Three iridium photosensitizers, [Ir(dCF 3 ppy) 2 (N−N)] + , where N−N is 1,4,5,8-tetraazaphenanthrene (TAP), pyrazino[2,3-a]phenazine (pzph), or benzo[a]pyrazino[2,3-h]phenazine (bpph) and dCF 3 ppy is 2-(3,5-bis(trifluoromethylphenyl)pyridine), were found to be remarkably strong photo-oxidants with enhanced light absorption in the visible region. In particular, judicious ligand design provided access to Ir-bpph, with a molar absorption coefficient, ε = 9800 M −1 cm −1 , at 450 nm and an excited-state reduction potential, E(Ir + * /0 ) = 1.76 V vs NHE. These complexes were successful in performing light-driven charge separation and energy storage, where all complexes photo-oxidized seven different electron donors with rate constants (0.089−3.06) × 10 10 M −1 s −1 . A Marcus analysis provided a total reorganization energy of 0.7 ± 0.1 eV for excited-state electron transfer.
Among all molecules developed for anticancer therapies, photodynamic therapeutic agents have a unique profile. Their maximal activity is specifically triggered in tumors by light and toxicity of even systemically delivered drug is prevented in non-illuminated parts of the body. Photosensitizers exert their therapeutic effect by producing reactive oxygen species via a lightactivated reaction with molecular oxygen. Consequently, the lowering of pO2 deep in solid tumors limits their treatment and makes essential the design of oxygen-independent sensitizers. In this perspective, we have recently developed Ir(III)-based molecules able to oxidize biomolecules by type I processes under free-oxygen conditions. We examine here their photo-toxicity in relevant biological models. We show that drugs, which are mitochondria-accumulated, induce upon light irradiation a dramatic decrease of the cell viability, even under low oxygen conditions. Finally, assays on 3D tumor spheroids highlight the importance of the light-activation step and the oxygen consumption rate on the drug activity.
Photo‐induced electron transfer chemistry between molecules is a central theme in several fields including biology, physics and chemistry. Specifically, in photoredox catalysis, greater use has been made of iridium(III) complexes as they exhibit ground‐ and excited‐state redox potentials that span a very large range. Unfortunately, most of these complexes suffer from limited visible light absorption properties. This concept article highlights recent developments in the synthesis of iridium(III) complexes with increased visible light absorption properties and their use as candidates for visible light driven redox catalysis. Fundamental tools are provided to enable the independent tuning of the HOMO and LUMO energy levels. Recent examples are given with the hope that this concept article will foster further developments of iridium(III)‐based sensitizers for visible light driven reactivity.
OmpA, a protein commonly found in the outer membrane of Gram-negative bacteria, has served as a paradigm for the study of b-barrel proteins for several decades. In Escherichia coli, OmpA was previously reported to form complexes with RcsF, a surface-exposed lipoprotein that triggers the Rcs stress response when damage occurs in the outer membrane and the peptidoglycan. How OmpA interacts with RcsF and whether this interaction allows RcsF to reach the surface has remained unclear. Here, we integrated in vivo and in vitro approaches to establish that RcsF interacts with the C-terminal, periplasmic domain of OmpA, not with the N-terminal b-barrel, thus implying that RcsF does not reach the bacterial surface via OmpA. Our results suggest a novel function for OmpA in the cell envelope: OmpA competes with the inner membrane protein IgaA, the downstream Rcs component, for RcsF binding across the periplasm, thereby regulating the Rcs response.
Photodynamic therapeutic agents are of key interest in developing new strategies to develop more specific and efficient anticancer treatments. In comparison to classical chemotherapeutic agents, the activity of photodynamic therapeutic compounds can be finely controlled thanks to the light triggering of their photoreactivity. The development of type I photosensitizing agents, which do not rely on the production of ROS, is highly desirable. In this context, we developed new iridium(III) complexes which are able to photoreact with biomolecules; namely, our Ir(III) complexes can oxidize guanine residues under visible light irradiation. We report the synthesis and extensive photophysical characterization of four new Ir(III) complexes, [Ir(ppyCF)(N^N)] [ppyCF = 2-(3,5-bis(trifluoromethyl)phenyl)pyridine) and N^N = 2,2'-dipyridyl (bpy); 2-(pyridin-2-yl)pyrazine (pzpy); 2,2'-bipyrazine (bpz); 1,4,5,8-tetraazaphenanthrene (TAP)]. In addition to an extensive experimental and theoretical study of the photophysics of these complexes, we characterize their photoreactivity toward model redox-active targets and the relevant biological target, the guanine base. We demonstrate that photoinduced electron transfer takes place between the excited Ir(III) complex and guanine which leads to the formation of stable photoproducts, indicating that the targeted guanine is irreversibly damaged. These results pave the way to the elaboration of new type I photosensitizers for targeting cancerous cells.
Time-resolved spectroscopy was exploited to gain new insights into the nature and dynamics of charge transfer excited states of bis-cyclometalated Ir(iii) complexes. We showed that its dynamics is strongly influenced by the nature of the diimine ligand due to the existence of a ligand-ligand charge transfer process in the picosecond timescale. All the results are supported by DFT/TD-DFT calculations and spectroelectrochemistry.
Germanium is particularly suitable for the design of FTIR-based biosensors for proteins. The grafting of stable and thin organic layers on germanium surfaces remains, however, challenging. To tackle this problem, we developed a calix[4]arene−tetradiazonium salt decorated with four oligo(ethylene glycol) chains and a terminal reactive carboxylic group. This versatile molecular platform was covalently grafted on germanium surfaces to yield robust readyto-use surfaces for biosensing applications. The grafted calixarene monolayer prevents nonspecific adsorption of proteins while allowing bioconjugation with biomolecules such as bovine serum albumin (BSA) or biotin. It is shown that the native form of the investigated proteins was maintained upon immobilization. As a proof of concept, the resulting calix[4]arene-based germanium biosensors were used through a combination of ATR-FTIR spectroscopy and fluorescence microscopy for the selective detection of streptavidin from a complex medium. This study opens real possibilities for the development of sensitive and selective FTIR-based biosensors devoted to the detection of proteins. 47 surfaces (i.e., oxidation and passivation) and lead usually to a 48 weak reproducibility. Moreover, once modified, the surfaces 49 present a poor stability, limiting their use in the field of 50 biosensing. Another strategy relies on the reductive grafting of 51 aryldiazonium salts, which leads to a strong and durable 52 attachment of an organic layer onto the germanium sur-53 face. 18,19 However, because of the high reactivity of the radicals 54 produced upon the reduction of diazonium cations, disordered 55 multilayers are generally obtained through this method. The 56 preparation of well-ordered monolayers with diazonium 57 chemistry remains thus highly challenging, 20−24 though this 58 is a key point when immobilizing receptors to warrant an 59 efficient and sensitive sensing. 25,26 60 In this context, we have recently developed a general 61 strategy for surface modification, which consists in the covalent 62 grafting of molecular platforms based on calix[4]arene− 63 tetradiazonium salts. 27−31 As demonstrated on various 64 materials or nanomaterials, the unique macrocyclic structure 65 of calix[4]arenes enables the formation of robust, dense, and
Dipstick assays using silver nanoparticles (AgNPs) stabilized by a thin calix[4]arene-based coating were developed and used for the detection of Anti-SARS-CoV-2 IgG in clinical samples. The calixarene-based coating enabled the covalent bioconjugation of the SARS-CoV-2 Spike Protein via the classical EDC/sulfo-NHS procedure. It further conferred remarkable stability to the resulting bioconjugated AgNPs, as no degradation was observed over several months. In comparison with lateral-flow immunoassays (LFIAs) based on classical gold nanoparticles, our AgNP-based system constitutes a clear step forward, as the limit of detection for Anti-SARS-CoV-2 IgG was reduced by 1 order of magnitude and similar signals were observed with 10 times fewer particles. In real clinical samples, the AgNP-based dipstick assays showed impressive results: 100% specificity was observed for negative samples, while a sensitivity of 73% was determined for positive samples. These values match the typical sensitivities obtained for reported LFIAs based on gold nanoparticles. These results (i) represent one of the first examples of the use of AgNP-based dipstick assays in the case of real clinical samples, (ii) demonstrate that ultrastable calixarene-coated AgNPs could advantageously replace AuNPs in LFIAs, and thus (iii) open new perspectives in the field of rapid diagnostic tests.
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