Near-infrared spectroscopy of newly developed PEGylated lipids

Near-infrared (NIR) spectroscopy has been used to analyze a suite of synthesized PEGylated lipids (1-3) trademarked as QuSomes™. The three amphiphiles used in this study, differ in their hydrophobic chain length and contain various units of polyethylene glycol (PEG) head groups. Whilst the spectra of QuSomes™ show a common pattern, differences in the spectra are observed which enable the lipids to be distinguished. NIR absorption spectra of these new artificial lipids have been recorded in the spectral range of 4800-9000 cm−1 (∼2100-1100 nm) by using a new miniaturized spectrometer based on micro-optical-electro-mechanical systems (MOEMS) technology. Three NIR spectral regions are identified, (a) the high wavenumber region between 6500 and 9000 cm−1 attributed to the first overtone of the hydroxyl stretching and second overtone of the C-H stretching mode; (b) the 5350-5900 cm−1 region attributed to first overtone of the C-H stretching mode; and (c) the 4800-5300 cm−1 region attributed to the combination O-H stretching and second overtone of the CO stretching mode. For each of these regions, the lipids show distinctive spectra which allow their identification and characterization. NIR spectroscopy is a less used technique which does have great potential for the study of lipids, particularly to examine the behaviour of nanovesicles (liposomes) formed from lipids in aqueous suspensions. The study of such lipids is important since they are used as membrane models and prominent candidate for substance and drug delivery systems.