Influence of terminal substitution on structural, DNA, Protein binding, anticancer and antibacterial activities of palladium(ii) complexes containing 3-methoxy salicylaldehyde-4(N) substituted thiosemicarbazones

Abstract

The variable chelating behavior of 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones was observed in equimolar reactions with [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various analytical, spectroscopic techniques (mass, (1)H-NMR, absorption, IR). All the new complexes were structurally characterized by single crystal X-ray diffraction. Crystallographic results showed that the ligands H(2)L(1) and H(2)L(4) are coordinated as binegative tridentate ONS donor ligands in the complexes 1 and 4 by forming six and five member rings. However, the ligands H(2)L(2) and H(2)L(3) bound to palladium in 2 and 3 as uninegative bidentate NS donors by forming a five member chelate ring. From this study, it was found that the substitution on terminal 4(N)-nitrogen may have an influence on the chelating ability of thiosemicarbazone. The presence of hydrogen bonding in 2 and 3 might be responsible for preventing the coordination of phenolic oxygen to the metal ion. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic binding mode of DNA has been proposed. The protein binding studies were monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using Lysozyme as model protein. Antibacterial activity studies of the complexes have been screened against pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. MIC50 values of the complexes showed that they exhibited significant activity against the pathogens and among them, 3 exhibited higher activity. Further, anticancer activity of the complexes on the lung cancer cell line A549 has also been studied.

DNA(CT), protein(BSA) binding studies, anti-oxidant and cytotoxicity studies of new binuclear Ni(II) complexes containing 4(N)-substituted thiosemicarbazones

“…It is further confirmed with the upfield shift of 33-50 cm -1 for ν (C-O) [41,42] . An azomethine nitrogen ν (C=N) band appeared at the region 1536-1593 cm -1 in the ligands has been shifted to higher frequency in all the complexes (1592-1611 cm -1 ) indicating the coordination of azomethine nitrogen atoms [41].…”

“…In the spectra of (H 2 L) 1-4 , a sharp singlet corresponding to the phenolic -OH group has appeared at δ 11.34-11.76 ppm. However, this singlet completely disappeared in all the complexes confirmed the involvement of phenolic oxygen in coordination [41,43,46]. The spectra of (H 2 L) [1][2][3][4] showed a singlet at δ 9.13-10.0 ppm corresponding to (N(2)H-C=S) group [41,43], but in the complexes 1-4 there was no resonance attributable to N(2)H, indicating the coordination of thiolate sulphur atom of the ligand in the anionic form after deprotonation at N(2) [41,46].…”

“…An azomethine nitrogen ν (C=N) band appeared at the region 1536-1593 cm -1 in the ligands has been shifted to higher frequency in all the complexes (1592-1611 cm -1 ) indicating the coordination of azomethine nitrogen atoms [41]. A sharp band appeared at 771-795 cm −1 corresponding to a ν C=S vibration in the ligands disappeared completely in all the complexes and a new band appeared around 731-738 cm −1 corresponding to a possible ν C-S vibration, indicating coordination of a thiolate sulphur atom after enolisation followed by deprotonation [41][42][43].…”

Synthesis, characterization and thermal behavior of copper(II) complexes with pyridoxal thiosemi (PLTSC)- and S-methylisothiosemicarbazone (PLITSC)

“…1630 cm -1 , which is assigned to m(C=N) vibration of azomethine group, is as a rule shifted toward higher energy, compared to its position in spectrum of the free ligand (1618 cm -1 ) [11,23,24]. Furthermore, mostly positive shift is found for m(C-O) band, located in the 1250-1320 cm -1 range [25,26]. These shifts indicate that PLTSC in complexes 1, 1a, 2, 2a and 3 and PLITSC in 4 are coordinated via phenolic oxygen and azomethine nitrogen.…”

New N(4)-methylthiosemicarbazone derivatives: Synthesis, characterization, structural properties, DNA interactions and antiproliferative activity

“…The discovery of the antiviral, antibacterial and antitumor activities of the thiosemicarbazone ligands has stimulated numerous investigation concerning synthesis, characterization and biological relevance of such compounds [1][2][3][4][5][6]. Thiosemicarbazones belong to a large group of thiourea derivatives, whose biological activities are a function of parent aldehyde or ketone moiety [7,8].…”