Synthesis and Photophysical Characterization of Several 2,3-Quinoxaline Derivatives: An Application of Pd(0)/PEG Nanoparticle Catalyst for Sonogashira Coupling

Photocatalytic Reduction of Fluorescent Dyes in Sunlight by Newly Synthesized Spiroindenoquinoxaline Pyrrolizidines

Spiroindenoquinoxaline pyrrolizidines (SIQPs)-7-nitro-2'-phenyl-5',6',7',7a'-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3'-pyrrolizine]-1',1'(2'H)-dicarbonitrile (SIQP I), 2'-(4-cyanophenyl)-7-nitro-5',6',7',7a'-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3'-pyrrolizine]-1',1'(2'H)-dicarbonitrile (SIQP II), and 2'-(4-methoxyphenyl)-7-nitro-5',6',7',7a'-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3'-pyrrolizine]-1',1'(2'H)-dicarbonitrile (SIQP III)-have been synthesized through a one-pot cascade Knoevenagel condensation reaction in acetonitrile (ACN) with 91, 98, and 87% yields, respectively. Structures are characterized by ¹H NMR and ¹³C NMR spectroscopy, nuclear Overhauser enhancement spectroscopy (NOESY), Fourier transform infrared (FT-IR) and UV-vis spectroscopy, thermogravimetric analysis (TGA), high-resolution mass spectroscopy (HRTEM), fluorescence and Raman spectroscopy, and energy-dispersive analysis by X-ray (EDX) spectroscopy. SIQPs in ACN photocatalyzed methylene blue (MB) but not phenolphthalein (HIn). SIQPs distinguished the quaternary atoms and dipoles of the fluorescent dye (MB) contrary to the quinonoid HIn structure. In sunlight, SIQPs without electricity input acted as a photonic sensor to detect fluorescent dyes in waste effluents of textile, paper, dyes, and other industries. Activation energy (E _a), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) calculated from UV-vis absorption spectra show photocatalytic reduction (PCR) activities in the order SIQP II > III > I. The N-atom of pyrrolizidine and -NO₂ of nitro-indenoquinoxaline (NIQ) induced the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) electrodynamics to enable the SIQPs to catalyze biochemical activities.

Utilizing waste corn-cob in biosynthesis of noble metallic nanoparticles for antibacterial effect and catalytic degradation of contaminants

In the present study, cost-effective, and environmentally friendly fabrication of silver and gold nanoparticles was performed by using aqueous extract of waste corn-cob. The formation of the metallic nanoparticles (MNPs) was optimized by UV-Vis method. The phytoconstituents were responsible for reduction of silver and gold ions to silver nanoparticles (CC-AgNPs) and gold nanoparticles (CC-AuNPs) which were demonstrated by Fourier-transform infrared (FTIR) spectroscopy while formation of AgCl was attributed to the presence of chloride ions in the aqueous extract. The crystalline nature of the AgNPs, AgCl, and AuNPs was confirmed using the X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. Morphological studies showed that the synthesized CC-AgNPs existed in spherical shape with the size ranging from 2 to 28 nm possessing an average value of 11 nm while CC-AuNPs were present in the multiple shapes with size ranging from 5 to 50 nm possessing an average value of 35 nm. For studies on bioactive application, the CC-AgNPs exhibited a high antibacterial activity against three bacterial strains including Salmonella typhimurium, Bacillus cereus, and Staphylococcus aureus. In addition, the catalytic efficiency of MNPs was investigated for reduction of o-, m-, p-nitrophenols, and degradation of organic dyes including Eosin Y and Rhodamine 6G. The rate constants calculated from the kinetical data revealed that the biosynthesized nanoparticles are excellent catalysts in potential applications for treatment of wastewater. Graphical abstract .

Silver and gold nanoparticles biosynthesized by aqueous extract of burdock root, Arctium lappa as antimicrobial agent and catalyst for degradation of pollutants

This study presents an efficient and facile method for biosynthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) using aqueous extract of burdock root (BR), A. lappa, and their applications. The nanoparticles were characterized by ultraviolet-visible spectrophotometry, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray, thermogravimetry, and differential thermal analysis. AgNPs capped the BR extract (BR-AgNPs) possessed roughly spherical geometry with an average diameter of 21.3 nm while uneven geometry of AuNPs capped the BR extract (BR-AuNPs) showed multi shapes in average size of 24.7 nm. The BR-AgNPs strongly inhibited five tested microorganism strains. In particular, the nanoparticles showed excellent catalytic activity for the conversion of pollutants within wastewater. Pseudo-first-order rate constants for the degradation of 4-nitrophenol, methyl orange, and rhodamine B were respectively found 6.77 × 10^-3, 3.70 × 10^-3, and 6.07 × 10^-3 s^-1 for BR-AgNPs and 6.87 × 10^-3, 6.07 × 10^-3, and 7.07 × 10^-3 s^-1 for BR-AuNPs. Graphical abstract ᅟ.