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Spectral, thermal, antimicrobial studies for silver(I) complexes of pyrazolone derivatives

Abstract

Background

Synthesize new complexes of Ag(I) to enhance efficacy or stability and also, pharmacological activities on the operation of pyrazolone's biological properties.

Results

Efficient and high yielding pathways starting from the versatile and readily available 3-methyl-1-phenyl-5-pyrazolone by Knoevenagel condensation of a sequence of 4-arylidene-3-methyl-1-phenyl-5-pyrazolone derivatives (2a-c) have been formed by the reaction of various substituted aromatic aldehydes Used as ligands to synthesize Ag(I) chelates. Synthesized compounds and their complexes have been characterized by elemental analysis, magnetic and spectroscopic methods (IR, 13C, 1HNMR, mass) and thermal analysis. The spectrophotometric determinations suggest distorted octaedral geometry for all complexes. Both ligands and their metal complexes have also been tested for their antibacterial and antifungal efficacy.

Conclusions

Newly synthesized compounds have shown potent antimicrobial activity. The results showed that the complex 's high activity was higher than its free ligands, and that Ag(I)-L3 had the highest activity.

Introduction

Pyrazolone chemistry began in 1883 when Ludwig Knorr first reacted to phenyl hydrazine with aceto-acetate ester. As pyrazolones were discovered as binding components for azo dyes in the late 1800s, they rapidly increased in importance. Today, pyrazolon is still an significant trade precursor to dyes and pharmaceuticals. Pyrazolone is a biologically important scaffold associated with different pharmacological activities such as antimicrobials [1,2,3,4,5], anti-inflammatory [6], analgesic [7], antidepressant [8], anticonvulsant [9], antidiabetic [10], antihyperlipidemic [11, 12], antiviral [13, 14], anti-tuberculosis [15, 16], antioxidant [17, 18] and anticancer [19, 20]. For several years, the preparation of pyrazolone and its derivatives has attracted significant attention from organic and medicinal chemists, as they belong to a class of compounds with promising results in medicinal chemistry. The heterocycles condensed to the pyrazole ring are an important source of bioactive molecules [21, 22]. Compounds containing both pyrazole and other essential heterocyclic active structural units usually demonstrate more remarkable biological activity. A number of condensed pyrazole derivatives have been reported as four-fold antibacterial agents against Gram-positive and Gram-negative bacteria compared to general pyrazole compounds [23, 24]. A digit of antimicrobial active silver(I) complexes have the capacity to disrupt microbial transpiration as well as block tyrosinase synthesis and are extremely cytotoxic to cancer cells [24]. Massive attention in silver ions (Ag(I)) as a broad spectrum antimicrobial has upped the size and importance of in vitro biocompatibility research [25]. Silver ions are toxic to many bacteria, viruses, algae and fungi. Silver-based medicines have been widely used for this task for decades [26]. The objective of this study is to display the synthesis and characterization of three Ag(I) pyrazolone complexes in an attempt to verify the mode of coordination and the biological properties of the final complexes.

Results and discussion

Synthesis and formulation

A sequence of derivatives of 4-arylidene-3-methyl-1-phenyl-5-pyrazolone (4-(4-dimethylamino benzylidene)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2a) L1, 4-(4-Thiophene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2b) L2, 4-(4-methoxy benzylidene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2c) L3) is synthesized by condensing 3-methyl-1-phenyl-5-pyrazolone with substituted aromatic aldehydes as shown in Scheme 1 [27]. Three Ag(I) complexes have been prepared with the L1, L2, L3 ligands as shown in Scheme 2. Based on physicochemical and spectral data (IR and 1HNMR), structure of the synthesized compounds (2a-c, Ag(I) complexes) has been evaluated.

Scheme 1
scheme1

Synthesis of 4-arylidene-3-methyl-1-phenyl-5-pyrazolone derivatives

Scheme 2
scheme2

The coordinationn mode of Ag (I) with three ligand

Infrared spectra

KBr disks registered mid-infrared spectra of L1, L2, L3 and their metal complexes. As expected, with changes in band intensities and wave numbers, the absorption bands characteristic of L1, L2, L3 acting as a monodentate unit are observed in the complexes. The proposed structures of the complexes must be considered prior to determining the assignments of the infrared spectra. Here, Ag(I) ion interacts with these monodentate ligands forming monomeric structure complexes in which the Ag(I) ion is four coordinated (Scheme 2) [27,28,29,30].

The complexes of three ligands with Ag(I) contain only one plane of symmetry and therefore the complexes that belong to CS symmetry and show 159 vibrational fundamentals, and all vibrations are distributed between movements of the types A\ and A1\\, all of which are monodegenrate, infra—red and Raman active. The free ligand infrared spectrum shows bands at 1496, 1508 and 1550 cm−1 due to the stretching vibration of hydrazono (C = N) groups [31]. Comparing the Ag(I) IR spectrum with the free ligand spectrum, the transfer of (C = N) groups to lower frequency values (1512, 1515, 1523 and 1527 cm−1) and the change in strength of (C = N) from medium to strong (Fig. 1 and Table 1) which confirms that the ligand molecule coordinated with metal ions through the hydrazon nitrogen atom [31]. A medium wide band for the H2O stretching vibrations of coordinated water molecules at 3379, 3364, and 3364 cm−1 [31];The stretching vibrations ν(C-H) of phenyl groups and −CH3 units in these complexes are assigned as a number of bands in the region 3066–3100 cm−1 [11, 12]. The ν(C = O) vibration appears in the region of 1666–1685 cm−1. The spectra of the isolated solid complexes revealed a number of new bands of different intensities for ν(M–N). The ν(Ag–N) bands observed at 813, 837 cm−1 for Ag(I)-L1, at 748, 794 cm−1 for Ag(I)-L2 and at 759, 779 cm−1 for Ag(I)-L3 (Table 1) which are absent in the spectrum of free three ligands [30,31,32]. The coordinating water in the three complexes are characterized by the appearance of ν(Ag–O) at 577, 515, 544 cm−1. Also the stretching vibrations at 813, 792, 779 cm−1 assigned to ν(Ag OH2), sponsored coordinating water participation [32]. The suggested structural formulas are defined in Scheme 2 on the basis of the IR tests.

Fig. 1
figure1

Infrared spectra for a L1, b [Ag(L1)2(H2O)2]NO3, c L2, d [Ag(L2)2(H2O)2]NO3.H2O, e L3 and f [Ag(L3)2(H2O)2]NO3

Table 1 Infrared frequencies (cm−1)a and tentative assignmentsb for (A) L1, (B) [Ag(L1)2(H2O)2]NO3, (C), L2 (D) [Ag(L2)2(H2O)2]NO3.H2O, (E) L3 and (F) [Ag(L3)2(H2O)2]NO3

UV–Visible Spectra

The application of ultraviolet spectroscopy is more general and can be useful for all chelate structural determinations as they are all absorbed in this region [33]. Electronic absorption spectra confirmed the development of metal ligand complexes. Electronic absorption spectra L1 for Ag(I), L2 for Ag(I) and L3 for Ag(I). Complexes within the spectrum of wavelengths between 200 and 800 nm are described in Additional file 1: Table S1 and Fig. 2. The free three-ligand UV spectrum (L1, L2 and L3) displays bands at 281, 297 and 297 nm that are assigned respectively to π-π*. And displays bands allocated to n-π * transitions at 330 nm. The modification of the reflectance band to higher (bathochromic shift) and lower values (hypochromic shift) and the appearance of new bands for complexes has resulted in the release of three ligands' complex actions towards metal ions. Complexes also present bands within the range 410–480 nm which can be due to the transition of ligand–metal charges for three ligands [34, 36]. The molar absorptivity (ε) values of the prepared metal complexes under investigation were determined (Additional file 1: Table S1) using the relation: A = εcl, where, A = absorbance, c = 1.0 × 10–3 M, l = length of cell (1 cm) [22]. The values of 10Dq (difference between t2g and eg) for the complexes were calculated by using the following Eq. 10Dq = E = hcν where E = energy, h = blank constant = 6.626 × 10−34 J.sec, c = 3 × 1010 cm/sec, ν = wave number cm−1 the data listed in Additional file 1: Table S1.

Fig. 2
figure2

Electronic absorption spectra for L1, [Ag(L1)2(H2O)2]NO3, L2, [Ag(L2)2(H2O)2]NO3.H2O, L3 and [Ag(L3)2(H2O)2]NO3

The 1H NMR spectra

Suggested structure of the isolated Ag(I) complexes confirm about the efficiency of 1H NMR spectra. Compared to the one of their complexes (Additional file 1: Table S2), the 1H NMR spectra of new free three ligands in DMSO-d6. The 1H NMR spectra of L1 and its metal complex shown in (Fig. 3a, b), the proton of (= CH-Ar) group observed in δ: 9.66 ppm and the protons of aromatic ring of (s, 9H, Aromatic–H) observed at δ: 7.14–7.97 ppm also the values of protons of -CH aliphatic observed in the range δ: 3.03–3.33 ppm (s, 6H, –N (CH3)2), the proton of (s, 3H, –CH3) group observed in δ 2.28 ppm, no major differences were observed as opposed to the Ag(I) complex except that the signal is observed in 3.46 ppm due to H2O molecules [36]. This supports the hypothesis that L1 interacts as a monodentate ligand bound to the Ag(I) ion through the hydrazono nitrogen group. [37]. The 1H NMR spectra of L2 and its Ag(I) complex shown in (Fig. 3c, d), the proton of (= CH-Ar) group observed in δ: 8.25 ppm and, the protons of aromatic ring of (s, 8H, Aromatic–H) observed at δ: 7.39–7.91 ppm [38]. The proton of (s, 3H, –CH3) group observed in δ 2.30 ppm, simple differences are shown in comparison to the metal complex and the signal is observed in π: 3.47 ppm due to H2O molecules. This reinforces the hypothesis that L2 reacts via the hydrazono nitrogen group as a monodentate ligand bound to the Ag(I) ion. The 1H NMR spectra of L3 and its Ag(I) complex shown in (Fig. 3 (E, F)), the proton of (= CH-Ar) group observed in δ: 8.71 ppm and the protons of aromatic ring of (s, 9H, Aromatic–H) observed at δ: 7.18–7.46 ppm also the values of protons of -CH aliphatic observed in the range δ: 3.31 ppm (s, 3H, –O-CH3), the proton of (s, 3H, –CH3) group observed in δ 2.33 ppm, no major variations were noticed as opposed to the Ag(I) series. This supports the assumption that L3 reacts as a monodentate ligand bound to the Ag(I) ion via the hydrazone nitrogen group.

Fig. 3:
figure3

1H NMR spectra for a L1, b [Ag(L1)2(H2O)2]NO3, c L2, d [Ag(L2)2(H2O)2]NO3.H2O, e L3 and f [Ag(L3)2(H2O)2]NO3

Thermal studies

The thermal degradation of ligand (L1) began at 190 °C and decay occurs at various temperatures at 310, 544 °C at one stage (Additional file 1: Fig. S1a). This step is accompanied by a net weight loss of 92.36 percent, equivalent to the predicted 92.07 percent. Corresponding to the loss of 8C2H2 + NH3 + CO + N2 molecule and 95.65KJ mol−1 (endothermic) activation energy. The residue value decomposes at a height of 800 °C and the actual losing weight at this point is 7.64 percent, close to the estimated 7.86 percent equal to 2C. The [Ag(L1)2(H2O)2]NO3 complex decomposed in two steps (Additional file 1: Fig. S1b), The first one begins at a limit of 189 °C and is followed by a 33.378 percent weight loss leading to a 9C2H2 + 2H2O loss similar to the estimated value of 33.062 percent with an activation energy of 34.37 kJ mol−1. The second step occurs at 366 and 562 °C followed by a weight loss of 52.79 percent; equivalent to a value of 8C2H2 + 4HCN + NO + 2N2O, potentially similar to the measured value of 53.798 percent. The residue value proceeds at 931 °C and the overall weight loss from this stage is 13.474 percent, referring to Ag, similar to the 13.14 percent estimated value (Table 2).

Table 2 Thermogravimetric data of L1, L2,L3 and their metal complexes

The ligand (L2) degradates at 273, 475 °C. This stage is followed by a complete loss of weight of 86.70 percent, close to 86.56 percent of the estimated value (Additional file 1: Fig. S1c). Equivalent to 6C2H2 + SO + N2 loss and 31.93 kJ mol−1 (endothermic) activation energy. Decomposition of the residual value occurs at 771 °C and the real weight loss from this stage is 13.30 percent, similar to the estimated value of 13.43 percent corresponding to 3C. The [Ag(L2)2(H2O)2]NO3.H2O complex decomposes at two levels of decay (Additional file 1: Fig. S1d), the first phase occurs at 99 °C and is followed by a weight loss of 2.08 per cent relating to the removal of H2O, activation energy of 79.28 kJ mol−1. The second step of decomposition occurs at temperature is 203, 528 and is accompanied by a weight loss of 75.90%; corresponding to the value of 10C2H2 + 4HCN + 2H2O + NO2 + SO + SO2 theoretically, close to the calculated value 76.404%. The Residue value decomposition occurs at maximum 881 °C and the actual weight loss from this step is 23.35%, corresponding to Ag + 6C, close to the calculated value 23.596%.

The thermal decay of L3 happens in two phases of degradation (Additional file 1: Fig. S1e), the first step arises at 291 °C and is followed by a weight loss of 70.55 percent leading to a loss of 8C2H2 similar to the measured value of 71.23 per cent with activation energy of 35.31 kJ mol−1. The second step occurs at 518 οC and is accompanied by a weight loss of 28.604%; corresponding to the value of 2CO + N2 theoretically, close to the calculated value 28.67%. The [Ag(L3)2(H2O)2]NO3 degradation takes place in two stages (Additional file 1: Fig. S1f), the first occurs at 244 οC and is accompained by a weight loss of 51.071% corresponding to loss of 14C2H2 + 2H2O close to the calculated value 50.60% with an activation energy 15.31 kJ mol−1. The second one begins at 543 οC and is followed by a weight loss of 30.17%; corresponding to C2H2 + CO + 2HCN + 3NO2 theoretically, close to the calculated value 31.25%. The Residue remains at 677 °C and the actual weight loss is 17.76%, equal to Ag + 3C, close to the calculated value 18.15%.

Kinetic data

The kinetic parameters (activation energy, E*, entropy, ΔS*, enthalpy, ΔH*, and Gibbs free energy, ΔG*) have been evaluated by using the two mentioned methods in the literature [39, 40] and shown in Additional file 1: Fig. S2 and listed in Table 3. The correlation coefficient for Arrhenius plots of thermal degradation stages were found to be in the range 0.943–0.985, revealing a good fit with linear function. The activation energies of decomposition were observed to be in the range 7.44–154.69 kJ mol−1. The negative values of ΔS* indicate that the activation complex has a more ordered structure than the reactants or the reactions are slow. The positive ΔH* values postulate an endothermic nature of the formed complexes. The greater positive values of E* indicate that the processes involving in translational, rotational, vibrational states and a changes in mechanical potential energy for complexes and reflect the thermal stability of the complexes [41].

Table 3 Thermal behavior and kinetic parameters determined using the Coats–Redfern (CR) and Horowitz–Metzger (HM) operated for L1, L2, L3 and their complexes

Mass spectra

The principle of a mass spectrometer focuses on the separation of fragments of ions based on the distribution of these ions with the mass to charge ratio (m/z). The L1, L2, L3 fragmentation patterns and their complexes were obtained from the mass spectra, and were in good agreement with the structure suggested. The L1 showed molecular ion peak (M+.) with m/z = 305 (100%). The molecular ion peak [a] losses C2H6N to give fragment [b] at m/z = 261 (3.13%), then [b] losses C6H4 to give fragment [c] at m/z = 185 (2.98%) and [c] losses CH3O to give [d] at m/z = 154(0.66%). The molecular ion peak [a] losses C9H11N to give fragment [e] at m/z = 172 (29.92%) and this [e] losses C7H8O to give fragment [f] at m/z = 64 (2.08%) (Fig. 4), (Scheme 3). Fragmentation pattern of the complex [Ag(L1)2(H2O)2]NO3 is given as an example in (Fig. 4), Additional file 1: Scheme S1. The molecular ion peak [a] appeared at m/z = 816 (20.5%) losses C18H22N2 to give [b] at m/z = 514 (17.7%) and it losses C2H6O2 to give [c] at m/z = 452 (11.7%). The L2 molecular ion peak [a] appeared at m/z = 268 (100%) losses C4H3S to give [b] at m/z = 185 (14.60%) then it losses CH3O to give [c] at m/z = 154 (0.2%), molecular ion peak[c] lossC6H5 to give [d] at m/z = 77(28.34%) and molecular ion peak [d] losses CH to give [e] at m/z = 64 (4.89%).(Fig. 4), Scheme 4. Fragmentation pattern of the complex [Ag(L2)2(H2O)2]NO3.H2O is given as an example in (Fig. 4), Additional file 1: Scheme S2. The molecular ion peak [a] appeared at m/z = 760 (35%) losses C10H8S2to give [b] at m/z = 532 (5%) and it losses C2H6O2 to give [c] at m/z = 470 (12%). The L3 molecular ion peak [a] appeared at m/z = 292 (100%) losses CH3O to give [b] at m/z = 261 (4%) then [a] losses C6H4 to give [c] at m/z = 185 (21.73%), molecular ion peak[c] loss CH to give [d] at m/z = 172(6.8%) and molecular ion peak [d] losses CH3O to give [e] at m/z = 141 (1.2%).(Fig. 4), Scheme 5. Fragmentation pattern of the complex [Ag(L3)2(H2O)2]NO3 is given as an example in (Fig. 4), Additional file 1: Scheme S3. The molecular ion peak [a] appeared at m/z = 790 (65%) losses C2H6O2to give [b] at m/z = 692 (2%), it losses C12H8 to give [c] at m/z = 540 (12.5%) and molecular ion peak [c] losses C2H2 to give [d] at m/z = 514 (25.3%) [42].

Fig. 4
figure4

Mass spectra diagrams for (A) L1, (B) [Ag(L1)2(H2O)2]NO3, (C), L2 (D) [Ag(L2)2(H2O)2]NO3.H2O, (E) L3 and (F) [Ag(L3)2(H2O)2]NO3

Scheme 3
scheme3

Fragmentation pattern of L1

Scheme 4
scheme4

Fragmentation pattern of L2

Scheme 5
scheme5

Fragmentation pattern of L3

Biological activity studies

Antimicrobial studies

The antimicrobial efficacy of L1, L2, L3 and their free ligand complexes are explored in this experiment. Studies were conducted on E. Coli ATCC11229, Coliform ATCC8729, S. aureus ATCC6538, and Salmonella typhi ATCC14028 and fungal species as A. niger and P. expansum screening was tested against and examination and evaluation of the prepared complexes [42]. The same results were reported for E. Coli ATCC11229 of Ag(I)-L2 and Ag (I)-L1 followed by Ag(I)-L3 considers that the lowest findings are equivalent to those of other complexes. The effect of free ligands on this strain has been shown to be below its complex and can be organized according to the sensitivity of the strains L2, L3 and L1 in the following ascending order. The effect of Ligands and their complexes on Coliform ATCC8729 showed that Ag(I)-L2 is highly important, giving 25.12 mm respectively. Although the remaining complexes showed lower results than the L2 complexes. The results obtained in Table 4 and Fig. 5 showed that lower activity on the same strain and these results ensured that free ligand complexes were more active than free ligand complexes. In gram + ve bacteria, S. aureus ATCC6538, Highly important antibacterial activity of metal complexes with L1 followed L3 complex. The lesser activity from ligand L2 and its complex. The antibacterial activity of metal complexes on Salmonella typhi ATCC14028 showed a good activity against (gram −ve), that recorded the best results Ag(I)-L3 > Ag(I)-L1 > Ag(I)-L2 respectively. The action of the free ligands on gram –ve bacteria has yielded results lower than their complexes which give respectively 12.6, 11.43 and 7.8 mm, L3, L1, L2. The presence of different ligands and other complexes on both fungal strains of the testes, A. niger recorded that Ag(I)-L3 showed a significant difference the highly results (20 ± 2.6) though free L3 results showed less than its complex. Others did not show any activity against tested fungi (A. niger). The effect of various significant ligands and other complexes on P. expansum did not show any activity whereas the the highest broad spectrum of activity on the same test strain showed the best results on L1 and its complexes [42].

Table 4 The inhibitation diameters zone values (mm) for L1, L2, L3 and its complexes
Fig. 5
figure5

Statistical representation for biological activity of L1, L2, L3 and its metal complexes

Normal antibiotic efficacy of antimicrobials (AMC, CTX, NS, FU). The AMC mixture give the effective against E. coli, Coliform, S. aureus and NS high inhibitory activity on A. niger. Other antibiotics have shown no action on other microorganisms. Eventually, the bacterial strains showed a varied response to the three free ligands and their complex antimicrobial activity, but the results indicated that the high activity of ligand complexes was better than their free ligands. The two fungal strains are more resistant to synthesis ligands and their complexes than bacterial strains [42,43,44,45,46].

Determination of MIC for the most sensitive organisms

The artificial ligands and their complexes developed the biological efficacy towaeds the more resistant bacteria and fungi (Table 5A–D) and Fig. 6). The order of The lowest MIC for in case of E. coli decrease in order: L1 = Ag (I) – L3 (0.02 mg/100 mL)˃ L3 (0.05 mg/100 mL)˃ Ag (I) – L1 = L2 (0.07 mg/100 mL) ˃ Ag (I) – L2 (0.1 mg / 100 mL) [42], Coliform decrease in order: Ag (I) – L2 (0.02 mg/100 mL) ˃ Ag (I) – L3 = L2 (0.07 mg/100 mL) ˃ L1 = Ag (I) – L1 = L3 (0.1 mg/100 mL). Salmonella typhi showed that, the amazing results of ligands and its complexes: L2, Ag(I) – L2 = Ag(I) – L1 (0.02 mg/100 mL) ˃ Ag (I) – L3 = L1 ( 0.05 mg/ 100 mL) ˃ L3 (0.1 mg/ 100 mL), S. aureus order: L3 = Ag(I) – L2 = Ag(I) – L1 = L1 = Ag(I) –L3 (0.1 mg/ 100 mL) ˃ L2 (0.05 mg/ 100 mL). Table 5E, F and Fig. 6 data showed that the lowest MIC for the two strains measured at conc. 0.02 mg/100 mL. Although MIC at complex L3 was recorded by A.niger, the same result was recorded on Ag(I)—L3 at conc. 0.02 mg/100 mL. Ligand L1 and its complexes demonstrate the strongest MIC on P. expansum, although no behavior is displayed by the other compounds and their complexes. These findings ensured that the activity of synthetic ligands and their complexes on pathogenic bacteria and fungi demonstrated a minimum inhibitor concentration (MIC) for the most vulnerable pathogens. [42, 47, 48].

Table 5 (A) Of One-way ANOVA: E. coli vs MIC Compounds. (B) Of One-way ANOVA: Coliform versus MIC Compounds. (C) Of One-way ANOVA: S. aureus vs MIC Compounds. (D) Of One-way ANOVA: Salm. typhi vs MIC Compounds. (E) Of One-way ANOVA: A. niger vs MIC Compounds. (E) Of One-way ANOVA: A. niger vs MIC Compounds. (F) Of One-way ANOVA: P.expansum vs MIC Compounds
Fig. 6
figure6

MIC for the most sensitive organisms

Conclusion

Development and characterisation of three novel complexes of some replaced pyrazole derivatives as ligands (4-(4-dimethylamino benzylidene)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2a) L1, 4-(4-Thiophene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2b) L2, 4-(4-methoxy benzylidene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2c) L3) with Ag(I) was achieved using physicochemical and spectroscopic methods.. In the resulting complexes, L1, L2, and L3 were bound by the nitrogen atom to the metal ion via ν(C = N). For the three ligands and their complexes, thermogravimetric kinetic parameters and their differential were evaluated using the Coats-Redfern and Horowitz-Metzger equations. Metal complexes exhibited higher inhibition against all tested microorganisms and pathogenic bacteria and fungi and were the most susceptible pathogens with a minimum inhibitory concentration ( MIC).

Methods

Chemistry

Analytical grade reagents, commercially available from multiple suppliers and used without further purification, were all the chemicals used in the complex preparation. Synthesized compounds and their complexes have been characterized by elemental analysis, magnetic and spectroscopic methods (IR, 13C, 1HNMR, mass) and thermal analysis using the known apparatuses [42].

Synthesis of the ligands

Common 3-methyl-1-phenyl-5-pyrazolone synthesis technique (1)

Pure ethyl acetoacetate (0.05 mol, 6.2 mL) was mixed with pure phenyl hydrazine (0.05 mol, 5 mL), 0.5 mL of acetic acid was added, according to knowm method [42]. Methyl phenyl pyrazolone was obtained as colorless crystals, 127 °C melting point and 83.6 percent yield [27].

Specific method for preparing derivatives of 4-arylidene-3-methyl-1-phenyl-5-pyrazolone (2a-c)

The oil bath heated a mixture of 1-aryl-3-methyl-5-pyrazolone (0.01 mol, 1.74 g) and replaced aromatic aldehydes (0.012 mol) at 150–160 °C for 2-4hrs. TLC has tracked the progress of the reaction using ethyl acetate: hexane (9:1) as solvent. The mixture was cooled, triturated and washed off with ether (20 mL). The colored residue was recrystallized from ethanol to provide the corresponding 4-arylidene-3-methyl-1-phenyl-5-pyrazolone (2a-c) as colored products, respectively [28].

4-(4-dimethylamino benzylidene)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2a) L1.

4-(4-Thiophene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2b) L2.

4-(4-methoxy benzylidene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2c) L3.

4-(4-dimethylamino benzylidene)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2a) L1

Brick Red, mp = 170 °C, yield 83% IR (KBr, v, cm−1): 3444 (OH), 1670 (C = O), and 1550 cm−1. 1H NMR (DMSO-d6, 300 MHz): δ = 2.28 (s, 3H, CH3), 3.03 (s, 6H, -N (CH3)2), 7.14 (S, 1H, = CH-Ar), 9.66 (d, 3H, Ar–H),. Anal. Calcd for C19H19N3O (305.19): C, 74.40; H, 6.22; N 13.76; Found C, 74.23; H, 6.13; N, 13.35%.

4-(4-Thiophene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2b) L2

Orange, mp = 125 °C, yield 74% IR (KBr, v, cm−1): 3448 (OH), 1681 (C = O), 1496 cm−1 (C = N) and 1056 cm−1(C = S). 1H NMR (DMSO-d6, 300 MHz): δ = 2.30 (s, 3H, CH3), 7.39 (S, 1H, = CH-Ar), 8.25 (d, 3H, Ar–H). Anal. Calcd for C15H12N2OS (268): C, 67.16; H, 4.47; N 10.44; S, 11.94; Found C, 67.00; H, 4.32; N, 10.21; S, 11.65%.

4-(4-methoxy benzylidene)-3-methyl-1-phenyl-1Hpyrazol-5(4H)-one (2c) L3

Orange, mp = 122 °C, yield 82% IR (KBr, v, cm−1): 3444 (OH), 1678 (C = O), 1508 cm−1 (C = N) and. 1H NMR (DMSO-d6, 300 MHz): δ = 1.91 (s, 3H, CH3), 3.69 (s, 3H, -OCH3), 7.20 (S, 1H, = CH-Ar), 8.71 (d, 3H, Ar–H).Anal. Calcd for C18H16N2O2 (292): C, 73.97; H, 5.47; N 9.58; Found C, 73.78; H, 5.13; N, 9.34%.

Synthesis of the complexes

The brown solid complex [Ag(L1)2(H2O)2]NO3 was prepared by adding 0.5 mmol (0.085 g) of AgNO3 in 20 ml of acetone to a stirred suspended solution 1 mmol (0.305 g) of L1 in 50 ml acetone. The reaction mixture was refluxed for 6 h, the precipitate was drained off, washed several times with acetone and dried under vacuum over anhydrous CaCl2. Dark brown [Ag(L2)2(H2O)2]NO3.H2O, [Ag(L3)2(H2O)2]NO3 solid complexes were prepared in the same manner as mentioned above.

[Ag(C19H19N3O)2(H2O)2]NO3 (AgC38H42N7O7) complex

Brown; Yield: 85%; m.p.: 160 οC; M.Wt: 816.65; Elemental analysis for AgC38H42N7O7: found, C, 55.31; H, 4.99; N, 12.00; Ag, 13.14; Calcd, C 55.89; H, 5.18; N, 12.01; Ag, 13.21; Λm = 115.75 S cm2 mol−1; IR (KBr, v, cm−1): 3450 m,br (OH), 1666 m (C = O), 1523vw cm−1(C = N) and 813w and 837w (M–N). 1H NMR (DMSO-d6, 300 MHz): δ = 2.49 (s, 3H, CH3), 3.46 (s, 2H, H2O), 2.27–2.33 (s, 6H, -N (CH3)2), 9.67 (S, 1H, = CH-Ar), 7.14–7.97 (m, 4H, Ar–H).

[Ag(C15H12N2OS)2(H2O)2]NO3.H2O (AgC30H30N5O8S2) complex

Dark brown; Yield: 74%; m.p.: 125 οC; M.Wt: 760.59; Elemental analysis for AgC30H30N5O8S2: found, C, 47.22; H, 3.91; N, 9.15; Ag, 14.13; Calcd, C, 47.37; H, 3.98; N, 9.21; Ag, 14.18; Λm = 135.50 S cm2 mol−1; IR (KBr, v, cm−1): 3444 m, br (OH), 1685 m (C = O), 1527vw cm−1 (C = N), 1099 m cm−1(C = S), 748w and 792w (M–N). 1H NMR (DMSO-d6, 300 MHz): δ = 2.49 (s, 3H, CH3), 3.37 (s, 2H, H2O), 8.64 (S, 1H, = CH-Ar), 7.20–7.94 (d, 3H, Ar–H).

[Ag(C18H16N2O2)2(H2O)2]NO3 (AgC36H36N5O9) complex

Dark brown; Yield: 90%; m.p.: 150 οC; M.Wt: 790.57; Elemental analysis for AgC36H36N5O9: found, C, 54.47; H, 4.11; N, 8.80; Ag, 13.60; Calcd, C, 54.69; H, 4.59; N, 8.86; Ag, 13.64; Λm = 114.52 S cm2 mol−1; IR (KBr, v, cm−1): 3444 (OH), 1678 (C = O), 1520 cm−1 (C = N), 759w and 779w (M–N). 1H NMR (DMSO-d6, 300 MHz): δ = 2.33 (s, 3H, CH3), 3.31 (s, 3H, -OCH3), 8.42 (S, 1H, = CH-Ar), 7.18–7.46 (d, 3H, Ar–H).

Availability of data and materials

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Abbreviations

EtOH:

Ethanol

NMR:

Nuclear magnetic resonance

IR:

Infrared radiation

DMSO:

Dimethyl sulfoxide

MIC:

Minimum inhibation concentrations

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Acknowledgements

The authors gratefully acknowledge to Zagazig University (http://www.zu.edu.eg/), Egypt, Univeristy of Bisha, Saudi Arabia and Center for Advanced Materials, Qatar University, Doha, for the support of this research work.

Funding

This research is not funded though any source to This publication was supported by Qatar University, internal grant number QUCG-CAM-20/21-2. The findings achieved herein are solely the responsibility of the authors.

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WSS and WHE carried the literature and designed synthetic schemes (synthesis and Purifcation) and records the 13CNMR of all compounds. SFM, AMA, MHS and WHE designed the research study and wrote the manuscript. WHE carried out the spectroscopic analysis and carried out the antimicrobial assays. WSS and WHE discussed the results and revised the manuscript. All authors read and approved the fnal manuscript.

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Correspondence to Aboubakr M. Abdullah or Walaa H. El-Shwiniy.

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Supplementary Information

Additional file 1: Table S1.

UV-Vis. spectral data of the free ligand L1, L2, L3 and their Ag(I)-complexes. Table S2. Selected 1H NMR data of L1, L2, L3 and its diamagnetic complexes. Fig. S1. TGA and DTG diagrams for a L1, b [Ag(L1)2(H2O)2]NO3, c, L2 d [Ag(L2)2(H2O)2]NO3.H2O, e L3 and f [Ag(L3)2(H2O)2]NO3. Fig. S2. The diagrams of kinetic parameters of L1, [Ag(L1)2(H2O)2]NO3, L2, [Ag(L2)2(H2O)2]NO3.H2O, L3 and [Ag(L3)2(H2O)2]NO3using Coats-Redfern (CR) and Horowitz-Metzger (HM) equations. Scheme S1. Fragmentation pattern of [Ag(L1)2(H2O)2]NO3. Scheme S2. Fragmentation pattern of [Ag(L2)2(H2O)2]NO3.H2O. Scheme S3. Fragmentation pattern of [Ag(L3)2(H2O)2]NO3

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Mohamed, S.F., Shehab, W.S., Abdullah, A.M. et al. Spectral, thermal, antimicrobial studies for silver(I) complexes of pyrazolone derivatives. BMC Chemistry 14, 69 (2020). https://doi.org/10.1186/s13065-020-00723-0

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Keywords

  • Pyrazolones
  • Ag(i) complexes
  • Knoevenagel condensation
  • Antimicrobial activity
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