Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (7): 1365-1373.doi: 10.3866/PKU.WHXB201505051

• SOFT MATTER • Previous Articles     Next Articles

Effects of Alkyl Chain Length and Peptide Charge Distribution on Self-Assembly and Hydrogelation of Lipopeptide Amphiphiles

WANG Ji-Qian, SUN Ying-Jie, DAI Jing-Ru, ZHAO Yu-Rong, CAO Mei-Wen, WANG Dong, XU Hai   

  1. Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, Shandong Province, P. R. China
  • Received:2015-03-03 Revised:2015-05-04 Published:2015-07-08
  • Contact: WANG Ji-Qian E-mail:jqwang@upc.edu.cn
  • Supported by:

    The project was supported by the Fundamental Research Funds for the Central Universities, China (14CX06036A, 14CX05040A, 14CX02126A) and National Natural Science Foundation of China (21473255).

Abstract:

The self-assembly and hydrogelation of two series of lipopeptide amphiphiles, CnV3K2 (n=12, 14, 16) and CmKV3K (m=14, 16), were studied to determine the effects of alkyl chain length and peptide charge distribution. Both the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results showed that all lipopeptide molecules in both series self-assembled into nanotapes with a bilayer structure. The width of the nanotapes decreased with increasing alkyl chain lengths. At a given alkyl chain length, the width of the CmKV3K nanotapes was wider than that of the CnV3K2 nanotapes. Based on the circular dichroism (CD) spectra of the nanotapes, all three CnV3K2 molecules adopted a secondary structure of β sheet. In contrast, the secondary structure of the CmKV3K nanotapes comprised a mixture of α helix and β sheet. For C14KV3K, the content of the α helix structures was higher than that of the β sheet structures. Conversely, for C16KV3K, the content of the β sheet was higher than that of the α helix structures. The nanotapes of lipopeptides with long alkyl chains were narrower than those with short chains, suggesting that the increased alkyl chain hydrophobicity inhibited lateral stacking of β sheets. When compared with CnV3K2, of which the two positive charges are arranged at the carbon terminal, the separate arrangement of the two positive charges in CmKV3K reduced electrostatic repulsion and favored lateral stacking of β sheets to produce wider nanotapes. The rheological data showed that all lipopeptides formed self-supporting hydrogels at 10 mmol·L-1 and pH 8.4. The hydrogel strength of the lipopeptides with different alkyl chain lengths was nearly the same within a given series. Furthermore, the hydrogel strength of the lipopeptides in the CmKV3K series was higher than that of the lipopeptides in the CnV3K2 series. The results indicated that the hydrogel rheological property was more influenced by charge arrangement at the peptide segment than by the alkyl chain length. Also, pH influenced to a great extent the self-assembly of the lipopeptides. The lipopeptides in the CmKV3K series were more sensitive to pH than those in the CnV3K2 series.

Key words: Lipopeptide amphiphile, Self-assembly, Hydrogel, Hydrophobic interaction, Charge distribution, Rheology

MSC2000: 

  • O648