The NMR peak of 59Co(III) cationic complexes shifts upfield upon interacting with anions when the interaction is mainly electrostatic; it shifts downfield when the hydrophobic interaction acts additively with the electrostatic interaction. These trends are enhanced in micellar solution systems.

59Co NMR spectroscopy was used to study the interactions of cationic or neutral octahedral cobalt(III) complexes such as [Co(NH3)6]3+, [Co(en)3]3+ (en = ethylenediamine), [Co(NO2)(NH3)5]2+, and [Co(acac)3] (acac = acetylacetonato) with surfactants in their nematic liquid crystalline solutions. The specific interactions of the complexes with the surfactants were studied in a replacement of one surfactant by another that had a different polar group. The extent of the binding of these complexes was monitored through the 59Co quadrupole splittings. The relationship between the extent of the binding and the magnitude of the quadrupole splitting did not hold when comparing the three cationic complexes. A comparison between the potassium dodecanoate (KDodec)/tetradecyl (or decyl)trimethylammonium bromide (TDTMABr or DTMABr) and the cesium N-dodecanoyl-L-alaninate (CsDDA)/tetradecyltrimethylammonium bromide (TDTMABr) mixed surfactant systems in the interaction with [Co(NH3)6]3+ and [Co(en)3]3+ complexes showed that these complexes bind to the alaninate polar group through a weakly interacting site in the range of the intermediate composition of the mixed surfactants; such a kind of the binding was negligible or smaller in the dodecanoate system. [Co(acac)3] complex was solubilized to liquid crystals and the interactions with the surfactant depended on their polar groups in spite of the electric neutrality of the complex.

The phase behavior of the aqueous cholesteric mesophase composed of potassium N-dodecanoyl-l-alaninate (L-KDDA) was studied in the presence of various cations such as a cobalt(III) complex and cesium ions using multinuclear magnetic resonance and laser and X-ray scatterings. The cobalt(III) complexes used are [Co(NH3)6]Cl3, [Co(en)3]Cl3 (en = ethylenediamine), Δ-[Co(chxn)3]Cl3 (chxn = (R,R)-1,2-cyclohexanediamine), [Co(tn)3]Cl3 (tn = trimethylenediamine), and [Co(phen)3]Cl3 (phen = 1,10-phenanthroline). Transition temperatures from anisotropic to isotropic phases determined by 2H2O NMR spectra were appreciably dependent on the kinds and concentrations of the added cations. The NH3-, en-, tn-, and phen-complex ions were more favorable for stabilizing the aqueous mesophase of L-KDDA compared to the chxn-complex ion. The change in the order parameters for the surfactant aggregates was monitored by anisotropic splittings of the 1H NMR spectra envelope and was compared to structural parameters of the mesophase obtained from the laser and X-ray scatterings. The relationship between the pitch length and the order parameter of the cholesteric mesophase in the phen-complex system and that in the chxn-complex one showed two extreme cases; that is, in the former case the order parameter significantly increased with addition of the complex ion despite the slight change in the pitch lengths while in the latter case the reverse relationship held. The specific behavior of the mesophase can be explained from the unique interactions of these two complex ions with the alaninate surfactant. The X-ray diffraction studies revealed that the mesophase structure tends to be formed when the micelles whose major axes are perpendicular to the capillary one become dominant over the parallel ones.

An estimation of the peak areas of the 59Co NMR spectra for cobalt(III) complex ions and of the 25Mg spectra for magnesium aqua ions gave population ratios of their hidden ions, which are defined as too strongly interacting with nematic lyomesophases (composed of cationic or anionic surfactants) to contribute to the NMR spectra. The cobalt(III) complex ions used were [Co(NH3)6]3+, [Co(en)3]3+ (en = ethylenediamine), [Co(phen)3]3+ (phen = 1,10-phenanthroline), and [Co(CN)6]3−. It was revealed that appreciable amounts of multivalent ions are present as hidden ions on the lyomesophase, whose sign of charge is opposite to that of the ion in question. For such hydrophilic ions as [Co(NH3)6]3+, [Co(en)3]3+, [Co(CN)6]3−, and magnesium ions, the ions binding to the mesophases are classified into two states based on the NMR spectra: One is an outer-sphere complex (ion pair); the other is a hidden ion. In these systems the hidden ion/total ion population ratios depending on the composition of the surfactant are roughly proportional to the ion pair/total ion population ratios, which are monitored by the magnitude of the quadrupole splitting. For the phen complex, the presence of a hidden ion was observed in the range where the fraction of the anionic surfactant is high; the quadrupole splittings were also observed only in limited composition ranges.