Yukio Yamawaki

Peptide-based gemini amphiphiles: phase behavior and rheology of wormlike micelles.

Aqueous binary phase behavior of a peptide-based gemini amphiphile with glutamic acid and lysine as spacer group, acylglutamyllysilacylglutamate (m-GLG-m where m = 12, 14, and 16), has been reported over a wide range of concentration and temperature. Lauroylglutamyllysillauroylglutamate, 12-GLG-12, self-assembles into spherical micelles above critical micelle concentration (CMC). The micellar region extends up to 32 wt %, and an ordering of spherical micelles into micellar cubic phase, I(1), takes place at 33 wt % at 25 °C. The phase transition, I(1) - hexagonal liquid crystal, (H(1)) - lamellar liquid crystal, (L(α)) has been observed with further increase in concentration; moreover, mixed phases are also observed between the pure liquid crystal domains. Similar phases were observed with 16-GLG-16 above 50 °C (Krafft temperature). The partial ternary phase behavior shows that the micellar solutions of m-GLG-m can solubilize a large amount of cationic amphiphile, alkyltrimethylammonium bromide, C(n)TAB, (where n = 14 (TTAB) and 16 (CTAB)) at 25 °C. An addition of C(n)TAB to the aqueous solutions of 16-GLG-16 in a dilute region forms a transparent solution of viscoelastic wormlike micelles at very low concentration (0.25 wt %) even at ambient condition. A mixture of oppositely charged amphiphiles, m-GLG-m and C(n)TAB, exhibits synergism as a result the amphiphile layer curvature, becomes less positive, and favors the transition from sphere to rod to transient networks (wormlike micelles). The gemini amphiphile, 16-GLG-16, forms wormlike micelles at relatively low concentrations compared to others reported so far. Viscosity increases by six orders of magnitude compared to that of pure solvent. The hydrophobic chain length of m-GLG-m and coamphiphile affects the rheology; the maximum viscosity achieved with 16-GLG-16/H(2)O/CTAB is higher than that of 14-GLG-14/H(2)O/CTAB, 12-GLG-12/H(2)O/CTAB, and 16-GLG-16/H(2)O/TTAB systems. These temperature-sensitive systems exhibited viscoelastic behavior described by the Maxwell mechanical model with a single stress relaxation mode.

Skin accumulation and penetration of a hydrophilic compound by a novel gemini surfactant, sodium dilauramidoglutamide lysine.

We investigated a novel peptide-based gemini amphiphilic compound, sodium dilauramidoglutamide lysine (DLGL), as a chemical enhancer for the skin penetration of l-ascorbic acid 2-glucoside (AAG). A three-dimensional cultured human skin product, TESTSKIN™ LSE-high (LSE-high), was used as a skin model. The penetration flux of AAG with DLGL and that obtained with sodium lauramidoglutamide (LG) as a conventional surfactant across LSE-high were increased by 12.56 and 69.29 times compared to the control, respectively. The ratio of AAG amount with DLGL in the skin (21.78% total dose) was significantly increased (p<0.05) compared to the control (7.23%) and to the AAG amount with LG (8.13%). The AAG amounts in receptor were 1.06% (control), 3.19% (+DLGL) and 21.00% (+LG). Thus, DLGL preserved AAG in skin, resulting in enhanced AAG penetration flux. However, LG might create the pathways through the skin. We conclude that DLGL is a gemini surfactant that accumulates a hydrophilic compound in skin and enhances the penetration flux. DLGL may therefore be a novel addition agent for skin local therapy.