Amphiphilic derivatives of a polyaspartamide: their aggregation and solubilization ability

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)-dl-aspartamide, 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 PHEA-PEG5000 copolymers.

Microwave-assisted synthesis of PHEA–oligoamine copolymers as potential gene delivery systems

Aims: To prepare new copolymers, useful for gene delivery, based on α, β-poly-(N-2-hydroxyethyl)-D, L-aspartamide (PHEA) as a polymeric backbone and bearing an oligoamine such as diethylenetriamine in the side chain. Moreover, in order to reduce solvent volume and make the reaction faster, microwave-assisted heating was used. Materials & methods: PHEA copolymers bearing different amounts of diethylenetriamine were prepared using bis(4-nitrophenyl) carbonate as a condensing agent with the use of microwaves. Chemical, physico–chemical and biological characterization of PHEA–diethylenetriamine copolymers and their complexes obtained with DNA were performed. Results: Copolymers showed good DNA complexing and condensing abilities depending on the oligoamine derivatization degree and good hemocompatibility. Moreover, plasmid DNA/copolymer polyplexes showed very good cytocompatibility on B16F10 and N2A cell lines. Conclusion: Results support the use of these copolymers as gene delivery systems in the future. Finally, the use of microwaves makes the proposed synthetic method advantageous as time and solvents are saved.