High-performance liquid chromatography of amino acids, peptides and proteins. XCI. The influence of temperature on the chromatographic behaviour of peptides related to human growth hormone

The influence of temperature on the gradient elution properties of synthetic peptides related to residues [6-13] of human growth hormone, e.g., Leu¹-Ser-Arg-Leu-Phe-Asp-Asn-Ala⁸, has been studied by using both an octadecylsilica and a polymeric fluorocarbon stationary phase. Correlation of changes in the solute hydrophobic contact area and affinity for the stationary phase, as given by Sand log k_o values respectively, revealed that the α- and imide forms are more conformationally stable than the β-linked peptide. In addition, negative values of the standard entropy changes, ?S^o _assoc, for the transfer of the solute to the stationary phase, were observed for both α- and β-linked peptides. These results are indicative of an increased ordering of the system upon solute adsorption and implies that the open-chain peptides exist in solution in more flexible conformations, while the helical structure of the cyclised imide is more rigid and constrained. The implications of the relative conformational stability of these peptides in their roles as insulin-potentiating agents is also discussed.