| Popis: |
The most distinctive quantities that describe structural features of lipid membranes are their phase transition temperatures which are usually determined by differential scanning calorimetry (DSC) [1]. Since the turbidity of lipid suspensions changes with temperature, it has recently been shown that UV/Vis spectroscopy can be used not only in the detection of phase transitions but also that low- and high- cooperative phase transitions can be recorded with almost equal sensitivity [2]. In this regard, we have examined suspensions of 1, 2-dipalmitoyl-sn- glycero-3-phosphocholine (DPPC) and 1, 2- dipalmitoyl-sn-glycero-3- phosphoethanolamine (DPPE) in aqueous solution of NaCl (I = 100 mM) by temperature-dependent UV/Vis spectroscopy (Figure 1.), DSC and molecular dynamics simulations. Aside the main phase transition temperatures (Tm) of DPPC ( 41 °C) and DPPE ( 63 °C) lipids and pretransition temperature (Tp) of DPPC ( 34 °C), multivariate analysis of acquired UV/Vis spectra of DPPE revealed certain changes in structural features on DPPE multilamellar aggregates about 10 degrees below Tm. Although this phenomenon does not appear in DSC curve of DPPE, the results of MD simulations imply that around this temperature the undulations of DPPE surface reach their maximum, but without formation of a ripple phase (like in DPPC). The results of this research unequivocally show that full potential of UV/Vis spectroscopy, coupled with appropriate multivariate approach, has yet to show itself in its full light in exploration of lipid bilayers structural features. |
