Binding properties of polyamidoamine dendrimers

Dendrimers are globular, hyperbranched polymers possessing a high concentration of surface functional groups and internal cavities. These unique features make them good host molecules for small ligands. To reveal relationships between dendrimer size and its encapsulating properties, the interactions of the fourth and the sixth generations of polyamidoamine dendrimers (PAMAM G4 and PAMAM G6) with a fluorescent dye 1-anilinonaphthalene-8-sulfonate (ANS) were studied. Because ANS is a fluorescent molecule and its fluorescence is very sensitive to changes in its microenvironment, it was possible to use spectrofluorometric methods to evaluate the interactions with dendrimers. A double fluorometric titration method was used to estimate a binding constant and the number of binding centers. There were two types of dendrimer binding centers characterized by different affinity towards ANS. For PAMAM G4, the values of K-b and n for low-affinity and high-affinity sites equaled to 2.6 x 10(5), 0.60 and 3.70 x 10(6), 0.34, respectively, whereas in the case of PAMAM G6, these values equaled to 1.2 x 10(5), 76.34 and 1.38 x 10(6), 22.73. It was observed that the size of the dendrimer had a strong impact on the number of ANS molecules that interacted with dendrimers and their location within the macromolecule. (c) 2006 Wiley Periodicals, Inc.