Reduction-responsive monoolein cubic phase containing hydrophobically modified poly(ethylene imine) and dithiodipropionic acid

Abstract

Reduction-responsive MO cubic phase was prepared by including hydrophobically modified poly(ethylene imine) (HmPEI) and dithiodipropionic acid(DTPA) in the water channel of cubic phase. HmPEI(1:2) and HmPEI(1:5) were synthesized by a condensation reaction using reaction mixtures whose hexanoyl chloride to PEI molar ratio was 1:2 and 1:5, respectively. On the 1H NMR spectrum, the PEI to hexanoyl chloride molar ratio of HmPEI(1:2) and HmPEI(1:5) was evaluated to be 1:1.0 and 1:5.1, respectively. The light scattering intensity of PEI solution was negligible, but the light scattering intensity of HmPEI solution was significantly high, possibly due to the micellization. On the plot of concentration-dependent air/water interfacial tension, HmPEI with more hydrocarbon chains (HmPEI(1:5)) showed lower minimum interfacial tension and higher surface activity. MO cubic phases containing HmPEI and DTPA were prepared by hydrating MO melt with the mixture aqueous solution of HmPEI and DTPA. The cubic phases exhibited lamellar bilayers on TEM photos, and HmPEI and DTPA had little effect on the lamellar structure. The phase transition temperature of MO cubic phase, determined by polarized optical microscopy, was about 63.5°C, and HmPEI and DTPA had no significant effect on the phase transition temperature. This was in accordance with the result obtained with differential scanning calorimetry. The release profiles of Auramine O loaded in MO cubic phase containing HmPEI and DTPA resembled 1st order release. The release degree increased upon the addition of dithiothreitol, possibly because the disulfide bond of DTPA was cleaved and the network of HmPEI and DTPA was broken down by the reducing agent.