Sugar-decorated dendritic nanocarriers: Encapsulation and release of the octahedral rhenium cluster complex [Re₆S₈(OH)₆]^4-

The encapsulation of a nanometer sized octahedral anionic rhenium cluster complex with six terminal hydroxo ligands [Re₆S₈(OH₆]^4- in maltose-decorated poly (propylene amine) dendrimers (POPAM, generation 4 and 5) has been investigated. Ultrafiltration experiments showed that maximal loading capacity of the dendrimers with the cluster complex is achieved after about ten hours in aqueous solution. To study the inclusion phenomena, three different methods have been applied: UV/vis, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser induced liquid bead ion desorption mass spectrometry (LILBID-MS). From the results obtained, it could be concluded that: (i) the hydrolytic stability of the rhenium cluster complex is significantly enhanced in the presence of dendritic hosts; (ii) the cluster anions are preferentially bound inside the dendrimers; (iii) the number of cluster complexes encapsulated in the dendrimers increases with rising dendrimer generation. On average, 4 – 5 cluster anions can preferentially be captured in the interior of sugar-coated dendritic carriers. An asymptotical progression of the release of cluster complexes from the loaded dendrimers was observed under physiologically relevant conditions (isotonic sodium chloride solution: ~ 93% within 4 days for loaded POPAM-G4-maltose; ~ 86% within 4 days for loaded POPAM-G5-maltose). Those encapsulation and release properties of maltose-decorated nanocarriers imply the possibility for the development of the next generation of dendritic nanocarriers with specific targeting of destined tissue for therapeutic treatments.