Chelating surfactants

The thesis summarizes and discusses results of studies regarding self-organization and complex formation of model chelating surfactants. In the study of self-organization in aqueous systems of the chelating surfactants, alkyl-N-iminodiacetic acids, the acidic constants are determined and the influence of the alkyl chain length is discussed. The crystal structures of alkyl-N-iminodiacetic acids are determined by single crystal X-ray diffraction. A short and strong hydrogen bond is identified in the structure, the oxygen-oxygen bond distance d(O(-H)...O)=2.455-2.480 Å, and the oxygen-hydrogen distance d(O-oxygen bond distance d(O-H) stretching frequency v(O-H)≈720 cm⁻¹ in methyl-N-iminodiacetic acid. The implications of the short and strong hydrogen bond in the solid state when dissolved in water, as a function of degree of aggregation, in aqueous systems are discussed. The properties of complex formation between alkyl-N-iminodiacetic acids and a selection of hard or borderline metal ions are studied, calcium(II), chromium(III), iron(III), and zinc(II). The binding properties of the amine nitrogen atom in the chelating surfactant complexes are studied in solid state and aqueous systems by extended X-ray absorption spectroscopy, EXAFS. Calcium(II) and chromium(III) ions form octahedral complexes to oxygen atoms. Iron(III) ions form octahedral complexes, in solid as oxo-bridged dimers and in aqueous solution with four bond to oxygen and two bonds to nitrogen atoms. Zinc(II) ions are generally four-coordinated to oxygen atoms in the solid state, in aqueous solution and depending on pH bonding further nitrogen atoms at longer distances, up to a six-coordination