A fluorescence emission study of the formation of induced premicelles in solutions of polyelectrolytes and ionic surfactants

The interactions between PSS-co-BVE copolymers and ionic surfactants (anionic and cationic) in aqueous solution have been investigated using pyrene as a photophysical probe. Static and dynamic fluorescence determinations have been used to obtain information about the microenvironments formed between both species. Micropolarity studies using the I1/I3 ratio of the vibronic bands of pyrene and the behavior of the I(E)/I(M) ratio between the monomer and excimer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and the oppositely charged surfactants lead to the formation of induced premicelles at surfactant concentrations lower than the cmc of the surfactants. This aggregation process is assumed to be due to electrostatic attraction. At the same concentration, the excimer-to-monomer emission ratio shows its first peak. At higher surfactant concentrations, near the cmc, micelles with the same properties as those found in pure aqueous solution are formed. On the other side, systems containing an anionic surfactant do not show this behavior at low concentrations. There is no apparent dependence of the cac on the composition of the polymer, reinforcing the assumption that the electrostatic interactions induce the formation of the premicelles. The values of the cac's follow the same trend as for the cmc's, DTAC>DTAB>CTAC. The polarity of the induced premicelles, as measured by the I1/I3 ratio, also indicates that the microdomains formed by the longer chain surfactants are more hydrophobic than those of the shorter chain surfactants, as also happens with real micelles.     

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.     

New zinc phosphates decorated by imidazole-containing ligands

Four new zinc phosphates [Zn(HPO4)(C6H9N3O2)] (1), [Zn(HPO4)(C4H6N2)].H2O (2), [Zn2(HPO4)2(C14H14N4)].2H2O (3), and [Zn(HPO4)(C14H14N4)] (4) were synthesized in the presence of d-histidine, 1-methylimidazole, 1,4-bis(imidazol-1-ylmethyl)benzene (L1), and 1,2-bis(imidazol-1-ylmethyl)benzene (L2), respectively, and their structures were determined by X-ray crystallography. The inorganic framework of compounds 1, 2, and 3 is composed of vertex-shared ZnO3N and HPO4 tetrahedra that form four rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 1 and 2 the organic groups (monoimidazole ligand) are located at each side of the ladders, while in 3 the bisimidazole ligand, 1,4-bis(imidazol-1-ylmethyl)benzene, links the ladders together to form a novel 2D structure. Compound 1 is the first zinc phosphate framework to be templated by an N-bonded chiral amino acid. In 4 the zero-dimensional four rings are joined together by the linear bridging ligand, 1,2-bis(imidazol-1-ylmethyl)benzene, to generate a one-dimensional framework with a new face-to-face structural motif. The 3D structure of compound 4 is stabilized by hydrogen-bonding, pi-pi interactions, and C-H...pi interactions. The approach of incorporating multifunctional ligands into zinc phosphate frameworks and linking the inorganic zinc phosphates subunits by an organic ligand provides opportunities for the design of new inorganic-organic open frameworks.     

M(R-dmet)2] bis(1,2-dithiolenes): a promising new class intermediate between [M(dmit)2] and [M(R,R'-timdt)2] (M = Ni, Pd, Pt)

We report the first examples of metal dithiolenes belonging to the class [M(R-dmet)(2)] [R-dmet = formally monoreduced N-substituted thiazolidine-2,4,5-trithione; R = Et, M = Ni (1), Pd (2), Pt (3)]. A comparative spectroscopic, electrochemical, and density functional theory theoretical investigation indicates that [M(R-dmet)(2)] complexes show features intermediate between those of the dithiolenes belonging to the previously reported classes [M(R,R'-timdt)(2)] and [M(dmit)(2)] (R,R'-timdt = formally monoreduced N,N'-disubstituted imidazolidine-2,4,5-trithione; dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). UV-vis-near-IR spectroscopy and cyclic voltammetry/differential pulsed voltammetry measurements performed on 1 and 3 proved that the new dithiolenes are stable as neutral, monoanionic, and bianionic species and feature a near-IR electrochromic absorption falling at about 1000 and 1250 nm for neutral and monoanionic species, respectively.     

Ytterbium triflate-promoted tandem one-pot oxidation-Cannizzaro reaction of aryl methyl ketones

[reaction: see text] Ytterbium triflate was shown to be an effective catalyst in promoting the synthesis of either isopropyl esters or free alpha-hydroxy-arylacetic acids from substituted aromatic glyoxals and aryl methyl ketones, respectively. The reaction to provide acids starting from differently substituted ketones was carried out by an environmentally friendly method using an aqueous medium as a solvent and giving the adducts in 78-99% yield without any further purification after the usual workup.     

X-ray spectroscopic characterization of Cu2+-phenanthroline complexes intercalated in α-zirconium phosphate

X-ray photoelectron spectroscopy provides evidence that when [Cu(phen)₂]²⁺(phen = 1,10-phenanthroline) is diffused between the layers of -zirconium phosphate, the complex species does not remain intact after intercalation, but some Cu-N bonds are broken, replaced with Cu-O bonds and the released nitrogen atoms can now interact with the PO₃-OH groups of the host. XPS also provides evidence for coordination of the Cu²⁺ ions when they are diffused by ion exchange in the phenanthroline--zirconium phosphate intercalation compound. Although Cu²⁺ and phen are in a 1 : 1 molar ratio in the interlayer region of the host, so that a 1 : 1 coordination could be expected between the two species, the characteristic peaks of the uncoordinated phenanthroline, even though at a low intensity, are still present. The differences between the two Cu(II)-intercalation compounds are discussed.     

Chemical and radiochemical characterization of depleted uranium (DU) in Kosovo soils

As is well known ammunitions containing depleted uranium (DU) were used by NATO during the Balkan war. The paper deals with the determination of uranium alpha emitting radiosotopes in Kosovo soils by chemical separation and alpha spectrometry. The samples were collected by CISAM (Centro Interforze Studi ed Applicazioni Militari, S. Piero a Grado, Livorno) in the period November 1999-April 2000. The DU distribution in soil appeared very disomogeneous; the isotope weight percentages for U-238, U-235 and U-234 resulted 99.76, 0.24 and 7.24.10(-4) respectively; consequently the activity distribution was 86.42%, 1.31%, 11.63% and the isotope ratios were 1.52.10(-2) and 0.134 for U-235/U-238 and U-234/U-238 showing clearly the presence of DU. A small peak at 4.49 MeV (U-236) in the alpha spectrum indicated that the used DU was the by-product of exhausted uranium reprocessing. In order to determine the chemical and physiological solubility of uranium a fractionation study was carried out by using the Tessier method: 55% of uranium showed a fair solubility, but 45% was solubilized only by 8 M HNO3.