Roles of rhenium diimine complexes as metal‐ion probes and photosensitizers in functional polyurethanes

Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10^?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003     

The interfacial conformation of polypropylene glycols and foam behaviour

The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol⁻¹). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability.     

Asymptotic conditions for the electromagnetic form factors of hadrons represented by the VMD model

A system of linear homogeneous algebraic equations for the coupling constant ratios of vector mesons to hadrons is derived by imposing the assumed asymptotic behavior upon the VMD pole parameterization of an hadron electromagnetic form factor. A similar system of equations with a simpler structure of the coefficients, taken as even powers of the vector-meson masses, is derived by means of integral superconvergent sum rules for the imaginary part of the considered form factor using its appropriate -function approximation. Although both systems have been derived starting from different properties of the electromagnetic form factor and they each have their own appearances, it is shown explicitly that they are fully equivalent. Received: 20 March 2002 / Revised version: 3 December 2002 / Published online: 7 March 2003     

Surface tension and density measurements for indium and uranium using a sessile-drop apparatus with glow discharge cleaning

The sessile-drop method is used to measure the surface tension and density of liquid indium and uranium under high vacuum. Measurements are made over the temperature range 156–500°C for In and at the melting point for U. Surface oxides are efficiently removed with a glow discharge system. Drop profiles are captured by photograph and processed using nonlinear regression to yield the surface tension and density. In this regression procedure, normal distances from calculated profiles to data points are minimized. For indium, the density and surface tension measurements yield _mp = 7.05 × 10³kg/m³, d/dT = −0.776 kg/m³·°C, and γ_mp = 0.568 N/m, dγ/dT = −9.45 × 10⁻⁵ N/m·°C. The results for uranium at the melting point are _mp = 17.47 × 10³ kg/m³ and γ_mp = 1.653 N/m.     

A 13C- and 195Pt-NMR. Study of the Complexes trans-PtCl2 (amine) (CH2CH2)

¹³C- and ¹⁹⁵Pt-NMR. spectra for the complexes trans-PtCl₂(amine)(CH₂?CH₂) have been measured. For amine = (S)-N-methyl-α-methylbenzylamine the two diastereomers present may be distinguished from the values ³J(Pt,C). The ¹⁹⁵Pt-chemical shift is shown to be sensitive to subtle differences stemming from intramolecular non-bonded interactions.     

A multipolymer system for organocatalytic alcohol oxidation

A system involving two polymer-supported reagents for the selective and organocatalytic oxidation of alcohols to aldehydes or ketones has been developed in which both polymeric reagents can be recovered and reused.     

Inner-shell and valence-shell electronic excitation of SF6, SeF6 and TeF6 by high energy electron impact: An investigation of potential barrier effects

Inner- and valence-shell electron energy loss spectra of gaseous SF₆, SeF₆ and TeF₆ have been measured at high impact energy (2.0–3.7 keV) and zero degree scattering angle. The resulting inner-shell excitation spectra include F 1s, S 2s and 2p in SF₆: F 1s, Se 3s, 3p and 3d in SeF₆ and F 1s, Te 4s, 4p, 4d and 3d in TeF₆. The results for each of these hexafluorides are interpreted, in the framework of the potential barrier model, as excitations to resonances involving a common manifold of virtual valence (inner-well) orbitals and also to Rydberg (outer-well) orbitals. The below-edge shape resonances in corresponding inner-shell excitation spectra of these hexafluorides show very similar variations in intensities in accord with expectations based on electric-dipole selection rules. This is an indication that these below-edge resonances in SeF₆ and TeF₆ are of the same symmetry as those in SF₆ (i.e. a_1g and t_1u). The continuum (above-edge) shape resonances in SeF₆ also show similar spectral behavior to those of SF₆ and can be understood by including Se 4d and S 3d orbitals in the basis for the respective MO schemes. However, in TeF₆ completely different spectral behavior is observed for the continuum resonances. In particular, there is a dramatic series of intense resonances observed above the Te 3d and 4d edges. The TeF₆ spectrum can only be understood by extending the MO basis set to include the Te 4f orbitals which are even lower lying than the Te 5d orbitals. Therefore, these continuum resonances which are also seen in the F 1 s and Te 3p spectra of TeF₆ are assigned to l=3 (f-type) continuum shape resonances due to involvement of the 4f orbitals rather than the l=2 (d-type) continuum resonances observed in SF₆ and SeF₆. This is the first reported observation of such f-type continuum shape resonances and such considerations will likely prove to be important in the understanding of near-edge spectra of heavy atom containing species. The VSEELS spectra which are very similar for the three hexafluorides also show significant continuum shape resonances. A consideration of both the ISEELS and the VSEELS spectra indicates that there is a weakening of the potential barrier in going through the series from SF₆, SeF₆ to TeF₆.     

Facile fabrication of AgCl@polypyrrole-chitosan core-shell nanoparticles and polymeric hollow nanospheres

A one-step sequential method for preparing AgCl@polypyrrole-chitosan core-shell nanoparticles and subsequently the formation of polypyrrole-chitosan hollow nanospheres is reported. The formation of the core and the shell is performed in one reaction medium almost simultaneously. Transmission electron microscopy (TEM) images show the presence of core-shell nanoparticles and hollow nanospheres. Ultraviolet-visible (UV-vis) studies reveal that AgCl was formed first followed by polypyrrole. X-ray diffration (XRD) and UV-vis studies show that AgCl was present in the core-shell nanoparticles and could be removed completely from the core.     

The Mitsunobu Reaction: Origin,Mechanism, Improvements,and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation–reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.