The host-guest chemistry of
dendrimer-biomacromolecule complexes is of great significance to both design and optimization of
dendrimer-based
drug delivery and host-guest systems. Here, we characterized the interactions between
dendrimer and
heparin by isothermal titration calorimetry (ITC), (1)H nuclear magnetic resonance ((1)H NMR), pulsed-field gradient (PFG) NMR, nuclear Overhauser effect spectroscopy (NOESY), and atomic force microscopy (AFM) studies. The calorimetric results suggest that miscellaneous aggregates are formed at different stages when
heparin was titrated into a
dendrimer solution:
dendrimer-
heparin "necklace" structures, followed by the formation of larger and more stable aggregates, and then macroscopic complexes which precipitate from the
solution. The binding process is significantly influenced by
dendrimer generation, surface functionality, and ion strength, indicating that the formation of
dendrimer-
heparin aggregates is predominantly driven by electrostatic interactions. The NMR results confirm the
dendrimer-
heparin binding models established by calorimetric measurement and present a new type of
dendrimer-
heparin aggregates at higher
heparin/
dendrimer molar ratios. Formulations containing generation 5 (G5) PAMAM
dendrimers with a
heparin/G5 molar ratio of 0.5-1.2 are proposed as effective ones for the treatment of
thrombosis in noninvasive delivery routes such as nasal, pulmonary, transdermal, and oral routes. The combination of ITC and NMR in this study provides new insight into the interactions between globular and linear
polymers and the delivery of macromolecular
therapeutics such as
heparin by
dendrimers.