Evidence of Modifications of Micellar Interface in Sol-Gel Glass
- PDF / 409,791 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 36 Downloads / 194 Views
0 .11 CNHCH 2 CH2 N(C H )2 2 5 CH3"CH 2 CH2CH 2 0 1
0 NQ
Structure 1 species of dibucaine and to identify its location in frozen solutions of Triton X-100 (neutral),hexadecyltrimethylammonium bromide (cationic) and lithium dodecyl sulfate (anionic) micelles, 5 and dipalmitoylphosphatidylcholine vesicles. 6 The distinct properties observed for the drug species (D and DH+) and their solubilization sites in these micelles and vesicles are consistent with a balance between hydrophobic force, surface polarity and the interfacial electrostatic potential present in the model membranes. In this paper, the dibucaine species partitioned in micelles and vesicles were immobilized in sol-gel derived glasses. The photophysical properties of drug species were examined during the gelation and xerogel stages. The results give evidence that (i) a direct interaction between the dibucaine and the sol-gel matrix dominates at the xerogel stage, and (ii) during the gelation stage, the interfacial electrostatic potential of model membrane is altered by the large hydrophilic nature of sol-gel matrix. EXPERIMENTAL The materials and methods for preparing dibucaine and dibucaine. HC1 in ethanol solutions, in Triton X- 100 (TX, neutral), lithium dodecyl sulfate (LDS, anionc), and hexadecyltrimethylammonium bromide (HTAB, cationic) micelles, and dipalmitoylphosphatidylcholine (DPPC) vesicles are similar to those reported previously. 3-6 The experimental set-up for recording the fluorescence and phosphorescence spectra and 4 lifetimes at 77 K has also been described elsewhere. ,5 The tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) were employed to process the sol-gel derived optically transparent glass for xl0-4 M dibucaine in ethanol solutions, and for lx 10-4 M dibucaine in micelles and vesicles, respectively. The micelles and vesicles were obtained by preparing the surfactant (TX, LDS, HTAB, or DPPC) in a phosphate buffer solution (pH = 6.5) at a concentration of the surfactant ten times higher than the critical micelle concentration value. The amounts of solution used for preparing gels with micelles (or vesicles) are as follows: 14.74 ml TMOS, 3.38 ml distilled water, 0.22 ml HC1 (pH = 4), and 4.58 ml dibucaine/micelles (or dibucaine/vesicles). For gels with ethanol-based solution, the following mixtures are used: 10 ml TEOS, 3.7 ml distilled water, 0.1 ml HC1 (pH =4), and 11.4 ml dibucaine/ethanol. The photophysical properties of dibucaine species were monitored at solution (before the incorporation into a gel), gelation, drying and xerogel stages. 1006
RESULTS AND DISCUSSION Emission of Dibucaine.HCI in Solutions The fluorescence and phosphorescence emission of dibucaine free base (D) in both nonpolar (methylcyclohexane, MCH) and hydrogen-bonding (ethanol) solvents at 77 K are best considered 3 ,4 to result from the In,Kt* and 3 7r,7t*, respectively. The free base and hydrogen-bonded dibucaine has a fluorescence maximum at 377.5 and 367.5 nm, a 0, 0 band of phosphorescence at 462.5 and 452.5 nm, a ratio of phosphorescence to f
Data Loading...
