Complexation studies of Sn(II) by N,N-dimethylformamide and free energy of transfer of Sn(II) from acetonitrile to N,N-dimethylformamide

Studies of the complexation of Sn(II) by N,N-dimethylformamide show that Sn(II) ion forms six successive complexes with the ligand. The stability constants were determined by the method of DeFord and Hume. The free energy of transfer of Sn(II) from acetonitrile to N,N-dimethylformamide and to their mixtures was obtained using the theory of Cox et al. The energy decreases with increasing N,N-dimethylformamide concentration, the decrease being most pronounced for nearly pure acetonitrile.     

Phenylenedioxydiacetamide—End group effect

A series of neutral ligands featuring ether and amide groups were prepared. The complexation studies suggest a strong participation of the extra terminal amide group.Taken in part from the Master's Thesis of Antonio Paulo Altoé, Instituto Militar de Engenharia, Rio de Janeiro, Brasil (1979).     

Alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced from sugar-cane bagasse

The objective of the present study was to seek alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced by the cuprammonium process. The alternatives used were: (a) replacement of the solvent Cu(NH₃)₄(OH)₂, used in the original process, with Cu(EDA)₂(OH)₂, and (b) increasing the reflux time of the bagasse purification process from 1.5 to 3.0 h. The experimental results were obtained by analysis of Cu(II) content in the membranes by atomic absorption, by complexometry via UV/Vis spectroscopy of the solutions of filter paper, bagasse and lignin, and by monitoring the various stages of the purification process (by FTIR and by loss of mass), i.e. pretreatment with 0.25 M NaOH followed by treatment with 4.2 M EDA and reflux with EtOH/HNO₃ (20%, v/v). The results showed that the Cu(II) content in the membranes decreased with the use of the Cu(EDA)₂(OH)₂ solvent, that the purification process could not be improved further since cellulose degradation was observed, and that the Cu(II) content in the membranes produced was still to high for their use for hemodialysis treatment.     

Solubility, dissociation and complexation with Nd(III) and Th(IV) of oxine, thenoyltrifluoroacetone and 1,10-phenanthroline in 5.0 m NaCl

Equilibria in the system of Nd(III) and Th(IV) with 8-hydroxyquinoline (oxine), thenoyltrifluoroacetone (HTTA) and 1,10-phenanthroline (phen) in 5.0 m NaCl solution have been investigated by spectroscopy and potentiometry. The solubility and deprotonation constants of the three organics were measured to be: pK_s = 3.09 ± 0.01, pK_a1 = 5.82 ±0.02, pK_a2= 10.00 ±0.01 for oxine; pK_s = 2.49 ± 0.01, pK_a1 = 6.47 ±0.03 for HTTA; pK_s = 2.86 ± 0.02, pK_a2 = 5.82 ± 0.05 for phen. The stabilities of the corresponding metal complexes are in the order M(oxine) > M(TTA) > M(phen), where M = Nd(III), Th(IV). For all three organic ligands, the Th(IV) complexation is stronger than that of Nd(III).     

Kinetics of metal ion complex formation in micellar media. A comparison between normal and polymerized micelles

Micellar media can be used to investigate the rate of complex formation between hydrophobic extractants and metal ions. Acceleration or retardation effects may be obtained, depending on factors such as the nature of the surfactant, the hydrophilic/lipophilic character and ionization state of the extractant, etc. The present work was aimed at studying the influence of some specific parameters in producing retardation effects, which have potential application for performing separation of metal ions on a kinetic basis. The stopped-flow technique was used to measure the rate of complex formation between Cu²⁺ and complexing agents with varying alkyl chain length. Micelles made of the nonionic surfactants C₁₂EO₆, Triton X-100 and Brij 35 were first considered, which did not show any direct correlation between the rate of complex formation and the thickness of the hydrophilic layer constituted by the polar heads of the surfactant molecules.In a second approach, we have used polymerized micelles obtained from undec-10-enyltrimethyl ammonium bromide, which we assumed to be more rigid than normal micelles. Although the absence of CMC was confirmed, the rates measured in these polymerized micelles were larger than those obtained in micellar solutions of CTAB and DTAB. The results are discussed in relation with the nature of the hydrophobic domains in the different situations.Institut Nancéien de Chimie Moléculaire (I.N.C.M.), FU CNRS n=8     

GRAFTING OF HUMIC ACID ONTO COTTON CELLULOSE (Ⅱ)*

Cotton cellulose reacted with epichlorohydrin under the catalytic action of HClO_4 and H_2O to form 3-chloro-2-hydroxypropyl ether with a substitution degree of 0.61. The chlorine-containing product was treated with aliphatic diamines (ethylenediamine, propylenediamine, etc.) to produce nitrogen-containing cellulose which further reacted with humic acid to give black fiberous graft cellulose. This product contains 27—35% humic acid, 0.90 meq/g acidic groups, possesses 0.49 meq/g Cu~(2+)-complexing capacity and good mechanical strength, and can be used under pH12.     

Modeling of tracer diffusion in liquids when solute–solvent interactions are present

The linear solvation energy relationship (LSER) model is employed to correlate the tracer diffusion coefficients of 550 binary systems at 298.15 K. Among the selected solutes and solvents there exist apolar, polar and hydrogen-bonding substances that can interact with themselves (solvent polymerization) or with the other compound (solute–solvent complexes formation). The results of the proposed formulas are compared with those of other predictive equations.     

Influence of the nature of the metal ions on the complexation with chitosan.: Application to the treatment of liquid waste

The capacity of the chitosan to complex metallic ions is one of its most important potentialities. This polymer shows a selectivity according to the considered cation. In the case of divalent ions the capacity to fix the metallic ions increases from 0.02 mmol/g of chitosan for Co²⁺, Ca²⁺ to 1.2 for Cu²⁺ in the same external conditions. Considering trivalent ions this capacity is from 0.2 mmol/g of chitosan for Pr³⁺ and Cr³⁺ to 1.47 for Eu³⁺ and Nd³⁺. This selectivity seems to be independent on the size and the hardness of the ions. This order in the selectivity is confirmed using potentiometric and spectrophotometric methods and does not depend on the physical form of chitosan. Recovery tests of metals were carried out on real effluents. The first results obtained confirm the initial interest in using chitosan as a depolluting agent, especially as a film.     

Comparative study on the transition metal complexes of a novel thiacalix[4]arene derivative

A comparative study on Zn²⁺ and Cu²⁺ complexes of the novel compound 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene, that possesses potential as a core unit for the construction of molecular receptors, is presented using semiempirical AM1 calculation. The possible structures of each metal complex and their corresponding energetic data are compared with the parent 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The complexation ability of both thiacalix[4]arenes towards the two metal ions is discussed on the basis of binding energies. Both thiacalix[4]arene 1:1 complexes show higher complexation ability towards Cu²⁺. However, 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene presents lower complexation ability when compared with the 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The results of liquid–liquid extraction experiments of the thiacalix[4]arenes are in good agreement with the theoretical calculations.     

Modification of 4-(2-pyridylazo)-resorcinol postcolumn reagent selectivity through competitive equilibria with chelating ligands

Aminopolycar☐ylate ligands were added to the 4-(2-pyridylazo)-resorcinol (PAR) postcolumn reagent to alter the reagent selectivity towards transition metals. Addition of ethylenediaminetetraacetic acid (EDTA) completely suppressed the reaction between PAR and the metal ions. Addition of 0.1 mM nitrilotriacetic acid (NTA) to 1 mM PAR lowered the response to specific transition metal ions, but completely suppressed the PAR response to the lanthanides. Increasing the NTA concentration to 8 mM resulted in complete suppression of the PAR response to all metal ions except Cu²⁺ and Co²⁺ for which the detection limits were 3 and 1 ng, respectively. The observed selectivity results from the slow rate of conversion of metal ions from the M(NTA)₂⁴⁻ form to M(PAR)₂.