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Novel and highly effective composites of silver and zinc oxide nanoparticles with some transition metal complexes against different microorganisms
⁎Corresponding author. orabiadel@hotmail.com (A.S. Orabi)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
New composites gave enhancement of the antimicrobial activity. AgNPs and ZnONPs could be used as delivery and release target molecules. The properties and the DFT and Docking calculation reveals the antimicrobial behavior of working compounds.
Abstract
Novel composites of Ag and ZnO nanoparticles with prepared transition metal complexes were obtained. The transition metal complexes are obtained by the interaction of the ligand N,N′-bis(salicylaldehyde)-o-phenylenediamine(H2B) with some transition metal ions (Co(II), Ni(II), Cu(II) and Zn(II)). The structures of the ligand and the formed complexes were characterized by elemental analysis, FTIR, UV–Vis, 1H NMR, mass spectra, thermal (TG/DTA), magnetic and conductivity measurements. The obtained complexes have the molecular formula [MB(H2O)x]. yH2O. The found conductivity revealed the non-electrolytic behavior of the formed complexes. The magnetic susceptibility and UV–Vis spectra indicated the octahedral structure of the formed complexes. The thermodynamic and kinetic parameters are estimated for the formed complexes. The interaction of the formed compounds with the FM-DNA was tested. The evaluation of the binding constant (Kb) using Bensi-Hildebrand plot, revealed the moderate interaction with electrostatic behavior. Silver and zinc oxide nanoparticles were prepared and characterized by XRD, UV–Vis, FTIR spectra and TEM analysis. The biological activity of the synthesized composites of Ag and ZnO nanoparticles with the prepared transition metal complexes were tested against some Gram positive and Gram negative bacteria as well as Fungi. The obtained inhibition zone supported the enhancement in the activity of the prepared compounds towards the target microorganism after forming the composites. Also, the interaction with the E. coli protein (FabH, PDB code: 1HNJ) was tested and evaluated using the docking operation with aid of some computational chemistry software. The obtained results agreed well with our experimental work.
Keywords
DNA
Nanoparticles
Biological activity
Docking
Complexes
Composites
1 Introduction
In recent years nanoparticles of silver have been found to exhibit interesting antibacterial activities (Pal et al., 2015; Shahverdi et al., 2007). Presently, the investigation of this phenomenon has regained importance due to the increase of bacterial resistance to antibiotics, caused by their overuse. Also, silver nanoparticles exhibiting antimicrobial activity have been reported (Panacek et al., 2006). Antibacterial activity of the silver containing materials can be used, for example, in medicine to reduce infections as well as to prevent bacteria colonization on prostheses (Roldán et al., 2005), catheters (Yin et al., 2004; Zhu et al., 2006), vascular grafts, dental materials (Maillard et al., 2002), stainless steel materials (Mock et al., 2002) and human skin (Durán et al., 2005; Maillard et al., 2002).
Because of the diverse properties of ZnO, both chemical and physical, zinc oxide is widely used in many areas (Das et al., 2011; Espitia et al., 2012; Gomez and Tigli, 2013; Larbi et al., 2014; Liu et al., 2013; Mansouri et al., 2012; Mirhosseini and Firouzabadi, 2013; Tang et al., 2009). It plays an important role in a very wide range of applications, ranging from tires to ceramics, from pharmaceuticals to agriculture, and from paints to chemicals.
Schiff bases are considered as a very important class of organic compounds, having wide applications in many biological aspects, proteins, visual pigments, enzymicaldolization and decarboxylation reactions (Çakır and Biçer, 2010; Orabi, 2012). They are also used as catalysts in polymer and dyes industry, beside some uses as antifertility and enzymatic agents (Kumar et al., 2009). There are many reports that including the use of Schiff bases in therapeutic or biological applications either as potential drug candidates or diagnostic probes and analytical tools. The activity of Schiff bases as anticancer compounds (Przybylski et al., 2009;Qin et al., 2013) involving radioactive nuclide complexes, antibacterial (Abdel Aziz et al., 2012; Amin et al., 2010; Karthikeyan et al., 2006; Ronad et al., 2010; Saravanan et al., 2010; Sinha et al., 2008; Vukovic et al., 2010), antifungal (Panneerselvam et al., 2005; Rathelot et al., 1995; Souza et al., 2007), antiviral agents (Jarrahpour et al., 2007), has been extensively studied. Moreover, Schiff bases are present in various natural, semi-synthetic as well as synthetic compounds and have been demonstrated to be essential for their biological activities (Bringmann et al., 2004; Guo et al., 2007).
DNA plays an important role in the life process since it contains all the genetic information for cellular function. However, DNA molecules are prone to be damaged under various conditions including, e.g., interactions with some molecules. This damage may lead to various pathological changes in living organisms (Liu et al., 2002). The binding interaction of small molecules with DNA (Hori et al., 2018; Liu et al., 2017a,b; Vellaisamy et al., 2018; Wang et al., 2018, 2017) is of interest for both therapeutic and scientific reasons (Johnston et al., 1995; Labuda et al., 1999). These interactions may also be used for conformational recognition to find new structures of DNA and sequence-specific differences along the helix of a DNA molecule (Barton, 1986; Griffin and Dervan, 1987; Palecek and Fojta, 2001).
The present work focused on the preparation and application of composites of transition metal complexes with Schiff bases and silver and zinc oxide nanoparticles as antibacterial and antifungal compounds. Antimicrobial activities of the synthesized compounds have been screened using the disc diffusion method. The interactions of the obtained composites with DNA entity were investigated to evaluate their modes and binding affinities by using Benesi–Hildebrand method.
2 Experimental and methods
2.1 Materials
All chemicals used in this study were of analytical grade. Salicylaldehyde (Koch-Light laboratories) was used as received. o-phenylenediamine was purchased from Aldrich. Tris–HCl buffer and highly polymerized fish-milt DNA (FM-DNA), Silver nitrate (AgNO3) and zinc acetate dihydrate were purchased from Sigma- Aldrich.
2.1.1 Synthesis of N,N'-bis(salicylaldehyde)-o-phenylenediamine (H2B)
The ethanolic solution (20 ml) of (1.08 g, 0.01 mol) o-phenylenediamine was prepared at room temperature. The accurate amount of the salicylaldehyde (2.10 ml, 0.02 mol) was added to the previous solution under nitrogen atmosphere. The mixture was refluxed while continuous stirring at ambient temperature for 2 hrs. Let the reaction content at the room temperature for one hour. Orange precipitate was formed, which collected by filtration. The product (90.33%) was recrystallized from hot ethanol and dried under a reduced pressure.
2.1.2 Synthesis of the target complexes
The prepared Schiff base (H2B) (1.0 mmol) was dissolved in 20 ml acetone. The metal nitrate (or chloride) (0.5 mmol) was dissolved in 10 ml acetone, which was added dropwise while stirring to the ligand solution. The pH of the mixture was adjusted to 6.55–7.0 by adding NH4OH. The whole mixture was refluxed with stirring for 2 hrs. The formed precipitate was filtered, washed with hot acetone and dried under vacuum over anhydrous CaCl2.
2.1.3 Synthesis of the silver nanoparticles
Silver nanoparticles were obtained using the chemical reduction method for the reduction of silver nitrate (5 mmol) as precursor at 90 °C under atmospheric pressure with 1% starch solution as reducing agent and also as stabilizer. The mixture was stirred at room temperature for 30 min the resulting transparent colorless solution was converted to bale yellow and gradually changed to yellowish brown after 30 min at 90 °C and then to reddish brown solution after 60 min at the same temperature, indicating the formation of silver nanoparticles (Sreeram et al., 2008). The silver nanoparticles thus prepared in starch were stable for 2 month without any change in Plasmon resonance as indicated from the absorption spectra at room temperature showing that, the starch could be act as a good reducing agent and stabilizing agent for preparing silver nanoparticles.
2.1.4 Synthesis of zinc oxide nanoparticles
One hundred milliliters of (0.1 M) zinc acetate dihydrated were added dropwise from the burette to beaker containing one hundred milliliters of (0.2 M) potassium hydroxide solution, kept at room temperature on a magnetic stirrer under constant stirring using Teflon coated magnet. When the viscosity of the mixture had increased, the revolution of the Teflon coated magnet was adjusted that vortex of stirring was seen. The mixture was then stirred for 20 min further. The precipitated zinc hydroxide was filtered and washed several times with distilled water. The formed product was calcined in a hot air oven at 150 °C for 8 h.
The obtained zinc hydroxide was suspended in distillated water, to obtain suspension of zinc oxide nanoparticles. The final product of the zinc oxide was spherical with diameter in the range 10–15 nm (Sangari, 2015).
2.1.5 Synthesis of the H2B-Ag composite
In a typical synthesis, the ethanolic solution (50 ml) of the Schiff bases (0.001 M) was stirred at room temperature. To the previous solution, 10 ml from Ag nanoparticles was added and the mixture was allowed to stirring for 2 h.
2.1.6 Synthesis of the H2B-Ni-Ag composite
The ethanolic solution (50 ml) of the Ni-H2B complex (0.001 M) was stirred at room temperature. 10 ml from Ag nanoparticles was added and the mixture was allowed to stirring for 2 h.
2.1.7 Synthesis of the H2B-ZnO composite
To the Schiff bases solution (0.05 M), and accurate weight of zinc oxide nanoparticles (0.1 M) dissolved in 30 ml ethanol was added. The mixture was stirred for 2 h and the resulting precipitate was filtered off and washes with de-ionized water several times then dried at room temperature for 3 h.
2.1.8 Synthesis of the H2B-Ni-ZnO composite
To the Ni-complex solution (0.05 M), 50 ml of the ethanolic suspension of the zinc oxide nanoparticles (0.1 M) was added. The mixture was stirred for 2 h and the resulting precipitate was filtered. The product was washed with de-ionized water several times then, dried in an oven at 100 °C for 1 h.
2.2 Instruments and physical measurements
C, H, and N % were estimated using a Heraus CHN-rapid analyzer. The 1H NMR spectra were recorded on Varian-Gemini 200 MHz spectrometer in DMSO‑d6 using TMS as internal standard. The mass spectra were recorded on DI Analysis Shimadzu Qp-2010 plus. The FTIR spectra were recorded (KBr disc) in the 4000–400 cm−1 range on Bruker Tensor27 American spectrometer. The electronic absorption spectra were obtained with EtOH solution in 1 cm quartz cell using UV-1601PC Shimadzu spectrophotometer. Magnetic susceptibility measurements were carried out using the modified Gouy method (Figgis et al., 1960) on MSB-MK1 balance at room temperature using mercury(II)tetrathiocyanatecobaltate(II). The effective magnetic moment, μeff, per metal atom was calculated from the expression μeff = 2.83 B.M., where χ is the molar susceptibility corrected using Pascal’s constant for the diamagnetism of all atoms in the complexes. TGA, DTG and DTA were recorded on Shimadzu 60 thermal analyzer under a dynamic flow of nitrogen (40 ml/min) and heating rate 10 °C/min from ambient temperature to 750 °C. Electrical conductivity measurements were carried out at room temperature on freshly prepared 10−3 M DMSO solutions using WTW conductivity meter fitted with L100 conductivity cell.
The resulting nanoparticles were characterized by ultraviolet/visible (UV–vis) at room temperature. The studies of the size, morphology and composition of the nanoparticles were performed by means of transmission electron microscopy (TEM-Jeol Jem 2100(Japan)). The electron microscope instrument was operated at an accelerating voltage of 90 KV. The samples were prepared by drop-coating the nanoparticles solution onto the carbon-coated copper grid and were loaded onto specimen holder. The crystal structure of the sample was analyzed by means of X-ray diffractometer using a type 1370/10 Philips diffractometer with Fe-filtered Cu-Kα radiation.
2.3 Kinetic and thermodynamic parameters
In order to assess the influence of the structural properties of the complexes on the thermal behavior, the kinetic parameters were evaluated using the Coats-Redfern equation (Coats and Redfern, 1964).
2.4 Antimicrobial activity
The antimicrobial activities of the synthesized compounds have been screened using different strains of bacteria (Streptococcus pneumonia, Bacillis subtilis, Pseudomonas aeruginosa, Escherichia coli) and pathogenic fungi (Aspergillus fumigatus, Candida albicans). The disc diffusion method technique was adapted for antibacterial activity (Barry and Brown, 1996) while the well technique was used for antifungal activity (Cruickshank et al., 1965). Mean zone of the inhibition in mm ± standard deviation beyond well diameter (6 mm) produced on a range of environmental and clinically pathogenic microorganisms using 1 mg/ml concentration of the tested samples. The test was done using the diffusion agar technique, Well diameter: 6.0 mm (100 µl was tested). This test was performed in the Regional Center for Mycology and Biotechnology – Al-Azhar University.
2.5 DNA interaction
The experiments were carried out in Tris–HCl buffer at pH 7.0. A solution of fish milt DNA (FM-DNA) gave a ratio of the UV/vis absorbance more than 1.8 at 260 and 280 nm, indicating that, DNA was sufficiently free from protein. The stock solution of FM-DNA was prepared by dissolving DNA in 10 mM of the Tris–HCl buffer at pH 7.0. DNA concentration of the stock solution was determined by UV–vis spectrophotometery, in properly diluted samples, using the molar absorption coefficient 6600 M−1 cm−1 at 260 nm (Cruickshank et al., 1965). The stock solutions were stored at 4 °C and used over no more than 4 days. Absorption titration experiments were performed with fixed concentrations of DNA (1 × 10−4 M) while gradually increasing the concentration of the complexes (0–10 × 10−3 M) at 25 °C. While measuring the absorption spectra, an amount of the ethanolic complex solution was added to the DNA solution.
3 Results and discussion
3.1 Characterization of the synthesized ligand (H2B)
The Schiff base N,N′-bis(salicylaldehyde)-o-phenylenediamine (H2B) was prepared as mention previously (El-Ajaily et al., 2013; Jamaluddin and Reazul, 2011; Padmaja et al., 2014; Wang et al., 2011). The purity of the prepared ligands were tested and characterized by using different tools, as listed in the following:
3.1.1 Physical properties and elemental analysis
The elemental (C, H, N %) analysis results, revealed the high purity of the formed ligands, where obtained data go well with the calculated values. The H2B ligand has the molecular formula C20H16N2O2 (M.wt = 316.36). H2B has orange crystalline moiety and melting point = 159 °C. The solubility of the ligand under consideration were investigated in some polar and nonpolar solvents, where it soluble in EtOH, MeOH, Acetone, DMF, DMSO meanwhile not soluble in benzene and ether. C% (calculated/found) = 75.93/76.22, H% = 5.10/4.91 and N% = 8.86/8.67.
3.1.2 FTIR spectra
The FTIR spectra of the H2B ligand gave the characteristic bands which belong to its functional groups. The medium band which appeared at 3292 cm−1 could be due to the stretching vibration of the O—H bond. The shape of the peak could be revealed the presence of weak H-bond due to the weak broadness behavior (El-Ajaily et al., 2013). The stretching vibration band of the C⚌N moiety appeared at 1587 as strong peak. The asymmetric and symmetric stretching bands of the C—O bond were appeared at 1381 and 1192 cm−1 respectively, as shoulder bands (El-Ajaily et al., 2013).
3.1.3 1H NMR spectra
The 1H NMR spectrum of the H2B ligand gave the characteristic isomer shift value for each type of hydrogen atom. The aromatic protons appeared at δ = 6.40–7.70 ppm (m, 12H, H-aromatic). The singlet band which appeared at δ = 8.90 ppm could be due to the 2H of the —CH⚌N groups (s, 2H, CH⚌N). The proton of the OH group appeared at δ = 12.96 ppm (s, 2H, H) (El-Ajaily et al., 2013; Parmar et al., 2013). 1H NMR spectrum of the H2B ligand revealed the purity of it.
3.1.4 Mass spectra of the synthesized ligand
The chromatogram figures of the H2B ligand indicate the purity of the formed product, where gave one peak. The mass spectrum of the H2B gave molecular ion peak at m/z = 316 (86%) which go well with the calculated molecular weight, which indicates the purity of it. The obtained fragments (316 (85.50), 299 (53.05), 287 (1.10), 269 (1.68), 239 (0.58), 223 (45.28), 210 (100.00), 196 (64.12), 180 (26.99), 167 (16.72), 152 (10.24), 134 (8.72), 120 (20.06), 115 (7.44), 102 (5.53), 77 (17.83), 65 (7.55), 52 (5.64)), could be represented schematically, as shown in Scheme 1. The postulated fragmentations processes go well with the obtained fragments.
3.2 The complexes which derived from H2B:
The formed complexes which prepared by using standard methods (El-Ajaily et al., 2013; Yong et al., 1996) where separated and characterized by using various tools, as the following:
3.2.1 Elemental analysis and physical properties
The reaction of the H2B ligand with the Co(II), Ni(II), Cu(II), Zn(II) and Mg(II) ions proceed by adding the metal salt solution to the solution of the ligand as 1:2 M ratio (M:L). The obtained complexes could be have the following formula: [Co(B)(H2O)2], [Ni(B)(H2O)], [Cu(B)(H2O)2], [Zn(B)(H2O)2] and [Mg(B)(H2O)2]·2H2O. The obtained elemental analysis (C, H, N %) and M %, go well with the postulated formula (Table 1). All the complexes were non-hygroscopic. Co(II) complex has deep brown pieces product, Ni(II) complex gave small sheets with red color, Cu(II) complex has light brown crystals, Zn(II) complex has yellow sheets and Mg(II) complex has yellow pieces. Ni(II), Zn(II) and Mg(II) complexes gave the maximum thermal stability where they unmelted till 360 °C.
| Comp. | Mwt | Color | M.P. °C | Elemental analysis (found/calculated) | Ωa (μS) | |||
|---|---|---|---|---|---|---|---|---|
| C% | H% | N% | M% | |||||
| H2B (C20H16N2O2) | 316.36 | Orange | 159 | 75.88 | 4.95 | 8.91 | – | – |
| 75.93 | 5.10 | 8.86 | ||||||
| [Co(B)(H2O)2] | 409.31 | Deep brown | 301 | 58.36 | 4.21 | 6.72 | 14.13 | 2.7 |
| 58.69 | 4.43 | 6.84 | 14.40 | |||||
| [Ni(B)(H2O)] | 391.05 | Red | >360 | 61.56 | 3.76 | 7.58 | 15.13 | 3.9 |
| 61.43 | 4.12 | 7.16 | 15.01 | |||||
| [Cu(B)(H2O)2] | 413.92 | Light brown | 288 | 58.33 | 3.87 | 6.35 | 15.15 | 2.3 |
| 58.04 | 4.38 | 6.77 | 15.35 | |||||
| [Zn(B)(H2O)2] | 415.76 | Yellow | >360 | 58.01 | 4.16 | 6.87 | 15.61 | 1.8 |
| 57.78 | 4.36 | 6.74 | 15.73 | |||||
| [Mg(B)(H2O)2]·2H2O | 410.71 | Yellow | >360 | 58.75 | 4.93 | 6.50 | 6.16 | 3.4 |
| 58.49 | 5.40 | 6.82 | 5.92 | |||||
3.2.2 Molar conductivity of the complexes
The electrical conductivity of the complexes solution (0.001 M) was measured in DMSO. All the formed complexes gave conductivity in the range 1.8–3.9 ohm−1 cm2 mol−1, which indicates the non-electrolytic behavior of the complexes, and could be formulated as [MB] form (Table 1).
3.2.3 FTIR spectra
The infrared spectra of the prepared complexes gave the characteristic vibration modes for the different types of the functional groups (Table 2). All the formed complexes gave new and weak bands in the range of the M-O and M-MN stretching vibration region, where M-O stretching band appeared at 543, 543, 536, 539 and 539 for the Co(II), Ni(II), Cu(II), Zn(II) and Mg(II) complexes respectively, meanwhile the M-N band appeared at 460, 457, 482, 462 and 464. The broad band which appeared in the range 3427–3435 cm−1 in all the formed complexes could be due to the stretching (symmetric and asymmetric) vibration mode of the H2O molecules. The stretching vibration υ(C⚌N) in the ligand (1587) undergoes red shift in all formed complexes, which indicates the participation of this group in the chelation process through the complexes formation. The υ(C—O) gave blue shift which enhancement the chelation of the C—OH group. The band which appeared at ∼1610 cm−1, could be due to the formation of the quinone structure as result from the resonated tautomerism (Orabi, 2008) (Scheme 2).
| Comp. | ν(H2O) ν(OH) |
ν(C⚌N) | ν(C—O) | ν(M—O) | ν(M—N) |
|---|---|---|---|---|---|
| H2B | 3292 m., br. | 1587 s. | 1381 br. | – | – |
| 1192 br. | |||||
| [Co(B)(H2O)2] | 3427 s., br. | 1609 s. | 1378 w. | 543 w. | 460 w. |
| 1565 sh. | 1326 m. | ||||
| 1522 m. | |||||
| [Ni(B)(H2O)] | 3433 m., br. | 1606 s. | 1371 m. | 543 w. | 457 w. |
| 1577 m. | 1338 m. | ||||
| 1518 s. | |||||
| [Cu(B)(H2O)2] | 3432 s., br. | 1607 s. | 1378 w. | 536 w. | 482 vw. |
| 1519 m. | 1335 w. | ||||
| [Zn(B)(H2O)2] | 3435 s., br. | 1618 m. | 1389 sh. | 539 w. | 462 w. |
| 1530 m. | 1351 w. | ||||
| 1326 w. | |||||
| [Mg(B)(H2O)2]·2H2O | 3430 s., br. | 1616 s. | 1387 w. | 539 w. | 464 w. |
| 1531 m. | 1328 w. | ||||
s. = strong sh. = shoulder w. = weak m. = medium br. = broad vw. = very weak.
3.2.4 Electronic spectra
The electronic spectra of the formed complexes were summarized in Table 3. The ultra violet–visible spectra of the complexes [Co(B)(H2O)2], [Ni(B)(H2O)], [Cu(B)(H2O)2], [Zn(B)(H2O)2] and [Mg(B)(H2O)2]·2H2O show three bands for each, at 333, 316 and 252 nm, 289, 254 and 226 nm, 343, 306 and 240 nm, 331, 288 and 239 nm, 330, 286 and 237 nm respectively. The observed bands could be assigned as π → π* and n → π* electronic transition. The variation of the bands which obtained for the formed complexes with the bands of the ligand revealed and proved the formation of the complexes under consideration.
| H2B | [Co(B)(H2O)2] | [Ni(B)(H2O)] | [Cu(B)(H2O)2] | [Zn(B)(H2O)2] | [Mg(B)(H2O)2]·2H2O | ||
|---|---|---|---|---|---|---|---|
| π → π* and n → π* |
nm | 332 | 333 | 289 | 343 | 331 | 330 |
| 269 | 316 | 254 | 306 | 288 | 286 | ||
| 231 | 252 | 226 | 240 | 239 | 237 | ||
| cm−1 | 30120 | 30030 | 34602 | 29155 | 30211 | 30303 | |
| 37175 | 31646 | 39370 | 32680 | 34722 | 34965 | ||
| 43290 | 39683 | 44248 | 41667 | 41841 | 42194 | ||
| CT | nm | – | – | – | – | 435 | 430 |
| 383 | 379 | ||||||
| cm−1 | – | – | – | – | 22989 | 23256 | |
| 26110 | 26385 | ||||||
| d → d | nm | – | 464 | 473 | 417 | – | – |
| 390 | 374 | 384 | |||||
| 356 | 308 | ||||||
| cm−1 | – | 21552 | 21142 | 23981 | – | – | |
| 25641 | 26738 | 26042 | |||||
| 28090 | 32468 | ||||||
| Postulated | – | 4T2g(F) ← 4T1g(F) | 3T2g(F) ← 3A2g(F) | 2A1 ← 2E | – | – | |
| Electronic | 4A2g(F) ← 4T1g(F) | 3T1g(F) ← 3A2g(F) | 2E ← 2E | ||||
| Transition | 4T1g(P) ← 4T1g(F) | 3T1g(P) ← 3A2g(F) | |||||
| B (cm−1) | – | 557 | 494 | – | – | – | |
| Β | – | 0.50 | 0.50 | – | – | – | |
| 10 Dq (cm−1) | – | 23450 | 21140 | 23981 | – | – | |
| µeff (B.M) | – | 3.17 | 3.59 | 1.66 | Dia | Dia | |
| Postulated structure | – | Octahedral | Octahedral | Distorted octahedral | octahedral | octahedral | |
Co(II) complex [Co(B)(H2O)2] gave electronic spectrum which shows absorption bands at 464 nm, 390 nm and 356 nm which could be assigned as: 4T2g(F) ← 4T1g(F) 4A2g(F) ← 4T1g(F) and 4T1g(P) ← 4T1g(F)
The observed bands could be due to the d → d electronic transition. The obtained data strongly proved the octahedral geometry around Co(II) ion. The predominant electronic transition obtained due to the spin allowed transition, meanwhile they are forbidden according to the parity (g → g). the obtained bands not exceeded 500 cm−1, which indicated the strong interaction of the H2B ligand with the Co(II) ion, which clearly appeared through the high value of the crystal field parameter (10Dq) and the small value of the nephelauxetic parameter (β) (Orabi et al., 2013).
The electronic spectrum of the [Ni(B)(H2O)] complex, which shows three bands at 473 nm, 374 nm and 308 nm, could be assigned as: 3T2g(F) ← 3A2g(F) 3T1g(F) ← 3A2g(F) and 3T1g(P) ← 3A2g(F) which is conformity with octahedral geometry around Ni(II) ion (Orabi et al., 2013).
The electronic spectrum of the [Cu(B)(H2O)2] complex which shows two bands at 417 nm and 384 nm which could be assigned as: 2E ← 2E 2A1 ← 2E which is conformity with destroyed octahedral geometry around Cu(II) ion (Lever, 1968). The splitting of the 2T2g has value = 2061 cm−1.
The complex [Zn(B)(H2O)2], gave two bands at 435 nm and 383 nm, which could be assigned as CT bands. Also the complex [Mg(B)(H2O)2]·2H2O, gave two bands at 430 nm and 379 nm, which could be assigned as CT bands. The low nephelauxetic value for the Co(II) and Ni(II) complexes indicate the high covalent character of the bonds which formed between the ligands and the central metal ions in the formed complexes. The postulated structures of the formed complexes were represented in the Scheme 2.
3.2.5 Magnetic measurements
The effective magnetic moment measurements of the synthesized complexes are given in the Table 3. The [Co(B)(H2O)2] complex has µeff value = 3.17B.M. The obtained μeff value, indicates the strong spin-spin interaction and/or the configuration equilibrium between octahedral and square tetragonal structure (Holt et al., 1964; Nyburg and Wood, 1964).
The observed magnetic moment of [Ni(B)(H2O)] complex is found to be 3.59B.M., which indicates the paramagnetic (high spin) nature of the complex and falls within the range of the octahedral geometry through the bridging water ligand (Ketan et al., 2012). Thus, on the basis of ultra violet – visible spectra and magnetic data revealed the postulated octahedral geometry around the Ni(II) ion (Orabi et al., 2013).
The [Cu(B)(H2O)2] complex has µeff value = 1.66B.M. corresponding to the presence of one unpaired electron (Ketan et al., 2012). The magnetic moment value and electronic spectrum confirmed the destroyed octahedral geometry around the Cu(II) ion (Lever, 1968).
3.2.6 Thermal analysis
The working complexes were subjected to TG-DTA analysis from ambient temperature up to 750 °C under nitrogen atmosphere. The decomposition temperature ranges, the percentage of the mass losses and the thermal effects accompanying the decomposition process are given in Table 4. Representative thermal curves TG/DTG-DTA of the complexes under consideration are given in Fig. 1 (as an example).
| Compound | Temp. range (°C) | DTA peak temp. (°C) | Peak type | Mass loss % | Process | Expected products | Residue % | |
|---|---|---|---|---|---|---|---|---|
| Found | Calcd. | Found (Calcd.) | ||||||
| [Co(B)(H2O)2] | 117–250 | 140 | Endo. | 9.10 | 8.80 | Coordination sphere | 2H2O | CoO |
| 320–374 | 350 | Exo. | 17.29 | – | Partial Ligand decomp. | 0.23 H2B | 18.64 | |
| 374–483 | 400 | Exo. | 64.61 | – | Final decomp. | 0.84 H2B | (18.31) | |
| [Ni(B)(H2O)] | 80–250 | – | – | 4.55 | 4.61 | Coordination sphere | H2O | |
| 360–600 | 363 | Endo. | 80.08 | 80.39 | Ligand decomposition | H2B | ||
| 474 | Exo. | – | ||||||
| 538 | Exo. | |||||||
| [Cu(B)(H2O)2] | 50–125 | 88 | Endo. | – | – | Phase transition | ||
| 125–260 | 248 | Endo. | 7.35 | 8.7 | Coordination sphere | 2H2O | – | |
| 300–400 | 352 | Exo. | 21.56 | – | Partial Ligand decomp. | 0.28 H2B | ||
| [Zn(B)(H2O)2] | 50–125 | 77 | Endo. | – | – | Phase transition | ||
| 125–215 | 185 | Endo. | 9.01 | 8.67 | Coordination sphere | 2H2O | – | |
| 215–550 | 378 | Exo. | 15.37 | – | Partial Ligand decomp. | 0.20 H2B | ||
| 428 | Exo. | |||||||
| [Mg(B)(H2O)2]·2H2O | 50–130 | – | – | 7.82 | 8.77 | Crystallization | 2H2O | |
| 130–250 | 149 | Endo. | 8.65 | 8.77 | Coordination sphere | 2H2O | MgO | |
| 300–498 | 377 | Exo. | 9.1 | – | Partial Ligand decomp. | 0.12 H2B | 10.00 | |
| 450 | Exo. | 88.0 | – | (9.82) | ||||
| 498–700 | 548 | Exo. | Final decomposition | 0.88 H2B | ||||
| 594 | Exo. | |||||||
![The thermal decomposition of the [Co(B)(H2O)2] complex.](/content/184/2020/13/1/img/10.1016_j.arabjc.2018.06.016-fig3.png)
The TGA/DTG-DTA thermograms of the Co(II) complex [Co(B)(H2O)2] are shown in Fig. 1. The coordinated water was liberated within the temperature range 117–250 °C, with DTA peak temperature = 140 °C as endothermic peak. The weight loss of this process = 9.10% which indicate the liberation of two molecules of water as shown in Table 4. The weight loss over the range 320–374 °C, which could be due to the partial ligand decomposition. The decomposition process accompanied with one separate DTA peak at 350 °C (exo). The weight loss value indicates the liberation of 0.23 H2B (H2B = ligand). The final decomposition step appeared at temperature range 374–483 °C with one separate DTA temperature peak = 400 °C (exo) with weight loss = 64.61%, reveal the complete decomposition of the rest of the ligand (0.84 H2B). The residual mass % = 18.64, go well with the calculated residual value (18.31%) for the formed CoO.
The TGA/DTG-DTA thermograms of the Ni(II) complex [Ni(B)(H2O)] are evaluated and their data was listed in Table 4. The coordinated water was liberated within the temperature range 80–250 °C, with the weight loss of this process = 4.55% which indicate the liberation of one molecule of water. The weight loss over the range 360–600 °C, could be due to the complete ligand decomposition. The ligand decomposition process was accompanied with three separate DTA peaks at 363 °C (endo), 474 °C (exo) and 538 °C (exo), followed by mass loss % = 80.08.
The thermal analysis of the copper complex strongly enhanced postulated formulae: [Cu(B)(H2O)2]. The obtained data were represented in Table 4. The ligand decomposition action proceeds by many decomposition steps with different temperature ranges as: 50–125 °C with one separate DTA peak at 88 °C (endo), which indicate the phase transition process. The coordinated water was liberated within the temperature range 125–260 °C, with weight loss = 7.35% which indicate the liberation of two molecules of water. The partial ligand decomposition proceeds within the temperature range 300–400 °C with the exothermic DTA peak at 352 °C. The weight loss %, revealed the partial decomposition of the ligand with the liberation of 0.28 from the ligand. These steps indicate the uncompleted decomposition of the ligand until the maximum working temperature (750 °C). Due to uncompleted decomposition of the ligand, the residual mass % not detected.
The TGA/DTG-DTA thermograms of the Zn(II) complex [Zn(B)(H2O)2] are represented in Table 4. The ligand decomposition proceeds by many decomposition steps with different temperature ranges as: 50–125 °C with one separate DTA peak at 77 °C (endo), which indicate the phase transition process. The coordinated water was liberated within the temperature range 125–215 °C, with weight loss = 9.01% which indicate the liberation of two molecules of water. The ligand decomposition proceeds with the temperature range 215–550 °C with the two exothermic DTA peaks at 378 °C and 428 °C. The weight loss %, revealed the partial decomposition of the ligand with the liberation of 0.20 from the ligand. These steps indicate the uncompleted decomposition of the ligand until the maximum working temperature (750 °C). Due to uncompleted decomposition of the ligand, the residual mass % not detected.
The thermal analysis of the Mg(II) complex strongly enhanced the postulated formula: [Mg(B)(H2O)2]·2H2O. The obtained data were represented in Table 4. The thermal decomposition of the complex proceeds through four consecutive steps:
Step I: occurred at temperature range 50–130 °C, with weight loss % which accompanied with this step, revealed the liberation of two molecules of water of crystallization.
Step II: this step give one endothermic peak at 149 °C. This step could be due to the liberation of the coordinated water molecule. The mass loss % revealed the liberation of two molecules from water.
Step III: this step proceeds within the temperature range 300–498 °C with the two exothermic DTA peaks at 377 °C and 450 °C. The weight loss %, revealed the partial decomposition of the ligand with liberation of 0.12 from the ligand.
Step IV: this step occurred at temperature range 498–700 °C with the two exothermic DTA peaks at 548 °C and 594 °C, could be due to the liberation of the rest of the ligand (0.88 of the ligand). The residual mass % = 10.00, go well with the calculated residual value (9.82%) for the formed MgO.
The comparative studies of the different decomposition steps in the complexes revealed the following orders:
1 – Thermal stability of the water of coordination:
2 – Thermal stability of the ligand decomposition:
From the obtained order, could be summarized the following results:
[a] Cu(II) complex has the most thermally stable coordinated water, while Ni(II) complex the least.
[b] Zn(II) complex has the most thermally stable ligand, while Co(II) complex the least.
3.2.7 Kinetic parameters
The decomposition steps were selected for the complexes of Co(II), Cu(II), Zn(II) and Mg(II) corresponding to their appearance and intensity. The selected steps were used to investigate the kinetic parameters of the thermal decomposition processes. The order of the decomposition reaction (n), the activation energy (ΔEa), and the pre-exponential factor (z) were calculated using the Coats-Redfern equation (Möllhoff and Sternberg, 2001). The thermodynamic parameters (ΔG#, ΔH# and ΔS#) which accompanied with the decomposition process were evaluated and listed in Table 5. The order of the liberation of the coordinate water was achieved with the second order reaction for Zn(II) complex meanwhile Co(II) and Mg(II) complexes proceed with 0.66 and 0 orders respectively. Also the order of the ligand decomposition was achieved with the 0.66 order reaction for Cu(II) complex. The obtained result indicate that, the liberation of the coordinated water proceed by different mechanisms in case of Co(II), Zn(II) and Mg(II) complexes. The obtained data, which listed in Table 5, clearly indicates the direct proportionality of the activation energy with the pre-exponential factor. So, according to the theoretical approach, we can discuss the obtained data as the following:
1- The ligand decomposition in case of the Cu(II) complex gave the largest pre-exponential factor (Z).
2- The order of the activation energy (ΔEa) of the liberation of the coordinated water gave the following trend: Zn(II) complex > Mg(II) complex > Co(II) complex
That’s meaning, Zn(II) complex need high energy (185 °C) to liberate its coordinate water rather than Co(II) complex (140 °C).
3- The order of the Z factor which accompanied with the liberation of the coordinate water is listed as: Zn(II) complex > Mg(II) complex > Co(II) complex
| Compound | Steps | Order (n) | Ts (K) | ΔEa (J/mol) | Z (s−1) | ΔS# (J/K.mol) | ΔH# (kJ/mol) | ΔG# (kJ/mol) |
|---|---|---|---|---|---|---|---|---|
| [Co(B)(H2O)2] | Coordinate water | 0.66 | 409 | 50.78 | 3.52E+05 | −141.38 | −3.35 | 54.48 |
| [Cu(B)(H2O)2] | Ligand decomposition | 0.66 | 626.6 | 157.40 | 3.47E+12 | −11.01 | −5.05 | 1.85 |
| [Zn(B)(H2O)2] | Coordinate water | 2 | 457.2 | 77.03 | 1.43E+08 | −92.43 | −3.72 | 38.49 |
| [Mg(B)(H2O)2]·2H2O | Coordinate water | 0 | 469.8 | 58.62 | 4.09E+05 | −141.28 | −3.85 | 62.53 |
The thermodynamic parameters which evaluated to the activated compounds were listed in Table 5. The change of the standard Gibbs free energy for the activated compounds (ΔG#) has positive values for all the thermal decomposition reaction. The positive values of the Gibbs free energy, obvious the non-spontaneous behavior of the decomposition process. The negative values of the ΔH#, revealed the exothermic behavior of the decomposition process, which lead to the formation of products more stable than the reactants, where the heat content of the products less than reactants. The negative values of the entropy change (ΔS#), indicate the thermally unfavorable of the decomposition process, where the disorder behavior of the products became lesser than the reactants (Muraleedharan and Radhakrishnan, 1995; Orabi et al., 2013; Wendlandt, 1974).
The data which obtained from the physico-chemical analysis: microanalysis, conductivity, FTIR, electronic spectra and thermal analysis, forced each other and finally could be postulated the structure of the synthesized complexes as shown in the Scheme 2.
3.3 Applications of the synthesized compounds
3.3.1 DNA interaction
3.3.1.1 Detection using electronic absorption spectroscopy
The uses of the electronic absorption spectroscopy in the studying of the DNA interaction, act as one of the most useful techniques (Satyanarayana et al., 1992). The absorption spectra of the H2B-Co(II), H2B-Ni(II), H2B-Cu(II), H2B-Zn(II), H2B-Mg(II) complexes (0–10 × 10−3 M) in presence of FM-DNA (10−4 M) and the binding constants Kb of the complexes which evaluated using Benesi-Hildebrand plot are given in Fig. 2 (as an example) and the obtained data are listed in Table 6.![(a) Electronic spectra of DNA ([DNA] = 10−4 M) with increasing the concentration of the complex [Co(B)(H2O)2] ([Complex] = 0–10 × 10−3 M); (b) Benesi–Hildebrand fitting curve.](/content/184/2020/13/1/img/10.1016_j.arabjc.2018.06.016-fig4.png)
| Compound | Kb (M−1) | Hyper. % | Δλ |
|---|---|---|---|
| [Co(B)(H2O)2] | 1.3 × 104 | 80.0 | −3.00 |
| [Ni(B)(H2O)] | 1.0 × 105 | 18.7 | 0 |
| [Cu(B)(H2O)2] | 1.2 × 104 | 35.3 | −0.78 |
| [Zn(B)(H2O)2] | 2.2 × 104 | 53.1 | −0.24 |
| [Mg(B)(H2O)2]·2H2O | 0.3 × 105 | 47.0 | 0 |
The interaction of the synthesized complexes with FM-DNA was investigated by titration of the fixed amount of the FM-DNA (10−4 M) with the complexes (0–10 × 10−3 M) and concomitant recording the electronic spectra. The absorption spectra of these complexes with the DNA, exhibit hyperchromism effects with increasing the complexes concentration (Yu et al., 2004). The hyperchromism effects are the spectral features of DNA concerning its double-helix structure (Yang et al., 1994). The obtained hyperchromism effect could be due to the external contact (electrostatic binding) effect (Pasternack et al., 1983) or partial uncoiling of the helix structure of the DNA (Pratviel et al., 1998). The potential FM-DNA binding ability of the complexes was studied by following the intensity changes of the intra ligand π → π* transition bands in the uv–vis. region. The intrinsic binding constant Kb was calculated from the spectroscopic titration data using Benesi-Hildebrand plots (Benesi and Hildebrand, 1949). The values of the obtained Kb indicate that, the complexes moderately bind (electrostatic binding) to FM-DNA, with almost the same affinity. However, these values are smaller than those of classical intercalators and metalointercalators whose Kb values are in order of 107 M−1 (Cory et al., 1985). The order of the binding constant according to the nature of the Mn+ ion, could be arranged as the following: [Ni(B)(H2O)] > [Mg(B)(H2O)2]·2H2O > [Zn(B)(H2O)2] > [Co(B)(H2O)2] > [Cu(B)(H2O)2]
3.3.2 Nanoparticles and biological activity
3.3.2.1 Characterization of the synthesized nanoparticles:
3.3.2.1.1 Ultraviolet–Visible (UV–Vis) spectral analysis
The synthesized AgNPs exhibits strong absorption band in the visible range due to the surface plasmon resonance (SPR) (Henglein, 1993). UV–Vis spectra of the synthesized nanoparticles showed a maximum absorbance peaks at 420 nm for AgNPs and at 370 nm for ZnONPs. Observation of this surface plasmon peak has been well documented for various AgNPs, with sizes ranging from 2 to 100 nm (Henglein, 1993; Sastry et al., 1998). In case of ZnONPs UV–Vis spectra showed a single narrow peak, indicating the formation of the ZnO nanoparticles. There is a relationship between the UV–Vis absorbance spectrum, size and shape of nanoparticles (Birla et al., 2013). With the increase in the particle size, the optical absorbance spectra of metal nanoparticles that are dominated by surface plasmon resonance shift towards longer wavelengths (red shift) (Birla et al., 2013). Small blue or red shift in the wavelength of the absorbance peaks could be related to the size and shape of the formed NPs (Birla et al., 2013).
3.3.2.1.2 Transmission electron microscopy (TEM)
The TEM measurements were carried out to determine the morphology and shape of the formed nanoparticles. Transmission electron microscope micrograph of silver nanoparticles (Fig. 13A) revealed that they were spherical and well dispersed without agglomeration. The polycrystalline nature of the AgNPs was confirmed by the selective area electron dispersion (SAED) pattern (Fig. 3B). Fig. 3C shows the histogram of the formed particle size. The obtained data could be summarized as the following:
-
Generally the formed particle size ranged from 12 to 38 nm.
-
The maximum abundant of the particle size belong the size range 12–30 nm.
-
The particle size 20 nm act as the average abundant size (Henglein, 1993).
Transmission electron microscope micrograph of synthesized zinc oxide nanoparticles denoted by Fig. 4, revealed that they were spherical with little agglomeration. Most of particles were present in the range 10–15 nm in size and possess an average size of 12 nm (Fig. 4B).
3.3.2.1.3 X-Ray diffraction studies (XRD)
XRD pattern of the prepared Zinc oxide nanoparticles was represented in Fig. 5. The diffraction peaks were appeared at 2θ = 31.70°, 34.37°, 36.21°, 47.47°, 56.57°, 62.80°, 67.89° and 68.99° which associated with (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (1 1 2) and (2 0 1) indices respectively. The sharp (strong and narrow) diffraction peaks indicate the high purity and good crystallinity of the grown nanostructures. All the reflections can be assigned to the standard powder pattern for the pure hexagonal phase of ZnO with lattice constants a = 3.2516 Å, c = 5.2000 Å. The (hkl) values are agreed well with the standard card of ZnO powder sample (Faber and Fawcett, 2002).
3.3.2.1.4 Fourier transform infrared spectroscopy (FTIR)
The FTIR spectrum of the AgNPs indicate the presence of bands at 3455, 2256, 1638 and 542 cm−1 while ZnONPs spectrum showed bands at 3420, 1632, 1380, 1116, 1035 and 650 cm−1. The well-defined peak, at 3455 cm−1 could be due to (i) stretching vibration (symmetric and asymmetric) of aliphatic hydroxyl (OH) group of the protecting molecules and (ii) the stretching vibrational band of H2O molecules. The bands which observed at 2256 cm−1 assigned as aliphatic C—H stretching, while the peak at 1638 cm−1 could be assigned as a bending band of the H2O molecule and a stretching vibrational band of carbonyl group (C⚌O) resulting from the residue of the starch molecule.
FTIR spectrum of the synthesized ZnO nanoparticles showed bands at 3420 cm−1 which corresponds to the stretching vibration (symmetric and asymmetric) of hydroxyl (OH) group as well as asymmetric and symmetric stretching H—O—H vibration, while the bending H—O—H vibration band is observed at 1632 cm−1, not even that, but could be accompanied with the stretching vibration of the carbonyl group (C⚌O). Bands which observed at 1035, 1116 and 1380 cm−1 are due to the C—O stretching vibration, could be due to the presence of some acetate group. The band at 650 indicates the stretching vibrations of ZnO nanoparticle.
3.3.2.2 Antibiotic susceptibility pattern
The Schiff bases, metal complexes and their composites with metal nanoparticles were known to have antimicrobial role since many years (Aazam and El-Said, 2014; Abu-Khadra et al., 2016; Halawani, 2016; Shah et al., 2016). The antimicrobial activities of the synthesized compounds have been screened using different strains of bacteria (Streptococcus pneumonia RCMB 010010 (Gram positive), Bacillis subtilis RCMB 010067 (Gram positive), Pseudomonas aeruginosa RCMP 010043(Gram negative), Escherichia Coli RCMB 010052 (Gram negative)) and pathogenic fungi (Aspergillus fumigatus RCMB 02568 and Candida albicans RCMB 05036). The obtained results were compared with usable antibiotics (as standard): Amphotericin B, Ampicillin and Gentamicin using disc-diffusion method. The antimicrobial effect was evaluated by measuring the zone of inhibition.
3.3.2.2.1 Antimicrobial activity of the synthesized Schiff bases
The antimicrobial activities of the H2B Schiff bases towards some microorganisms (Gram positive, Gram negative bacteria and Fungi), were listed in Tables 7 and 8. Generally, the results show that the Schiff base under consideration act as inactive compounds towards the Pseudomonas aeruginosa (Gram negative bacteria) and Candida albicans (Fungi). The antimicrobial activities could be arranged as the following: [1]- For gram positive bacteria: Ampicillin > H2B, [2]- For gram negative bacteria: Gentamicin > H2B, [3]- For fungi: Amphotericin B > H2B, [4]- For Escherichia coli: Gentamicin ≈ H2B.
| Compounds | The inhibition zone of the investigated compounds (mm)* | |||
|---|---|---|---|---|
| Gram positive bacteria | Gram negative bacteria | |||
| Bacillis subtilis | Streptococcus pneumoniae | Escherichia coli | Pseudomonas aeruginosa | |
| H2B | 18.3 ± 2.1 | 17.4 ± 1.5 | 18.2 ± 1.2 | Inactive |
| Ampicillin | 32.4 ± 0.3 | 23.8 ± 0.2 | – | – |
| Gentamicin | – | – | 19.9 ± 0.3 | 17.3 ± 0.1 |
3.3.2.2.2 Antimicrobial activity of the H2B ligand and its complexes
The results which listed in Tables 9, 10 and shown in Fig. 6 indicating the valuable activity of the H2B Schiff base and its metal complexes towards some gram positive, gram negative bacteria and Fungi. It is clear that, the Cu(II) complex gave the largest activity towards the fungi. Co(II) complex shows high synergism towards the selected bacteria and fungi. In case of Ni(II) complex it is clear that the inhibition zone is the lowest among the other metal complexes. Zn(II) complex shows the largest activity towards the Escherichia Coli. H2B ligand and its metal complexes do not have any activity towards the Pseudomonas aeruginosa (gram negative bacteria) and Candida albicans (fungi). The antimicrobial activities of the H2B ligand and its metal complexes could be summarized as the following:
1- Collectively, the antibacterial activity toward the gram positive bacteria has the following trend (Fig. 6): Ampicillin > Co(II) complex ≈ Cu(II) complex > Zn(II) complex > H2B > Mg(II) complex > Ni(II) complex
2- Antibacterial activity against the gram negative bacteria gave the following order: Zn(II) complex > Gentamicin > Cu(II) complex > H2B > Co(II) complex > Mg(II) complex > Ni(II) complex.
3- Antifungal activity can be arranged as the following trend: Amphotericin B > Cu(II) complex > Co(II) complex > H2B > Zn(II) complex > Mg(II) complex > Ni(II) complex.
| Compounds | The inhibition zone of the investigated compounds (mm)* | |||
|---|---|---|---|---|
| Gram positive bacteria | Gram negative bacteria | |||
| Bacillis subtilis | Streptococcus pneumoniae | Escherichia coli | Pseudomonas aeruginosa | |
| H2B | 18.3 ± 2.1 | 17.4 ± 1.5 | 18.2 ± 1.2 | Inactive |
| [Co(B)(H2O)2] | 21.1 ± 0.3 | 19.2 ± 0.3 | 17.4 ± 0.6 | Inactive |
| [Ni(B)(H2O)] | 16.3 ± 0.3 | 14.2 ± 0.4 | 10.4 ± 0.3 | Inactive |
| [Cu(B)(H2O)2] | 21.3 ± 1.2 | 18.3 ± 0.7 | 18.3 ± 0.6 | Inactive |
| [Zn(B)(H2O)2] | 19.2 ± 0.6 | 18.3 ± 0.6 | 20.3 ± 0.7 | Inactive |
| [Mg(B)(H2O)2]·2H2O | 17.4 ± 0.7 | 15.3 ± 0.6 | 14.5 ± 0.6 | Inactive |
| Ampicillin | 32.4 ± 0.3 | 23.8 ± 0.2 | – | – |
| Gentamicin | – | – | 19.9 ± 0.3 | 17.3 ± 0.1 |
| Compounds | The inhibition zone of the investigated compounds (mm)* | |
|---|---|---|
| Aspergillus fumigates | Candida albicans | |
| H2B | 17.3 ± 2.1 | Inactive |
| [Co(B)(H2O)2] | 18.2 ± 0.6 | Inactive |
| [Ni(B)(H2O)] | 11.3 ± 0.3 | Inactive |
| [Cu(B)(H2O)2] | 20.3 ± 0.6 | Inactive |
| [Zn(B)(H2O)2] | 15.6 ± 0.6 | Inactive |
| [Mg(B)(H2O)2]·2H2O | 13.2 ± 1.2 | Inactive |
| Amphotericin B | 23.7 ± 0.1 | 25.4 ± 0.1 |
3.3.2.2.3 Antimicrobial activity of the H2B-Ni-AgNPs composite
The results which listed in Tables 11, 12 and shown in Figs. 7–9 indicating that the presence of moderate enhancement in the antimicrobial activity of the H2B-Ni-AgNPs composite relatively to the individual components. The obtained result could be due to the spatial arrangement structure of the formed composites and their electronic structure.
| Compounds | The inhibition zone of the investigated compounds (mm)* | |||
|---|---|---|---|---|
| Gram positive bacteria | Gram negative bacteria | |||
| Bacillis subtilis | Streptococcus pneumoniae | Escherichia coli | Pseudomonas aeruginosa | |
| H2B | 18.3 ± 2.1 | 17.4 ± 1.5 | 18.2 ± 1.2 | Inactive |
| [Ni(B)(H2O)] | 16.3 ± 0.3 | 14.2 ± 0.4 | 10.4 ± 0.3 | Inactive |
| AgNPs | 17.3 ± 0.6 | 15.3 ± 0.6 | 12.3 ± 1.2 | Inactive |
| H2B with AgNPs | 20.1 ± 1.2 | 18.2 ± 0.7 | 16.4 ± 0.6 | Inactive |
| H2B-Ni-AgNPs | 21.2 ± 0.6 | 20.4 ± 2.1 | 18.9 ± 1.5 | Inactive |
| Ampicillin | 32.4 ± 0.3 | 23.8 ± 0.2 | – | – |
| Gentamicin | – | – | 19.9 ± 0.3 | 17.3 ± 0.1 |
| Compounds | The inhibition zone of the investigated compounds (mm)* | |
|---|---|---|
| Aspergillus fumigates | Candida albicans | |
| H2B | 17.3 ± 2.1 | Inactive |
| [Ni(B)(H2O)] | 11.3 ± 0.2 | Inactive |
| AgNPs | 14.2 ± 1.2 | Inactive |
| H2B with AgNPs | 16.3 ± 1.2 | Inactive |
| H2B-Ni-AgNPs | 19.3 ± 1.2 | Inactive |
| Amphotericin B | 23.7 ± 0.1 | 25.4 ± 0.1 |
The antimicrobial activity of the H2B ligand, H2B-Ni(II) complex, H2B-AgNPs composite and H2B-Ni-AgNPs composite towards some gram positive, gram negative bacteria and Fungi were listed in Tables 11, 12 and represented in Figs. 7–9. Generally, the interaction of the AgNPs with the ligand and its complexes, gave moderate enhancement in their antimicrobial activities. On the other hand the H2B-Ni-AgNPs composite gave the largest activity towards the gram negative bacteria and fungi, meanwhile H2B-Ni(II) complex the lowest. H2B Schiff base, H2B-Ni(II) complex, H2B-AgNPs composite and H2B-Ni(II) complex-AgNPs composite do not have any activity towards the Pseudomonas aeruginosa (gram negative bacteria) and Candida albicans (fungi).
Collectively, the antimicrobial activity of the compounds under consideration could be summarized as the following:
1- Antibacterial activity toward the gram positive bacteria has the following trend: Ampicillin > H2B-Ni(II) complex-AgNPs composite > H2B-AgNPs composite > H2B > AgNPs > H2B-Ni(II) complex
2- Antibacterial activity against the gram negative bacteria gave the following order: Gentamicin > H2B-Ni(II) complex-AgNPs composite > H2B > H2B-AgNPs composite > AgNPs > H2B-Ni(II) complex.
3- Antifungal activity can be arrangement as the following trend: Amphotericin B > H2B-Ni(II) complex-AgNPs composite > H2B > H2B-AgNPs composite > AgNPs > H2B-Ni(II) complex.
3.3.2.2.4 Antimicrobial activity of the H2B-Ni-ZnONPs composite
The results which listed in Tables 13, 14 and shown in Figs. 10–12 show the antimicrobial activity of the H2B Schiff base, H2B-Ni(II) complex, H2B-ZnONPs composite and H2B-Ni-ZnONPs composite towards some gram positive, gram negative bacteria and Fungi. The inhibition zone of H2B-Ni(II) complex is smaller than that of H2B Schiff base as it causes antagonism towards bacteria and fungi. H2B-Ni-ZnONPs composite gave the lowest activity. The H2B Schiff base, H2B-Ni(II) complex, H2B-ZnONPs composite and H2B-Ni-ZnONPs composite do not have any activity towards the Pseudomonas aeruginosa (gram negative bacteria) and Candida albicans (fungi). Also H2B-Ni-ZnONPs composite do not have any activity towards Streptococcus pneumoniae (gram positive bacteria) and Aspergillus fumigatus (fungi). Generally, the analysis of the antimicrobial activity of the compounds under consideration towards some microorganisms could be summarized as the following: Ampicillin > Amphotericin B > Gentamicin > ZnONPs > H2B > H2B-ZnONPs composite > H2B-Ni(II) complex > H2B-Ni(II) complex-ZnONPs composite
| Compounds | The inhibition zone of the investigated compounds (mm)* | |||
|---|---|---|---|---|
| Gram positive bacteria | Gram negative bacteria | |||
| Bacillis subtilis | Streptococcus pneumoniae | Escherichia coli | Pseudomonas aeruginosa | |
| H2B | 18.3 ± 2.1 | 17.4 ± 1.5 | 18.2 ± 1.2 | Inactive |
| [Ni(B)(H2O)] | 16.3 ± 0.3 | 14.2 ± 0.4 | 10.4 ± 0.3 | Inactive |
| ZnONPs | 20.6 ± 0.6 | 17.3 ± 1.5 | 18.4 ± 1.2 | Inactive |
| H2B with ZnONPs | 18.1 ± 1.2 | 16.8 ± 0.3 | 17.4 ± 0.3 | Inactive |
| H2B-Ni-ZnONPs | 13.2 ± 1.2 | Inactive | 10.1 ± 1.5 | Inactive |
| Ampicillin | 32.4 ± 0.3 | 23.8 ± 0.2 | – | – |
| Gentamicin | – | – | 19.9 ± 0.3 | 17.3 ± 0.3 |
| Compounds | The inhibition zone of the investigated compounds (mm)* | |
|---|---|---|
| Aspergillus fumigates | Candida albicans | |
| H2B | 17.3 ± 2.1 | Inactive |
| [Ni(B)(H2O)] | 11.3 ± 0.3 | Inactive |
| ZnONPs | 18.2 ± 1.2 | Inactive |
| H2B with ZnONPs | 16.8 ± 0.4 | Inactive |
| H2B-Ni-ZnONPs | Inactive | Inactive |
| Amphotericin B | 23.7 ± 0.1 | 25.4 ± 0.1 |
3.3.2.2.5 Minimum inhibitory concentrations (MICs) of the studied compounds
The results which listed in Tables 15, 16 show the minimum inhibitory concentrations (μg/ml) of the H2B-Ni(II) complex, AgNPs and H2B-Ni-AgNPs composite towards some gram positive, gram negative bacteria and Fungi. The minimum inhibitory concentration of the H2B-Ni-AgNPs composite is lower than that of H2B-Ni(II) complex and AgNPs. H2B-Ni(II) complex, AgNPs and H2B-Ni-AgNPs composite do not have any activity towards the Pseudomonas aeruginosa (gram negative bacteria) and Candida albicans (fungi). H2B-Ni-AgNPs composite shows moderate activity towards the selected bacteria and fungi.
| Compounds | Minimum inhibitory concentrations (μg/ml) | |||
|---|---|---|---|---|
| Gram positive bacteria | Gram negative bacteria | |||
| Bacillis subtilis | Streptococcus pneumoniae | Escherichia coli | Pseudomonas aeruginosa | |
| [Ni(B)(H2O)] | 31.2 | 62.5 | 125 | Inactive |
| AgNPs | 3.9 | 3.9 | 15.6 | Inactive |
| H2B-Ni-AgNPs | 3.9 | 3.9 | 3.9 | Inactive |
| Ampicillin | 1.0 | 1.9 | – | – |
| Gentamicin | – | – | 3.9 | 15.63 |
| Compounds | The inhibition zone of the investigated compounds (mm)* | |
|---|---|---|
| Aspergillus fumigates | Candida albicans | |
| [Ni(B)(H2O)] | 125 | Inactive |
| AgNPs | 7.81 | Inactive |
| H2B-Ni- AgNPs | 3.9 | Inactive |
| Amphotericin B | 1.0 | 1.0 |
The antimicrobial activity as MICs ((μg/ml) can be arrangement as the following: For gram positive bacteria: Ampicillin < Ni(II)-composite ≈ Ag nanoparticles < Ni(II) complex, For gram negative bacteria: Gentamicin < Ni(II)-composite < Ag nanoparticles < Ni(II) complex and for antifungal activity: Amphotericin B < Ni(II)-composite < Ag nanoparticles < Ni(II) complex. H2B-Ni-AgNPs composite gave moderate small MICs towards the antibacterial activity, meanwhile H2B-Ni(II) complex the largest.
3.3.3 Docking of the synthesized compounds
Till now, bacterial infection steal acting as a serious threat to human lives because of emerging resistance to existing antibiotics, which is an increasing public health problem (Wang et al., 2006). In order to prevent or just minimize this serious medical problem, the elaboration of new types of antibacterial agents or enhancement the bioactivity of the previous drugs is a very important task (Leeb, 2004). To meet critical clinical needs, especially to overcome the emerging drug resistance, the discovery of novel antibiotic chemical scaffolds with new modes of action is crucial for saving lives.
Fortunately, compounds containing Schiff base moiety show antimicrobial activity against various bacteria, including inhibitors of FabH (Cheng et al., 2009; Lv et al., 2010; Shi et al., 2010). Docking simulations were carried out to minimize the distance between the theoretical and actual view, also to understanding the interaction of the target compounds with certain protein. Molecular docking of the H2B ligand into the three-dimensional were selected as example represented the compounds under consideration.
X-ray structure of E. coli FabH (PDB code: 1HNJ) was used as targeting protein for the synthesized compounds (Fig. 13). The three-dimensional structures of the aforementioned compounds were constructed using Chem 3D ultra 12.0 software [Chemical Structure Drawing Standard; Cambridge Soft corporation, USA (2010)], then they were energetically minimized by using MMFF94 with 5000 iterations and minimum RMS gradient of 0.10. The crystal structures of E. coli FabH were retrieved from the RCSB Protein Data Bank (http://www.rcsb.org/pdb/home/home.-do). All bound water and ligands were eliminated from the protein and the polar hydrogen was added. The whole E. coli FabH was defined as a receptor and the site sphere was selected based on the ligand binding location of malonyl-CoA, then the malonyl-CoA molecule was removed and H2B ligand was placed during the molecular docking procedure. Types of interactions of the docked protein with targeting compound were analyzed after the end of molecular docking (Wang et al., 2012). All molecular modeling studies were performed on Hewlett-Packard Pentium Dual-Core T4300 2.10 GHz running Windows 7 Ultimate using molecular operating environment MOE 2008.10 molecular modeling software (Chemical Group Inc., 2008).
The molecular docking of the H2B ligand with E. coli Fabh was represented in Figs. 14, 15. The binding model of the H2B ligand indicates the weak tendency toward the 1HNJ via hydrogen bonds with GLU 211 (HD, 2.32 Å) and 6-ring TRP 32 (H-pi interaction, 3.33 Å). The moderate negative value of the docking energy (−15.80 kcal/mol) pronounced the binding affinity to FabH.
4 Conclusions
The obtained results strongly suggest that nanoparticle composites could be employed in environmentally friendly, effective control strategies for microbial entities. The synthesized ligand and its complexes has moderate affinity to the DNA, which could uses as bioactive compounds. The obtained values indicating that, the complexes are moderately binding (electrostatic binding) to the FM-DNA moiety. The order of the binding constant, relatively depending on the nature of the metal ion. Nanoparticles gave some specific antimicrobial enhancement for Ni(II) complexes, which gave the minimum MICs. Docking simulations were carried out to minimize the distance between the theoretical and actual view, also to understanding the interaction of the target compounds with certain protein.
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