Biosynthesis of Silver Nanoparticles Functionalized with Histidine and Phenylalanine Amino Acids for Potential Antioxidant and Antibacterial Activities.

Due to biochemically active secondary metabolites that assist in the reduction, stabilization, and capping of nanoparticles, plant-mediated nanoparticle synthesis is becoming more and more popular. This is because it allows for ecologically friendly, feasible, sustainable, and cost-effective green synthesis techniques. This study describes the biosynthesis of silver nanoparticles (AgNPs) functionalized with histidine and phenylalanine using the Lippia abyssinica (locally called koseret) plant leaf extract. The functionalization with amino acids was meant to enhance the biological activities of the AgNPs. The synthesized nanoparticles were characterized using UV-Visible absorption (UV-Vis), powder X-ray diffraction (pXRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The surface plasmonic resonance (SPR) peak at about 433 nm confirmed the biosynthesis of the AgNPs. FTIR spectra also revealed that the phytochemicals in the plant extract were responsible for the capping of the biogenically synthesized AgNPs. On the other hand, the TEM micrograph revealed that the morphology of AgNP-His had diameters ranging from 5 to 14 nm. The antibacterial activities of the synthesized nanoparticles against Gram-positive and Gram-negative bacteria showed a growth inhibition of 8.67 ± 1.25 and 11.00 ± 0.82 mm against Escherichia coli and Staphylococcus aureus, respectively, at a concentration of 62.5 µg/mL AgNP-His. Moreover, the nanoparticle has an antioxidant activity potential of 63.76 ± 1.25% at 250 µg/mL. The results showed that the green-synthesized AgNPs possess promising antioxidant and antibacterial activities with the potential for biological applications.

Highly selective detection of 2,4,6-trinitrophenol and Cu(2+) ions based on a fluorescent cadmium-pamoate metal-organic framework.

A luminescent cadmium-pamoate metal-organic framework, [Cd2 (PAM)2 (dpe)2 (H2 O)2 ]⋅0.5(dpe) (1), has been synthesized under hydrothermal conditions by using π-electron-rich ligands 4,4'-methylenebis(3-hydroxy-2-naphthalenecarboxylic acid) (H2 PAM) and 1,2-di(4-pyridyl)ethylene (dpe). Its structure is composed of both mononuclear and dinuclear Cd(II) building units, which are linked by the PAM and dpe ligands, resulting in a (4,8)-connected 3D framework. The π-conjugated dpe guests are located in a 1D channel of 1. The strong emission of 1 could be quenched efficiently by trace amounts of 2,4,6-trinitrophenol (TNP), even in the presence of other competing analogues such as 4-nitrophenol, 2,6-dinitrotoluene, 2,4-dinitrotoluene, nitrobenzene, 1,3-dinitrobenzene, hydroquinone, dimethylbenzene, and bromobenzene. The high sensitivity and selectivity of the fluorescence response of 1 to TNP shows that this framework could be used as an excellent sensor for identifying and quantifying TNP. In the same manner, 1 also exhibits superior selectivity and sensitivity towards Cu(2+) compared with other metal ions such as Zn(2+) , Mn(2+) , Mg(2+) , K(+) , Na(+) , Ni(2+) , Co(2+) , and Ca(2+) . This is the first MOF that can serve as a dual functional fluorescent sensor for selectively detecting trace amounts of TNP and Cu(2+) .

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.

Ligand effects on the structural dimensionality and antibacterial activities of silver-based coordination polymers.

Four Ag-based coordination polymers [Ag(Bim)] (1), [Ag2(NIPH)(HBim)] (2), [Ag6(4-NPTA)(Bim)4] (3) and [Ag2(3-NPTA)(bipy)0.5(H2O)] (4) (HBim = 1H-benzimidazole, bipy = 4,4'-bipyridyl, H2NIPH = 5-nitroisophthalic acid, H2NPTA = 3-/4-nitrophthalic acid) have been synthesized by hydrothermal reaction of Ag(i) salts with N-/O-donor ligands. Single-crystal X-ray diffraction indicated that these coordination polymers constructed from mononuclear or polynuclear silver building blocks exhibit three typical structure features from 1-D to 3-D frameworks. These compounds favour a slow release of Ag(+) ions leading to excellent and long-term antimicrobial activities, which is distinguished by their different topological structures, towards both Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus). In addition, these compounds show good thermal stability and light stability under UV-vis and visible light, which are important characteristics for their further application in antibacterial agents.