Cobalt blood levels after total hip replacement (THR): a new follow-up study in Trieste (Italy)

Cobalt and chromium release in patients undergone a metal-on-metal total hip replacement (THR) is a matter recently discussed and whose we do not have enough information about it yet. In literature there is little data and not completely indicative, in the biological fluids and organs the amounts of released metals are different. This is also due to the fact that cobalt and chromium blood levels can change depending on physical and working activity, individual feeding and metabolism. The results obtained confirm the presence of an increase of cobalt inthe blood of patients after total hip replacement, while the chromium levels are almost alike: average values in patients operated are 4.1 +/- 1.5 microg/L for cobalt (0.3 +/- 0.1 microg/L in the control group) and 4.5 +/- 2.9 microg/L for chromium (4.7 +/- 2.4 microg/L in the control group). In spite of the cobalt values stand below the concentration generally considered dangerous, the difference between the two examined groups points out that a risk exists for the health of these patients. These results must be confirmed by further studies, providing better information and more reliable and biocompatible materials.     

A novel application of the Diels-Alder reaction: nitronaphthalenes as normal electron demand dienophiles

Thermal reactions between nitronaphthalenes and butadienes were studied. It was demonstrated that these reactions are capable of undergoing the normal electron demand Diels-Alder reaction, with a variety of dienes affording the phenanthrene derivatives. The influence of the extension and type of substitution was also discussed. When the electron-withdrawing activation of the naphthalenic nucleus or the donor properties of the dienes were not enough, N-naphthylpyrroles were detected as main product, suggesting that a competitive reaction would probably take place. The results clearly confirmed the dienophilic nature of nitronaphthalenic double bonds and provided an alternative procedure for phenanthrene derivatives and N-naphthylpyrroles' synthesis. The relative reactivity of the reactants and the viability of the reactions were discussed from a theoretical point of view.     

On the layering transition of an SOS surface interacting with a wall. II. The Glauber dynamics

We continue our study of the statistical mechanics of a 2D surface above a fixed wall and attracted towards it by means of a very weak positive magnetic fieldh in the solid on solid (SOS) approximation, when the inverse temperature is very large. In particular we consider a Glauber dynamics for the above model and study the rate of approach to equilibrium in a large cube with arbitrary boundary conditions. Using the results proved in the first paper of this series we show that for allh(h _k+1 ^* ,h _k ^* ) ({h _k ^* } being the critical values of the magnetic field found in the previous paper) the gap in the spectrum of the generator of the dynamics is bounded away from zero uniformly in the size of the box and in the boundary conditions. On the contrary, forh=h _k ^* and free boundary conditions, we show that the gap in a cube of sideL is bounded from above and from below by a negative exponential ofL. Our results provide a strong indication that, contrary to what happens in two dimensions, for the three dimensional dynamical Ising model in a finite cube at low temperature and very small positive external field, with boundary conditions that are opposite to the field on one face of the cube and are absent (free) on the remaining faces, the rate of exponential convergence to equilibrium, which is positive in infinite volume, may go to zero exponentially fast in the side of the cube.Work partially supported by grant SC1-CT91-0695 of the Commission of European Communities.     

On the two-dimensional stochastic Ising model in the phase coexistence region near the critical point

We consider the two-dimensional stochastic Ising model in finite square with free boundary conditions, at inverse temperature >₀ and zero external field. Using duality and recent results of Ioffe on the Wulff construction close to the critical temperature, we extend some of the results obtained by Martinelli in the low-temperature regime to any temperature below the critical one. In particular we show that the gap in the spectrum of the generator of the dynamics goes to zero in the thermodynamic limit as an exponential of the side length of , with a rate constant determined by the surface tension along one of the coordinate axes. We also extend to the same range of temperatures the result due to Shlosman on the equilibrium large deviations of the magnetization with free boundary conditions.     

Tungsten(VI)-gluconic acid complexes: Polarimetric and13C-N.m.r. Studies in an excess of tungsten(VI)

Summary A polarimetric study of the tungsten (VI)-gluconic acid system in an excess of metal reveals the formation of four stable complexes: two monomers with 1 : 2 and 2: 1 stoichiometries and two dimers of 2:2 composition. The pH ranges of these species, the amount of acid equivalents their formation requires, and their conditional stability constants have also been calculated.The probable coordination of the organic ligand to the metallic centre in solutions containing different metal : ligand ratios has been investigated by¹³C-n.m.r. spectroscopy. The results confirm the formation of different complexes depending on the reagent which is in excess. The behaviour of the system when the metal is in excess is related to that of other polyhydroxylic ligands such as mannitol and sorbitol.     

The deprotonation of benzyl alcohol radical cations: a mechanistic dichotomy in the gas phase as in solution

The gas-phase acidity of ionized benzyl alcohol and of some of its derivatives with selected reference bases has been studied by Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry. The aim was to relate the gas-phase reactivity to the behavior in aqueous solution of the radical cations of benzyl alcohols bearing methoxy substituent(s) on the phenyl ring which are known to undergo deprotonation at both the CH2 and OH groups. The dual reactivity behavior is confirmed in the gas phase, in which the prototypical ion, C6H5CH2OH*+, is deprotonated at both the CH2 and OH groups, whereas the ring hydrogens are not involved. An increasing extent of O-deprotonation is shown as the strength of the base increases. Appropriate methyl substitution, as in the radical cations of C6H5C(Me)2OH and C6H5CH2OMe, allows only O- or C-acidity. The two processes are characterized by comparable thermodynamic features with a Gas-phase Basicity (GB) value of 852 kJ mol(-1) for the cumyloxyl radical and 850 kJ mol(-1) for the alpha-methoxybenzyl radical. The possible origin of the observed mechanistic dichotomy is discussed.     

Preparation and self-assembly of chiral porphyrin diads on the gold electrodes of quartz crystal microbalances: a novel potential approach to the development of enantioselective chemical sensors

Porphyrin diad 1 was synthesized by reaction of the acyl chloride of porphyrin 2 and trans-1,2-dithiane-4,5-diol. The Co complex of this diad was studied as a potential enantioselective receptor for chiral recognition in solution and in the solid state. In solution both enantiomers of limonene induce significant changes in the visible and circular dichroism (CD) spectra of [Co2(1)], while a different behavior is observed in the case of the enantiomeric pair of trans-1,2-diaminocyclohexane. A different efficiency of [Co2(1)] chiral recognition is obtained for these compounds, with a remarkable degree of enantiodiscrimination observed in the case of limonene. Self-assembled monolayers of [Co2(1)] were deposited onto the gold electrodes of quartz crystal microbalances to be used as sensing materials of nanogravimetric sensors operating in the gas phase. The enantiodiscrimination properties of these sensors towards the enantiomeric pairs of chiral analytes have been studied. While in the case of analytes bearing donor ligand atoms we did not observe a remarkable enantioselectivity, a significant degree of chiral discrimination was observed in the case of limonene; this result is particularly encouraging for the potential development of enantioselective chemical sensors for use in an array configuration.     

Acidity of a Cu-bound histidine in the binuclear center of cytochrome C oxidase

Cytochrome c oxidase (CcO) is a crucial enzyme in the respiratory chain. Its function is to couple the reduction of molecular oxygen, which takes place in the Fea3-CuB binuclear center, to proton translocation across the mitochondrial membrane. Although several high-resolution structures of the enzyme are known, the molecular basis of proton pumping activation and its mechanism remain to be elucidated. We examine a recently proposed scheme (J. Am. Chem. Soc. 2004, 126, 1858; FEBS Lett. 2004, 566, 126) that involves the deprotonation of the CuB-bound imidazole ring of a histidine (H291 in mammalian CcO) as a key element in the proton pumping mechanism. The central feature of that proposed mechanism is that the pKa values of the imidazole vary significantly depending on the redox state of the metals in the binuclear center. We use density functional theory in combination with continuum electrostatics to calculate the pKa values, successively in bulk water and within the protein, of the Cu-bound imidazole in various Cu- and Cu-Fe complexes. From pKas in bulk water, we derived a value of -266.34 kcal.mol(-1) for the proton solvation free energy (Delta). This estimate is in close agreement with the experimental value of -264.61 kcal.mol(-1) (J. Am. Chem. Soc. 2001, 123, 7314), which reinforces the conclusion that Delta is more negative than previous values used for pKa calculations. Our approach, on the basis of the study of increasingly more detailed models of the CcO binuclear center at different stages of the catalysis, allows us to examine successively the effect of each of the two metals' redox states and of solvation on the acidity of imidazole, whose pKa is approximately 14 in bulk water. This analysis leads to the following conclusions: first, the effect of Cu ligation on the imidazole acidity is negligible regardless of the redox state of the metal. Second, results obtained for Cu-Fe complexes in bulk water indicate that Cu-bound imidazole pKa values lie within the range of 14.8-16.6 throughout binuclear redox states corresponding to the catalytic cycle, demonstrating that the effect of the Fe oxidation states is also negligible. Finally, the low-dielectric CcO proteic environment shifts the acid-base equilibrium toward a neutral imidazole, further increasing the corresponding pKa values. These results are inconsistent with the proposed role of the Cu-bound histidine as a key element in the pumping mechanism. Limitations of continuum solvation models in pKa calculations are discussed.     

Synthesis of N-methyl-3-aza[10] paracyclophane: A rigid analog of phenethylamine

The synthesis of N-methyl-3-aza[10]paracyclophane is reported which represents the first example of this ring system being formed via an acyloin reaction. This 3-aza[10]paraeyclophane ring system behaves physiochemically inbetween the normal [9]- and [10]paracyclophane ring systems. Reductive desulfurization of N-methyl-3-aza[10]paracyclophane-6-ethylene thioketal in ethanol provides a small amount of the title compound and an unexpected, ring-opened product, N-ethyl-N-methyl-p-heptylphenethylamine. A possible mechanism for the ring-opening process is suggested.     

Unusual nitration of substituted 7-amino-1,8-naphthyridine in the synthesis of compounds with antiplatelet activity

Several 1,8-naphthyridine derivatives have been diazotizated to obtain the corresponding hydroxy derivatives or mixture of hydroxy and hydroxy nitro derivatives. The respective amounts of hydroxy and hydroxy nitro derivatives depends on the nature of the substituents, on their position on the naphthyridine nucleus, on the amount of sodium nitrite and on the reaction temperature. A study of the electronic density of some molecules suggests a possible explanation of the effects induced by the nature of the substituents and of their position. Some of the compounds were tested for their ability to inhibit human platelet aggregation in vitro induced by arachidonic acid. Only compound 26 showed interesting antiplatelet activity.