Phase behavior of ascorbyl palmitate in PEG400 solution

BENEDINI LUCIANO; MESSINA PAULA; SCHULZ PABLO; ALLEMANDI DANIEL; PALMA SANTIAGO

Córdoba

Congreso; 1era Reunión Internacional de Ciencias Farmacéuticas; 2010

Facultad de Ciencias Químicas - UNC

INTRODUCTION Liquid crystals (LC) have a high degree of internal order and symmetry, combined with a large interfacial area and balanced hydrophobic and hydrophilic domains content. These properties make the LC excellent universal drug carriers, with numerous advantages over most other systems currently used1. That is the reason why phase behavior of Ascorbyl Palmitate (Asc16) in solution of polietileneglycol 400 (PEG 400) have been developed. The knowledge of phase behaviors is important to describe possible zones where mesophases are present. Stabilization of these phases may carry out to new drug carrier. MATERIALS AND METHODS Ascorbyl Palmitate (AP) was purchased from (Flukka-Italia). Redistilled water by Allchemistry (Buenos Aires, Argentina) was used in all experiments. PEG 400 was purchased from (Parafarm-Argentina). Solvent was prepared with 25% Peg 400 and 75% water. Nine samples were prepared; 10, 20, 30, 40, 50, 60, 70, 80 and 90 % weight/weight (w/w). Calorimetric measurements were performed with a Q20 Differential Scanning Calorimeter (TA Instruments). Samples were prepared using sealed aluminium pans which have been weighed with a fifth cipher balance Sartorius (Germany). All runs were performed at the rate 5 ºC.min-1. The samples were treated cooling to - 20ºC during 5 minutes. Then, they were heated to 150ºC at a rate of 5 ºC.min-1 . Eventually, they were kept at this temperature for a minute. Optical microscopy was performed with a Nikon Eclipse E-200 POL polarizing (Tokyo, Japan) microscope. The scatters were heated until the temperature that DSC thermograms have been shown a phase change. RESULTS The phase diagram showed the existence of three different lamellar liquid crystals (LLC) depending on the concentration, which show different textures. One of them exists below 60% (w/w) of surfactant, with typical thin, smooth and a few birefringent oily streaks. Other kind of LLC is in between 60 and 90 % showing thick oily streaks with transversal groove and very birefringent. Finally, at very high proportions of surfactants, the system shows thin low birefringent oily streaks, a texture quite similar to that appeared below 60 % Asc16- solution. Below 60% (w/w) the mesophase has free solvent. Between 60 and 90 % (w/w) of surfactant, all solvent is associated to polar surface. Above 90 % (w/w) there is only solvation (strongly attached) solvent and pure Asc16. Below 60º C isotropic solution, crystals and gel phase has appeared below 60% (w/w). Above this concentration there is no free water; different types of crystals of surfactant appear. CONCLUSIONS The phase diagram of the system Asc16-solution (25% (w/w) PEG400 in 75% (w/w) has been done. The PEG 400 added to solution reduces the transition temperatures because it decreases the compactness of the lamellar structure . The degree of diminution of the transition temperatures produced by this proportion of PEG400 with regard to Asc16-water system was not singinficant. However, to work with LC at room temperature, we have to achieve stabilization of this mesophase. Stable liquid crystals phase is the future of the development of Asc16 applications.