Fluorescent metallacycle-cored polymers via covalent linkage and their use as contrast agents for cell imaging

Abstract

The covalent linkage of supramolecular monomers provides a powerful strategy for constructing dynamic polymeric materials whose properties can be readily tuned either by the selection of monomers or the choice of functional linkers. In this strategy, the stabilities of the supramolecular monomers and the reactions used to link the monomers are crucial because such monomers are normally dynamic and can disassemble during the linking process, leading to mixture of products. Therefore, although noncovalent interactions have been widely introduced into metallacycle structures to prepare metallosupramolecular polymers, metallacyclecored polymers linked by covalent bonds have been rarely reported. Herein, we used the mild, highly efficient amidation reaction between alkylamine and N-hydroxysuccinimide-activated carboxylic acid to link the pendent amino functional groups of a rhomboidal metallacycle 10 to give metallacycle-cored polymers P1 and P2, which further yielded nanoparticles at low concentration and transformed into network structures as the concentration increased. Moreover, these polymers exhibited enhanced emission and showed better quantum yields than metallacycle 10 in methanol and methanol/water (1/9, vol/vol) due to the aggregationinduced emission properties of a tetraphenylethene-based pyridyl donor, which serves as a precursor for metallacycle 10. The fluorescence properties of these polymers were further used in cell imaging, and they showed a significant enrichment in lung cells after i.v. injection. Considering the anticancer activity of rhomboidal Pt(II) metallacycles, this type of fluorescent metallacycle-cored polymers can have potential applications toward lung cancer treatment.fluorescent polymers | supramolecular coordination complex | covalent linkage | aggregation-induced emission | cell imaging F luorescent polymers have received much attention in the chemical and life sciences due to their promising applications in biological labeling, tracking, monitoring, imaging, and diagnostics (1-3). Compared with other fluorophores such as small molecules and quantum dots, they are advantageous as biomaterials because of their good biocompatibility, ease of preparation, and biomimetic character (4-6). Conventional fluorophores show good emission in dilute solution but experience varying degrees of aggregation-caused quenching due to the intense intermolecular interactions, which will decay or relax the excited state back to the ground state via nonradiative channels (7). Such fluorophores are not ideal candidates for the preparation of fluorescent polymers, because they need to be aggregated by the polymerization process, which will more or less decrease the fluorescence emissions and the quantum yields of the derived fluorescent polymers.In 2001, Tang and coworkers (8) reported an opposite fluorescence effect named as aggregation-induced emission (AIE). In such cases, fluorophores are nearly nonemissive as discrete molecules, but they exhibit strong fluorescence in concentrated solution or in the s...

Cucurbit[7]uril Enables Multi-Stimuli-Responsive Release from the Self-Assembled Hydrophobic Phase of a Metal Organic Polyhedron

“…15a,16 Stang showed that Pt-based supramolecular coordination complexes can be utilized as theranostic supramolecular nanoparticles. 17 Nitschke and Mascarenas demonstrated that host•guest binding of an Fe-cage to an oligoarginine peptides triggered the cellular uptake of the peptide. 18 Recently, we reported a Fujita-type cubooctahedral MOP studded with 24 methyl viologen groups which non-covalently recruited CB[8] and doxorubicin prodrugs by heteroternary complexation and its ability to deliver doxorubicin to HeLa cells.…”

Antitumor Activity of a Unique Polymer That Incorporates a Fluorescent Self-Assembled Metallacycle

“…As shown in Figure 1, Pt-PAZMB- b -POEGMA was synthesized via an amidation reaction of NHS-PAZMB- b -POEGMA with a metallacyle M , where the precursors were obtained via a reversible addition-fragmentation chain-transfer polymerization reaction (Scheme S1 and Figure S1–S4) and via a literature adopted procedure, 6c respectively. The material was fully characterized by multinuclear NMR ( 1 H and 31 P) and gel permeation chromatography (GPC) analyses.…”

“…This is because in these materials the Pt←Pyridyl coordination interactions somewhat restricted the intramolecular rotations of the TPE units and impart a better emission. 6 The polymer also exhibits an aggregation induced emission property. As shown in Figure 2b, the emission intensity of an acetone solution of the polymer gradually increased upon the incremental addition of water.…”

Multicomponent Porphyrin‐Based Tetragonal Prismatic Metallacages and their Photophysical Properties

“…The F D values of metallacages 4 a and 4 c are even higher than that of TPP because the Pt(II) would promote intersystem crossing, [18] benefiting better 1 O 2 generation efficiency for metallacages. Considering the potential anticancer activity of Pt(PEt 3 ) 2 (OTf) 2 , [19] these metallacages could be potentially used as cancer theranostic agents including bio-imaging, chemotherapy and photodynamic therapy. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56…”