°The investigation of thermal behaviors and subsequent changes in the conformational order of lipids and liposomes is of
importance in understanding various phenomena such as the formation and fusion of vesicles, trans-membrane diffusion
and membrane interactions with drugs and proteins. In this work, the thermal behavior of a suite of newly developed
self-forming synthetic non-phospholipid (PEGylated) lipids and its nanovesicles in buffer suspensions were investigated
by variable-temperature thin-layered Fourier Transform Infrared (FTIR) transmission spectroscopy. The temperature-induced
infrared spectra of such lipids composed of 1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12)
and 1,2-distearoyl-rac-glycerol-3-triicosaethylene glycol (GDS-23) were acquired by using FTIR spectrometer in
conjunction with a custom built temperature-controlled demountable liquid cell. In contrast to conventional
phospholipids, these novel lipids form liposomes spontaneously upon hydration, without the supply of external
activation energy. It was found that the thermal stability of the PEGylated lipids defer greatly depending upon the acyl
chain-lengths as well as number of associated head group units. Particularly, GDM-12 (saturated 14 hydrocarbon chains)
shows one sharp order-disorder transition with temperature increasing from 3 to 5 °C. Similarly, GDS-23 (saturated 18
hydrocarbon chains) exhibits comparatively broad order-disorder transition profiles between temperature 17 and 22 °C.
However, the phase transition temperature becomes significantly higher for lipid nanovesicles formed in aqueous
suspensions. The results obtained in this study may find applications in various areas including the development of lipid
based substance and drug delivery systems.