Synthesis of Silver (I) Coordination of Aspirinate Azo Ligands as Potential Antibacterial Agents

The rise of antimicrobial resistance for infectious bacteria has become an alarming issue to human health. New antimicrobial drugs are in dire need and pivotal to overcome this issue. In this study, aspirinate azo ligands bearing different halogens L1-5 has been prepared via diazo-coupling reaction. The ligands L1-5 were coordinated with silver, Ag (I) metal to produce Ag (I) aspirin-azo complexes C1-5. The antibacterial properties of L1-5 and C1-5 were evaluated against Staphylococcus aureus and Escherichia coli using turbidimetric kinetic method. The complexes C1-5 showed comparable growth inhibition activity towards E. coli (MIC 82-105 ppm) and S. aureus (MIC 80-105 ppm) compared to ligands L1-5 with E. coli (MIC 83-200 ppm), S. aureus (80-131 ppm) and ampicillin (MIC 93 and 124 ppm, respectively). The excellent bacterial resistance of both L1-5 and C1-5 indicates the potential of aspirinate azo and their complexes as new antibacterial agents, which significantly benefit to the pharmaceutical industries.

Engineering Dirhodium Artificial Metalloenzymes for Diazo Coupling Cascade Reactions

<p>Artificial metalloenzymes (ArMs) are now commonly used to control the stereoselectivity of catalytic reactions, but controlling ArM chemoselectivity remains challenging. In this study, we engineer a dirhodium ArM to catalyze diazo cross-coupling to form an alkene that, in a one-pot cascade reaction, is reduced to an alkane with high enantioselectivity (typically >99% e.e.) by an alkene reductase. The numerous protein and small molecule components required for the cascade reaction had minimal effect on ArM catalysis, while the dirhodium cofactor itself provided only O-H insertion products from reaction with water and glucose under the same conditions. Directed evolution of the ArM led to improved yields and E/Z selectivities for a variety of substrates, which translated well to cascade reaction yields. MD simulations of ArM variants were used to understand the structural role of the cofactor on large-scale scaffold structural dynamics. These results highlight the ability of ArMs to control both catalyst stereoselectivity and chemoselectivity to enable reactions in complex media that would otherwise lead to undesired side reactions.</p>

Engineering Dirhodium Artificial Metalloenzymes for Diazo Coupling Cascade Reactions

<p>Artificial metalloenzymes (ArMs) are now commonly used to control the stereoselectivity of catalytic reactions, but controlling ArM chemoselectivity remains challenging. In this study, we engineer a dirhodium ArM to catalyze diazo cross-coupling to form an alkene that, in a one-pot cascade reaction, is reduced to an alkane with high enantioselectivity (typically >99% e.e.) by an alkene reductase. The numerous protein and small molecule components required for the cascade reaction had minimal effect on ArM catalysis, while the dirhodium cofactor itself provided only O-H insertion products from reaction with water and glucose under the same conditions. Directed evolution of the ArM led to improved yields and E/Z selectivities for a variety of substrates, which translated well to cascade reaction yields. MD simulations of ArM variants were used to understand the structural role of the cofactor on large-scale scaffold structural dynamics. These results highlight the ability of ArMs to control both catalyst stereoselectivity and chemoselectivity to enable reactions in complex media that would otherwise lead to undesired side reactions.</p>

Speciation Study of Nitrite/Nitrate through Diazo-Coupling Reaction Using Silica-Perchloric Acid as a Novel Catalyst at Trace Level: Application to Environmental Samples

A simple, sensitive and rapid spectrophotometric method has been developed based on the diazo coupling reaction in the quantification of nitrite/nitrate at trace level using silica perchloric acid (SPCA) as an acid catalyst. 5-Amino-2-mercapto benzimidazole has been used as a novel amine and coupled with N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) to produce an intense coloured azo dye. The proposed method showed wide linearity in the concentration range 0.1-1000 ppm of nitrite. The molar absorptivity and Sandell′s sensitivity were found to be 1.6 × 106 L mol–1 cm–1 and 0.0012 μg cm–2 respectively. Nitrate was measured after its reduction to nitrite using optimized copper-cadmium reductor column. The proposed method has been successfully applied to measure trace level nitrite/nitrate from a variety of sample matrices like water, soil, milk and radiator coolant.