Polymorphic transformation of 1,3-distearoyl-sn-2-linoleoyl-glycerol

Polymorphic transformation behavior of sub-alpha (1), sub-alpha (2), alpha, and gamma in 1,3-distearoyl-sn-2-linoleoyl-glycerol (SLS) has been studied with X-ray diffraction, differential scanning caloremetry, and Fourier-tra nsform infrared spectroscopy. Synchrotron radiation X-ray beam was employed to observe rapid transformation processes from the sub-alpha and alpha for ms to the gamma form. The chain length structures were double in sub-alpha (1), sub-alpha (2), and alpha, whereas gamma was of triple chain-length str ucture. The subcell packing was pseudohexagonal for the two sub-alpha forms , hexagonal for the a form, and parallel type for the gamma form. In compar ison with 1,3-distearoyl-sn-2-oleoyl-glycerol (SOS), the occurrence behavio r of sub-alpha, alpha, and gamma of SLS was the same as that of SOS. Howeve r, the absence of beta' and beta was unique for SLS. The chain-chain intera ctions between the linoleoyl moieties may stabilize the gamma form, prohibi ting the transformation into beta' or beta forms. The presence of two cis d ouble bonds may cause this stabilization, revealing the disordered chain co nformation of the unsaturated chains.