Re(I) carbonyl complexes: Multimodal platforms for inorganic chemical biology

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Re(I) carbonyl complexes: Multimodal platforms for inorganic chemical Biology, Coordination Chemistry Reviews 351 (2017) 172–188

 

Fluorescence microscopy is one of the most widely used techniques for the visualization and study of biological processes. Its good spatial resolution (a few hundreds of nanometers for conventional microscopy experiments) makes it well suited for sub-cellular imaging, since typical eukaryotic cell diameters are in the range of a few tens of micrometers. In addition, due to its good spatial resolution, fluorescence imaging in live cells is achievable, providing relevant dynamic information. A large set of fluorescent probes with high quantum yields and diverse excitation and emission wavelengths are available, thus enabling sensitive and multi color imaging. Although highly valuable, fluorescence techniques also suffer from some drawbacks, such as photobleaching and photodamage of cells. Moreover, the fluorescence quantum yield of a probe is often sensitive to its environment (pH, hydrophobicity, polarity) and self-quenching can occur, for instance in the case of local accumulation of the probe (e.g. in a membrane). This means that intensity of fluorescence does not always correlate with quantity, which generally makes reliable quantification difficult. Ratiometric systems are proposed in the literature to solve these issues, but the question of the possible dependence on the relative quantum yields with environment and self-quenching extinction remains.

 

 

Owing to their unique photophysical properties, Re(I) metal carbonyl complexes have been extensively used in biological contexts as probes, 99mTc surrogates, drugs and as photosensitizers for photodynamic therapies. In this review we focused on their application as probes for bio-imaging, and in particular for the imaging of peptides and proteins. Several strategies aiming at labelling peptides and proteins with Re complexes have been highlighted. These strategies have enabled the study of these biomolecules at different scales by several bio-imaging techniques involving UV–vis or infrared light. Although tuning the photophysical properties of the (L)(X)Re(CO)x complexes can be achieved by modifying the ligands (L and X), no rationale have clearly emerged so far. Examples of probes possessing fully biocompatible properties enabling live imaging are still lacking and this constitutes a limitation for the use of these complexes. However, the inertness of some Re (CO)X complexes, the ease of their synthesis and functionalization may offer the opportunity to develop suitable probes for live imaging by IR or fluorescence.

 

 

Résumé: 

Coordination Chemistry Reviews 351 (2017) 172–188

 

Bio-imaging, by enabling the visualization of biomolecules of interest, has proved to be highly informative in the study of biological processes. Although fluorescence microscopy is probably one of the most used techniques, alternative methods of imaging, providing complementary information, are emerging. In this context, metal complexes represent valuable platforms for multimodal imaging, since they may combine interesting spectroscopic features and biologically relevant functionalization on a single molecular core. In particular, d6 low-spin rhenium tri-carbonyl complexes display unique luminescence and vibrational properties, and can be readily functionalized. Here we review their applications and potential as probes or drugs relying on their photophysical properties, before focusing on their use as multimodal probes for the labelling and imaging of peptides and proteins.

 

 

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Re(I) carbonyl complexes: Multimodal platforms for inorganic chemical Biology

 

Sarah Hostachy, Clotilde Policar, Nicolas Delsuc 

 

Coordination Chemistry Reviews 351 (2017) 172–188

 

doi : 10.1016/j.ccr.2017.05.004