Reversible Switching between Hydrophilic and Hydrophobic Superparamagnetic Iron Oxide Microspheres via One-Step Supramolecular Dynamic Dendronization: Exploration of Dynamic Wettability

We describe the use OF hydrophobic poly(aryl ether) dendrons to peripherally functionalize hydrophilic amine-containing superparamagnetic iron oxide microspheres (SPIO-NH(2)) in one step via imine formation. The reversible Formation of imine bonds in the absence/presence of water renders dynamic control of the hydrophilicity and hydrophobicity of the microspheres (SPIO-Gn). The dynamic nature of the imine-containing dendronized microspheres (SPIO-Gn) can be fixed by locking the, reversible 2,6-diiminopyridyl moieties with metal cations (Zn(2+), Co(2+), and Ni(2+)) to afford kinetically stable dendronized, microspheres (SPIO-Gn-M), Isolation of these microspheres is facilitated by convenient magnetic separation by an externally applied magnetic held. Characterization of these novel organic-inorganic hybrid microspheres has been performed by various techniques using UV/visible absorption and Fourier transform infrared spectroscopies, transmission electron microscopy, thermogravimetric analysis, and a vibrating sample magnetometer. We have demonstrated the stability and reversible switching of hydrophilicity/hydrophobicity by contact-angle measurements, in particular, the hydrophilic SPIO-NH(2) microspheres demonstrated a contact angle of 42 +/- 2 degrees when p a drop of water was added to a SPIO-NH(2)-coated mica surface. On the other hand, the hydrophobic SPIO-Gn-M dendronized microspheres demonstrated a contact angle of 85 +/- 2 degrees, an observation that involves an increase of the contact angle of over 400: Furthermore, when a drop of water was placed on a dynamic SPIO-Gn-coated mica surface, the contact angle or the water droplet decreased in time. Comparatively, the rate of decrease of the contact angle is H(2)O > 1 % Co(OAc)(2)/H(2)O > N,N'-dimethylformamide/H(2)O (1:1)