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Background : Essential metal ions play a specific and fundamental role in human metabolism. Their homeostasis is finely tuned and any concentration imbalance in form of deficiency or excess could lead to a progressive reduction and failure of normal biological function, to severe physiological and clinical outcomes till death. Conversely, non-essential metals are not necessary for life and only noxious effects could arise after their exposure. Large environmental amounts of such chemicals come from both natural and anthropogenic sources, with the latter being predominant because of human activities. The dissipation of toxic metals contaminates water, air, soil, and food, causing a series of chronic and acute syndromes. Objective : This review discusses the toxicity of non-essential metals considering their peculiar chemical characteristics such as different forms, hard-soft character, oxidation states, binding capabilities and solubility, which can influence their speciation in biological systems, and subsequently, the main cellular targets. Particular focus is given to selected toxic metals, major non-essential metals or semimetals related to toxicity such as mercury, lead, cadmium, chromium, nickel and arsenic. In addition, we provide indications on the possible treatments/interventions on metal poisoning based on chelation therapy. Conclusion: Toxic metal ions can exert their peculiar harmful effects in several ways. They strongly coordinate to important biological molecules on the basis of their chemical-physical characteristics (manly HSAB properties) or replace essential metal ions from their natural locations in proteins, enzymes or in hard structures such as bones or teeth. Metals with redox properties could be key inducers of reactive oxygen species, leading to oxidative stress and cellular damage. Therapeutic detoxification, through complexation of toxic metal ions by specific chelating agents, appears an efficacious clinical strategy mainly in acute cases of metal intoxication.

Cadmium (Cd) is a toxic metal for the human organism and for all ecosystems. Cd is naturally found at low levels; however, higher amounts of Cd in the environment result from human activities as it spreads into the air and water in the form of micropollutants as a consequence of industrial processes, pollution, waste incineration, and electronic waste recycling. The human body has a limited ability to respond to Cd exposure since the metal does not undergo metabolic degradation into less toxic species and is only poorly excreted. The extremely long biological half-life of Cd essentially makes it a cumulative toxin; chronic exposure causes harmful effects from the metal stored in the organs. The present paper considers exposure and potential health concerns due to environmental cadmium. Exposure to Cd compounds is primarily associated with an elevated risk of lung, kidney, prostate, and pancreatic cancer. Cd has also been linked to cancers of the breast, urinary system, and bladder. The multiple mechanisms of Cd-induced carcinogenesis include oxidative stress with the inhibition of antioxidant enzymes, the promotion of lipid peroxidation, and interference with DNA repair systems. Cd2+ can also replace essential metal ions, including redox-active ones. A total of 12 cancer types associated with specific genes coding for the Cd-metalloproteome were identified in this work. In addition, we summarize the proper treatments of Cd poisoning, based on the use of selected Cd detoxifying agents and chelators, and the potential for preventive approaches to counteract its chronic exposure.

Rhodium is one of the most used metals in catalysis both in laboratory reactions and industrial processes. Despite the extensive exploration on “classical” ligands carried out during the past decades in the field of rhodium-catalyzed reactions, such as phosphines, and other common types of ligands including N-heterocyclic carbenes, ferrocenes, cyclopentadienyl anion and pentamethylcyclopentadienyl derivatives, etc., there is still lively research activity on this topic, with considerable efforts being made toward the synthesis of new preformed rhodium catalysts that can be both efficient and selective. Although the “golden age” of homogeneous catalysis might seem over, there is still plenty of room for improvement, especially from the point of view of a more sustainable chemistry. In this review, temporally restricted to the analysis of literature during the past five years (2015–2020), the latest findings and trends in the synthesis and applications of Rh(I) complexes to catalysis will be presented. From the analysis of the most recent literature, it seems clear that rhodium-catalyzed processes still represent a stimulating challenge for the metalloorganic chemist that is far from being over.

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The spike protein (S) of SARS-CoV-2 has been shown to bind to the human angiotensin-converting enzyme 2 (ACE2) receptor with much higher affinity compared to other coronaviruses. The binding interface between the ACE2 receptor plays a critical role in the entry mechanism of SARS-CoV-2 virus. There are specific amino acids involved in the interaction between S protein and ACE2 receptor. This specificity is critical for the virus to establish a systemic infection and cause COVID-19 disease. In the ACE2 receptor, the largest number of amino acids that play a crucial role in the mechanism of interaction and recognition with the S protein are located in the C-terminal part which represents the main binding region between ACE2 and S. This fragment is abundant in coordination residues such as aspartates, glutamates and histidine that could be targeted by metal ions. Zn2+ ion binds to the ACE2 receptor in its catalytic site and modulates its activity, but it could also contribute to the structural stability of the entire protein. The ability of the human ACE2 receptor to coordinate metal ions, such Zn2+, in the same region where it binds to the S protein could have a crucial impact in the mechanism of recognition and interaction of ACE2-S with consequences on their binding affinity that deserve to be investigated. To test this possibility, this study aims to characterize the coordination ability of Zn2+, and also Cu2+ for comparison, with selected peptide models of the ACE2 binding interface using spectroscopic and potentiometric techniques.