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Article

Synthesis, Structural Characterization and Biological Activity of Novel Cyclohexane-1,3-dione Ligands and Their Metal Complexes

by
Nevin Turan
1,*,
Hanifi Körkoca
2,
Ragıp Adigüzel
3,
Naki Çolak
4 and
Kenan Buldurun
1
1
Department of Chemistry, Faculty of Arts and Sciences, Muş Alparslan University, 49250 Muş, Turkey
2
Nursing Department, School of Health, Muş Alparslan University, 49250 Muş, Turkey
3
Department of Chemical Engineering, Faculty of Engineering, Tunceli University, 62000 Tunceli, Turkey
4
Department of Chemistry, Faculty of Arts and Sciences, Hitit University, 19100 Çorum, Turkey
*
Author to whom correspondence should be addressed.
Molecules 2015, 20(5), 9309-9325; https://doi.org/10.3390/molecules20059309
Submission received: 1 April 2015 / Revised: 12 May 2015 / Accepted: 15 May 2015 / Published: 21 May 2015
(This article belongs to the Section Organic Chemistry)
Browse Figures
Versions Notes

Abstract

:
Some new Zn(II) and Cu(II) complexes [Cu(L1)(OAc)2]∙H2O, [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O, [Zn(L1)(NO3)2]∙4.5H2O, [Zn(L1)(OAc)2(H2O)2]∙3H2O, [Cu2(L2)(OAc)4]∙2H2O∙2DMF, [Cu(L2)2]∙2NO3∙1.5DMF∙H2O, [Zn(L2)2(NO3)2]∙DMF and [Zn2(L2)(OAc)4(H2O)4]∙5H2O; L1 = 2-[2-(2-methoxyphenyl)hydrazono]cyclohexane-1,3-dione and L2 = 2-[2-(3-nitrophenyl)hydrazono]cyclohexane-1,3-dione were synthesized and characterized by IR, 1H-NMR,13C-NMR and ultraviolet (UV-Vis.) spectroscopy, elemental analysis, magnetic susceptibility, mass spectrometry and thermogravimetry-differential thermal analysis (TGA-DTA). The synthesized ligands and their complexes were tested for antibacterial activity against Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, and Salmonella typhimurium CCM 583. Some of complexes showed medium-level antibacterial activity against the test bacteria compared with ampicillin.

1. Introduction

Cyclohexane-1,3-dione and its derivatives are important building blocks. The cyclohexane-1,3-dione skeleton is a characteristic molecular fragment common for a class of natural and synthetic herbicides and drugs inhibiting 4-hydroxyphenylpyruvate deoxygenase [1,2]. The inhibitory properties of this class of compounds are a result of their ability to chelate the ferrous ion in the active site of the enzyme.
Arylhydrazones of mono-, di- and triketones as well as cyclic 1,3-diones viz., cyclohexane-1,3-dione have been reported in the literature. Such compounds have been extensively used as precursors of potential anti-diabetic drugs [3]. Hydrazones are compounds whose molecules contain the C=N-NH- triatomic linkage. The biological, chemical and industrial versatility of hydrazones and their complexes continue to attract considerable attention [4,5]. The role of hydrazones in treating tuberculosis is well known. Substituted hydrazones have established spasmolytic activity, activity against leukemia, and sarcomas [6]. Also they possess anti-inflammatory, analgesic, antipyretic, antibacterial and antitumor activities [7].
In order to investigate the relationship of ligands L1 and L2 and their complexes with their biological activities, we synthesized two new ligand, 2-[2-(2-methoxyphenyl)hydrazono]cyclohexane-1,3-dione (L1) 2-[2-(3-nitrophenyl)hydrazono]cyclohexane-1,3-dione (L2). Then, their Zn(II) and Cu(II) complexes were synthesized by reaction of Zn(NO3)2∙6H2O, Cu(NO3)2∙2H2O, Zn(OAc)2∙2H2O and Cu(OAc)2∙H2O, respectively. The structure of the ligands is shown in Figure 1. Finally, all of the synthesized compounds were tested for their antibacterial activities against Escherichia coli ATCC 25922 (non-β-lactamase producing), vancomycin susceptible Enterococcus faecalis ATCC 29212, methicillin susceptible Staphylococcus aureus ATCC 25923, and Salmonella typhimurium CCM 583.
Molecules 20 09309 g001 550
Figure 1. Structures of the ligands L1 and L2.
Figure 1. Structures of the ligands L1 and L2.
Molecules 20 09309 g001

2. Results and Discussion

2.1. Infrared Spectra

IR absorptions of both L1 and L2 and their metal complexes along with assignments are summarized in the experimental section. All complexes are air stable and insoluble in most organic solvents and water, but freely soluble in coordinating solvents such as pyridine, DMF or DMSO. All have higher melting or decomposition points than the parent ligands.
In the IR spectrum of L1 the characteristic peaks are seen at 2955–3500 cm−1 ν(NH), 1280 cm−1 ν(OCH3), 1696, 1671 cm−1 ν(C=O), and 1505 cm−1 ν(C=C) [8,9,10,11]. The L1 shows a broad NH band at 3343 cm−1 due to the hydrazone NH group. The position and broadness of the band are indicative of intramolecular hydrogen bonding between the hydrazone proton and the carbonyl oxygen. The hydrazone can coordinate to transition metals either in the enolic form (N=N-C=C-OH) or in ketonic form (HN-N=C-C=O). In L1 and L2 the characteristic hydrazone group >CONH- peaks indicate that the ligand exists in the keto form in the solid state. This NH band shifted upon complexation of the ligand with metals due to coordination of the hydrazone proton in [Cu2(L2)(OAc)4]∙2H2O∙2DMF and all of the Zn(II) complexes [12,13].
The strong bands at 1696, 1671 and 1686 cm−1, in the spectra of L1 and L2, respectively, may be assigned to ν(C=O). In the spectra of all complexes, except those of [Zn(L1)(NO3)2]∙4.5H2O, [Zn(L1)(OAc)2(H2O)2]∙3H2O and [Zn(L2)2(NO3)2]∙DMF, these bands are found to be shifted to lower frequency, indicating the participation of the carbonyl oxygen in coordination. Peaks at 1671, 1686 cm−1 ν(C=O), 1626, 1633 cm−1 ν(C=O….H) and 1592 cm−1 ν(C=N) also support the H-bonded hydrazone structure in the solid state [14]. In the [CuL1(NO3)H2O]∙NO3∙3.5H2O and [Cu(L2)2]∙2NO3∙1.5DMF∙H2O complexes, bands appearing at 1384 and 1382 cm−1, respectively, suggest the presence of ionic nitrate in the complexes [14].
In the IR spectrum of L2, the characteristic peaks are at 1686 and 1353 cm−1, which are assigned to ν(C=O) and ν(NO2), and at 1614 cm−1 which is assigned to the ν(C=N) group [15,16]. In addition, the spectrum of the ligand L2 shows broad bands in the 3500–3100 cm−1 region, which may be assigned to a ν(NH) band. In the IR spectra of L2, the bands assigned to ν(C=O) and ν(C=N) are shifted by ±16–35 cm−1 in the spectra of complexes, indicating coordination through the exocyclic carbonyl oxygen and C=N nitrogen of L2. In the spectra of the metal complexes of the L2, the band at 1353 cm−1 for the NO2 group did not shift [17], showing that in these complexes the NO2 group did not participate in complex formation. In the IR spectra of the complexes, ν(OCH3) remains unmodified, indicating that the methoxy group is also not involved in the coordination.
The infrared spectra of all complexes, except that of [Zn(L2)2(NO3)2]∙DMF complex, exhibited intense broad bands at 3560–3311 cm−1 that are attributed to ν(OH) of the lattice or coordinated water molecules, while the ν(H2O) bands observed at approximately 876–764 cm−1 are assigned to coordinated water molecules [18,19,20]. The spectra of the complexes show a few new absorption bands in the 491–455 cm−1 and 585–510 cm−1 ranges, assigned to ν(M-N) and ν(M-O), respectively.
The complexes [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O, [Zn(L1)(OAc)2(H2O)2]∙3H2O and [Zn2(L2)(OAc)4(H2O)4]∙5H2O show a broad band at 3468–3311 cm−1 indicating the coordination of water to the metal ion. From the IR results, it may be concluded that the L1 and L2 ligands are bi- or tridentate and coordinate with the metal ions through the carbonyl oxygen, hydrazone nitrogen and/or acetic acid oxygen atoms.
The ν(N-N) bands of the L1 and L2 ligands at 1025, 1010 cm−1 are found to be shifted to higher energies (1041–1020 cm−1) in the spectra of the complexes, indicating coordination via the nitrogen atoms. This is confirmed by bands in the range of 491–455 cm−1, which have been assigned to the ν(Zn-N) ν(Cu-N) bands [21].
The IR spectra of the [Cu2(L2)(OAc)4]∙2H2O∙2DMF, [Cu(L2)2]∙2NO3∙1.5DMF∙H2O and [Zn(L2)2(NO3)2]∙DMF complexes show strong bands around 1660 cm−1 assigned to a ν(C=O) vibration of the DMF molecules [22]. The IR spectra of [Cu(L1)(OAc)2]∙5H2O, [Zn(L1)(OAc)2(H2O)2]∙3H2O, [Cu2(L2)(OAc)4]∙2H2O∙2DMF and [Zn2(L2)(OAc)4(H2O)4]∙5H2O show two new bands at 1555 and 1384 cm−1 assignable to the νas(C–O) and νs(C–O) bands of the acetate group [23,24], respectively, which are consistent with monodentate acetate coordination. The IR spectra of the [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O, [Zn(L1)(NO3)2]∙4.5H2O and [Zn(L2)2(NO3)2]∙DMF complexes show strong bands at 1385 and 1285 cm−1 assigned to νas(NO3−) and νs(NO3−), respectively, indicating the presence of terminally bounded monodentate nitrate groups [25,26].

2.2. 1H-NMR and 13C-NMR Spectra

The 1H-NMR spectra of L1, L2 and their Zn(II) complexes were recorded in dimethylsulfoxide (DMSO-d6) solution using tetramethylsilane (TMS) as internal standard. The 1H-NMR spectrum of L1 shows a singlet at 4.00 ppm that may be assigned to the protons of the methoxy group, a singlet at 15.00 ppm that may be assigned to the proton of the NH group, a multiplet at 7.20–7.80 ppm that may be assigned to the aromatic protons and another at 2.00–2.70 ppm that may be assigned to the hexane ring protons. Similar peaks are observed for the ligand L2. The 1H-NMR spectrum of the diamagnetic Zn(II) complexes shows almost the same values as the ligands. The signals due to the -NH proton are shifted downfield in the spectra of the Zn(II) complexes, indicating the coordination of the ligand through the nitrogen of the -NH groups to the metal ions. The hydrogen bonding decreases the electron density around the proton and thus moves the proton absorption to a lower field [27]. In addition, H2O and acetate proton signals are seen in NMR spectra of complexes.

2.3. Electronic Spectra and Magnetic Properties

The electronic spectra of L1, L2 and their metal complexes were recorded in 3 × 10–3 molar DMF solutions in the range from 200 to 800 nm. The electronic spectrum of the ligands shows broad bands at 218, 242 and 316–393 nm; the first two absorption bands may be assigned to n→π* and π→π* transitions of >C=O and >C=N moieties [28], the third absorption band may be due to high-intensity charge transfer transitions.
The [Cu(L1)(OAc)2]∙5H2O complex shows square-planar geometry. It shows intense absorption bands in the 254–269 and 414 nm range which can be assigned to the π→π* transition of the C=N or C=O groups and charge-transfer bands, respectively. The electronic spectrum of the complex shows an absorption band in the range 580 nm, attributed to 2T2g→2Eg transition suggesting a square-planar geometry [29].
The electronic absorption spectrum of the [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O complex in DMSO solution shows three bands at 254–295, 353, 393 and 428–450 nm, assignable to the 2B1g→2B2g, 2B1g→2Eg, and 2B1g→2A1g transitions and two intra-ligand charge transfer bands. These data and the magnetic moment value of 1.72 B.M. suggest square-planar geometry around Cu(II) [30,31].
Square planar geometry is suggested for [Cu2(L2)(OAc)4]∙2H2O∙2DMF from the presence of bands at 600 and 454 nm for the complex. These bands are assigned to the 2B1g→2A1g and 2B1g→2Eg transitions, while the second band is due to charge transfer. The magnetic moment values for the Cu(II) complex are normal and lower (1.66 B.M.) than expected 1.7–2.2 B.M. for one unpaired electron [32,33].
The electronic spectrum of Cu(II) complex shows bands in the regions of 254, 376 and 470 nm which may be assigned to the 2B1g→2A1g transitions in a square-planar geometry. The magnetic moment value of [Cu(L2)2]∙2NO3∙1.5DMF∙H2O complex is 2.22 B.M. [34].
The electronic spectra of the Zn(II) complexes show only a high-intensity band at 357–425 cm−1 assigned to ligand-metal charge transfer.

2.4. Thermal Studies

The thermal stability of the ligands and complexes is investigated using thermogravimetric analysis. The TGA curves are obtained at a heating rate of 10 °C∙min−1 under a nitrogen atmosphere in a temperature range of 25.0–800.0 °C. The results obtained are in good agreement with the theoretical formula suggested from the elemental analyses. The thermal data are summarized in Table 1.
The [Cu2(L1)2(AcO)2]∙5H2O complex is stable up to 95 °C and its decomposition starts at this temperature. A 16.92(17.39%) weight loss is observed at 195 °C corresponding to five moles of water of crystallization. The DTA curve of the complex shows one endothermic peak at 350.50–360.00 °C. For the Cu(II) complex, the DTA curve shows an endothermic process around 350.50 °C that corresponds to the rupture of the coordinated bond and simultaneous melting of the complex [35].
The [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O complex was stable up to 85 °C and its decomposition started at this temperature. The first decomposition stage at 160 °C is attributed to the removal of 3.5 moles of water of crystallization and 1 mole of nitrate ion with a 24.62(24.29%) loss. The second weight loss stage of 234.48–494.55 °C corresponds to the removal of the H2O, NO3– and C6H6O2N as a fragment of the ligand decomposition. The DTA curve of the Cu(II) complex shows two endothermic peaks at 150.10 °C, 380.50 °C and one exothermic peak at 485.25 °C.
The [Zn(L1)(NO3)2]∙4.5H2O complex decomposed in three stages. In the first stage, loss of 4.5 moles of water of crystallization and in the second stage, loss of two moles of NO3– and C13H14O2N2 groups resulted. In the third stage, the complex decomposed to ZnO. The DTA curve of the complex shows two endothermic peaks at 450.00–470.20 °C. For the Zn(II) complex, these peaks corresponds to simultaneous melting of the complex [35].
The [Zn(L1)(OAc)2(H2O)2]∙3H2O complex decomposed in two stages. The first is due to removal of the crystallization water molecule with a weight loss of 18.76(18.83%). The second weight loss is associated with the removal of two moles of water as well as 2C2H3O2− from the ligand [36]. The DTA curve of the Zn(II) complex shows two endothermic peaks at 280.10 °C, 330.50 °C and one exothermic peak at 420.25 °C.
Table
Table 1. Proposed decomposition steps and the respective mass losses of ligands (L1 and L2) and their complexes.
Table 1. Proposed decomposition steps and the respective mass losses of ligands (L1 and L2) and their complexes.
EquationsTemperature (°C)% Loss in Weight
% Found(% Calculated)		Decomp. Products
[Cu(L1)(OAc)2]∙5H2O
C17H30N2O12Cu95.50–250.0016.92(17.39)5 H2O
C17H20N2O7Cu250.00–514.2940.00(40.36)2 OAc−, C6H5N
C7H9NO3Cu514.29–650.0024.62(23.96)C6H6NO2
CH3OCu650–Cont.
[Cu(L1)(NO3)H2O]∙NO3∙3.5H2O
C13H16N4O10Cu∙3.5H2O85.25–234.4824.62(24.29)3.5 H2O, NO3−
C13H16N3O7Cu234.48–494.5540.00(39.64)H2O and NO3−,C6H6O2N
C7H8NOCu494.55–Cont.
[Zn(L1)(NO3)2]∙4.5H2O
C13H14N4O9Zn∙4.5H2O76.19–457.1415.39(15.69)4.5 H2O
C13H14N4O9Zn457.14–495.2367.69(68.55)2NO3−, C13H14O2N2
ZnO495.23–Cont.
[Zn(L1)(OAc)2(H2O)2]∙3H2O
C17H30N2O12Zn80.32–284.7518.76(18.83)3 H2O
C17H24N2O9Zn284.75–423.5029.23(29.65)2 H2O and 2 C2H3O2−
C13H14N2O3Zn423.50–Cont.
[Cu2(L2)(OAc)4]∙2H2O∙2DMF
C26H41N5O16Cu2180.12–240.3223.08(22.58)2 H2O and 2DMF
C20H23N3O12Cu2240.32–285–34029.23(29.27)4 OAc−
C12H11N3O4Cu2285–340
[Cu(L2)2]∙2NO3∙1.5DMF∙H2O
C24H24N8O15Cu∙1.5DMF100.05–280.1424.62(24.79)H2O, 1.5 DMF, 2 NO3−
C24H22N6O8Cu280.14–600.0058.46(58.55)C24H22N6O7Cu
CuO
[Zn(L2)2(NO3)2]∙DMF
C24H22N7O16Zn160.53–241.209.23(9.30)DMF
C21H15N6O15Zn241.20–277.5544.61(44.10)2 NO3−, C12H14N2O2
C9HN2O7Zn277.55–458.33
[Zn2(L2)(OAc)4(H2O)4]∙5H2O
C20H41N3O21Zn275–120.2012.30(11.39)5H2O
C20H31N3O16Zn2120.20–190.5510.76(9.12)4 H2O
C20H23N3O12Zn2190.55–360.3529.23(29.87)4 C2H3O2−
C12H11N3O4Zn2360.35–Cont.15.38(15.70)C6H6O2N
C6H5N2O2Zn2
[Cu2(L2)(OAc)4]∙2H2O∙2DMF shows two decomposition steps. The first decomposition step in the temperature range of 180.12–240.32 °C may be attributed to the loss of crystallization water molecules and two DMF molecules [36,37]. The second step within the temperature range of 240.32–285.34 °C 29.23(29.27%) corresponds to the removal of four moles of acetate molecules as deduced from weight loss calculations. The DTA curve of the Cu(II) complex shows two endothermic peaks at 160.50 °C and 190.10 °C. The endothermic peaks are likely due to the loss of water of hydration and DMF molecules.
The complex [Cu(L2)2]2NO3∙1.5DMF∙H2O is stable up to 100 °C and its decomposition started at this temperature. In the decomposition process of the Cu(II) complexes, the mass losses corresponded to one mole H2O, 1.5 moles DMF and two moles of NO3− in the first stage of the decomposition, respectively. The Cu(II) complex is stable up to 160.00–240.00 °C and after this temperature other decomposition ensues. The DTA curve of the Cu(II) complex shows endothermic peaks at 100.20 °C and 215.50 °C corresponding to the loss of H2O, DMF and NO3– and one exothermic peak at 500.10 °C corresponding to the second weight loss.
The [Zn2(L2)(OAc)4(H2O)4]∙5H2O complex followed a four-staged decomposition, in which five moles of water of crystallization, four moles of coordinated water, four moles of acetate ions, and an 2-iminocyclohexane-1,3-dione group and the rest of the ligand decomposed successively. The DTA curve of the Zn(II) complex shows two endothermic peaks at 130.50 °C and 180.10 °C. The endothermic peaks are likely due to the loss of molecules of water of hydration.
The decomposition curve of [Zn(L2)2(NO3)2]∙DMF begins with a step at 160.53–241.20 °C, displaying a 9.23(9.30%) weight loss corresponding to the removal of DMF [38]. The second step within the temperature range of 241.20–277.55 °C corresponds to the removal of two moles of NO3− and C12H14N2O2 groups 44.61(44.10%) as deduced from weight loss calculations. The DTA curve of the Zn(II) complex shows one endothermic peak at 170.50 °C and two exothermic peaks at 300.60 °C and 350.40 °C. The first one is related to removal of the DMF molecule, whereas the other is the second step of decomposition [18].
The final products formed during thermal analysis of the complexes could not be determined because the decompositions of the complexes were not complete at 800 °C, except for the [Zn(L1)(NO3)2]∙4.5H2O and [Cu(L2)2]∙2NO3∙1.5DMF∙H2O complex.

2.5. Mass Spectra

The mass spectra peaks of the [Cu(L1)(OAc)2]∙5H2O, [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O, [Zn(L1)(OAc)2(H2O)2]∙3H2O and [Zn(L1)(NO3)2]∙4.5H2O complexes of the L1 ligand are attributable to the related molecular ions m/z: 516.20 [M–H]−, 515.20 [M+H]+, 517.20 [M–2H]2−and 517.21 [M+H]+, respectively. The mass spectra peaks of the other L2 complexes [Cu2(L2)(OAc)4]∙2H2O∙2DMF, [Cu(L2)2]∙2NO3∙1.5DMF∙H2O, [Zn(L2)2(NO3)2]∙DMF and [Zn2(L2)(OAc)4(H2O)4]∙5H2O are attributable to the related molecular ions m/z: 807.21 [M+H]+, 838.14 [M+H]+, 785.32 [M+H]+ and 545.20 [M-2OAc−-7H2O]2+, respectively. The observed free ligand L1 peaks for all of the complexes are m/z: 247.11 [L+H]+ [38,39]. The observed free ligand L2 peaks for each two complexes are similarly m/z: 262.08 [L+H]+ except for the [Zn(L2)2(NO3)2]∙DMF complex. The highest peaks in the abundance percent were considered in the spectra.
Single crystals of the complexes could not be isolated from any solutions, thus no definite structure could be described. However, the analytical, spectroscopic and magnetic data enable us to propose the possible structures shown below in Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9.

2.6. Biological Evaluation

The synthesized compounds were screened for their antibacterial activity using Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, and Salmonella typhimurium CCM 583. The results are shown in Table 2. Control experiments were carried out under similar conditions using ampicillin as standard. The inhibition zone measurements in mm show that the compounds [Zn(L1)(OAc)2(H2O)2]∙3H2O, [Cu(L2)2]∙2NO3∙1.5DMF∙H2O and [Zn2(L2)(OAc)4(H2O)4]∙5H2O are more active than other tested compounds against the test bacteria. The other complexes [Zn(L1)(NO3)2]∙4.5H2O, [Cu(L1)(OAc)2]∙5H2O, [Cu(L1)(NO3)H2O]∙NO3∙3.5H2O, [Zn(L2)2(NO3)2]∙DMF and [Cu2(L2)(OAc)4]∙2H2O∙2DMF did not show antibacterial activity against test microorganisms like Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, and Salmonella typhimurium CCM 583.
Table
Table 2. Antibacterial activity against test bacteria of the novel cyclohexane-1,3-dione ligands and their metal complexes.
Table 2. Antibacterial activity against test bacteria of the novel cyclohexane-1,3-dione ligands and their metal complexes.
Chemicals Escherichia coli ATCC 25922Enterococcus faecalis ATCC 29212Staphylococcus aureus ATCC 25923Salmonella typhimurium CCM 583
BacteriaZone Diameter (mm) (blank disk diameter, 6 mm)
[Cu(L1)(OAc)2]∙5H2O 0000
[Cu(L1)(NO3)H2O]∙NO3∙3.5H2O 0000
[Cu2(L2)(OAc)4]∙2H2O∙2DMF 0000
[Cu(L2)2]∙2NO3∙1.5DMF∙H2O 00117
[Zn(L1)(NO3)2]∙4.5H2O 0000
[Zn(L1)(OAc)2(H2O)2]∙3H2O 100118
[Zn(L2)2(NO3)2]∙DMF 0000
[Zn2(L2)(OAc)4(H2O)4]∙5H2O 0070
Ampicillin 16223226

3. Experimental Section

3.1. Reagents and Instrumentation

All solvents used were of analytical grade and no further purifications were performed. The metal salts Zn(NO3)2∙6H2O, Cu(NO3)2∙2H2O, Zn(OAc)2∙2H2O, Cu(OAc)2∙H2O and starting materials for the ligands were Merck (Darmstadt, Germany), Aldrich (St. Louis, MO, USA), and Alfa Aesar (Karlsruh, Germany) products.
Elemental analyses were carried out on a CHNS-O model 932 elemental analyzer (Leco, St. Joseph, MI, USA). 1H-NMR and 13C-NMR spectra were recorded using a model DPX-400 MHz FT spectrometer (Bruker GmbH, Billerica, MA, USA). IR spectra were recorded on a Precisely Spectrum One spectrometer (Perkin Elmer, Akron, OH, USA) using KBr discs in the wavenumber range of 4000–400 cm−1. Electronic spectra studies were conducted on a model UV-1700 spectrophotometer (Shimadzu, Kyoto, Japan) in the wavelength 1100–200 nm. Magnetic susceptibility measurements were performed using the standard Gouy tube technique. Hg[Co(SCN)4] was used for calibration calibrate. LC/MS-API-ES mass spectra were recorded using an Agilent model 1100 MSD mass spectrophotometer (Minneapolis, MN, USA). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out in nitrogen atmosphere with a heating rate of 10 °C∙min−1 using a Shimadzu DTG-60 AH thermal analyzer.

3.2. Antibacterial Activity Studies

The disk diffusion method was used for determining the antibacterial activity of ligands and complexes. Antibacterial activity against Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Salmonella typhimurium CCM 583 was investigated. Mueller–Hinton agar (Oxoid Ltd., Basingstoke, Hampshire, UK) was used for all bacterial strains, except for Enterococcus faecalis ATCC 29212 for which Mueller Hinton agar with 5% defibrinated sheep blood was used. The media were melted at 100 °C, autoclaved at 121 °C for 15 min, cooled 45 °C to 50 °C and were poured into plates of 9 cm diameter in quantities of 20 mL, and left on a flat surface to solidify and the surface of media was dried at 37 °C. Then, preparation of the inoculums was used for colony growth method in Mueller–Hinton broth to a turbidity equivalent to a 0.5 McFarland (108 cfu∙mL–1) standard. The organisms were streaked on Petri dishes using sterile cotton swab. The surface of the media was allowed to dry 3–5 min at room temperature. The 10 mg∙mL–1 (in DMSO, Merck), of compound impregnated blank discs (Oxoid Ltd.) were applied to the surface of inoculated plates. The Mueller-Hinton agar plates were incubated at 35 ± 2 °C for 18–24 h. The plates were examined and the diameter of the inhibition zone was measured by surrounding discs. The antibiotic ampicillin (10 μg, Oxoid) was used as the standard [40,41].

3.3. Synthesis of the Ligands L1 and L2

A hydrochloric acid solution (2.5 mL) of 3-methoxyaniline (1.23 g, 10 mmol) and an aqueous solution (10 mL) of sodium nitrite (0.69 g, 10 mmol) were mixed and stirred at 273 K for 1 h. To this solution, an ethanol solution (10 mL) of the coupling component cyclohexane-1,3-dione (1.12 g, 10 mmol) was added and the stirring was continued at 273 K for 4 h. The resulting product was filtered and washed with water, dried and crystallized from ethanol (yield 77%). A similar synthesis was performed for L2 using 3-nitroaniline (1.38 g, 10 mmol) instead of 3-methoxyaniline.
L1; Yield: (77.0%). FW: 246.10 g∙mol−1. m.p.: 330 °C. Anal. Calcd. for C13H14N2O3: C, 63.40, H, 5.73, N, 11.38. Found: C, 64.00, H, 5.84, N, 11.49. Selected IR data (KBr, ν cm−1): 2955–3500 (N-H), 1696, 1671 (C=O), 1592 (C=N), 1505 (C=C), 1025 (N-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 218, 242 (1453, 1613), 316–393 (2106–2620) nm; 1H-NMR (400 MHz, DMSO-d6): δ 15.00 (s, 1H, NH), 7.00–7.80 (m, 4H, Ar-CH), 2.00 (4H, CH2), 2.70 (2H, CH2), 4.00 (s, 3H, CH3). 13C-NMR (DMSO-d6): δ 30.12 (CH3), 55.87 (3CH2), 119.13 (Ar-H), 122.65 (Ar-H), 132.64 (Ar-NH-N), 147.00 (C=N), 197.00 (C=O), 197.10 (C=O). MS [ES]: m/z 247 [M+H]+. Color: Brown.
L2; Yield: (79.0%). FW: 261.10 g∙mol−1. m.p.: 332 °C. Anal. Calcd. for C12H11N3O4: C, 55.15, H, 4.21, N, 16.08. Found: C, 55.00, H, 4.84, N, 16.49. Selected IR data (KBr, ν cm−1): 3500–3100 (N-H), 1686 (C=O), 1614 (C=N), 1527 (C=C), 1010 (N-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 218,240 (1453, 1612), 316–393 (2106–2620) nm; 1H-NMR (400 MHz, DMSO-d6): δ 14.56 (s, 1H, NH), 7.62–8.02 (m, 4H, Ar-CH), 2.60 (4H, CH2), 2.66 (2H, CH2). 13C-NMR (DMSO-d6): δ 30.12 (CH2), 52.37 (2CH2), 118.69 (Ar-H), 120.75 (Ar-H), 131.47 (Ar-NH-N), 143.05 (C=N), 193.37 (C=O), 197.55 (C=O). MS [ES]: m/z 262.08 [M+H]+. Color: Orange.

3.4. Synthesis of the Zn(II) and Cu(II) Complexes of the Ligands

L1 (1 g, 4 mmol) was dissolved in absolute methanol (15 mL). A solution of 4.0 mmol of metal salts [Zn(NO3)2∙6H2O (1.19 g), Cu(NO3)2∙2H2O (0.94 g), Zn(OAc)2∙2H2O (0.88 g), and Cu(OAc)2∙H2O (0.80 g)] in an absolute mixture of methanol and DMF (10 mL) was added drop wise over 15 min. with continuous stirring at room temperature. The reaction mixtures were then further stirred for 6 h at 80 °C. The resulting precipitates were filtered, washed with absolute ether and dried at room temperature. Similar syntheses were performed for the L2 complexes using Zn(NO3)2∙6H2O (0.60 g, 2 mmol), Cu(NO3)2∙2H2O (0.48 g, 2 mmol), Zn(OAc)2∙2H2O (0.89 g, 4 mmol), and Cu(OAc)2∙H2O (1.60 g, 8 mmol), L2 (1 g, 4 mmol).
[Cu(L1)(OAc)2]∙5H2O (Figure 2): Yield: (78.0%). FW: 517.64 g∙mol−1. m.p.: >400 °C. μeff(B.M.): 1.61. Anal. Calcd. for C17H30N2O12Cu: C, 39.41, H, 5.80, N, 5.41. Found: C, 39.50, H, 5.77, N, 5.39. Selected IR data (KBr, ν cm−1): 3468 (O-H), 3450 (N-H), 1665 (C=O), 1558 (C=N), 1507 (C=C), 1044 (N-N), 551–521 (M-O), 455–480 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 254,269 (1693–1793), 414 (266), 580 (386) nm; MS [ES]: m/z 516.64 (calc), 516.20 (found) [M–H]–, 247.10 (calc.), 247.11 (found) [L+H]+. Color: Dark black.
Molecules 20 09309 g002 550
Figure 2. Structure of [(CuL1)(OAc)2]∙5H2O complex.
Figure 2. Structure of [(CuL1)(OAc)2]∙5H2O complex.
Molecules 20 09309 g002
[Cu(L1)(NO3)H2O]∙NO3∙3.5H2O (Figure 3): Yield: (80.0%). FW: 514.64 g∙mol−1. m.p.: >390 °C. μeff(B.M.): 1.72. Anal. Calcd. for C13H16N4O10Cu∙3.5H2O: C, 30.31, H, 4.47, N, 10.88. Found: C, 30.45, H, 4.55, N, 10.87. Selected IR data (KBr, ν cm−1): 3545 (O-H), 3313 (N-H), 1663 (C=O), 1593 (C=N), 1509 (C=C), 1041 (N-N), 585 (M-O), 491 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 254–295, 353, 393 (1693–1966, 2353, 262), 428–450 (285–300) nm; MS [ES]: m/z 515.64 (calc), 515.20 (found) [M+H]+, 247.10 (calc.), 247.11 (found) [L+H]+. Color: Dark green.
Molecules 20 09309 g003 550
Figure 3. Structure of [Cu(L1)(NO3)H2O]NO3∙3.5H2O complex.
Figure 3. Structure of [Cu(L1)(NO3)H2O]NO3∙3.5H2O complex.
Molecules 20 09309 g003
[Zn(L1)(NO3)2]∙4.5H2O (Figure 4): Yield: (75.0%). FW: 516.37 g∙mol−1. m.p.: 330 °C. μeff(B.M.): Dia. Anal. Calcd. for C13H14N4O9Zn∙4.5H2O: C, 30.21, H, 4.45, N, 10.84. Found: C, 30.22, H, 4.38, N, 10.86. Selected IR data (KBr, ν cm−1): 3496 (O-H), 3317 (N-H), 1671 (C=O), 1590 (C=N), 1504 (C=C), 1042 (N-N), 543–514 (M-O), 475 (M-N). UV-VIS (in DMF): λmax(ε, L∙mol−1∙cm−1) 257–308 (1713–2053), 357 (2380) nm; MS [ES]: m/z 517.37 (calc), 517.21 (found) [M+H]+, 247.10 (calc.), 247.11 (found) [L+H]+. Color: Brown.
Molecules 20 09309 g004 550
Figure 4. Structure of [Zn(L1)(NO3)2]∙4.5H2O complex.
Figure 4. Structure of [Zn(L1)(NO3)2]∙4.5H2O complex.
Molecules 20 09309 g004
[Zn(L1)(OAc)2(H2O)2]∙3H2O (Figure 5): Yield: (75.0%). FW: 519.47 g∙mol−1. m.p.: 320 °C. μeff(B.M.): Dia. Anal. Calcd. for C17H30N2O12Zn: C, 39.27, H, 5.78, N, 5.39. Found: C, 39.31, H, 5.76, N, 5.40. Selected IR data (KBr, ν cm−1): 3400 (O-H), Broad (N-H), 1671 (C=O), 1555 (C=N), 1506 (C=C), 1042 (N-N), 540–513 (M-O), 474 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 357–399 (2380–2660) nm; MS [ES]: m/z 517.47 (calc), 517.20 (found) [M–2H]2−,247.10 (calc.), 247.11 (found) [L+H]+. Color: Light brown.
Molecules 20 09309 g005 550
Figure 5. Structure of [Zn(L1)(OAc)2(H2O)2]∙3H2O complex.
Figure 5. Structure of [Zn(L1)(OAc)2(H2O)2]∙3H2O complex.
Molecules 20 09309 g005
[Cu2(L2)(OAc)4]∙2H2O∙2DMF (Figure 6): Yield: (76.0%). FW: 806.18 g∙mol−1. m.p.: >400. μeff(B.M.): 1.66. Anal. Calcd. for C26H41N5O16Cu2: C, 38.70, H, 5.09, N, 8.68. Found: C, 38.57, H, 5.12, N, 8.73. Selected IR data (KBr, ν cm−1): 3436 (O-H), 3320 (N-H), 1660 (C=O), 1584 (C=N), 1528 (C=C), 1030 (N-N), 571–518 (M-O), 466 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 257–375 (1713–2500), 454 (302), 600 (66) nm; MS [ES]: m/z 807.18 (calc), 807.21 (found) [M+H]+, 542.18 (calc), 542.14 (found) [M-2AcO−-2H2O]2+ (Cationic complex) 262.10 (calc.), 262.08 (found) [L+H]+. Color: Dark brown.
Molecules 20 09309 g006 550
Figure 6. Structure of [Cu2(L2)(OAc)4]∙2H2O∙2DMF complex.
Figure 6. Structure of [Cu2(L2)(OAc)4]∙2H2O∙2DMF complex.
Molecules 20 09309 g006
[Cu(L2)2]∙2NO3∙1.5DMF∙H2O (Figure 7): Yield: (72.0%). FW: 837.24 g∙mol−1. m.p.: >400. μeff(B.M.): 2.20. Anal. Calcd. for C24H24N8O15Cu∙1.5DMF: C, 40.85, H, 3.88, N, 15.89. Found: C, 40.86, H, 3.92, N, 15.91. Selected IR data (KBr, ν cm−1): 3441 (O-H), 3367 (N-H), 1663 (C=O), 1609 (C=N), 1528 (C=C), 1023 (N-N), 574–510 (M-O), 491–466 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 254–376 (1693–3760), 470 (313) nm; MS [ES]: m/z 838.24 (calc), 838.14 (found) [M+H]+, 574.74 (calc), 574.26 (found) [M-NO3−-1.5DMF-H2O]+ (Cationic complex) 262.10 (calc.), 262.08 (found) [L+H]+. Color: Green.
Molecules 20 09309 g007 550
Figure 7. Structure of[Cu(L2)2]∙2NO3∙1.5DMF∙H2O complex.
Figure 7. Structure of[Cu(L2)2]∙2NO3∙1.5DMF∙H2O complex.
Molecules 20 09309 g007
[Zn(L2)2(NO3)2]∙DMF (Figure 8): Yield: (68.0%). FW: 784.57 g∙mol−1. m.p.: 359. μeff(B.M.): Dia. Anal. Calcd. for C24H22N7O16Zn: C, 41.30, H, 3.70, N, 14.28. Found: C, 40.33, H, 3.72, N, 14.26. Selected IR data (KBr, ν cm−1): 3300 (N-H), 1662 (C=O), 1606 (C=N), 1514 (C=C), 1020 (N-N), 580–520 (M-O), 473 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 357–375 (2380–2500) nm; MS [ES]: m/z 785.57 (calc), 785.32 (found) [M+H]+. Color: Dark brown.
Molecules 20 09309 g008 550
Figure 8. Structure of [Zn(L2)2(NO3)2]∙DMF complex.
Figure 8. Structure of [Zn(L2)2(NO3)2]∙DMF complex.
Molecules 20 09309 g008
[Zn2(L2)(OAc)4(H2O)4]∙5H2O (Figure 9): Yield: (64.0%). FW: 789.74 g∙mol−1. m.p.: 335. μeff(B.M.): Dia. Anal. Calcd. for C20H41N3O21Zn2: C, 30.38, H, 5.19, N, 5.31. Found: C, 30.41, H, 5.20, N, 5.34. Selected IR data (KBr, ν cm−1): 3411 (O-H), (N-H)broad, 1668 (C=O), 1607 (C=N), 1528 (C=C), 1023 (N-N), 570–510 (M-O), 491–470 (M-N). UV-VIS (in DMF): λmax (ε, L∙mol−1∙cm−1) 254–376 (1693–3760) nm; MS [ES]: m/z 545.84 (calc), 545.20 (found) [M-2AcO−-7H2O]2+ (Cationic complex) 262.10 (calc.), 262.08 (found) [L+H]+. Color: Black.
Molecules 20 09309 g009 550
Figure 9. Structure of [Zn2(L2)(OAc)4(H2O)4]∙5H2O complex.
Figure 9. Structure of [Zn2(L2)(OAc)4(H2O)4]∙5H2O complex.
Molecules 20 09309 g009

4. Conclusions

We have prepared two new ligands and their metal complexes. Structures of the ligands and complexes were confirmed by spectral and analytical techniques. Antibacterial activities of the complexes were tested against Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, and Salmonella typhimurium CCM 583, respectively. Some complexes showed average level antibacterial activity against the test bacteria compared to ampicillin, but some of the complexes did not exhibit antibacterial activity against the test microorganisms. For these reasons, these complexes may not be useful for preparing new active agents.

Acknowledgments

Chemistry Department and Nursing Department of Muş Alparslan University, Muş, Turkey and Chemistry Department of Inönü University, Malatya, Turkey are thanks for their supporting to this research.

Author Contributions

Nevin Turan formulated the research idea and participated in the preparation of manuscript; Nevin Turan, Ragıp Adigüzel, Naki Çolak and Kenan Buldurun carried out the experimental, interpreted the data and prepared the manuscript; Hanifi Korkoca performed the biological part. All authors have read and approved the final manuscript.

Conflicts of Interest

We (Nevin Turan, Hanifi Körkoca, Ragıp Adigüzel, Naki Çolak, Kenan Buldurun) declare that there is no conflict of interests regarding the publication of this article.

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  • Sample Availability: Samples of the newly synthesized compounds are available from the authors.

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MDPI and ACS Style

Turan, N.; Körkoca, H.; Adigüzel, R.; Çolak, N.; Buldurun, K. Synthesis, Structural Characterization and Biological Activity of Novel Cyclohexane-1,3-dione Ligands and Their Metal Complexes. Molecules 2015, 20, 9309-9325. https://doi.org/10.3390/molecules20059309

AMA Style

Turan N, Körkoca H, Adigüzel R, Çolak N, Buldurun K. Synthesis, Structural Characterization and Biological Activity of Novel Cyclohexane-1,3-dione Ligands and Their Metal Complexes. Molecules. 2015; 20(5):9309-9325. https://doi.org/10.3390/molecules20059309

Chicago/Turabian Style

Turan, Nevin, Hanifi Körkoca, Ragıp Adigüzel, Naki Çolak, and Kenan Buldurun. 2015. "Synthesis, Structural Characterization and Biological Activity of Novel Cyclohexane-1,3-dione Ligands and Their Metal Complexes" Molecules 20, no. 5: 9309-9325. https://doi.org/10.3390/molecules20059309

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