ABSTRACT
Nowadays, silver-N-heterocyclic carbene (silver-NHCs) complexes are widely used in medicinal chemistry due to their low toxic nature toward humans. Due to the success of silver-NHCs in medicinal applications, interest in these compounds is rapidly increasing. Therefore, the interaction of N,N-disubstituted benzimidazolium salts with Ag2 O in dichloromethane to prepare novel Ag(I)-NHCs complexes was carried out at room temperature for 120 h in the absence of light. The obtained complexes were identified and characterized by 1 H and 13 C nuclear magnetic resonance, Fourier-transform infrared, UV-Vis, and elemental analysis techniques. Then, the silver complexes were applied for three-component coupling reactions of aldehydes, amines, and alkynes. The effect of changing the alkyl substituent on the NHCs ligand on the catalytic performance was investigated. In addition, it has been found that the complexes are antimicrobially active and show higher activity than the free ligand. The silver-carbene complexes showed antimicrobial activity against specified microorganisms with MIC values between 0.24 and 62.5 µg/ml. These results showed that the silver-NHC complexes exhibit an effective antimicrobial activity against bacterial and fungal strains. A density functional theory calculation study was performed to identify the stability of the obtained complexes. All geometries were optimized employing an effective core potential basis, such as LANL2DZ for the Ag atom and 6-311+G(d,p) for all the other atoms in the gas phase. Electrostatic potential surfaces and LUMO-HOMO energy were computed. Transition energies and excited-state structures were obtained from the time-dependent density functional theory calculations.
Subject(s)
Anti-Bacterial Agents/pharmacology , Antifungal Agents/pharmacology , Methane/analogs & derivatives , Silver Compounds/pharmacology , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/chemistry , Antifungal Agents/chemical synthesis , Antifungal Agents/chemistry , Bacteria/drug effects , Density Functional Theory , Drug Stability , Fungi/drug effects , Heterocyclic Compounds/chemical synthesis , Heterocyclic Compounds/chemistry , Heterocyclic Compounds/pharmacology , Methane/chemical synthesis , Methane/chemistry , Methane/pharmacology , Microbial Sensitivity Tests , Silver Compounds/chemical synthesis , Silver Compounds/chemistry , Static Electricity , Structure-Activity Relationship , Time FactorsABSTRACT
This work presents, for the first time, a kinetic study of the solar photo-Fenton process at neutral pH mediated by the Fe3+-NTA complex (molar ratio 1: 1) applied to remove contaminants of emerging concern (CECs). To this end, wastewater treatment plant (WWTP) secondary effluents were treated in a raceway pond reactor (RPR) at pilot plant scale with 0.1 mM Fe3+-NTA and 0.88 mM H2O2 under average solar UVA irradiance of 35 W/m2. Sulfamethoxazole and imidacloprid, at 50 µg/L of initial concentration each, were selected as model CECs. Up to 40% of the sum of both model CECs was removed from simulated WWTP effluent by the Fe3+-NTA Fenton-like process, and >80% was removed by solar photo-Fenton. The effect of liquid depth in the reactor was evaluated, showing an increase of the treatment capacity from 12 mg CEC/m2·h to 18 mg CEC/m2·h when liquid depth increased from 5 to 15 cm. Afterwards, these results were validated with real WWTP effluents and compared with the results obtained with the Fe3+-EDDS complex under the same operating conditions. The same CEC removal rates were obtained with Fe3+-NTA and Fe3+-EDDS at 5 cm of liquid depth (kinetic constants of 0.110 min-1 and 0.046 min-1 for sulfamethoxazole and imidacloprid, respectively). Conversely, at 15 cm of liquid depth, the degradation rates were lower with Fe3+-NTA (kinetic constants of 0.034 min-1 for sulfamethoxazole and 0.017 min-1 for imidacloprid), whereas with Fe3+-EDDS the values were 0.076 min-1 and 0.047 min-1 for sulfamethoxazole and imidacloprid, respectively. Regarding process cost estimation, the use of NTA as iron chelate for solar photo-Fenton at neutral pH at pilot plant scale resulted very cost-effective (0.13-0.14 /m3) in comparison with the use of EDDS (0.46-0.48 /m3) at the two liquid depths tested.
ABSTRACT
In arid Mediterranean countries, such as Tunisia, wastewater often has high salinity, being an obstacle to the elimination of microcontaminants for the reuse of water in agriculture. In this paper, the photo-Fenton process in raceway pond reactors (RPRs) has been successfully applied to a simulated secondary effluent from a Tunisian urban wastewater treatment plant (WWTP), with high chloride load. A mixture of three contaminants of emerging concern (CECs) was used as model pollutants at 50 µg/L each (one antibiotic, sulfamethoxazole and two pesticides, pyrimicarb and imidacloprid). All the assays were conducted at neutral pH with 0.1 mM Fe(III):EDDS at 1:1 molar ratio. The effect of hydrogen peroxide initial concentration (20, 30, and 90 mg/L) on microcontaminant removal was studied. Different liquid depths (5 and 15 cm) were selected to assess the relationship between the microcontaminant removal and the volumetric rate of photon absorption (VRPA). Although the reaction rate was initially photo-limited, after a short reaction time of 15 min, the final yield (≈ 80% of CEC removal) was limited by the photo-degradation of the Fe(III):EDDS complex and excess H2O2 was found at all concentrations used. Therefore, treatment times below 15 min should be used. The treatment capacity was three times higher when the liquid depth was increased from 5 to 15 cm. For the first time, these results show that the operation of a 15 cm-deep RPR in continuous flow mode would be suitable for large-scale implementation of the solar photo-Fenton process.
