Aggregation of bis(N-octanoylaminocarboxylato) magnesium(II) complexes in water/organic solvents

sThe aggregation of magnesium(II) complex surfactants of bis(N-octanoylalaninato) (= Mg(oct-ala)2) and bis(N-octanoylphenylalaninato) (= Mg(oct-phe)2) in water/organic solvent (= chloroform, 1-hexanol, and cyclohexanol) mixtures and the effect of water on the aggregation behavior were studied using electric conductivity, NMR spectroscopy, and viscosity. Because of the moderate hydrophile–lipophile balance, Mg(oct-ala)2 and Mg(oct-phe)2 form aggregates in hydrophobic organic solvents by encapsulating water which assists the dissolution and aggregation of the metal complexes. A change in the structure from a reverse micelle to an onset of bicontinuous microemulsion in water/1-hexanol or water/cyclohexanol mixed solvent was detected with an increase in the water content. The strong ionic interaction between the magnesium ion and the ligand was reflected in the characteristic aggregation behavior of the magnesium surfactants. Correlation times of the hydration water bound to the metal-complex aggregates in wet chloroform system were determined by the measurements of 2H2O longitudinal relaxation times.

Graphical abstractDiffusion coefficients of magnesium surfactant of octanoylalaninate (=Mg(OA)2) and those of 1-hexanol show that at lower water content the aggregates like a reverse micelle grow with an increase in the water content but that above the break point this structure may transform to an onset of the bicontinuous emulsion of water–hydrophobic alcohol mixtures.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Magnesium surfactants form microemulsions in aqueous 1-hexanol solutions. ► Ionicity of the magnesium–ligand bond is reflected in the aggregation behavior. ► Aggregation is significantly different between 1-hexanol and cyclohexanol. ► Reverse micelle was changed to bicontinuous one with an increase in water content.