This disclosure relates to compositions for delivering agents to a subject, and in particular, to compositions for delivery of therapeutic agents or diagnostic agents in the presence or absence of targeting moieties. In part, this disclosure relates to compositions comprising a hydrophobic group with a first end and a second end, a first metal binding domain linked to the hydrophobic group, a metal ion capable of being chelated to the first metal binding domain, and an agent linked to a second metal binding domain capable of chelating to the metal ion.