Metal complexes of gliclazide: Preparation, spectroscopic and thermal characterization. Biological potential study of sulphonylurea gliclazide on the house fly, Musca domestica (Diptera – Muscidae)

2.1 Materials and reagents

All chemicals used were of the analytical reagent grade (AR), and of highest purity available. They included gliclazide (UniPharma); copper(II) chloride dihydrate (Prolabo); cobalt(II) and nickel(II) chlorides hexahydrates (BDH); zinc(II) chloride dihydrate (Ubichem), chromium(III) chloride hexahydrate (Sigma); manganese(II) chloride and ferric(III) chloride hexahydrate (Prolabo). Zinc oxide, disodium salt of ethylenediaminetetraacetic acid; EDTA; (AnalaR), ammonia solution (33% v/v) and ammonium chloride (El-Nasr pharm. Chem. Co., Egypt). Organic solvents used included absolute ethyl alcohol, diethylether, and dimethylformamide (DMF). These solvents were spectroscopic pure from BDH. Hydrogen peroxide, hydrochloric and nitric acids (MERCK) were used. De-ionized water collected from all glass equipments was usually used in all preparations.

2.2 Instruments

The molar conductance of solid complexes in DMF was measured using Sybron–Barnstead conductometer (Meter-PM.6, E = 3406). Elemental microanalyses of the separated solid chelates for C, H, N and S were performed at the Microanalytical Center, Cairo University, using CHNS-932 (LECO) Vario Elemental Analyzers. The analyses were repeated twice to check the accuracy of the data. Infrared spectra were recorded on a Perkin–Elmer FT-IR type 1650 spectrophotometer in wave number region 4000–400 cm⁻¹. The spectra were recorded as KBr pellets.

The solid reflectance spectra were measured on a Shimadzu 3101pc spectrophotometer. The molar magnetic susceptibility was measured on powdered samples using the Faraday method. The diamagnetic corrections were made by Pascal’s constant and Hg[Co(SCN)₄] was used as a calibrant. The thermogravimetric (TG and DTG) analysis was carried out in dynamic nitrogen atmosphere (20 mL min⁻¹) with a heating rate of 10 °C min⁻¹ using Shimadzu TGA-50H thermal analyzer.

2.3 Synthesis of metal complexes

The metal complexes were prepared by the addition of hot solution (60 °C) of the appropriate metal chloride salts (1 mmol) in an ethanol–water mixture (1:1, 25 mL) to the hot solution (60 °C) of GLZ (0.4 g, 1 mmol) in the same solvent (25 mL). The resulting mixture was stirred under reflux for 1 h whereupon the complexes precipitated. They were collected by filtration, washed with a 1:1 ethanol:water mixture and diethyl ether. The analytical data for C, H, N and S were repeated twice.

2.4 Determination of the metal content of the chelates

An accurately weighed portion of the different chelates ranged from 10 to 30 mg was placed in Kjeldahl flask. A measured volume of concentrated nitric acid ranged from 5 to 10 mL was added initially to the powdered chelates, to start the fast wet oxidation digestion. This mixture had been digested with some drops of H₂O₂ solution using a gradual heating. This treatment was conducted until most of the powdered complexes were diminished and the remained solution had the colour of the corresponding metal salt. This solution was then diluted up to a 50 mL with bidistilled water and the metal content was determined by titration against standard EDTA solution at a suitable pH value using the suitable indicator.

2.5 Biological activity

In the present study, the larvae of Musca domestica were collected from the permanent colony of insect colony of Entomology Department, Faculty of Science, Cairo University. Insect were reared in the laboratory according to the method of Nassar (1988) with some modification.

2.6 Bioassay and statistical analysis

Larval mortalities were observed during the larval period, while pupal and adult mortalities were calculated based on the successfully emerged individuals from the treated larvae. The developmental rates were also studied. Data obtained were analyzed by the Student^’s t-distribution and refined by Bessel correction (Moroney, 1956).

3.1 Composition and structures of metal complexes

The isolated solid complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) ions with the GLZ ligand are subjected to elemental analyses (C, H, N, S and metal content), IR, magnetic moment studies, molar conductance and thermal analyses (TG and DTG), to identify their tentative formulae in a trial to elucidate their molecular structures. The results of elemental analyses listed in Table 1 suggest the formulae [M(HL)Cl₃(H₂O)]·3H₂O (M = Cr(III) and Fe(III)), [M(HL)Cl₂(H₂O)₂]·yH₂O (M = Co(III), Ni(II) and Cu(II), y = 0–2) and [M(HL)Cl₂]·yH₂O (M = Mn(II) and Zn(II), y = 0–1).

3.2 Molar conductivity measurements

The chelates are dissolved in DMF and the molar conductivities of 10⁻³ M of their solutions at 25 °C are measured. It is concluded from the results listed in Table 1 that the chelates are found to have molar conductance values of 13.20–30.10 Ω⁻¹ mol⁻¹ cm² indicating that all the metal chelates are non-electrolytes.

3.3 IR spectral studies

The IR data of the spectra of GLZ ligand and its complexes are listed in Table 2. The IR spectra of the complexes are compared with those of the free GLZ ligand in order to determine the coordination sites that may be involved in chelation. The tautomeric equilibrium depends on the extent of conjugation, nature and position of the substituents, polarity of the solvent etc.

This phenomenon has drawn considerable attention by several investigators and characteristic spectral bands have been assigned to the individual tautomers. As an example, Fig. 2 shows the IR spectrum of Zn(II) complex.

Close

Figure 2

The FT-IR of Zn–gliclazide complex.

Export to PPT

The sharp band at 1640 cm⁻¹ can be assigned to the amide carbonyl of the saturated side chain moiety. A broad band spreading over the region 3400–3100 cm⁻¹ can be ascribed to NH groups. Some authors have reported that the amide carbonyl group present in the saturated side chain moiety enolises. However, the strong α-effect due to heterocyclic nitrogen atom on the saturated side chain moiety prevents the enolization of this carbonyl group. The complexes under investigation have a band near 3150–3045 cm⁻¹, which is due to the N–H stretching of the saturated side chain moiety which support the presence of the amide NH in the keto form (ii) and not in the enol form (iii) (Yao and Resnick, 1962). This band is masked with a very broad band in the region 3500–3000 cm⁻¹ in the spectra of the complexes under investigation which may be due to the intermolecular hydrogen bonding in the solid state.

Close

Export to PPT

Therefore, GLZ drug behaves as a neutral bidentate ligand coordinating to the metal ions via amide-O and enolic sulphonamide-OH.

3.4 Electronic spectral studies

Three spin allowed transitions at ν₁: ⁴A_2g → ⁴T_2g, ν₂: ⁴A_2g → ⁴T_2g(F), and ν₃: ⁴A_2g → ⁴T_1g(P) (Cotton et al., 1999) are observed for octahedral Cr(III) complex. The diffused reflectance spectrum of the Cr(III) chelate shows three absorption bands at 18,770 (ν₁), 27,450 (ν₂), and 28,360 cm⁻¹ (ν₃) which are in reasonable agreement with those in the literature for octahedral Cr(III) complexes (Cotton et al., 1999).

From the diffused reflectance spectrum it is observed that, the Fe(III) chelate exhibits a band at 22,090 cm⁻¹, which may be assigned to the ⁶A_1g → T_2g(G) transition in octahedral geometry of the complexes (Rosenberg et al., 1999). The ⁶A_1g → ⁵T_1g transition appears to be split into two bands at 16,960 and 15,450 cm⁻¹ (Cotton et al., 1999). The spectrum shows also a band at 27,780 cm⁻¹ which may be attributed to ligand to metal charge transfer. The diffused reflectance spectrum of the Mn(II) complex shows three bands at 15,675, 21,900 and 26,915 cm⁻¹ assignable to ⁶A_1g → ⁴T_1g, ⁶A_1g → ⁴T_2g(G) and ⁶A_1g → ⁴T_2g(D) transitions, respectively (Cotton et al., 1999), which indicates the presence of Mn(II) complex in tetrahedral structure.

The electronic spectrum of the Co(II) complex with the formula [Co(HL)Cl₂(H₂O)₂] gives three bands at 14,990, 17,420 and 22,250 cm⁻¹. The bands observed are assigned to the transitions ⁴T_1g(F) → ⁴T_2g(F) (ν₁), ⁴T_1g(F) → ⁴A_2g(F) (ν₂) and ⁴T_1g(F) → ⁴T_2g(P) (ν₃), respectively, suggesting the presence of Co(II) complex in octahedral geometry (Zayed et al., 2007; Cotton et al., 1999). The region at 25,660 cm⁻¹ refers to the charge transfer band.

For Ni(II) complex; [Ni(HL)Cl₂(H₂O)₂]·2H₂O, the electronic spectrum displays three bands at ν₁: 15,790 cm⁻¹: ³A_2g → ³T_2g; ν₂: 18,750 cm⁻¹: ³A_2g → ³T_1g(F) and ν₃: 22,245 cm⁻¹: ³A_2g → ³T_1g(P). The spectrum shows also a band at 25,047 cm⁻¹ which may be attributed to ligand to metal charge transfer (Zayed et al., 2007; Cotton et al., 1999). The reflectance spectrum of the Cu(II) chelate shows low intensity shoulder bands centered at 15,790 and 21,870 cm⁻¹. Under the influence of the tetragonal distortion, the ²E_g and ²T_2g states of the octahedral Cu(II) ion (d⁹) split such as to cause the three transitions ²B_1g → ²B_2g; ²B_1g → ²E_g and ²B_1g → ²A_1g remain unresolved in the spectra (Manonmani et al., 2000). An intense peak observed at 25490 cm⁻¹ is due to ligand to metal charge transfer transition. The Zn(II) complex is diamagnetic and tetrahedral geometry is proposed for this complex.

3.5 Magnetic susceptibility studies

The room temperature magnetic moment is found to be 4.65 B.M., which corresponds to the presence of Cr(III) in octahedral geometry (Cotton et al., 1999). The observed magnetic moment value of Fe(III) complex is found to be 5.58 B.M., indicating octahedral geometry around the Fe(III) complex (Zayed et al., 2007; Cotton et al., 1999).

In addition to that, the Mn(II) complex is found to have a magnetic moment value of 4.62 B.M., which indicates the presence of Mn(II) complex in tetrahedral structure. The Co(II) complex is found to have magnetic susceptibility value of 5.46 B.M. (Table 1) which is an indicative of octahedral geometry. Meanwhile, the Ni(II) complex has a room temperature magnetic moment value of 3.74 B.M., which is in the normal range observed for octahedral Ni(II) complexes (Zayed et al., 2007; Cotton et al., 1999). The magnetic moment value of the Cu(II) complex is found to be 1.98 B.M., falls within the range normally observed for octahedral Cu(II) complexes (Manonmani et al., 2000).

3.6 Thermal analyses (TG and DTG)

In the present investigation, the weight losses for each chelate are calculated within the corresponding temperature ranges. The obtained data are listed in Table 3. [Cr(HL)Cl₃(H₂O)]·3H₂O complex is thermally decomposed in three decomposition steps within the temperature range of 50–700 °C. The first decomposition step with an estimated mass loss of 9.38% (calc. 9.75%) within the temperature range 50–120 °C may be attributed to the liberation of three water molecules of hydration. The activation energy of this dehydration step is found to be 32.90 kJ mol⁻¹. The remaining decomposition steps were found within the temperature range 120–700 °C with an estimated mass loss of 77.85% (calc. 76.46%) can be reasonably accounted for the removal of coordinated water, HCl, Cl₂ and GLZ molecules as gases. The activation energies were listed in Table 4.

The thermogram of [Fe(HL)Cl₃(H₂O)₂]·3H₂O chelate shows that the first step of decomposition within the temperature range 30–250 °C corresponds to the loss of hydrated and coordinated water molecules, Cl₂ and HCl gases with a mass loss of 32.34% (calc. 32.17%). The subsequent steps (250–1000 °C) correspond to the removal of the GLZ ligand leaving metal oxide as a residue. The overall weight loss amounts to 85.56% (calc. 85.84%).

Fig. 3 shows the TGA curve of the Ni(II) complex. The TG curves of the Mn(II) and Ni(II)-chelates show four stages of decomposition within the temperature range of 30–1000 and 30–600 °C, respectively. The stages at 30–250 °C correspond to the loss of water molecules of hydration and coordination and anions. The energy of activation for these steps is calculated using Coats–Redfern method and the data are listed in Table 4. The subsequent stages involve the loss of ligand molecules with an overall weight loss amounts to 84.45% (calc. 84.79%) and 85.88% (calc. 86.11%) for Mn(II) and Ni(II) complexes, respectively.

Close

Figure 3

(a) TG of Ni–gliclazide complex, and (b) DTG of Ni–gliclazide complex.

Export to PPT

The TG curves of the Co(II), Cu(II) and Zn(II) chelates represent two decomposition steps as shown in Table 3. The two decomposition steps occur within the temperature range from 100–800, 100–900 and 150–700 °C and can be attributed to the loss of coordinated water, Cl₂ and GLZ molecules with an estimated mass losses of 85.76% (84.59%), 84.49% (calc. 83.90%) and 82.25% (calc. 82.36%) for Co(II), Cu(II) and Zn(II) complexes, respectively. The energy of activation for these decomposition steps are listed in Table 4. CoO, CuO and ZnO are the residues of decomposition.

3.7 Kinetic data

The thermodynamic activation parameters of decomposition processes of dehydrated complexes namely activation energy (E*), enthalpy (ΔH*), entropy (ΔS*) and Gibbs free energy change of the decomposition (ΔG*) are evaluated graphically by employing the Coats–Redfern relation (Coats and Redfern, 1964). The data are summarized in Table 4.

The activation energies of decomposition are found to be in the range 29.76–205.6 kJ mol⁻¹. The high values of the activation energies reflect the thermal stability of the complexes. The entropy of activation is found to have negative values in all the complexes which indicate that the decomposition reactions proceed with a lower rate than the normal ones.

3.8 Structural interpretation

The structures of the complexes of GLZ drug with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) ions are confirmed by the elemental analyses, IR, molar conductance, magnetic, solid reflectance and thermal analyses (TG and DTG) data. Therefore, from the IR spectra, it is concluded that GLZ drug behaves as a neutral bidentate ligand coordinated to the metal ions via the amide-O and sulphonamide-OH. The molar conductance data, it is found that the complexes are non-electrolytes. On the basis of the above observations and from the magnetic and solid reflectance measurements, octahedral and tetrahedral geometries are suggested for the investigated complexes. As a general conclusion, the complexes structures can be given as shown in Fig. 4.

Close

Figure 4

Structures of GLZ metal complexes.

Export to PPT

3.9 Biological activity

The data show that GLZ drug under investigation and its metal complexes have the capacity of inhibiting the metabolic growth of the larvae to a different extent. The size of the inhibition zone depends upon the culture medium, incubation conditions, rate of diffusion and the concentration of the antibacterial agent.

The activities of all tested complexes may be explained on the basis of chelation theory: chelation reduces the polarity of the metal atom mainly because of the partial sharing of its positive charge with the donor groups and possible π electron delocalization within the whole chelate ring. Also, chelation increases the lipophilic nature of the central atom which subsequently favors its permeation through the lipid layer of the cell membrane (Caudhary and Singh, 2003).

In testing the biological activity of GLZ and its metal complexes, we used larvae of M. domestica to increase the chance of detecting antibiotic principles in the tested materials.

3.10 Lethal effects

In focusing the data recorded in Table 5, the potential effects of the different compounds of GLZ and its complexes (Mn(II), Fe(III) and Ni(II)) against the treated larvae of M. domestica are clear. Larval mortality is found to be 30%, 20% and 10% due to the effect of Mn(II), Fe(III) and Ni(II) complexes, respectively, whereas GLZ has no effect. While the three compounds; GLZ, Mn(II) and Fe(III), are found to cause 40% and Ni(II) complex is found to cause 80% of the pupal mortality. The higher adult mortality is found to be 60%, 40%, 30% and 10% by the effect of GLZ, Fe(III), Mn(II), and Ni(II) complexes, respectively, in comparison to 0.0% mortality of control insect (Table 5).

3.11 Morphogenic effects

Typical application of GLZ and its complexes on the different developmental stages of M. domestica resulted in different morphogenic abnormalities of pupation and adult emergence. On the other hand, the pupation program is impaired in different degrees by the various compounds. This effect is approximately a compound-dependent. Contrary to the previous fact, the GLZ drug has no effect on the larvae. On the other hand, the larval-pupal and adult deformations are increased by the effect of Mn(II), Fe(III) and Ni(II) complexes. The majority of the observed morphogenic effects represented as shrinking of skin with black colour and larval-pupal intermediate.

The toxicity effect of GLZ, seems to be due to the penetration of the different chemical compounds, is inversely proportional to the thickness of the insect cuticle. These results are in good agreement with those previously published (Bruck, 1979; Nassar et al., 2008; Samarasekera et al., 2004). It is clear from the data obtained that the larval instar was more tolerant to the chemical compounds than the pupal and adult stages. This can be attributed to insect size (Ikeda et al., 1979). On the other hand, toxicity effects of GLZ and its complexes can be attributed also to the decrease of blood glucose level in insect (Amin et al., 2004). Sulphonylurea drugs such as GLZ were found to inhibit fluid secretion and metabolism of Drosophila melanogaster fly (Evan et al., 2005). The insecticidal efficacy on 3rd larval instar and adult fecundity of M. domestica was due to the metabolism disturbance by the effect of Trigonella foenum extracts (Adel Halim and Morsy, 2006). In comparison, the variable effects of GLZ on the different developmental stages of M. domestica is found to be strengthen resistance for some complexes.

The complexes that found to produce morphological abnormalities can be attributed to their effects on total protein content which inhibited the cholinesterase, esterase enzymes and alkaline acid phosphatases in the blood of the different stages of M. domestica (Ghoneim et al., 1992). Typical application of the GLZ complexes on the larval instars of the M. domestica, in the present study, resulted in pronouncedly prohibition of the pupation and adult emergence. It may be considered as a result of the haemolymph ecdysteroids. In other words, GLZ complexes are classified in the category of chitin inhibitors.

The possible morphogenic action of GLZ on the larvae, pupae and adult eclosion programmes, available data in the present study unambiguously prevailed increased deformity, approximately, by the decreasing dose-level of M. domestica (Nassar, 1995), M. stabulans (Ghoneim et al., 1992; Nassar, 1995) and Rhynchophorus ferrugineus (Ghoneim et al., 2007; Nassar et al., 2008).