Studies on comblike polymers. X. Characterization of comblike polyesters by 13C NMR spectroscopy

The ¹³C NMR spectra of aromatic comblike polyesters obtained from 1,2-icosanediol and isomeric phthalic acids are reported and discussed. The analysis shows that the most informative spectral regions are those of the carbonyl and quaternary carbon resonances, whose peak multiplicities have been interpreted in terms of dyad and triad sequences. The results indicate that the extent of structural characterization possible for the polymers examined is dependent on the type of isomerism of the aromatic acid involved.     

Aggregation behavior of tetrakis(4-sulfonatophenyl)porphyrin in AOT/water/decane microemulsions

AOT/water/decane microemulsions have been used to entrap the water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4). Quasi-elastic light scattering technique has confirmed the confinement of the porphyrin and its various aggregates into the inner water pool. Various species have been detected as function of the size of the microemulsions, concentration of the porphyrin, pH, and aging of the solutions by using a combination of UV-vis absorption, steady fluorescence emission, fluorescence lifetime measurements, and time-resolved fluorescence anisotropy. Under neutral pH conditions, the porphyrin is present as the free base monomer (S414) in the inner water compartment, and it is free to rotate when the size of the droplet is large enough and the porphyrin concentration is low. On increasing the concentration and/or decreasing the microemulsion size, a H-dimer of the free base (S406) is prevalently formed. Aging both the S414 and S406 species leads to the formation of a new species (S424), which has been postulated as a H-type dimer of the diacid porphyrin. On decreasing the pH, the species S414 and S406 almost instantaneously convert into the diacid porphyrin, which is monomeric (S434). This latter is an intermediate in the eventual formation of J-aggregated TPPS4 (S490). A marked stability has been observed for the S424 species, which do not interconvert on changing the pH of the bulk aqueous phase.     

Localization Operators and Exponential Weights for Modulation Spaces

We study localization operators within the framework of ultradistributions. More precisely, given a symbol a and two windows φ₁, φ₂, we investigate the multilinear mapping from to the localization operator Results are formulated in terms of modulation spaces with weights which may have exponential growth. We give sufficient and necessary conditions for a to be bounded or to belong to a Schatten class. As an application, we study symbols defined by ultra-distributions with compact support, that give trace class localization operators.     

The electrostatics of Einstein’s unified field theory

When sources are added at their right-hand sides, and g_(ik) is a priori assumed to be the metric, the equations of Einstein’s Hermitian theory of relativity were shown to allow for an exact solution that describes the general electrostatic field of n point charges. Moreover, the injunction of spherical symmetry of g_(ik) in the infinitesimal neighbourhood of each of the charges was proved to yield the equilibrium conditions of the n charges in keeping with ordinary electrostatics. The tensor g_(ik), however, cannot be the metric of the theory, since it enters neither the eikonal equation nor the equation of motion of uncharged test particles. A physically correct metric that rules both the behaviour of wave fronts and of uncharged matter is the one indicated by Hély.In the present paper it is shown how the electrostatic solution predicts the structure of the n charged particles and their mutual positions of electrostatic equilibrium when Hély’s physically correct metric is adopted.     

Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity

We theoretically and experimentally investigated the reorganization of cladding modes in high-refractive-index- (HRI-) coated long-period gratings (LPGs), focusing on the influence of refractive-index sensitivity. When azimuthally symmetric nanoscale HRI coatings are deposited along LPG devices, a significant modification of the distribution of cladding modes occurs, depending on the layers' features (refractive index and thickness) and on the external refractive index. In particular, if these parameters are properly chosen, a transition between cladding modes and overlay modes occurs. Numerical and experimental effects of the mode transition on the sensitivity of the surrounding refractive index are described.     

Electrochemical deposition and structural characterization of Au-Sn alloys

In the present work the electrochemical deposition of Au-Sn alloys is addressed and a cyanide-free process is presented. The electrolyte is an acidic thiourea solution containing gold as a Au[CS(NH₂)₂]⁺ complex and tin as stannous ions. Results concerning the plating process development and deposit characterization are reported. Au-Sn alloy films with a Sn content up to 50 at% and a single-phase structure can be obtained from the acidic thiourea–Au(I) solution under pulsed current plating conditions. Alloy deposits show three main crystal structures: a face centred cubic (fcc) Au(Sn) solid solution, extending up to 7 at% Sn; a hexagonal close-packed structure, of the same type as the metallurgical phase, up to about 18 at% Sn; and a NiAs-type structure, corresponding to the phase of the equilibrium diagram, with an enlarged homogeneity range. Mechanical properties of thin layers of Au-Sn alloys derived from micro-indentation measurements follow the structural modification with the alloy composition. The ordered intermetallic phases occurring in the equilibrium binary system, in particular the and phases at 8 at% and 16 at% Sn, respectively, are not detected in the electrodeposited alloys. The main factors controlling electrochemical phase formation are pointed out, considering the differences between the phase structure of the electrodeposited alloys and the equilibrium phase diagram.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Nature of urea-fluoride interaction: incipient and definitive proton transfer

1,3-bis(4-nitrophenyl)urea (1) interacts through hydrogen bonding with a variety of oxoanions in an MeCN solution to give bright yellow 1:1 complexes, whose stability decreases with the decreasing basicity of the anion (CH3COO- > C6H5COO- > H2PO4- > NO2- > HSO4- > NO3-). The [Bu4N][1.CH3COO] complex salt has been isolated as a crystalline solid and its molecular structure determined, showing the formation of a discrete adduct held together by two N-H...O hydrogen bonds of moderate strength. On the other hand, the F- ion first establishes a hydrogen-bonding interaction with 1 to give the most stable 1:1 complex, and then on addition of a second equivalent, induces urea deprotonation, due to the formation of HF2-. The orange-red deprotonated urea solution uptakes carbon dioxide from air to give the tetrabutylammonium salt of the hydrogencarbonate H-bond complex, [Bu4N][1.HCO3], whose crystal and molecular structures have been determined.     

Does a Reinforced Kinetic Macrocyclic Effect Exist? The Demetallation in Strong Acid of Copper(II) Complexes with Open and Cyclic Tetramines Containing a Piperazine Fragment

The demetallation in acidic solution of the Cu(II) complexes with open-chain and cyclic tetramines containing a piperazine unit (2 and 3) has been investigated in terms of its kinetic aspects and compared with the behaviour of unsubstituted counterparts (tetramines 1 and 4). The presence of the piperazine fragment slows demetallation of the open-chain-ligand complex owing to the activation barrier associated with the conformational change from boat-to-half-boat; however, it does not affect the demetallation of the macrocyclic complex, which involves the spontaneous boat-to-twist conformational change. Thus, lateral reinforcement of a cyclam-like ligand does not add any further contribution to the typical inertness in demetallation of macrocyclic complexes.     

Further insights on the high-low spin interconversion in nickel(II) tetramine complexes. Solvent and temperature effects

The spin interconversion equilibrium involving the [Ni(II)(cyclam)]2+ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between DeltaHdegrees and Gutmann's Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the Ni(II)-to-Ni(III) oxidation process and negative linear relationship has been found between the E1/2(Ni(III)/Ni(II)) and DN. General behaviour is related to the intensity of the metal-solvent axial bonds in the octahedrally elongated cyclam complexes (of both Ni(II) and Ni(III)).