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Antimicrobial and antifungal activities of bifunctional cooper(ii) complexes with non-steroidal anti-inflammatory drugs, flufenamic, mefenamic and tolfenamic acids and 1,10-phenanthroline

  • Lenka Hudecova , Klaudia Jomova , Peter Lauro , Miriama Simunkova EMAIL logo , Saleh H. Alwasel , Ibrahim M. Alhazza , Jan Moncol and Marian Valko
Published/Copyright: December 6, 2020
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Open Chemistry
From the journal Open Chemistry Volume 18 Issue 1

Abstract

Cooper(ii) complexes represent a promising group of compounds with antimicrobial and antifungal properties. In the present work, a series of Cu(ii) complexes containing the non-steroidal anti-inflammatory drugs, tolfenamic acid, mefenamic acid and flufenamic acid as their redox-cycling functionalities, and 1,10-phenanthroline as an intercalating component, has been studied. The antibacterial activities of all three complexes, [Cu(tolf-O,O′)2(phen)] (1), [Cu(mef-O,O′)2(phen)] (2) and [Cu(fluf-O,O′)2(phen)] (3), were tested against the prokaryotic model organisms Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and their antifungal activities were evaluated towards the yeast, Saccharomyces cerevisiae (S. cerevisiae). The antibacterial activity of both strains has been compared with the antibiotic Neomycin. The calculated IC50 values revealed slight differences in the antibacterial activities of the complexes in the order 1 ∼ 3 > 2. The most profound growth inhibition of E. coli was observed, at its highest concentration, for the complex 1, which contains chlorine atoms in the ligand environment. The trend obtained from IC50 values is generally in agreement with the determined MIC values. Similarly, the complex 1 showed the greatest growth inhibition of the yeast S. cerevisiae and the overall antifungal activities of the Cu(ii) complexes were found to follow the order 1 > 3 ≫ 2. However, for complex 2, even at the highest concentration tested (150 μM), a 50% decrease in yeast growth was not achieved. It appears that the most potent antimicrobial and antifungal Cu(ii) complexes are those containing halogenated NSAIDs. The mechanisms by which Cu(ii) complexes cause antibacterial and antifungal activities can be understood on the basis of redox-cycling reactions between cupric and cuprous species which lead to the formation of free radicals. The higher efficacy of the Cu(ii) complexes against bacterial cells may be due to an absence of membrane-protected nuclear DNA, meaning that on entering a cell, they can interact directly with its DNA. Contrastingly, for the complexes to interact with the DNA in yeast cells, they must first penetrate through the nuclear membrane.

Keywords: Cu(ii) complexes; antimicrobial activity; antifungal activity; NSAID; Escherichia coli; Saccharomyces cerevisiae

1 Introduction

It has been reported that in the USA alone, more than 50,000 patients die annually from multiresistant bacterial infections [1]. Since the antibiotic resistance of various bacteria is becoming a serious medical threat globally, there is an urgent requirement to discover new classes of antibiotics, of which redox metal-based complexes with biologically active ligands are promising examples [2,3,4,5,6,7]. Copper is one of the most abundant elements in the human body and is also a redox active metal, whose positive effects on human health were first noted as early as the late 19th century, when it was reported by Doctor Luton that a mixture of copper chloride and sodium salicylate was effective in the treatment of rheumatoid arthritis, rheumatic fever and other disorders [8]. This observation was later augmented during the first half of the 20th century in Finland, where miners who worked in copper mines were found to suffer a considerably lower incidence of arthritis than the majority of population.

Copper occurs most commonly in biological systems in either +2 or +1 oxidation states (referred to as cupric or cuprous species, respectively) [9]. To date, there is no direct proof that Cu(iii) species exist in biological systems, which would require the presence of a redox active cofactor. Most common are those complexes containing copper in the +2 oxidation state and these show inhibitory effects toward the growth of a variety of bacteria, fungi and viruses [10,11,12,13]. Cooper(ii) complexes containing coordinated, structurally flat ligands, such as 1,10-phenanthroline, exhibit cytotoxic effects which have been attributed predominantly to their ability to cleave DNA, as a result of either complete or partial intercalation of the phenanthroline moiety in between the DNA base pairs [14,15,16]. In addition to this intercalation mechanism, a process of redox cycling, with the formation of DNA damaging ROS, may occur.

In the present work, we report the antibacterial and antifungal activities of Cu(ii) complexes bearing 1,10-phenanthroline as an intercalating ligand and the non-steroidal anti-inflammatory drugs: tolfenamic acid, mefenamic acid and flufenamic acid, to provide redox-cycling functionalities (Figure 1). The antibacterial activities of these Cu(ii) complexes were gauged against the frequently studied prokaryotic model organisms, E. coli and S. aureus, and their antifungal activities were determined against S. cerevisiae, a yeast that is widely employed in the baking and brewing industries.

Figure 1 The structures of ligands used for preparation of studied Cu(ii) complexes.
Figure 1

The structures of ligands used for preparation of studied Cu(ii) complexes.

2 Experimental

2.1 Materials

Copper acetate, methanol, 1,10-phenanthroline, flufenamic acid, tolfenamic acid and mefenamic acid were all obtained from Merck (Germany). To evaluate antimicrobial activity of Cu(ii) complexes, E. coli DH5α and S. aureus ATCC25923 were used, as obtained from the Institute of Plant Genetics of the Slovak Academy of Sciences in Nitra. S. cerevisiae CCY27-22-6 was used in order to determine the antifungal activities of the Cu(ii) complexes. The particular strain was obtained from the Institute of Chemistry of the Slovak Academy of Sciences, Bratislava.

2.2 Preparation of Cu(ii) complexes with phenanthroline and non-steroidal anti-inflammatory drugs

[Cu(tolf-O,O′)2(phen)] (1). To 50 mL of Cu(ii) acetate (0.200 g) methanol solution (0.02 M) 0.198 g of phenanthroline monohydrate was added. The solution was stirred for 10 min and then 0.523 g of solid tolfenamic acid was added to achieve the 1:2 ratio of phenanthroline: tolfenamic acid. The resulting olive-coloured mixture was stirred for a further 24 h until a precipitate was formed, which was filtered off and air-dried for one month. Suitable monocrystals for X-ray analysis were obtained by slow evaporation of the solvent.

[Cu(mef-O,O′)2(phen)] (2). To 50 mL of Cu(ii) acetate (0.200 g) dissolved in methanol (0.02 M) 0.198 g of phenanthroline monohydrate was added. The solution was stirred for 10 min and then 0.483 g of solid mefenamic acid was added to achieve the 1:2 ratio of phenanthroline:mefenamic acid. The resulting mixture was stirred for 24 h until a precipitate was formed, which was filtered off and air-dried for one month. Suitable monocrystals for X-ray analysis were obtained by slow evaporation of the solvent.

[Cu(fluf-O,O′)2(phen)] (3). The Cu(ii) complex with flufenamic acid was prepared analogously to above described complexes. To 50 mL of Cu(ii) acetate (0.200 g) dissolved in methanol (0.02 M) 0.198 g of phenanthroline monohydrate was added. The solution containing copper acetate and phenanthroline in methanol was stirred for 10 min. Into this solution, 0.483 g of solid flufenamic acid was added to achieve the 1:2 ratio of phenanthroline: flufenamic acid. The reaction mixture was stirred for 24 h until a precipitate was formed, which was filtered off and air-dried for one month. Suitable monocrystals for X-ray analysis were obtained by slow evaporation of the solvent.

2.3 Determination of the antibacterial activity for Cu(ii) complexes

To investigate the antibacterial activity of the complexes, the prokaryotic model organism E. coli DH5α and S. aureus were used, as obtained from the Institute of Plant Genetics of the Slovak Academy of Sciences in Nitra. DH5-strain alpha was used because it appears to be suitable for high efficiency transformation in a wide variety of routine applications such as plasmid isolation and other procedures.

Bacterial cells were incubated in a liquid LB (Lysogen Broth, Luria-Bertani) medium containing 0.5% yeast extract, 1% tryptone and 1% NaCl. For solid LB media, the composition was enriched with 2% agar. The media were sterilized at 125°C for 30 min. Prior to inoculation of the bacterial cells, an ampicillin selection agent (50 mg/mL) was added to the medium.

The bacterial culture was seeded under sterile conditions into 20 mL of prepared LB medium, and the cultivation was performed in a 250 mL Erlenmeyer flask at 37°C over 16 h, with continuous stirring at 150 rpm (Heidolf Unimax 1010, Germany). Once grown, the culture was diluted with pure LB medium to achieve an optical density (OD600) of 0.1, which represents a concentration of 1–2 × 108 cells/mL. The optical density was determined spectrophotometrically (Varioskan Flash, Thermo Scientific). Thus prepared, the inoculum was pipetted into 25 mL Erlenmeyer flasks.

To each flask was added different concentrations of the substance to be tested, but this additional volume was maintained to equal exactly 1% of the total volume of the test culture. The cultures were incubated at 37°C, with continuous stirring at 150 rpm.

The effect of the studied substance on the bacterial cell growth was monitored from an absorbance measurement made every two hour, over a period of 24 h. The growth profiles of bacterial cultures, determined as a function of multiple concentrations of each test substance, were compared with those for a control culture where no test substances were present. Data were obtained in triplicate and used for the calculation of the IC50 values (i.e. the concentration of the test substance that causes 50% inhibition of bacterial growth).

Since its fraction in the medium did not exceed 1%, the effect of the DMSO solvent on the growth curve could be excluded in the consideration of the antibacterial activities of the Cu(ii) complexes 1–3 [17].

In order to determine minimum inhibitory concentration (MIC) values of the Cu(ii) complexes against E. coli and S. aureus, the rapid p-iodonitrotetrazolium chloride (INT) colorimetric assay was used [18]. Briefly, both E. coli and S. aureus were diluted with sterile broth (Müller and Hinton) to reach final inocula of cca. 106 CFU mL−1. Stock solutions of cooper(ii) complexes were dissolved in DMSO to reach the concentration of 25 mg mL−1. 100 µL solution of each Cu(ii) complex was diluted with redistilled and deionized water (Merck Millipore) in a 96 well microtiter microplates (Thermo Fischer scientific) to reach final concentrations ranging from 3 to 300 µL mL−1. As a positive control against bacterial strains, 1 mg mL−1 solution of the antibiotic Neomycin (Sigma-Aldrich, FRG) was applied with final concentrations in the range 2.5–270 µL mL−1. Individual bacteria (100 µL) were added to wells and incubated at 36.8°C for 24 h. p-Iodonitrotetrazolium chloride (45 µL of 0.2 mg mL−1 solution) from Sigma Aldrich (FRG) was used to indicate the bacterial growth at 36.8°C for 24 h. p-Iodonitrotetrazolium undergoes colour change from colourless to red upon its reduction by active organisms. The values of MIC were obtained visually as the lowest concentrations resulting in growth inhibition.

2.4 Determination of antifungal activity of Cu(ii) complexes

A model organism S. cerevisiae CCY 27-22-6 was used in order to determine the antifungal activities of the Cu(ii) complexes. The particular strain was obtained from the Institute of Chemistry of the Slovak Academy of Sciences, Bratislava. Yeast cells were cultured in a liquid YPD (Yeast Extract–Peptone–Dextrose) medium containing: 2% peptone, 2% glucose and 1% yeast extract. In the case of solid YPD media, the composition was enriched by adding 2% agar. The media were sterilized for 30 min at 125°C and the yeast culture was inoculated under sterile conditions into 20 mL of the prepared liquid YPD medium. The cultivation was made over 16 h in a 250 mL sterile Erlenmeyer flask maintained at 30°C, with continuous stirring at 150 rpm (Heidolf Unimax 1010, Germany). Once grown, the culture was diluted with pure YPD medium, so that the optical density OD600 reached value of 0.1, which corresponded to 1–2 × 108 cells/mL. The optical density was determined spectrophotometrically (Varioskan Flash, Thermo Scientific). Thus prepared, the yeast culture was used as a vegetative inoculum for all yeast cell assays, inoculums, and was pipetted into 25 mL Erlenmeyer flasks. To each Erlenmeyer flask was then added the complex to be studied at different concentrations so that the volume of the solution occupied 1% of the total volume. The cultures were incubated at 30°C and stirred continuously at 150 rpm. The change in yeast culture growth caused by the tested complex was monitored from spectrophotometric measurements, made every two hour, over a 24 h period. The growth of bacterial cultures in the presence of the tested complexes was compared with a control culture in which these complexes were absent. Each measurement was performed in triplicate and the data obtained were used to calculate IC50 values (i.e. the concentration of the test substance required to cause a 50% inhibition in the growth of the yeast culture).

3 Results and discussion

The aim of the present work was to evaluate both antibacterial and antifungal properties of selected bifunctional Cu(ii) complexes, bearing NSAID ligands to provide redox-cycling functionalities and with 1,10-phenanthroline as an intercalating agent. The antimicrobial activities of the Cu(ii) complexes were determined using the prokaryotic organisms, E. coli and S. aureus, and the eukaryotic organism, S. cerevisiae, was used for the determination of antifungal activity.

3.1 Structure of Cu(ii) complexes with NSAIDs and 1,10-phenanthroline

The molecular structures of the cooper(ii) complexes [Cu(tolf-O,O′)2(phen)] (1), [Cu(mef-O,O′)2(phen)] (2) and [Cu(fluf-O,O′)2(phen)] (3) are shown in Figure 2. All three complexes are monomeric and crystallize in the monoclinic space group, and in each case, the Cu(ii) ion is chelated in the equatorial plane by the two 1,10-phenanthroline nitrogen atoms and a total of four carboxylate oxygen atoms from two molecules of the particular NSAID [14]. The equatorial plane of all three complexes (2N2O) has a regular planar geometry. Conversely, the axial positions of the Cu(ii) complexes are distorted, due to the limited bonding capacity of the bidentate, tolfenamte, mefanamate and flufenamate anions. In the solid state, the molecular structures of the Cu(ii) complexes are stabilized by intermolecular hydrogen bonds, which are, however, disrupted upon their introduction into the fluid environment.

Figure 2 Molecular structures of the Cu(ii) complexes. (a) Molecular structure of complex [Cu(tolf-O,O′)2(phen)] (1). (b) Molecular structure of complex [Cu(mef-O,O′)2(phen)] (2). (c) Molecular structure of complex [Cu(fluf-O,O′)2(phen)] (3).
Figure 2

Molecular structures of the Cu(ii) complexes. (a) Molecular structure of complex [Cu(tolf-O,O′)2(phen)] (1). (b) Molecular structure of complex [Cu(mef-O,O′)2(phen)] (2). (c) Molecular structure of complex [Cu(fluf-O,O′)2(phen)] (3).

3.2 Antibacterial activity

Antibacterial activity of all three Cu(ii) complexes was studied against E. coli and S. aureus. The effect of the Cu(ii) complexes on the growth of prokaryotic E. coli was investigated over a 24 h period. During the initial 12 h, data were recorded at two hourly intervals. The concentration range employed for all three Cu(ii) complexes was 10–150 μmol. At the lowest concentration tested (10 μmol), a slight decrease in absorbance for complexes 1 and 3 was observed, but practically no effect for the complex 2, as compared with the control (Figures 3–5). A gradual decrease in the absorbances, with increasing concentrations of the Cu(ii) complexes, indicates a sensitivity of the bacterial culture to their presence, which is manifested by an inhibition of cell culture growth.

Figure 3 Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 1.
Figure 3

Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 1.

Figure 4 Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 2.
Figure 4

Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 2.

Figure 5 Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 3.
Figure 5

Growth curves of E. coli during the course of a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μmol of the complex 3.

From the measured absorbance values determined following 24 h of cell culture growth, the IC50 values were calculated for each complex (Table 1). The IC50 value corresponds to the concentration of the complex that causes 50% inhibition of bacterial growth. Although, at first sight, the graphs (Figures 3–5) indicate the effects of the Cu(ii) complexes to be similar, the calculated IC50 values reflect slight activity differences in the order of 1 ∼ 3 > 2. The most profound growth inhibition was observed at the highest concentration of the complex 1, which contains coordinated NSAIDs, each bearing a chlorine atom. A slightly lower inhibitory activity was observed for complex 3, which contains NSAIDs, each with three fluorine atoms. The lowest antibacterial activity was observed for the complex 2, with its methyl-substituted NSAID ligands. From the growth curves of all three Cu(ii) complexes, and at all concentrations tested, the stationary phase of bacterial culture growth of E. coli is apparent after 12 h. For the complex 3, at concentrations of 80 μmol and higher, decreases in the absorbance are measured after 12 h (Figure 5), which indicates bacterial cell death.

Table 1

Inhibitory concentrations of complexes 1–3 required to cause a 50% decrease in the growth of E. coli bacterial culture (IC50) at 24 h

ComplexIC50 (%)
[Cu(tol-O,O′)2(phen)] (1)112.4
[Cu(mef-O,O′)2(phen)] (2)148.2
[Cu(flu-O,O′)2(phen)] (3)120.1

Minimum inhibitory concentrations for both Gram-negative E. coli and Gram-positive S. aureus bacteria were determined. The standard antibiotic Neomycin was used as a control for antibacterial activity of both strains. The results are summarized in Table 2. From the obtained results, we can see a relatively good correlation with above-presented IC50 values for E. coli. The best inhibitory activity against both E. coli as well as S. aureus has been obtained for complex 1, followed by complex 3. Complex 2 shows the least activity against both strains. From the obtained results, it can be concluded that all three Cu(ii) complexes exhibit better inhibitory activity against S. aureus. This can be due to the absence of outer membrane of Gram-positive bacteria S. aureus, which makes them more susceptible to certain antibiotics or molecules with antibiotic affects such as Cu(ii) complexes. Further modifications in ligand sphere (both redox-cycling and intercalating functionalities) are necessary to achieve better antibacterial activity of Cu(ii) complexes.

Table 2

Minimum inhibitory concentrations (µg mL−1) of Cu(ii) complexes against S. aureus and E. coli

ComplexGram (+) S. aureusGram (−) E. coli
[Cu(tol-O,O′)2(phen)] (1)65.7274.25
[Cu(mef-O,O′)2(phen)] (2)95.62105.56
[Cu(flu-O,O′)2(phen)] (3)77.2980.66
Neomycin9.353.25

3.3 Antifungal activity

The effect of the Cu(ii) complexes on the growth of the eukaryotic model microorganism S. cerevisiae was studied over the period of 20 h. During the initial 12 h, as with the E. coli measurements, we recorded data at two hourly intervals. The complexes 1–3 were all measured in the same concentration range, 10–150 μM (Figures 6–8).

Figure 6 Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 1.
Figure 6

Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 1.

Figure 7 Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 2.
Figure 7

Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 2.

Figure 8 Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 3.
Figure 8

Growth curves of S. cerevisiae during a 24 h cultivation in the presence of 10; 30; 80; 100; and 150 μM of complex 3.

The growth curves shown in Figures 6–8 exhibit a sigmoidal character. In contrast with the growth of the bacterial cells, in each experiment performed, the yeast cultures of S. cerevisiae all demonstrated exponential growth phases up to a period of 12 h. Based on these growth curves, the Cu(ii) complexes under investigation can be ordered according to their antifungal activity as: 1 > 3 ≫ 2. Similarly, due to its low antibacterial activity, the results showed that complex 2 exhibits minimal antifungal activity (Table 3). Hence, we may conclude that, overall, the order of antifungal activities for all three Cu(ii) complexes accords with their antibacterial activities against E. coli.

Table 3

Inhibitory concentrations of complexes 1–3 required to cause a 50% decrease in the growth of S. cerevisiae (IC50) estimated after a 24 h period

ComplexIC50 (%)
[Cu(tol-O,O′)2(phen)] (1)95.5
[Cu(mef-O,O′)2(phen)] (2)—
[Cu(flu-O,O′)2(phen)] (3)147.2

Based on our in vitro studies, which unequivocally confirmed that interaction of Cu(ii) complexes with DNA takes place, we assumed that oxidative damage had occurred at the DNA level with subsequent inhibition of cell culture growth. The mechanism by which Cu(ii) complexes cause toxicity can be understood on the basis of redox-cycling reactions between cupric and cuprous species which result in the formation of free radicals [14,19]. Under aerobic conditions, this redox cycling leads to the occurrence of oxidative damage by the production of superoxide radical anions and highly reactive hydroxyl radicals. The present results demonstrated that the antibacterial activities of the Cu(ii) complexes were generally higher than their antifungal activities, other than the single exception of the rather high activity of complex 1 against S. cerevisiae. Indeed, complex 1, with its Cu(ii)-coordinated chlorinated NSAID ligand, appears to be the most effective agent against both bacteria and fungi. The overall greater activity of the Cu(ii) complexes against bacteria than fungi may be due to the fact that these agents can interact directly with the DNA upon entry into a bacterial cell, which, unlike a fungal cell, does not have membrane-protected nuclear DNA [20]. In contrast, for the complexes to interact with DNA in yeast cells, they must first penetrate through the nuclear membrane.

The results obtained demonstrate a correlation between the cytotoxic effects of the complexes toward the studied microorganisms and their observed SOD mimetic activities, as recently reported by our group (1 ∼ 3  > 2) [14]. To recapitulate, briefly, the SOD mimetic activity of the studied complexes rests upon their ability to dismutate the superoxide radical anion and produce hydrogen peroxide, according to the reaction [9].

2O2⋅−+2H+⟶SODH2O2+O2

Thus formed, hydrogen peroxide can give rise to formation of a highly reactive hydroxyl radical according to the Fenton reaction [14,21].

H2O2⟶Cu,FeO⋅H+OH−

When generated in a living cell, hydroxyl radicals may disrupt the integrity of the bacterial membrane and cause damage to important cellular components such as bacterial DNA, RNA and proteins, resulting in a range of deleterious effects, and even cell death. Nonetheless, we note that the cytotoxic effects of the added complexes toward the studied microorganisms may not necessarily correspond with their SOD mimetic activities, because in actual living cells, hydroxyl radicals may also damage other structures and so the spectrum of possible action mechanisms is accordingly broadened [22,23].

4 Conclusions

In this paper, the antimicrobial and antifungal properties of cooper(ii) complexes containing biologically active non-steroidal anti-inflammatory drugs, tolfenamic acid, mefenamic acid and flufenamic acid, and 1,10-phenanthroline were studied. Based on the IC50 and MIC values, it can be concluded that Cu(ii) complexes exhibit promising antibacterial activity against E. coli and S. aureus, of which the most powerful effect is observed for complex 1, which contains a chlorine atom on each tolfenamic acid moiety. Interestingly, the most potent anticancer activities, against several cancer cell lines, have been observed for Cu(ii) complexes containing halogenated NSAIDs. We suggest that, in addition to these complexes causing ROS-induced damage to bacteria, their NSAID halogen atoms are involved in hydrogen bond formation with particular hydrogen atoms at the DNA surface.

With respect to their antifungal activities, the results indicate that the Cu(ii) complexes can be arranged in the order 1 > 3 ≫ 2. The lower activity observed for Cu(ii) complexes against S. cerevisiae can be accounted for by the presence of a nuclear membrane in yeast cells, which protects their DNA from attack by external agents such as Cu(ii) complexes.

Acknowledgements

This work was supported by Scientific Grant Agency (VEGA Project 1/0482/20) and Research and Development Support Agency (APVV-15-0079). S. Alwasel would like to extend his sincere appreciation to the Researchers Supporting Project (RSP-2020/59), King Saud University, Riyadh, Saudi Arabia, for support. M. S. would like to thank STU Grant scheme Support of Excellent Teams of Young Researches CuSPK for financial support.

  1. Conflict of interest: The authors declare no conflicts of interest.

  2. Ethical approval: The conducted research is not related to either human or animal use.

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Received: 2020-09-07
Revised: 2020-10-22
Accepted: 2020-10-22
Published Online: 2020-12-06

© 2020 Lenka Hudecova et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

  1. Regular Articles
  2. Electrochemical antioxidant screening and evaluation based on guanine and chitosan immobilized MoS2 nanosheet modified glassy carbon electrode (guanine/CS/MoS2/GCE)
  3. Kinetic models of the extraction of vanillic acid from pumpkin seeds
  4. On the maximum ABC index of bipartite graphs without pendent vertices
  5. Estimation of the total antioxidant potential in the meat samples using thin-layer chromatography
  6. Molecular dynamics simulation of sI methane hydrate under compression and tension
  7. Spatial distribution and potential ecological risk assessment of some trace elements in sediments and grey mangrove (Avicennia marina) along the Arabian Gulf coast, Saudi Arabia
  8. Amino-functionalized graphene oxide for Cr(VI), Cu(II), Pb(II) and Cd(II) removal from industrial wastewater
  9. Chemical composition and in vitro activity of Origanum vulgare L., Satureja hortensis L., Thymus serpyllum L. and Thymus vulgaris L. essential oils towards oral isolates of Candida albicans and Candida glabrata
  10. Effect of excess Fluoride consumption on Urine-Serum Fluorides, Dental state and Thyroid Hormones among children in “Talab Sarai” Punjab Pakistan
  11. Design, Synthesis and Characterization of Novel Isoxazole Tagged Indole Hybrid Compounds
  12. Comparison of kinetic and enzymatic properties of intracellular phosphoserine aminotransferases from alkaliphilic and neutralophilic bacteria
  13. Green Organic Solvent-Free Oxidation of Alkylarenes with tert-Butyl Hydroperoxide Catalyzed by Water-Soluble Copper Complex
  14. Ducrosia ismaelis Asch. essential oil: chemical composition profile and anticancer, antimicrobial and antioxidant potential assessment
  15. DFT calculations as an efficient tool for prediction of Raman and infra-red spectra and activities of newly synthesized cathinones
  16. Influence of Chemical Osmosis on Solute Transport and Fluid Velocity in Clay Soils
  17. A New fatty acid and some triterpenoids from propolis of Nkambe (North-West Region, Cameroon) and evaluation of the antiradical scavenging activity of their extracts
  18. Antiplasmodial Activity of Stigmastane Steroids from Dryobalanops oblongifolia Stem Bark
  19. Rapid identification of direct-acting pancreatic protectants from Cyclocarya paliurus leaves tea by the method of serum pharmacochemistry combined with target cell extraction
  20. Immobilization of Pseudomonas aeruginosa static biomass on eggshell powder for on-line preconcentration and determination of Cr (VI)
  21. Assessment of methyl 2-({[(4,6-dimethoxypyrimidin-2-yl)carbamoyl] sulfamoyl}methyl)benzoate through biotic and abiotic degradation modes
  22. Stability of natural polyphenol fisetin in eye drops Stability of fisetin in eye drops
  23. Production of a bioflocculant by using activated sludge and its application in Pb(II) removal from aqueous solution
  24. Molecular Properties of Carbon Crystal Cubic Structures
  25. Synthesis and characterization of calcium carbonate whisker from yellow phosphorus slag
  26. Study on the interaction between catechin and cholesterol by the density functional theory
  27. Analysis of some pharmaceuticals in the presence of their synthetic impurities by applying hybrid micelle liquid chromatography
  28. Two mixed-ligand coordination polymers based on 2,5-thiophenedicarboxylic acid and flexible N-donor ligands: the protective effect on periodontitis via reducing the release of IL-1β and TNF-α
  29. Incorporation of silver stearate nanoparticles in methacrylate polymeric monoliths for hemeprotein isolation
  30. Development of ultrasound-assisted dispersive solid-phase microextraction based on mesoporous carbon coated with silica@iron oxide nanocomposite for preconcentration of Te and Tl in natural water systems
  31. N,N′-Bis[2-hydroxynaphthylidene]/[2-methoxybenzylidene]amino]oxamides and their divalent manganese complexes: Isolation, spectral characterization, morphology, antibacterial and cytotoxicity against leukemia cells
  32. Determination of the content of selected trace elements in Polish commercial fruit juices and health risk assessment
  33. Diorganotin(iv) benzyldithiocarbamate complexes: synthesis, characterization, and thermal and cytotoxicity study
  34. Keratin 17 is induced in prurigo nodularis lesions
  35. Anticancer, antioxidant, and acute toxicity studies of a Saudi polyherbal formulation, PHF5
  36. LaCoO3 perovskite-type catalysts in syngas conversion
  37. Comparative studies of two vegetal extracts from Stokesia laevis and Geranium pratense: polyphenol profile, cytotoxic effect and antiproliferative activity
  38. Fragmentation pattern of certain isatin–indole antiproliferative conjugates with application to identify their in vitro metabolic profiles in rat liver microsomes by liquid chromatography tandem mass spectrometry
  39. Investigation of polyphenol profile, antioxidant activity and hepatoprotective potential of Aconogonon alpinum (All.) Schur roots
  40. Lead discovery of a guanidinyl tryptophan derivative on amyloid cascade inhibition
  41. Physicochemical evaluation of the fruit pulp of Opuntia spp growing in the Mediterranean area under hard climate conditions
  42. Electronic structural properties of amino/hydroxyl functionalized imidazolium-based bromide ionic liquids
  43. New Schiff bases of 2-(quinolin-8-yloxy)acetohydrazide and their Cu(ii), and Zn(ii) metal complexes: their in vitro antimicrobial potentials and in silico physicochemical and pharmacokinetics properties
  44. Treatment of adhesions after Achilles tendon injury using focused ultrasound with targeted bFGF plasmid-loaded cationic microbubbles
  45. Synthesis of orotic acid derivatives and their effects on stem cell proliferation
  46. Chirality of β2-agonists. An overview of pharmacological activity, stereoselective analysis, and synthesis
  47. Fe3O4@urea/HITh-SO3H as an efficient and reusable catalyst for the solvent-free synthesis of 7-aryl-8H-benzo[h]indeno[1,2-b]quinoline-8-one and indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine derivatives
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  49. Enhancement of thermal properties of bio-based microcapsules intended for textile applications
  50. Exploring the effect of khat (Catha edulis) chewing on the pharmacokinetics of the antiplatelet drug clopidogrel in rats using the newly developed LC-MS/MS technique
  51. A green strategy for obtaining anthraquinones from Rheum tanguticum by subcritical water
  52. Cadmium (Cd) chloride affects the nutrient uptake and Cd-resistant bacterium reduces the adsorption of Cd in muskmelon plants
  53. Removal of H2S by vermicompost biofilter and analysis on bacterial community
  54. Structural cytotoxicity relationship of 2-phenoxy(thiomethyl)pyridotriazolopyrimidines: Quantum chemical calculations and statistical analysis
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  61. Treatment of Parkinson’s disease using focused ultrasound with GDNF retrovirus-loaded microbubbles to open the blood–brain barrier
  62. New derivatives of a natural nordentatin
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  65. Saliva proteomic analysis reveals possible biomarkers of renal cell carcinoma
  66. Withania frutescens: Chemical characterization, analgesic, anti-inflammatory, and healing activities
  67. Design, synthesis and pharmacological profile of (−)-verbenone hydrazones
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  69. Stability-indicating HPLC-DAD assay for simultaneous quantification of hydrocortisone 21 acetate, dexamethasone, and fluocinolone acetonide in cosmetics
  70. A novel lactose biosensor based on electrochemically synthesized 3,4-ethylenedioxythiophene/thiophene (EDOT/Th) copolymer
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  76. A Dy(iii)–organic framework as a fluorescent probe for highly selective detection of picric acid and treatment activity on human lung cancer cells
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  88. Effect of isovalent substitution on the crystal structure and properties of two-slab indates BaLa2−xSmxIn2O7
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  90. An improved reduction method for phase stability testing in the single-phase region
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  93. A turbidity sensor development based on NL-PI observers: Experimental application to the control of a Sinaloa’s River Spirulina maxima cultivation
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https://doi.org/10.1515/chem-2020-0180
Keywords for this article
Cu(ii) complexes; antimicrobial activity; antifungal activity; NSAID; Escherichia coli; Saccharomyces cerevisiae
Creative Commons
BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Electrochemical antioxidant screening and evaluation based on guanine and chitosan immobilized MoS2 nanosheet modified glassy carbon electrode (guanine/CS/MoS2/GCE)
  3. Kinetic models of the extraction of vanillic acid from pumpkin seeds
  4. On the maximum ABC index of bipartite graphs without pendent vertices
  5. Estimation of the total antioxidant potential in the meat samples using thin-layer chromatography
  6. Molecular dynamics simulation of sI methane hydrate under compression and tension
  7. Spatial distribution and potential ecological risk assessment of some trace elements in sediments and grey mangrove (Avicennia marina) along the Arabian Gulf coast, Saudi Arabia
  8. Amino-functionalized graphene oxide for Cr(VI), Cu(II), Pb(II) and Cd(II) removal from industrial wastewater
  9. Chemical composition and in vitro activity of Origanum vulgare L., Satureja hortensis L., Thymus serpyllum L. and Thymus vulgaris L. essential oils towards oral isolates of Candida albicans and Candida glabrata
  10. Effect of excess Fluoride consumption on Urine-Serum Fluorides, Dental state and Thyroid Hormones among children in “Talab Sarai” Punjab Pakistan
  11. Design, Synthesis and Characterization of Novel Isoxazole Tagged Indole Hybrid Compounds
  12. Comparison of kinetic and enzymatic properties of intracellular phosphoserine aminotransferases from alkaliphilic and neutralophilic bacteria
  13. Green Organic Solvent-Free Oxidation of Alkylarenes with tert-Butyl Hydroperoxide Catalyzed by Water-Soluble Copper Complex
  14. Ducrosia ismaelis Asch. essential oil: chemical composition profile and anticancer, antimicrobial and antioxidant potential assessment
  15. DFT calculations as an efficient tool for prediction of Raman and infra-red spectra and activities of newly synthesized cathinones
  16. Influence of Chemical Osmosis on Solute Transport and Fluid Velocity in Clay Soils
  17. A New fatty acid and some triterpenoids from propolis of Nkambe (North-West Region, Cameroon) and evaluation of the antiradical scavenging activity of their extracts
  18. Antiplasmodial Activity of Stigmastane Steroids from Dryobalanops oblongifolia Stem Bark
  19. Rapid identification of direct-acting pancreatic protectants from Cyclocarya paliurus leaves tea by the method of serum pharmacochemistry combined with target cell extraction
  20. Immobilization of Pseudomonas aeruginosa static biomass on eggshell powder for on-line preconcentration and determination of Cr (VI)
  21. Assessment of methyl 2-({[(4,6-dimethoxypyrimidin-2-yl)carbamoyl] sulfamoyl}methyl)benzoate through biotic and abiotic degradation modes
  22. Stability of natural polyphenol fisetin in eye drops Stability of fisetin in eye drops
  23. Production of a bioflocculant by using activated sludge and its application in Pb(II) removal from aqueous solution
  24. Molecular Properties of Carbon Crystal Cubic Structures
  25. Synthesis and characterization of calcium carbonate whisker from yellow phosphorus slag
  26. Study on the interaction between catechin and cholesterol by the density functional theory
  27. Analysis of some pharmaceuticals in the presence of their synthetic impurities by applying hybrid micelle liquid chromatography
  28. Two mixed-ligand coordination polymers based on 2,5-thiophenedicarboxylic acid and flexible N-donor ligands: the protective effect on periodontitis via reducing the release of IL-1β and TNF-α
  29. Incorporation of silver stearate nanoparticles in methacrylate polymeric monoliths for hemeprotein isolation
  30. Development of ultrasound-assisted dispersive solid-phase microextraction based on mesoporous carbon coated with silica@iron oxide nanocomposite for preconcentration of Te and Tl in natural water systems
  31. N,N′-Bis[2-hydroxynaphthylidene]/[2-methoxybenzylidene]amino]oxamides and their divalent manganese complexes: Isolation, spectral characterization, morphology, antibacterial and cytotoxicity against leukemia cells
  32. Determination of the content of selected trace elements in Polish commercial fruit juices and health risk assessment
  33. Diorganotin(iv) benzyldithiocarbamate complexes: synthesis, characterization, and thermal and cytotoxicity study
  34. Keratin 17 is induced in prurigo nodularis lesions
  35. Anticancer, antioxidant, and acute toxicity studies of a Saudi polyherbal formulation, PHF5
  36. LaCoO3 perovskite-type catalysts in syngas conversion
  37. Comparative studies of two vegetal extracts from Stokesia laevis and Geranium pratense: polyphenol profile, cytotoxic effect and antiproliferative activity
  38. Fragmentation pattern of certain isatin–indole antiproliferative conjugates with application to identify their in vitro metabolic profiles in rat liver microsomes by liquid chromatography tandem mass spectrometry
  39. Investigation of polyphenol profile, antioxidant activity and hepatoprotective potential of Aconogonon alpinum (All.) Schur roots
  40. Lead discovery of a guanidinyl tryptophan derivative on amyloid cascade inhibition
  41. Physicochemical evaluation of the fruit pulp of Opuntia spp growing in the Mediterranean area under hard climate conditions
  42. Electronic structural properties of amino/hydroxyl functionalized imidazolium-based bromide ionic liquids
  43. New Schiff bases of 2-(quinolin-8-yloxy)acetohydrazide and their Cu(ii), and Zn(ii) metal complexes: their in vitro antimicrobial potentials and in silico physicochemical and pharmacokinetics properties
  44. Treatment of adhesions after Achilles tendon injury using focused ultrasound with targeted bFGF plasmid-loaded cationic microbubbles
  45. Synthesis of orotic acid derivatives and their effects on stem cell proliferation
  46. Chirality of β2-agonists. An overview of pharmacological activity, stereoselective analysis, and synthesis
  47. Fe3O4@urea/HITh-SO3H as an efficient and reusable catalyst for the solvent-free synthesis of 7-aryl-8H-benzo[h]indeno[1,2-b]quinoline-8-one and indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine derivatives
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  49. Enhancement of thermal properties of bio-based microcapsules intended for textile applications
  50. Exploring the effect of khat (Catha edulis) chewing on the pharmacokinetics of the antiplatelet drug clopidogrel in rats using the newly developed LC-MS/MS technique
  51. A green strategy for obtaining anthraquinones from Rheum tanguticum by subcritical water
  52. Cadmium (Cd) chloride affects the nutrient uptake and Cd-resistant bacterium reduces the adsorption of Cd in muskmelon plants
  53. Removal of H2S by vermicompost biofilter and analysis on bacterial community
  54. Structural cytotoxicity relationship of 2-phenoxy(thiomethyl)pyridotriazolopyrimidines: Quantum chemical calculations and statistical analysis
  55. A self-breaking supramolecular plugging system as lost circulation material in oilfield
  56. Synthesis, characterization, and pharmacological evaluation of thiourea derivatives
  57. Application of drug–metal ion interaction principle in conductometric determination of imatinib, sorafenib, gefitinib and bosutinib
  58. Synthesis and characterization of a novel chitosan-grafted-polyorthoethylaniline biocomposite and utilization for dye removal from water
  59. Optimisation of urine sample preparation for shotgun proteomics
  60. DFT investigations on arylsulphonyl pyrazole derivatives as potential ligands of selected kinases
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  62. New derivatives of a natural nordentatin
  63. Fluorescence biomarkers of malignant melanoma detectable in urine
  64. Study of the remediation effects of passivation materials on Pb-contaminated soil
  65. Saliva proteomic analysis reveals possible biomarkers of renal cell carcinoma
  66. Withania frutescens: Chemical characterization, analgesic, anti-inflammatory, and healing activities
  67. Design, synthesis and pharmacological profile of (−)-verbenone hydrazones
  68. Synthesis of magnesium carbonate hydrate from natural talc
  69. Stability-indicating HPLC-DAD assay for simultaneous quantification of hydrocortisone 21 acetate, dexamethasone, and fluocinolone acetonide in cosmetics
  70. A novel lactose biosensor based on electrochemically synthesized 3,4-ethylenedioxythiophene/thiophene (EDOT/Th) copolymer
  71. Citrullus colocynthis (L.) Schrad: Chemical characterization, scavenging and cytotoxic activities
  72. Development and validation of a high performance liquid chromatography/diode array detection method for estrogen determination: Application to residual analysis in meat products
  73. PCSK9 concentrations in different stages of subclinical atherosclerosis and their relationship with inflammation
  74. Development of trace analysis for alkyl methanesulfonates in the delgocitinib drug substance using GC-FID and liquid–liquid extraction with ionic liquid
  75. Electrochemical evaluation of the antioxidant capacity of natural compounds on glassy carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene
  76. A Dy(iii)–organic framework as a fluorescent probe for highly selective detection of picric acid and treatment activity on human lung cancer cells
  77. A Zn(ii)–organic cage with semirigid ligand for solvent-free cyanosilylation and inhibitory effect on ovarian cancer cell migration and invasion ability via regulating mi-RNA16 expression
  78. Polyphenol content and antioxidant activities of Prunus padus L. and Prunus serotina L. leaves: Electrochemical and spectrophotometric approach and their antimicrobial properties
  79. The combined use of GC, PDSC and FT-IR techniques to characterize fat extracted from commercial complete dry pet food for adult cats
  80. MALDI-TOF MS profiling in the discovery and identification of salivary proteomic patterns of temporomandibular joint disorders
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  82. Structure and some physicochemical and functional properties of water treated under ammonia with low-temperature low-pressure glow plasma of low frequency
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  89. Synthesis, spectral and thermo-kinetics explorations of Schiff-base derived metal complexes
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  91. Comparative analysis of chemical composition of some commercially important fishes with an emphasis on various Malaysian diets
  92. Development of a solventless stir bar sorptive extraction/thermal desorption large volume injection capillary gas chromatographic-mass spectrometric method for ultra-trace determination of pyrethroids pesticides in river and tap water samples
  93. A turbidity sensor development based on NL-PI observers: Experimental application to the control of a Sinaloa’s River Spirulina maxima cultivation
  94. Deep desulfurization of sintering flue gas in iron and steel works based on low-temperature oxidation
  95. Investigations of metallic elements and phenolics in Chinese medicinal plants
  96. Influence of site-classification approach on geochemical background values
  97. Effects of ageing on the surface characteristics and Cu(ii) adsorption behaviour of rice husk biochar in soil
  98. Adsorption and sugarcane-bagasse-derived activated carbon-based mitigation of 1-[2-(2-chloroethoxy)phenyl]sulfonyl-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) urea-contaminated soils
  99. Antimicrobial and antifungal activities of bifunctional cooper(ii) complexes with non-steroidal anti-inflammatory drugs, flufenamic, mefenamic and tolfenamic acids and 1,10-phenanthroline
  100. Application of selenium and silicon to alleviate short-term drought stress in French marigold (Tagetes patula L.) as a model plant species
  101. Screening and analysis of xanthine oxidase inhibitors in jute leaves and their protective effects against hydrogen peroxide-induced oxidative stress in cells
  102. Synthesis and physicochemical studies of a series of mixed-ligand transition metal complexes and their molecular docking investigations against Coronavirus main protease
  103. A study of in vitro metabolism and cytotoxicity of mephedrone and methoxetamine in human and pig liver models using GC/MS and LC/MS analyses
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  105. Erratum
  106. Erratum to: A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor
  107. Review Articles
  108. Sinoporphyrin sodium, a novel sensitizer for photodynamic and sonodynamic therapy
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  115. Studies on the Anti-Gouty Arthritis and Anti-hyperuricemia Properties of Astilbin in Animal Models
  116. Effects of organic fertilizer on water use, photosynthetic characteristics, and fruit quality of pear jujube in northern Shaanxi
  117. Characteristics of the root exudate release system of typical plants in plateau lakeside wetland under phosphorus stress conditions
  118. Characterization of soil water by the means of hydrogen and oxygen isotope ratio at dry-wet season under different soil layers in the dry-hot valley of Jinsha River
  119. Composition and diurnal variation of floral scent emission in Rosa rugosa Thunb. and Tulipa gesneriana L.
  120. Preparation of a novel ginkgolide B niosomal composite drug
  121. The degradation, biodegradability and toxicity evaluation of sulfamethazine antibiotics by gamma radiation
  122. Special issue on Monitoring, Risk Assessment and Sustainable Management for the Exposure to Environmental Toxins
  123. Insight into the cadmium and zinc binding potential of humic acids derived from composts by EEM spectra combined with PARAFAC analysis
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  125. Special Issue on 13th JCC 2018
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  129. Size-dependent growth kinetics of struvite crystals in wastewater with calcium ions
  130. The effect of silica-calcite sedimentary rock contained in the chicken broiler diet on the overall quality of chicken muscles
  131. Physicochemical properties of selected herbicidal products containing nicosulfuron as an active ingredient
  132. Lycopene in tomatoes and tomato products
  133. Fluorescence in the assessment of the share of a key component in the mixing of feed
  134. Sulfur application alleviates chromium stress in maize and wheat
  135. Effectiveness of removal of sulphur compounds from the air after 3 years of biofiltration with a mixture of compost soil, peat, coconut fibre and oak bark
  136. Special Issue on the 4th Green Chemistry 2018
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  140. Synthesis of amorphous aluminosilicate from impure Indonesian kaolin
  141. Special Issue on the International Conf on Science, Applied Science, Teaching and Education 2019
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  143. The effect of nitrite food preservatives added to se’i meat on the expression of wild-type p53 protein
  144. Biocompatibility and osteoconductivity of scaffold porous composite collagen–hydroxyapatite based coral for bone regeneration
  145. Special Issue on the Joint Science Congress of Materials and Polymers (ISCMP 2019)
  146. Effect of natural boron mineral use on the essential oil ratio and components of Musk Sage (Salvia sclarea L.)
  147. A theoretical and experimental study of the adsorptive removal of hexavalent chromium ions using graphene oxide as an adsorbent
  148. A study on the bacterial adhesion of Streptococcus mutans in various dental ceramics: In vitro study
  149. Corrosion study of copper in aqueous sulfuric acid solution in the presence of (2E,5E)-2,5-dibenzylidenecyclopentanone and (2E,5E)-bis[(4-dimethylamino)benzylidene]cyclopentanone: Experimental and theoretical study
  150. Special Issue on Chemistry Today for Tomorrow 2019
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  153. Special Issue on Advances in Chemistry and Polymers
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  155. Special Issue on 3rd IC3PE 2020
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  157. Special Issue on IC3PE 2018/2019 Conference
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  159. Advancing biodiesel production from microalgae Spirulina sp. by a simultaneous extraction–transesterification process using palm oil as a co-solvent of methanol
  160. Topical Issue on Applications of Mathematics in Chemistry
  161. Omega and the related counting polynomials of some chemical structures
  162. M-polynomial and topological indices of zigzag edge coronoid fused by starphene
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