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  1. Probing the active sites of site-specific nitrogen doping in metal-free graphdiyne for electrochemical oxygen reduction reactions
    Chen X, Ong WJ, Kong Z, Zhao X, Li N
    Sci Bull (Beijing), 2020 Jan 15;65(1):45-54.
    PMID: 36659068 DOI: 10.1016/j.scib.2019.10.016
    The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology. Herein, the site-specific nitrogen doping of graphdiyne (GDY) including grap-N, sp-N(I) and sp-N(II) GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory (DFT). Our results indicate that the doped nitrogen atom can significantly improve the oxygen (O2) adsorption activity of GDY through activating its neighboring carbon atoms. The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction (ORR) in both O2 dissociation and association mechanisms. It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates. Especially, sp-N(II) GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V. This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY.
  2. Photodynamic inactivation of Burkholderia cepacia by curcumin in combination with EDTA
    Hu J, Lin S, Tan BK, Hamzah SS, Lin Y, Kong Z, et al.
    Food Res Int, 2018 09;111:265-271.
    PMID: 30007685 DOI: 10.1016/j.foodres.2018.05.042
    Burkholderia cepacia (B. cepacia) is an aerobic Gram-negative bacillus found in various aquatic environments and can cause food contamination. We investigated the photodynamic antibacterial effects of food additive curcumin combined with EDTA on B. cepacia. We found a ~4-log reduction in B. cepacia viability when photo-irradiated with curcumin at 50 μM by blue LED light (16 mW/cm2) for 30 min with 0.4% (w/v) EDTA. Moreover, the bacterial morphological alterations and the leakage of intracellular contents were observed after photodynamic treatment. There were also obvious genomic DNA cleavage and a general loss of bacterial proteins assigned to large-scale protein degradation after photodynamic inactivation treatment. Collectively, curcumin in combination with EDTA illuminated by blue LED is a potential candidate for photodynamic inactivation of B. cepacia.
  3. Enhancement of photodynamic bactericidal activity of curcumin against Pseudomonas Aeruginosa using polymyxin B
    Zhou F, Lin S, Zhang J, Kong Z, Tan BK, Hamzah SS, et al.
    Photodiagnosis Photodyn Ther, 2021 Dec 08;37:102677.
    PMID: 34890782 DOI: 10.1016/j.pdpdt.2021.102677
    BACKGROUND: Pseudomonas aeruginosa (P. aeruginosa) is an emerging opportunistic pathogen, which can cause bacterial skin diseases such as green nail syndrome, interdigital infections and folliculitis. Curcumin-mediated antimicrobial photodynamic therapy (aPDT) has been demonstrated as a promising therapeutic option for the treatment of skin infection though its inactivation of gram-negative bacteria such as P. aeruginosa.

    MATERIALS AND METHODS: In the present study, we examined the adjuvant effect of polymyxin B on the antibacterial activity of curcumin-mediated aPDT against P. aeruginosa. P. aeruginosa was treated with curcumin in the presence of 0.1-0.5 mg/L polymyxin B and irradiated by blue LED light (10 J/cm2). Bacterial cultures treated with curcumin alone served as controls. Colony forming units (CFU) were counted and the viability of P. aeruginosa was calculated after aPDT treatment. The possible underlying mechanisms for the enhanced killing effects were also explored.

    RESULTS: The killing effects of curcumin-mediated aPDT against P. aeruginosa was significantly enhanced by polymyxin B (over 2-log reductions). Moreover, it was also observed that addition of polymyxin B in the curcumin-mediated aPDT led to the apparent bacterial membrane damage with increased leakage of cytoplasmic contents and extensive DNA and protein degradation.

    DISCUSSION: The photodynamic action of curcumin against P. aeruginosa could be significantly enhanced by the FDA-approved drug polymyxin B. Our results highlight the potential of introducing polymyxin B to enhance the effects of aPDT treatment against gram-negative skin infections, in particular, P. aeruginosa.

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