Effect of Palmitic Acid Conjugation on Physicochemical Properties of Peptide KTTKS: A Preformulation Study

Lys-Thr-Thr-Lys-Ser (KTTKS) minimally crosses the skin because of hydrophilicity; therefore, its palmitoyl derivative, palmitoyl-KTTKS (Pal-KTTKS), is used in cosmetic products. In spite of this, there is insuffi cient information on its physicochemical properties and the effects of palmitoylation on such properties. The aim of this study was to investigate these properties. Such information would help appropriate formulation development. KTTKS and Pal-KTTKS were synthesized and characterized for ultra violet (UV) absorption, structure [X-ray diffraction (XRD)], morphology (electron microscopy), birefringence (polarized light microscopy), partitioning,solubility, thermal behavior (melting, thermogravimetric analysis, and differential scanning calorimetry), surface activity, critical micelle concentration (CMC, by tensiometry), and stability. KTTKS and Pal-KTTKS decomposed at about 154 and 150°C, respectively, and did not show a melting point before decomposition. The maximum UV absorbance of peptides was less than 200 nm. Both peptides showed birefringence, irregular flake morphologies, and hygroscopicity. KTTKS was freely soluble in water at room temperature (logP = -1.6 ± 0.15), indicating its hydrophilic nature. logP of Pal-KTTKS was calculated to be about 3.7, indicating a lipophilic compound. Pal-KTTKS showed surface activity with a CMC value of 0.024 ± 0.004 mM (19.25 ± 2.9 mg/L),whereas KTTKS did not show such surface activity. Palmitoylation demonstrated sharp peaks in the XRD pattern of KTTKS. KTTKS and Pal-KTTKS differ mainly in terms of chemical properties and show some similarity in physical properties. These results can be used for formulation developments.