Elucidation of The Self-assembly Behavior of The Amphiphilic Oligopeptides on The Surfaces

• Main Authors: Sz-yan Yu, 余思燕
• Other Authors: Yung-son Hon
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/78624883668175940157

碩士 === 國立中正大學 === 化學所 === 96 === In this thesis, we designed two oligopeptides of different length and amino acid sequence and examined their adsorption behavior on different surfaces. One is an amphiphilic 21-amino acid peptide, Hel-LK21, which consists of leucine and lysine. Another is a 16-amino acid peptide, Hel-LKC16, which is shorter than Hel-LK21 with a cysteine unit at the N-terminal. The two oligopeptides were designed such that in a-helix conformation there are hydrophilic side and hydrophobic side along the helix due to the proper disposition of all hydrophilic side chains (and all hydrophobic side chains) toward the same direction. Hel-LK21 was dissolved in 50% HFIP to maximize the a-helix percentage. Gold substrates with hydrophobic octadecanethiol monolayer or hydrophilic 16-mercaptohexadecanoic acid monolayer surfaces was placed in the oligopeptide solution for adsorption. The substrates were characterized by by ellipsometry, RA-IR, contact angle measurement and AFM. The adsorption of Hel-LK21 on two different surfaces yielded different surface structure in terms of surface coverage, morphology, peptide orientation, and wetting properties. On the octadecanethiol surface, Hel-LK21 showed grain-shape distribution with a height about 2.9 nm. On the mercaptohexadecanoic acid monolayer surface, Hel-LK21 showed sheet-like distribution and the adsorption of monolayer. After immersion for two hours, Hel-LK21 on octadecanethiol surface gradually changed from flat-lying orientation to up-right orientation. However, Hel-LK21 on the acid surface underwent this change in half an hour. In the second part, Hel-LKC16 was used whose thiol group will bind to the gold surface by Au-S bond. A SAM of propanethiol on gold surface was made and exchange reaction in Hel-LKC16 solution was carried out. The RA-IR showed that Hel-LKC16 maintained a flat-lying orientation on the gold surface. It is suggested that the hydrophobic side chains of Hel-LKC16 are in the same side when Hel-LKC16 formed a helix structure, and the hydrophobic interaction is strong to make Hel-LKC16 lying on the alkyl surface and dispersed around.