Study of the hydrophobic behavior of the aliphatic side chain in the peptide

• Main Authors: Pi-Fen Li, 李碧芬
• Other Authors: Ruoh-Chyu Ruaan
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/34618903329612609680

碩士 === 中原大學 === 化學工程研究所 === 90 === This thesis comprises two parts. The first part studies the adsorption mechanism of small peptides which contain hydrophobic amino acids of aliphatic side chain on various hydrophobic adsorbents . The second part studies the possibility to use hydrophobic interaction chromatography to determine the hydrophobicity of amino acids When the four peptides,Gly-Ala-Ale-Gly (GAAG),Gly-Vle-Vle-Gly (GVVG),Gly-Ile-Ile-Gly(GIIG),Gly-Leu-Leu-Gly(GLLG),were applied to an Octyl-Sepharose column, it was found that Gly-Ala-Ale-Gly was the first eluted peptide, followed byGly-Vle-Vle-Gly, Gly-Ile-Ile-Gly. The peptide Gly-Leu-Leu-Gly came out the last. It suggested that the hydrophobicity of amino acids follow the order : Leu, Ile, Val, and Ala.This result is slightly different from what obtained from liquid-liquid partitioning since Ile is assumed more hydrophobic than Leu according to their partition coefficients in the octanol/water system. The capacity factor obtained from hydrophobic interaction chromatography was affected by both the mobile phase composition and the surface characteristics of the solid phase. We have studied the effect of the length and density of the hydrophobic ligands on the solid phase. We also studied the effect of mobile phase salt concentration on the hydrophobicity measurement. Although the values of capacity factor increased with the ligand length, the ligand density and the salt concentration, the elution order remained the same. The results suggested that the hydrophobicity of amino acids could be estimated by hydrophobic interaction chromatography. The adsorption enthalpy was estimated by the method if van’t Hoff plot. The adsorption entropy could therefore be calculated. It was found that both the adsorption enthalpy decreased and the adsorption entropy decreased as the peptides became more hydrophobic. For GVVG the adsorption enthalpy and entropy were both positive indicating that the adsorption was entropy driven. The surface dehydration is probably the determining process for the adsorption to occur. However, the adsorption enthalpy became more negative and the adsorption entropy became more negative as the peptide hydrophobicity increased. These results suggested that the direct interaction between the peptides and the ligands played a much more important role during the adsorption as the hydrophobicity of the peptides increased .