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The aim of this study is to encapsulate two drugs: 5-fluorouracil (5-FU) with the hydrophobic properties and 1-β-D-arabinofuranosylcytosine (Ara-C) with the amphiphilic properties into liposomes prepared by the modified reverse-phase evaporation method (mREV) from L-α-phosphatidylcholine dipalmitoyl (DPPC). We studied the thermotropic phase behavior of liposome entrapped 5-FU and Ara-C. It is known that the stability of liposomes depends not only on the method of chemical gradient loading, the use of membrane stabilizer such as sterols, but also on the phase transition temperature ( T) of phospholipids, which undergoes an alteration after encapsulation of drugs to liposomes. The competition of these two drugs entrapped in liposomes was analyzed by the use of two spectroscopies: H NMR and UV on the basis of the analysis of the signals of each drug in the liposome-drug system. The percent of encapsulation in DPPC/Ara-C/5-FU liposome obtained by the use of UV spectroscopy amounted 93.84 and 96.05% for 5-FU and Ara-C, respectively. Phase transition temperature T of liposomes containing Ara-C did not significantly change while for the liposomes containing 5-FU it increased in comparison with T of the reference liposomes formed from DPPC. [ABSTRACT FROM AUTHOR]

Transmission electron micrographs (TEM) showed that liposome vesicles prepared from DL-α-phosphatidylcholine dimyristoyl (1,2-ditetradecanoyl-rac-glycerol-3-phosphocholine) (DMPC) by the modified reverse-phase evaporation method (mREV) were spherical in shape and in majority of them were less than 100 nm in diameter. Differential scanning calorimetry (DSC) method was used to determine the influence of cholesterol content and pH of Tris-HCl buffer used for the preparation of liposomes on the temperature of phase transition T C of phospholipids which form the investigated liposome vesicles. The use of DSC method made it possible to determine not only the temperature of the main phase transition of phospholipids but also the temperature of the phospholipid phase transition from the tilted gel phase( L β′) to the ripple gel phase( P β′). The results were compared with those obtained with EPR study. EPR study was carried out in the temperature range from 284 to 310 K i.e. below and above the phase transition temperature T C of DMPC. On the basis of EPR spectra of spin marker 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) incorporated into the liposome, the values of parameters f were determined. Hence TEMPO can be used to observe the change in partition between aqueous and fluid lipid regions. The change in the relative values of f determined for DMPC as a function of temperature shows that this phospholipid undergoes a transition from a ‘gel phase’ to a lamellar smectic liquid crystalline phase in the presence of excess water. The EPR study of TEMPO allowed us to determine the transition temperature T C. The results were compared with those obtained with DSC method. [ABSTRACT FROM AUTHOR]

From the TG data of rubber granulates, different polyurethane and composites it can be seen that the thermal decomposition for the rubber granulate and all of the composites start above 520 K. Two major mass losses for the rubber granulates and majority of the composites were observed and thermal decomposition is essentially complete by ~820 K. The changes of activation energies of lower and higher temperature decomposition, calculated according to the different equations were observed for a priori assumed first-order reaction for devolatilisation. Differences between determined and calculated results could suggest a possible reaction between polyurethane agents and rubber granulate during the composites formations. [ABSTRACT FROM AUTHOR]