Preparation of glutamic acid cholesterol ester and its gel properties

Abstract

ABSTRACT In order to overcome the problems such as low yield and complex products caused by direct esterification reaction of glutamic acid and cholesterol for the preparation of glutamic cholesterol ester (GCE), the new synthesis protocol was proposed. In this process, the amino of glutamic acid was first protected with a phthalimido group to produce followed N-phthaloyl-glutamic anhydride. Then, the glutamic anhydride was combined with cholesterol to form N-phthaloyl-glutamic cholesterol ester (NP-GCE). Finally, a de-protected GCE was obtained by hydrazine hydrate. The structures of GCE and NP-GCE were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance spectrum (1H and 13C NMR) and high-resolution mass spectra (HR-MS). The gelation properties of GCE and NP-GCE were evaluated in 15 solvents. The thermodynamic parameters of gels were studied by gel-sol transition temperature. The X-ray diffraction (XRD) was used to characterize the gelation mechanism and possible accumulation models of GCE. The results indicated that the new reaction route can eliminate the interference of amino group from glutamic acid, and the yield of GCE can reach 89.62 w%, which increased by 41.99 w% in comparison with the direct synthesis of glutamic acid and cholesterol. The gelling property demonstrated that GCE performs good gel properties in 5 solvents while NP-GCE only can from gel in 3 solvents. The gel-sol transition enthalpy of GCE is greater than that of NP-GCE, revealing the thermal stability of the gel from GCE is enhanced. XRD and SEM showed that GCE gel accumulated in lamellar structure due to the π-π stacking and hydrogen bond interactions.