Abstract
Molybdenum octahedral clusters, when incorporated into an appropriate polymer matrix, are considered as promising agents for a range of biological applications. This work describes the one-pot synthesis, morphology and cellular toxicity of nano-sized polystyrene beads doped with luminescent cluster complexes [(Mo6X8)(NO3)6]2- (X=Cl, Br or I). Specifically, the particles were obtained by free radical dispersion copolymerisation of styrene and methacrylic acid or 4-vinylpyridine in the presence of the cluster complexes. The effects of the cluster loading in the reaction mixture on both the content of the final material and number-average molar mass of the copolymers were evaluated.
Highlights
IntroductionDoping of conventional polymers such as poly(methyl methacrylate) (PMMA), poly(Nvinylcarbazole), polystyrene (PS), polyurethane, etc. by phosphorescent hexanuclear octahedral cluster complexes [{M6X8}L6]m (where M is Mo and X is Cl, Br or I or M is Re and X is S or Se, while L is an apical ligand) has recently emerged as a simple and a convenient method to prepare new luminescence materials.[1,2,3,4,5,6,7,8,9,10,11,12,13,14] These hybrid materials demonstrated potential for both materials-based applications including fibrous materials for photonics and data transmission,[1, 2] polymer light-emitting diodes,[3] oxygen sensing[4] and for biomedicine, e.g. as agents for optical bioimaging[5, 6] (including X-ray luminescence computed tomography7), photodynamic therapy and photoinactivation of bacteria.[15]
Among the whole family of hexanuclear metal-clusters, octahedral molybdenum cluster complexes are at the moment the most thoroughly studied moieties due to their outstandingly high photoluminescence quantum yields that can be achieved by careful selection of inner and apical ligands.[11, 16,17,18,19,20,21]
Several routes were explored to incorporate these cluster complexes into organic matrices including (i) co-dissolution of metal clusters and polymers followed by solvent evaporation;[11], (ii) free radical polymerisation of organic monomers with pre-made cluster complexes featuring vinyl-group functionality within their ligands or counter-ions[2, 4, 8], and (iii) impregnation of cluster complexes, having labile apical ligands, into functionalised organic polymers.[5, 6]
Summary
Doping of conventional polymers such as poly(methyl methacrylate) (PMMA), poly(Nvinylcarbazole), polystyrene (PS), polyurethane, etc. by phosphorescent hexanuclear octahedral cluster complexes [{M6X8}L6]m (where M is Mo and X is Cl, Br or I or M is Re and X is S or Se, while L is an apical ligand) has recently emerged as a simple and a convenient method to prepare new luminescence materials.[1,2,3,4,5,6,7,8,9,10,11,12,13,14] These hybrid materials demonstrated potential for both materials-based applications including fibrous materials for photonics and data transmission,[1, 2] polymer light-emitting diodes,[3] oxygen sensing[4] and for biomedicine, e.g. as agents for optical bioimaging[5, 6] (including X-ray luminescence computed tomography7), photodynamic therapy and photoinactivation of bacteria.[15]. We studied the cellular toxicity of the obtained micro-spheres using the larynx carcinoma (Hep-2) cell line as a model. These materials are interesting in the context of in vitro bioimaging (for assay development and preliminary screening applications) and in vitro theranostic applications whereby imaging can be coupled with bead-mediated delivery. In contrast to metal clusters conventional fluorophores whilst widely used in many different labelling and imaging applications suffer from the very serious drawback of photobleaching. This phenomenon is problematic for all organic. In our other works 6, 14, as well as in the current work we demonstrate that octahedral molybdenum clusters have extremely low toxicity
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