Probing the antibacterial and anticancer potential of tryptamine based mixed ligand Schiff base Ruthenium(III) complexes

Development of new chemotherapeutic agents to treat microbial infections and recurrent cancers is of pivotal importance. Metal based drugs particularly ruthenium complexes have the uniqueness and desired properties that make them suitable candidates for the search of potential chemotherapeutic agents. In this study, two mixed ligand Ru(III) complexes [Ru(Cl)₂(SB)(Phen] (RC-1) and [Ru(Cl)₂(SB)(Bipy)] (RC-2) were synthesised and characterized by elemental analysis, IR, UV–Vis, ¹H, ¹³C NMR spectroscopic techniques and their molecular structure was confirmed by X-ray crystallography. Antibacterial activity evaluation against two Gram-positive (S. pneumonia and E. faecalis) and four Gram-negative strains (P. aurogenosa, K. pneumoniae, S. enterica, and E. coli) revealed their moderate antibacterial activity with MIC value of ≥250 μg/mL. Anticancer activity evaluation against a non-small lung cancer cell line (H1299) revealed the tremendous anticancer activity of these complexes which was further validated by DNA binding and docking results. DNA binding profile of the complexes studied by UV–Visible and fluorescence spectroscopy showed an intercalative binding mode with CT-DNA and an intrinsic binding constant in the range of 3.481–1.015× 10⁵ M⁻¹. Both the complexes were also found to exert weak toxicity to human erythrocytes by haemolytic assay compared to cisplatin. Potential of these complexes as anticancer agents will be further delineated by in vivo studies.     

Molecular docking,QSAR properties and DNA/BSA binding,anti-proliferative studies of 6-methoxy benzothiozole imine base and its metal complexes

Abstract

The molecular and QSAR (Quantitative Structure–Activity Relationship) properties of title compound 2-((6-Methoxybenzo[d]thiazol-2-ylimino)methyl)-6-ethoxyphenol (HL) were evaluated employing HyperChem 7.5 tools. The interaction of the 1a–1e complexes of HL with calf thymus DNA (CT-DNA) was investigated by absorption titrations, Fluorescence quenching and viscosity measurements. The experimental data suggest that these complexes bind to CT-DNA through an intercalative mode, wherein DNA-binding affinity of 1e is found to be greater compared to other complexes. The tryptophan emission-quenching with bovine serum albumin (BSA) experiment revealed stronger binding of 1e than other complexes in the hydrophobic region of protein. The photocleavage of plasmid pBR322 DNA investigated in the presence of the title complexes inferred conversion of supercoiled form of DNA plasmid to circular nicked form. Free-radical scavenging activity studies of HL and its metal complexes determined by their interaction with the stable free-radical DPPH have shown promising antioxidant property. Further cytotoxicity studies with HeLa and MCF-7 cell lines indicated that the compounds can efficiently inhibit the cell proliferation in a dose dependent manner. The DAPI staining assay studies revealed the higher potency of 1e to induce apoptosis. Abbreviations BSA Bovine serum albumin protein

CT-DNA Calf thymus DNA

DMSO Dimethyl sulfoxide

DAPI 4′,-6-Diamidino-2-phenylindole dihydrochloride

ESI–MS Electrospray ionization mass spectrometry

IC₅₀ Half-maximal inhibitory concentration

MBTYE 2-((6-methoxybenzo[d]thiazol-2-ylimino) methyl)-6-ethoxyphenol

MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide

PBS Phosphate-buffered saline

Tris Tris(hydroxymethyl)aminomethane

Communicated by Ramaswamy H. Sarma     

Metal complexes of naphthoquinone based ligand: synthesis,characterization, protein binding,DNA binding/cleavage and cytotoxicity studies

Protein binding, DNA binding/cleavage and in vitro cytotoxicity studies of 2-((3-(dimethylamino)propyl)amino)naphthalene-1,4-dione (L) and its four coordinated M(II) complexes [M(II) = Co(II), Cu(II), Ni(II) and Zn(II)] have been investigated using various spectral techniques. The structure of the ligand was confirmed by spectral and single crystal XRD studies. The geometry of the complexes has been established using analytical and spectral investigations. These complexes show good binding tendency to bovine serum albumin (BSA) exhibiting high binding constant values (10⁵ M^?1) when compared to free ligand. Fluorescence titration studies reveal that these compounds bind strongly with CT-DNA through intercalative mode (K_app 10⁵ M^?1) and follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > L. Molecular docking study substantiate the strength and mode of binding of these compounds with DNA. All the complexes efficiently cleaved pUC18-DNA via hydroxyl radical mechanism and the Cu(II) complex degraded the DNA completely by converting supercoiled form to linear form. The complexes demonstrate a comparable in vitro cytotoxic activity against two human cancer cell lines (MCF-7 and A-549), which is comparable with that of cisplatin. AO/EB and DAPI staining studies suggest apoptotic mode of cell death, in these cancer cells, with the compounds under investigation.     

Synthesis and spectroscopic characterization study of new palladium complexes containing bioactive O,O-chelated ligands: evaluation of the DNA/protein BSA interaction,in vitro antitumoural activity and molecular docking

[Pd{(C,N)–C₆H₄CH₂NH(Et) (Qu)] (2) and [Pd{(C,N)–C₆H₄CH₂NH(Et) (Nar)] (3) (Qu = Quercetin, Nar = Naringin) mononuclear palladium (II) complexes have been synthesized and characterized using elemental analysis, IR and electronic spectroscopy. The interaction of the prepared complexes with calf thymus DNA and bovine serum albumin (BSA), monitored by UV–visible and fluorescence titrations, respectively, have been carried out to better understand the mode of their action under biological conditions. Intercalative binding mode between the complexes and DNA is suggested by the binding constant (K_b) values of 2.5 × 10⁶ and 3.2 × 10⁶ for complexes 2 and 3, respectively. In particular, the in vitro cytotoxicity of the complexes on two cancer cells lines (bladder carcinoma TCC and breast cancer MCF7) showed that the compounds had broad spectrum, anti-cancer activity with low IC₅₀ values and the order of in vitro anticancer activities is consistent with the DNA-binding affinities. In the meantime, the quenching of tryptophan emission with the addition of complexes using BSA as a model protein indicated the protein binding ability. The quenching mechanisms of BSA by the complexes were static processes, according to the results obtained. The competitive binding using Warfarin, Digoxin and Ibuprofen site markers, which contain definite biding sites, demonstrated that the complexes bind to site I on BSA. Ultimately, the binding sites of DNA and BSA with the complexes have been determined by molecular modelling studies.     

Design,synthesis, in vitro anticancer,antioxidant and antibacterial activity; DNA/BSA binding,photoleavage and docking studies of Cu(II) ternary metal complexes

Abstract

Three mononuclear, mixed ligand ternary Cu(II) complexes of 3-((Z)-1-(2-hydroxyphenylimino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (HEHMP) viz; [Cu-(Phen) (HEHMP)] (1a), [Cu-(Bpy)(HEHMP)] (1?b) and [Cu-Bpy(NCS)(HEHMP)] (1c) were synthesized and characterized by data obtained from various spectral techniques. The binding affinities of these complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) protein were explored by absorption and fluorescence quenching titrations. The results indicated strong affinity of the title compounds to bind with both CT-DNA and BSA. The antioxidant properties of the synthesized compounds evaluated by free-radical scavenging method using spectrophotometric technique indicated their affirmative potential activity. Gel electrophoresis experiments revealed the efficacy of metal complexes in resulting the cleavage of pBR322 supercoiled DNA. In vitro cytotoxicity studies of these complexes evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against HeLa and MCF-7 cancer cell lines indicated relatively high effectiveness of the complex 1c. Confocal microscopy signified the potential of the complexes to induce apoptosis in HeLa cell lines. In addition, the antibacterial activity of the compounds carried out by disc diffusion method revealed significantly enhanced antibacterial activity in Cu (II) ternary complexes compared to the activity of ligands in unbound form signifying the implicit role of metal ion in inducing lipophilic character.     

New bio-sensitive and biologically active single crystal of pyrimidine scaffold ligand and its gold and platinum complexes: DFT,antimicrobial, antioxidant,DNA interaction,molecular docking with DNA/BSA and anticancer studies

Novel gold and platinum complexes [AuL₂]·Cl, 1 and [PtL₂]·2Cl, 2 with ligand, 2-methoxy-6-((2-(4-(trifluoromethyl)pyrimidin-2-yl)hydrazono)methyl)phenol (HL) have been synthesized and screened for their antimicrobial, antioxidant, DNA binding and anticancer (in vitro) activities. The single crystal of ligand HL was obtained by slow evaporation technique. The molecular structure of HL was confirmed from single crystal X-ray technique. Density functional theory calculations have been performed to gain insights into the electronic structure of these metal complexes. Antimicrobial result shows that, HL and complexes (1 and 2) have good antimicrobial agents against E. coli (bacteria) and C. albicans (fungi) than others bacterial and fungal strains. Antioxidant assay results suggest that, HL and complexes (1 and 2) possess good radical scavenging activity against diverse free radicals (DPPH, SOD, NO and H₂O₂). The intercalative interactions of HL and complexes (1 and 2) with CT-DNA were confirmed from spectroscopic titrations and viscometric measurements. Furthermore, the interactions of prepared compounds with DNA were confirmed by molecular docking analysis. In order to understand the nature of interactions between these metal complexes and BSA protein results clearly shows that complex 1 binds better than that of complex 2. The antitumor activities of prepared products were tested against single normal and different tumor cell lines by MTT assay. These results reveal that prepared complexes (1 and 2) have significant cytotoxic effect against tumor cell lines.     

Impacts of hydrophobicity and ionicity of phendione-based cobalt(II)/(III) complexes on binding with bovine serum albumin

Abstract

For efficient designing of metallodrugs, it is imperative to analyse the binding affinity of those drugs with drug-carrying serum albumins to comprehend their structure–activity correlation for biomedical applications. Here, cobalt(II) and cobalt(III) complexes comprising three phendione ligands, [Co(phendione)₃]Cl₂ (1) and [Co(phendione)₃]Cl₃ (2), where, phendione = 1,10-phenanthroline-5,6-dione, has been chosen to contrast the impact of their hydrophobicity and ionicity on binding with bovine serum albumin (BSA) through spectrophotometric titrations. The attained hydrophobicity values using octanol/water partition coefficient method manifested that complex 1 is more hydrophobic than complex 2, which could be attributed to lesser charge on its coordination sphere. The interaction of complexes 1 and 2 with BSA using steady state fluorescence studies revealed that these complexes quench the intrinsic fluorescence of BSA through static mechanism, and the extent of quenching and binding parameters are higher for complex 2. Further thermodynamics of BSA-binding studies revealed that complexes 1 and 2 interact with BSA through hydrophobic and hydrogen bonding/van der Waals interactions, respectively. Further, UV–visible absorption, circular dichroism and synchronous fluorescence studies confirmed the occurrence of conformational and microenvironmental changes in BSA upon binding with complexes 1 and 2. Molecular docking studies have also shown that complex 2 has a higher binding affinity towards BSA as compared to complex 1. This sort of modification of ionicity and hydrophobicity of metal complexes for getting desirable binding mode/strength with drug transporting serum albumins will be a promising pathway for designing active and new kind of metallodrugs for various biomedical applications.

Communicated by Ramaswamy H. Sarma     

Norfloxacin Zn(II)-based complexes: acid base ionization constant determination, DNA and albumin binding properties and the biological effect against Trypanosoma cruzi

Zn(II) complexes with norfloxacin (NOR) in the absence or in the presence of 1,10-phenanthroline (phen) were obtained and characterized. In both complexes, the ligand NOR was coordinated through a keto and a carboxyl oxygen. Tetrahedral and octahedral geometries were proposed for [ZnCl₂(NOR)]·H₂O (1) and [ZnCl₂(NOR)(phen)]·2H₂O (2), respectively. Since the biological activity of the chemicals depends on the pH value, pH titrations of the Zn(II) complexes were performed. UV spectroscopic studies of the interaction of the complexes with calf-thymus DNA (CT DNA) have suggested that they can bind to CT DNA with moderate affinity in an intercalative mode. The interactions between the Zn(II) complexes and bovine serum albumin (BSA) were investigated by steady-state and time-resolved fluorescence spectroscopy at pH 7.4. The experimental data showed static quenching of BSA fluorescence, indicating that both complexes bind to BSA. A modified Stern–Volmer plot for the quenching by complex 2 demonstrated preferential binding near one of the two tryptophan residues of BSA. The binding constants obtained (K _b ) showed that BSA had a two orders of magnitude higher affinity for complex 2 than for 1. The results also showed that the affinity of both complexes for BSA was much higher than for DNA. This preferential interaction with protein sites could be important to their biological mechanisms of action. The analysis in vitro of the Zn(II) complexes and corresponding ligand were assayed against Trypanosoma cruzi, the causative agent of Chagas disease and the data showed that complex 2 was the most active against bloodstream trypomastigotes.     

(Arene)Cl₂Ru(II) complexes with N-coordinated estrogen and androgen isonicotinates: interaction with sex hormone binding globulin and anticancer activity

(Arene)dichloridoruthenium(II) complexes with N-coordinated isonicotinates of androgens (6) and estrogens (9) were prepared and tested for affinity to the estrogen receptor (ERα) and sex hormone binding globulin (SHBG), as well as for cytotoxicity in cancer cells. None of the new complexes bound noticeably to the ER and most of them also bound less strongly to SHBG than the corresponding unmetallated steroids 7. In MTT assays the Ru(p-cymene) complexes 9 of 2-substituted estrones were equally or even more cytotoxic than the metal-free steroids against hormone-dependent (MCF-7 breast and KB-V1 cervix carcinomas) and hormone-independent (518A2 melanoma) cells. The addition of external SHBG to MTT assays lowered the cytotoxicities of the complexes 9 and distinctly more so those of some steroids 7, probably by the way of sequestration and reduction of the cellular uptake. In the absence of SHBG the estrogen complexes 9 were internalized by 518A2 melanoma cells and ruthenated their DNA as quantified by ICP-OES. They also ruthenated salmon sperm DNA but did not change the topology of plasmid DNA in EMSA experiments. In addition, the Ru(p-cymene) complex of 2-ethoxyestrone (9c) was shown to reduce the motility of 518A2 melanoma cells in a wound-healing assay.     

Biological evaluation,molecular docking and DNA interaction studies of coordination compounds gleaned from a pyrazolone incorporated ligand

Abstract

In this work, we have synthesized a few novel mononuclear complexes of Cu(II), Co(II), Ni(II) and Zn(II) using a pyrazolone-derived Schiff base ligand. They were characterized by spectroscopic and analytical methods. The elemental analyses, UV-Vis, magnetic moment values and molar conductance of the complexes reveal that the complexes adopt an octahedral arrangement around the central metal ions. The interaction of complexes with CT-DNA was studied by absorption spectral titration and viscosity measurements. The observed data show that the complexes bind with CT-DNA via an intercalation mode. Efficient pUC18 DNA cleavage ability of the synthesized compounds was explored by gel electrophoresis. The antimicrobial activity of these compounds against a set of bacterial and fungal strains reveals that the complexes exhibit better activity than the free ligand. Moreover, all the complexes were evaluated against two cancer (HeLa and HepG2) and one normal (NHDF) cell lines. The data were compared with cisplatin. Anti–inflammatory activity has been experimentally validated which proves that theoretical predictions concur with the experimental results. In addition, molecular docking studies have been performed to consider the nature of binding mode and binding affinity of these compounds with DNA (1BNA) and protein (3hb5). These studies reveal that the mode of binding is intercalation and the complexes have higher binding energy scores than the free ligand.     

Synthesis,characterization, redox behavior,DNA and protein binding and antibacterial activity studies of ruthenium(II) complexes of bidentate schiff bases

Two new ruthenium(II) complexes of Schiff base ligands (L) derived from cinnamaldehyde and ethylenediamine formulated as [Ru(L)(bpy)₂](ClO₄)₂, where L¹ = N,N’-bis(4-nitrocinnamald-ehyde)ethylenediamine and L² = N,N’-bis(2-nitrocinnamaldehyde)-ethylenediamine for complex 1 and 2, respectively, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of the complexes with calf thymus DNA (CT-DNA) using absorption, emission spectral studies and electrochemical techniques have been used to determine the binding constant, K_b and the linear Stern–Volmer quenching constant, K_SV. The results indicate that the ruthenium(II) complexes interact with CT-DNA strongly in a groove binding mode. The interactions of bovine serum albumin (BSA) with the complexes were also investigated with the help of absorption and fluorescence spectroscopy tools. Absorption spectroscopy proved the formation of a ground state BSA-[Ru(L)(bpy)₂](ClO₄)₂ complex. The antibacterial study showed that the Ru(II) complexes (1 and 2) have better activity than the standard antibiotics but weak activity than the ligands.     

Cobalt (II) complex with novel unsymmetrical tetradentate Schiff base (ON) ligand: in vitro cytotoxicity studies of complex,interaction with DNA/protein,molecular docking studies,and antibacterial activity

[C₂₀H₁₇N₃O₂] and cobalt (II) complex [Co(L²)(MeOH)₂].ClO₄, (L² = 4-((E)-1-((2-(((E)-pyridin-2-ylmethylene) amino) phenyl) imino) ethyl) benzene-1, 3-diol) novel Schiff base has been synthesiszed and chracterized by Fourier transform infrared, UV–vis, ¹H-NMR spectroscopy, and elemental analysis techniques. The interaction of Co(II) complex with DNA and BSA was investigated by electronic absorption spectroscopy, fluorescence spectroscopy, circular dichroism, and thermal denaturation studies. Our experiments indicate that this complex could strongly bind to CT-DNA via minor groove mechanism. In addition, fluorescence spectrometry of BSA with the complex showed that the fluorescence quenching mechanism of BSA was of static type. The complex exhibited significant in vitro cytotoxicity against three human cancer cell lines (JURKAT, SKOV3, and U87). The molecular docking experiment effectively proved the binding of complex to DNA and BSA. Finally, antibacterial assay over gram-positive and gram-negative pathogenic bacterial strains was studied.     

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

Iron(III) complexes [Fe(L)₂]Cl (1-3), where L is monoanionic N-salicylidene-arginine (sal-argH for 1), hydroxynaphthylidene-arginine (nap-argH for 2) and N-salicylidene-lysine (sal-lysH for 3), were prepared and their DNA binding and photo-induced DNA cleavage activity studied. Complex 3 as its hexafluorophosphate salt [Fe(sal-lysH)₂](PF₆)·6H₂O (3a) was structurally characterized by single crystal X-ray crystallography. The crystals belonged to the triclinic space group P-1. The complex has two tridentate ligands in FeN₂O₄ coordination geometry with two pendant cationic amine moieties. Complexes 1 and 2 with two pendant cationic guanidinium moieties are the structural models for the antitumor antibiotics netropsin. The complexes are stable and soluble in water. They showed quasi-reversible Fe(III)/Fe(II) redox couple near 0.6 V in H₂O-0.1 M KCl. The high-spin 3d⁵-iron(III) complexes with μ_eff value of ∼5.9 μ_B displayed ligand-to-metal charge transfer electronic band near 500 nm in Tris-HCl buffer. The complexes show binding to Calf Thymus (CT) DNA. Complex 2 showed better binding propensity to the synthetic oligomer poly(dA)·poly(dT) than to CT-DNA or poly(dG)·poly(dC). All the complexes displayed chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent and cleaved supercoiled pUC19 DNA to its nicked circular form. They exhibited photo-induced DNA cleavage activity in UV-A light and visible light via a mechanistic pathway that involves the formation of reactive hydroxyl radical species.     

Synthesis and biological evaluation of pyrazole linked benzothiazole-β-naphthol derivatives as topoisomerase I inhibitors with DNA binding ability

A series of new pyrazole linked benzothiazole-β-naphthol derivatives were designed and synthesized using a simple, efficient and ecofriendly route under catalyst-free conditions in good to excellent yields. These derivatives were evaluated for their cytotoxicity on selected human cancer cell lines. Among those, the derivatives 4j, 4k and 4l exhibited considerable cytotoxicity with IC₅₀ values ranging between 4.63 and 5.54?µM against human cervical cancer cells (HeLa). Structure activity relationship was elucidated by varying different substituents on benzothiazoles and pyrazoles. Further, flow cytometric analysis revealed that these derivatives induced cell cycle arrest in G2/M phase and spectroscopic studies such as UV–visible, fluorescence and circular dichroism studies showed that these derivatives exhibited good DNA binding affinity. Additionally, these derivatives can effectively inhibit the topoisomerase I activity. Viscosity studies and molecular docking studies demonstrated that the derivatives bind with the minor groove of the DNA.     

Reassessing buried surface areas in protein–protein complexes

The buried surface area (BSA), which measures the size of the interface in a protein–protein complex may differ from the accessible surface area (ASA) lost upon association (which we call DSA), if conformation changes take place. To evaluate the DSA, we measure the ASA of the interface atoms in the bound and unbound states of the components of 144 protein–protein complexes taken from the Protein–Protein Interaction Affinity Database of Kastritis et al. (2011). We observe differences exceeding 20%, and a systematic bias in the distribution. On average, the ASA calculated in the bound state of the components is 3.3% greater than in their unbound state, and the BSA, 7% greater than the DSA. The bias is observed even in complexes where the conformation changes are small. An examination of the bound and unbound structures points to a possible origin: local movements optimize contacts with the other component at the cost of internal contacts, and presumably also the binding free energy.     

Example of two novel thiocyanato bridged copper (II) complexes derived from substituted thiosemicarbazone ligand: structural elucidation,DNA/albumin binding,biological profile analysis,and molecular docking study

Two novel copper (II) substituted thiosemicarbazone Schiff base complexes [Cu(L₁)(µ-SCN)]_n(NO₃)₂ (1) and [Cu₂(µ-SCN)(SCN)(L₂)₂](NO₃) (2) have been synthesized by condensing substituted thiosemicarbazides like 4-methyl-3-thiosemicarbazide or 4-ethyl-3-thiosemicarbazide with 2-acetylpyridine. Both the metal complexes 1 and 2 are characterized using different spectroscopic techniques like IR, UV-Vis, ESR spectroscopy followed by elemental analysis, cyclic voltammetric measurement and single crystal X-ray structure analysis. X-ray crystal structure analysis reveal that complex 1 is polymeric while complex 2 is dimeric in nature. The coordination geometry around Cu(II) are square pyramidal in which thiosemicarbazone Schiff base ligand coordinate to the central Cu(II) atom in tridentate fashion. The prominent interaction patterns of 1 and 2 with CT-DNA were examined by employing electronic absorption and emission spectral titrations, cyclic voltammetry and viscosity measurements. All the results show that CT-DNA binds with both copper (II) complexes 1 and 2. Furthermore, protein binding ability in vitro of complexes 1 and 2 with both BSA and HSA were carried out using multispectroscopic techniques and a static quenching pattern was observed in both cases. Molecular docking study was employed to ascertain the exact mechanism of action of 1 and 2 with DNA and protein molecules (BSA and HSA). In vitro cytotoxicity activity of complexes 1 and 2 toward AGS and A549 was evaluated using MTT assay which demonstrates that both complexes 1 and 2 have superior prospectus to act as anticancer agents.

Communicated by Ramaswamy H. Sarma     

Synthesis,characterization, DNA and HSA binding studies of isomeric Pd (II) antitumor complexes using spectrophotometry techniques

Two new Palladium(II) isomeric complexes, [Pd (Gly)(Leu)](I) and [Pd (Gly)(Ile)](II), where Gly is glycine, and Leu and Ile are isomeric amino acids (leucine and isoleucine), have been synthesized and characterized by elemental analysis, molar conductivity measurements, FT-IR, ¹H NMR, and UV–Vis. The complexes have been tested for their In vitro cytotoxicity against cancer cell line K₅₆₂ and their binding properties to calf thymus DNA (CT-DNA) and human serum albumin (HSA) have also been investigated by multispectroscopic techniques. Interactions of these complexes with CT-DNA were monitored using gel electrophoresis. The energy transfer from HSA to these complexes and the binding distance between HSA and the complexes (r) were calculated. The results obtained from these studies indicated that at very low concentrations, both complexes effectively interact with CT-DNA and HSA. Fluorescence studies revealed that the complexes strongly quench DNA bound ethidium bromide as well as the intrinsic fluorescence of HSA through the static quenching procedures. Binding constant (K_b), apparent biomolecular quenching constant (k_q), and number of binding sites (n) for CT-DNA and HSA were calculated using Stern–Volmer equation. The calculated thermodynamic parameters indicated that the hydrogen binding and vander Waals forces might play a major role in the interaction of these complexes with HSA and DNA. Thus, we propose that the complexes exhibit the groove binding with CT-DNA and interact with the main binding pocket of HSA. The complexes follow the binding affinity order of I > II with DNA- and II > I with HSA-binding.     

Topoisomerase II inhibition activity of new square planar Ni(II) complexes containing N-substituted thiosemicarbazones: Synthesis, spectroscopy, X-ray crystallography and electrochemical characterization

New Ni(II) thiosemicarbazone complexes containing triphenylphosphine namely [Ni(Sal-mtsc)(PPh₃)](2) and [Ni(Nap-mtsc)(PPh₃)] (3) (where Sal-mtsc = salicylaldehyde-N(4)-methylthiosemicarbazone and Nap-mtsc = 2-hydroxy-1-naphthaldehyde-N(4)-methylthiosemicarbazone) have been synthesised and characterized by elemental analysis, IR, electronic and ¹H NMR spectroscopy. The crystal structures of the complexes have been determined by single crystal X-ray diffraction technique. In all the complexes the thiosemicarbazone ligand coordinated to nickel through ONS mode. The electrochemical behavior of the complexes has been investigated by using cyclic voltammetry in acetonitrile. The new complexes were subjected to test their DNA topoisomerase II inhibition efficiency. The complex [Ni(Nap-mtsc)(PPh₃)] (3) showed 95% inhibition. The observed inhibition activity was found to be more potent than the activity of conventional standard Nalidixic acid.     

Impact of protein binding on the analytical detectability and anticancer activity of thymoquinone

Thymoquinone (TQ), an active component of Nigella sativa L., is known to have anti-cancer and anti-inflammatory effects; however, no studies on its analytical detection in serum and its protein binding have been published. Using high performance liquid chromatography analysis, we show that the average recovery of TQ from serum is 2.5% at 10 μg/ml of TQ and 72% at 100 μg/ml. The low recovery of TQ from serum is due to its extensive binding to plasma proteins, as more than 99% of TQ was bound within 30 min of incubation. The binding of TQ to the major plasma proteins, bovine serum albumin (BSA) and alpha −1 acid glycoprotein (AGP), was studied and found to be 94.5 ± 1.7% for BSA and 99.1 ± 0.1% for AGP. Mass spectrometric analysis revealed that TQ was bound covalently to BSA, specifically on Cyst-34. Using WST-1 proliferation assay, we showed that BSA plays a protective role against TQ-induced cell death; pre-incubation with BSA prevented TQ from exerting its anti-proliferative effects against DLD-1 and HCT-116 human colon cancer cells. On the other hand, binding of TQ to AGP did not alter its anti-proliferative activity against both cell lines. When TQ was pre-incubated with AGP prior to the addition of BSA, the activity of TQ against DLD-1 was maintained, suggesting that AGP prevented the binding of TQ to BSA. This is the first time the covalent binding and inhibitory effect of BSA on TQ is documented. These data offer new grounds for TQ future pharmacokinetic analysis in vivo.     

Template synthesis of novel carboxamide dinuclear copper (II) complex: spectral characterization and reactivity towards calf-thymus DNA

Dinuclear complexes Bis [aqua 1,8-(1,2-dicarboxamido benzene) 3,6-diazaoctane copper (II)/nickel (II)] tetrachloride (1 and 2) were synthesized by a two component one-pot metal template condensation between phthalic anhydride and 1,8-diamino 3,6-diazaoctane. Elemental analysis, molar conductance measurements, electronic absorption, infra-red, electron paramagnetic resonance, nuclear magnetic resonance, atomic absorption, and electron spray mass spectral studies have been performed to probe the nature and structure of the complexes. The interaction of copper (II) complex with calf thymus (CT-DNA) has been studied by using absorption, emission and circular dichoric spectral methods, viscometry, and cyclic voltammetry. A strong hyperchromism along with a red shift in UV bands and hypochromism in the ligand field band of the complex 1 on interaction with CT-DNA imply a covalent mode of DNA binding. This is further confirmed by studying the reactivity of complex 1 using circular dichroism and viscosity measurements. The variation in relative emission intensity of DNA-bound ethidium bromide observed upon treatment with the complex 1 parallel the trend of DNA binding studies. Cyclic voltammetry studies reveal that the complex 1 prefers to bind to DNA in Cu(II) rather than Cu(I) oxidation state.