Abstract
Three new photoactive polymeric materials embedding a hexanuclear molybdenum cluster (Bu4N)2[Mo6I8(CH3COO)6] (1) have been synthesized and characterized by means of Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and emission spectroscopy. The materials are obtained in the format of transparent and thin sheets, and the formulations used to synthesize them are comprised of 2-hydroxyethyl methacrylate (HEMA), as a polymerizable monomer, and ethylene glycol dimethacrylate (EGDMA) or poly(ethylene glycol)dimethacrylate (PEGDMA), as cross-linkers. All the polymeric hydrogels generate singlet oxygen (1O2) upon irradiation with visible light (400-700 nm), as demonstrated by the reactivity toward two chemical traps of this reactive species (9,10-dimethylanthracene and 1,5-dihydroxynaphthalene). Some differences have been detected between the photoactive materials, probably attributable to variations in the permeability to solvent and oxygen. Notably, one of the materials resisted up to 10 cycles of photocatalytic oxygenation reactions of 1,5-dihydroxynaphthalene. All three of the polyHEMA hydrogels doped with 1 are efficient against S. aureus biofilms when irradiated with blue light (460 nm). The material made with the composition of 90% HEMA and 10% PEGDMA (Mo6@polymer-III) is especially easy to handle, because of its flexibility, and it achieves a notable level of bacterial population reduction (3.0 log10 CFU/cm2). The embedding of 1 in cross-linked polyHEMA sheets affords a protective environment to the photosensitizer against aqueous degradation while preserving the photochemical and photobactericidal activity.
Highlights
Antibiotic-resistant bacteria are a great menace for modern societies since uncontrolled spreading of such pathogens can lead to serious nosocomial infections, which imply an enormous economic burden for public health systems.[1]
We have shown that (Bu4N)2[Mo6I8(CH3COO)6] (1) supported on macroporous and gel type cationic polystyrene is able to kill gram-positive (Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa) bacteria.[46,47]
Polymers based on monomer HEMA have been described in the literature for years due to their high water permeability and biocompatibility
Summary
Antibiotic-resistant bacteria are a great menace for modern societies since uncontrolled spreading of such pathogens can lead to serious nosocomial infections, which imply an enormous economic burden for public health systems.[1]. Antimicrobial photodynamic inactivation (aPDI) of microorganisms like bacteria, fungi and viruses is an attractive tool recently employed to prevent the spreading and growth of microbial pathogens This approach implies the use of a photosentitizer, which in combination with light leads to the generation of cytotoxic species like singlet oxygen (1O2) or superoxide (O2.-).[4,5,6,7,8,9] A great number of publications have appeared during the last years, advocating for the use of this strategy, with emphasis in the development of materials,[10,11,12,13,14] especially to be used for the manufacture of healthcare-related objects.[15,16,17]. We hope that these results will contribute to develop the field of aPDI, against bacterial biofilms, and to boost the use of this new class of {Mo6} nanoclusters in healthcare materials, such as catheters, gloves, thermometers, or in ordinary objects, such as computer keyboards, doorknobs, and mobile phone screens
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