Peculiar Mechanism of Solubilization of a Sparingly Water SolubleDrug into Polymeric Micelles. Kinetic and Equilibrium Studies

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Complementary kinetic and equilibrium studieson the solubilization process of the sparingly water solubletamoxifen (TAM) drug in polymeric aqueous solutions havebeen performed by using the spectrophotometric method. Inparticular, the amphiphilic copolymers obtained by derivatizationof polymeric chain of poly(N-2-hydroxyethyl)-DLaspartamide,PHEA, with poly(ethylene glycol)s, PEG (2000or 5000 Da), and/or hexadecylamine chain, C16, namelyPHEA-PEG2000-C16, PHEA-PEG5000-C16, PHEA-C16, havebeen employed. Preliminary to the kinetic and equilibriumdata quantitative treatment, the molar absorption coefficient ofTAM in polymeric micelle aqueous solution has beendetermined. By these studies the solubization sites of TAMinto the polymeric micelles have been determined and the solubilization mechanism has been elucidated through anonconventional approach by considering the TAM partitioned between three pseudophases, i.e., the aqueous pseudophase, thehydrophilic corona, and the hydrophobic core. The simultaneous solution of the rate laws associated with each step of theproposed mechanism allowed the calculation of the rate constants associated with the involved processes, the values of which areindependent of both the copolymer concentration and nature, with the exception of the rate of the TAM transfer from thecorona to the core. This has been attributed to the steric barrier, represented by the corona, which hampers the solubilizationinto the core. The binding constant values of the TAM to the hydrophilic corona of the polymeric micelles, calculated throughthe quantitative analysis of the equilibrium data, depend on the thickness of the hydrophilic headgroup, while those of thehydrophobic core are almost independent of the copolymer type. Further confirmation to the proposed solubilization mechanismhas been provided by performing the kinetic and equilibrium measurements in the presence of PHEA-PEG2000 and PHEAPEG5000copolymers.
Lingua originaleEnglish
pagine (da-a)5037-5046
Numero di pagine10
Stato di pubblicazionePublished - 2012

All Science Journal Classification (ASJC) codes

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  • ???subjectarea.asjc.2500.2508???
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