Reijo Aksela

Photodegradation of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine disuccinic acid (EDDS) within natural UV radiation range

The rate of photodegradation of two chelating agents, ethylenediaminetetraacetic acid (EDTA) and an isomeric mixture of ethylenediamine disuccinic acid (EDDS), was analysed in humic lake water and in distilled water using exposure to sunlight, and in the laboratory using lamps emitting UV radiation in the range 315-400 nm. Degradation was studied using Fe(III) complexes and sodium salts of chelates. Fe(III) complexes were illuminated at pH 3.1 and 6.5. The results demonstrated that the rate of photodegradation of Fe(III)-EDTA and Fe(III)-EDDS complexes seems to be pH dependent. In the laboratory experiments degradation occurred much faster when the original pH was 3.1 rather than 6.5. The photodegradation of the isomeric mixture of EDDS was markedly faster than the degradation of EDTA both in the laboratory and field experiments, and both in humic and distilled water. The results indicated that in natural waters photodegradation of EDDS is independent of initial speciation of EDDS, while degradation of EDTA is dependent on its existence as Fe(III)-EDTA species.

Complexation of [S,S] and mixed stereoisomers of N,N′-ethylenediaminedisuccinic acid (EDDS) with Fe(III), Cu(II), Zn(II) and Mn(II) ions in aqueous solution

The protonation and complex formation equilibria of N,N′-ethylenediaminedisuccinic acid (EDDS) in the isomeric form [S,S] and a mixture of EDDS isomers (25% [S,S], 50% [R,S], 25% [R,R]) with Fe(III), Cu(II), Zn(II) and Mn(II) have been studied in aqueous 0.1 M NaCl solution at 25 °C by potentiometric titrations. The calculations were carried out with the computer program SUPERQUAD.

Studies on biodegradable chelating ligands: complexation of iminodisuccinic acid (ISA) with Cu(II), Zn(II), Mn(II) and Fe(III) ions in aqueous solution

In a search for biodegradable chelating ligands for industrial applications, study was made of the protonation and complex formation equilibria of iminodisuccinic acid (ISA) as a mixture of two of its stereoisomers (50% [S,S] and 50% [R,S]) with Cu(II), Zn(II), Mn(II) and Fe(III) ions in aqueous 0.1 M NaCl solution by potentiometric titration at 25 °C. The model of the complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metals the complex formation was dominated by stable MLn − 4 complexes. Biodegradable and of low nitrogen content, ISA was found to be a good chelating agent in pulp bleaching.

Density Functional Complexation Study of Metal Ions with Cysteine

Metal complexes of cysteine have been studied using a density functional theory based method together with a continuum solvation model. Complexation geometries for metal complexes of cysteine with Zn(2+), Mg(2+), Ca(2+), Fe(3+), and Mn(2+) have been determined. Different coordination modes have been considered for MCys(2) and MCys(3) complexes. Complexation energies have been determined, and they have been corrected with (empirical) metal- and ligand-specific parameters, the latter of which was determined separately for Cys(N,O,S) and Cys(N,S) ligands. The results indicate that the preferred binding mode for Zn(2+) with cysteine is bidentate (N,S) type binding in tetrahedral or trigonal bipyramidal geometry while Mg(2+) and Ca(2+) prefer sulfur-free binding sites in octahedral geometry. Fe(3+) prefers binding via sulfur and nitrogen atoms, whereas for Mn(2+) several equally stable structures were found. The new correction parameters can be applied for other sulfur-containing ligands to evaluate the binding strength of a new ligand with metal ions. The observed preferences of metal ions in binding are in agreement with the previous knowledge of the behavior of metal ions.

Density functional complexation study of metal ions with (amino) polycarboxylic acid ligands

We have studied metal complexation with (amino)polycarboxylic acid ligands using density functional methods. Geometry optimisations, continuum-solvation model (COSMO), mixed cluster–continuum model, and Car–Parrinello molecular dynamics simulations have been carried out. The metal solvation energies for Mg2+, Ca2+, Mn2+, Fe3+, and Zn2+, and their complexation energies with seven (amino)polycarboxylic acid-ligands (total charges between −6 and −4) have been calculated. The solvation energies are not very accurate. The complexation energies with ligands are overestimated, but the trends are reproduced correctly. An effective parametrisation is introduced to correct for omitted contributions to energies. Explicit calculation of these corrections is discussed. The effective parametrisation results in an easy to use and fast procedure to estimate the metal ion complexation constant with different ligands.

Use of enantio-, chemo- and regioselectivity of acylase I. Resolution of polycarboxylic acid esters

Abstract Acylase I was used to catalyze the enantioselective butanolysis of trimethyl 2-[(carboxymethyl)oxy]succinate ( E =30) and N -carboxymethylaspartate ( E =9) exclusively at the most sterically hindered of the three ester groups (the position α to the asymmetric centre). Gram-scale resolution allowed the preparation of the less reactive trimethyl ( S )-2-[(carboxymethyl)oxy]succinate (96% e.e.), that of the ( R )-butyldimethyl regioisomer (78% e.e.) at 55% conversion and finally the preparation of the corresponding trisodium carboxylate by saponification. Acylase I was shown to transform (±)-methyl N -acetylmethionine and (±)-valine to the corresponding ( S )-amino acids through ester hydrolysis- N -acetyl transfer sequence with absolute chemo- and enantioselectivity. Butanolysis of methyl N -acetylmethionine stopped in the formation of the butyl ester ( E =12), the valine derivative being totally unreactive.

Complexation of 3-hydroxy-2,2′-iminodisuccinic acid (HIDS) with Mg2+, Ca2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ ions in aqueous solution

In a search for environmental-friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of 3-hydroxy-2,2′-iminodisuccinic acid with Mg2+, Ca2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ ions in aqueous 0.1 mol L−1 NaCl solution were studied at 25°C by potentiometric titration. The model for complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. In all cases, complex formation was dominated by stable ML n −4 complexes.

Complexation of N-tris[(1,2-dicarboxyethoxy)ethyl]amine with Ca(II), Mn(II), Cu(II) and Zn(II) in aqueous solution

In a search for environmentally friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of N-tris[(1,2-dicarboxyethoxy)ethyl]amine (TCA6) with Ca(II), Mn(II), Cu(II) and Zn(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. A model for complexation and stability constants of the complexes were determined. With all of the metals, complex formation was dominated by ML4−. Comparison of TCA6 and six other chelating agents showed TCA6 to be suitable for applications where strong calcium binding is essential.

Complexation of [S,S,S]- and [R,S,R]-isomers of N-bis [2-(1,2-dicarboxyethoxy)ethyl] aspartic acid with Mg(II), Ca(II), Mn(II), Fe(III), Cu(II) and Zn(II) ions in aqueous solution

In a search for environmentally friendly metal chelating ligands for industrial applications, the protonation and complex formation equilibria of [S,S,S]- and [R,S,R]-isomers of N-bis[2-(1,2-dicarboxyethoxy)ethyl] aspartic acid (BCA6) with Mg(II), Ca(II), Mn(II), Fe(III), Cu(II) and Zn(II) ions in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. The model for complexation and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metal ions (M n+), stable ML n−6 complexes dominated complex formation for both isomers. Differences in complexation models were found for binuclear species.

The complexation of novel amino acid derivatives with La(III) ion in aqueous solution

In a search for environmentally friendly metal chelating ligands the complex formation equilibria of N-bis[2-(1,2-dicarboxyethoxy)ethyl] glycine (BCA5), N-bis[2-(1,2-dicarboxyethoxy)ethyl] aspartic acid (BCA6), and N-tris[(1,2-dicarboxyethoxy)ethyl] amine (TCA6) with La(III) in aqueous 0.1 M NaCl solution were studied at 25°C by potentiometric titration. The models of the complexation and stability constants of the different complexes were determined using the computer program SUPERQUAD. With TCA6 and BCA6 complex formation was dominated by stable LaL3− and with BCA5 by LaL2− complexes.