Raji Feyisa Bogale

Silver carboxylate metal-organic frameworks with highly antibacterial activity and biocompatibility.

Two novel Ag-based metal-organic frameworks (MOFs) [Ag2(O-IPA)(H2O)·(H3O)] (1) and [Ag5(PYDC)2(OH)] (2) were synthesized under the hydrothermal conditions using aromatic-carboxylic acids containing hydroxyl and pyridyl groups as ligands (HO-H2IPA=5-hydroxyisophthalic acid and H2PYDC=pyridine-3, 5-dicarboxylic acid). Single crystal X-ray diffraction indicated that two compounds exhibit three-dimensional frameworks constructed from different rod-shaped molecular building blocks. Both compounds favor slow release of Ag(+) ions leading to excellent and long-term antimicrobial activities towards Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus). Their antibacterial potency was evaluated by using a minimal inhibition concentration (MIC) benchmark and an inhibition zone testing. High-resolution transmission electron microscope images indicate that the Ag-based MOFs could rupture the bacterial membrane resulting in cell death. Hematological study showed that these MOFs exhibit good biocompatibility in mice. In addition, good thermal stability and optical stability under UV-visible and visible light are beneficial for their antibacterial application.

A Water-Stable Dual-Channel Luminescence Sensor for UO2 2+ Ions Based on an Anionic Terbium(III) Metal-Organic Framework

A stable 3D TbIII -based metal-organic framework [Tb(BPDC)2 ]⋅(CH3 )2 NH2 (DUT-101) was synthesized, and it is the first efficient dual-channel luminescence sensor for aqueous UO22+ ions. DUT-101 contains an anionic three-dimensional framework and protonated dimethylamine molecules embedded within the channels. The intense green emission of DUT-101 could be highly selectively and sensitively quenched by UO22+ ions even in the presence of other competing metal ions. A possible sensing mechanism was proposed based on both suppression of luminescence resonance energy transfer and enhancement of intermolecular electron transfer. Furthermore, visual green fluorescent test papers based on DUT-101 were fabricated and could be used to discriminate UO22+ ions among various metal ions.

A terbium(III)-based coordination polymer for selective and sensitive sensing of nitroaromatics and ferric ion: synthesis, crystal structure and photoluminescence properties

A potent luminescent sensor for the detection of 4-nitrophenol (4-NP) and Fe3+ ion was developed based on a terbium(III)-based coordination polymer, [Tb(H2O)5(BTEC)][H(C5H6N2)]·3H2O (1), which was prepared under hydrothermal condition using a benzene-1,2,4,5-tetracarboxylate (BTEC) bridging ligand. 1 possesses one-dimensional zig-zag chains decorated with carboxylate functional sites and protonated 4-aminopyridine guests located in interlayer channels. The strong green emission of 1 could be efficiently quenched by trace amounts of 4-NP through a luminescence quenching mechanism even in the presence of other aromatic compounds such as 1,2-dimethylbenzene, bromobenzene, phenol, 4-bromophenol, 4-nitrotoluene, 1,2-dinitrobenzene, nitrobenzene, 2,6-dinitrotoluene, and 2,4,6-trinitrophenol. Furthermore, 1 exhibits superior luminescence quenching behavior towards Fe3+ ion over other competing interfering metallic ions such as Cr3+, Cu2+, Na+, Mg2+, Mn2+, Co2+, Fe2+, Pb2+, Pd2+, and Zn2+. The possible luminescence quenching mechanisms were also discussed. Moreover, visual fluorescent test papers based on 1 were fabricated and could be utilized for selective detection of nitroaromatic compounds and metal ions.

Template-induced synthesis and superior antibacterial activity of hierarchical Ag/TiO2 composites

Hierarchical Ag/TiO2 composites were successfully synthesized via a hydrated magnesium carbonate hydroxide template-induced route. The prepared composites possess hierarchical flower-like structure and high Brunauer–Emmett–Teller (BET) surface area of 131.9 m2 g−1. The amount of silver nanoparticles (Ag NPs) with diameter of 20–40 nm in the composite can be adjusted by the concentration of AgNO3 solution. The antibacterial potency of Ag/TiO2 composites was investigated against Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus) by determining the minimal inhibitory concentration (MIC), the growth curve of bacteria and using the zone of inhibition technique. The synergistic effect of Ag NPs and TiO2 lead to superior and long-term antimicrobial activities of the composites with a bacteriostatic rate as high as 99.99%. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the fluorescence microscopy showed the integrity of membrane of the bacteria was destroyed by adding a given amount of composites resulting in cell death as well. The mechanism of antibacterial activity of composites was also taken into account by using TEM, inductively coupled plasma atomic emission spectrometry (ICP-AES), ultraviolet visible diffuse reflectance spectroscopy and fluorescent microscopy.