Structure and redox stability of [Au(III)(X^N^X)PR3] complexes (X = C or N) in aqueous solution: The role of phosphine auxiliary ligand

(P^N^C) Ligands to Stabilize Gold(III): A Straightforward Access to Hydroxo, Formate, and Hydride Complexes

A novel class of (P^N^C) pincer ligands capable of stabilizing elusive gold(III) species is reported here. Straightforward access to (P^N^C)gold(III) hydroxo, formate, and hydride complexes has been streamlined by first incorporating a cycloauration step devoid of toxic metals or harsh conditions. The resulting gold complexes exhibit remarkable stability in solution as well as in the solid state under ambient conditions, which enabled their characterization by X-ray diffraction analyses. Interestingly, the influence of the ligand allowed the preparation of gold(III)-hydrides using mild hydride donors such as H-Bpin, which contrasts with sensitive super hydrides or strong acids and cryogenic conditions employed in previous protocols. A detailed bonding characterization of these species is complemented by reactivity studies.

%VBur index and steric maps: from predictive catalysis to machine learning

Steric indices are parameters used in chemistry to describe the spatial arrangement of atoms or groups of atoms in molecules. They are important in determining the reactivity, stability, and physical properties of chemical compounds. One commonly used steric index is the steric hindrance, which refers to the obstruction or hindrance of movement in a molecule caused by bulky substituents or functional groups. Steric hindrance can affect the reactivity of a molecule by altering the accessibility of its reactive sites and influencing the geometry of its transition states. Notably, the Tolman cone angle and %VBur are prominent among these indices. Actually, steric effects can also be described using the concept of steric bulk, which refers to the space occupied by a molecule or functional group. Steric bulk can affect the solubility, melting point, boiling point, and viscosity of a substance. Even though electronic indices are more widely used, they have certain drawbacks that might shift preferences towards others. They present a higher computational cost, and often, the weight of electronics in correlation with chemical properties, e.g. binding energies, falls short in comparison to %VBur. However, it is worth noting that this may be because the steric index inherently captures part of the electronic content. Overall, steric indices play an important role in understanding the behaviour of chemical compounds and can be used to predict their reactivity, stability, and physical properties. Predictive chemistry is an approach to chemical research that uses computational methods to anticipate the properties and behaviour of these compounds and reactions, facilitating the design of new compounds and reactivities. Within this domain, predictive catalysis specifically targets the prediction of the performance and behaviour of catalysts. Ultimately, the goal is to identify new catalysts with optimal properties, leading to chemical processes that are both more efficient and sustainable. In this framework, %VBur can be a key metric for deepening our understanding of catalysis, emphasizing predictive catalysis and sustainability. Those latter concepts are needed to direct our efforts toward identifying the optimal catalyst for any reaction, minimizing waste, and reducing experimental efforts while maximizing the efficacy of the computational methods.

Antibactericidal Ir(III) and Ru(II) Complexes with Phosphine-Alkaloid Conjugate and Their Interactions with Biomolecules: A Case of N-Methylphenethylamine

The phosphine ligand (Ph2 PCH2 N(CH3 )(CH2 )2 Ph, PNMPEA) obtained by the reaction of the (hydroxymethyl)diphenylphosphine with naturally occurring alkaloid N-methylphenethylamine, was used to synthesize the half-sandwich iridium(III) (Ir(η5 -Cp*)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, IrPNMPEA) and ruthenium(II) (Ru(η6 -p-cymene)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, RuPNMPEA) complexes. They were characterized using a vast array of methods, including 1D and 2D NMR, ESI(+)MS spectrometry, elemental analysis, cyclic voltammetry (CV), electron spectroscopy in the UV-Vis range (absorption, fluorescence) and density functional theory (DFT). The initial antimicrobial activity in vitro toward Gram-positive and Gram-negative bacterial strains was examined, indicating that both complexes are selective towards Gram-positive bacteria, e. g., Staphylococcus aureus, where the IrPNMPEA has been more bactericidal compared to RuPNMPEA. Additionally, the interactions of these compounds with various biomolecules, such as DNA (ctDNA, plasmid DNA, 9-ethylguanine (9-EtG), and 9-methyladenine (9-MeA)), nicotinamide adenine dinucleotide (NADH), glutathione (GSH), and ascorbic acid (Asc) were described. The results showed that both Ir(III) and Ru(II) complexes accelerate the oxidation process of NADH, GSH and Asc that appeared to occur by an electron transfer mechanism. Interestingly, only IrPNMPEA leads to the formation of various biomolecule adducts, which can explain its higher activity. Furthermore, RuPNMPEA and IrPNMPEA have been interacting with the DNA through weak noncovalent interactions.

Chemistry towards Biology-Instruct: Snapshot

The knowledge of interactions between different molecules is undoubtedly the driving force of all contemporary biomedical and biological sciences. Chemical biology/biological chemistry has become an important multidisciplinary bridge connecting the perspectives of chemistry and biology to the study of small molecules/peptidomimetics and their interactions in biological systems. Advances in structural biology research, in particular linking atomic structure to molecular properties and cellular context, are essential for the sophisticated design of new medicines that exhibit a high degree of druggability and very importantly, druglikeness. The authors of this contribution are outstanding scientists in the field who provided a brief overview of their work, which is arranged from in silico investigation through the characterization of interactions of compounds with biomolecules to bioactive materials.

The role of tridentate ligands on the redox stability of anticancer gold(III) complexes

Gold(III) complexes are promising compounds for cancer chemotherapy, whose action depends on their redox stability. In this context, the choice of ligands is crucial to adjust their reactivity and biological response. The present study addressed the effect of the gold coordination sphere on the reduction potential (E^o) for ten gold(III) complexes containing five or six-membered rings tridentate ligands - [Au^III(trident)Cl]³⁺ⁿ (trident = N^N^N, C^N^N, C^C^N, C^N^C, and N^C^N). The calculated E^o covered a broad range of 2500 mV with the most stable complexes containing two AuC bonds (E^o = -1.85 V for [Au^III(C^C^N)Cl] - f). For complexes with one AuC bond, the N^C^N ligands stabilize the gold(III) complex more efficiently than N^N^C; however, the inclusion of the non-innocent ligand bipy (2,2'-bipyridine) in N^N portion provides an extra stabilization effect. Among the derivatives with one AuC bond, [Au^III(N^N^C)Cl]⁺ (N^N = bipy) (a) showed E^o = -1.20 V. For the complexes with N^N^N ligands, E^o was positive and almost constant (+0.60 V). Furthermore, the kinetics for ligand exchange reactions (Cl^-/H₂O, H₂O/Cys and Cl^-/Cys) were monitored for the most stable compounds and the energy profiles compared to the reduction pathways.

Synthesis, physicochemical characterization and antiproliferative activity of phosphino Ru(II) and Ir(III) complexes

Herein, we present the synthesis of new complexes based on ruthenium(II) (Ru(η⁶-p-cymene)Cl₂PPh₂CH₂OH (RuPOH) and Ru(η⁶-p-cymene)Cl₂P(p-OCH₃Ph)₂CH₂OH (RuMPOH)) and iridium(III) (Ir(η⁵-Cp*)Cl₂P(p-OCH₃Ph)₂CH₂OH (IrMPOH) and Ir(η⁵-Cp*)Cl₂PPh₂CH₂OH (IrPOH)) containing phosphine ligands with/without methoxy motifs on phenyl rings (P(p-OCH₃Ph)₂CH₂OH (MPOH) and PPh₂CH₂OH (POH)). The complexes were characterized by mass spectrometry, NMR spectroscopy (1D: ¹H, ¹³C{¹H}, and ³¹P{¹H} and 2D: HMQC, HMBC, and COSY NMR) and elemental analysis. All the complexes were structurally identified by single-crystal X-ray diffraction analysis. The Ru(II) and Ir(III) complexes have a typical piano-stool geometry with an η⁶-coordinated arene (Ru^II complexes) or η⁵-coordinated (Ir^III compounds) and three additional sites of ligation occupied by two chloride ligands and the phosphine ligand. Oxidation of NADH to NAD⁺ with high efficiency was catalyzed by complexes containing P(p-OCH₃Ph)₂CH₂OH (IrMPOH and RuMPOH). The catalytic property might have important future applications in biological and medical fields like production of reactive oxygen species (ROS). Furthermore, the redox activity of the complexes was confirmed by cyclic voltamperometry. Biochemical assays demonstrated the ability of Ir(III) and Ru(II) complexes to induce significant cytotoxicity in various cancer cell lines. Furthermore, we found that RuPOH and RuMPOH selectively inhibit the proliferation of skin cancer cells (WM266-4; IC₅₀, after 24 h: av. 48.3 μM; after 72 h: av. 10.2 μM) while Ir(III) complexes were found to be moderate against prostate cancer cells (DU145).

Terpyridines as promising antitumor agents: an overview of their discovery and development

INTRODUCTION

The fused aromatic system of terpyridines makes them good, innocent ligands for various metals. The resulting complexes have been extensively studied for both their biological activity and physico-chemical properties. However, although free ligands also have an interesting biological activity, their share in recent research is considerably limited.

AREAS COVERED

This review covers the literature on the anticancer activity of terpyridines with special attention being paid to their use as free ligands. Whenever possible, the mechanism of action has been discussed, thereby providing evidence of the substantial differences between sole ligands or less stable complexes and those that have heavier elements.

EXPERT OPINION

The existing literature indicates that there is a specific attitude for investigating terpyridines and their transition metal complexes. While the latter have been well explored and recognized in the scientific community, the free terpyridines are considered to be useful solely due to their complexing ability. At the same time, terpyridines could have similar or even higher anticancer potency than their complexes. Moreover, a mechanistic analysis of the stability and intracellular activity would provide information that would be useful for designing new drugs.

Computational Studies of Au(I) and Au(III) Anticancer MetalLodrugs: A Survey

Owing to the growing hardware capabilities and the enhancing efficacy of computational methodologies, computational chemistry approaches have constantly become more important in the development of novel anticancer metallodrugs. Besides traditional Pt-based drugs, inorganic and organometallic complexes of other transition metals are showing increasing potential in the treatment of cancer. Among them, Au(I)- and Au(III)-based compounds are promising candidates due to the strong affinity of Au(I) cations to cysteine and selenocysteine side chains of the protein residues and to Au(III) complexes being more labile and prone to the reduction to either Au(I) or Au(0) in the physiological milieu. A correct prediction of metal complexes' properties and of their bonding interactions with potential ligands requires QM computations, usually at the ab initio or DFT level. However, MM, MD, and docking approaches can also give useful information on their binding site on large biomolecular targets, such as proteins or DNA, provided a careful parametrization of the metal force field is employed. In this review, we provide an overview of the recent computational studies of Au(I) and Au(III) antitumor compounds and of their interactions with biomolecular targets, such as sulfur- and selenium-containing enzymes, like glutathione reductases, glutathione peroxidase, glutathione-S-transferase, cysteine protease, thioredoxin reductase and poly (ADP-ribose) polymerase 1.

A Novel Hybrid of Chloroquine and Primaquine Linked by Gold(I): Multitarget and Multiphase Antiplasmodial Agent

Plasmodium parasites kill 435 000 people around the world every year due to unavailable vaccines, a limited arsenal of antimalarial drugs, delayed treatment, and the reduced clinical effectiveness of current practices caused by drug resistance. Therefore, there is an urgent need to discover and develop new antiplasmodial candidates. In this work, we present a novel strategy to develop a multitarget metallic hybrid antimalarial agent with possible dual efficacy in both sexual and asexual erythrocytic stages. A hybrid of antimalarial drugs (chloroquine and primaquine) linked by gold(I) was synthesized and characterized by spectroscopic and analytical techniques. The CQPQ-gold(I) hybrid molecule affects essential parasite targets, it inhibits β-hematin formation and interacts moderately with the DNA minor groove. Its interaction with PfTrxR was also examined in computational modeling studies. The CQPQ-gold(I) hybrid displayed an excellent in vitro antimalarial activity against the blood-stage of Plasmodium falciparum and liver-stage of Plasmodium berghei and efficacy in vivo against P. berghei, thereby demonstrating its multiple-stage antiplasmodial activity. This metallic hybrid is a promising chemotherapeutic agent that could act in the treatment, prevention, and transmission of malaria.