1,720,986 research outputs found
Phosphorus-31 nuclear magnetic resonance study of aluminium(III) ortho-phosphate complexes in aqueous solution
No full textPreviously, a model for aluminium(III) phosphate complexation in 3 M (Na)ClO4 aqueous solution at 25 degrees C has been proposed, on the basis of potentiometric titration data, in which there are eleven phosphorus-containing species. Support for this model is provided by the assignment to these species of eight peaks in P-31 NMR spectra obtained, under the same conditions of temperature and ionic strength, from a set of Al(ClO4)(3)-H3PO4 NaH2PO4 solutions. The assignment was made by correlating fractional NMR peak areas with fractional complex concentrations calculated using the potentiometric data model. The chemical shift in the range 0.3-0.91 ppm is assigned to H3PO4, H3PO4- H-6(PO4)(2)(-), H-5(PO4)(2)(-), and in part to Al3H-8(H3PO4)(5)(+) and Al3H-6(H(3)pO(4))(4)(3+), in fast proton exchange. The peaks at -6.8, -7.4 and -12.4 ppm are.assigned to isomers of Al(H2PO4)(2)(+). The signal at -7.4 is also due to AlH2PO42+. Polynuclear complexes have been assigned as follows. Al3H-5(H3PO4)(2)(4+) -11.5, Al3H-6(H3PO4)(4)(3+) -11.7, Al3H-8,(H3PO4)(5)(+) -12.3 and Al3H-6(H3PO4)(4)(3+) -16.8 ppm. A further four peaks were observed but could not be assigned. All chemical shifts are relative to 85% phosphoric acid as external reference
An investigation of the complexes formed by Aluminium(III) with phosphate in aqueous solution by NMR Spectroscopy.
No full textComplex formation equilibria of phosphocreatine with sodium, potassium and magnesium ions
No full textThe formation of complexes between phosphocreatine, H2O3PNHC(=NH)N(CH3)CH2CO2H, and the ions Na+, K+ and Mg2+ have been investigated under physiological conditions (aqueous solution, T=37degreesC and I=0.25 mol dm(-3)) by means of P-31 NMR spectroscopy. Only 1:1 complexes have been identified. Stability constants have been determined with the aid of the new computer program HYPNMR-2000. log(10) K values were found to be -0.5(2),-0.3(2) and 1.43(3), respectively. The formation constant for the potassium complex is two orders of magnitude less that the literature value
Stepwise electron-induced demolition of the Ni-I sigma-bond in complexes with tetradentate tripodal ligands: A theoretical rationalization of structural and electrochemical results
No full textThe X-ray structural analysis of the compound [(pp3)Nil]BPh4 (complex d), pp3 = P(CH2CH2PPh2)3, is presented. The complex cation has an almost regular trigonal bipyramidal geometry (TBP) with distances Ni-I and Ni-Pax of 2.546(2) and 2.142(3) Å, respectively. This structure completes a series of strictly related nickel complexes, namely [(np3)Nil]I, complex a; (np3)Nil, complex b; (np3)Ni, complex c; [(pp3)NiHClO4), complex e; [np3 = N(CH2CH2PPh2)3] The complexes are redox derivatives [Ni(II), Ni(I), Ni(O)] that can be isolated via chemistry and/or electrochemistry. In the solid state complexes c and e have a trigonal pyramidal (TP) structure, whereas, electrochemical measurements suggest that in solution the TBP structure with a very elongated Ni-I bond can also have a finite lifetime. EHMO calculations offer a satisfying interpretation of the main structural trends in complexes a rarr e, in particular, those relative to axial bond stretching, and clarify the different roles of phosphine vs. the amine axial donor. Moreover, the correlation is discussed between the electrode potentials and the nature of the Ni-I sgr* MO that accepts or releases the electrons exceeding thed 8 configuration of Ni(II)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Complexation of beryllium(II) ion by phosphinate ligands in aqueous solution. Synthesis and XRPD structure determination of Be[(PhPO2)(2)CH2](H2O)(2)
No full textTwo bifunctional ligands, phenyl(carboxymethyl)phosphinate (ccp(2-)) and P,P'-diphenylmethylenediphosphinate (pcp(2-)), have been tested as chelating agents of beryllium(II). Both ligands have the same charge and a similar chelating structure, but whereas the 1:1 adduct of pcp(2-), Be(pcp)((HO)-O-2)(2), could be isolated as a white powder, no pure compound could be isolated from solutions containing beryllium(II) and ccp(2-). Instead, the solutions were examined by means of potentiometry and Be-9 NMR spectroscopy. Analysis of the potentiometric titration data with the program HYPERQUAD suggested the formation of the complex species BeL, [BeHL](+), [BeL2](2-), and [BeHL2](-) (L = ccp). The formation constants for these species were determined at 25 degreesC and / = 0.5 mol dm(-3) NaCIO4. The Be-9 NIVIR spectra are consistent with this model. The formation constants found for the ccp(2-) complexes are lower than those reported for related phosphonate ligands. However, the effective stability constant (which gives a better indication of the intrinsic coordinating capacity of the ligand at a particular pH) of the complex [Be(ccp)(2)](2-) at pH < 4 is greater than the effective constants of the corresponding phosphonoacetate and methylenediphosphonate complexes. The structure of Be(pcp)(H2O)(2) was determined by X-ray powder diffraction methods and consists of discrete molecules interconnected by an extended 2D network of hydrogen bonds, resulting in a stacking of double layers with a polar core and a lipophilic surface. Crystal data: C13H16BeO6P2, fw 339.21, monoclinic P2(1)/c, a 16.174(1) Angstrom, b = 8.979(1) Angstrom, c = 10.929(1) Angstrom, beta = 90.398(9)degrees, V = 1587.2(3) Angstrom(3), Z = 4
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