Crystal structure of supramolecular complexes formed by 18-crown-6 andcis-anti-cis-dicyclohexano-18-crown-6 (host) with 3,4-diaminofurazane (guest)

An X-ray—diffraction study is reported for two molecular complexes containing 3,4-diamino-1,2,5-oxadiazole as guest (G) with 18-crown-6 (18-C-6) andcis-anti-cis-dicyclohexano-18-crown-6 (DCH-6B) as host. Both complexes are of the polymeric-chain structure with the guest molecule bridging two crown neighbours. ComplexI: [18-C-6*G*H₂O], 111, monoclinic,P2₁/n,a=8.171(1),b=15.042(2),c=16.209(6) Å, =101.15(2)°, finalR-factor 0.068. ComplexII: [DCH-6B*G], 11, monoclinicC2/c,a=21.212(4),b=9.380(2),c=13.049(3) Å, =108.61(3)°, finalR 0.047.     

Different strategies to assess Cu and Pb mobilization in polluted river sediments

Summary For studying the mechanisms of trace metal mobilization in sediments several strategies have been employed, such as single extraction, sequential extractions, ion exchange, or progressive acidification. Several authors assert that sequential extraction is the best option. In this study two procedures are used in order to assess the mobility of copper and lead in heavily polluted river sediments: sequential extraction using a modified Tessier procedure, and progressive acidification, using an automated method. Six heavily polluted sediment samples are studied by applying the two procedures. The amount of metal released at different pH-values (pH 5 and pH 2) is compared with the resulting distribution when the sequential extraction procedure is applied. The information obtained from the two different approaches is discussed. For both metals a different behaviour is observed when applying each of the two procedures. Thus, copper is more easily released than lead when progressive acidification is followed, whereas an inverse situation is observed when sequential extraction is applied.     

Delphinidin–Aluminum(III) Complexes in Aqueous and Non-Aqueous Media: Spectroscopic Characterization and Theoretical Study

Summary. The study of delphinidin complexation with trivalent aluminum in acidic aqueous buffered (pH 3.0 and 3.8) and methanolic solutions was performed utilizing electronic absorption spectroscopy and quantum chemical calculations. In its structure delphinidin possesses several chelating sites in competition towards aluminum(III). Molar ratio plots denoted the formation of only one aluminum(III):delphinidin complex of stoichiometry of 1:1 in both investigated media. Semiempirical calculations, performed at the restricted HF AM1 level, enabled the determination of the structural features of free delphinidin and structural modifications caused by chelation of aluminum(III). Considering the pigment molecular structure and the results of the theoretical calculations it is possible to equally implicate C3′–C4′ and C4′–C5′ hydroxyl groups as those with the predominant chelating power.     

PHYSIOLOGICAL RELATIONSHIPS BETWEEN PHYTOCHROME EFFECTS ON INTERNODE EXTENSION GROWTH AND DRY MATTER ACCUMULATION INLIGHT-GROWN MUSTARD

The physiological relationships between the effects of phytochrome photoequilibrium (Pfr/P) on internode extension growth and dry matter accumulation were investigated in white light (WL)-grown Sinapis alba L. seedlings. After 11 days under continuous WL, the seedlings were exposed: (a) to pulses of light providing different Pfr/P, followed by 24 h darkness (D); (b) to pulses of light providing different Pfr/P, followed by 3 h D and 24 h continuous WL; (c) to continuous WL with or without supplementary far-red light (to reduce Pfr/P); or (d) to pulses of light providing different Pfr/P followed by D, in factorial combination with either water or a saturating (0.2 M) sucrose solution applied to one of the leaves. In D (“a” and “d”) low, compared to high Pfr/P increased both internode extension growth and dry weight to the same extent. Under WL (“b” and “c”) low PfrlP promoted internode extension growth but had no proportional effects on internode dry weight. Sucrose promoted internode extension growth with a lag of at least 8 h (compared to the rapid effect of low Pfr/P) and did not reduce the effect of low Pfr/P. These results indicate that Pfr/P effects on internode extension growth are not the consequence of changes in photoassimilate translocation from the leaves. Under WL, PfdP effects on internode length occur partially at the expense of internode dry matter per unit length.     

Coordination modes between copper(II) and N-acetylneuraminic (sialic) acid from a 2D-simulation analysis of EPR spectra. Implications for copper mediation of sialoglycoconjugate chemistry relevant to human biology

The equilibrium distribution of species formed between Cu(II) and N-acetylneuraminic (sialic) acid (I, LH) at 298 K has been determined using a two-dimensional (2D) simulation analysis of electron paramagnetic resonance (EPR) spectra. In acidic solutions (pH values < 4), the major species present are Cu(2+), [CuL]+ [logbeta = 1.64(4)], and [CuL2] [logbeta = 2.77(5)]. At intermediate pH values (4.0 < pH < 7.5), [CuL2H-1]- [logbeta = -2.72(7)] and two isomers of [CuLH-1] [logbeta (overall) = -3.37(2)] are present. At alkaline pH values (7.5 < pH < 11), the major species present is [CuL2H-2]2-, modeled as three isomers with unique giso and Aiso values [logbeta (overall) = -8.68(3)]. Two further species ([CuLH-3]2- and [CuL2H-3]3-) appear at pH values > 11. It is proposed that [CuL]+ most likely features I coordinated via the deprotonated carboxylic acid group (O1) and the endocyclic oxygen atom (OR) forming a five-membered chelate ring. Select Cu(II)-I species of the form [CuLH-1] may feature I acting as a dianionic tridentate chelate, via oxygen atoms derived from O1, OR, and one deprotonated hydroxy group (O7 or O8) from the glycerol tail. Alternatively, I may coordinate Cu(II) in a bidentate fashion as the tert-2-hydroxycarboxylato (O1,O2) dianion. Spectra predicted for Cu(II)-I complexes in which I is coordinated in either a O1,OR {I1-} or O1,O2 {I2-} bidentate fashion {e.g., [CuL]+ (O1,O R), [CuL2] (bis-O1,O R), [CuLH-1] (isomer: O1, O2), [CuL2H-1]- (O1, O R; O1, O2), and [CuL2H-2]2- (isomer: bis-O1, O2)} have "irregular" EPR spectra that are ascribed to the existence of Cu(II)-I(monomer) <==> Cu(II)-I(polymer) equilibria. The formation of polymeric Cu(II)-I species will be favored in these complexes because the glycerol-derived hydroxyl groups at the complex periphery (O, 7O, 8O9) are available for further Cu(II) binding. The presence of polymeric Cu(II)-I species is supported by EPR spectral data from solutions of Cu(II) and the homopolymer of I, colominic acid (Ipoly). Conversely, spectra predicted for Cu(II)-I complexes where I is coordinated in a {I2-} tridentate {e.g., [CuLH-1] (isomer: O1, O R, O7, or O8) and [CuL2H-2]2- (isomer: bis-O1,O R,O7, or O8)} or tetradentate fashion {I3-} {e.g., [CuLH-3]2- (O1, O R, O, 8O9)} are typical for mononuclear tetragonally elongated Cu(II) octahedra. In this latter series of complexes, the tendency toward the formation of polymeric Cu(II)-I analogues is small because the polydentate I effectively wraps up the mononuclear Cu(II) center. This work shows that Cu(II) could potentially mediate the chemistry of sialoglycoconjugate-containing proteins in human biology, such as the sialylated amyloid precursor protein of relevance to Alzheimer's disease.     

Measurement of the carbonaceous component in the Milan urban particulate matter

The carbonaceous component in the Milan urban particulate matter, i.e. the two components black carbon (BC) and organic carbon (OC), has been measured by means of a thermogravimetric analyzer combined with an infrared spectrophotometer (TGA/FT-IR). While black carbon may be considered a primary pollutant, organic carbon includes both primary emissions and secondary organic aerosols. Since carbonaceous aerosol (including a small quantity of inorganic carbon, too) makes up roughly from 25% to 50% of the average annual PM 2.5 mass concentration, a deeper understanding of this component is required. The TGA/FT-IR technique, employed for the first time to our knowledge for the quantification of the particulate matter carbonaceous component, allows, thought the results here presented are preliminary, to assess the two components BC and OC in a simple way especially if compared with the methods reported in the literature. The total carbon (TC) determinations performed by TGA/FT-IR on Milan urban particulate matter are in good agreement with the results obtained by a total organic carbon (TOC) analyzer operating directly on the solid sample.     

Pollutants leaching behaviour from solidified wastes: a selection of adapted various models

Leaching tests are essential in the environmental assessment of stabilized wastes. Research programmes were conducted on their interpretation in order to develop tools for the evaluation of long term release of pollutants contained in solidified wastes. Models for the leaching of porous materials are discussed in this paper according to the specificity of the chemical species (i.e. transport model with total dissolution of species-diffusional model; transport model with progressive dissolution of species due to limitation of solubility-shrinking core model; and the model coupling transport and chemical phenomena). The leaching behaviour of pollutants (i.e. lead) solidified in a cement matrix was studied under different chemical conditions. Results have shown that the release of species whose solubilities depend on the physico-chemical conditions, and especially the pH (e.g. amphoteric metals), is governed by the solubility of the species in the pore water at local conditions and by the pH evolution within the matrix. A coupled dissolution/diffusion model was developed to describe the release of chemically complex species contained in a porous medium in contact with water. Leaching tests of cement matrices and artificial porous matrices containing calcium hydroxide and pollutants were conducted in order to validate the coupled dissolution/diffusion model. A good assessment of the retention of some pollutants contained in cement matrices could then be obtained by the association of two tests: solubilization of the pollutants related to the chemical context (pH) under steady state conditions and monolithic long term dynamic leaching tests in order to characterize the evolution of the chemical context (pH) and consequently the release of pollutants. The objective is to integrate this approach in the standardization process (CEN TC 292- WG 6, in progress).     

Evaluation of 40K in food by determining total potassium using neutron activation analysis

Summary Potassium is an extremely important major element to the human body. Potassium is made up of three isotopes with abundances of ³⁹K at 93.1%, ⁴⁰K at 0.0118% and ⁴¹K at 6.88%. It is also very well known that ⁴⁰K with its 1.3 ^. 10⁹ years half-life is a major naturally occurring isotope in the body and food. The usual way to determine total ⁴⁰K is to measure the single 1460.8 keV photon from beta-decay. However, this procedure requires a significant amount of sample and typical counting periods of at least a day in well-shielded germanium counting system. Another approach is to determine total potassium via neutron activation analysis using the well known ⁴¹K(n,g)⁴²K (T_1/2 = 12.8 h) reaction and then evaluate ⁴⁰K using the usual activity equation A = lN. In our laboratory we have effectively used epithermal neutron activation analysis and Compton suppression to determine potassium in air filters and other geological material. Upwards to 10-15 samples can be analyzed in one day using only gram quantities of material. In such way one can increase the output of determining ⁴⁰K by at least one order of magnitude. Results of a detailed investigation optimization of the methodology, quality control and detection limits will be presented for reference material and various food samples.     

Electrocatalytic reduction of ROOH by iron porphyrins

Electrocatalytic reduction of a series of chemical oxidants of different power (tert-butyl hydroperoxide, potassium peroxomonosulfate, peracetic acid, and m-chloroperbenzoic acid) at iron-porphyrin-modified graphite electrodes is studied in buffered aqueous solutions by rotating disk and ring-disk voltammetry. Both ferric and ferrous porphyrins are catalytically active. Turnover of ferric catalysts is slower than that of the ferrous analogues and involves competing catalytic reduction and disproportionation. The kinetic data are consistent with reactant binding being the rate-determining step in catalysis by Fe(III). In catalysis by Fe(II), the turnover is controlled by the first electron transfer. The covalently linked proximal imidazole ligand is found to be crucial for achieving the Fe(III) catalysis.     

A new thermoelectric material: CsBi4Te6

The highly anisotropic material CsBi(4)Te(6) was prepared by the reaction of Cs/Bi(2)Te(3) around 600 degrees C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) A, b = 4.4025(1) A, c = 14.5118(3) A, beta = 101.480(1) degrees, V = 3250.75(11) A(3), and Z = 8. The final R values are R(1) = 0.0585 and wR(2) = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi(4)Te(6)] anionic layers and Cs(+) ions residing between the layers. The [Bi(4)Te(6)] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) A. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi(4)Te(6) can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI(3) doping resulted in p-type behavior and a maximum power factor of 51.5 microW/cm.K(2) at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 microW/cm.K(2) at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi(4)Te(6) and comparisons to those of p-type.