Elsevier

Journal of Molecular Structure

Volume 1047, 5 September 2013, Pages 267-276
Journal of Molecular Structure

Spectroscopic, thermal analyses, structural and antibacterial studies on the interaction of some metals with ofloxacin

https://doi.org/10.1016/j.molstruc.2013.04.076Get rights and content

Highlights

Abstract

Reaction between the fluoroquinolone antibacterial agent ofloxacin and V(IV), Zr(IV) and U(VI) in methanol and acetone was studied. The ability of ofloxacin to form metal complexes is high. The isolated solid complexes were characterized by elemental analysis, magnetic moment, conductance measurements, infrared, electronic, 1H NMR spectra and thermal investigation. In all complexes the ofloxacin ligand is coordinated through the pyridone and carboxylate oxygen forming 1:2 M:HOfl complexes. The calculated bond length and force constant, F(Udouble bondO), in the uranyl complex are 1.73 Å and 640.83 N m−1, respectively. The metal–ligand binding of the V(IV) and Zr(IV) complexes was predicted by using the density functional theory (DFT) at the B3LYP-CEP-31G level of theory and total energy, dipole moment estimation of different V(IV) and Zr(IV) ofloxacin structures. All the synthesized complexes exhibited higher biocidal activity against S. aureus K1, Bacillus subtilis K22, Br. otitidis K76, Escherichia coli K32, Pseudomonas aeruginosa SW1 and Klebsiella oxytoca K42. compared to parent compounds and standard drugs.

Introduction

The fluoroquinolone (quinolone) class of chemotherapeutic agents are considered by prudent physicians to be a drug of last resort to treat serious and life threatening bacterial infections[1], [2]. Ofloxacin (Scheme 1) is one of fluoroquinolone class and is a synthetic chemotherapeutic antibiotic [3], [4] considered to be a second-generation fluoroquinolone. Ofloxacin was first patented in 1982 (European Patent Daiichi) and received approval from the U.S. Food and Drug Administration (FDA) on December 28, 1990. Ofloxacin is sold under a wide variety of brand names as well as generic drug equivalents, for oral and intravenous administration. It exhibits strong activity against Gram-negative and some Gram-positive bacteria, through many anaerobic strains are resistant After oral administration of a single dose of ofloxacin tablet (200 mg) good penetration into body tissues and fluids is observed [5], [6].

Studies of interaction between ofloxacin and several metal cations commonly found in several drugs used as antacids have been reported in the literature [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [6], [17], [18], [19], [20], [21], [22], [23], [24], [25]. These studies have been mainly directed towards identifying the groups directly attached to the metal site, and establishing the structure of the coordination compounds thus formed. The crystal structure of ofloxacin [7], [8] and its complexes [9], [10], [26], [27], [28], [29] have been very limited studied. From their X-ray crystal data, it was found that the metal ion is coordinate bonded to the ofloxacin in the complexes through ring carbonyl and one of the carboxylic oxygen atoms.

Connecting with our previous studies in the trend of fluoroquinolones metal complexes [30], [31], we are reporting in the present article, the isolation and characterization of some new metal complexes formed from the interaction of ofloxacin with V(IV), Zr(IV) and U(VI) in the solvent. Density functional theory (DFT) is used to compute the cation type influence on theoretical parameters of the Zr(IV) and V(IV) complexes of ofloxacin and shows if the two oxygen atoms (Opyr and Ocarboxilic) of ofloxacin lie at trans or at cis positions so the two diastereoisomers of the studied complexes are going to be calculated. Such computational characterization reduces time consuming experiments for biomedical and pharmaceutical studies of the drugs and its complexes. Profiles of the optimal set and geometry of these complexes are going to be simulated by applying the GAUSSIAN 98W package of programs [32] at B3LYP/CEP-31G [33] level of theory. The prepared solid complexes will confirmed by using spectroscopic and thermal analyses techniques. The thermal behavior of these complexes is going also to be studied. The antibacterial activity of the investigated complexes, metal salts and free ofloxacin are going to be tested against three Gram-positive bacteria such as S. aureus K1, Bacillus subtilis K22, Br. otitidis K76 and three Gram-negative species Escherichia coli K32, Pseudomonas aeruginosa SW1 and Klebsiella oxytoca K42.

Section snippets

Chemicals

Ofloxacin was purchased from Egyptian Company for Chemicals & Pharmaceuticals (ADWIA), VOSO4·H2O was from Aldrich Chemical, ZrOCl2·8H2O, UO2(NO3)2·6H2O and all solvents were purchased from Fluka Chemical Co. All the chemicals and solvents were analytical reagent grade and were used as purchased without further purification.

Synthesis of metal complexes

The complexes have been prepared by direct reaction between HOfl with the corresponding metal cations in the form of water-soluble salts, such as sulfate and chloride. NaOH

Results and discussion

Ofloxacin (HOfl) reacted with V(IV), Zr(IV) and U(VI) in methanol and acetone at room temperature to form a solid complexes with a characteristic color of every metal ions. The molar ratio for all complexes synthesized is HOfl:M = 2:1 which was established from the results of the chemical analysis, also all the prepared complexes contain water molecules. The number of bound water molecules in these complexes being different. The thermogravimetric and infrared spectroscopic data also confirmed the

Computational method

The geometric parameters and energies will computed by density functional theory at the B3LYP/CEP-31G level, using the GAUSSIAN 98W package of programs, on geometries that were optimized at CEP-31G basis set. The high basis set was chosen to detect the energies at a highly accurate level. The atomic charges were computed using the natural atomic orbital populations. The B3LYP is the hybrid functional [58], which is a linear combination of the gradient functionals proposed by Becke [59] and Lee

Conclusion

The three new solid complexes were obtained as colored powdered materials and were characterized using magnetic measurements, melting point, molar conductance, infrared, electronic, 1H NMR spectra and thermogravimetric analyses. The V(IV), Zr(IV) and U(VI) were coordinated to a deprotonated carboxylate oxygen and pyridone oxygen of ofloxacin to form a six-membered chelate ring and one oxygen of water molecule to complete the coordination number for U(VI). The elemental analyses were in good

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