Effect of the Interionic Distance on the Interfacial Behavior of Double-Chain Zwitterionic Amphiphiles

Abstract

A series of double-chained zwitterionic sulfobetain amphiphiles (denoted as 2C16 NnSO₃, n = 2, 3, 4, and 6) having different interionic distances (spacer) was synthesized and investigated by means of surface pressure (π) – average molecular area (A) isotherms. The influences of the spacer on the 2C16 NnSO₃ monolayer, the 2C16 NnSO₃/dipalmitoylphosphatidylcholine (DPPC) binding and the 2C16 NnSO₃/DNA complex were studied. The monolayers showed obvious different interfacial behavior on pure water subphase, while the properties of the DPPC/2C16 NnSO₃ mixed monolayers are independent of the spacer length. Few interactions between 2C16 NnSO₃ and DNA were observed when n < 6 until divalent magnesium ions (Mg²⁺) was added. In comparison, significant effect of DNA on the isotherms of 2C16N6SO₃ is observed. The results demonstrated that both the spacer length played an important role in the interfacial behavior of zwitterionic amphiphiles.

Keywords:

• DNA
• double-chain amphiphile
• monolayer
• spacer
• zwitterionic

Acknowledgements

This work was supported by Natural Science Foundation of China (No. 20673021) and Ph.D. Programs Foundation of Ministry of Education of China (No. 20050386007). We are grateful to Dr. Guo-Cheng Zhang of the Institute of Chemistry, the Chinese Academy of Sciences, Beijing, People's Republic of China for providing experimental support and many useful discussions.