Chelatable, or mobile, forms of zinc play critical signaling roles in numerous biological processes. Elucidating the action of mobile Zn(II) in complex biological environments requires sensitive tools for visualizing, tracking, and manipulating Zn(II) ions. A large toolbox of synthetic photoinduced electron transfer (PET)-based fluorescent Zn(II) sensors are available, but the applicability of many of these probes is limited by poor zinc sensitivity and low dynamic ranges owing to proton interference. We present here a general approach for acetylating PET-based probes containing a variety of fluorophores and zinc-binding units. The new sensors provide substantially improved zinc sensitivity and allow for incubation of live cells and tissue slices with nM probe concentrations, a significant improvement compared to the μM concentrations that are typically required for a measurable fluorescence signal. Acetylation effectively reduces or completely quenches background fluorescence in the metal-free sensor. Bi...

http://pubs.acs.org/doi/pdf/10.1021/acssensors.5b00022

Reaction-Based Probes for Imaging Mobile Zinc in Live Cells and Tissues

The mechanism responsible for peptide bond hydrolysis by Co(III) and Cu(II) complexes with (oxa)cyclen ligands has been revisited by means of computational tools. We propose that the mechanism starts by substrate coordination and an outer-sphere attack on the amide C atom of a solvent water molecule assisted by the metal hydroxo moiety as a general base, which occurs through six-membered ring transition states. This new mechanism represents a more likely scenario than the previously proposed mechanisms that involved an inner-sphere nucleophilic attack through more strained four-membered rings transition states. The corresponding computed overall free-energy barrier of 25.2 kcal mol-1 for hydrolysis of the peptide bond in Phe-Ala by a cobalt(III) oxacyclen catalyst (1) is consistent with the experimental values obtained from rate constants. Also, we assessed the influence of the nature of the ligand throughout a systematic replacement of N by O atoms in the (oxa)cyclen ligand. Increasing the number of coordinating O atoms accelerates the reaction by increasing the Lewis acidity of the metal ion. On the other hand, the higher reactivity observed for the copper(II) oxacyclen catalyst with respect to the analogous Co(III) complex can be attributed to the larger Bronsted basicity of the copper(II) hydroxo ligand. Ultimately, the detailed understanding of the ligand and metal nature effects allowed us to identify the double role of the metal hydroxo complexes as Lewis acids and Bronsted bases and to rationalize the observed reactivity trends.

Peptide Hydrolysis by Metal (Oxa)cyclen Complexes: Revisiting the Mechanism and Assessing Ligand Effects.

The computational study of bioinorganic complexes between transition metals and flexible ligands is still challenging, given that, besides requiring extensive conformational searches, the treatment of metal-ligand bonds demands the application of quantum chemical methods. Herein, the adducts formed between molybdocene, which exhibits antitumor activity and reacts with thiol groups to give stable water-soluble complexes, and the tripeptide glutathione, which is a major source of biological thiols, are studied. Conformational searches are performed using the semiempirical PM6 method followed by geometry optimizations and single-point calculations using density functional theory methods. In addition, molecular dynamics simulations of the molybdocene-glutathione complex involved in the regioselective hydrolysis of the Cys-Gly linkage are performed in explicit solvent. The reactive process is also studied theoretically on cluster models of both the molybdocene-bound and the free peptide.

Molecular modeling of bioorganometallic compounds: thermodynamic properties of molybdocene-glutathione complexes and mechanism of Peptide hydrolysis.

To improve their properties or to introduce entirely new functionalities, the intriguing scaffolds of nucleic acids have been decorated with various modifications, most recently also organometallic ones. While challenging to...

Organometallic Modification Confers Oligonucleotides New Functionalities

Synthetic metal complexes catalyzing the hydrolysis of peptide bonds of proteins or phosphodiester bonds of RNA or DNA have been designed to mimic proteases, ribonucleases, or deoxyribonucleases. Various attempts were made to raise the catalytic rate and selectivity in the structure of the substrate and the cleavage site. In particular, effective artificial proteases and artificial metallonucleases were synthesized by combining the catalytic metal centers with organic moieties recognizing the substrate structures. Examples are artificial metalloproteases selectively removing the pathogenic proteins of amyloid diseases and artificial metallodeoxyribonucleases cleaving double-stranded DNA at predetermined positions.

Artificial Metalloproteases and Metallonucleases

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Artificial Metalloproteases and Metallonucleases