Abstract
Porphyrin-based metal coordination polymers (MCPs) have attracted significant attention due to their great promise for applications in phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT). However, the detailed self-assembly process of porphyrin-based MCPs is still poorly understood. This work provides a detailed study of the self-assembly process of MCPs constructed from Mn2+ and TCPP (TCPP: 5,10,15,20-tetrakis(4'-carboxyphenyl)porphyrin) in aqueous solution. Unlike the traditional nucleation and growth mechanism, we discover that there is a metastable metal-organic intermediate which is kinetically favored in the self-assembly process. And the metastable metal-organic intermediate nanotape structures could convert into thermodynamically favored nanosheets through disassembling into monomers followed by a reassembling process. Moreover, the two structurally different assemblies exhibit distinct photophysical performances. The intermediate Mn-TCPP aggregates show good light-induced singlet oxygen 1O2 generation for PDT while the thermodynamically favored stable Mn-TCPP aggregates exhibit an excellent photothermal conversion ability as photothermal agents (PTAs). This study could facilitate the control of the self-assembly pathway to fabricate complex MCPs with desirable applications.
Highlights
Metal coordination polymers (MCPs) are constructed from coordination metal ions and organic linkers followed by supramolecular assembly with hydrogen bonding, π–π stacking or hydrophobic interactions.[1,2,3,4,5] Owing to their facile synthetic procedure, high drug loading capability and low long-term toxicity, the metal coordination polymers (MCPs) have attracted numerous interest in biomedical application.[6,7,8,9,10] In the past decades, large numbers of metal-organic nanomaterials for anticancer therapy were fabricated with different sizes and morphologies. 4,11−12 Among the reported MCPs, porphyrin-based MCPs are widely studied.[13,14,15,16] Porphyrins are well-known photosensitizers for photodynamic therapy due to their highly efficient singlet oxygen 1O2 generation under light irradiation.[16,17] Zheng et, al reported that porphyrins could possess photothermal conversion capability when porphyrins aggregated with high packing density.[18,19] So, porphyrins could be utilized as photothermal agents (PTAs) for photothermal therapy (PTT)
The size and morphology of the formed Mn-TCPP assemblies were characterized by transmission electron microscope (TEM) and dynamic light scattering (DLS)
Energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) profiles (Figure S3 and Figure S4) confirmed the constituent of the Mn-TCPP nanosheets consisted of Mn and N element
Summary
Metal coordination polymers (MCPs) are constructed from coordination metal ions and organic linkers followed by supramolecular assembly with hydrogen bonding, π–π stacking or hydrophobic interactions.[1,2,3,4,5] Owing to their facile synthetic procedure, high drug loading capability and low long-term toxicity, the MCPs have attracted numerous interest in biomedical application.[6,7,8,9,10] In the past decades, large numbers of metal-organic nanomaterials for anticancer therapy were fabricated with different sizes and morphologies. 4,11−12 Among the reported MCPs, porphyrin-based MCPs are widely studied.[13,14,15,16] Porphyrins are well-known photosensitizers for photodynamic therapy due to their highly efficient singlet oxygen 1O2 generation under light irradiation.[16,17] Zheng et, al reported that porphyrins could possess photothermal conversion capability when porphyrins aggregated with high packing density.[18,19] So, porphyrins could be utilized as photothermal agents (PTAs) for photothermal therapy (PTT). The intermediate Mn-TCPP aggregates show good light-induced singlet oxygen 1O2 generation for PDT while the thermodynamic favored stable Mn-TCPP aggregates exhibit good photothermal conversion ability as photothermal agents (PTAs). We discovered that during the self-assembly process, kinetically formed metastable amorphous Mn-TCPP intermediates (tape structures) were first formed before converting into thermodynamically favored form.
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