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Main Species (main + species)
Selected AbstractsOxido Pincer Ligands , Exploring the Coordination Chemistry of Bis(hydroxymethyl)pyridine Ligands for the Late Transition MetalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009Axel Klein Abstract Coordination of the 2,6-bis(hydroxymethyl)pyridine-based oxido pincer ligands RR,pydimH2 [R = R, = H (pydimH2); R = R, = Me (pydipH2); R = 2-tolyl, R, = Me (pydotH2)] towards late transition metals CoII, NiII, CuII, ZnII, PdII and PtII allows the formation of molecular species (complexes), which exhibit three main structural motifs in the solid state. The two main species are pentacoordinate [(RR,pydimH2)MCl2] and hexacoordinate [(RR,pydimH2)2M]X2, both of which are stable in solution and can be interconverted by changing the solvent polarity. The disproportionation equilibrium [(RR,pydimH2)MCl2] [rlhar2] [(RR,pydimH2)2M]2+ + [MCl4]2, was studied by optical spectroscopy. The chiral ligand pydotH2 allows the formation of chiral complexes. In the square-planar complexes [(pydimH2)2MCl2] (M = PdII or PtII) the oxido donor functions of the ligands do not take part in the coordination.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Hexaazamacrocycle Containing Pyridine and Its Dicopper Complex as Receptors for Dicarboxylate AnionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2005Feng Li Abstract The host,guest binding interactions of the hexaazamacrocycle [26]py2N4, in its tetraprotonated form H4[26]py2N44+ as well as in its dicopper(II) complex [Cu2([26]py2N4)(H2O)4]4+, with dicarboxylate anions of different stereoelectronicrequirements, such as oxalate (ox2,), malonate (mal2,), succinate (suc2,), fumarate (fu2,) and maleate (ma2,), were evaluated. The association constants were determined using potentiometric methods in aqueous solution, at 298.0 K and 0.10 mol·dm,3 KCl. These values for the tetraprotonated ditopic receptor with the dicarboxylate anions revealed that the main species in solution corresponds to the formation of {H4[26]py2N4(A)}2+ (pH , 4,9), A being the substrate anion. The values determined are not especially high, but the receptor exhibits selectivity for the malonate anion. The study of the cascade complexes revealed several species in solution, involving mononuclear and dinuclear complexes, mainly protonated and hydrolysed species, as well as the expected complexes [Cu2([26]py2N4)(A)(H2O)x]2+ or [Cu2([26]py2N4)(A)2(H2O)y]. Ox2, and mal2, form cascade complexes with only one anion, which will necessarily bridge the two copper atoms because of the symmetrical arrangement of the dinuclear complex. The two other studied anions, suc2, and ma2,, form species involving two substrate anions, although species with only one suc2, anion were also found. UV/Vis and EPR spectroscopy have shown that the dicopper complex can operate as a sensor to detect and quantitatively determine oxalate spectrophotometrically because of the red shift of the maximum of the visible band observed by addition of ox2, to an aqueous solution of the dinuclear copper complex. However the selectivity of [Cu2([26]py2N4)(H2O)4]4+ as a receptor for ox2, in the studied series is not sufficiently high to detect ox2, spectrophotometrically in the presence of the other anions. Molecular dynamics simulations indicated that the H4[26]py2N44+ receptor provides a large and flexible cavity to accommodate the studied anions. Molecular recognition is based in electrostatic interactions rather than in multiple hydrogen-bonding interactions acting cooperatively. By contrast, the [Cu2([26]py2N4)]4+ receptor has a well-shaped cavity with adequate size to uptake these anions as bridging ligands with formation of four Cu,O bonds. The ox2, anion is encapsulated within the cascade complex while the remaining anions are located above the N6 macrocyclic plane, suggesting a selective coordination behaviour of this receptor. In spite of our molecular simulation being carried out in gas phase, the modelling results are consistent with the solution studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Malassezia yeast species isolated from Iranian patients with pityriasis versicolor in a prospective studyMYCOSES, Issue 4 2010Abbas Rasi Summary The goal of this study was to determine the prevalence of Malassezia species in pityriasis versicolor lesions and to examine if the range of species varies with patients characteristics such as: age, sex and family history and also clinical findings such as site and number of the lesions. In a prospective study from July 2006 to July 2007, the patients with a clinical diagnosis of pityriasis versicolor (n = 166) were asked to participate in the study. A total of 116 patients had positive culture for Malassezia species: M. globosa was found in 52 (31.3%) cases, M. furfur in 34 (20.5%) cases, M. pachydermatis in 12 (7.2%) cases, M. restricta in 12 (7.2%) cases, M. slooffiae in 6 (3.6%) cases. According to our data, M. globosa is the main species causing pityriasis versicolor, M. furfur was found to be the second-most frequent species. M. sympodialis and M. obtusa were not found in any case, and in 30.2% of patient's Malassezia culture was negative. [source] Influence of buffered propionic acid on the development of micro-organisms in hayMYCOSES, Issue 5-6 2002Der Einfluss gepufferter Propionsäure auf das Wachstum von Mikroorganismen im Heu Farmerlunge; Prävention; Propionsäure Summary. We tested the benefit of using buffered propionic acid (BPA) as a means of preventing farmer's lung disease (FLD). BPA, a new formulation of propionic acid, a hay preservative with no deleterious effect on farm machinery or cattle, reduces the development of micro-organisms in hay. Twenty pairs of round bales were analysed for concentration of micro-organisms measured in the winter following hay treatment. Each pair included one untreated bale and one bale treated with BPA during haymaking. Our results showed the following decreases in concentration in treated bales: total fungal species, 40% (P < 0.05); Eurotium amstelodami (the main species found), 65% (P < 0.01); and thermophilic actinomycetes, 60% (not significant), respectively. We conclude that BPA could be used to prevent FLD. Zusammenfassung. Wir untersuchten den Nutzen einer Anwendung gepufferter Propionsäure (BPA) als Mittel zur Vorbeugung der Farmerlunge (FLD). Gepufferte Propionsäure, eine neue Propionsäure-Formulierung, ein Heukonservierungsmittel ohne negative Auswirkungen, auf landwirtschaftliche Geräte, oder Vieh, vermindert das Wachstum von Mikroorganismen im Heu. Zwanzig Paar runder Heuballen wurden im Winter, nach einer Behandlung mit BPA, auf Mikroorganismenbefall untersucht. Jedes Paar bestand aus einem unbehandelten und einem während der Herstellung mit BPA behandelten Heuballen. Unsere Ergebnisse zeigten folgende Verringerung der Mikroorganismenkonzentration in den behandelten Heuballen: Gesamte Pilzarten minus 40% (P, < 0.05), Eurotium amstelodami (die am häufigsten gefundene Art) minus 65% (P ,< 0.01) und thermophile Actinomyceten minus 60% (NS). Dies belegt, daß BPA zur Vorbeugung einer FLD verwendet werden könnte. [source] Importance of Interfacial Adsorption in the Biphasic Hydroformylation of Higher Olefins Promoted by Cyclodextrins: A Molecular Dynamics Study at the Decene/Water InterfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Nicolas Sieffert Abstract We report herein a molecular dynamics study of the main species involved in the hydroformylation of higher olefins promoted by cyclodextrins in 1-decene/water biphasic systems at a temperature of 350,K. The two liquids form a well-defined sharp interface of approximately 7,Å width in the absence of solute; the decene molecules are generally oriented "parallel" to the interface where they display transient contacts with water. We first focused on rhodium complexes bearing water-soluble TPPTS3, ligands (where TPPTS3, represents tris(m -sulfonatophenyl)phosphine) involved in the early steps of the reaction. The most important finding concerned the surface activity of the "active" form of the catalyst [RhH(CO)(TPPTS)2]6,, the [RhH(CO)2(TPPTS)2]6, complex, and the key reaction intermediate [RhH(CO)(TPPTS)2(decene)]6, (with the olefin ,-coordinated to the metal center) which are adsorbed at the water side of the interface in spite of their ,6 charge. The free TPPTS3, ligands themselves are also surface-active, whereas the ,9 charged catalyst precursor [RhH(CO)(TPPTS)3]9, prefers to be solubilized in water. The role of cyclodextrins was then investigated by performing simulations on 2,6-dimethyl-,-cyclodextrin ("CD") and its inclusion complexes with the reactant (1-decene), a reaction product (undecanal), and the corresponding key reaction intermediate [RhH(CO)(TPPTS)2(decene)]6, as guests; they were all shown to be surface-active and prefer the interface over the bulk aqueous phase. These results suggest that the biphasic hydroformylation of higher olefins takes place "right" at the interface and that the CDs promote the "meeting" of the olefin and the catalyst in this peculiar region of the solution by forming inclusion complexes "preorganized" for the reaction. Our results thus point to the importance of adsorption at the liquid/liquid interface in this important phase-transfer-catalyzed reaction. [source] | ||||||||||