| Popis: |
Interactions of progesterone with zwitterionic dipalmitoyl phosphotidylcholine (DPPC) multilamellar liposomes (MLVs) were investigated as a function of temperature and progesterone concentration by using three non-invasive techniques of Fourier transform infrared (FTIR) spectroscopy, turbidity at 440 nm and differential scanning calorimetry (DSC). The results show that 1mol% of progesterone does not induce a significant change in the shape of thermotropic profile of DPPC. However as progesterone concentration increases, the main transition temperature decreases and phase transition curve broadens. Higher concentrations (12, 18 and 24mol%) also decreased the transition temperature but not as significantly as lower concentrations. The characteristic pretransition of DPPC was completely disappeared upon the addition of progesterone. Progesterone disorders the phospholipid membranes in a concentration dependent manner. Furthermore, low concentrations of progesterone (3, 6 and 9mol%) increase the fluidity of the system but high concentrations (12, 18 and 24mol%) stabilize the membranes by decreasing the mobility of the acyl chains. The opposite effect of progesterone on membrane dynamics of low and high concentrations was also supported by turbidity studies at 440 nm. DSC peaks broaden and shift to lower temperature degrees with increasing concentrations up to 9mol% of progesterone. At 6 and 12mol% of progesterone, the curve contains more than one peak. This indicates the existence of phase separation. The pretransition of liposomes was eliminated for all samples containing progesterone. Analysis of C=O stretching bond in FTIR spectroscopy showed that progesterone does not make any hydrogen bonds with the interfacial region of DPPC liposomes, instead it induces free carbonyl groups in the system. Ester groups were found to be disordered by the addition of progesterone and the effect is profound with 6 and 9mol% concentrations. The head group of liposomes were found to make hydrogen bonding in the vicinity of 3mol% of progesterone in both phases and of 6mol% of progesterone in liquid crystalline phase by infrared spectroscopy of PO- 2 stretching mode. This hydrogen bonding is made either with the hydroxyl group of progesterone or with the water molecules around the head group. With other concentrations of progesterone, there is no evidence of hydrogen bond formation. |
