Synthesis, characterization, and biological evaluation of some 4-((thiophen-2-yl-methylene)amino)benzenesulfonamide metal complexes

Background Sulfonamides (sulfa drugs) and the metals like mercury, copper, and silver bear antimicrobial properties. The discovery of broad-spectrum antibiotics such as penicillins, cephalosporins, and fluoroquinolones has reduced their use. However, in some instances these drugs are the first-line treatment. The metal-based sulfonamide (e.g., silver sulfadiazine) is considered as first choice treatment in post-burn therapy while the use of silver nanoparticle-cephalexin conjugate to cure Escherichia coli infection explains the synergistic effect of sulfa drugs and their metal conjugates. With growing interest in metal-based sulfonamides and the Schiff base chemistry, it was decided to synthesize sulfonamide Schiff base metal complexes as antioxidant and antimicrobial agent. Results The Fe (III), Ru (III), Co (II), Ni (II), Cu (II), Pd (II), Zn (II), Cd (II), and Hg (II) metal complexes of 4-((thiophen-2-ylmethylene)-amino)-benzenesulfonamide (TMABS) were prepared and studied for thermal stability, geometry, and other electronic properties. The ligand TMABS (Schiff base) and its metal complexes were screened in-vitro for 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and antimicrobial properties against Gram-positive (+ve) Bacillus subtilis (MTCC-441), Staphylococcus aureus (MTCC 7443), Gram-negative (-ve) Escherichia coli (MTCC 40), Salmonella typhi (MTCC 3231), and fungal strains Aspergillus niger (MTCC-1344) and Penicillium rubrum by agar well diffusion method. Results summarized in Tables 3, 4, and 5 represent the inhibitory concentration (IC50) in micromole (μM). The zone of inhibition (ZI) in millimeter (mm) represents antimicrobial properties of TMABS and its metal complexes. Conclusions The synthesized sulfanilamide Schiff base (TMABS) behaved as a neutral and bidentate ligand coordinating with metal ions through its azomethine nitrogen and thiophene sulfur to give complexes with coordination number of 4 and 6 (Fig. 3). The nucleophilic addition of sulfanilamide amino group (–NH2) group to carbonyl carbon (>C=O) of benzaldehyde gave sulfanilamide Schiff base (imine) (Fig. 2). All the metal complexes were colored and stable at room temperature. With IC50 of 9.5 ± 0.1 and 10.0 ± 0.7 μM, the Co, Cu, and Pd complexes appeared better antioxidant than the ligand TMABS (155.3±0.1 μM). The zone of inhibition (ZI) of Hg (28 mm) and Ru complexes (20 mm) were similar to the ligand TMABS (20 mm) against Aspergillus niger (MTCC-1344) as in Figs. 4, 5, and 6. None of the synthesized derivatives had shown better antimicrobial properties than the standard streptomycin sulfate and fluconazole.

Physical, Chemical and Biological Degradation of Mycotoxins in Foods and Agricultural Commodities

Aflatoxin is partially or completely degraded by irradiation, heat, or treatment with strong acids or bases, oxidizing agents or bisulfite. Hydrogen peroxide plus riboflavin denature aflatoxin in milk. Mycelia of Aspergillus parasiticus can degrade aflatoxin, possibly via fungal peroxidase. Such degradation is affected by strain of A. parasiticus, amount of mycelium, temperature, pH and concentration of aflatoxin. Adsorbants, including bentonite and activated charcoal, can physically remove aflatoxin and patulin from liquid foods. Patulin is stable at low pH values but not in the presence of large amounts of vitamin C or bisulfite. Patulin can be degraded by actively fermenting yeasts and rubratoxin can be degraded by the mycelium of Penicillium rubrum.

Fungi Associated with Dates in Saudi Arabia

The fungal counts per gram of air-dried dates, of eight local date-palm varieties, varied markedly on different synthetic media. Seri and Shakra varieties had highest fungal counts whereas Medina had the lowest. Aspergilus flavus, A. niger, Penicillium rubrum, P. oxalicum, Rhizopus stolonifer, Stemphylium verruculosum and Fusarium sp. were generally associated with various date varieties. Apparent colonization of the fungi was obtained by increasing the relative humidity to 90% at 30 and 40°C. Best growth of the isolated fungi in artificial media was obtained at 60% glucose concentration.

The Rubratoxins: Causative Agents in Food/Feedborne Disease1

The rubratoxins, toxic metabolites elaborated by Penicillium rubrum and Penicillium purpurogenum, have long been implicated in livestock disease. Because of this and renewed interest in these metabolites, this review was prepared. The following topics are discussed: rubratoxin occurrence; animal and microbial toxicity; morphology; isolation, identification and analysis; physical and chemical properties; new analytical methodologies; biosynthesis and toxin synthesis under controlled conditions.

Bioproduction of rubratoxin in a glucose–mineral salts broth with nutritional supplements and metabolic inhibitors

A sterile glucose–salts broth fortified with various metabolic inhibitors and nutritional supplements was inoculated with conidia of Penicillium rubrum P3290, and incubated quiescently at 28 °C for 14 days. Potassium sulfite and sodium metabisulfite at all test concentrations caused moderate reduction in rubratoxin formation; at high concentrations (≥2.7 × 10−2 M) accumulation of fungal tissue was also retarded. Production of rubratoxin and cell mass was inhibited by p-aminobenzoic acid; syntheses of toxin were completely blocked by 7.5 × 10−2 M of the vitamin. Effects of sodium fluoride on P. rubrum cultures grown on inorganic nitrogen sources varied from inhibition of mold growth and (or) rubratoxin A production to reduction in formation of rubratoxin B. With organic nitrogen sources, fluoride caused a 30 and 60% reduction in synthesis of rubratoxins A and B, respectively. Sodium acetate at all test concentrations enhanced formation of rubratoxin; mold growth was enhanced when acetate concentration was ≥6.0 × 10−2 M. A moderate reduction in mold growth was caused by lower acetate concentrations (1.2 × 10−2 M or 2.4 × 10−2 M). Sodium arsenite and iodoacetate at test concentrations blocked mold growth and toxin formation; sodium azide and 2,4-dinitrophenol caused a marked reduction in mold growth but inhibited toxin formation completely. However, sodium azide permitted slight growth and toxin formation when mold cultures were incubated for 28 days.