Synchronous fluorimetric determination of salicylic acid and diflunisal in human serum using partial least-squares calibration

The simultaneous determination of salicylic acid and diflunisal in human serum has been accomplished by synchronous fluorimetry, in combination with partial least-squares multivariate calibration. The total luminescence information of the analytes has been used to optimize the spectral data set for the calibration, by analysis of the three-dimensional excitation-emission matrices. The synchronous spectrum, maintaining a constant difference of Deltalambda = 128 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. The method is based on the fluorescence of these compounds in chloroform containing 1% (v/v) acetic acid. Serum samples are treated with trichloroacetic acid to remove the proteins, and both analytes are extracted into chloroform-1% (v/v) acetic acid prior to the determination. For concentrations ranging from 60-240 mug ml(-1) of each drug, analytical recoveries range from 96% to 103% for salicylic acid and from 97% to 105% for diflunisal.     

Factors influencing the distribution pattern of porphyrins in cell membranes

The mechanism of the sensitizer-membrane interactions has been studied by following the distribution properties of selected porphyrins, including haematoporphyrin (HP) and protoporphyrin (PP), into unilamellar liposomes of dipalmitoyl phosphatidylcholine (DPPC). The endomembrane distribution of HP and PP has been checked as a function of the membrane fluidity and composition by fluorescence polarization and quenching techniques. At porphyrin concentrations below 0.5 microM, HP and PP exclusively localize in the inner phospholipid monolayer; at higher concentrations, the outer monolayer also becomes populated. The porphyrin binding sites in liposomes, however, are different for HP and PP: HP preferentially distributes into water-accessible lipid regions, while PP localizes in the most hydrophobic loci of the lipid matrix. A porphyrin redistribution occurs when the fluidity properties of the liposomes are changed by addition of cholesterol or cardiolipin. In DPPC-cholesterol vesicles, all HP molecules dissolve in DPPC-rich regions while all PP molecules partition in cholesterol-rich environments. In DPPC-cardiolipin vesicles both porphyrins preferentially localize in regions accessible to the external medium. The effect of the nature of the carrier on porphyrin distribution in membranes has been studied by following the uptake and photosensitization properties of free and DPPC-incorporated PP and HP with rat liver mitochondria. The porphyrin photosensitizing efficiency has been checked by following the impairment of the respiratory function of mitochondria upon irradiation. Liposome-bound HP is less active than aqueous HP in determining membrane photodamage in mitochondria. On the contrary, aqueous PP is a very poor sensitizer as compared to a DPPC liposome-entrapped drug.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modeling of <Superscript>226</Superscript>Ra behavior in a Spanish estuary affected by the phosphate industry

The Odiel and Tinto rivers, southwest Spain, form a fully mixed estuary. An industrial area that includes a complex dedicated to the production of phosphate fertilizers is located by the Odiel River. This complex released phosphogypsum wastes directly to the Odiel River and also disposed them on open air piles located by the Tinto River. Due to new EU regulations, wastes are not directly released to the Odiel from 1998 on, although they are still disposed on the open air piles. The behavior of ²²⁶Ra in a system like this estuary is complex, since radionuclides are affected by tidal actions and interactions with sediments through adsorption/desorption reactions and erosion/deposition processes. A numerical 2D depth-averaged model of the estuary has been developed, including processes mentioned above. It has been applied to reproduce experimental data measured after a release from the industrial complex in the Odiel River and after an accidental release in the Tinto River from the gypsum piles. The model has also been applied to simulate the self-cleaning process observed in the estuary after the direct releases from the fertilizer complex were stopped.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Binuclear copper(II) oxidation products from copper(I) complexes with tridentate ligands. Magnetostructural characterization

The bis-pyridine tridentate ligands (6-R-2-pyridylmethyl)-(2-pyridylmethyl) benzylamine (RDPMA, where R = CH(3), CF(3)), (6-R-2-pyridylmethyl)-(2-pyridylethyl) benzylamine (RPMPEA, where R = CH(3), CF(3)), and the bidentate ligand di-benzyl-(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) have been synthesized and their copper(I) complexes oxidized in a methanol solution to afford self-assembled bis-micro-methoxo-binuclear copper(II) complexes (1, 2, 4, 6) or hydroxo- binuclear copper(II) complexes (3). Oxidation of the nonsubstituted DPMA (R = H) in dichloromethane gives a chloride-bridged complex (5). The crystal structures for [Cu(MeDPMA)(MeO)](2)(ClO(4))(2) (1), [Cu(RPMPEA)(MeO)](2)(ClO(4))(2) (for 2, R= Me, and for 4, R = CF(3)), [Cu(BiBzMePMA)(MeO)](2)(ClO(4))(2) (6), [Cu(FDPMA)(OH)](2)(ClO(4))(2) (3), and [Cu(DPMA)(Cl)](2)(ClO(4))(2) (5) have been determined, and their variable-temperature magnetic susceptibility has been measured in the temperature range of 10-300 K. The copper coordination geometries are best described as square pyramidal, except for 6, which is square planar, because of the lack of one pyridine ring in the bidentate ligand. In 1-4 and 6, the basal plane is formed by two pyridine N atoms and two O atoms from the bridging methoxo or hydroxo groups, whereas in 5, the bridging Cl atoms occupy axial-equatorial sites. Magnetic susceptibility measurements show that the Cu atoms are strongly coupled antiferromagnetically in the bis-methoxo complexes 1, 2, 4, and 6, with -2J > 600 cm(-)(1), whereas for the hydroxo complex 3, -2J = 195 cm(-)(1) and the chloride-bridged complex 5 shows a weak ferromagnetic coupling, with 2J = 21 cm(-)(1) (2J is an indicator of the magnetic interaction between the Cu centers).     

Expeditious approach to 5-aroyl-pyrrolidinones by a novel PIFA-mediated alkyne amidation reaction

[reaction: see text] A novel metal-free approach to the alkyne amidation reaction is presented. The oxidation of properly substituted amides by the hypervalent iodine reagent PIFA provides the generation of a nitrenium ion that can react intramolecularly with a triple bond, leading to the construction of the title compounds.     

Liquid-gas coexistence and critical point shifts in size-disperse fluids

Specialized Monte Carlo simulations and the moment free energy (MFE) method are employed to study liquid-gas phase equilibria in size-disperse fluids. The investigation is made subject to the constraint of fixed polydispersity, i.e., the form of the "parent" density distribution rho(0)(sigma) of the particle diameters sigma, is prescribed. This is the experimentally realistic scenario for, e.g., colloidal dispersions. The simulations are used to obtain the cloud and shadow curve properties of a Lennard-Jones fluid having diameters distributed according to a Schulz form with a large (delta approximately 40%) degree of polydispersity. Good qualitative accord is found with the results from a MFE method study of a corresponding van der Waals model that incorporates size dispersity both in the hard core reference and the attractive parts of the free energy. The results show that polydispersity engenders considerable broadening of the coexistence region between the cloud curves. The principal effect of fractionation in this region is a common overall scaling of the particle sizes and typical interparticle distances, and we discuss why this effect is rather specific to systems with Schulz diameter distributions. Next, by studying a family of such systems with distributions of various widths, we estimate the dependence of the critical point parameters on delta. In contrast to a previous theoretical prediction, size dispersity is found to raise the critical temperature above its monodisperse value. Unusually for a polydisperse system, the critical point is found to lie at or very close to the extremum of the coexistence region in all cases. We outline an argument showing that such behavior will occur whenever polydispersity affects only the range, rather than the strength of the interparticle interactions.     

Intrinsic reaction coordinate calculations for reaction paths possessing branching points

A 3-21+G energy surface corresponding to the proton transfer reaction in the hydroperoxyl anion solvated by one water molecule presents interesting topological features. In particular the intrinsic reaction coordinate that begins at the transition state does not lead to a minimum but to a saddle point of second order passing through two branching points. A new strategy to obtain the true reaction path in these cases is proposed.     

Synthesis and properties of compressed dihydride complexes of iridium: theoretical and spectroscopic investigations

Reaction of [Cp*Ir(P-P)Cl][B(C6F5)4] (P-P = bisdimethydiphosphinomethane (dmpm), bisdiphenyldiphosphinomethane (dppm)) with [Et3Si][B(C6F5)4] in methylene chloride under 1 atm of hydrogen gas affords the dicationic compressed dihydride complexes [Cp*Ir(P-P)H2][B(C6F5)4]2. These dicationic complexes are highly acidic and are very readily deprotonated to the corresponding monohydride cations. When the preparative reaction is carried out under HD gas, the hydride resonance exhibits JHD = 7-9 Hz, depending upon the temperature of observation, with higher values of JHD observed at higher temperatures. A thermally labile rhodium analogue, [CpRh(dmpm)(H2)][B(C6F5)4]2, was prepared similarly. A sample prepared with HD gas gave JHD = 31 Hz and J(HRh) = 31 Hz, allowing the Rh complex to be identified as a dihydrogen complex. Quantum dynamics calculations on a density functional theory (DFT) potential energy surface have been used to explore the structure of the Ir complexes, with particular emphasis on the nature of the potential energy surface governing the interaction between the two hydride ligands and the Ir center.