TEMPERATURE-CHANGE OF THE LAMELLAR STRUCTURE OF DPPC DISACCHARIDE/WATER SYSTEMS WITH LOW WATER-CONTENT/

Temperature change in L-alpha-dipalmitoyl phosphatidylcholine (DPPC)/d isaccharide systems with low water content (less than 8 wt.%) was inve stigated using X-ray diffraction within a range of two transition temp eratures. X-ray diffraction above the higher transition temperature sh owed a broad symmetric peak, indicating the L alpha phase. Below the h igher transition temperature, two overlapping diffraction peaks we:re observed. After peak separation, temperature change in these systems w as analyzed using peak parameters of the two peaks. Peak parameters of the lower angle peak changed continuously up to and above the higher transition temperature, suggesting the systems to be in a liquid cryst al phase below the higher transition temperature. Fourier-transform in frared (FT-IR) spectra of the DPPC/trehalose system with 5.5 wt.% wate r showed the wave number of asymmetric stretching of phosphate groups to change at the lower transition temperature and that of symmetric st retching of CH2 groups, to change between the lower and higher transit ion temperatures. Thus, below the lower transition temperature, the sy stem is shown to be in a gel phase. Conformational change in phosphate groups occurred at the lower transition temperature. Within the lower and higher transition temperatures, two phases were found to coexist and transition from the gel phase to L alpha phase to occur continuous ly. Above the higher transition temperature, the system is in the L al pha phase. (C) 1998 Elsevier Science B.V. All rights reserved.