Hydrolytic and photoinduced degradation of tribenuron methyl studied by HPLC-DAD-MS/MS

The paper studies, with the help of HPLC-DAD-MS/MS technique, the hydrolytic and photoinduced degradation processes that take place in aqueous solutions of tribenuron methyl, both when preserved in the dark and when undergoing solar box irradiation under conditions that simulate sun light. The results indicate that the degradation products formed by hydrolysis alone and by photoirradiation are the same, but kinetics of the hydrolysis reaction is much slower. The degradation products are identified as 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (P1), methyl 2-aminosulfonylbenzoate (P2), and saccharin (P3) and quantified. Ecotoxicological biotests performed on 0.1 microg L(-1) photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization.     

Mixed Co/Fe oxide nanoparticles in block copolymer micelles

Small iron oxide and Co-doped iron oxide nanoparticles (NPs) were synthesized in a commercial amphiphilic block copolymer, poly(ethylene oxide)-b-poly(methacrylic acid) (PEO 68-b-PMAA8), in aqueous solutions. The structure and composition of the micelles containing guest molecules (metal salts) or NPs (metal oxides) were studied using transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, and X-ray powder diffraction. The enlarged micelle cores after incorporation of metal salts are believed to be formed by both PMAA blocks containing metal species and penetrating PEO chains. The nanoparticle size distributions in PEO 68-b-PMAA8 were determined using small-angle X-ray scattering (SAXS) in bulk. Two independent methods for SAXS data interpretation for comprehensive analysis of volume distributions of metal oxide NPs showed presence of both small particles and larger entities containing metal species which are ascribed to organization of block copolymer micelles in bulk. The magnetometry measurements revealed that the NPs are superparamagnetic and their characteristics depend on the method of the NP synthesis. The important advantage of the PEO 68-b-PMAA8 stabilized magnetic nanoparticles described in this paper is their remarkable solubility and stability in water and buffers.     

A crystallographic and DFT study on a NHC complex of niobium oxide trifluoride

The complex [NbOF₃(Ipr)]₂, 1, was afforded in crystalline form by reaction of NbF₅ with the bulky NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) in toluene by slow contact with moisture air. The molecular structure of 1 was ascertained by X-ray diffraction, providing the first example of a dinuclear NbOF₃ derivative and also a rare case of niobium compound with a monodentate NHC. A DFT investigation has shown that the Nb–C bond consists of a weak NHC to Nb σ donation, reinforced by an electrostatic contribution presumably favored by the presence of the ancillary fluoride ligands. The computed enthalpy for the dissociation of one Ipr from 1 is ca. 36 kcal mol^?1. The presence of bulky 2,6-diisopropylphenyl substituents on the carbene ligand has negligible influence on the Nb–C bond, as highlighted by DFT analyses on simplified models.     

Effect of Titanium on Fluxional Behavior of Unbridged Metallocene Catalysts

Summary: Thanks to the use of a ligand consisting of a saturated ring fused to the cyclopentadienyl moiety, which sensibly increases the stability of titanocenes, it was possible to investigate the oscillating behavior of titanium catalysts in propylene polymerization for the first time. The titanium‐based catalysts yield poly(propylene)s with new and interesting microstructures. Indeed, in spite of the significantly lower isotactic pentad content [mmmm], the average lengths of the isotactic blocks (N_iso) are similar or even higher than that obtained with the zirconium‐based homologues. Accordingly, differential scanning calorimetry (DSC) analysis shows melting peaks which are more evident than those obtained with the zirconium homologues. The study of the microstructure of the poly(propylene)s obtained with these catalysts allowed us to participate in the still open discussion on the oscillating mechanism of unbridged metallocenes.

The titanium‐based catalysts employed in this study.     

Persistence of the Feigenbaum Attractor in One-Parameter Families

Consider a map ψ₀ of class C ^r for large r of a manifold of dimension n greater than or equal to 2 having a Feigenbaum attractor. We prove that any such ψ₀ is a point of a local codimension-one manifold of C ^r transformations also exhibiting Feigenbaum attractors. In particular, the attractor persists when perturbing a one-parameter family transversal to that manifold at ψ₀. We also construct such a transversal family for any given ψ₀, and apply this construction to prove a conjecture by J. Palis stating that a map exhibiting a Feigenbaum attractor can be perturbed to obtain homoclinic tangencies. Received: 4 August 1998 / Accepted: 11 May 1999     

Two hydrates of 2,6‐bis­(1H‐benzimidazol‐2‐yl)­pyridine

The structures of the mono‐ and sesquihydrates of 2,6‐bis(1H‐benz­imi­da­zol‐2‐yl)­pyridine (bbip) are reported. Phase (I), C₁₉H₁₃N₅·H₂O, has one water and one bbip mol­ecule in the asymmetric unit, while phase (II), C₁₉H₁₃N₅·1.5H₂O, has three water mol­ecules and two bbip mol­ecules in the asymmetric unit. The compounds exhibit very similar molecular geom­etries but different packing organizations, which result from intricate hydrogen‐bonding schemes.     

[2,6‐Bis(1H‐benzimidazol‐2‐yl‐κN3)­pyridine‐κN](di­methyl­form­amide‐κO)­(thio­sulfato‐κ2O,S)­nickel(II) mono­hydrate

The structure of the title compound, [Ni(ths)(bbip)(dmf)]·­H₂O [ths is thio­sulfate, S₂O₃; bbip is 2,6‐bis(1H‐benz­imidazol‐2‐yl)­pyridine, C₂₁H₁₃N₅; and dmf is di­methyl­form­amide, C₃H₇NO], is monomeric, with the nickel ion octahe­drally surrounded by an N,N′,N′′‐tridentate bbip mol­ecule, an S,O‐bidentate ths mol­ecule and an O‐monodentate dmf mol­ecule. The H atoms of the hydration water mol­ecule and the amino groups of bbip are involved in hydrogen bonding and determine a spatial organization of broad layers parallel to (001), which are connected by weak interactions.     

Si-Fluoro substituted quasisilatranes (N → Si) FYSi(OCH2CH2)2NR

The reaction of fluorosilanes XYSiF₂ (X = Y = F; X = F, Y = Ph; X = Ph, Y = Me) with diethanolamines and their O-trimethylsilyl derivatives affords novel Si-fluoro substituted quasisilatranes 3, 5 and 9. These compounds were characterized by the multinuclear NMR spectroscopy and X-ray diffraction analysis. Experimental and theoretically calculated electron density distribution functions in crystal structure of 9 have shown that the N → Si coordination bond corresponds to polar bond with pronounced ionic contribution. Calculated N → Si bond order in the compound 9 does not exceed 1/3 of the normal Si-N bond. A strong N → Si coordination bond exists in compounds 3, 5 and 9 the length of which varies in the range 1.98-2.175 Å.     

Voltammetric Sensing of Mercury and Copper Cations at Poly(EDTA‐like) Film Modified Electrode

Complexing polymer‐coated electrodes have been synthesized by oxidative electropolymerization of ethylenediamine tetra‐N‐(3‐pyrrole‐1‐yl)propylacetamide (monomer L ). The presence of four polymerizable pyrrole fragments on the same EDTA skeleton was thought to confer enhanced rigidity and controlled dimensionality to the resulting complexing materials, which were used for the electrochemical detection of Hg(II), Cu(II), Pb(II) and Cd(II) ions by means of the chemical preconcentration‐anodic stripping technique. The polyamide electrode material showed particularly a significant selectivity towards mercury ions, even in the presence of a large excess of other metal cations. Moreover, the use of imprinted polymer‐coated electrodes prepared by electropolymerization of L in the presence of metal cations turned out to significantly improve the detection limits, down to 5×10^?10 mol L^?1 for Hg(II) and Cu(II) species.