Single‐Component Upconverting Polymeric Nanoparticles

Low‐power light upconversion is a highly desirable feature for a broad range of applications and new materials enabling this process are sought in both bulk and particulate form. Here, the preparation of upconverting nanoparticles is reported from a methacrylic terpolymer bearing diphenylanthracene and meso‐phenoxytris(heptyl)porphyrin pendant groups by a microemulsion technique. The use of a terpolymer in which the upconvering dye molecules are covalently attached mitigates some of the drawbacks of triplet–triplet annihilation upconverting nanoparticles made by other techniques, in particular dye leakage from the nanoparticles, and limited control of the sensitizer and emitter concentration within each nanoparticle. Size and morphology of the new upconverting nanoparticles are investigated by dynamic light scattering and transmission electron microscopy and elucidated their upconverting properties by luminescence spectroscopy.

     

Surface properties and aggregation of basic aluminium sulphate hydrolysis products: 1. Electrokinetic potential and hydration of BAS hydrolysis product particles

The action of pre-hydrolysed coagulants such as basic aluminium chloride (BAC) and sulphate (BAS) in water treatment is of considerable practical and fundamental interest. Variables such as working solution concentration, dosage, pH and ionic strength are known to be important. We have investigated the influence of these variables on the ζ-potential and degree of hydration of hydrolysis products of basic aluminium sulphate samples with different basicities. The products were characterised by a timed ferron complexation procedure, giving information on the degree of polymerisation of the BAS samples. Electrokinetic measurements showed that the ζ-potentials of hydrolysis product particles were consistently higher (more positive) for the higher basicity samples. The ζ-potential decreased with increasing concentration of the working solution and with increased dosage.

The degree of hydration of the hydrolysis products was investigated using the spin-lattice relaxation time of protons of water molecules bound to their surfaces. This was found to decrease with increasing basicity of BAS, indicating a greater degree of hydration. Since this effect is expected to decrease ζ potential by a displacement of the electrokinetic shear plane, the observed increase in ζ is probably due to the adsorption of highly charged positive hydrolysis products of BAS.     

High-power sub-10-fs Ti:sapphire oscillators

Received: 10 March 1997/Revised version: 16 April 1997     

Synthesis of melanervin from melaleuca quinquenervia,the first naturally occurring compound with a triphenylmethane structure

Melanervin from Melaleuca quinquenervia, the first naturally occurring compound with a triphenylmethane structure, has been synthesized and its structure thereby confirmed.     

Oxidation of SnF2 stannous fluoride in aqueous solutions

The rate of oxidation of SnF₂ in aqueous solutions has been studied by redox titrations and Mössbauer spectroscopy on frozen solutions versus the acidity of the solutions and versus time. Tin(II) oxidizes in aqueous solutions; however, the rate of oxidation is much slower than previously reported. Redox titrations show that the amount of tetravalent tin increases continuously with time. Oxygen dissolved in water seems to be the oxidizing species. The oxidation rate is faster in acidic solutions. Mössbauer spectroscopy on frozen solutions shows the slow formation of tetravalent tin; it also indicates that divalent tin in aqueous solutions is similar to that observed in solid SnF₂, except that one water molecule coordinates tin.     

Study of vector mesons in dimuon production in a large kinematic region in p-W and S-W interactions at 200 GeV/c/nucleon

Results are presented on and production in p–W and S–W interactions at 200 GeV/c/nucleon measured via the dimuon decay in a large kinematic region. The data are normalized to the charged particle multiplicity in the same rapidity interval. They have been collected using the HELIOS/3 muon spectrometer at the CERN SPS. The ratio , where is the relevant resonance branching fraction, increases between proton and sulphur projectiles, and is somewhat enhanced going from peripheral to central S–W interactions. This results from an increase in the number of produced 's per charged particle. The ratio is measured in different intervals of p and rapidity. It is not clearly dependent on p, but is larger at higher rapidities. production, likewise normalized to charged multiplicity, is significantly lower in S–W compared to p–W interactions. Received: 27 October 1997 / Revised version: 5 March 1998 / Published online: 13 July 1998     

1,2,5-thiadiazole-1-oxides,IV, ring transformation to 1,2,3,5-thiatriazole- and 1,2,4,6-thiatriazene-1-oxide

2-Alkyl-1,2,5-thiadiazole-3-one-1-oxides were converted to 1,2,3,5-thiatriazole-1-oxides and 1,2,4,6-thiatriazene-1-oxides. The postulated intermediate of these rearrangements, a sulfinylamine, was isolated.     

Oxidation of divalent tin in aqueous solutions of SnF2 and 3D transition metals allowed to crystallize slowly in air

Chlorides, nitrates and sulfates of M (M=Mn, Fe, Co, Ni and Zn) were dissolved in aqueous solutions of SnF₂ at M/Sn molar ratios of 0.5 to 3. No HF was used. The solutions were allowed to evaporate in air. Very small amounts of hexagonally shaped crystals of unknown materials were obtained for M=Mn, Co, Ni and Zn. Fe did not yield this phase. X-ray powder diffraction gives identical patterns for the four materials, which are therefore most likely isostructural, and showed that the products are not MSn₂F₆·6H₂O or MSnF₆·6H₂O. Tin-119 Mössbauer spectroscopy gives a single line at negative isomer shift, characteristic of [Sn(IV)F₆]^2– ions.     

Experimental mathematics. I. Computational study on the limit cycle behavior of a two-dimensional chemical oscillator

A computational procedure, developed from the power series method, is used to investigate oscillating systems. In addition to its great accuracy and reduced computer time, the method is very easily programmable since the algorithm is provided by the reaction mechanism itself.