Synthesis and N.m.r. studies of bis-trisubstituted phosphine platinum(o) and palladium(o) complexes with push-pull olefins

Summary Platinum(0) and palladium(0) complexes of the type: P₂M(R₁R₂C=CR₃R₄) (P=trisubstituted phosphine; R₁, R₂, R₃ and R₄ are different groups having electron acceptor or electron donor properties; M=Pt or Pd) with so called pushpull olefins, have been prepared and characterized. In some cases unusual patterns in the n.m.r. spectra of olefinic protons were observed. The spectra were analyzed by computer simulation and general rules for ABMX patterns for this type of complexes are given.     

Origin and development of the concept of wave

The modern notion of wave is the conclusion of a long intellectual process performed during two centuries. The first concept of wave was suggested by the configurations of a vibrating string, but later it was discovered that these configurations may admit singularities, opening, in this wave, the route to the theory of schock waves. The most recent results consist in the characterization of schock fronts in materials with memory.General Lecture presented (in Italian) at the 10th Italian National Congress of Theoretical and Applied Mechanics; AIMETA, Pisa, October 1990.     

Micelle-Bound Metalloporphyrins as Highly Selective Catalysts for the Epoxidation of Alkenes

The porphyrin–surfactant interaction determines the activity of the title catalysts. Amphiphilic porphyrin derivatives (e.g. 1 with M=MnCl, R=CH₂CH₂(OCH₂CH₂)₂OH) are easy to prepare and can be included in micellar phases.     

Coulomb Friction Driving Brownian Motors

We review a family of models recently introduced to describe Brownian motors under the influence of Coulomb friction, or more general non-linear friction laws. It is known that, if the heat bath is modeled as the usual Langevin equation (linear viscosity plus white noise), additional non-linear friction forces are not sufficient to break detailed balance, i.e. cannot produce a motor effect. We discuss two possibile mechanisms to elude this problem. A first possibility, exploited in several models inspired to recent experiments, is to replace the heat bath's white noise by a "collisional noise", that is the effect of random collisions with an external equilibrium gas of particles. A second possibility is enlarging the phase space, e.g. by adding an external potential which couples velocity to position, as in a Klein-Kramers equation. In both cases, non-linear friction becomes sufficient to achieve a non-equilibrium steady state and, in the presence of an even small spatial asymmetry, a motor effect is produced.     

Synthesis, Characterization, and Electrochemistry of Ruthenium Porphyrins Containing a Nitrosyl Axial Ligand

Two ruthenium nitrosyl porphyrins have been synthesized and characterized by spectroscopic and electrochemical methods. The investigated compounds are represented as [(TPP)Ru(NO)(H(2)O)]BF(4) and (TPP)Ru(NO)(ONO) where TPP is the dianion of 5,10,15,20-tetraphenylporphyrin. (TPP)Ru(NO)(ONO) crystallizes in the tetragonal space group I4, with a = 13.660(1) ?, c = 9.747(1) ?, V = 1818.7(3) ?(3), and Z = 2, 233 K. The most chemically interesting feature of the structure is that the nitrosyl and O-bound nitrito groups are located axial and trans to one another. Both complexes undergo an irreversible reduction at the metal center which is accompanied by dissociation of the axial ligand trans to NO. The addition of 1-10 equiv of pyridine to [(TPP)Ru(NO)(H(2)O)]BF(4) in CH(2)Cl(2) containing 0.1 M TBAP leads to the formation of [(TPP)Ru(NO)(py)](+), a species which is reversibly reduced at E(1/2) = -0.29 V. The electrochemical data indicate that (TPP)Ru(NO)(ONO) can also be converted to [(TPP)Ru(NO)(py)](+) in CH(2)Cl(2) solutions containing pyridine but only under specific experimental conditions. This reaction does not involve a simple displacement of the ONO(-) axial ligand from (TPP)Ru(NO)(ONO) but occurs after reduction of (TPP)Ru(NO)(ONO) to (TPP)Ru(NO)(py) followed by reoxidation to [(TPP)Ru(NO)(py)](+).     

Sul principio dell'effetto giroscopico per i solidi di massa variabile

Sunto Per un giroscopio di massa variabile si stabilisce che condizione necessaria e sufficiente perchè il principio dell'effetto giroscopico conservi la forma classica (pensandovi però variabile il momento di inerzia) è che il momento equatoriale delle forze esterne (ivi comprese le forze del getto) abbia direzione non invariabile nel corpo. A Giovanni Sansone nel suo 70^mo compleanno.     

Sulla propagazione di onde ordinarie di discontinuità in un solido incomprimibile soggetto a transformazioni reversibili adiabatiche

Sunto Si stabiliscono, e si applicano ad un caso particolare notevole, le condizioni atte ad assicurare la propagazione di onde ordinarie adiabatiche in solidi incomprimibili. Ad Antonio Signorini nel suo 70^mo compleanno.