Research

, Volume: 17( 2)

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Polarographic Study and Thermodynamic Parameters of Bioinorganic [Zn (II)-Antibiotics-Phenacetin] Ternary System

*Correspondence:

Amul Kumar Kesharwani
Department of Chemistry,
Dr. H.S. Gour University,
Madhya Pradesh,
India,
Tel: 919407000000,
E-mail: amulkumarkesharwani@gmail.com

Abstract

Thermodynamic parameters viz. enthalphy change (ΔH), free energy(ΔG) and entropy change (ΔS) and kinetic parameters such as transfer coefficient (α), degree of irreversibility (λ), diffusion coefficient (D) and standard rate constant (κ) and stability constants (logβ) of Zn(II) complexes with neomycin, chlortetracyclin, oxytetracyclin, tetracyclin, penicillin-V and penicillin-G as primary ligands and phenacetin as secondary ligand were determined polarographically at pH = 7.30 ± 0.01 and an ionic strength of µ = 1.0 M NaClO at 25°C. The study showed that the complexes are not stable at higher temperature.

Keywords

Thermodynamics; Kinetic parameters; Stability constants; [Zn(II)-antibiotics-phenacetin] complexes

Introduction

Antibiotics are well known naturally occurring compounds which are produced mostly by plant organisms [1]. These antibiotics are used in several diseases in plants, animals and human being [2-4]. The in-vitro activity has been found to be effective with even lower concentration of these antibiotics, on the other hand, paracetamol is a biologically active drug used as antipyretic agent to bring down the body temperature in high fever, therefore, and the complex study of these drugs with Zn has great importance. A literature survey reveals that there are no references available about ternary complexes of Zn with selected antibiotics and phenacetin, so, authors have undertaken the present study and report the mixed ligands complexation of Zn with neomycin, chlortetracyclin, oxytetracyclin, tetracyclin, penicillin-V and penicillin-G as primary ligands and phenacetin as secondary ligand with the view to determine the values of thermodynamic parameters and finally with these data, the position of transition state has also been pointed out.

Materials and Methods

Antibiotics and drug paracetamol used from the Fluka products and there solutions were prepared in double distilled water. The concentration of Zn(II) in all analytes was 0.5 mM while 1.0 M NaClO₄ was used to maintain the ionic strength as well as used as supporting electrolyte. NaCl-agar-agar plug together with sintered disc were used in Latinine-Lingane cell which connect the polarographic cell with SCE [5,6]. The resistance of cell was lower than 200 ohms as to make no correction for IR.

The concentration of primary ligands varied from 0.5 mM to 30 mM at two constant concentration of phenacetin at 0.025 M and 0.050 M at pH=7.30 ± 0.01 at 25°C. The p^H of the analytic was maintained by using the requisite amount of HClO₄ and NaOH (both B.D.H.) solutions. Potassium dihydrogen phosphate-sodium hydroxide buffer was used to stabilize the p^H of the analyte at 7.30 ± 0.01.

A manual polarograph (AJCO electronics, Poona) with PL-50 polyflex Toshniwal galvanometer was used to record the current voltage data. The capillary (5.00 cm long and 0.04 mm in diameter) characteristics were m^2/3. t_1/6 = 2.40 mg^2/3S^-1/2 at 60.02 cms (calculated) effective height of mercury. An Elico (LI-120) p^H-meter was used to record the pH of the analytes. The C-V data for the analytes were recorded after passing the pure hydrogen gas. All the measurements were carried out at 25°C.

Results

Zn(II) gave a well-defined two electron quasireversible waves in 1.0 M NaClO₄ at p^H range 7.10 to 8.50 at 25°c, but p^H=7.30 was selected to investigate the complex formation in human blood p^H range. The 0.001 % solution of Tritone- X 100 was used as suppressor. Devries and Kroon method was used to determine the number of electrons involved in the reduction processes [7]. The values of E_1/2 quasireversible of Zn (II) was found -1.010 V vs SCE which by Gellings method gave E_1/2 reversible = -0.985 V [8]. Similarly E_1/2 reversible from E_1/2 quasireversible for complexes of Zn(II) with neomycin, chlortetracyclin, oxytetracyclin, tetracyclin, penicillin-V, penicillin-G as primary ligands and phenacetin as secondary ligand for different concentration of primary ligands (varried from 0.5 mM to 30 mM) and secondary ligand (at a fixed concentration at 0.025 M and 0.050 M) were determined. In all these cases it has been observed that irreversibility increases with increase of the ligand concentration. Zn formed 1: 1 and 1: 2 complexes with phenacetin and the stability constants [9-13] are given in (Table 1).

Table 1. Stability constants of [Zn-antibiotic-phenacetin] complexes.

Polarography of [Zn(II)-penicillin-G-phenacetin] complexes

The half wave potential increased with increase of concentrations of secondary ligand i.e. phenacetin to the [Zn-antibiotics] system showed ternary complex formation. The values of stability constants are given in (Table 2). The polarographic characteristics & F_ij[X Y] values for the [Zn(II)-penicillin-G-phenacetin] system are given in (Table 2) and plot of F_ij[X Y] vs [penicillin-G] is given in (Figure 1).The plots of [(E-0.0591/n){log (id - i)/i}] vs i for Zn and its complexes are given in (Figures 1,2).The quasireversible waves for Zn(II) and its complexes were confirmed by the slope of current voltage curves and kinetic parameters which are given in (Table 3).

Table 2. The polarographic characteristics & F_ij[X Y] values for the [Zn(II)-penicillin-G-phenacetin] system.

Table 3. Kinetic parameters such as standard rate constant (k), degree of irreversibility (l) and charge transfer coefficient (a) for the [Zn(II)-penicillin-G-phenacetin] complexes.

Kinetic parameters of [Zn(II)-penicillin-G-phenacetin] complexes

The kinetic parameters such as standard rate constant (k), degree of irreversibility (l) and charge transfer coefficient (a) for the [Zn(II)-penicillin-G-phenacetin] complexes were given in (Table 3). The parameter Z, which is measure of degree of irreversibility, is given by the following equation 10

The values of standard rate constant (k) of Zn and its complexes are found to be order of 10^-3 cm. sec^-1, confirmed that the electrode processes are quasi reversible and the reduction of the electro active species at the surface of the electrode is not fast. The charge transfer coefficient (α), which can be regarded as the fraction of the applied potential, either assists or hinders the process under consideration; also have the expected values. The values of α comes about 0.500 confirming the transition state lies in the midpoint of dropping mercury electrode and mercury solution interface.

Thermodynamic parameters of [Zn(II)-antibiotics-phenacetin] complexes

Theromodynamic parameters such as enthalpy change (Δ), free energy change (ΔG) and entropy change (ΔS) of the complexes have been determined at 25°C and 35°C by using the following equations.

The values of ΔS, ΔG and ΔH are given in the (Table 4). From these values it is clear that ΔS are more negative at higher temperature while the values of ΔG are less negative at higher temperature confirmed that the complex are not stable at higher temperature. The negative values of ΔH ensured that the reactions are exothermic in nature.

Table 4. Thermodynamic parameters (the values of DS, DG and DH) for [Zn(II)-antibiotics-phenacetin].

Stability constants of the [Zn (II)-antibiotics-phenacetinl] complexes

Stability constants for [Zn (II)-antibiotics-phenacetin] complexes are given in (Table 1). Stability of the complexes can be compared by the value of mixing constant (log Km) which is given by the following equation.

log Km = log b₁₁-1/2 [log b₂₀+ logb₀₂]

The values of log Km for the complexes [Zn(II)-neomycin- phenacetin], [Zn(II)-chlortetracyclin- phenacetin], [Zn(II)- oxytetracyclin- phenacetin], [Zn(II)-penicillin-V- phenacetin] and [Zn(II)-penicillin-G- phenacetin] are -0.030, -0.370, -0.370, +3.825, -0.155 respectively. The value of log Km for [Zn(II)-tetracyclin-paracetamol] is not calculated because [Zn(II)-tetracycline- phenacetin] complex is not found in this case.

Ternary complexes with negative values of log Km are less stable than their parent binary complexes and those with positive log Km are more stable than their parent binary complexes.

The value of stability constants (from Table 1) of neomycin complexes showed that this antibiotic formed the complexes of lowest stability amongst all the selected primary ligands because there is steric hindrance between metal and various groups present in the neomycin. In the complexes of chlortetracyclin, oxytetracyclin and tetracyclin, bonding takes place with metal ion through the oxygen of amide group and the oxygen of carbon atom. All tetracyclins have the same structures but they differ only in the group R₁ and R₂. The chlortetracyclin complexes is less stable than oxytetracyclin complexes, can be explained as the basis of the presence of electronegative chlorine atom at R₁ in chlortetracyclin while oxygen atom in OH group of R₂ in oxytetracyclin. Due to higher electronegativity of chlorine it attracts electrons very rapidly from groups present in the chlortetracyclin while oxygen does not attract electron as rapidly as chlorine, and so in case of chlortetracyclin there is higher electronic disturbance than in oxytetracyclin causes the less stability of chlortetracyclin complexes than oxytetracyclin complexes. The pK values of these drugs are also support this order of stability.

Discussion

Since there is no such electronegative atoms are present in case of tetracyclin, results no electronic disturbance in tetracyclin and so it forms highly stable complexes amongst all the selected tetracyclins.

In case of penicillin-V and penicillin-G, oxygen atom of carboxylic group and ring nitrogen may take part in formation of complex with Zn. High stability of penicillin-G complexes than penicillin-V is supported by besic strength of these drugs. In case of penicillin-G the value of log K is 4.77 while in case of penicillin-V it is found 3.98.

As a result of lesser steric hindrance in penicillin complexes than other antibiotics, penicillin complexes are highly stable than other. The trend of stability of the complexes is neomycin <chlortetracyclin <oxytetracyclin < tetracyclin < penicillin-V <penicillin-G.

The stability constants of the complexes of Zn with antibiotics are of great importance in pharmaceutical sciences. The values of stability constants obtained are not high, so Zn toxicity in-vivo can be reduced by using these drugs .

Conclusion

The overall view for the water analysis parameters is complicated in terms of maintaining best quality of water on our planet. Imbalance in one of them creates misbalance in other parameters. Thus, we have to take extreme care to preserve the natural resource of water in its purest form.

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