Adsorption/desorption characteristics of cis-platin on mercapto-silylated silica surfaces

High-dose cancer treatment with cis-platin (CP, cis-[Pt(NH3)(2)Cl-2]), although of therapeutic value, is limited by its toxicity. Fast removal of excess drug shortly after administration and site-specific drug release are potential partial solutions of this problem. As a first stage toward these solutions, several adsorption/desorption properties of CP have been determined and analyzed. The main adsorbent selected for this study was silica silylated with (3-mercaptopropyl)trimethoxysilane (MPTS). The properties of this mercapto-derivatized silica (SiSH) were compared with an organically modified silica sol-gel material (Ormosil) using MPTS as modifier and with nonderivatized silica (SiOH). Although Langmuirian at first glance, a more detailed analysis of the adsorption isotherm of the CP/SiSH system revealed a cooperative mechanism of adsorption, namely, an increase in adsorption affinity with coverage. This cooperativity was detected by employing a coverage-dependent adsorption-equilibrium constant. Active shifting of the adsorption equilibrium toward the desorption side was achieved with 2,3-dimercapto-1-propane sulfonic acid sodium salt in solution. On the basis of the differences in adsorption affinities between SiSH and SiOH, we demonstrated, we believe for the first time, the ability to achieve interparticle migration of an adsorbate (CP) from one matrix to another.