On the competiting role of mean-field and residual interactions in flow observables

Theoretical analyses of heavy-ion reactions are performed in the framework of the semi-classical Landau-Vlasov approach. The incident energies are investigated in the range from intermediate to low energy regimes, where transverse collective motion has been experimentally evidenced. The influence of the equation of state (E.O.S.) parameters on various collective observables is studied in relation with the action of the residual interactions. From the sensitivity to both aspects, and taking into account the experimental biases limitations, our investigation indicates that E.O.S. signatures should be more expected at energies below 100 MeV per nucleon.     

Ion pairing between Cl- or ClO4- and alkali metal complexes of ionophore antibiotics in organic solvents: a multinuclear NMR and FT-IR study

The extent of ion pairing in chloride and perchlorate salts was studied by measurement of the Cl- and ClO4- resonances and the observation of the perchlorate stretching frequency by use of nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FT-IR), respectively, for a variety of ionophores in various solutions and in large unilaminar vesicles (LUVs). The NMR line widths of chloride and perchlorate were larger in solutions containing the neutral ionophores valinomycin (Val) and nonactin (Non) than in solutions containing the negatively charged ionophores nigericin (Nig), lasalocid (Las), and monensin (Mon). The viscosity-corrected perchlorate NMR line widths in solutions containing Val and Las were significantly negatively correlated (r2 > or = 0.99) with the dielectric constant of the solvent. Solvents with low dielectric constants favored ion pair formation. From methanolic solutions containing the Li+, Na+, K+, and Cs+ salts of Cl- and ClO4-, it was determined that the cation with the highest selectivity for the ionophore affords the most ion pairing. A decrease in pH from 7 to 3 had no significant effect on the NMR line widths of chloride and perchlorate in methanolic solutions containing Val, whereas a similar decrease in pH in a methanolic solution containing Mon caused a 2-fold increase in the line widths. The FT-IR difference spectrum of KClO4 in a methanolic solution containing Val showed splitting at the perchlorate stretching frequency. No band splitting was observed in the FT-IR difference spectrum of KClO(4) in methanolic solutions containing Las. The efflux of 35Cl in LUVs containing the neutral ionophore Val followed first-order kinetics with an efflux constant of 1.70 x 10(-3) x min(-1), as determined by 35Cl NMR spectroscopy. The induction of increased membrane permeability in LUVs by the ionophore was determined to be negligible for Val and Nig by fluorescence spectroscopy.     

Synthesis and antifolate activity of 2,4-diamino-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine analogues of trimetrexate and piritrexim

2,4-Diamino-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidines with di- and trimethoxyaralkyl substitution at the 6-position were synthesized from the N⁶-unsubstituted compound and appropriate aralkyl bromides in N,N-dimethylformamide solution containing a catalytic amount of sodium iodide. An improved method of preparation of 2,4-diamino-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine from 2-amino-6-benzyl-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-4(3H)-one was also developed, in which N² was protected by reaction with pivalic anhydride and the resulting product was subjected consecutively to reaction with 4-chlorophenylphosphorodichloridate and 1,2,4-triazole, ammonolysis to replace the 4-imidazolido group and remove the N²-pivaloyl group, and catalytic hydrogenolysis to remove the 6-benzyl group. In assays of the ability of the products to inhibit dihydrofolate reductase from Pneumocystis carinii, and Toxoplasma gondii, and rat liver the most active of the compounds tested was 2,4-diamino-6-(2′-bromo-3′,4′,5′-trimethoxybenzyl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine. The concentration of this compound needed to inhibit enzyme activity by 50% was 0.51 μM against the P. carinii enzyme, 0.09 μM against the T. gondii enzyme, and 0.35 μM against the rat enzyme. Thus, there was selectivity of binding to T. gondii enzyme, but not P. carinii enzyme, relative to rat enzyme. 2′,5′-Dimethoxybenzyl analogues were less active than the corresponding 3′,4′,5′-trimethoxybenzyl analogues, and compounds with a CH₂CH₂ or CH₂CH₂CH₂ bridge were less active than those with a CH₂ bridge. 2,4-Diamino-6-(2′-bromo-3′,4′,5′-trimethoxybenzyl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine showed greater selectivity than trimetrexate or piritrexim for the P. carinii and T. gondii enzyme, but was less selective than trimethoprim or pyrimethamine. However its molar potency against both enzymes was greater than that of trimethoprim, the antifolate most commonly used, in combination with sulfamethoxazole, for initial treatment of opportunistic P. carinii and T. gondii infections in patients with AIDS and other disorders of the immune system.     

Determination of simple bromophenols in marine fishes by reverse-phase high performance liquid chromatography (RP-HPLC)

Brominated phenols 2- and 4-bromophenol (2-BP and 4-BP); 2,4- and 2,6-dibromophenol (2,4-DBP and 2,6-DBP) and 2,4,6-tribromophenol (2,4,6-TBP) have been identified as key flavor compounds found in seafoods. Depending on their concentrations, they were responsible for marine or ocean flavor (shrimp/crab/fish/sea salt-like) or for phenolic/iodine/iodoform-like off-flavor. In this work a new analytical methodology was developed to determine, simultaneously, such bromophenols in fish meats, based on reversed-phased high-performance liquid chromatographic separation (RP-HPLC). The separation of bromophenols was made onto a Lichrospher 100 RP-18 column using water:acetonitrile gradient at a flow rate of 1.0 mL min⁻¹, using absorbance detection at 286 nm, were the 2-BP, 4-BP, 2,4- and 2,6-DBP show significant absorbtivity values and at 297 nm for 2,4,6-TBP. They were separated in 20 min with a good chromatographic resolution (Rs) for the isomeric compounds: 2- and 4-BP, Rs = 1.23; 2,4- and 2,6-DBP, Rs = 1.63. The calibration curves were linear in the bromophenols concentration range of 200.0-1000 ng mL⁻¹. Under optimized conditions, the detection limit of the HPLC method was 127 ng mL⁻¹ for 2-BP; 179 ng mL⁻¹ for 4-BP; 89.0 ng mL⁻¹ for 2,4-DBP; 269 ng mL⁻¹ for 2,6-DBP and 232 ng mL⁻¹ for 2,4,6-TBP. This method has been applied in determination of bromophenols, isolated by combined steam distillation-solvent extraction with 2 mL of pentane/diethyl ether (6:4), from Brazilian fishes samples, collected on the Atlantic coast of Bahia (13°01′S and 38°31′W), Brazil. The concentration range determined were 0.20 ng g⁻¹ (2-BP) to 299 ng g⁻¹ (2,4,6-TBP). The method proposed here is rapid and suitable for simultaneous quantification of simple bromophenols in fish meat. As long as we know, it is the first analytical methodology, using RP-HPLC/UV, which was developed to determine simple bromophenols in fish meat.     

Can weak interactions modify the binding properties of a strong nitrogen donor? Unusual N-coordination of a phosphoranylidene-substituted pyrazolone unit towards palladium(II) centres: an experimental and theoretical study

Selective N(2)-binding of 3-methyl-1-phenyl-4-(triphenylphosphoranylidene)-2-pyrazolin-5-one (L) has been found in two palladium(II) complexes, [PdCl(2)L(2)](2) and [Pd(o-C(6)H(4)CH(2)NMe(2))Cl](3). X-Ray diffraction studies show that the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located out of the plane defined by the pyrazole ring(s)(dihedral angle between the plane and the Pd-N vector approximately 30 degrees). To investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex , where a single pyrazolone ligand was replaced by NH(3). From this study it could be inferred that the out-of-plane distortion mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the N(1)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh(3) group.     

Antiferromagnetic versus ferromagnetic exchange interactions in bis(μ-O(oximate))dinickel(II) units for a series of closely related cube shaped carboxamideoximate-bridged Ni(4) complexes. A combined experimental and theoretical magneto-structural study

The syntheses, crystal structures, and the experimental and theoretical magnetochemical characterization for three tetrametallic Ni(II) clusters, namely, [Ni(4)(L)(4)(Cl)(2)(MeOH)(2)](ClO(4))(2)·4MeOH (1), [Ni(4)(L)(4)(N(3))(2)(MeOH)(2)](ClO(4))(2)·2MeOH (2), and [Ni(4)(L1)(4)(pyz)(2)(PhCOO)(2)(MeOH)(2)](ClO(4))(2)·7MeOH (3) (where HL and HL1 represent bipyridine-2-carboxamideoxime and pyrimidine-2-carboxamideoxime, respectively) are reported. Within the Ni(4)(2+) units of these compounds, distorted octahedral Ni(II) ions are bridged by carboxamideoximato ligands to adopt a distorted tetrahedral disposition. The Ni(4)(2+) unit, of C(2) symmetry, can also be viewed as a cube with single [O-atom] and double [NO oxime] bridging groups as atom edges, which define two almost square-planar Ni(O)(2)Ni rings and four irregular hexagonal Ni(NO)(2)Ni rings. To analyze the magnetic properties of 1-3, we have considered the simplest two-J model, where J(1) = J(2) (exchange interactions between the Ni(II) ions belonging to the Ni(O)(2)Ni square rings) and J(a) = J(b) = J(c) = J(d) (exchange interactions between the Ni(II) ions belonging to the Ni-(NO)(2)Ni hexagonal rings) with the Hamiltonian H = -J(1)(S(1)S(2) + S(3)S(4)) - J(a)(S(1)S(3) + S(1)S(4) + S(2)S(3) + S(2)S(4)). The J(1) and J(a) values derived from the fitting of the experimental susceptibility data are -5.8 cm(-1) and -22.1 cm(-1) for 1; -2.4 cm(-1) and -22.8 cm(-1) for 2, and +15.6 cm(-1) and -10.8 cm(-1) for 3. The magneto-structural results and density-functional theory (DFT) calculations demonstrate that the exchange interactions inside the Ni(μ-O)(2)Ni square rings depend on the Ni-O-Ni bridging angle (θ) and the out-of-plane angle of the NO oximate bridging group with respect to the Ni(O)(2)Ni plane (τ), whereas the interactions propagated through the Ni-N-O(Ni)-Ni exchange pathways defining the side of the hexagonal rings depend on the Ni-N-O-Ni torsion angle (α). In both cases, theoretical magneto-structural correlations were obtained, which allow the prediction of the angle for which ferromagnetic interactions are expected. For compound 3, the existence of the axial magnetic exchange pathway through the syn-syn benzoate bridge may also contribute (in addition to the θ and τ angles) to the observed F interaction in this compound through orbital countercomplementarity, which has been supported by DFT calculations. Finally, DFT calculations clearly show that the antiferromagnetic exchange increases when the dihedral angle between the O-Ni-O planes of the Ni(μ-O)(2)Ni square ring, β, increases.     

Determination of Cd and Pb in biological reference materials by electrothermal atomic absorption spectrometry: A comparison of three ultrasonic-based sample treatment procedures

Three different ultrasonic-based sample treatment approaches, the automated ultrasonic slurry sampling, the ultrasonic assisted acid solid-liquid extraction (ASLE) and the enzymatic probe sonication (EPS) were compared and discussed for the determination of Cd and Pb by ET-AAS in biological reference materials. The sample mass chosen to perform the analysis was 10 mg and the liquid volume was 1 ml of nitric acid 1 M. The best results were obtained with the slurry procedure with which it was possible accurate and precise determination of the Cd and Pb content in four of the five reference materials studied. Optimum performance (total metal extraction) of ASLE assisted by ultrasound for Cd was only achieved in two of the four materials assessed whereas total Pb recovery was only possible in three of the five samples. Total extraction with the enzymatic probe sonication was only obtained for Cd in oyster tissue. Neither ASLE nor EPS were able to extract Cd or Pb from spruce needles. Pb concentration obtained after EPS was found to be highly dependent from sample centrifugation speed and time.