Greener Approach for Synthesis of δ-MnO2 Nanoparticles: Access to Pharmaceutically Important Pyrimidines and their Antimicrobial Activity Studies.

A sustainable approach for pharmaceutically important pyrimidine derivatives is achieved by using biogenically produced single-phase δ-MnO2 NPs under external ligand-free conditions. The phytochemicals that comprise the extract of Areca Nut Husk (ANH) have been discovered to serve as reducing agents. The role of phytochemicals is not only to aid in the reduction of Mn(VII) into Mn(IV), but they also have an important role in stabilizing the catalyst. The establishment of δ-MnO2 NPs was confirmed inveterate by FE-SEM, p-XRD, ICP-OES (Mn content = 43.17% w/w), EDX, and with an active Mn content of 43.17% w/w. A series of pyrimidine derivatives were prepared in good yields using a one-pot multicomponent synthesis approach under atmospheric conditions. In addition, hot filtration tests, control experiments, gram-scale synthesis, and mechanistic investigations were demonstrated. Additionally, antimicrobial activity studies of δ-MnO2 NPs and pyrimidine derivatives against the Gram-negative bacteria E. coli, growth curve and minimum inhibitory concentration were studied.

Room-Temperature Synthesis of Biogenic δ-MnO2 NPs for the Dehydrogenative Coupling of Diamines with Alcohols for Benzimidazole and Quinoxaline Synthesis: An Efficient Catalyst for Electrochemical Applications.

An efficient, unique, and eco-friendly biogenic synthesis of single-crystalline δ-phase manganese oxide nanoparticles (MnO2 NPs) using Gliricidia sepium leaves (GSL) extract at room temperature has been revealed for the first time. The active chemicals present in the GSL extract were found to serve as both reducing and stabilizing agents. The catalyst shows an excellent surface area of 301.13 m2 g-1, a mean pore diameter of 4.01 nm, and 39.97% w/w of active metal content. The reactivity of the synthesized catalyst was demonstrated by achieving a one-pot synthesis of benzimidazoles and quinoxalines via an acceptorless dehydrogenative coupling strategy utilizing biorenewable alcohols. The release of hydrogen gas was observed as the only side product and proven by its successful utilization for alkene reduction which supports the mechanistic elucidation. The release of hydrogen gas as a useful byproduct highlights the scientific importance of the present methodology. Additionally, gram-scale synthesis and catalyst recyclability studies are deliberated. Importantly, the δ-MnO2 NP catalyst exhibited superior catalytic activity and high durability toward hydrogen evolution reaction in alkaline media, highlighting the dual use of the catalyst. The δ-MnO2 NPs attain the current density of 10 mA/cm2 at an overpotential of 154 mV with a Tafel slope of 119 mV/dec.