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Metal Ion Coordination, Conditional Stability Constants and Solution Behavior of Chelating Surfactant Metal Complexes
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
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2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 16, 4605-4612 p.Article in journal (Refereed) Published
Abstract [en]

Coordination complexes of some divalent metal ions with the DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of chelation and solution behavior. The headgroup of 4-C 12-DTPA contains eight donor atoms that can participate in the coordination of a metal ion. Conditional stability constants for five transition metal complexes with 4-C12-DTPA were determined by competition measurements between 4-C12-DTPA and DTPA, using electrospray ionization mass spectrometry (ESI-MS). Small differences in the relative strength between the coordination complexes of DTPA and 4-C12-DTPA indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. The coordination of Cu2+ ions was investigated in particular, using UV-visible spectroscopy. By constructing Job's plots, it was found that 4-C12-DTPA could coordinate up to two Cu2+ ions. Surface tension measurements and NMR diffusometry showed that the coordination of metal ions affected the solution behavior of 4-C 12-DTPA, but there were no specific trends between the studied divalent metal complexes. Generally, the effects of the metal ion coordination could be linked to the neutralization of the headgroup charge of 4-C 12-DTPA, and the resulting reduced electrostatic repulsions between adjacent surfactants in micelles and monolayers. The pH vs concentration plots, on the other hand, showed a distinct difference between 4-C12-DTPA complexes of the alkaline earth metals and the transition metals. This was explained by the difference in coordination between the two groups of metal ions, as predicted by the hard and soft acid and base (HSAB) theory.

Place, publisher, year, edition, pages
2014. Vol. 30, no 16, 4605-4612 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:miun:diva-21401DOI: 10.1021/la5002336ISI: 000335297300011Scopus ID: 2-s2.0-84899622360OAI: oai:DiVA.org:miun-21401DiVA: diva2:698031
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2016-09-29Bibliographically approved
In thesis
1. Fundamental Characterization and Technical Aspects of a Chelating Surfactant
Open this publication in new window or tab >>Fundamental Characterization and Technical Aspects of a Chelating Surfactant
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this study was to investigate the fundamental characteristics of a chelating surfactant in terms of solution behaviour, chelation of divalent metal ions, and interaction in mixtures with different foaming agents and divalent metal ion, as well as examining its prospects in some practical applications. Chelating surfactants are functional molecules, with both surface active and chelating properties, which are water soluble and therefore suitable for chelation in many aqueous environments. The dual functionality offers the possibility to recover the chelating surfactant as well as the metals.

The DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 4-C12-DTPA (2-dodecyldiethylenetriaminepentaacetic acid) was synthesized at Mid Sweden University. In the absence of metal ions, all eight donor atoms in the headgroup of 4-C12-DTPA are titrating and the headgroup charge can be tuned from +3 to -5 by altering the pH. The solution properties, studied by surface tension measurements and NMR diffusometry, were consequently found strongly pH dependent. pH measurements of chelating surfactant solutions as a function of concentration was used to extract information regarding the interaction between surfactants in the aggregation process.

Small differences in the conditional stability constants (log K) between coordination complexes of DTPA and 4-C12-DTPA, determined by competition measurements utilizing electrospray ionization mass spectrometry (ESI-MS), indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. This was further confirmed in hydrogen peroxide bleaching of thermomechanical pulp (TMP) treated with 4-C12-DTPA.

Interaction parameters for mixed systems of 4-C12-DTPA and different foaming agents were calculated following the approach of Rubingh’s regular solution theory. The mixtures were also examined with addition of divalent metal ions in equimolar ratio to the chelating surfactant. Strong correlation was found between the interaction parameter and the phase transfer efficiency of Ni2+ ions during flotations. Furthermore, a significant difference in log K between different metal complexes with 4-C12-DTPA enabled selective recovery of the metal ion with the highest log K.

The findings in this study contribute to the understanding of the fundamental characteristics of chelating surfactants, which can be further utilized in practical applications.

Place, publisher, year, edition, pages
sundsvall: Mid Sweden University, 2014. 48 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 179
Keyword
chelating surfactant, DTPA based surfactant, pH-responsive, characterization, surface tension, NMR diffusometry, conditional stability constants, interaction parameter, ion flotation
National Category
Physical Chemistry
Identifiers
urn:nbn:se:miun:diva-21405 (URN)978-91-87557-39-2 (ISBN)
Public defence
2014-03-21, Sal M102, Mittuniversitetet, sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2014-02-20Bibliographically approved
2. On metal ion chelates and conditional stability constant determination: Method development and selective ion flotation of chelating surfactants
Open this publication in new window or tab >>On metal ion chelates and conditional stability constant determination: Method development and selective ion flotation of chelating surfactants
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2014. 36 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 111
National Category
Chemical Sciences
Identifiers
urn:nbn:se:miun:diva-24029 (URN)978-91-87557-59-0 (ISBN)
Supervisors
Available from: 2015-01-02 Created: 2015-01-02 Last updated: 2015-03-13Bibliographically approved

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Svanedal, IdaBoija, SusanneAlmesåker, AnnPersson, GerdAndersson, FredrikHedenström, ErikBylund, DanNorgren, MagnusEdlund, Håkan
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