The ligand effect on the hydrolytic reactivity of Zn(II) complexes toward phosphate diesters

The catalytic effects of the Zn(II) complexes of a series of poliaminic ligands in the hydrolysis of the activated phosphodiesters bis-p-nitrophenyl phosphate (BNP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) have been investigated. The reactions show first-order rate dependency on both substrate and metal ion complex and a pH dependence which is diagnostic of the acid dissociation of the reactive species. The mechanism of the metal catalyzed transesterification of HPNP has been assessed by solvent isotopic kinetic effect studies and involves the intramolecular nucleophilic attack of the substrate alcoholic group, activated by metal ion coordination. The intrinsic reactivity of the different complexes is controlled by the nature and structure of the ligand: complexes of tridentate ligands, particularly if characterized by a facial coordination mode, are more reactive than those of tetradentate ligands which can hardly allow binding sites for the substrate. In the case of tridentate ligands that form complexes with a facial coordination mode, a linear Br?nsted correlation between the reaction rate (log k) and the pK(a) of the active nucleophile is obtained. The beta(nuc) values are 0.75 for the HPNP transesterification and 0.20 for the BNP hydrolysis. These values are indicated as the result of the combination of two opposite Lewis acid effects of the Zn(II) ion: the activation of the substrate and the efficiency of the metal coordinated nucleophile. The latter factor apparently prevails in determining the intrinsic reactivity of the Zn(II) complexes.     

Surface chemistry study of RuO2/IrO2/TiO2 mixed-oxide electrodes

DSA metal oxide electrodes such as the RuO(2)/IrO(2)/TiO(2) mixed system are widely studied for their excellent electrocatalytic activity. In order to understand their catalytic properties, the comprehension of the surface chemistry involved during electrochemical treatments is crucial. With this aim, RuO(2)/IrO(2)/TiO(2) mixed-oxide electrodes having various noble metal contents were studied by means of secondary ion mass spectrometry (SIMS). In particular, cathodic and anodic polarization and O(2) evolution reactions were carried out to test the electrode behaviour and SIMS analyses were performed after all these treatments. In this way, surface changes induced by electrochemical treatments and depending on electrode composition were widely investigated by SIMS, revealing, for example, the presence of hydration or preferential dissolution phenomena induced by electrochemical processing.     

Thermodynamics of ionization processes for chloro-substituted benzoic acids in water—dimethysulfoxide mixtures at 25°C

The ionization enthalpies of o-, m-, and p-chloro-benzoic acid were measured calorimetrically at 25°C in water—DMSO mixtures ranging from pure water up to 0.8 DMSO mole fraction. In the same mole fraction range, molar free energies and entropies were calculated for the ionization process.The different results obtained for the three acids were explained by taking into account the different effects displayed on the solvation and ionization phenomena by the chlorine atom in the various positions on the aromativ ring.Using the transfer enthalpy of benzoic acid in the same mixtures as a reference point, a solvation sequence is proposed both for the ions and undissociated molecules.     

Synthesis of 2-substituted 1,3-butadienyl compounds by palladium-catalyzed regioselective 1,2-elimination reaction of methylvinylcarbinol acetates

Alkylation of the dianion of 3-methyl-3-buten-2-ol, followed by acetylation and palladium-catalyzed 1,2-elimination reaction of the so obtained methylvinylcarbinol acetates allows to synthesize regioselectively 2-substituted 1,3-butadienyl compounds having high isomeric purity.     

Synthesis of 5H-10,11-dihydropyrazolo[5,1-c]-[1,4]benzodiazepinederivatives. II

Ethyl 3(5)-formylpyrazole-5(3)-carboxylate, 2-nitrobenzyl bromide or 2-nitrobenzoyl chloride are the starting basic materials to prepare with a few reaction steps, pyrazolo[5,1-c][1,4]benzodiazepines bearing at position 2 a substituted propionic chain ( 7–9 ) or bearing at position 5 a carbonyl group ( 12 ). Compounds 7–9, 12 are to be considered aza analogs of the antitumor antibiotic antramycin.     

A New,Stereoselective Approach to the [3.3.3]Propellane System: Synthesis of (±)-modhephene. Preliminary communication

The unusual propellane skeleton of the sesquiterpene modhephene ( 1 ) has been synthesized starting from cyclopentenone ( 2 ). The key step 6 → 7 is an efficient and highly stereoselective intramolecular thermal ene-reaction. Further elaboration of the propellane 7 gave the enone 10 which had been previously converted to (±)-modhephene ( 1 ) in three steps.     

Synthesis and 13C-NMR study of pyrazolo[4,5-c] and pyrazolo[4,3-c benzazepines. III

The synthesis of pyrazolo[4,5-c][1]benzazepin-10-ones 10 and 13 and pyrazolo[4,3-c][1]benzazepin-10-ones 11 and 12 is reported. The structure of compounds 10-13 and that of their parent compounds 2-5 ensues from a ¹³C nmr study.     

Comparative modal analysis of NRD parallelepiped dielectric resonators

The resonance modes of dielectric resonators having parallelepiped shape are extensively investigated in this work referring to the nonradiative dielectric (NRD) topology. Different numerical techniques, both rigorous and approximated (boundary elements, point matching, finite elements, transmission line approaches), are proposed and implemented to compute the relevant resonance spectrum as a function of the involved geometric and electromagnetic parameters. The theoretical results are discussed and compared also in connection with experimental investigations, carried out on suitable prototypes of NRD components. Qualitative and quantitative information is thus achieved to characterize with accuracy and efficiency the basic parameters (resonant frequencies, field configurations, etc.) involved in filter design and in other applications at microwaves and millimeter waves.