Silica-supported antimony(III) chloride as a mild and reusable catalyst for the Paal–Knorr pyrrole synthesis

Heterogeneous catalysts are used for control of environmental pollution. Heterogeneous catalysts are easily separated from the reaction mixture, thus allowing their recovery and re-use. There is a need for catalysts that are efficient under mild conditions. Here, we show that silica-supported antimony(III) chloride (SbCl₃/SiO₂) acts as a highly efficient heterogeneous Lewis acid catalyst for the Paal–Knorr pyrrole synthesis at room temperature. We found that condensation of hexane-2,5-dione with aromatic and aliphatic primary amines in hexane using SbCl₃/SiO₂ with 7.6 wt% SbCl₃ was the best reaction condition. The silica support facilitated the workup of the reaction mixture and provided a reusable catalyst at least for 7 runs without significant loss in activity. Indeed, the yield was 98% for the first run and 84% for the 7th run. We conclude that low catalyst loading, operational simplicity, practicability and applicability to various substrates make this reaction an interesting alternative to previously applied procedures. From the environmental standpoint, this eco-friendly catalyst is stable, highly active, easy to prepare and handle.     

Vitamin B1 as a metal-free organocatalyst for greener Paal–Knorr pyrrole synthesis

This investigation discloses a greener reaction to prepare pyrrole derivatives. Metal-free catalysts are greener alternatives to existing metal catalysts in synthetic organic chemistry. Indeed, transition metals are often costly and toxic. They may be found as traces in health reaction products such as pharmaceuticals. Alternatively small organic molecules termed “organocatalysts” allow the synthesis of valuable products without traces of toxic metals. Here, we show for the first time the use of vitamin B₁ as new organocatalyst for the Paal–Knorr pyrrole synthesis under ambient conditions. Reaction conditions were optimized for the reaction of hexane-2,5-dione with 4-methoxyaniline. Ethanol was the most effective solvent. The conversion was quantitative using vitamin B₁, by comparison with a low yield of 30?% without catalysis. The best conditions were performed in ethanol with 5?mol % of vitamin B₁ during 1?h. This reaction was tested using various aromatic amines. To conclude the use of vitamin B₁ for the Paal–Knorr pyrrole, cyclocondensation has mild reaction conditions, is simple to perform, and gives moderate to excellent yields. It is therefore a promising reaction for the preparation of various pyrrole derivatives.     

Concentrations of Cd,Ni, Pb,and Cr in the two edible fish species Liza klunzingeri and Sillago sihama collected from Hara biosphere in Iran

The concentrations of four metals (Cd, Ni, Pb, and Cr) were determined in the muscles, gills, and livers of two edible fish species (Liza klunzingeri and Sillago sihama) caught from the Hara biosphere of Southern Iran. In both fish species, metal concentrations and bioaccumulation factors were in the sequence liver?>?gill?>?muscle. Bioaccumulation factors were found to be highest in S. sihama. The metal concentrations were descending in the order of Ni?>?Cr?>?Pb?>?Cd, except for muscle samples from S. sihama showing an inversion of Pb and Cr. There is a significant negative correlation between the concentrations of the metals in each tissue with length, weight, and age, except for muscle in L. klunzingeri. Some metal levels in the muscle exceeded the limits recommended by FAO, WHO, and FEPA.     

Antiaflatoxigenic activity of Carum copticum essential oil

Plants are unique sources of useful metabolites. Plant essential oils display a wide range of antimicrobial effects against various pathogens. Here, we studied the essential oil from the seeds of Carum copticum. We monitored aflatoxin by high-performance liquid chromatography. Results show that Carum copticum essential oil inhibits Asergillus parasiticus growth and prevents aflatoxin production. The half-maximal inhibitory concentration (IC₅₀) is 127.5 μg mL^?1 for aflatoxin B₁ and 23.22 μg mL^?1 for aflatoxin G₁. Our findings show that Carum copticum essential oil is a potential candidate for the protection of foodstuff and feeds from toxigenic fungus growth and their subsequent aflatoxin contamination.     

Investigating the phenol removal from aqueous media by photocatalytic magnetized graphene oxide nanocomposite

As a large and diverse group of secondary metabolites, phenolic compounds are one of the most common chemical pollutants present in water resources. these compounds can have toxic effects on ecosystems and humans. Therefore, their removal from water sources appears to be of great importance. In this study, a magnetic graphene oxide (MGO) photocatalyst was synthesized and used to remove phenol from water. The fabricated GO magnetic nanocomposites were determined by SEM and FTIR techniques. Afterward, these nanoparticles were used to remove phenol from aquatic media considering different operational parameters, including pH of the solution, initial concentration of phenol, contact time, and adsorbent dosage. The results showed that the magnetized GO nanoparticles could remove 90.83% of phenol molecules under the optimal conditions of solution pH = 3.0, initial phenol concentration of 20 mg/L, adsorbent concentration of 300 mg/L, and contact time of 120 min. additionally have compared the results of UV, Fe₃O₄/GO, and Fe₃O₄/GO/UV on the removal of phenol under optimum conditions. Accordingly, the phenol removal efficiencies for UV alone, Fe₃O₄/GO, and Fe₃O₄/GO/UV were obtained at 4.5, 65.73, and 90.83%, respectively. Based on the findings, the prepared magnetic GO nanoparticles have extended capabilities such as easy and rapid separation from sample and high potential in removing phenolic compounds, so, it can be introduced as an appropriate adsorbent for removal of this pollutant from water and wastewater.     

Organochlorine pesticide and polychlorinated biphenyl residues in feathers of birds from different trophic levels of South-West Iran

Persistent organochlorine pesticides (OCPs), such as dichlorodiphenyltrichloroethane (DDT) and its metabolites, hexachlorobenzene (HCB), alpha, beta and gamma-hexachlorocyclohexane (HCH) isomers, together with polychlorinated biphenyl (PCB) congeners (IUPAC Nos. 28, 52, 101, 138, 153 and 180), were determined in tail feathers from 37 birds belonging to 18 species, all originating from the South-West of Iran (Khuzestan, coast of the Persian Gulf). This is the first report on organochlorine contaminants in feathers from museum collections and it is an indication of the concentrations of OCPs and PCBs in the past (1991-1996). Median concentrations of HCHs, DDTs, PCBs and HCB were 22, 14, 11 and 10 ng/g feather, respectively. Significant correlations (p<0.05) were calculated between OCPs (except HCB) and PCBs in the bird feathers. p,p'-DDE and gamma-HCH were the most abundant OCPs, while CB 180, CB 138 and CB 101 were the predominant PCB congeners in almost all species. Significant differences (p<0.05) in the mean concentrations of DDTs and PCBs were detected among species grouped according to their feeding habits. Levels of DDTs and PCBs were highest in the carnivorous species and lowest in the herbivorous species. Levels of OCPs and PCBs in feathers of bids in the 1990s were generally below the thresholds reported to affect reproduction.     

Assessing Multi-site Drought Connections in Iran Using Empirical Copula

Drought is a multi-dimensional natural hazard with stochastic characteristics usually related to each other. Separate univariate statistical models cannot capture the important relationships among drought characteristics, that is, severity and duration. In this study, an empirical copula is employed to construct a bivariate model of droughts, where droughts are defined as continuously negative standardized precipitation index (SPI) periods with one SPI value reaching ?1 or less. Bivariate frequency analyses in terms of recurrence intervals are performed using the established empirical copula-based bivariate drought model. The inter-connection among different regions of droughts is explored by a lower tail dependence coefficient. A nonparametric estimation based on an empirical copula is employed pairwisely to calculate the lower tail dependence coefficient among stations. The proposed method is applied to six rainfall gauge stations in Iran to explore drought properties of single sites as well as the inter-connection among multi-sites. The results show that greater mean drought severity and duration are associated with the least arrival rate of drought events, which occurs at the Ahwaz station. The tail dependence analysis reveals that distance between stations is not a key parameter. Generally, the Ahwaz and Isfahan stations have the highest probability of simultaneous droughts among the six stations.     

Design of on-line river water quality monitoring systems using the entropy theory: a case study

The design of a water quality monitoring network is considered as the main component of water quality management including selection of the water quality variables, location of sampling stations and determination of sampling frequencies. In this study, an entropy-based approach is presented for design of an on-line water quality monitoring network for the Karoon River, which is the largest and the most important river in Iran. In the proposed algorithm of design, the number and location of sampling sites and sampling frequencies are determined by minimizing the redundant information, which is quantified using the entropy theory. A water quality simulation model is also used to generate the time series of the concentration of water quality variables at some potential sites along the river. As several water quality variables are usually considered in the design of water quality monitoring networks, the pair-wise comparison is used to combine the spatial and temporal frequencies calculated for each water quality variable. After selecting the sampling frequencies, different components of a comprehensive monitoring system such as data acquisition, transmission and processing are designed for the study area, and technical characteristics of the on-line and off-line monitoring equipment are presented. Finally, the assessment for the human resources needs, as well as training and quality assurance programs are presented considering the existing resources in the study area. The results show that the proposed approach can be effectively used for the optimal design of the river monitoring systems.     

Simultaneous derivatization and extraction of nitrophenols in soil and rain samples using modified hollow-fiber liquid-phase microextraction followed by gas chromatography–mass spectrometry

A simple and sensitive method based on a modified hollow-fiber liquid-phase microextraction followed by gas chromatography–mass spectrometry has been successfully developed for the extraction and simultaneous derivatization of some nitrophenols (NPs) in soil and rain samples. Microwave-assisted solvent extraction was used for the extraction of NPs from the soil, while the rain sample was directly applied to the previously mentioned method. Briefly, in this method, the analytes were extracted from aqueous samples into a thin layer of organic solvent (dodecane?+?10 % tri-n-octylphosphine oxide) sustained in the pores of a porous hollow fiber. Then, they were back-extracted using a small volume of organic acceptor solution (25 μl; 10 mg/L N-methyl-N-(trimethylsilyl)trifluoroacetamide, as derivatization reagent, in acetonitrile) that was located inside the lumen of the hollow fiber. Under the optimized extraction conditions, enrichment factors of 255 to 280 and limits of detection of 0.1 to 0.2 μg/L (S/N?=?3) with dynamic linear ranges of 1–100 μg/L were obtained for the analytes. The accuracy of the approach was tested by the relative recovery experiments on spiked samples, with results ranging from 93 to 113 %. The method was shown to be rapid, cost-effective, and potentially interesting for screening purposes.