Liquid-phase oxidation of betulin over supported Ag NPs catalysts: Kinetic regularities, catalyst deactivation and reactivation

Catalytic reduction of organic pollutants, antibacterial and antifungal activities of AgNPs@CuO nanoparticles-loaded mesoporous silica

In this work, the mesoporous silica MCM-41 was prepared by a hydrothermal method and then modified using silver and copper. The obtained samples were used as antibacterial/antifungal agents and as catalysts for the reduction of the following dyes: Methylene Blue (MB), Congo Red (CR), Methyl Orange (MO), and Orange G (OG). Several parameters affecting the reduction of dyes were investigated and discussed such as the catalyst nature, the initial concentration of the dye, the dye nature, the selectivity of the catalyst in a binary system as well as the catalyst reuse. The catalysts were characterized using XRD, nitrogen sorption measurements, XRF, FTIR, XPS, SEM/EDS, and TEM. XRD, XPS, and TEM analysis clearly showed that the calcination of copper- and silver-modified silica leads to the formation of well-dispersed CuO and AgNPs having sizes between 5 and 10 nm. As determined by XRF analysis, the content of silver nanoparticles was higher compared to CuO in all samples. It has been shown that the dye reduction is influenced by the size and the content of nanoparticles as well as by their dispersions. The catalytic activity was shown to be the highest for the Ag-Cu-MCM(0.05) catalyst with a rate constant of 0.114, 0.102, 0.093, and 0.056 s^-1 for MO, MB, CR, and OG dyes in the single-dye system, respectively. In the binary system containing MB/OG or MB/MO, the catalyst Ag-Cu-MCM(0.05) was more selective toward the MB dye. The reuse of the catalyst for three consecutive cycles showed higher MB conversion in a single system with an increase in reaction time. For antifungal and antibacterial properties, the application of calcined and uncalcined materials toward six different strains showed good results, but uncalcined materials showed the best results due to the synergistic effect between CuO and unreduced species Ag⁺ which are considered responsible for the antibacterial and antifungal action.

28-[1-(3-(Propionyloxy)propyl)-1H-1,2,3-triazol-4-yl]carbonylbetulin

Betulin has a broad spectrum of biological and pharmacological properties, such as anticancer, antibacterial, antifungal, and antiviral. Unfortunately, the low bioavailability makes it difficult to use in medicine. The introduction of a triazole ring to the betulin structure leads to the obtainment of new compounds with higher activity and better bioavailability. The title compound was obtained from the triazole derivative of betulin by conversion of the hydroxyl group to an ester moiety in the Steglich reaction. The chemical structure of the hybrid was characterized by nuclear magnetic resonance (1H NMR, 13C NMR, HSQC, HMBC) and HRMS spectroscopy.