad F.; Wang, Fei; Abukhdeir, Abde M.; Salah, Wajeeh; Layden, Brian T.; Geraldes, Carlos F. G. C.; Freitas, Duarte Mota de
    We studied the efficacy of the tris-glycinatocobaltate(II) complex ([Co(gly)3]-) as a shift reagent (SR) for chloride by 35Cl NMR spectroscopy and compared to that of Co2+(aq). Due to the relatively low thermodynamic stability of [Co(gly)3]-, a 1:3 Co(II)/gly stoichiometric solution at physiological pH is approximately a 2:1 mixture of [Co(gly)2(H2O)2] and [Co(gly)(H2O)4]+. This SR was found to be stable up to higher pH values than Co2+(aq), better preventing Co(OH)2 formation at alkaline pH. No significant differences in the 35Cl- NMR chemical shift induced by Co(II)/gly or Co2+(aq) were observed in the presence of physiological concentrations of either Ca2+ or Mg2+,...

  10. Interactions of Influenza Virus with Cultured Cells: Detailed Kinetic Modeling of Binding and Endocytosis

    Nunes-Correia, Isabel; Ramalho-Santos, João; Nir, Shlomo; Lima, Maria C. Pedroso de
    We performed a detailed kinetic analysis of the uptake of influenza virus (A/PR8/34) by Madin Darby canine kidney (MDCK) cells in culture. Experimental procedures were based on the relief of fluorescence self-quenching of the fluorescent probe octadecylrhodamine B chloride (R18) incorporated in the viral envelope. Equilibrium for binding of influenza virus to MDCK cells (2.5 × 106/mL) was reached quicker with temperature increases due to a faster dynamic mobility of the particles. We deduced that there are two kinds of binding sites for influenza virus in MDCK cells and determined the kinetic parameters of the binding process (adhesion and detachment...

  11. Controlling the Morphology in DNA Condensation and Precipitation

    Pinto, Maria F. V.; Morán, M. Carmen; Miguel, M. Graça; Lindman, Björn; Jurado, Amália S.; Pais, Alberto A. C. C.
    This work addresses the influence of solution inhomogeneity on conformation, aggregation, and coil/globule and bundle/single chain coexistence of T4 DNA molecules. The inhomogeneity is induced by mixing two solutions containing, respectively, protamine and DNA, with different relative concentrations, but aiming at producing the same final concentrations. The study was conducted by means of fluorescence microscopy (FM), complemented with scanning electron microscopy (SEM). It is shown that the degree of precipitation, the structures formed, and the relative population of compacted and unfolded structures are highly dependent on the method of preparation of the mixtures that contain the DNA/protamine complexes. Most of...

  12. Photoluminescent Layered Lanthanide Silicate Nanoparticles

    Ananias, Duarte; Ferdov, Stanislav; Paz, Filipe A. Almeida; Ferreira, Rute A. Sá; Ferreira, Artur; Geraldes, Carlos F. G. C.; Carlos, Luís D.; Lin, Zhi; Rocha, João
    The first examples of nanoparticles of pure layered Ln2(SiO4H)(OH)2(H2O)Cl (where Ln ) Eu, Gd, and Tb) and mixed microcrystalline layered lanthanide silicates containing different Eu/Gd and Tb/Gd ratios have been reported. The crystal structure of these silicates has been solved from synchrotron powder X-ray diffraction data. These materials display interesting and tuneable photoluminescence (PL) properties, such as energy transfer between different Ln3+ centers, illustrated here with the pairs Eu3+/Gd3+ and Tb3+/Gd3+. The PL properties of the mixed Eu3+/Gd3+ sample change upon F– for Cl- ion exchange, and this raises the possibility that this material may be exploited for sensing these ions.

  13. Multinuclear magnetic resonance study of the structure and dynamics of lanthanide(III) complexes of the bis(propylamide) of diethylenetriaminepentaacetic acid in aqueous solution

    Geraldes, Carlos F. G. C.; Urbano, Ana M.; Hoefnagel, Mattheus A.; Peters, Joop A.
    The structure and dynamics of the lanthanide(II1) complexes of the bis(propy1amide) of diethylenetriaminepentaacetate (DTPA-PA3 in aqueous solution have been investigated by I3C and I7O NMR. With the use of the longitudinal 13C relaxation times of the NdlI1 complex it is shown that the organic ligand is bound to the lanthanide(II1) ion in an octadentate fashion via the three nitrogens of the diethylenetriamine backbone, the three carboxylate groups, and the two amide oxygens. I7O NMR measurements show that the coordination sphere is completed by one water ligand. The inversion of the lanthanide-bound nitrogens is precluded, and therefore four diastereomeric pairs of isomers are possible for these complexes....

  14. Lithium-7 NMR relaxation study of lithium binding in human erythrocytes

    Rong, Qinfen; Espanol, Maryceline; Freitas, Duarte Mota de; Geraldes, Carlos F. G. C.
    We used 7Li NMR spin-lattice (TI) and spin-spin (Tz) relaxation time measurements to investigate the binding of Li+ in human red blood cell (RBC) suspensions. In RBCs containing 1.4 mM Li+, the intracellular 7Li NMR T2 relaxation value (0.30 f 0.03 s) was much smaller than the corresponding TI value (6.0 f 0.1 s), yielding a ratio of TI to T2 of 20. For 1.5 mM LiCl solutions whose viscosities were adjusted to 5 CP with glycerol, the values of the T1/T2 ratios were as follows: 49 for unsealed RBC membrane (2.0 mg of protein/mL); 4.4 for spectrin (1.9 mg/mL); 1.5 for 5.4 mM 2,3-bisphosphoglycerate...

  15. Transverse Acoustic Modes of Biogenic and α,ω-Polyamines: A Study by Inelastic Neutron Scattering and Raman Spectroscopies Coupled to DFT Calculations

    Carvalho, Luís A. E. Batista de; Marques, M. Paula M.; Tomkinson, John
    A complete analysis of the transverse acoustic modes (TAMs) for the homologous series of α,ω-diamines (H2N(CH2)nNH2) (n = 2−10, n = 12) as well as for the biogenic polyamines spermidine and spermine was undertaken, by Raman and inelastic neutron scattering (INS) spectroscopies combined with density functional theory (DFT) calculations. A complete assignment of the whole set of TAMs was carried out, for both the undeuterated and N-deuterated species. 1,2-Diaminoethane was found to display exceptional behavior, probably due to the formation of dimers in the solid state. An n-even/n-odd dependence of the low frequency INS pattern was observed for these polyamines....

  16. Caseinolytic Specificity of Cardosin, an Aspartic Protease from the Cardoon Cynara cardunculus L.: Action on Bovine αs- and β-Casein and Comparison with Chymosin

    Macedo, I. Queiroz; Faro, Carlos J.; Pires, Euclides M.
    The action of cardosin on bovine αs- and β-casein at 30 °C in 50 mM citrate buffer (pH 6.2) was studied. Peptides were isolated by reversed-phase HPLC on C18 columns and identified from their amino acid composition and N-terminal amino acid sequence. The relative susceptibility of peptide bonds cleaved was Phe23-Phe24 > Trp164-Tyr165 > Tyr166-Val167 > Tyr165-Tyr166 > Phe153-Tyr154 > Phe145-Tyr146 ≈ Leu149-Phe150 ≈ Leu156-Asp157 ≈ Ala163-Trp164 for αs1-casein and Leu192-Tyr193 > Leu191-Leu192 ≈ Leu165-Ser166 > Phe190-Leu191 ≥ Ala189-Phe190 ≈ Leu127-Thr128 for β-casein. In αs2-casein, cardosin cleaved the bonds Phe88-Tyr89 and Tyr95-Leu96. The enzyme shows a clear preference for bonds...

  17. A common mechanism for influenza virus fusion activity and inactivation

    Ramalho-Santos, João; Nir, Shlomo; Düzgünes, Nejat; Carvalho, Arsélio Pato de; Lima, Maria da Conceição Pedroso de
    The fusion of influenza virus (A/PR/8/34 strain) with PC- 12 cells was monitored by a fluorescence assay, and the results were analyzed with a mass-action model which could explain and predict the kinetics of fusion. The model accounted explicitly for the reduction in the fusion rate constant upon exposure of the virus to low pH, either for the virus alone in suspension or for the virus bound to the cells. When the pH was lowered without previous viral attachment to cells, an optimal fusion activity was detected at pH 5.2. When the virus was prebound to the cells, however, reduction of pH below 5.2 resulted...

  18. A Schiff-Base Bibracchial Lariat Ether Forming a Cryptand-like Cavity for Lanthanide Ions

    González-Lorenzo, Marina; Platas-Iglesias, Carlos; Avecilla, Fernando; Geraldes, Carlos F. G. C.; Imbert, Daniel; Bünzli, Jean-Claude G.; Blas, Andrés de; Rodríguez-Blas, Teresa
    We report here a structural and photophysical study of lanthanide(III) complexes with the di-deprotonated form of the bibracchial lariat ether N,N‘-bis(2-salicylaldiminobenzyl)-1,10-diaza-15-crown-5. The X-ray crystal structures of [Ce(L2-2H)](ClO4)·0.5H2O (2) and [Sm(L2-2H)](ClO4)·C3H8O (5b) show the metal ion being nine-coordinated and deeply buried in the cavity of the dianionic receptor. Thanks to the formation of a pseudomacrocycle through π−π interaction between one of the phenol rings and one of the benzyl rings, the complexes present a cryptand-like structure in the solid state. 1H and 13C NMR studies on the La(III) complex point that the solid state structure is essentially maintained in acetonitrile solution....

  19. Study of Biogenic and α,ω-Polyamines by Combined Inelastic Neutron Scattering and Raman Spectroscopies and by Ab Initio Molecular Orbital Calculations

    Marques, M. Paula M.; Carvalho, Luís A. E. Batista de; Tomkinson, John
    A study of the biogenic polyamines spermidine and spermine, as well as of the diamines H2N(CH2)nNH2 (n = 2−10 and n = 12), was carried out by both inelastic neutron scattering (INS) and Raman spectroscopies, for both their undeuterated and N-deuterated forms. Ab initio density functional theory (DFT) methods were also used, to obtain the calculated vibrational spectra of those molecules. A thorough vibrational analysis was performed, leading to the assignment of the solid-state spectra, both Raman and INS, of the polyamines studied, comprising all their longitudinal acoustic modes (LAM's).

  20. NMR Transversal Relaxivity of Suspensions of Lanthanide Oxide Nanoparticles

    Norek, Małgorzata; Pereira, Giovannia A.; Geraldes, Carlos F. G. C.; Denkova, Antonia; Zhou, Wuzong; Peters, Joop A.
    Aqueous suspensions of paramagnetic lanthanide oxide nanoparticles have been studied by NMR relaxometry. The observed relaxivities are explained by the static dephasing regime (SDR) theory. The corresponding R2 relaxivities are considerably smaller and are strongly dependent on the interval between the two refocusing pulses. The experimental data are rationalized by assuming the value of the diffusion correlation time, τD, to be very long in a layer with adsorbed xanthan on the particle's surface. In this layer, the refocusing pulses are fully effective and R2 ≈ 0. Outside this layer, the diffusion model for weakly magnetized particles was applied. From the...

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