Xanthate complexes of nickel with nitrogen donor ligands. Part V

Nickel(II) xanthate complexes of general formula, [Ni(Rxa)₂(L)] [R = i-Pr, i-Am, xa = OCS^– ₂, L = 4,7-diphenyl-1,10-phenanthroline(baphen), 4,4-dimethyl-2,2-bipyridyl (me₂bpy), 2-9-dimethyl-1,10-phenanthroline(neo) or trans-1,2-diaminocyclohexane (dch)] and [Ni(Rxa)(cyclam)](Rxa) (= 1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized by elemental analyses, i.r. and electronic spectroscopy, magnetic and conductivity measurements. The complexes with cyclam were studied by cyclic voltammetry. Values of magnetic moments at room temperature lie within the 3.25–3.51 B.M. range and thus indicate the presence of two unpaired electrons, except for the complexes with cyclam, where the anomalous values of 1.76 and 1.74 B.M. were obtained in respect to the nickel(II) complexes. Magnetic susceptibility data for [Ni(i-Prxa)(cyclam)](i-Prxa) were measured over the 79–298 K range and indicate no exchange interaction between paramagnetic nickel(II) centres.     

Holo- and hemidirected lead(II) in the polymeric [Pb(4)(mu-3,4-TDTA)2(H2O)2]*4H2O complex. N,N,N',N'-tetraacetate ligands derived from o-phenylenediamines as sequestering agents for lead(II)

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.     

A highly reactive mononuclear Zn(II) complex for phosphodiester cleavage

The activity of a Zn(II) complex of a tetradentate, tripodal ligand for catalyzing phosphodiester cleavage is enhanced 750-fold by introducing three hydrogen bond donors to the ligand. Inhibition studies show that the Zn-aqua complex is the kinetically active form and that it binds the transition state with a formal dissociation constant of 3 x 108 M-1. The effect of these ligand modifications on the transition-state affinity is comparable to the rate acceleration provided by the metal ion itself. Overall, this mononuclear complex is more active than the most reactive dinuclear Zn(II) complexes reported to date.     

Ligand adsorption on an activated carbon for the removal of chromate ions from aqueous solutions

The results presented in this work are related to the design of a guideline to develop specific properties at the surface of an activated carbon (AC). For this, two model aromatic compounds have been synthesized and their electrolytic behavior in aqueous solutions was studied by a potentiometric method. The textural characteristics of the activated carbon were determined by porosimetry methods. The nature of oxygen-carrying functions and the acid-base behavior of the AC surface were characterized by TPD and potentiometric titration methods, respectively. The adsorption and desorption equilibria of the aromatic compounds on activated carbon were measured in aqueous solutions, and the hysteresis between adsorption and desorption, which reveals irreversible adsorption, was discussed on the basis of the frontier orbital theory. HOMO and LUMO orbitals of the adsorbent and adsorbates were calculated, and irreversible adsorption was attributed to the small energy difference between HOMO and LUMO of the aromatic adsorbates and the adsorbent. Adsorption equilibria of K2CrO4 in aqueous solution on the AC alone and on the AC-aromatic ligand adsorbents, respectively, prove the efficient development of specific chemical functions at the carbon surface provided by the adsorbed aromatic compounds.     

Determination of ethyl biscoumacetate and its metabolite 7-hydroxyethyl biscoumacetate in human serum by high-performance liquid chromatography and mass spectrometry.

An efficient reversed-phase high-performance liquid chromatographic method has been developed for the determination of ethyl biscoumacetate (EBA) and its metabolite in human serum, using the mu Bondapak C18 column and methanol-water-phosphoric acid (56:46.8:0.2, v/v/v) as the mobile phase. This method permitted the determination of both EBA and a metabolite in human serum. The latter has been mentioned by other authors only in urine samples, where significant concentrations were found. Identification of the metabolite as 7-hydroxyethyl biscoumacetate was based on its chromatographic separation, followed by isolation from the eluate and direct mass spectrometric identification. It has been found that the higher EBA concentrations in human serum described by Brodie et al. [J. Pharmacol. Exp. Ther., 106 (1952) 453] were caused by the insufficient resolving power of the spectrophotometric method used, leading to overlapping of the UV spectra of the parent drug and its metabolite.     

Static electric dipole polarizability of small sodium aggregates

We present pseudopotential local-spin-density calculations of the static electric polarizability of sodium dimers and trimers and their respective cations. The electronic polarizabilities are obtained from self-consistent calculations in the presence of an external electric field, which is kept sufficiently small to avoid non-linear effects. The calculated polarizability tensor has a strong anisotropy directly related to the geometric and electronic structures of the molecules, the anisotropy being larger for the neutral clusters. The polarizabilities are averaged over the vibrational motion and rotations of the aggregates in order to be compared with the experimental measurements. The obtained values show an improvement in the agreement with experiment with respect to the values calculated in the spherical approximation.     

Synthesis and characterization of trifluoromethyl fluoroformyl peroxycarbonate,CF3OC(O)OOC(O)F

The synthesis of CF(3)OC(O)OOC(O)F is accomplished by the photolysis of a mixture of (CF(3)CO)(2)O, FC(O)C(O)F, CO, and O(2) at -15 degrees C using a low-pressure mercury lamp. The new peroxide is obtained in pure form in low yield after repeated trap-to-trap condensation and is characterized by NMR, IR, Raman, and UV spectroscopy. Geometrical parameters were studied by ab initio methods [B3LYP/6-311+G(d)]. At room temperature, CF(3)OC(O)OOC(O)F is stable for many days in the liquid or gaseous state. The melting point is -87 degrees C, and the boiling point is extrapolated to 45 degrees C from the vapor pressure curve log p = 8.384 - 1715/T (p/mbar, T/K). A possible mechanism for the formation of CF(3)OC(O)OOC(O)F is discussed, and its properties are compared with those of related compounds.     

Early-late heterobimetallic alkoxides as model systems for late-transition-metal catalysts supported on titania

Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies.     

Cholesterol modulates amiodarone-membrane interactions in model and native membranes

The effects of cholesterol, a lipid mostly found in the sarcolemmal membranes, on the interaction of amiodarone with synthetic models of dimyristoylphosphatidylcholine (DMPC) and with native models of mitochondria and brain microsomes was studied. Alterations on the structural order of lipids were assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) probing the bilayer core, and of the propionic acid derivative 3-(p-(6-phenyl)-1,3,5-hexatrienyl)phenylpropionic acid (DPH-PA) probing the outer regions of the bilayer. As detected by the probes and according to classic observations, cholesterol progressively increased the molecular order in the fluid phase of DMPC. Additionally, it modulated the type and extension of amiodarone effects. For low cholesterol concentrations (≤10–15 mol%), amiodarone (50 μM) ordered DMPC bilayers and the effects were almost identical to those observed in pure DMPC. For higher cholesterol concentrations, amiodarone ordering effects decreased slightly and faded for cholesterol concentrations as high as 25 and 30 mol%, when detected by DPH-PA and DPH, respectively. Above these high cholesterol concentrations, a crossover from ordering to disordering effects of amiodarone was apparent, either in the upper region of the bilayer or the hydrophobic core. The effects of amiodarone in native membranes of mitochondria and brain microsomes, in which "native" cholesterol accounts for about 0 and 25 mol%, respectively, correlated reasonably with the results in models of synthetic lipids. There is a close relationship between cholesterol concentration and amiodarone effects, in either synthetic models or native model membranes. Therefore, it may be predicted that the lipid physicochemical properties regulated by cholesterol concentration will also modulate the effects of amiodarone in sarcolemma.     

Evaluation of indoor exposition to benzene, toluene, ethylbenzene, xylene, and styrene by passive sampling with a solid-phase microextraction device

A solid-phase microextraction (SPME) sampling method is developed to evaluate indoor exposure to benzene, toluene, ethylbenzene, xylene, and styrene with gas chromatography and flame ionization detection for quantitative analysis. An SPME holder with a 100-pm polydimethylsiloxane (PDMS) and 65-pm PDMS-divinylbenzene fiber coating is tested in different air relative humidity conditions. The method gives good resolution, shows a linear response, is repeatable, and presents high sensitivity. This method is compared with National Institute of Occupational Safety and Health (NIOSH) active sampling.