A method was recently developed to determine the conditional stability constant, Kf′, using ion chromatography (IC) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) (C. Huang and D. Beauchemin, J. Anal. At. Spectrom., 2006, 21, 317–320 and C. Huang, D. Beauchemin, J. Anal. At. Spectrom., 2006, 21, 1419–1422).1,2 It involves the separation of a metal complex from the free metal ion by ion exchange with on-line detection of eluting metal-containing species by ICP-MS. The relative amounts of the complexed and free metals were simply obtained from the area of the corresponding peaks in the time-resolved chromatograms. A plot of the logarithm of the peak area ratio of the complex over the free metal as a function of the logarithm of the analytical concentration of the ligand gave log Kf′ as the intercept and the chelation number, n, as the slope. Although this method was demonstrated to allow the accurate determination of the conditional stability constant of a simple system (EDTA complexes of Co and Zn),1,2 the corresponding chelation numbers were significantly off from the expected unity value. A close scrutiny of the method revealed the main source of the discrepancy: it assumed that the ligand was in excess, which was not the case. Furthermore, it neglected other complexes than that with EDTA4−, such as those with HEDTA3−, H2EDTA2−, etc. In this work, no asuumption is made and a linear regression of the logarithm of the peak area ratio of the complex over the free metal versus the logarithm of the concentration of the uncomplexed chelating reagent is shown to accurately give both log Kf′ as the intercept and the chelation number as the slope. This revised method was successfully applied to Co-EDTA and Zn-EDTA complex systems with 0.1 M NH4NO3 as the supporting electrolyte.

Determination of stability constants of metal complexes with IC-ICP-MS

............................................................................................................... viii I INTRODUÇÃO ..................................................................................................... 1 I.1 Complexos metálicos ................................................................................ 1 I.2 Aspectos gerais .......................................................................................... 3 I.2.a Ferro ............................................................................................. 3 I.2.b Azoteto .......................................................................................... 4 I.2.c Tetraidrofurano ........................................................................... 5 I.2.d Acetona ......................................................................................... 6 I.2.e Dioxano ......................................................................................... 6 I.3 Constantes de estabilidade ou de formação ........................................... 7 I.4 Constantes de estabilidade condicionais ................................................. 8 I.5 Funções empregadas na determinação de constantes de estabilidade . 9 I.5.a Número médio de ligantes ........................................................... 9 I.5.b Grau de complexação .................................................................. 10 I.5.c Método gráfico de Leden ............................................................. 11 I.5.d Grau de formação da espécie ..................................................... 12 I.6 Determinação experimental de constantes de estabilidade .................. 13 I.7 Considerações gerais sobre métodos indiretos ....................................... 14 II OBJETIVOS ......................................................................................................... 17

Estudo potenciométrico sobre a formação de complexos no sistema ferro (III)/azoteto, em meio não totalmente aquoso

Titration potentiometry and spectrophotometry have both been used to determine stability constants for mixed complexes of Cu(II) with creatinine and EDTA. Stability constants of the ternary system were evaluated by a method suggested by the Irving-Rossotti procedure. Conditional constants were established as a function of pH; the maximum values of the conditional formation constants were found to be in agreement with the mixed-ligand complex formation constants in a given pH region. The mole fractions of mixed complexes were calculated using the formation constants. The stability constants of mixed-ligand complexes at 25°C are: log K| = 5.29, log K2 = 4.97, with ionic strength being kept constant at I = 0.1 with NaC104. Also, Cu(II)-I-glutamic acid-creatinine and Cu(II)-EDTA-creatinine complex formation, as examined by the spectrophotometric method, gave results that were in agreement with those of the Potentiometrie method. K e y w o r d s : creatinine, EDTA, 1-glutamic acid, copper(II) complexes, mixed complex, stability constants.

DETERMINATION OF STABILITY CONSTANTS OF MIXED LIGAND COMPLEXES OF Cu(II) WITH CREATININE AND ETHYLENEDIAMINE TETRAACETIC ACID OR I-GLUTAMIC ACID: POTENTIOMETRIC AND SPECTROPHOTOMETRIC METHODS

In this study, a potentiometric titration technique has been used to determine stability constants for the various complexes of Zn(II), Co(II), Cd(II) and Mn(II) with creatinine and two amino acids. Stability constants of ternary systems have been evaluated by the method suggested by Irving-Rossotti at 25°C and 0.11M ionic strength (kept constant with NaC104) in aqueous solution. In addition, the conditional con­ stants were calculated as a function of pH. The maximum values of the conditional formation constants were found to be in accordance with the mixed-ligand complex formation constants in a given pH region. In addition, the mole fractions of different species from mixed complexes were calculated by means of formation constants. The values of stability constants of mixed-ligand complexes at 25°C were calculated as follows: logK=3.20 for Zn(II)-L-cysteine-creatinine,logK1=4.24 and logK2=3.58 for Co(II)-L-cysteinecreatinine2, logK=3.22 for Cd(II) L-cysteine creatinine, logK=3.65 for Mn(II) L-cysteine creatinine and logK=5.34 for Co(II)-BDHL-cysteine-creatinine, logK=5.30 for Cd(II)-BDHL-cysteine-creatinine, logK,=5.35 and logK =3.93 for Zn(II) BDHL-cysteine creatinine^, logK,=5.40 and logK =3.49 for Mn(II) BDHL-cysteine creatinine,,

The determination of the stability constants of mixed Li- gand comlexes of creatinine-l-cysteine and creatinine-l- cysteine hydrochloride with Co(Ii), Cd(Ii), Zn(Ii), Mn(Ii): Using potentiometric method

N-(Aryloxy)imines, readily accessible by condensation/tautomerization of (pseudo)benzylic primary amines and 2,6-di-tert-butyl-1,4-benzoquinone, undergo efficient allylation to afford a wide range of homoallylic primary amines following hydrolytic workup. Deprotonation of N-(aryloxy)imines generates a delocalized 2-azaallyl anion-type nucleophile that engages in dearomative C-C bond-forming reactions with allylpalladium(II) electrophiles generated from allylic tert-butyl carbonates. This reactivity umpolung enables the formal α-allylation of (pseudo)benzylic primary amines. Mechanistic studies reveal that the apparent regioselectivity of the desired bond-forming event is a convergent process that is initiated by unselective allylation of N-(aryloxy)imines to give several regioisomeric species, which subsequently rearrange via stepwise [1,3]- or concerted [3,3]-sigmatropic shifts, ultimately converging to provide the desired regioisomer of the amine products.

M. Pekin

Papers

The Determination of Stability Constants of Para Substituted N-Benzylideneaniline Metal Complexes by a Potentiometric Method

DETERMINATION OF STABILITY CONSTANTS OF MIXED LIGAND COMPLEXES OF Cu(II) WITH CREATININE AND ETHYLENEDIAMINE TETRAACETIC ACID OR I-GLUTAMIC ACID: POTENTIOMETRIC AND SPECTROPHOTOMETRIC METHODS