A novel slightly distorted octahedral complex of Cr(III) of norfloxacin (Nor) with the formula [
Quinolones are the broad spectrum synthetic antibiotics containing 4-oxo-3-carboxylic-1,4-dihydroquinoline skeleton, with bactericidal effect, good oral absorption, excellent bioavailability, and good penetration into tissues [
Molecular structure of Nor and its zwitterion.
In the last few years, the synergetic effect of transition metal ions with quinolones has been the subject of active research in bioinorganic chemistry. It has been observed that metal complexes with appropriate ligands are biologically more significant and specific than the metal ions and the ligand itself [
In order to investigate the coordination behaviour of Nor we have synthesised a novel mixed ligand complex of Cr(III) metal ion in presence of
During literature survey it has been found that all of the reported synthesised metalloquinolones are screened against animal pathogenic microbes (fungus and bacteria). In this present work we have screened our synthesised complex against four phytopathogenic fungi for suppression of various plant diseases to develop the agriculture science by protecting crops and vegetables for the production of a plentiful supply of high-quality and affordable food.
Nor was purchased from Sigma Aldrich. Bipy and the metal salt CrCl3·6H2O were obtained from Merck. All the chemicals used for this work were of analytical grade.
An equimolar mixture of CrCl3·6H2O and Bipy in 15 mL of 1 : 1 solvent mixture of methanol and acetone was stirred for 10 minutes on a magnetic stirrer at room temperature. Then 5 mL equimolar solution of Nor in the same solvent mixture was added drop by drop under stirring condition. Further, the resulting mixture was heated in a hydrothermal vessel in programmed temperature oven at 100°C for 24 hrs. Then it was gradually cooled to room temperature after 72 hrs, leading to a bright green needle shaped crystal.
Calc. for C28H35Cl3CrFN5O5: C, 48.11; H, 5.05; N, 10.02%. Found: C, 48.40; H, 4.91; N, 10.61%.
Fourier transform infrared (FT-IR) spectra were recorded on a spectrometer Perkin Elmer Spectrum BX II in the range of 400–4000 cm−1 by preparing sample pellets with KBr. Electronic spectra were recorded in solid state on an instrument Shimadzu UV-3101PC spectrometer. C, H, and N elemental analysis was performed on an Elementer vario ELIII instrument. Thermogravimetric analysis (TGA) measurements were carried out in an oxygen atmosphere from ambient temperature to 900°C using Perkin Elmer Diamond. Single-crystal X-ray diffraction (XRD) was collected in a Bruker D8 diffractometer, using Cu Kα radiation.
The
FT-IR band assignments were done by comparing the spectra of the synthesised complex with those of the free ligand, Nor. FT-IR spectra of free ligand in KBr disk show that the peak at 1617 cm−1, assigned for pyridine stretch
Electronic spectra of the synthesized Cr(III) metal complex and the free ligand Nor were recorded in the range of 200–900 nm in solid state. Two bands have been found at 285 nm and 335 nm in case of free ligand. These two bands were assigned to
Thermal analysis of metal complex and free ligand was also studied starting from ambient temperature to 900°C with controlled heating rate of 10°C min−1 under oxygen atmosphere. The temperature ranges, percentage weight loss, eliminated moiety of every decomposition, and melting point are listed in Table
Thermogravimetric data of Nor and [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH.
Entry | Step | Temp. range (°C) | Weight loss (%) |
M. P (°C) |
---|---|---|---|---|
nor | First | 25–273 | 9.0 | 221 |
Second | 273–579 | 70.63 | ||
Third | 579–727 | 20.25 | ||
|
||||
[Cr(Nor)(Bipy)Cl2]Cl·2CH3OH | First | 31–101 | 2.82 | 372 |
second | 101–304 | 3.78 | ||
Third | 304–508 | 47.31 | ||
Fourth | 508–902 | 17.47 |
TGA pattern of (a) Nor and (b) [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH.
It has been also observed that the melting point of the synthesized complex (372°C) is more than that of parent quinolone (221°C). From the above thermal study, it is obvious that the synthesized complex is more thermally stable than its parent ligand Nor.
A single crystal suitable for X-ray diffraction for compound [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH was mounted on a capillary tube for indexing and intensity data collection at 183(2) K on an Oxford Xcalibur CCDC single-crystal diffractometer (MoKα radiation,
Single crystal X-ray crystallographic data for compound [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH.
Empirical formula | C28H34Cl3CrFN5O5 |
|
2 |
Formula weight | 697.95 |
|
1.532 |
Crystal system | Triclinic |
|
0.696 |
Space group |
P-1 |
Reflection collected | 15448 |
|
10.6127 (6) | Unique (Rint) | 4711 |
|
12.0733 (7) | Observed |
|
|
13.5624 (8) | Parameters | 400 |
|
68.548 (5) | Gof | 1.035 |
|
69.524 (5) |
|
0.0519 |
|
85.285 (4) |
|
0.1352 |
|
1513.10 (15) |
[a]
In the synthesised complex [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH, Nor behaves as a bidentate ligand and is coordinated to Cr (III) through pyridone oxygen and one of the carboxylate oxygen atoms. The crystal structure is shown in Figure
Bond lengths (Å) and angles (°) of [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH around Cr(III).
Angles | (Å) | Bonds | (°) |
---|---|---|---|
Cl1–Cr1–Cl2 | 177.51(4) | Cr1–N1 | 2.067(3) |
Cl1–Cr1–O1 | 90.55(8) | Cr2–N2 | 2.052(3) |
Cl2–Cr1–O2 | 88.92(8) | Cr1–O1 | 1.944(2) |
Cl1–Cr1–N1 | 90.03(8) | Cr1–O2 | 1.934(2) |
N2–Cr1–Cl2 | 90.58(8) | Cr1–Cl1 | 2.3288(10) |
N1–Cr1–N2 | 78.63(10) | Cr1–Cl2 | 2.3284(10) |
O2–Cr1–N1 | 171.10(10) | ||
O1–Cr1–N2 | 174.03(10) |
ORTEP diagram (50% probability factor for thermal ellipsoid) of the molecule [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH; color code: carbon: grey; nitrogen: blue; oxygen: red; fluorine: green; chlorine: dark green; chromium: orange (only hydrogen atoms were not shown for clarity).
Further details on the crystal structure data may be obtained from Cambridge data base, Oxford, on quoting the depository number
Antifungal activity of the free ligand and the complex against selected four pathogenic fungi
Percentage inhibition of (a) Nor, (b) bipy, and (c) [Cr(Nor)(Bipy)Cl2]Cl·2CH3OH against PA, SR, RS, and RB.
The synthesis and the characterization of neutral mononuclear mixed ligand metal complex of Nor and Bipy with Cr(III) metal ion have been realized with physicochemical and spectroscopic method. Nor coordinated with Cr(III) in a monodentate way and possesses distorted octahedral geometry. The complex shows more activity as compared with the standard ligand indicating that metal complexation enhances the activity of the parent ligand; this may be explained by chelation theory [
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to acknowledge University Grant Commission (UGC), Delhi, for financial support, National Centre of Integrative Pest Management, Pusa, for the screening of the drugs, and Department of Chemistry, University of Delhi, for providing instrumental facilities.