Novel fluorescence palladium-alkoxime complexes: Synthesis, characterization, DNA/BSA spectroscopic and docking studies, evaluation of cytotoxicity and DNA cleavage mechanism

Binuclear palladacycles with ionisable and non-ionisable tethers as anticancer agents

The search for novel anticancer agents to replace the current platinum-based treatments remains an ongoing process. Palladacycles have shown excellent promise as demonstrated by our previous work which yielded BTC2, a binuclear palladadycle with a non-ionisable polyethylene glycol (PEG) tether. Here, we explore the importance of the PEG-tether length on the anticancer activity of the binuclear palladacycles by comparing three analogous binuclear palladacycles, BTC2, BTC5 and BTC6, in the oestrogen receptor positive MCF7 and triple-negative MDA-MB-231 breast cancer cell lines. In addition, these are compared to another analogue with an ionisable morpholine tether, BTC7. Potent anticancer activity was revealed through cell viability studies (MTT assays) revealed that while BTC6 showed similar potent anticancer activity as BTC2, it was less toxic towards non-cancerous cell lines. Interestingly, BTC7 and BTCF were less potent than the PEGylated palladacycles but showed significantly improved selectivity towards the triple-negative breast cancer cells. Cell death analysis showed that BTC7 and BTCF significantly induced apoptosis in both the cancer cell lines while the PEGylated complexes induced both apoptosis and secondary necrosis. Furthermore, experimental and computational DNA binding studies indicated partial intercalation and groove binding as the modes of action for the PEGylated palladacycles. Similarly, experimental and computational BSA binding studies indicated and specific binding sites in BSA dependent on the nature of the tethers on the complexes.

New anthracene-based Oxime-Palladium complexes loaded on albumin nanoparticles, in vitro cytotoxicity, mathematical release mechanism studies and biological macromolecules interaction investigation

In this research work, two new palladium complexes [trans-Pd(C15H10NOCH3)2]Cl2 (1) and [cis- Pd(C15H10NOCH3)(PPh3)2Cl]Cl (2) were synthesized using an alkoxyme ligand named isophethalaldoxime. Then structure characterization has been done by FT-IR and different NMR (1H, 13C and 31P) spectroscopy. Then, their interactions with biological macromolecules including deoxyribonucleic acid and bovine serum albumin were studied using various spectroscopic methods such as UV-Vis absorption, fluorescence emission spectroscopy and circular dichroism. The results showed the binding of the prepared complexes to the deoxyribonucleic acid via grooves and different binding sites of bovine serum albumin. Fluorescence emission data showed that the mechanism of extinction of albumin emission by these compounds is static. Competitive titration was performed on albumin with eosin-Y, ibuprofen and digoxin as site markers I, II and III. The antitumor activity and toxicity of these compounds were evaluated on cancer cell lines A549 (leukemia) and K562 by in-vitro cytotoxicity test. The IC50 values showed the good activity of these complexes in inhibiting cancer cells. In the last section, the release mechanism of synthesized complexes from albumin nanoparticles (BNPs) was investigated and theoretical calculations were performed that showed Korsmeyer-Peppas mechanism for complex (1) and Quadratic mechanism for complex (2).

The biguanide-sulfonamide derivatives: synthesis, characterization and investigation of anticholinesterase inhibitory, antioxidant and DNA/BSA binding properties

A number of new biguanidine-sulfonamide derivatives (1-16) were synthesized and their structures were characterized by spectroscopic and analytical methods. Crystal structures of the compounds 1, 4, 8, 10 and 14 were determined by single crystal X-ray diffraction studies. X-ray crystallographic data showed the π-electron delocalization through the biguanide units. The AChE and BChE cholinesterase inhibitor, DPPH antioxidant and DNA/BSA binding properties of the synthesized compounds were evaluated. Results of cholinesterase inhibitory properties have shown that the compounds containing electron-withdrawing (-F, -Cl) groups have higher AChE/BChE inhibitory and antioxidant activities. Compound 3 showed higher BChE inhibitory activity than tacrine with IC50 value of 28.4 µM. The compounds interact with DNA via minor groove binding mode. The compounds with a naphthyl group in its structure strongly binds with DNA/BSA biomolecules.Communicated by Ramaswamy H. Sarma.

bis[N-(4-Bromophenyl)pyridine-2-carboxamidato]palladium

We report the crystal structure of bis[N-(4-bromophenyl)pyridine-2-carboxamidato]Palladium (C1) which was isolated from the reaction of aqueous potassium tetrachloropalladate(II) and N-(4-bromophenyl)-pyridine-2-carboxamide in dichloromethane under nitrogen flow. The structure was characterised by the following spectroscopic methods 1H NMR, FT-IR and X-ray diffraction.

Exploring the interactions of acenaphthene with bovine serum albumin: Spectroscopic methods, molecular modeling and chemometric approaches

The interaction of acenaphthene (ACN), a widespread environmental pollutant, with bovine serum albumin (BSA) was explored using spectroscopic methods, molecular modeling and chemometric approaches. The multivariate curve resolution-alternating least squares (MCR-ALS) analysis decomposed the overlapped excitation-emission matrix (EEM) spectra of mixture of ACN and BSA successfully and extracted spectral profiles of pure BSA, ACN and BSA-ACN complex. Based on fluorescence quenching analysis, ACN quenched the inherent fluorescence of BSA remarkably via a static mechanism. The obtained value of binding constant (K_b = 3.82 × 10⁵ L mol^-1) revealed a high binding affinity of ACN to BSA which facilitates its distribution by blood circulation system. Furthermore, the binding parameters values revealed that one binding site in BSA was involved in BSA-ACN complex. FT-IR, UV-Vis and CD spectra showed that the conformation of BSA was altered in presence of ACN slightly. Molecular docking simulation suggested that ACN was located in the IA region of BSA and the main interactions between ACN and BSA, are van der Waals forces. The obtained results provide some insight into interactions between ACN and serum albumins at the molecular level.

Potent cyclometallated Pd(II) antitumor complexes bearing α-amino acids: synthesis, structural characterization, DNA/BSA binding, cytotoxicity and molecular dynamics simulation

A rational approach was adopted to design high-potential metal-based antitumor agents. A series of organometallic Pd(ii) complexes with a general formula of [Pd{κ2(C,C)-[(C6H4-2)PPh2]CH(CO)C6H4Ph-4}{κ2(N,O)}] (N,O = alanine (Pd-A), valine (Pd-V), leucine (Pd-L), l-isoleucine (Pd-I) and phenylalanine (Pd-F)) were prepared by cyclopalladation of the phosphorus ylide, bridge cleavage reaction and subsequent chelation of natural α-amino acids. The complexes were fully identified using IR and multinuclear 1H, 13C, 31P NMR spectroscopic methods. X-ray crystallography exhibited that the Pd(ii) atom is located in a slightly distorted square-planar environment surrounded by C,C-orthometallated phosphorus ylide as well as NO-pendant amino acid functionality. In vitro cytotoxicity evaluation of new cyclometallated Pd(ii) complexes toward a human leukemia (K562) cancer cell line indicated promising results. The highest cytotoxic activity was discovered in the case of phenylalanine (CH2C6H5). IC50 values of this complex on a panel of human tumor cell lines representative of liver (HepG2), breast (SKBR-3), and ovarian (A2780-Resistance/Sensitive) cancers also indicated promising antitumor effects in comparison with standard cisplatin. The binding interaction ability of the phenylalanine-containing orthopalladated complex, as the most efficient compound, with calf-thymus deoxyribonucleic acid (CT-DNA) and bovine serum albumin (BSA) was investigated. UV-Vis spectroscopy, competitive emission titration, and circular dichroism (CD) techniques demonstrated the intercalative binding of the Pd(ii) complex with DNA. Molecular docking studies also fully agreed with the experimental data. Examination of the reactivity towards the protein BSA revealed that the static quenching mechanism of BSA intrinsic fluorescence by the Pd(ii) complex with a binding constant (Kb) of ∼105 is indicative of the high affinity of the complex. The competitive binding experiment using site markers with definite binding sites demonstrated that the hydrophobic cavities of site I (subdomain IIA) are responsible for the bimolecular interaction between protein BSA and the complex. Molecular docking studies effectively confirmed the significance of hydrophobic interactions in Pd(ii)-BSA binding. The results of this study could greatly contribute to exploring new potent metal-based anticancer drugs.

Role of π-conjugation on the coordination behaviour, substitution kinetics, DNA/BSA interactions, and in vitro cytotoxicity of carboxamide palladium(II) complexes

Treatments of N-(pyridin-2-ylmethyl)pyrazine-2-carboxamide (L1), N-(quinolin-8-yl)pyrazine-2-carboxamide (L2), N-(quinolin-8-yl)picolinamide (L3) and N-(quinolin-8-yl)quinoline-2-carboxamide (L4) with [PdCl2(NCMe)]2 afforded the corresponding Pd(ii) complexes, [Pd(L1)Cl] (PdL1); [Pd(L2)Cl] (PdL2); [Pd(L3)Cl] (PdL3); and [Pd(L4)Cl] (PdL4) in moderate yields. Structural characterisation of the compounds was achieved by NMR and FT-IR spectroscopies, elemental analyses and single crystal X-ray crystallography. The solid-state structures of complexes PdL2-PdL4 established the presence of one tridentate carboxamide and Cl ligands around the Pd(ii) coordination sphere, to give distorted square planar complexes. Electrochemical investigations of PdL1-PdL4 showed irreversible one-electron oxidation reactions. Kinetics reactivity of the complexes towards bio-molecules, thiourea (Tu), l-methionine (L-Met) and guanosine 5'-diphosphate disodium salt (5'-GMP) decreased in the order: PdL1 > PdL2 > PdL3 > PdL4, in tandem with the density functional theory (DFT) data. The complexes bind favourably to calf thymus (CT-DNA), and bovine serum albumin (BSA), and the order of their interactions agrees with the substitution kinetics trends. The in vitro cytotoxic activities of PdL1-PdL4 were examined in cancer cell lines A549, PC-3, HT-29, Caco-2, and HeLa, and a normal cell line, KMST-6. Overall, PdL1 and PdL3 displayed potent cytotoxic effects on A549, PC-3 HT-29 and Caco-2 comparable to cisplatin. All the investigated complexes exhibited lower toxicity on normal cells than cisplatin.

BSA nanoparticles as controlled release carriers for isophethalaldoxime palladacycle complex; synthesis, characterization, in vitro evaluation, cytotoxicity and release kinetics analysis

BSA nanoparticles were synthesized as a biodegradable carrier by the desolvation method.