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PurposeThe evaluation of the ecotoxicity effects of some heavy metals on the plant growth and metal accumulation in Ocimum basilicum L. cultivated on unpolluted and polluted soils represented the objective of the present study.Materials and methodsThe basil aromatic herb was evaluated in a laboratory experiment using soil contaminated with Cd, Co, Cr, Cu, Ni, Pb, and Zn, similar to the one from a mining area. The soils and different organs of the basil plants were analyzed, the total contents of the added elements being determined using inductively coupled plasma optical emission spectrometry. The ability of basil plants to accumulate metals from soil and to translocate them in their organs was evaluated by transfer coefficient, translocation factor, enrichment factor, and geo-accumulation index determinations.Results and discussionThe basil plants grown in the metal-polluted soil showed stimulation effects comparing with the plants from the control soil. At the end of the exposure period, the plants had a visible increase of biomass and presented inflorescences and the leaves’ green pigment was intensified. The metals gathered differently in plant organs: Cd, Co, Cr, and Pb were accumulated in roots, while Cu, Ni, and Zn in flowers. Cr and Pb exceeded the toxic levels in roots. Also, the heavy metal intake depends on the plant development stages; thus, Cd, Cr, and Pb were accumulated more in mature plant leaves. The Cd and Pb contents were higher than the World Health Organization and European Commission permissible limits.ConclusionsThe experimental results revealed that the basil plants exposed to a mixture of heavy metals have the potential to reduce the metal mobility from soil to plants. Translocation process from roots to flowers and to leaves was observed for Cu, Ni, and Zn, emphasizing a competition between metals. The calculated bioaccumulation factors were insignificant, but Cd and Pb concentrations exceeded the legal limits in the mature plants, being restricted for human or animal consumption.

Due to its conjugated structure, 1,4,6,8-tetrakis((E)-2-(thiophen-2-yl)vinyl)azulene (L) has a high potential for nonlinear optics and coloring. This compound was studied electrochemically using cyclic voltammetry, pulse differential voltammetry and rotating disk voltammetry in organic electrolytes. The main processes occurring during oxidation and reduction scans were highlighted and characterized. Density functional theory (DFT) calculations were conducted to assess the chemical reactivity of this compound. UV-Vis studies of L were performed in acetonitrile to establish the optical parameters in this solvent and its complexing power towards heavy metal (HM) ions. Chemically modified electrodes (CMEs) based on L were prepared by electrooxidation of L in organic electrolytes. To evaluate the electrochemical behavior of the CMEs, they were characterized with a ferrocene redox probe. They were also tested for the analysis of synthetic samples of heavy metal ions (HM): Cd(II), Pb(II), Cu(II) and Hg(II) by anodic stripping. Specific responses were obtained for Pb(II) and Cd(II) ions. The preparation conditions have an influence on the electrochemical responses. This study is relevant for the design and further development of advanced materials based on this azulene for the analysis of HMs in water samples. Electrochemical experiments and DFT calculations recommended L as a new ligand for modifying the electrode surface for the analysis of HMs.

This work introduces 2-(azulen-1-yldiazenyl)-5-(thiophen-2-yl)-1,3,4-thiadiazole (L) as a functional monomer capable of forming stable, redox-active films with high affinity for lead in aqueous solutions. L was synthesized and characterized using physical chemical methods and electrochemistry. Polymer films of L were prepared through oxidative electro polymerization on glassy carbon electrodes in L solutions in 0.1 M TBAP in acetonitrile. They were characterized through electrochemistry. The surface of chemically modified electrodes (CMEs) prepared through controlled potential electrolysis (CPE) at variable concentrations, potentials, and electric charges was characterized through scanning electron spectroscopy, atomic force microscopy, and Raman spectroscopy, which confirmed the films’ formation. Electrochemical sensing of the films deposited on these CMEs was tested with respect to heavy metal (HM) ion analysis in aqueous solutions to obtain sensors for HMs. The obtained CMEs presented the best characteristics for the recognition of Pb among the investigated HMs (Cd, Pb, Cu, and Hg). Calibration curves were obtained for the analysis of Pb(II) in aqueous solutions, which allowed for the estimation of a good detection limit of this cation (<10−8 M) for non-optimized CMEs. The resulting CMEs show promise for deployment in portable environmental monitoring systems, with implications for public health protection and environmental safety.

AbstractThe environmental impact of hydroxy- and amino-polysubstituted benzenes—constituents of natural and synthetic molecules of interest in food, pharmaceutical, and textile industries—demands new procedures for degradation of such pollutants, electrochemical oxidation being an important tool. Electrochemical studies have been performed to characterize these benzene derivatives by cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and rotating disk electrode voltammetry (RDE). Their oxidation potential (EOX) has been measured by CV, DPV, and SWV. Linear correlations EOX vs. pH were established for the nondissociated forms of these compounds and good fitting was noticed for EOX vs. Hammett constant for the meta and para-substituted compounds. Diffusion coefficients were also estimated. According to the reversibility of their electrochemical oxidation, studied by CV, the compounds were classified into two main groups: reversible-type I (benzene-1,2-diol, benzene-1,4-diol, and benzene-1,2,4-triol) and irreversible-type II (benzene-1,3-diol, benzene-1,2,3-triol, benzene-1,3,5-triol, 4-aminophenol, benzene-1,4-diamine, and 3,4,5-trihydroxybenzoic acid). A quantitative structure–property relationship (QSPR) study has revealed the characteristics that influence their EOX values. A very good agreement resulted between the calculated and experimental EOX values. The proposed descriptors may be used in the prediction of EOX value for other related compounds. Thus, the optimal conditions for the degradation by electrochemical procedures of environmental pollutants containing such structures can be easily estimated.Graphic abstract

New aspects of the Ni(II)-salophen complex and salophen ligand precursor were found during deep electrochemical and optical characterization, as well as biological studies for new pharmacological applications. Physicochemical and spectroscopic methods (1H- and 13C-NMR, FT-IR and UV-Vis, electrospray ionization mass spectroscopy, thermogravimetric analysis, and molar conductance measurements) were also used to prove that the salophen ligand acts as a tetradentate and coordinates to the central metal through nitrogen and oxygen atoms. The electrochemical behavior of the free Schiff salophen ligand (H2L) and its Ni(II) complex (Ni(II)L) was deeply studied in tetrabutylammonium perchlorate solutions in acetonitrile via CV, DPV, and RDE. Blue films on the surfaces of the electrodes as a result of the electropolymerization processes were put in evidence and characterized via CV and DPV. (H2L) and Ni(II)L complexes were tested for their antimicrobial, antifungal, and antioxidant activity, showing good antimicrobial and antifungal activity against several bacteria and fungi.

Tetrahydroacridines arouse particular interest due to the potential possibilities of application in the medical field and protection against corrosion. Bis-tetrahydroacridines were newly synthesized by Pfitzinger condensation of 5,5′-(ethane-1,2-diyl) diindoline-2,3-dione with several cyclanones. NMR, MS, and FT-IR were used to prove their molecular structure. In addition, a computer-aided study was performed for the lowest energy conformers of each structure, in vacuum conditions, at ground state using DFT models to assess their electronic properties. UV–Vis and voltammetric methods (cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry) were used to investigate their optical and electrochemical properties. The results obtained for these π-conjugated heteroaromatic compounds lead to the conclusion that they have real potential in applications in different fields such as pharmaceuticals and especially as corrosion inhibitors.

The electrochemical study of 2‐Sulfanylidene‐1,3‐thiazolidin‐4‐one (rhodanine, R) was performed on a glassy carbon working electrode by using three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) at rotating disk electrode voltammetry (RDE). The CV, DPV, and LSV at RDE curves for R were recorded at different concentrations in 0.1 M TBAP/CH3CN. Polymeric films were formed by successive cycling at different potentials and by controlled potential electrolysis. The film formation was proved by recording the CV curves of the chemically modified electrodes (CMEs) in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. The obtained CMEs were used for the detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd (II), Pb (II), Cu (II), Hg (II)) of concentrations between 10−7 and 10−5 M were analyzed using CMEs prepared in different conditions. The most intense signal was obtained for Pb(II) ion (estimated detection limit = 10−7 M), which shows that these CMEs can be used for Pb(II) ion detection. The ability of R to form complexes with Pb(II) ion was also tested by UV‐Vis spectrometry. The obtained results showed the formation of Pb(II)R2 as the most stable complex.

Electrochemical and spectral studies of benzylidenerhodanine (BR) were performed in order to develop new sensors for heavy metals (HMs) based on chemically modified electrodes (CMEs). CMEs were obtained by cycling and by controlled potential electrolysis at different potentials and charges. Film formation was demonstrated by recording the CV curves of CMEs in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. BR-CMEs were used for the analysis of HMs. Samples of Cd(II), Pb(II), Cu(II), and Hg(II), each possessing concentrations between 10−7 and 10−5 M, were analyzed by using CMEs prepared in different conditions. The most intense signal was obtained for the Pb(II) ion. These BR-CMEs can be used for the analysis of Pb(II) in monitored waters. An electrochemical study was performed at different concentrations of BR in 0.1 M TBAP/CH3CN on a glassy carbon electrode by differential pulse voltammetry, cyclic voltammetry, and rotating disk electrode voltammetry. The complexation ratio in the homogeneous solution has been established by the Mollard method in acetonitrile solutions.

Chemically modified electrodes based on derivatives of 2-thioxothiazolidin-4-one were mentioned as possible solutions for heavy metal (HM) ions heterogeneous recognition. Such ligands form thin films with reversible responses in the ferrocene redox probe with a well-defined symmetrical peak and symmetrical values for the anodic and cathodic currents. Their selectivity in coordinating HM ions was proven. In this paper, a computer-added study was performed using density functional theory (DFT) based on two methods, B3LYP and ωB97XD, to arrive at a better inside of their structure. Properties related to their reactivity concerning experimental electrochemical behaviour and spectral results were calculated using specific molecular descriptors. DFT-calculated HOMO-LUMO energies were found in good linear correlation with experimental redox potential. The accuracy of the calculations was also proven by a good agreement between the energy calculated by the DFT method and the UV-Vis spectra for the studied ligands. Such a computational approach can be used to evaluate the properties of possible new ligands for such electrochemical applications. The strong correlation between DFT-predicted quantum parameters and experimental redox potentials underscores the relevance of these computational approaches in designing selective molecular sensors. The results obtained using the two functionals are in good agreement, although there are also situations and parameters for which the results are not identical. There is a symmetry of the values obtained by the electrochemical and spectral methods with those calculated by DFT.

Previous studies performed on 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) showed that T is a ligand with complexing properties towards heavy metals (HMs) in solution and can be attached to electrode surfaces. Films of T were deposited on glassy carbon to obtain chemically modified electrodes (T-CMEs), either through scanning or using controlled potential electrolysis in tetrabutylammonium perchlorate in acetonitrile. They were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and spectroelectrochemistry. All methods provided evidence for showing the formation of insulating films, with properties depending on their electropolymerization potential. CV and EIS studies of T-CMEs in tetrabutylammonium perchlorate in acetonitrile as supporting electrolyte, and in the presence of a ferrocene redox probe resulted in a thickness of ~10 µm, an active surface area about 6 times higher than the geometrical one, and conductivity of about 10−6 S/cm. This characterization performed using voltammetric techniques reveals the symmetry of the reversible anodic and cathodic redox CV peaks for the polymer, while spectroelectrochemistry shows the intensification of the charge transport process through polarons, due to the anodic polarization of the film.