The Pd (II) complexes with a series of halosubstituted benzylamine ligands (BLs) have been synthesized and characterized with different spectroscopic technique such as FTIR, UV/Vis, LCMS, 1H, and 13C NMR. Their molecular sustainability in different solvents such as DMSO, DMSO : H2O, and DMSO : PBS at physiological condition (pH 7.2) was determined by UV/Vis spectrophotometer. The
After a tremendous discovery of cisplatin, the synthesis and biological evaluation of new transition metal-based compounds are fields of growing interest [
The aim of this paper is to synthesize new series of palladium (II) complexes and evaluate their
Palladium dichloride (PdCl2), benzylamine ligands (BLs), DMSO, and ethanol (>99.5%) were purchased from Sigma Aldrich and used without further modifications. Elemental analysis was made with a Euro vector CHN analyzer, and UV/Vis spectra were recorded with a Spectro 2060 plus spectrophotometer over 200–600 nm in a 1 cm path length cuvette. FTIR (Perkin Elmer) spectra were taken with KBr palate where polystyrene thin film was used as a calibration standard. 1H and 13C NMR spectra were recorded in DMSO-d6 (NMR, 99.99%) with a Bruker-Biospin Avance-III 500 MHz FT-NMR spectrometer. Mass spectra were obtained with PE SCIEX API 165 with +
Initially, PdCl2 and BLs (molar ratio 1 : 2, resp.) were separately dissolved in freshly prepared solvent (absolute ethanol and Milli-Q water in 1 : 1.5) using 1 MLH magnetic stirrer. Then, the BLs solutions were added dropwise to metal compound solution with continuous stirring at room temperature. After 10 h, the mixture turned from light red brown to greenish color and after 16 h, precipitates were formed. The precipitates were filtered off, washed several times with chilled water/ethanol in 1 : 1 ratio, and kept overnight in vacuum oven at room temperature for absolute dryness.
Electronic spectra were recorded with a Spectro 2060 plus model UV/Vis spectrophotometer from 200 to 600 nm using 1 cm path length cuvette. DMSO was used for solution preparation. The stability of compounds was determined by preparing a solution in DMSO, DMSO/water, and DMSO/phosphate buffer of pH 7.2. Buffer solution was prepared by adding 70 mL 0.1 M aqueous NaOH solution to 0.1 M aqueous KH2PO4 solution. The pH of the resultant buffer was checked with RS-232 modelled CyberScan pH 2100, EUTECH pH meter instrument. Their concentration for the UV study with DMSO, DMSO : water, and DMSO : PBS was kept constant at 1 × 10−3 M.
The TEM images of the Pd2MBA were taken by HRTEM Jeol Jem 2100 at different magnification. The sample analysis was done by dispersing the sample in water and then dropped on carbon coated copper grid. After complete dryness of the sample on grid, the grid was inserted in specimen and then the images were taken.
The synthesized palladium (II) complexes tested against 6 microbes for their biological potential. They screened their antibacterial activities against human pathogenic bacteria, namely, Gram-negative (
Antioxidant activities have been studied on free radical scavenging of stable 1-2, 5- diphenyl-2-picrylhydrazyl (DPPH•). For this purpose stock solution of complexes and DPPH• (0.002%) were mixed in DMSO + water (1 : 1) for Pd (II) complexes. For sample preparation, the DPPH• solution was mixed with a complex solution in 1 : 1, followed by vigorous shaking, and thereafter kept for incubation of 30 min in dark. The UV absorbance was measured at 517 nm with UV/Vis spectrophotometer and a decrease in DPPH• absorbance was noted which indicates a radical-scavenging activity calculated with the following equation:
PdCl(BLs)2 have been synthesized allowing reaction of PdCl2 with different BLs (Figure
Structures of the ligands (L = BLs).
The 3300 to 3119 cm−1 stretching frequencies inferred presence of NH2 of benzylamine ligands in the complexes and similarly from 1497 to 1453 cm−1 predicted C=C in phenyl ring. The 495.92 to 438.78 cm−1 and 380–348 cm−1 bands indicate the Pd–N and Pd–Cl bands, respectively [
Structure of synthesized Pd (II) complexes.
To investigate a solid state structure retained in solution, the UV/Vis spectral behaviour was investigated in DMSO and DMSO + water as well as in DMSO + phosphate buffer for PdCl(BLs)2. The overall patterns of spectra for complexes solution were found similar to different mediums to ensure their molecular sustainability in different solvents. The absorption spectrum consists of a band at 400 nm and may be assigned as
UV spectra of Pd (II) complexes in DMSO at 0.001 M.
UV spectra of Pd (II) complexes in DMSO : water.
UV spectra of Pd (II) complexes in DMSO : phosphate buffer at 7.2 pH.
The TEM images reports from the SAED pattern were taken at different magnification suggesting the presence of different elements which are semicrystalline and homogeneous in shape (Figure
SAED pattern of Pd2MBA.
Biological evaluation was made by Kirby Beurs Disc Diffusion Method as per standard procedure [
Antimicrobial activity of Pd (II) complexes.
Complexes | Gram-positive bacteria | Gram-negative bacteria | Fungi (yeast) | Fungi (mould) | ||
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Pd2CBA | 5.25 | 7.76 | 7.98 | 6.99 | — | — |
Pd3CBA | 6.98 | 8.23 | 9.1 | 8.09 | — | — |
Pd4CBA | 7.79 | 8.15 | 8.76 | 6.27 | — | — |
Chloramphenicol | 28.67 | 24.44 | 29.63 | 26.30 | NA | NA |
Ciprofloxacin | 21.11 | 22.23 | 22.33 | 21.34 | NA | NA |
Amphotericin-B | NA | NA | NA | NA | 14.23 | 15.34 |
Antimicrobial studies of Pd (II) complexes.
The scavenging activities have been investigated to support the biological potential of PdCl(BLs)2 [
Free radical-scavenging activities of synthesized complexes.
The highest 94.49, 72.36, and 70.79% for Pd2CBA, Pd3CBA, and Pd4CBA, respectively, inferred Pd2CBA a strong antioxidant among them. The obtained values also compared with the control ascorbic acid which inferred that the results are very closer to control range. Thus, the antioxidant activities of Pd complexes have inferred their significance in medicinal as well as material sciences.
Genome studies have provided a better understanding of the closer distance between the microbial kingdom and the human species. The synthesized PdCl(BLs)2 complexes showed selective and moderate activity against different microbes and the interesting results were obtained for Gram-positive species, which are common in the environment. Apart from their microbial studies, the complexes have also expressed significant free radical-scavenging activities acting as antioxidants and could be used for medicinal purposes. However, in present study, we have focused on their antimicrobial and antioxidant activities and their other activities relevant to medical, biophysical, and biochemical processes are being pursued. The anticancer activity on suitable cell line against solid tumours, apoptosis, and DNA binding studies are under progress.
The authors declare that there are no competing interests regarding the publication of this paper.
The authors are thankful to Central University of Gujarat, Gandhinagar, for financial and infrastructural support and experimental facilities.