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Scheller, Judith S.; Irvine, Gordon W.; Stillman, Martin J.
doi: 10.1039/c7dt03319bpmid: 29431781
Metallothioneins (MTs) are small, cysteine-rich proteins, found throughout Nature. Their ability to bind a number of different metals with a range of stoichiometric ratios means that this protein family is critically important for essential metal (Zn2+ and Cu+) homeostasis, metal storage, metal donation to nascent metalloenzymes as well as heavy metal detoxification. With its 20 cysteines, metallothionein is also considered to protect cells against oxidative stress. MT has been studied by a large number of researchers over the last 6 decades using a variety of spectroscopic techniques. The lack of distinguishing chromophores for the multitude of binding sites has made the evaluation of stoichiometric properties for different metals challenging. Initially, only 113Cd-NMR spectroscopy could provide strong evidence for the proposed cluster formation of Cd-MT. The extraordinary development of electrospray ionization mass spectrometry (ESI-MS), where all coexisting species in solution are observed, revolutionized MT research. Prior to the use of ESI-MS data, a range of “magic numbers” representing metal-to-MT molar ratios were reported from optical spectroscopic studies. The availability of ESI mass spectral data led to (i) the confirmation of cluster formation, (ii) a conceptual understanding of the cooperativity involved in multiple metal binding events, (iii) the presence of domain specificity between regions of the protein and (iv) mechanistic details involving both binding affinities and rate constants. The kinetic experiments identified the presence of multiple individual binding sites, each with a unique rate constant and an analogous binding affinity. The almost linear trend in rate constants as a function of bound As3+ provided a unique insight that became a critical step in the complete understanding of the mechanistic details of the metalation of MT. To fully define the biological function of this sulfur-rich protein it is necessary to determine kinetic rate constants and binding affinities for the essential metals. Recently, Zn2+ competition experiments between both of the isolated fragments (α and β) and the full-length protein (βα-MT 1a) as well as Zn2+ competition between βα-MT 1a and carbonic anhydrase were reported. From these data, the trend in binding affinities and the values of the Kf of the 7 bimolecular reactions involved in metalation were determined. From the analysis of ESI-MS data for Cu+ binding to βα-MT 1a at different pH-values, a trend in the 20 binding affinities for the complete metalation mechanism was reported. This review details a personal view of the historical development of the determination of stoichiometry for metal binding, the structure of the binding sites, the rates of the metalation reactions and the underlying binding affinities for each metalation step. We have attempted to summarize the experimental developments that led to the publication in May 2017 of the experimental determination of the 20 binding constants for the 20 sequential bimolecular reactions for Cu+ binding to the 20 Cys of apoMT as a function of pH that show the appearance and disappearance of clusters. We report both published data and in a series of tables an assembly of stoichiometries, and equilibrium constants for Zn2+ and Cu+ for many different metallothioneins.
doi: 10.1039/c8dt00017dpmid: 29498725
The hydrolysis reaction between Brønsted basic organometallic or metal–amide reagents with Brønsted acidic OH groups from water or metal–hydroxides may act as a controlled stoichiometric strategy for the formation of M–O–M bonds, if careful consideration of reaction conditions is employed. This article explores the utilisation of highly reactive organometallic and metal–amide complexes from across the periodic table as reagents for the synthesis of metal-oxo clusters, oxo-bridged heterobimetallics and metal oxide nanoparticles. Such reactivity typically occurs at low temperatures with the release of hydrocarbon or amine by-products. The impact of ligand coordination, M–C bond strength, M–OH acidity and reaction temperature are discussed.
Chen, Liyu; Luque, Rafael; Li, Yingwei
doi: 10.1039/c8dt00092apmid: 29492493
Metal–organic frameworks (MOFs) have been demonstrated to be excellent hosts for metal nanostructures. Herein, a perspective of recent development achieved to control the location, composition, shape, and structure of the encapsulated metal nanostructures is provided. The interesting properties and potential applications of the designed metal@MOF composites as well as future challenges and opportunities in this field are also discussed.
Tzubery, Avia; Melamed-Book, Naomi; Tshuva, Edit Y.
doi: 10.1039/c7dt04828apmid: 29451281
Two differently substituted fluorescent salen Ti(iv) complexes were developed. One was inactive on human cancer cells, whereas the other showed high cytotoxicity. Based on live cell imaging, both complexes penetrated the cell, but were not detected in the nuclei. Moreover, the inactive complex was trapped in endocytic vesicles, whereas the active complex accumulated in the perinuclear region and inflected phototoxicity upon continuous irradiation.
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