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Showing papers by "University of Coimbra published in 1986"


Journal ArticleDOI
TL;DR: The fluorescence quantum yield of N-phenyl-1-naphthylamine (NPN) increases about 10-fold and the wavelength of maximum fluorescence emission is blue-shifted when this molecule partitions into the apolar core of micellar structures from the aqueous phase, which allowed the utilization of NPN as a fluorescent indicator of micelle formation by 14 different surfactants belonging to the families of alkyltrimethylammonium halides.

186 citations


Journal ArticleDOI
TL;DR: In this article, a general procedure for constructing the potential energy surfaces of small polyatomic molecules and van der Waals molecules has been used to obtain explicit functions for HeH2 ([Xtilde], 1 A′), HeLi2 (1 A′) and HO2 (2 A′).
Abstract: A general procedure recently proposed by one of the authors for constructing the potential energy surfaces of small polyatomic molecules and van der Waals molecules has been used to obtain explicit functions for HeH2 ([Xtilde], 1 A′), HeLi2 ([Xtilde], 1 A′) and HO2 ([Xtilde], 2 A″). The HeH2 and HeLi2 potentials compare well the best available correlated ab initio energies, and should be suitable for studying both vibration-rotation inelasticity in atom-diatom collisions and atom (H, Li) recombination in the presence of He atoms. For HO2, the surface conforms with the ab initio data of Melius and Blint for the 3-body energy, and shows good agreement with available spectroscopic data for the energy and geometry of the minima referring to the equilibrium triatomic. Two secondary minima which have chemical interest are predicted. One refers to a T-shaped (C 2v ) H-O2 weakly bound (℞ 25 kJ mol-1 with respect to the H + O2 dissociation limit) species, while the other is related to a linear (C ∞v ) weak hydroge...

57 citations


Journal ArticleDOI
TL;DR: In this article, the structure of the thermotropic mesophases of lead(II) decanoate was reassigned following optical and X-ray diffraction studies, which indicated formation of a lower temperature mesophase involving mainly increased lateral disorder, and a higher temperature Lα phase resulting from chain disordering and decreased lead-carboxylate interaction.
Abstract: Structures of the thermotropic mesophases of lead(II) decanoate are reassigned following optical and X-ray diffraction studies. These results, and those of D.S.C., Raman and 207Pb N.M.R. spectroscopy, indicate formation of a lower temperature mesophase involving mainly increased lateral disorder, and a higher temperature Lα (smectic A) phase resulting from chain disordering and decreased lead-carboxylate interaction. Comparison of experimental thermodynamic data for the phase transitions with theoretical data in the literature indicates that the entropy change for the lower to higher mesophase transition is dominated by the increase in chain disorder.

52 citations


Journal ArticleDOI
TL;DR: It is concluded that Mg2+ (millimolar range) couples ATP hydrolysis to Ca2+ uptake and that active transport of cations can proceed without a compensatory countertransport of a divalent cation.

49 citations


Journal ArticleDOI
TL;DR: It is concluded that high‐affinity binding of the Ca2+ blockers by SPM is not correlated with inhibition of theca2+ fluxes through channels in synaptosomes under conditions of minimal Na+/Ca2+ exchange.
Abstract: The binding of [3H]nimodipine to purified synaptic plasma membranes (SPM) isolated from sheep brain cortex was characterized, and the effects of nimodipine, nifedipine, and (+)-verapamil on the [3H]nimodipine binding were compared to the effects on 45Ca2+ translocation under conditions that separate 45Ca2+ fluxes through Ca2+ channels from 45Ca2+ uptake via Na+/Ca2+ exchange. [3H]Nimodipine labels a single class of sites in SPM, with a KD of 0.64 +/- 0.1 nM, a Bmax of 161 +/- 27 fmol X mg-1 protein, and a Hill slope of 1.07, at 25 degrees C. Competition of [3H]nimodipine binding to purified SPM with unlabelled Ca2+ channel blockers shows that: nifedipine and nimodipine are potent competitors, with IC50 values of 4.7 nM and 5.9 nM, respectively; verapamil and (-)-D 600 are partial competitors, with biphasic competition behavior. Thus, (+)-verapamil shows an IC50 of 708 nM for the higher affinity component and the maximal inhibition is 50% of the specific binding, whereas for (-)-verapamil the IC50 is 120 nM, and the maximal inhibition is 30%; (-)-D 600 is even less potent than verapamil in inhibiting [3H]nimodipine binding (IC50 = 430 nM). However, (+)-verapamil, nifedipine, and nimodipine are less potent in inhibiting depolarization-induced 45Ca2+ influx into synaptosomes in the absence of Na+/Ca2+ exchange than in competing for [3H]nimodipine binding. Thus, (+)-verapamil inhibits Ca2+ influx by 50% at about 500 microM, whereas it inhibits 50% of the binding at concentrations 200-fold lower, and the discrepancy is even larger for the dihydropyridines. The Na+/Ca2+ exchange and the ATP-dependent Ca2+ uptake by SPM vesicles are also inhibited by the Ca2+ channel blockers verapamil, nifedipine, and d-cis-diltiazem, with similar IC50 values and in the same concentration range (10(-5)-10(-3) M) at which they inhibit Ca2+ influx through Ca2+ channels. We conclude that high-affinity binding of the Ca2+ blockers by SPM is not correlated with inhibition of the Ca2+ fluxes through channels in synaptosomes under conditions of minimal Na+/Ca2+ exchange. Furthermore, the relatively high concentrations of blockers required to block the channels also inhibit Ca2+ translocation through the Ca2+-ATPase and the Na+/Ca2+ exchanger. In this study, clear differentiation is made of the effects of the Ca2+ channel blockers on these three mechanisms of moving Ca2+ across the synaptosomal membrane, and particular care is taken to separate the contribution of the Na+/Ca2+ exchange from that of the Ca2+ channels under conditions of K+ depolarization.

40 citations


Journal ArticleDOI
TL;DR: The correlation between the high affinity binding of Ca2+ channel blockers to purified synaptic plasma membranes (SPM) and the effect of these drugs in blocking the 45Ca2+ uptake and the release of [3H]gamma-aminobutyric acid [( 3H]GABA) by preloaded synaptosomes is studied.

37 citations


Journal ArticleDOI
TL;DR: In this article, Proton and 13C evidence is presented on the number, stoichiometry, geometry and relative stability of the complexes formed in the systems Mo(VI) + L-lactic acid, Mo( VI) + D,L-thiolactic acid and Mo(II) +D,Lthiomalic acid in aqueous solutions at pH values in the range 3-8.

25 citations


Journal ArticleDOI
TL;DR: In this paper, the boundary of the set of non-differentiable points of ∂W c(A) is investigated, where W c (A) denotes the boundary.
Abstract: Let A be an n × n complex matrixc = (γ1, … γn)τ e Cn and Λn the set of all n-tuples of orthonormal vectors in Cn. Let ∂W c(A) denote the boundary of the set In this note certain kinds of nondifferentiable points of ∂W c(A) are investigated.

21 citations


Journal ArticleDOI
TL;DR: In this paper, the 1,4, 7-triazacyclononane-N,N′,N″ -triacetic acid (NOTA) with the paramagnetic trivalent lanthanide canons have been examined by proton and 13 C magnetic resonance spectroscopy.

21 citations


Journal ArticleDOI
TL;DR: ADP and ATP form in acidic aqueous solutions strong complexes with Mo(VI) oxocations in different stoichiometries with predominantly phosphate groups of the nucleotides.

20 citations


Journal ArticleDOI
TL;DR: Graft copolymers used to immobilize proteins gave a useful degree of immobilization of cells of Bacillus stearothermophilus, as did a poly(maleic anhydride/styrene)‐cocellulose system, but attempts to improve the activity by using grafts based on other polysaccharide supports met with mixed success.
Abstract: Poly(maleic anhydride styrene) graft copolymers of cellulose, pectin polygalacturonic acid salt, calcium polygalacturonate, and starch were prepared and used to immobilize proteins. The cellulose grafts coupled quite appreciable quantities of acid phosphatase, glucose oxidase, and trypsin. However, the general retention of activity was somewhat disappointing. Further investigation with acid phosphatase showed that the amount of enzyme immobilized increased as the amount of anhydride in the graft copolymer increased but no such relationship existed for the enzymic activity. The cellulose graft copolymers were hydrolyzed and it appeared that the carboxyl group aided adsorption of the enzyme. Attempts to couple acid phosphatase using CMC through the free carboxyl groups, created by hydrolysis, gave only a small increase in the extent of protein coupling. However, the unhydrolyzed system gave a useful degree of immobilization of cells of Bacillus stearothermophilus, as did a poly(maleic anhydride/styrene)-cocellulose system. Attempts to improve the activity by using grafts based on other polysaccharide supports met with mixed success. Pectin products were soluble. Polygalacturonic acid products were partially soluble and extremely high levels of enzymic activity were obtained. This was probably due in part to the hydrophilic nature of the system, which also encouraged absorption of the enzyme. Attempts were made to reduce the solubility by using the calcium pectinate salt. Immobilization of acid phosphatase and trypsin resulted in inceased protein coupling but relatively poor activities were attained. A starch based system gave similar results. Calcium polygalacturonate was used to prepare an insoluble graft copolymeric system containing acrylonitrile-comaleic anhydride. The resulting gels gave excellent coupling with acid phosphatase which had a very good retention of activity.

Journal ArticleDOI
TL;DR: In this paper, the molar volume of DCl was measured from 162 to 236 K and of HCl from 160 to 218 K, and the difference in Vml of the two compounds in this range does not exceed 0.1 per cent.

Journal ArticleDOI
TL;DR: In this paper, the modified overrelaxation (MSOR) method is applied to a linear system Ax=b, where A has property A. The authors obtained convergence conditions for the MSOR method when A is strictly diagonally dominant.

Journal ArticleDOI
TL;DR: It is concluded that both α1‐ and α2‐adrenoceptors are present in the human uterine artery.
Abstract: Prazosin and yohimbine were used to differentiate postjunctional alpha-adrenoceptors in the human uterine artery in-vitro. Two postjunctional alpha-adrenoceptor subtypes were distinguished by the affinities of the receptor for yohimbine and prazosin. The pA2 for prazosin was 8.91 against phenylephrine with a slope not significantly different from unity (0.91), and the pA2 for yohimbine was 7.25 against naphazoline and 8.70 against clonidine, with slopes not significantly different from unity (1.11 and 1.18, respectively). Yohimbine was not very active against phenylephrine, while prazosin was very active against the mixed and selective alpha 2-adrenoceptor agonist noradrenaline and clonidine; the intercepts of the Schild plot were 8.80 and 8.82 but with slopes significantly less than unity (0.77 and 0.67, respectively). Prazosin competitively antagonized phenylephrine at the alpha 1-adrenoceptor, whereas yohimbine competitively antagonized naphazoline and clonidine at the alpha 2-adrenoceptor. It is concluded that both alpha 1- and alpha 2-adrenoceptors are present in the human uterine artery.

Journal ArticleDOI
TL;DR: The many-body expansion method has been applied to polyatomic potentials which have non-analytic features as mentioned in this paper, and three types of surface intersection on triatomic surfaces have been distinguished which require different uses of two and three-body terms in the potential matrix.
Abstract: The many-body expansion method has been applied to polyatomic potentials which have non-analytic features. Three types of surface intersection on triatomic surfaces have been distinguished which require different uses of two-body and three-body terms in the potential matrix. These features have been illustrated by the examples H2O, H3, Li2Na and LiNa2.

Journal ArticleDOI
TL;DR: In this article, the tautomeric equilibria of some β-ketobutanamides in solution were investigated by proton and carbon-13 Nuclear Magnetic Resonance (NMR) Spectroscopy.

Journal ArticleDOI
TL;DR: In this article, it was shown that a set of vector fields on a differentiable manifold M is uniformly controllable (ucc) if there exists a nonnegative integer N such that evert pair (p, q) of point of M can be joined by a trajectory, or positive orbit, of F which involves at most N switches between two points.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the ratio between width and energy of the nuclear giant resonances is of the order of 1, essentially independent of the multipolarity, which is due to the fact that the boundary is externally imposed.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the apparent rates of the fluorescence quenching of aromatic molecules by the uranyl ion in ethanol solutions are considerably higher than the rate of diffusion.

Journal ArticleDOI
TL;DR: An irrotational nuclear fluid dynamical scheme, on the basis of the quantal action principle, where the effect of temperature is taken into account, is presented in this paper. But it does not take into account the nuclear radius, chemical potential, excitation energy and incompressibility of hot nuclei.
Abstract: An irrotational nuclear fluid dynamical scheme, on the. basis of the quantal action principle, is presented, where the effect of temperature is taken into account. A low temperature expansion, retaining terms up to T', is considered. The temperature dependence of the energies of isoscalar giant resonances is calculated. The nuclear radius, chemical potential, excitation energy and incompressibility of hot nuclei are investigated as functions of the temperature.

Journal ArticleDOI
TL;DR: In this article, a classical model for the calculation of activation free energies of chemical reactions is applied to the study of sigmatropic shifts and cycloaddition reactions, and the effect of substituents is explained in terms of an increase in the bond order of the transition state, n, due to an increase of the electronic charge produced by the substitusents on the carbon skeleton.


Journal ArticleDOI
TL;DR: In this paper, it was shown that the determinant of the sum of a positive definite hermitian and a skew-hermitian matrix, with eigenvalues α j and iγ j, j = 1,γ j, j = 0, n, respectively, is contained in the convex hull of the points Π j=1 n (α j +iγ ϵ(j) ), ϵ∈S n.

Journal ArticleDOI
TL;DR: In this article, the properties of the set Δ c (A)={det(C+UAU ∗ ):U ϵ U n } are established, and certain analogies between Δ c(A) and the c -numerical range W c ( A ) of A are investigated.

Journal ArticleDOI
TL;DR: In this paper, an analytical expression for low energy (0 to ∼20 eV) electron-noble gas atom elastic scattering phase shifts is presented, allowing an accurate calculation of elastic integral and differential cross sections at any chosen energy through the use of appropriate formulae.
Abstract: Analytical expressions which reproduce recent reliable data on low energy (0 to ∼20 eV) electron-noble gas atom elastic scattering phase shifts are presented, allowing an accurate calculation of elastic integral and differential cross sections at any chosen energy through the use of the appropriate formulae. Fittings to the integral elastic cross sections thus obtained and to inelastic and total (elastic + inelastic) cross sections are also presented within this energy range. These expressions are of interest in Boltzmann and Monte Carlo calculations of electron drift phenomena in noble gases at low values of E p and are applicable to certain types of nuclear radiation detectors.

Journal ArticleDOI
TL;DR: In this article, a full pH range 1H and 13C NMR study was performed on the complexation of UO22+ with (D,L)- and meso-tartaric acids, for variable concentrations and molar ratios.

Journal ArticleDOI
TL;DR: In this article, a new least square estimation method for Bezier polynomial curves and surfaces is described and illustrated, and the Cartesian coordinates of the vertices of polygons defining the curves separated well natural populations of Anodonta cygnea L. and human sagittal profiles of different sexes and age classes.
Abstract: A new least squares estimation method for Bezier polynomial curves and surfaces is described and illustrated. The Cartesian coordinates of the vertices of polygons defining the curves separated well natural populations of Anodonta cygnea L. and human sagittal profiles of different sexes and age classes. Multivariate comparisons of the coordinates of Bezier polygon vertices and Euclidean distance measures showed that the polygon coordinates revealed shape differences better than distances between homologous points on the curves. Further, polygon coordinates separated groups for more than two variables as well as or better than the equivalent number distances. In addition, polygon coordinates permit construction of mean shapes and their variances. Possible applications in trend surface analyses and for illustration in computer-aided identification programs are suggested.

Journal ArticleDOI
TL;DR: In this paper, a boson expansion was applied to the Heisenberg model of S = 1 2 ferromagnet, which incorporated the T3/2-law for the magnetization at low temperatures.
Abstract: A boson expansion, which takes into account fluctuations around a mean-field description at finite temperatures, is applied to the Heisenberg model of S= 1 2 ferromagnet. The approach incorporates the T3/2-law for the magnetization at low temperatures and, without considering dynamical interactions, provides a better estimate of the critical temperature than the conventional energy renormalized magnon theory and the random-phase approximation.

Journal ArticleDOI
TL;DR: In this paper, the grafting of styrene/maleic anhydride/vinyl acetate onto cellulose from mixed monomer compositions has been studied as a preliminary to the use of the resulting graft copolymers in enzyme immobilisation studies.

Journal ArticleDOI
TL;DR: This study examines the coefficient of inbreeding in the population of Rio de Onor (Portugal), for a period of 120 years, using the dispensations for consaguineous marriages and isonymy.
Abstract: This study examines the coefficient of inbreeding in the population of Rio de Onor (Portugal), for a period of 120 years. Two distinct methods were used: the dispensations for consaguineous marriages and isonymy. The two methods produced different results and these differences are explained, for the period after 1960, in terms of emigration.