CHARACTERIZATION OF STARBURST DENDRIMERS AND VESICLE SOLUTIONS AND THEIR INTERACTIONS BY CW-EPR AND PULSED-EPR, TEM, AND DYNAMIC LIGHT-SCATTERING

Starburst dendrimers (SBDs) of different generations (size) and level of protonations of their surface amino groups and solutions of dimyris toylphosphatidylcholine (DMPC) vesicles were analyzed, both separately and in mixtures of the two components, by negative-staining transmiss ion electron microscopy (TEM), dynamic light scattering (DLS), and, ma inly, by computer-aided continuous wave (CW)- and pulsed-electron para magnetic resonance(EPR). For the EPR study, the SBDs were labeled with a nitroxide radical (SBD-T). TE micrographs showed the vesicles as mu ltilamellar structures of spherical shape with diameters ranging from 0.2 to 1.2 m. DLS measurements provided the mean vesicle diameter (d) at ca. 400 nm, whereas the diameter of generation 6 was 7 nm. No large -sized permanent supramolecular structures (d > 400 nm) were formed. E PR measurements at room temperature were poorly informative, since (1) a fraction of the dendrimers was not interacting with the vesicles, a nd (b) the labels that were interacting with the vesicles were rotatin g quickly around the main axis. Interactions between the dendrimers an d the vesicles (tested by a decrease in rotational mobility of the lab el) became EPR-observable and quantifiable below the freezing transiti on of a portion of the solution, which could not be detected by EPR an alysis. The fraction of the dendrimers interacting with the vesicles u nderwent a glass transition. Dendrimer-vesicle interactions modified t he direction of the fast-rotation axis of the radical, and the interac tion was more effective for protonated dendrimers of a larger size, i. e., later generation. A ''complex'' was formed between one solvent mol ecule and the nitroxide radical. Interactions between the SBD-T and th e vesicle partially compressed the hydration layer of the N-O group, a nd/or the hydration layer of the vesicle headgroups was compressed ont o the unpaired-electron site. This study provides information on the p ossible utilization of starburst dendrimers as gene carriers.