Single-chain polymeric nanoparticles:Toward in vivo imaging and catalysis in complex media

Folding an amphiphilic polymer around a transition metal affords homogeneous, water-soluble, and stable catalysts that are active in complex, cellular media. This chapter summarizes the progress made in this area over the last decade and explores how far research at the interface of polymer chemistry, homogeneous transition-metal-based catalysis, and disease biology can provide solutions to the treatment of complex diseases such as cancer. We start with a short overview on how single polymer chains can be constrained in their conformation by intramolecular covalent and noncovalent cross-linking processes. We then continue with discussing the compatibility of these folded/collapsed single polymer chains in and around cells. Because the stability and compatibility for these systems in water and complex media is promising, a number of biomedical applications are highlighted. First, gadolinium- and gallium-based folded polymers are attractive for magnetic resonance imaging and single-photon emission computerized tomography, respectively. In addition, folded polymers successfully serve as carriers for porphyrin-based systems that upon irradiation produce singlet oxygen, which is highly promising for photodynamic therapy. Moreover, folded polymers are also promising candidates for drug-carrier materials. Finally, examples are presented in which folded polymers operate as either carriers of reactive species or carriers of transition-metal-based catalysts to induce synthesis in living cells. The field of folded single-chain polymers is still young, and the examples discussed in this chapter highlight that many exciting challenges in the area of biomedical applications are awaiting. To successfully integrate current and future systems in complex cellular media, a seamless integration of the different disciplines is crucial.