%0 Journal Article
%T pH Responsive Self-Assembly of Cucurbit[7]urils and Polystyrene-Block-Polyvinylpyridine Micelles for Hydrophobic Drug Delivery
%A Basem A. Moosa
%A Afnan Mashat
%A Wengang Li
%A Karim Fhayli
%A Niveen M. Khashab
%J Journal of Nanomaterials
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/719168
%X Polystyrene-block-polyvinylpyridine (PS-b-P4VP) polypseudorotaxanes with cucurbit[7]urils (CB[7]) were prepared from water soluble PS-b-P4VPH+ polymer and CB[7] in aqueous solution at room temperature. At acidic and neutral pH, the pyridinium block of PS-b-P4VP is protonated (PS-b-P4VPH+) pushing CB[7] to preferably host the P4VP block. At basic pH (pH 8), P4VP is not charged and thus is not able to strongly complex CB[7]. This phenomenon was verified further by monitoring the release of pyrene, a hydrophobic cargo model, from a PS-b-P4VPH+/CB[7] micellar membrane. Release study of UV active pyrene from the membrane at different pH values revealed that the system is only operational under basic conditions and that the host-guest interaction of CB[7] with P4VPH+ significantly slows down cargo release. 1. Introduction Self-assembly of polystyrene-block-poly(4-vinylpyridine) PS-b-P4VP amphiphilic block copolymer has been studied extensively with different metals (because a variety of metal salts can be selectively coordinated to the PVP block) and at different temperatures and pH values [1¨C8]. PS-b-P4VP is a well-known block copolymer that is commercially available and can be easily synthesized by sequential anionic polymerization of styrene followed by 4-vinylpyridine (4VP) in tetrahydrofuran (THF) at £¿78¡ãC under nitrogen [9]. Multiple changes in aggregate morphology (spheres, rods, lamellae, and mixture of aggregates) of this block copolymer have been described as a function of pH [7]. The reason for this behavior or morphological complexity can be ascribed to the amphiprotic nature of P4VP where the addition of acid or base introduces ionic groups into the corona chains. Polymer micellar morphologies are useful in the field of controlled drug release, and so we reported the morphological changes and Dox release from PS-b-P4VP micellar membrane at different pH values [8]. Cucurbit[n]urils (CB[n], of glycoluril units) are a class of barrel-shaped macrocyclic hosts with symmetric carbonyl-lined portals [10¨C16]. They are capable of forming inclusion complexes with appropriately sized guest compounds in water with high affinity ( £¿M£¿1) [17]. Cucurbit[7]uril (CB[7]) has been shown to form a variety of strong, stable complexes with pyridinium cation type compounds. Polymers with such aromatic moieties promote the creation of a wide range of macromolecular architectures in water, which are held together by host-guest interaction with CB[7]. Pseudorotaxanes, a class of supramolecular species in which a molecular thread is encircled by a molecular bead, have been
%U http://www.hindawi.com/journals/jnm/2013/719168/