Abstract
A family of fifteen quaternary ammonium salts (QAs), bearing the 1,2-bis(4-pyridyl)ethane core, were obtained using for the first time two different green methods, such as microwave (MW) and ultrasounds (US) irradiation, with very good yields and in much shorter times compared to the classical method, and an assay on their antimicrobial action against Escherichia coli (E. coli) was carried out. While 12 to 24 h were required for complete alkylation of 1,2-bis(4-pyridyl)ethane by reactive halogenated derivatives in anhydrous solvent under reflux conditions, MW and US irradiation reduced the reaction time and the desired products were achieved in a few min. One of the aims of this study was to evaluate the antibacterial potential of the synthesized QAs against pathogenic bacteria, along with their impact on germination activity of wheat seeds (Triticum aestivum L.). The antibacterial activity of the QAs against Escherichia coli was explored by determining the minimum inhibitory concentration (MIC). The MIC values varied from 0.312 to 2.5 mg/mL, highlighting the lowest values attained for the derivatives containing methoxy, chlorine and benzofurane functional groups. The viability of aerobic bacteria was determined with the Tetrazolium/Formazan Test, a method that was found to be the best alternative approach with respect to the difuzimetric method. Seeds of Triticum aestivum L. were used for the evaluation of the germination indicators, such as seed germination (SG), the relative seed germination (RSG), the relative radicle growth (RRG), and the seed germination index (GI). The toxicity studies of QAs 1, 4 and 7, at two different concentrations, showed no inhibitory effect on seed germination.
Highlights
A family of fifteen quaternary ammonium salts (QAs), bearing the 1,2-bis(4-pyridyl)ethane core, were obtained using for the first time two different green methods, such as microwave (MW)
The extremely fast procedure resulted in extremely fast procedure resulted in successfully obtaining all fifteen QAs with very good yields successfully obtaining all fifteen QAs with very good yields that were very close to those of the classical that were very close to those of the classical method, where much higher solvent volumes are used method, where much higher solvent volumes are used (150 equivalents of anhydrous acetonitrile)
Considering the wide spectrum of potential applications of QAs as surfactants that are widely used for the control of bacterial growth in medical, food, and industrial environments, we investigated the effects of three selected QAs, with electronic withdrawing effects (-I and/or -E), on wheat seed germination, as the first step towards estimating the potential hazard of these chemical substances to the enviroment
Summary
A family of fifteen quaternary ammonium salts (QAs), bearing the 1,2-bis(4-pyridyl)ethane core, were obtained using for the first time two different green methods, such as microwave (MW). One of the aims of this study was to evaluate the antibacterial potential of the synthesized QAs against pathogenic bacteria, along with their impact on germination activity of wheat seeds (Triticum aestivum L.). The antibacterial activity of the QAs against Escherichia coli was explored by determining the minimum inhibitory concentration (MIC). A number of authors have reported the microwave-assisted synthesis of various organic compounds, which have been widely applied in the drug discovery field, due to enhanced reaction rates, high yields, improved purity, and greener reaction condition [2,3,4,5,6]. Numerous reports have shown that microwave heating have the capacity to accelerate chemical reactions, to increase reaction yield and to enhance product’s purity and material’s properties as compared to conventional experiments in which heating by convection or conduction is used
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