39 research outputs found
Peculiar Mechanism of Solubilization of a Sparingly Water Soluble Drug into Polymeric Micelles. Kinetic and Equilibrium Studies
Complementary kinetic and equilibrium studies
on the solubilization process of the sparingly water soluble
tamoxifen (TAM) drug in polymeric aqueous solutions have
been performed by using the spectrophotometric method. In
particular, the amphiphilic copolymers obtained by derivatization
of polymeric chain of poly(N-2-hydroxyethyl)-DLaspartamide,
PHEA, with poly(ethylene glycol)s, PEG (2000
or 5000 Da), and/or hexadecylamine chain, C16, namely
PHEA-PEG2000-C16, PHEA-PEG5000-C16, PHEA-C16, have
been employed. Preliminary to the kinetic and equilibrium
data quantitative treatment, the molar absorption coefficient of
TAM in polymeric micelle aqueous solution has been
determined. By these studies the solubization sites of TAM
into the polymeric micelles have been determined and the solubilization mechanism has been elucidated through a
nonconventional approach by considering the TAM partitioned between three pseudophases, i.e., the aqueous pseudophase, the
hydrophilic corona, and the hydrophobic core. The simultaneous solution of the rate laws associated with each step of the
proposed mechanism allowed the calculation of the rate constants associated with the involved processes, the values of which are
independent of both the copolymer concentration and nature, with the exception of the rate of the TAM transfer from the
corona to the core. This has been attributed to the steric barrier, represented by the corona, which hampers the solubilization
into the core. The binding constant values of the TAM to the hydrophilic corona of the polymeric micelles, calculated through
the quantitative analysis of the equilibrium data, depend on the thickness of the hydrophilic headgroup, while those of the
hydrophobic core are almost independent of the copolymer type. Further confirmation to the proposed solubilization mechanism
has been provided by performing the kinetic and equilibrium measurements in the presence of PHEA-PEG2000 and PHEAPEG5000
copolymers
DYNAMICS OF THE OSCILLATORY BELOUSOV-ZHABOTINSKY REACTION IN THE PRESENCE OF A NON-IONIC POLYMER
Ultra-small mono and bimetallic nanoparticles synthesized by a novel technique in dry envronment
Effetto del polimero polipropilenglicole sulla dinamica della reazione di Belousov-Zabotinsky
Synthesis and characterization of bimetallic nanoparticles confined in dry reversed micelles
Spectrophotometric evidence for the solubilization site of betalain pigments in membrane biomimetic systems
The solubilization site of two betalain pigments, namely, betanin and indicaxantin, into L-\u3b1-dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) vesicles was investigated by a spectrophotometric study. Pigment absorbance was monitored by varying phospholipid concentration, at a constant temperature that was varied in a range including the main phase transition temperature (Tm) of the relevant phospholipid bilayer. Maximum betanin absorption increased with the increase of DPPC concentration within the entire temperature range, reaching a plateau. The binding constant (Kb) of the pigment, calculated according to a pseudo-two-phase model, varied with the temperature, indicating that betanin is located at the hydrophobic interior of the bilayer. Other measurements of binding of betanin to DMPC and of indicaxanthin to either DPPC or DMPC vesicles ruled out that these compounds were solubilized in the hydrophobic interior of these bilayers