M. de Moraes

Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates in aqueous solution

Abstract The protonation constants of 4-methylbenzylidenepyruvate (4Me-BP) and 4-isopropylbenzylidenepyruvate (4IP-BP) as well as the stability constants of their binary 1:1 complexes with Cu(II), La(III), Pr(III), Sm(III), Eu(III), Yb(III), Sc(III) and Th(IV) have been determined spectrophotometricaily in aqueous solution at 25 °C and ionic strength 0.500 M, maintained with sodium perchlorate. For all metal ions considered, the stability changes move in the same direction as the p K a of the ligands. Linear free energy relationships, as applied to oxygen donor substances, suggest the -COCOO − moiety as the metal binding site of the ligands. The results are discussed mainly taking into account that benzylidenepyruvates, besides the α-keto canonical form, may display other forms in aqueous solution with changing pH and the possible occurrence of extra intra-ligand charge polarization, induced by metal ions.

Ionic medium effects on equilibrium constants Part I. Proton, copper(II), cadmium(II), lead(II) and acetate activity coefficients in aqueous solution.

The molar single ion activity coefficients associated with hydrogen, copper(II), cadmium(II) and lead(II) ions were determined at 25 degrees C and ionic strengths between 0.100 and 3.00 M (NaClO4), whereas for acetate the ionic strengths were fixed between 0.300 and 2.00 M, held with the same inert electrolyte. The investigation was carried out potentiometrically by using proton-sensitive glass, copper, cadmium and lead ion-selective electrodes and a second-class Hg|Hg2(CH3COO)2 electrode. It was found that the activity coefficients of these ions (y(i)) can be assessed through the following empirical equations: log y(H) = -0.542I(0.5) + 0.451I; log y(Cu) = -1.249I(0.5) + 0.912I; log y(Cd) = -0.829I(0.5) + 0.448I(1.5); log y(Pb) = -0.404I(0.5) + 0.117I(2); and log y(Ac) = 0.0370I

Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates and cinnamylidenepyruvate in aqueous solution

Abstract The protonation constants of benzylidenepyruvate, 2-chloro-, 4-chlorobenzylidinepyruvate and cinnamylidenepyruvate as well as the stability constants of their binary 1:1 complexes with Cu(II), La(III), Pr(III), Sm(III), Lu(III), Sc(III) and Th(IV) have been determined spectrophotometrically in an aqueous medium at 25 °C and ionic strength 0.500 M, held with sodium perchlorate. Coordination centres in the aforementioned ligands are suggested.

4-Dimethylaminocinnamylidenepyruvic acid: synthesis, characterization and complexation with trivalent lanthanides, yttrium(III), scandium(III), thorium(IV) and uranium(VI) in aqueous solution

Abstract 4-Dimethylaminocinnamylidenepyruvic acid (H-DMCP)and its sodium salt (Na-DMCP) have been synthesized and characterized. The protonation constant of DMCP as well as the stability constants of its binary 1:1 complexes with trivalent lanthanides (except Pm), Yttrium(III), Scandium(III), Thorium(IV) and Uranium(VI) were determined in an aqueous medium at 25 °C and ionic strength 0.500 M. The mode of coordination of this ligand is discussed.

Ionic medium effects on equilibrium constants. Part II. Binary systems comprising some bivalent cations and monocarboxylates in aqueous solution

Simple equations were derived relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous sodium perchlorate media, at 25 degrees C, as a function of ionic strength (I), allowing the interconversion of parameters from one ionic strength to another, up to I=3.00 M. In addition, thermodynamic formation constants as well as activity coefficients of the species involved in the equilibria were estimated. The results show that the proposed calculation procedure is very consistent with critically selected experimental data.

Environmental Coordination Chemistry: Binary Systems Comprising Some Bivalent Cations and Monocarboxylates in Aqueous Solution. Ionic Medium Effects on Equilibrium Constants

Abstract The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25°C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO4, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg2Pr2 electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log ypr = –0.185 J3/2 + 0.104 I2. Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25°C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the comple...

Sistema TS-FF-AAS com chama acetileno-ar como alternativa em relação à chama acetileno-óxido nitroso em FAAS na determinação de estanho

This work propose the development of analytical procedure for on line tin determination in analytical solutions by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) as alternative to nitrous oxide-acetylene flame by atomic absorption spectrometry, whose oxidant presents high costs with respect to air. Parameters were evaluated for the optimization of the system: flow of the carrier (air), volume of injected sample and concentration of the acid (HCl). The linear analytical curve [A= -0,00163 +0,00319 Sn], (r = 0,9998) ] was constructed on interval of 10 the 80 mg L-1 Sn. The detection limit, the relative standard deviations (n=12) and analytical frequency were: 1,7 mg L-1 Sn, £ 2,7% and 120 h-1, respectively. The TS-FF-AAS is an alternative for the determination of Sn.

Controle de plantas daninhas na cultura do algodoeiro (Gossypium hirsutum L.) em solo anteriormente ocupado por vegetação de Cerrado

It was conduced field trial with the objective to study the effects of herbicides, isolated or combined, in cotton crop (Gossypium hirsutum L.) and weeds control, in a soil previously occuped by cerrado vegetation, at Selviria, MS, Brazil. The experimental design used was randomized block with 12 treatments and four repetitions. The treatments, dosis at kg a.i./ha, were: alachlor at 2.15 and 2.58 and diuron at 1.6 on preemergence application, trifluralin at 0.96 on preplant incorporated isolated or combined with MSMA at 1.89, or bentazon at 0.72 or diuron at 1.2 on postemergence applications; MSMA at 2.52, linuron at 1.0 and diuron at 1.6 on postemergence application and checks with or without hoeing. The treatments alachlor, diuron on preemergence application and trifluralin combined with diuron controlled Digitaria sanguinalis (L.) Scop and Amaranthus viridis (L.) during 90 days after the sowing of cotton, decreased 80% or more of dry matter of weeds. The herbicides did not caused phytotoxicity on crop. The weed competition reduced 58.9% of cotton yield.

Determinação direta e simultânea de Al, As, Fe, Mn e Ni em cachaça por espectrometria de absorção atômica em forno de grafite

This work describes a simple and fast method for the direct and simultaneous determination of Al, As, Fe, Mn and Ni in cachaca by graphite furnace atomic absorption spectrometry (GFAAS). The upside of platform of the graphite tube was coated with a W-based film (W xCyOz). The optimized heating program (temperature, ramp time, hold time) involved the following heating cycle: drying 1 (100oC, 5 s, 5 s); drying 2 (120oC, 5 s, 5 s); pyrolysis (1300oC, 10 s, 30 s); atomization (2200oC, 1 s, 6 s) and cleaning (2550oC, 1s, 3 s). The relative standard deviations (n=3) were: < 4.4%, < 0.7%, < 11%, < 6%, < 1.2% for Al, As, Fe, Mn and Ni, respectively. The recoveries of Al, As, Fe, Mn and Ni added to cachaca samples varied from 80% to 105%, 81% to 92%, 82 to 106%, 83 to 106% and 83% to 108%, respectively. The limits of detection (LOD) were 9.7 µg l-1 Al, 2.3 µg l-1 As, 12 µg l-1 Fe, 14 µg l-1 Mn and 0.8 µg l-1 Ni.

A New Approach for Determining Stability Constants of Metal Ion Complexes in Aquatic Systems Based on Flow Injection-Ion Exchange-Flame Atomic Absorption Spectrometry Coupling

Abstract A method based on ion exchange(IE)-atomic absorption spectrometry(AAS) coupled by flow techniques, allowing the determination of formation constants of, at least, the first species of complex systems, in aqueous solution, was developed. The IE-AAS coupling reduces significantly the number of experimental steps in comparison with IE batch methods, resulting in an important increase in analytical rate. The method is simple both from experimental and computational points of view, making possible its utilization by workers without special expertise in the field of complex equilibria in solution. On the other hand, taking into account mainly the amount of hollow cathode lamps available to date, the developed procedure may be applied, within certain limitations, to the study of many systems whose features prevent the use of traditional approaches.