Microbial resistance to current drugs associated with food spoilage and complications in diseases' treatment have resulted in increased mortality rate globally. Schiff bases are an important versatile class of organic compounds with notable pharmacological properties for various industrial applications. They are usually synthesized from a condensation reaction between a primary amine and a carbonyl. They have a wide range of activities against microbes and demonstrate good antimicrobial activity against fungi, bacteria, parasites, and viruses. The antimicrobial activity of Schiff base ligands is usually better upon metal complexation as a result of their chelating behaviour. The synthesis of Schiff bases and their metal complexes are well-documented. Therefore, it is important to categorize and compile them according to their biological significance. In this review, the antibacterial, antifungal, antiparasitic and antiviral activity of some selected heterocyclic Schiff bases and their metal complexes are discussed.

A series of Schiff bases (3.a-f) bearing benzimidazole moiety was successfully synthesized in ethanol by refluxing Oct-2-ynoic acid (1,3-dihydrobenzimidazole-2-ylidene)amide with substituted amines. Fourier transform infrared (FTIR), ultra violet light (UV-VIS), elemental analysis, proton (1 H) and carbon (13 C) nuclear magnetic resonance spectroscopy were used to characterize the newly synthesized Schiff bases. Micro dilution method was used to determine the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of the Schiff bases, against 14 human pathogenic bacteria (8 Gram negative and 6 Gram positive) and against 7 fungal strains (5 Aspergillus and 2 Fusarium) representatives. Antimalarial activity against Plasmodium falciparum and antitrypanosomal property against Trypanosoma brucei was studied in vitro at a single dose concentration of the Schiff bases. Cytotoxicity of the Schiff bases was assessed against human cervix adenocarcinoma (HeLa) cells. Results obtained show that the newly synthesized Schiff bases are very potent antimicrobial agents. Gram negative bacteria Klebsiella pneumonia and Escherichia coli were more affected on exposure to Compounds 3.c-f (MIC 7.8 µg/mL) which in turn exhibited more antibacterial potency than nalidixic acid reference drug that displayed MICs between 64 and 512 µg/mL against K. pneumonia and E. coli respectively. The test compounds also demonstrated high cytotoxic effect against Aspergillus flavus and Aspergillus carbonarius as they displayed MFC 7.8 and 15.6 µg/mL. Compound 3.c exhibited the highest fungicidal property from this series with MFC alternating between 7.8 and 15.6 µg/mL against the investigated strains. The malarial activity revealed Compounds 3.c and 3.d as the more potent antiplasmodial compounds in this group exhibiting 95% and 85% growth inhibition respectively. The IC 50 of Compounds 3.c and 3.d were determined and found to be IC 50 26.96 and 28.31 µg/mL respectively. Compound 3.a was the most cytotoxic agent against HeLa cells in this group with 48% cell growth inhibition. Compounds 3.c, 3.d and 3.f were biocompatible with HeLa cells and displayed low toxicity. With a very low cytotoxic effect against HeLa, compound 3.c stands out to be a very good antiparasitic agent and consideration to further evaluate the candidate drug against others cell lines is necessary.

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Ferrocenylimidazolium salts with methylene and phenyl groups bridging the ferrocenyl and alkylimidazolium moieties were synthesized and characterized by spectroscopic and analytical methods. Crystal structures of two new compounds are also reported. Cyclic voltammetry was used to analyze the influence of the two bridging groups or spacers on electrochemical properties of the salts relative to the shifts in the formal electrode or peak potentials (E 0 or E 1/2 ) of the ferrocene/ferrocenium redox couple. Results from this study showed that all the salts exhibited higher electrode potentials relative to ferrocene, which is due to the electron-withdrawing effect of the imidazolium ion on the ferrocenyl moiety. Application of the salts as catalysts in transfer hydrogenation of ketones resulted in high conversion of saturated ketones to corresponding alcohols and turnover numbers as high as 1880. The catalysts were chemoselective towards reduction of the C ═ C bonds of conjugated 3-penten-2-one and 4-hexen-3-one to yield saturated ketones, while unconjugated 5-hexen-2-one was hydrogenated to an unsaturated alcohol.

New flat sheet membranes possessing both organic antifouling and antibacterial properties were fabricated. The successive modification of PES with HPEI and nAg resulted in enhanced membrane properties. Most of the membranes exhibited good antibacterial activities against the bacterial strains tested. Membrane samples with nAg also displayed good antibacterial activities against bacteria E Coli. The use of cost friendly HPEI and low levels of modification, and ease of membrane fabrication was achieved.

The crystal structure of the title compound, (C23H33N2)[FeCl4], consists of 1,3-bis­(1-adamant­yl)imidazolium (BAIM) cations and tetra­hedral tetra­chloridoferrate(III) (TCF) anions. The BAIM cation possesses m symmetry, with the central imidazole ring and four C atoms of each terminal adamantyl group located on a mirror plane. The Fe and two Cl atoms of the TCF anion are also located on the mirror plane. The cyclo­hexane rings of the adamantyl groups adopt normal chair conformations.

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