Palladium Compounds Research Articles

Optical and supramolecular properties of cyclometalated palladium nanostructures with tumor targeting properties in living mice: a quantum mechanics interpretation.

The recent discovery that metallophilic interactions between cyclometalated palladium supramolecular nanostructures - with efficient tumour accumulation rate in a skin melanoma model - maintain excellent photodynamic properties even in a hypoxic microenvironment has inspired the present study focused on the theoretical predictions of optical properties of the bis-cyclometalated palladium compound in different contexts. More specifically, structural and UV/Vis absorption properties of both monomeric and dimeric forms of this anticancer drug are well reproduced with a Time-Dependent Density Functional Theoretical (TD-DFT) approach based on Exchange-Correlation (XC) hybrid functionals in conjunction with conductor-like and polarization solvation effects. A further novelty is represented by a fine investigation of the supramolecular interactions between the different subunits of the drug via dispersion force correction andQuantum Theory of Atoms in Molecules (QTAIM). This contribution while supporting the photoexcitation properties derived in laboratory following the self-assembly of monomeric units when passing from dimethyl sulfoxide (DMSO) to a H2O/DMSO mixture at 298K, shed some light on the nature of the chemical interactions modulating the formation of nano-size aggregates.

Breaking New Ground towards Innovative Synthesis of Palladacycles: The Electrochemical Synthesis of a Tetranuclear Thiosemicarbazone-[C,N,S] Palladium(II) Complex.

The electrochemical oxidation of anodic metals (M = nickel and palladium) in an acetonitrile solution of the thiosemicarbazone ligands (E)-2-(1-(4-methoxyphenyl)ethylidene)-N-methylhydrazine-1-carbothioamide (a), (E)-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (b), and (E)-N-phenyl-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (c) yielded the homoleptic complexes [ML2], 1a, 1b, 1c, and 2c and [M4L4], 2a as air-stable solids. The crystal structures for 1a, 1b, 1c, and 2c show the ligands in a transoid disposition with the [S,S] and [N,N] donor atom pairs occupying cis positions on the nearly square planar coordination plane of the metal. The structure for 2a of S4 symmetry comprises a tetranuclear palladacycle where the metalated ligands are arranged around a central Pd4S4 environment: a crown ring with alternating palladium and sulfur atoms. The latter complex is the first example of an electrochemical preparation of a cyclometalated palladium compound, marking a milestone in the chemistry of such species. The compounds have been fully characterized by elemental microanalysis, mass spectrometry, infrared (IR), and 1H nuclear magnetic resonance (NMR) spectra.

No Switching Cooperativity between Coordinated Azo Ligands on Complexes Having {MII(phosphane-κ2P)}2+ (M = Pd, Pt) Scaffolds.

A series of square-planar palladium and platinum compounds with cis-blocking phosphanes and terminal azobenzene ligands [M(dppp)(azo)2](OTf)2 (azo = CN(C6H4)-N═N-(C6H4)CN (iso-cyano), CN(C6H4)-N═N-(C6H5) (iso-Ph)) and [{M2(tpbz)}(azo)4](OTf)4 (azo = CN(C6H4)-N═N-(C6H5) (iso-Ph)) have been synthesized and fully characterized. Similarly to the uncoordinated ligands, the new coordination compounds have shown to be photochemically active with respect to their trans-to-cis isomerization process. Their cis-to-trans back spontaneous reaction have been studied as a function of solvent, temperature and pressure and the corresponding activation parameters determined in order to investigate the mechanism of these transformations. The results obtained are indicative of the operation of a rotational mechanism with no cooperativity between the azo ligands attached to the same metal. Density functional theory calculations have been carried out in order to estimate the relative energies of the different photoisomers for the theoretical interpretation of the experimental data.

Synthesis, characterization and the catalytic application of the N-heterocyclic carbene-PdCl2-cyanopyridine complexes

Six monoligated N-heterocyclic carbene-PdCl2-cyanopyridine complexes were prepared (N-heterocyclic carbene = NHC). X-ray single crystal diffraction analysis indicated that the complexes showed mononuclear Pd–NHC structures with two chlorides and the N-donor from cyanopyridine as ancillary ligands. The lengths of the Pd–C bonds in all complexes were 1.959(5)–1.976(3) Å, comparable to those found in the corresponding Pd–NHC catalysts. The catalytic activities of the well-defined Pd–NHC complexes have been evaluated with respect to the Hiyama cross-coupling reactions of aryl trialkoxysilanes with aryl chlorides. With 1.0 mol% Pd-catalyst, all synthesized palladium compounds have shown moderate to good catalytic activities for the coupling reactions.

Preparation of 3D Composite Nanomaterials Based on Opal Matrices by Reduction of Palladium and Platinum Compounds

Preparation of 3D Composite Nanomaterials Based on Opal Matrices by Reduction of Palladium and Platinum Compounds

Comparative Linkage of Novel Anti-Tumor Pd(II) Complex with Bio-Macromulecules: Fluorescence, UV-Vis, DFT, Molecular Docking and Molecular Dynamics Simulation Studies.

A novel mononuclear palladium complex, [Pd(dach)(SSA)], where dach and SSA are diaminocyclohexane and sulfosalicylic acid ligands, respectively, has been synthesized and identified utilizing analytical and spectral methods. DFT calculations, namely geometry optimization, MEP, HOMO-LUMO and NBO analysis, have been conducted at B3LYP level by aug-ccpVTZ-PP and 6-311G(d, p) basis sets. NBO and HOMO-LUMO analysis exhibited that the palladium compound is stable. MEP showed the potential sites of molecule for the interaction. By employing MTT assay, the cytotoxicity activity of the aforesaid compound was examined on K562 cell line, which revealed a proper activity compared to cisplatin. To ascertain the lipophilicity of the newly made compound, the partition coefficient measurement was accomplished, which follows the order of cisplatin < Pd(II) complex. Next, investigation of binding properties of the studied compound with DNA of calf thymus and BSA were done by spectroscopic (CD, fluorescence emission and electronic adsorption) and non-spectroscopic (viscosity measurements, DNA gel electrophoresis, molecular docking and molecular dynamics simulation) methods. The outcomes of CD and UV-Vis spectroscopy demonstrated that the title compound refolded the protein via increasing the alpha helix percentage. The data obtained from UV-Vis studies indicated the non-intercalative mutual action between Pd(II) complex with DNA. It also revealed that the Kapp magnitude of CT-DNA (7.43 × 104 M- 1) is higher than the BSA (5.17 × 103 M- 1), and L1/2 (midpoint of transition) of CT-DNA (5 µM) is lower than the BSA (5.7 µM), indicating that the complex has a greater binding affinity to CT-DNA than BSA. Fluorescence quenching mechanism of the two biomolecules by the metal complex is static and the calculated thermodynamic parameters (ΔS° < 0 and ΔH° < 0) suggested the hydrogen bonding and/ or van der Waals forces with DNA and BSA. Further, molecular docking indicated that the studied compound fits into the groove of DNA and the site I of BSA. The stability of metal compound-DNA/-BSA in the presence of H2O solvent and over the time were validated via molecular dynamics simulation.

L3-edge X-ray spectroscopy of rhodium and palladium compounds.

L3-edge high-energy-resolution fluorescence-detection X-ray absorption near-edge structure (XANES) spectra for palladium and rhodium compounds are presented, with focus on their electronic structures. The data are compared with transmission XANES spectra recorded at the K-edge. A correlation between the absorption edge energy and the metal ion oxidation state is not observed. Despite the different filling of the 4d orbitals and different local coordination, the Rh and Pd compounds show remarkably similar spectral shapes. Calculation of the density of states and of the L3-XANES data reproduce the experimental results.

Novel ferrocene cyclopalladated compounds: Synthesis, and in‐vitro antitumor activity study

AbstractMetal complexes have a significant impact on the treatment of human cancer. However, the scarcity of these compounds, resulting from their limited synthesis, hinders the comprehensive investigation of their anticancer mechanisms. Organic palladium compounds, known for their distinctive stability and properties, are thus an essential area of research in the development of anti‐tumor therapy. In our study, we synthesized two novel ferrocene cyclopalladated compounds (C2 and C4). Its configuration was thoroughly characterized by employing 1H, 13C NMR, ESI‐MS, and elemental analysis techniques. The molecular structures were determined by X‐ray single‐crystal diffraction. In an in vitro anticancer study, it was observed that both C2 and C4 exhibited excellent suppression of viability in various tumor cell lines. These compounds showed better potency than cisplatin and demonstrated lower toxicity in normal cells. Particularly, C4 displayed approximately 22 times greater potency than cisplatin in suppressing melanoma cells (B16F10). Our study suggests that ferrocene cyclopalladated compounds have the potential to be promising candidates for the development of innovative anticancer drugs.

Pt(II) and Pd(II) complexes with coumarin-thiosemicarbazone hybrid ligands and triphenylphosphine coligand as potential anti T. cruzi agents

Chagas disease is a neglected tropical disease caused by the parasite Trypanosoma cruzi. The disease is endemic in 21 Latin American countries, but it has also been found worldwide. Current treatments for Chagas disease are not effective in all stages of the disease and can have severe side effects. In recent years, there has been a growing interest in the development of new drugs for the treatment of Chagas disease, including metal complexes containing bioactive ligands. In this work, we designed and synthesized eight novel palladium and platinum complexes of the formula [M(L)(PPh3)] containing four different coumarin-thiosemicarbazone hybrid ligands (H2L) as bioactive ligands and triphenylphosphine as lipophilic co-ligand. Compounds were characterized in the solid state and in solution including the resolution of the crystal structure of two of them by single crystal X-ray diffraction. The activity of these hybrids and their corresponding complexes against T. cruzi, along with their unspecific cytotoxicity, was assessed. The results showed that the palladium complexes fairly improved the ligands’ anti-T. cruzi activity in vitro but also the cytotoxicity on some mammalian cell lines. The most active palladium compound decreased the rate of parasitic infection of Vero cells. Synergy studies with benznidazole were also performed for this compound. In addition, we explored mitochondrion disruption and ROS generation as potential modes of action for the obtained compounds. Further studies are needed to optimize the design of new compounds to attain less unspecific toxicity and higher anti T. cruzi activity.

The cytotoxicity of palladium (II) complexes containing 1,2‐ or 1,4‐diazine bridging ligands on squamous cell carcinoma cells in vitro: Insights in the mechanisms of action

Binuclear [{Pd (dien)}2(μ‐pz)](ClO4)4 (Pd1) and [{Pd (dien)}2(μ‐pydz)](ClO4)4 (Pd2) complexes, where pz is 1,4‐diazine and pydz is 1,2‐diazine bridging ligands and dien (diethylenetriamine) is a tridentately coordinated triamine ligand, were synthesized and characterized using elemental analysis, NMR (1H and 13C) spectroscopy, and UV–Vis spectrophotometry. Electronic absorption spectrophotometry and fluorescence spectroscopy were used to study the interactions of the prepared Pd1 and Pd2 complexes with deoxyribonucleic acid (CT‐DNA) and bovine serum albumin (BSA). According to the UV–Vis spectrophotometric data, the complexes interact with CT‐DNA and bind to the BSA as a possible carrier to the target site. The antitumor properties of the tested palladium compounds were evaluated on three types of human cancer cells, namely, squamous cell carcinoma cells SCC‐4, cervical carcinoma cells HeLa and colorectal carcinoma cells HCT116, and one type of malignantly unchanged cells, MRC‐5 fibroblasts. The highest cytotoxicity was shown by the Pd1 compound against SCC‐4 cell, with an IC50 value of 5.4 ± 1.2 μM. The results showed that the cytotoxic potential against SCC‐4 cells of our new palladium complexes Pd1 and Pd2 was comparable with the cytotoxic potential of cisplatin and oxaliplatin. However, Pd1 and Pd2 displayed significantly lower cytotoxicity in comparison with cisplatin and oxaliplatin against non‐malignant cells, fibroblasts MRC5, so these results may suggest that local and systemic complications of antitumor therapy could be reduced and/or avoided. Both compounds selectively decreased the viability of SCC‐4 cells by induction of apoptosis. Also, Pd1 and Pd2 induced S‐phase cell cycle arrest in human SCC‐4 cells, so that could be another mechanism to halt the uncontrolled growth and division of cancer cells. Moreover, the precise molecular mechanism of Pd1 and Pd2 complexes‐induced apoptosis was the activation of the intrinsic signaling pathway of apoptosis, which also included activation of caspase‐3. Therefore, our new palladium (II) complexes might have a promising role as the potential future cytostatic agents.

Origin of the Magnetic-Optical Properties of Palladium Compounds, an Ab Intio Study

Abstract: The structural, magnetic, and magneto-optical properties of the PdM (M=Fe, Co, Ni) alloy are investigated using first-principles calculations with the exciting code. The study employs the full potential linearized augmented plane wave method (FP-LAPW) based on density functional theory (DFT). The exchange-correlation energy is described in the generalized gradient approximation developed by Perdew-Burke-Ernzerhof (PBE-GGA). The calculated lattice parameters are in good agreement with theoretical and experimental results. The magnetic properties reveal a ferromagnetic stability phase for all compounds. Additionally, the total (TDOS) and partial (PDOS) density of states, along with the band structure, indicate that PdM (M = Fe, Co, Ni) exhibits metallic behavior. The total and local magnetic moments are investigated. We conducted a study on the polar magneto-optical Kerr effect and calculated Kerr spectra. The microscopic origins of the peaks found in Kerr's angle are interpreted as interband transitions, primarily arising from the states (d to d) in the PdNi and (S to d) in the PdFe and PdCo alloys. Keywords: P-MOKE, DFT, GGA-PBE, Intermetallic.

Palladium (II) compounds containing oximes as promising antitumor agents for the treatment of osteosarcoma: An in vitro and in vivo comparative study with cisplatin

Drug resistance, evasion of cell death and metastasis are factors that contribute to the low cure rate and disease-free survival in osteosarcomas (OS). In this study, we demonstrated that a new class of oxime-containing organometallic complexes called Pd-BPO (O3) and Pd-BMO (O4) are more cytotoxic than cisplatin (CDDP) for SaOS-2 and U2OS cells using the MTT assay. Annexin-FITC/7-AAD staining demonstrated a greater potential for palladium-oxime complexes to induce death in SaOS-2 cells than CDDP, an event confirmed using the pan-caspase inhibitor Z-VAD-FMK. Compared to CDDP, only palladium-oxime complexes eradicated the clonogenicity of SaOS-2 cells after 7 days of treatment. The involvement of the lysosome-mitochondria axis in the cell death-inducing properties of the complexes was also evaluated. Using LysoTracker Red to label the acidic organelles of SaOS-2 cells treated with the O3 and O4 complexes, a decrease in the fluorescence intensity of this probe was observed in relation to CDDP and the control. Lysosomal membrane permeabilization (LMP) was also induced by the O3 and O4 complexes in an assay using acridine orange (A/O). The greater efficiency of the complexes in depolarizing the mitochondrial membrane compared to SaOS-2 cells treated with CDDP was also observed using TMRE (tetramethyl rhodamine, ethyl ester). For in vivo studies, C. elegans was used and demonstrated that both complexes reduce body bends and pharyngeal pumping after 24 h of treatment to the same extent as CDDP. We conclude that both palladium-oxime complexes are more effective than CDDP in inducing tumor cell death. The toxicity of these complexes to C. elegans was like that induced by CDDP. These results encourage preclinical studies aimed at developing more effective drugs for the treatment of osteosarcoma (OS). Furthermore, we propose palladium-oxime complexes as a new class of antineoplastic agents.

Efficient catalysts based on substitutional solid solutions and intermetallic compounds of palladium for acetylene selective hydrogenation to ethylene

Efficient catalysts based on substitutional solid solutions and intermetallic compounds of palladium for acetylene selective hydrogenation to ethylene

Palladium and platinum complexes of primary 2-pyridinethioamide

Primary thioamide, 2-pyridinethioamide reacts with palladium and platinum compounds K2PdCl4, K2PtCl4 and Pd(CH3COO)2 to give the products [PdCl2(2-pyridinethioamide)].2DMF (1), [PtCl2(2-pyridinethioamide)] (2a), [Pd(2-pyridinethioamide)2]Cl2 (3), [Pt(2-pyridinethioamide)2]Cl2 (4) and [Pd(2-pyridinethioamidinate)2] (5), respectively. The structures 1, [PtCl(DMSO)(2-pyridinethioamidinate)] (2b), which was obtained from crystallization of 2a in DMSO, 4 and 5 were determined by X-ray crystallography. Compound 3 was spectroscopically analyzed and found to have a structure similar to that of 4. The ligand coordinates in a neutral form in complexes 1, 2a, 3 and 4, but in 2b and 5 it exists in a deprotonated form. Compounds 3 and 4 are cationic complexes with Cl− counterions in the structure. The ligand prefers coordination as the bidentate N(py),S-mode in all the crystallized compounds. In the bis-chelates, the sulfur and the nitrogen atoms are mutually trans-located. Computational DFT calculations and topological charge density analysis were utilized to clarify the coordination modes and to interpret the spectral information.

Assign_v2: a novel bonded-force field parameterization software for square planar palladium molecular dynamics simulations

In the present study, a requisite bonded force field for conducting molecular dynamics simulations of palladium compounds was derived utilizing a novel technique termed the “numbering system,” implemented through a program named assign.py. A significant challenge in deriving a bonded force field for square-planar palladium compounds emanates from their cis-trans characteristics, whereby the bond angles of identical atoms diverge across different compounds due to the presence of cis and trans isomers. To navigate this challenge, atoms surrounding the palladium were assigned numerical identifiers; consecutively numbered neighboring atoms were designated as “cis,” while atoms alternately numbered were regarded as “trans” relative to each other. Through the employment of the newly developed assign.py program, atoms common to GAFF were automatically assigned, facilitating the seamless integration of GAFF with the newly derived force field for cis and trans configurations. The tested innovative force field demonstrated results in close proximity to experimental findings. This research introduced two novel elements: firstly, a comparatively extensive force field was derived for palladium compounds, enabling the simulation of the previously non-simulable square planar geometry of palladium. Secondly, new software, assign.py, was developed, capable of amalgamating “numbering system atom types” with GAFF atom types into a unified force field. Conclusive tests within the study affirmed that the innovative bonded force field and technique utilizing the assign.py program was successful, simulating the square-planar geometry of palladium in a manner highly congruent with the experimental geometry. The program, licensed under Apache2, can be accessed via the following link: https://github.com/bkurt00/palladiumFF2/blob/main/assign_v2/assign_v2.py Communicated by Ramaswamy H. Sarma

CATALYST BASED ON PALLADIUM(II), COPPER(II) COMPOUNDS AND THERMALLY-MODIFIED TRIPOLI FOR THE PREPARATION OF RESPIRATORY REMEDIES FROM CARBON MONOXIDE IN EMERGENCY SITUATIONS

Nowadays, the number of emergency situations related to fires is quite high. The high percentage of human deaths is mainly due to poisoning by gaseous toxic substances including carbon monoxide. The most problematic issue is the development or application of existing catalysts in means of individual protection of human respiratory organs – respirators, gas masks, self-rescuers. The compositions based on thermally modified tripoli obtained by the method of impregnation of the carrier by moisture content with compounds of copper(II), palladium(II) and potassium bromide were investigated. According to X-ray phase analysis, it was established that thermally modified tripoli is a polyphase crystalline mineral containing the following main phases: a-quartz, a-tridymite, b-cristobalite, a-cristobalite. The influence of the initial concentration of CO, which does not exceed 15 MPC, on the kinetic and stoichiometric parameters of the reaction varied in the range from 100 to 300 mg/m3. It was noted that the reaction rate in the stationary mode (Wst) is directly proportional to the increase in the initial concentration of carbon monoxide in the gas phase. The values of the constant kI and the degree of CO conversion (ηst) do not depend on CinCO, which also confirms the first order of CO concentration. Particular attention is paid to the aspects of ensuring protection against carbon monoxide when its concentration exceeds 15 MPC. Usually, special equipment, such as filtering self-rescuers, is used to clean the air from carbon monoxide at concentrations from 1000 to 6500 mg/m3. The catalyst developed by us is intended for use in lightweight personal respiratory protective equipment (RPE) at concentrations not exceeding 15 MPC. Therefore, there was an interest in researching the possibilities of using this catalyst in the self-saving filter system. The concentration of carbon monoxide in the gas-air mixture was varied from 400 to 2500 mg/m3 in the presence of the К2PdCl4-Cu(NO3)2-КBr/300-Tr(K) system. It was established that Wst increases in direct proportion with an increase in the gas-air mixture up to 1250 mg/m3, which indicates the first order of the reaction according to carbon monoxide. It was found that at CinCO = 1000 mg/m3 only under the condition τ´ = 1.13 s (mk = 10 g) the К2PdCl4-Cu(NO3)2-KBr/Tr catalyst provides air purification below the breakthrough CO concentration (CfCO = 200 mg/m3). Experiments on the influence of SO2 on the activity of carbon monoxide oxidation catalysts have shown that they lose their activity, so in air purification systems from CO, it is necessary to provide for the stage of capturing sulfur dioxide.

Palladium-catalyzed allylation of norbornadiene: Experimental and quantum chemical research

Objectives. Catalytic processes involving norbornadiene (NBD) and norbornene (NBN) derivatives provide exceptional opportunities for the synthesis of a wide range of carbocyclic hydrocarbons. By significantly expanding this range, it becomes possible to obtain materials offering a wide variety of predictable properties. The aim of the present review is to summarize the latest achievements in the creation of novel processes catalyzed by palladium compounds. Considerable attention is paid to the study of the mechanisms of NBD allylation reactions by a combination of experimental and theoretical methods.Results. Various strategies of the molecular design of palladium catalysts for syntheses based on NBN and NBD are considered. The possibility of implementing various directions of NBD allylation is demonstrated. Factors influencing the direction of the reactions, by which means individual products can be selectively obtained, are discussed.Conclusions. The effective development of new catalytic processes involving NBD and NBN derivatives requires the complex application of synthetic, kinetic, isotopic, and quantum chemical approaches. By combining instrumental and theoretical methods with constant feedback, it becomes possible to optimize the search for original catalytic systems, obtain information about the mechanisms of their action, and influence technological parameters in a targeted manner.

Atroposelective Synthesis of C-N Vinylindole Atropisomers by Palladium-Catalyzed Asymmetric Hydroarylation of 1-Alkynylindoles.

Transition-metal-catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1-alkynylindoles with organoborons for the synthesis of chiral C-N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio-, stereo- (Z-selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Atroposelective Synthesis of C−N Vinylindole Atropisomers by Palladium‐Catalyzed Asymmetric Hydroarylation of 1‐Alkynylindoles

AbstractTransition‐metal‐catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1‐alkynylindoles with organoborons for the synthesis of chiral C−N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio‐, stereo‐ (Z‐selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Taming the Biological Activity of Pd(II) and Pt(II) Complexes with Triazolato "Protective" Groups: 1H, 77Se Nuclear Magnetic Resonance and X-ray Crystallographic Model Studies with Selenocysteine to Elucidate Differential Thioredoxin Reductase Inhibition.

The biological activity of Pd(II) and Pt(II) complexes toward three different cancer cell lines as well as inhibition of selenoenzyme thioredoxin reductase (TrxR) was modulated in an unexpected way by the introduction of triazolate as a "protective group" to the inner metal coordination sphere using the iClick reaction of [M(N3)(terpy)]PF6 [M = Pd(II) or Pt(II) and terpy = 2,2':6',2″-terpyridine] with an electron-poor alkyne. In a cell proliferation assay using A549, HT-29, and MDA-MB-231 human cancer cell lines, the palladium compound was significantly more potent than the isostructural platinum analogue and exhibited submicromolar activity on the most responsive cell line. This difference was also reflected in the inhibitory efficiency toward TrxR with IC50 values of 0.1 versus 5.4 μM for the Pd(II) and Pt(II) complexes, respectively. UV/Vis kinetic studies revealed that the Pt compound binds to selenocysteine faster than to cysteine [k = (22.9 ± 0.2)·10-3 vs (7.1 ± 0.2)·10-3 s-1]. Selective triazolato ligand exchange of the title compounds with cysteine (Hcys) and selenocysteine (Hsec)─but not histidine (His) and 9-ethylguanine (9EtG)─was confirmed by 1H, 77Se, and 195Pt NMR spectroscopy. Crystal structures of three of the four ligand exchange products were obtained, including [Pt(sec)(terpy)]PF6 as the first metal complex of selenocysteine to be structurally characterized.