Self-assembly of a tetranuclear Ni4 cluster with an S = 4 ground state: the first 3d metal cluster bearing a mu4-eta2:eta2-O,O carbonate ligand

Reaction of nickel(II) acetate with H(3)L (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) yields [Ni(2)L(OAc)(H(2)O)(2)].3MeCN.2H(2)O (1.3MeCN.2H(2)O), crystallographically characterized. 1 is unstable in solution for a long time and hydrolyzes to give [Ni(2)L(o-OC(6)H(3)BrCHO)(H(2)O)].2.25MeCN.H(2)O (2.2.25MeCN.H(2)O). In addition, 1 uptakes CO(2) from air in a basic methanol/acetonitrile solution, yielding [[Ni(2)L(MeOH)](2)(CO(3))].1.5MeOH.MeCN.H(2)O (3.1.5MeOH.MeCN.H(2)O). The X-ray characterization of 3 reveals that it is a tetranuclear nickel cluster, which can be considered as the result of a self-assembly process from two dinuclear [Ni(2)L](+) blocks, joined by a mu(4)-eta(2):eta(2)-O,O carbonate ligand. The coordination mode of the carbonate anion is highly unusual and, to the best of our knowledge, it has not been described thus far for first-row transition metal complexes or magnetically studied until now. Magnetic characterization of 1 and 3 shows net intramolecular ferromagnetic coupling between the metal atoms in both cases, with S = 2 and S = 4 ground states for 1 and 3, respectively.     

Barrier height homogeneity for 4.5 kV 4H-SiC Schottky diodes

4.5 kV SiC Schottky diodes have been fabricated using Ni as the Schottky contact. A manufacturing yield of 40% is reached for the bigger area diodes (1.6×1.6 mm²) and of 70% for the smaller ones (0.4×0.4 mm²). The measured variations of barrier height and ideality factor with temperature do not agree with the thermionic model. This has been interpreted in terms of barrier height inhomogeneities using the Werner model. We extracted an average barrier height and its standard deviation . These two parameters are almost independent of the diode size. The variation of the barrier height distribution with field has also been investigated and shows a dependence similar to that of Schottky diodes realized from other semiconductor materials.     

Asymmetric Rh-catalyzed hydrogenation using a furanoside phosphite-phosphoroamidite and diphosphoroamidite ligand library

A furanoside phosphite-phosphoroamidite and diphosphoroamidite ligand library L1-L5a-f was tested in the asymmetric Rh-catalyzed hydrogenation of α,β-unsaturated carboxylic acid derivatives and enamides. Enantioselectivity depended strongly on the ligand parameters. High enantioselectivities were obtained in the reduction of dimethyl itaconate (up to >99% ee), α-dehydroamino acid esters (up to 99% ee) and several enamides (up to 92% ee). Kinetic and NMR studies on the intermediates of the catalytic cycle of the reaction indicate that the [Rh(P(1)-P(2))(substrate)](+) species is the resting state of the reaction and that the rate dependence is first order in rhodium and hydrogen pressure and zeroth order in the substrate.     

Efficient reverse click labeling of azide oligonucleotides with multiple alkynyl Cy-Dyes applied to the synthesis of HyBeacon probes for genetic analysis

A convenient method of oligonucleotide labeling using click chemistry has been developed. A 2′-mesyloxyethyl ribothymidine phosphoramidite monomer was incorporated into DNA at several loci during solid phase oligonucleotide synthesis and converted to 2′-azidoethyl ribothymidine in high yield on the synthesis resin. The resultant azide oligonucleotides were doubly and triply labeled with alkyne-modified cyanine dyes and their biophysical properties were studied. The influence of the dye structures and method of labeling on the fluorescence properties of the DNA probes is discussed and compared with a standard labeling method using active esters of Cy-Dyes.     

Strong Reflexivity of Abelian Groups

A reflexive topological group G is called strongly reflexive if each closed subgroup and each Hausdorff quotient of the group G and of its dual group is reflexive. In this paper we establish an adequate concept of strong reflexivity for convergence groups. We prove that complete metrizable nuclear groups and products of countably many locally compact topological groups are BB-strongly reflexive.     

Identification of photocatalytic degradation products of non-ionic polyethoxylated surfactants in wastewaters by solid-phase extraction followed by liquid chromatography-mass spectrometric detection

The photodegradation of non-ionic surfactants (nonylphenol- and alcohol-polyethoxylates, NPEO_x and C_nEO_x) was investigated in different waters with and without a photoinducter (Fe(III)). Deionized water and industrial effluent spiked at 0.5 mg/L with C₁₀EO₆ and NPEO₉ were irradiated using a xenon arc lamp. Aliquots of the test solutions were taken at different time intervals and were preconcentrated using solid phase extraction (SPE) with C₁₈ cartridges. Liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was used to identify the chemical species generated from phototransformation of non-ionic surfactants. 2 ) and nonylphenol ethoxy acetic acid (NPE₂C). Much smaller amounts of degradation products of NPEO₉ having only the alkyl chain carboxylated were also formed in the photocatalysis experiment. The identified C₁₀EO₆ photoproducts included fatty alcohols and acids. Polyethylene glycols (PEGs) were also formed as the consequence of the central scission of C₁₀EO₆ and the deethoxylation of NPEO₉. The photodegradation in wastewater samples was more efficient than in deionized water being the half-life (t_1/2) of C₁₀EO₆, 48 h and 29 h in deionized water and wastewater, respectively, and for NPEO₉, 17 h and 14 h in deionized water and wastewater, respectively. When induced photodegradation was undertaken, the t_1/2 for NPEO₉ was 21 min and 29 min in deionized water and wastewater, respectively. Disappearance of parent compounds was observed after 120 h from the beginning of the photodegradation experiment, or after 210 min of irradiation for the photocatalysis. Received: 27 September 2000 / Revised: 11 January 2001 / Accepted: 14 January 2001     

Enthalpy relaxation in a partially cured epoxy resin

The enthalpy relaxation of a partially cured (70%) epoxy resin, derived from diglycidyl ether of bisphenol-A cured by methyl-tetrahydrophthalic anhydride with accelerator, has been investigated. The key parameters of the structural relaxation (the apparent activation energy Δh*, the nonlinearity parameter x, and the nonexponentiality parameter β) are compared with those of the fully cured epoxy resin. The aging rates, characterized by the dependences of the enthalpy loss and peak temperature on log(annealing time), are greater in the partially cured epoxy than they are in the fully cured resin at an equivalent aging temperature (T_a = T_g − 20°C). There is a significant reduction in Δh*, from 1100 kJ mol⁻¹ for the fully cured system to 615 kJ mol⁻¹, as the degree of cure is reduced. The parameter x determined by the peak-shift method appears essentially independent of the degree of cure (x = 0.41 ± 0.03 for the partially cured resin compared with 0.42 ± 0.03 obtained previously for the fully cured resin), and does not follow the usually observed correlation of increasing x as Δh* decreases. This invariability of the parameter x seems to indicate that it is determined essentially by the local chemical structure of the backbone chain, and rather little by the supramolecular structure. On the other hand, the estimated nonexponentiality parameter β lies between 0.3 and 0.456, which is significantly lower than in the fully cured epoxy (β ≅ 0.5), indicative of a broadening of the distribution of relaxation times as the degree of cross-linking is reduced. Like the parameter x, this also does not follow the usual correlation with Δh*. These results are discussed in the framework of strong and fragile behavior of glass-forming systems, but it is difficult to reconcile these results in any simple way with the concept of strength and fragility. © 1996 John Wiley & Sons, Inc.     

Self-Assembled Binaphthyl-Bridged Amphiphilic AABB Phthalocyanines: Nanostructures for Efficient Antimicrobial Photodynamic Therapy

Herein, the photodynamic activity of phthalocyanine (pc)-assembled nanoparticles against bacterial strains is demonstrated. The photosensitizers (PS) studied in this work are two chiral Zn^IIPcs ( PS-1 and PS-2 ), with an AABB geometry (where A and B refer to differently substituted isoindole constituents). They contain differently functionalized, chiral binaphthyloxy-linked A isoindole units, which determine the hydrophobicity of the system, and cationic methyl pyridinium moieties in the other two isoindoles to embody hydrophilicity. Both compounds have the ability to self-assemble into nanoparticles in aqueous media and have proved efficient in the photo-inactivation of Staphylococcus aureus and Escherichia coli, selected as models of Gram-positive and Gram-negative bacteria. The average size of the nanoparticles was determined by substitution at the binaphthyl core and, in turn, influences the toxicity of the PS. Thus, PS-1 , presenting a nonsubstituted binaphthyl core, forms larger nanoparticles with a larger cationic surface than the octyl-functionalized PS-2 . Although both PSs present similar structure and photophysical features, the self-assembled nanostructures of PS-1 are more effective at killing both types of strain, showing an outstanding photo-inactivation capacity with the Gram-negative E. coli.     

Synthesis of anacardic acids by nucleophilic substitution on 2-aryloxazolines

A new direct synthesis for anacardic acids based in a nucleophilic substitution of a methoxy group in 2-aryloxazolines by long-chained Grignard reagents is reported.