title: Investigations of thermotropic phase behavior of newly developed synthetic PEGylated lipids using Raman spectro-microscopy.
abstract: In this article, a temperature-controlled Raman spectro-microscopic technique has been utilized to detect and analyze the phase behaviors of two newly developed synthetic PEGylated lipids trademarked as QuSomes, which spontaneously form liposomes upon hydration in contrast to conventional lipids. The amphiphiles considered in this study differ in their hydrophobic hydrocarbon chain length and contain different units of polyethylene glycol (PEG) hydrophilic headgroups. Raman spectra of these new artificial lipids have been recorded in the spectral range of 500-3100 cm(-1) by using a Raman microscope system in conjunction with a temperature-controlled sample holder. The gel to liquid phase transitions of the sample lipids composed of pure 1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl-rac-glycerol-3-triicosaethylene glycol (GDS-23) have been revealed by plotting peak intensity ratios in the C-H stretching region as a function of temperature. From this study, we have found that the main phase transitions occur at a temperature of approximately 5.2 and 21.2 degrees C for pure GDM-12 and GDS-23, respectively. Furthermore, the lipid GDS-23 also shows a postphase transition temperature at 33.6 degrees C. To verify our results, differential scanning calorimetry (DSC) experiments have been conducted and the results are found to be in an excellent agreement with Raman scattering data. This important information may find application in various studies including the development of lipid-based novel substances and drug delivery systems.
authors.affiliation: Department of Physics, University of Nevada, Reno, Nevada 89557, USA. rajan@unr.edu
authors.forename: Rajan K
authors.initials: RK
authors.lastname: Bista
authors.forename: Reinhard F
authors.initials: RF
authors.lastname: Bruch
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Covington
authors.forename: Alexander
authors.initials: A
authors.lastname: Sorger
authors.forename: Thoralf
authors.initials: T
authors.lastname: Gerstmann
authors.forename: Alexander
authors.initials: A
authors.lastname: Otto
mesh_terms: D006358:Hot Temperature; D008055:Lipids / Q000138:chemical synthesis / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008853:Microscopy / Q000379:methods*; D044367:Phase Transition; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D008055:Lipids; D008081:Liposomes; D011092:Polyethylene Glycols