Kinetics, mechanism and equilibrium studies on the substitution reactions of Pd(II) in reference to Pt(II) complexes with bio-molecules

Influence of acid-base equilibrium on interactions of some monofunctional coumarin Pd(II) complexes with biologically relevant nucleophiles-comprehensive kinetic study

This aimed to develop a comprehensive theoretical protocol for examining substitution reaction processes. The researchers used a theoretical quantum-mechanical protocol based on the QM-ORSA approach, which estimates the kinetic parameters of thermodynamically favourable reaction pathways. This theoretical protocol was validated by experimentally investigating substitution mechanisms in two previously synthesised Pd(II) complexes: chlorido-[(3-(1-(2-hydroxypropylamino)ethylidene)chroman-2,4-dione)]palladium(II) (C1) and chlorido-[(3-(1-(2-mercaptoethylamino)-ethylidene)-chroman-2,4dione)]palladium(II) (C2), along with biologically relevant nucleophiles, namely L-cysteine (l-Cys), L-methionine (l-Met), and guanosine-5'-monophosphate (5'-GMP). Reactions were investigated under pseudo-first-order conditions, monitoring nucleophile concentration and temperature changes using stopped-flow UV-vis spectrophotometry. All reactions were conducted under physiological conditions (pH = 7.2) at 37 °C. The reactivity of the studied nucleophiles follows the order: l-Cys > l-Met > 5'-GMP, and the reaction mechanism is associative based on the activation parameters. The experimental and theoretical data showed that C2 is more reactive than C1, confirming that the complexes' structural and electronic properties greatly affect their reactivity with selected nucleophiles. The study's findings have confirmed that the primary interaction occurs with the acid-base species L-Cys, mostly through the involvement of the partially negative sulfur atom (87.2%). On the other hand, C2 has a higher propensity for reacting with L-Cys-, primarily through the partially negative oxygen atom (92.6%). The implementation of this theoretical framework will significantly restrict the utilization of chemical substances, hence facilitating cost reduction and environmental protection.

Unsymmetrical Pd(II) Pincer Complexes with Benzothiazole and Thiocarbamate Flanking Units: Expedient Solvent-Free Synthesis and Anticancer Potential

Driven by the growing threat of cancer, many research efforts are directed at developing new chemotherapeutic agents, where the central role is played by transition metal complexes. The proper ligand design serves as a key factor to unlock the anticancer potential of a particular metal center. Following a recent trend, we have prepared unsymmetrical pincer ligands that combine benzothiazole and thiocarbamate donor groups. These compounds are shown to readily undergo direct cyclopalladation, affording the target S,C,N-type Pd(II) pincer complexes both in solution and in the absence of a solvent. The solid-phase strategy provided the complexes in an efficient and ecologically friendly manner. The resulting palladacycles are fully characterized using nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy and, in one case, by single-crystal X-ray diffraction (XRD). The solvent-free reactions are additionally analyzed by powder XRD. The pincer complexes exhibit remarkable cytotoxicity against several solid and blood cancer cell lines, including human colorectal carcinoma (HCT116), breast cancer (MCF7), prostate adenocarcinoma (PC3), chronic myelogenous leukemia (K562), multiple plasmacytoma (AMO1), and acute lymphoblastic leukemia (H9), with the dimethylamino-substituted derivative being particularly effective. The latter also induced an appreciable level of apoptosis in both parental and doxorubicin-resistant cells K562 and K562/iS9, vindicating the high anticancer potential of this type of palladacycles.

Modulation of the Cytotoxic Properties of Pd(II) Complexes Based on Functionalized Carboxamides Featuring Labile Phosphoryl Coordination Sites

Platinum-based drugs are commonly recognized as a keystone in modern cancer chemotherapy. However, intrinsic and acquired resistance as well as serious side effects often caused by the traditional Pt(II) anticancer agents prompt a continuous search for more selective and efficient alternatives. Today, significant attention is paid to the compounds of other transition metals, in particular those of palladium. Recently, our research group has suggested functionalized carboxamides as a useful platform for the creation of cytotoxic Pd(II) pincer complexes. In this work, a robust picolinyl- or quinoline-carboxamide core was combined with a phosphoryl ancillary donor group to achieve hemilabile coordination capable of providing the required level of thermodynamic stability and kinetic lability of the ensuing Pd(II) complexes. Several cyclopalladated derivatives featuring either a bi- or tridentate pincer-type coordination mode of the deprotonated phosphoryl-functionalized amides were selectively synthesized and fully characterized using IR and NMR spectroscopy as well as X-ray crystallography. The preliminary evaluation of the anticancer potential of the resulting palladocycles revealed a strong dependence of their cytotoxic properties on the binding mode of the deprotonated amide ligands and demonstrated certain advantages of the pincer-type ligation.

Cytotoxicity Induced by Newly Synthesized Palladium (II) Complexes Lead to the Death of MCF-7 and MDA-MB-435 Cancer Cell Lines

Purpose: Breast cancer is the most common female malignancy and melanoma is the most lethal type of skin cancer. Traditional therapy for cancer treatment is far from satisfactory due to drug resistance and side effects, thus a search for new medicines is being emphasized. Palladium(II) complexes have been reported as anticancer potential agents. In this work, the anticancer activities and cell death induction of a new series of square-planar Pd(II) complexes were evaluated against MCF-7 and MDA-MB-435 cancer cells. Methods: MCF-7 (breast carcinoma) and MDA-MB-435 (melanoma) cells were cultivated, and treated with ligand and Pd(II) complexes. Cell growth, migration and adhesion inhibition, morphological alterations, cell death induction and, DNA interaction upon treatment were studied. Results: Pd(II) complexes exhibited both short and long-term antiproliferative effects on both cell lines, reducing by 80% cell growth in the SRB assay and abolishing longterm proliferation, estimated by the clonogenic assay. Complexes reduced significantly (P<0.05) cell migration and adhesion when compared to the control group. Complexes induced morphological alterations in cell lines and significant (P<0.05) cellular shrinkage. Cell death was induced and the complexes were able to interact with DNA, inducing cleavage of double-stranded DNA, which may account for the complexes cytotoxic effects, observed against both MCF-7 and MDA-MB-435 cells. Conclusion: Overall, the complexes exhibited cytotoxic activities and induced cell death. These observations emphasize an anticancer role with a potential therapeutic value for Pd(II) complexes to improve the outcome of patients with breast cancer and melanoma.

Oxidative DNA cleavage mediated by a new unexpected [Pd(BAPP)][PdCl4] complex (BAPP = 1,4-bis(3-aminopropyl)piperazine): crystal structure, DNA binding and cytotoxic behavior

A novel Pd(ii) double complex, [Pd(BAPP)][PdCl₄], containing the 1,4-bis(3-aminopropyl)piperazine (BAPP) ligand is investigated. X-ray crystallography of a single crystal confirmed the structure of the [Pd(BAPP)][PdCl₄] complex. The spectroscopic behavior was also elucidated using elemental analysis, nuclear magnetic resonance and Fourier-transform infrared spectroscopy, and mass spectrometry. The antimicrobial susceptibility of the [Pd(BAPP)][PdCl₄] complex against all tested microbial strains was lower than that of the BAPP ligand except for C. albicans. The cytotoxic impacts of the BAPP ligand and its [Pd(BAPP)][PdCl₄] complex were evaluated in vitro for HepG2, CaCo-2 and MCF7 cell lines as well as the WI-38 normal cell line. The anticancer activity was markedly improved by the complexation. The [Pd(BAPP)][PdCl₄] complex could selectively inhibit the tested cancer cells in a safe way to the non-tumorigenic cell (WI-38). From the DNA binding studies with ultraviolet-visible spectrophotometry, the [Pd(BAPP)][PdCl₄] complex interacts more efficiently with the calf thymus DNA than its BAPP ligand through the intercalative binding mode. In the absence of an external reductant, the [Pd(BAPP)][PdCl₄] complex cleaved the intact supercoiled pBR322 DNA under physiological conditions in a concentration-dependent manner. Additionally, electrophoretic experiments were performed in the presence of different radical scavengers, namely DMSO, NaN₃ and KI, and ruled out the hydrolytic mechanistic pathway of the reaction and suggested that the oxidative mechanism is the preferred one. The results of the binding affinity of the [Pd(BAPP)][PdCl₄] complex to human DNA were modeled using a molecular docking study showing that the complex interacts more strongly with human DNA than the ligand. Finally, an in vitro pharmacokinetic study was assessed through in silico ADME predictions.

Investigation of the influence of chirality and halogen atoms on the anticancer activity of enantiopure palladium(ii) complexes derived from chiral amino-alcohol Schiff bases and 2-picolylamine

In order to evaluate the impact of chirality and halogen-substitution pattern on biological activity, four mixed-ligand enantiomeric pairs of Pd(ii) complexes were synthesized and characterized.

Palladium(ii) and platinum(ii) complexes with ONN donor pincer ligand: synthesis, characterization and in vitro cytotoxicity study

New Pd(ii) and Pt(ii) complexes with ONN donor pincer ligand are synthesized. Antiproliferative activity of the complexes is explored towards HCT116, HepG2, MCF-7 and A549 cell lines.

Nitrogen Atom Transfer Catalysis by Metallonitrene C-H Insertion: Photocatalytic Amidation of Aldehydes

C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to Pd^II. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N₃SiMe₃. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.

Bis(triazinyl)pyridine complexes of Pt(II) and Pd(II): studies of the nucleophilic substitution reactions, DNA/HSA interactions, molecular docking and biological activity

Four new complexes of Pt(II) and Pd(II), [Pd(L1)Cl]Cl 1, [Pd(L2)Cl]Cl 2, [Pt(L1)Cl]Cl 3 and [Pt(L2)Cl]Cl 4 (where L1 = 2,6-bis(5,6-diphenyl-1,2,4-triazin-3-yl)pyridine and L2 = 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine), were synthesized. Characterization of the complexes was performed using elemental analysis, IR, ¹H NMR spectroscopy and MALDI-TOF mass spectrometry. The substitution reactions of 1-4 complexes with L-methionine (L-met), L-cysteine (L-cys) and guanosine-5'-monophosphate (5'-GMP), were studied spectrophotometrically at physiological conditions. Complexes with ligand L1 (1 or 3) were more reactive than those with ligand L2 (2 or 4) by a factor ranging up to 1.57 and 3.71, respectively. The order of reactivity of the nucleophiles was: L-met > L-cys > 5'-GMP. The interactions of complexes with calf thymus-DNA (CT-DNA) and human serum albumin (HSA) were studied by Uv-Vis absorption and fluorescence emission spectroscopy. Competitive binding studies with intercalative agent ethidium bromide (EB) and minor groove binder Hoechst 33258 were performed as well. All studied complexes can interact with DNA through the intercalation and minor groove binding, where the latter was preferred. The binding constants (10³ and 10⁴ M^-1) for the interaction of complexes with HSA indicate the moderate binding affinity of complexes 1-4 to protein. The trends in the experimental results of binding studies between complexes 3 and 4 with DNA and HSA were compared to those obtained from the molecular docking study. Biological evaluation of cytotoxicity of 1 and 2 on HCT-116 and MDA-MB-231 cell lines showed significant cytotoxic and prooxidative character, while 2 also exerted extraordinary selectivity towards colon cancer in comparison to breast cancer cells. The nucleophilic substitution reactions, DNA/HSA interactions, molecular docking and biological activity of bis(triazinyl)pyridine complexes of Pt(II) and Pd(II) were studied.

Homo and heterobimetallic palladium and platinum complexes bearing μ-diphosphane bridges involved in biological studies

Given the increasing reports of well-defined bimetallic molecular complexes as potential anticancer agents in the last decades, along with the prevalence of platinum in anticancer therapy, we report here a detailed survey of bimetallic platinum and palladium complexes investigated as potential anticancer agents. Specifically, we will concentrate on the synthesis, characterisation and biological (anticancer) studies of a sub-class of these agents, namely homo and heterobimetallic complexes bearing a bridging phosphane ligand of the type: [L_nM₁(μ-R₂P(CH₂)_nPR₂)M₂L_m] (where M₁ is platinum or palladium, M₂ is any other transition metal, R = alkyl or aryl substituents, L_n or L_m are co-ligands, n = 1-6). We will review the in vitro and in vivo activities and any mechanistic anticancer studies of these complexes with a view of trying to delineate patterns in biological activity and structure-activity relationships (SAR). We do not include the review of bimetallic complexes in this class that have not undergone any anticancer testing, nor those that have been involved in other biological investigations unrelated to cancer studies.

Palladium(II) Pincer Complexes of Functionalized Amides with S-Modified Cysteine and Homocysteine Residues: Cytotoxic Activity and Different Aspects of Their Biological Effect on Living Cells

In the search for potential new metal-based antitumor agents, two series of nonclassical palladium(II) pincer complexes based on functionalized amides with S-modified cysteine and homocysteine residues have been prepared and fully characterized by 1D and 2D NMR (¹H, ¹³C, COSY, HMQC or HSQC, ¹H-¹³C, and ¹H-¹⁵N HMBC) and IR spectroscopy and, in some cases, X-ray diffraction. Most of the resulting complexes exhibit a high level of cytotoxic activity against several human cancer cell lines, including colon (HCT116), breast (MCF7), and prostate (PC3) cancers. Some of the compounds under consideration are also efficient in both native and doxorubicin-resistant transformed breast cells HBL100, suggesting the prospects for the creation of therapeutic agents based on the related compounds that would be able to overcome drug resistance. An analysis of different aspects of their biological effects on living cells has revealed a remarkable ability of the S-modified derivatives to induce cell apoptosis and efficient cellular uptake of their fluorescein-conjugated counterpart, confirming the high anticancer potential of Pd(II) pincer complexes derived from functionalized amides with S-donor amino acid pendant arms.

Synthesis, Characterization and Antiproliferative Evaluation of Pt(II) and Pd(II) Complexes with a Thiazine-Pyridine Derivative Ligand

Chemical, pharmacological, and clinical research on anticancer coordination complexes has led to noteworthy anticancer drugs such as cisplatin, carboplatin and oxaliplatin. Although these compounds are effective chemotherapeutic agents in the treatment of different tumors, they are associated with high toxicity and numerous side effects. Several studies have shown that the range of platinum complexes with antitumor activity is not limited to structural analogs of cisplatin. Therefore, the development of convenient anticancer drugs that can be effectively used for the treatment of human tumors has become the main goal of most research groups in this field. In this sense, active platinum complexes without NH groups, transplatinum complexes, multinuclear complexes, cationic complexes, and several classes of palladium(II) complexes have emerged. Herein, the synthesis and characterization of two Pt(II) or Pd(II) complexes with PyTz (2-(2-pyridyl)iminotetrahydro-1,3-thiazine), a thiazine derivative ligand, with the formula [MCl₂(PyTz)]·C₂H₆O (M = Pt(II) or Pd(II)) were reported. The potential anticancer ability of both complexes was evaluated in epithelial cervix carcinoma HeLa, human ovary adenocarcinoma SK-OV-3, human histiocytic lymphoma U-937, and human promyelocytic leukemia HL-60 cell lines. Interestingly, the Pt(II) complex showed great cytotoxic potential against all tumor cell lines tested, whereas the Pd(II) complex displayed slight antitumor actions.

Heteroleptic enantiopure Pd(ii)-complexes derived from halogen-substituted Schiff bases and 2-picolylamine: synthesis, experimental and computational characterization and investigation of the influence of chirality and halogen atoms on the anticancer activity

To investigate the effect of chirality and different halogen substituents on the anticancer activity, seven enantiomeric pairs of palladium complexes were synthesized and characterized.

Photoactive PtII and PdII complexes of N,N-diethyl-N′-3,4,5-trimethoxybenzoylthiourea: synthesis, crystal structures, DFT and cytotoxicity studies

New trans-Pd^II/Pt^II acylthiourea complexes prepared by photo-induced isomerism are found to be more cytotoxic than cis-Pd^II/Pt^II against human prostate cancer and normal embryonic kidney cell lines.

Controlling the reactivity of [Pd(II)(N^N^N)Cl]+ complexes using 2,6-bis(pyrazol-2-yl)pyridine ligands for biological application: Substitution reactivity, CT-DNA interactions and in vitro cytotoxicity study

Four [(N^N^N)Pd^(II)Cl]⁺ complexes [chloride-(2,2':6',2''-terpyridine)Pd(II)]Cl (PdL1), [chlorido(2,6-bis(N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL2), [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL3) and [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-ylmethyl)pyridine)Pd(II)]BF₄ (PdL4) were synthesized and characterized. The rates of substitution of these Pd(II) complexes with thiourea nucleophiles viz; thiourea (Tu), N,N'-dimethylthiourea (Dmtu) and N,N,N',N'-tetramethylthiourea (Tmtu) was investigated under pseudo first-order conditions as a function of nucleophile concentration [Nu] and temperature using the stopped-flow technique. The observed rate constants vary linearly with [Nu]; k_obs = k₂[Nu] and decreased in the order: PdL1 > PdL2 > PdL3 ≫ PdL4. The lower π-acceptability of the cis-coordinated N-pyrazol-2-yl groups (which coordinates via pyrazollic-N π-donor atoms) of the PdL2-4 significantly decelerates the reactivity relative to PdL1. Furthermore, the six-membered chelates having methylene bridge in PdL4 do not allow π-extension in the ligand and introduces steric hindrance further lowering the reactivity. Trends in DFT calculated data supported the observed reactivity trend. Spectrophotometric titration data of complexes with calf thymus DNA (CT-DNA) and viscosity measurements of the resultant mixtures suggested that associative interactions occur between the complexes and CT-DNA, likely through groove binding with high binding constants (K_b = 10⁴ M^-1). In vitro MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cytotoxic activity data showed that PdL1 was the most potent complex against MCF7 breast cancer cells; its IC₅₀ value is lower than that of cisplatin. The results demonstrate how modification of a spectator ligand can be used to slow down the reactivity of Pd(II) complexes. This is of special importance in controlling drug toxicity in both pharmaceutical and biomedical applications.

Studies of the stability, nucleophilic substitution reactions, DNA/BSA interactions, cytotoxic activity, DFT and molecular docking of some tetra- and penta-coordinated gold(iii) complexes

The stability in water and at pH = 7.2, substitution reactions with Tu, 5’-GMP, GSH and l-Met, DNA/BSA interactions, cytotoxicity, DFT and molecular docking of gold(iii) complexes with phenanthroline derivatives as inert ligands were studied.

Synthesis, characterization, DNA/BSA interactions and in vitro cytotoxicity study of palladium(II) complexes of hispolon derivatives

Thirteen novel palladium(II) complexes of the general formula [Pd(bipy)(O,O'-dkt)](PF₆), (where bipy is 2,2'-bipyridine and O,O'-dkt is β-diketonate ligand hispolon or its derivative) have been prepared through a metal-ligand coordination method that involves spontaneous formation of the corresponding diketonate scaffold. The obtained palladium(II) complexes have been characterized by NMR spectroscopy, ESI-mass spectrometry as well as elemental analysis. The cytotoxicity analysis indicates that most of the obtained palladium(II) complexes show promising growth inhibition in three human cancer cell lines. Flow cytometry analysis shows complex 3e could promote intracellular reactive oxygen species (ROS) accumulation and lead cancer cell death. And the suppression of ROS accumulation and the rescue of cell viability in HeLa cells by N-acetyl-L-cysteine (NAC) suggest the possible link between the increase in ROS generation and cytotoxicity of complex 3e. Flow cytometry analysis also reveal that complex 3e cause cell cycle arrest in the G2/M phase and collapse of the mitochondrial membrane potential, promote the generation of ROS and lead to tumor cell apoptosis. The interactions of complex 3e with calf thymus DNA (CT-DNA) have been evaluated by UV-Vis spectroscopy, fluorescence quenching experiments and viscosity measurements, which reveal that the complex interact with CT-DNA through minor groove binding and/or electrostatic interactions. Further, the results of fluorescence titration and site marker competitive experiment on bovine serum albumin (BSA) suggest that complex 3e can quench the fluorescence of BSA via a static quenching process and bind to BSA in Sudlow's site II.

Synthesis, characterization, DFT study, DNA/BSA-binding affinity, and cytotoxicity of some dinuclear and trinuclear gold(III) complexes

In this study, we have synthesized a series of dinuclear and trinuclear gold(III) complexes of the general formula [Au₂(N-N)Cl₆] (1-3) for dinuclear and [Au₃(N-N)₂Cl₈]⁺ (4-6) for trinuclear compounds, respectively, in which N-N is a bidentate ligand (1,4-diaminobutane; 1,6-diaminohexane or 1,8-diaminooctane). These complexes were characterized by elemental analysis, molar conductivity, and spectroscopic techniques (IR, UV-Vis, ¹H NMR, ESI-MS). We performed DFT calculations to get insight into the geometry of the studies complexes. DNA-binding studies were performed by UV-Vis spectrophotometry and fluorescence spectroscopy. The results of competitive reactions between gold(III) complexes and ethidium bromide (EB) towards DNA have shown that selected complexes can displace EB from DNA-EB adduct. In addition, these experiments confirm that polynuclear gold(III) complexes interact with DNA covalently or via intercalation. Furthermore, high values of binding constants of gold(III) complexes towards bovine serum albumin (BSA) protein indicate good binding affinity. In addition, redox stability of complexes in the presence of DNA/BSA was confirmed by cyclic voltammetry. Results of the interactions between gold(III) complexes with DNA/BSA were discussed in reference to molecular docking data obtain by Molegro virtual docker. The cytotoxic activity of synthesized gold(III) complexes was evaluated on human breast cancer cell line (MDA-MB-231), human colorectal cancer cell line (HCT-116), and normal human lung fibroblast cell line (MRC-5). All complexes dose-dependently reduced cancer and normal cells viabilities, with significant cytotoxic effects (IC₅₀ < 25 μM) for trinuclear gold(III) complexes (4, 5) on HCT-116 cells.

New dinuclear palladium(II) complexes with benzodiazines as bridging ligands: interactions with CT-DNA and BSA, and cytotoxic activity

Three new dinuclear Pd(II) complexes with general formula [{Pd(en)Cl}₂(μ-L)](NO₃)₂ [L is bridging ligand quinoxaline (Pd1), quinazoline (Pd2) and phthalazine (Pd3)] were synthesized and characterized by elemental microanalyses, UV-Vis, IR and NMR (¹H and ¹³C) spectroscopy. The interaction of dinuclear Pd1-Pd3 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV-Vis and fluorescence emission spectroscopy in aqueous phosphate buffer solution (PBS) at pH 7.40 and 37 °C. In addition, these experimental conditions have been applied to investigate the binding affinities of Pd1-Pd3 complexes to the bovine serum albumin (BSA) by fluorescence emission spectroscopy. In vitro antiproliferative and apoptotic activities of the dinuclear Pd(II) complexes have been tested on colorectal and lung cancer cell lines. All tested Pd(II) complexes had lower cytotoxic effect than cisplatin against colorectal cancer cells, but also had similar or even higher cytotoxicity than cisplatin against lung cancer cells. All complexes induced apoptosis of colorectal and lung cancer cells, while the highest antiproliferative effect exerted Pd2 complex.

A palladium(II) complex with the Schiff base 4-chloro-2-(N-ethyliminomethyl)-phenol: Synthesis, structural characterization, and in vitro and in silico biological activity studies

The synthesis and characterization of the Pd(II) complex of the formula [Pd(L)₂] 1 with the Schiff base 4-chloro-2-(N-ethyliminomethyl)-phenol (HL) as derived in situ via the condensation reaction of 5-chloro-salicylaldehyde and ethylamine was undertaken. The structure of 1 was verified by single-crystal X-ray crystallography. The ability of 1 to interact with calf-thymus (CT) DNA was studied by UV-vis and viscosity experiments, and its ability to displace ethidium bromide (EB) from the DNA-EB conjugate was revealed by fluorescence spectroscopy. It was found that intercalation is the most possible mode of interaction with CT DNA. Additionally, DNA electrophoretic mobility experiments showed that 1 interacts with the plasmid pBluescript SK(+) (pDNA) as proved by the formation of unusual mobility DNA bands and degradation of relaxed pDNA at concentration of 5 mM. The interaction of 1 with human (HSA) and bovine serum albumin (BSA) was monitored revealing its reversible binding to albumins. The complex showed noteworthy antimicrobial activity against one (Bacillus subtilis) of the five tested bacteria. In order to explain the described in vitro activity of the compound, we adopted molecular docking studies on the crystal structure of HSA, BSA, CT DNA and DNA-gyrase. Furthermore, in silico predictive tools have been employed to study the properties of the complex. The in silico studies are adopted on a multitude of proteins involved in cancer growth, as well as prediction of drug-induced changes of gene expression profile, protein- and mRNA-based prediction results, prediction of sites of metabolism, cytotoxicity for cancer cell lines, etc.

ZnII Complexes for Bioimaging and Correlated Applications

Zinc is a biocompatible element that exists as the second most abundant transition metal ion and an indispensable trace element in the human body. Compared to traditional metal-organic complexes systems, d¹⁰ metal Zn^II complexes not only exhibit a large Stokes shift and good photon stability but also possess strong emission and low cytotoxicity with a relatively small molecular weight. The use of Zn^II complexes has emerged in the last decade as a versatile and convenient tool for numerous biological applications, including bioimaging, molecular and protein recognition, as well as photodynamic therapy. Herein, we review recent developments involving Zn^II metal complexes applied as specific subcellular compartment imaging probes and their correlated utilizations.

Water soluble, optically active monofunctional Pd(ii) and Pt(ii) compounds: promising adhesive and antimigratory effects on human prostate PC-3 cancer cells

Water soluble, enantiomerically pure “rule breakers” Pd(ii) and Pt(ii) compounds with promising anticancer potential are reported.

Determination of ultra-trace Pt, Pd and Rh in seawater using an off-line pre-concentration method and inductively coupled plasma mass spectrometry

A method was modified for the preconcentration of platinum (Pt), palladium (Pd) and rhodium (Rh) from seawater by a solid phase extraction using a commercially available resin Nobias-chelate PA1^®. All the determination was conducted using inductively coupled plasma mass spectrometry (ICP-MS) which had a low detection limit for Pt, Pd and Rh, about 16.53, 16.41 and 26.88 pg L^-1, respectively. It was found that the adsorption performance of the resin was closely related to the matrix, ligands and pH of the samples. Significant difference in recovery was found in various samples: seawater ≈ artificial seawater > ultra-pure deionized water. This method had low method blank in the range of 5.51-8.89 pg L^-1 and high enrichment factor of up to 180-200. The recoveries of Pt and Pd were 93 ± 4.2% in the spiked real seawater. However, the recovery of Rh on the resin was below 70% but stable in the range of 65-68%. It indicated that the Rh recovery seemed to be reproducible and higher volumes of seawater must be processed in order to obtain the lower limit of quantification and excellent recovery.

New monofunctional platinum(II) and palladium(II) complexes: Studies of the nucleophilic substitution reactions, DNA/BSA interaction, and cytotoxic activity

Four new complexes [Pd(H₂L^tBu)Cl]Cl (Pd1), [Pt(H₂L^tBu)Cl]Cl (Pt1), [Pd(Me₂L^tBu)Cl]Cl (Pd2) and [Pt(Me₂L^tBu)Cl]Cl (Pt2) (where H₂L^tBu = 2,6-bis(5-(tert-butyl)-1H-pyrazol-3-yl)pyridine and Me₂L^tBu = 2,6-bis(5-(tert-butyl)-1-methyl-1H-pyrazol-3-yl)pyridine) were synthesized and characterized by elemental microanalysis, IR, ¹H NMR and ESI-MS methods. The reactivity of complexes towards thiourea (Tu), l-methionine (l-Met), l-cysteine (l-Cys) and guanosine-5'-monophosphate (5'-GMP) was investigated. The obtained order was established as follows: Tu > l-Cys > l-Met > 5'-GMP. Complexes Pd1 and Pt1, that contain H₂L^tBu as chelator, showed higher reactivity towards biomolecules than those with Me₂L^tBu. The interaction of complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) was studied by UV-Vis and fluorescence spectroscopy. The results have shown that complexes can bind to DNA exhibiting high binding constants (K_b = 10⁴ M^-1). Obtained results during the examination of competitive reaction with ethidium bromide (EB) showed that complexes can replace EB-bound DNA. High values of binding constants indicate good binding affinity of complexes towards BSA. We evaluated the stability differences between complexes based on terpy as well as H₂L^tBu/Me₂L^tBu by DFT calculations (B3LYP(CPCM)/LANL2DZp), showing that both tridentate ligand systems lead to complexes of similar stability. The results of biological testing showed that all complexes exert moderate to high selective cytotoxicity, inducing apoptosis and autophagy in HeLa and PANC-1 tumor cell lines. Pd1 exhibited the strongest cytotoxic effect. Finally, cell cycle analysis showed that in HeLa cells Pd1, Pd2 and Pt1 induced accumulation of cells in S phase, whereas in PANC-1 cells Pd2 and Pt1 induced G2/M cycle arrest and Pd1 induced G0/G1 arrest.

New gold pincer-type complexes: synthesis, characterization, DNA binding studies and cytotoxicity

The complex [Au(H₂L^tBu)Cl]Cl₂(1) induced perturbations of the cell cycle and led to apoptosis in human melanoma A375 cells.

Platinum, palladium, gold and ruthenium complexes as anticancer agents: Current clinical uses, cytotoxicity studies and future perspectives

Metallodrugs offer potential for unique mechanism of drug action based on the choice of the metal, its oxidation state, the types and number of coordinated ligands and the coordination geometry. This review illustrates notable recent progress in the field of medicinal bioinorganic chemistry as many new approaches to the design of innovative metal-based anticancer drugs are emerging. Current research addressing the problems associated with platinum drugs has focused on other metal-based therapeutics that have different modes of action and on prodrug and targeting strategies in an effort to diminish the side-effects of cisplatin chemotherapy. Examples of metal compounds and chelating agents currently in clinical use, clinical trials or preclinical development are highlighted.

Hydrolysis of the amide bond in histidine- and methionine-containing dipeptides promoted by pyrazine and pyridazine palladium(II)-aqua dimers: Comparative study with platinum(II) analogues

Two dinuclear palladium(II) complexes, [{Pd(en)Cl}₂(μ-pz)](NO₃)₂ and [{Pd(en)Cl}₂(μ-pydz)](NO₃)₂, have been synthesized and characterized by elemental microanalysis and spectroscopic (¹H and ¹³C NMR, IR and UV-vis) techniques (en is ethylenediamine; pz is pyrazine and pydz is pyridazine). The square planar geometry of palladium(II) metal centers in these complexes has been predicted by DFT calculations. The chlorido complexes were converted into the corresponding aqua complexes, [{Pd(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pd(en)(H₂O)}₂(μ-pydz)]⁴⁺, and their reactions with N-acetylated l-histidylglycine (Ac-l-His-Gly) and l-methionylglycine (Ac-l-Met-Gly) were studied by ¹H NMR spectroscopy. The palladium(II)-aqua complexes and dipeptides were reacted in 1:1 M ratio, and all reactions performed in the pH range 2.0<pH<2.5 in D₂O solvent and at 37°C. In the reactions of these complexes with Ac-l-His-Gly and Ac-l-Met-Gly dipeptides, the hydrolysis of the amide bonds involving the carboxylic group of both histidine and methionine amino acids occurs. The catalytic activities of the palladium(II)-aqua complexes were compared with those previously reported in the literature for the analogues platinum(II)-aqua complexes, [{Pt(en)(H₂O)}₂(μ-pz)]⁴⁺ and [{Pt(en)(H₂O)}₂(μ-pydz)]⁴⁺.

Antiproliferative properties and biomolecular interactions of three Pd(II) and Pt(II) complexes

Three Pd(II) and Pt(II) complexes with chelating mono(imidazolin-2-imine) and bis(imidazolin-2-imine) ligands i.e. [Pd(DMEAIm^iPr)Cl₂] (1) (DMEAIm^iPr, 2-(1,3-diisopropyl-4,5-dimethylimidazolin-2-imine)ethan-1-dimethylamine), [Pd(DACH(Im^iPr)₂)Cl₂] (2) (DACH(Im^iPr)₂, N,N'-(cyclohexane-1,2-diyl)bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-imine)) and [Pt(DMEAIm^iPr)Cl₂] (3), are evaluated here as potential cytotoxic and anticancer agents. An acceptable solution behaviour was found for the three study compounds in terms of solubility and stability. Notably, the three metal complexes demonstrated moderate to high cytotoxic properties in selected cancer cell lines (liquid and solid tumor). To gain deeper mechanistic insight, the reactivity of the study complexes with model DNA oligos and protein molecules was investigated through spectrometric and spectroscopic methods; in both cases adduct formation was clearly documented by ESI-MS measurements. The binding of these metal complexes to calf thymus DNA (CT-DNA) was further examined by absorption (UV-Vis) and emission spectral studies (Ethidium bromide displacement studies, EtBr). Overall, the studied complexes 1-3 exhibited a remarkable DNA binding ability that might be linked to the observed cytotoxic effects. Interestingly our results revealed that DNA binding, as well as anticancer activity of 1-3 follows the order 2>3>1. The implications of these findings are discussed.