Nanoparticles for use as magnetic resonance imaging contrast agents are described. The nanoparticles are made up of a polymeric support and a manganese-oxo or manganses-iron-oxo cluster having magnetic properties suitable of a contrast agent. The manganese-oxo clusters may be Mn-12 clusters, which have known characteristics of a single molecule magnet. The polymer support may form a core particle which is coated by the clusters, or the clusters may be dispersed within the polymeric agent.

Provided herein, inter alia, are compositions, methods of detecting a diseased tissue in a subject, and methods of treating a subject having cancer.

Nanostructures that, after in vivo administration, are excreted in the urine via the kidneys without being phagocytosed by macrophages and/or metabolized, and their use as pharmaceutical compositions are disclosed. A nanostructure for in vivo administration contains (i) a spherical core formed by crosslinking one to three dextran molecules with an average molecular weight of 10,000 Da or less using a crosslinker and (ii) a discontinuous shell with divalent or trivalent iron ions coordinationally bonded to crosslinker-derived hydrophilic groups on the surface of the spherical core; and has (iii) a mass ratio of dextran to iron ranging from 100:2 to 100:10, and a charge ranging from 20 mV to 0 mV.

An embodiment of the present invention has an object of providing single-macromolecule particles each having a more accurately controlled hydrodynamic diameter, an active molecular complex, a method for producing the single-macromolecule particles, and a method for imaging biological tissue. In order to attain the object, provided are single-macromolecule particles characterized by each being formed of a single macromolecule and by having a molecular weight distribution M.sub.w/M.sub.n of not more than 1.5. This makes it possible to obtain particles each having an accurately controlled hydrodynamic diameter. The single macromolecule is preferably a structure consisting of a single hydrophilic macromolecule A or a structure in which one or more side chains are bonded to a main chain, the main chain being the single hydrophilic macromolecule A, each of the one or more side chains being a hydrophilic macromolecule B.

Provided are macrocyclic compounds and compounds with two or more macrocyclic groups, iron coordinated macrocyclic compounds, and iron coordinated compounds with two or more macrocyclic groups. The iron is high-spin iron(III). The iron coordinated compounds may exhibit a negative redox potential (e.g., relative to a normal hydrogen electrode at a biologically relevant pH, for example, a pH of 6.5-7.5). The compounds can be used as MRI contrast agents.

A copolymer includes a copolymer X and a chelating agent molecule bonded to the copolymer X. The copolymer X includes structural units of (A), (B), and (C),

##STR00001##

where R.sup.1, R.sup.2, and R.sup.3 are independently a hydrogen or a C.sub.1-3 alkyl, R.sup.4 is a C.sub.1-3 alkyl, R.sup.5 is a hydrogen, a C.sub.1-18 alkyl, a 3- to 8-membered cycloalkyl optionally having a substituent, an adamantyl, a C.sub.6-18 aryl optionally having a substituent, or a 5- to 10-membered heteroaryl group optionally having a substituent, X.sup.1, X.sup.2, and X.sup.3 are independently an oxygen, a sulfur, or NR.sup.7, R.sup.6 is a hydrogen, a leaving group, or a linker, R.sup.7 is a hydrogen or a C.sub.1-3 alkyl group, m is an integer in the range of 1 to 100, and n is an integer in the range of 0 to 3.