Jacques Lux

A Rapidly Shuttling Copper-Complexed [2]Rotaxane with Three Different Chelating Groups in Its Axis†

Molecular machines are particularly promising in relation to potential applications in the fields of information storage and processing, imaging, and nanoscale electroor photochemically driven mechanical devices, as illustrated by recent spectacular results. Catenanes and rotaxanes constitute an important subclass of such systems, and our research group has been particularly interested in transition-metalcomplexed interlocking compounds. Most of these previously reported systems were two-geometry compounds, which were able to switch between a stable five-coordinate copper(II) complex where the copper(II) center is coordinated to a bidentate and a tridentate chelate and a second form, which is a four-coordinate copper(I) complex. In the latter form, the copper(I) center is coordinated to two bidentate ligands. A rare example of a three-geometry system was reported in 1996, and was based on a [2]catenane that consisted of two identical rings, each ring incorporating two different chelating units (a biand a tridentate ligand). The copper center could thus be four-, five-, or six-coordinate. Molecular “shuttles” represent the archetype of molecular machines and, equally importantly, they are often used in the fabrication of real devices. The shuttle-like [2]rotaxanes reported to date are two-station systems. These rotaxanes consist of a mobile ring threaded by an axis that incorporates two distinct functional groups, which are able to interact with the ring. To the best of our knowledge, no molecular shuttles with three distinct stations have been reported to date. However, catenanes have been described in which one or two rings (considered as mobile) are threaded through a larger ring that incorporates three different functional groups, which are able to interact with the mobile ring(s). A particularly elegant compound that belongs to this family of catenane-based molecular machines was reported in 2003. This molecule was the first example of a catenane-based rotary motor, that is, a machine that displays controlled directionality during the dynamic process. Incidentally, non-interlocking rotary machines had already been reported by other research groups, 33] and continue to attract much attention. 35] Herein, we describe the synthesis and electrochemical behavior of a rotaxane that acts as an electrochemically driven molecular shuttle over a long distance. The rotaxane consists of a coordinating ring threaded by an axis that incorporates three different chelates. It was expected that by introducing an intermediate “station” between the two terminal chelating groups, the gliding motion of the metalcomplexed ring would be much faster than the analogous motion without the intermediate chelating group, as the distance between the terminal stations is the same for the two systems. In the present system, the distance between the two terminal coordination sites is approximately 23 . Without a relay between the two end-chelates of the axis, the shuttling motion between these two stations would be expected to be very slow. It has already been shown that the presence of an aromatic spacer between the end-stations slows the shuttling motion significantly. The two forms of the rotaxane are shown in Scheme 1. As discussed below, the introduction of a 2,2’-bipyridine (bipy) between the two end-chelates of the thread facilitates the gliding process. The translational motion over 23 is as fast as the related motion in a two-station rotaxane that incorporates a 2,9-diphenyl-1,10-phenanthroline (dpp) unit and a 2,2’,6’,2’’-terpyridine (terpy) chelate, that is, the same groups as the terminal chelates of the present system, but over a distance of less than 10 . The coordinating units on the axis are 1) a dpp chelate, 2) a bipy chelate and 3) terpy, which is a tridentate ligand. The ring incorporates an 8,8’-diphenyl-3,3’biisoquinoline (dpbiiq) bidentate ligand. This endocyclic but nonsterically hindering chelate is a key component, which favors fast translational or rotational motions within shuttlelike rotaxanes or pirouetting systems, respectively. 30] The principle of the electrochemically driven motion relies on the relative stabilities of the various copper(I) and copper(II) complexes formed with the various ligands. Within the following sequence, the thermodynamic stability of the copper(I) complexes increases from [Cu(terpy)(dpbiiq)] to [Cu(dpp)(dpbiiq)]: [Cu(terpy)(dpbiiq)]< [Cu(bipy)(dpbiiq)]< [Cu(dpp)(dpbiiq)]. The stability sequence is reversed for Cu complexes: [Cu(dpp)(dpbiiq)]< [Cu(bipy)(dpbiiq)]< [Cu(terpy)(dpbiiq)]. These relative stabilities of the complexes within these two sequences reflect the electrochemical properties of the models listed above and, in particular, their redox potentials. The Cu/Cu redox potentials of the threaded model complexes (see the Supporting Information) and those of the two-station shuttle 5(4) + as well as their chemical structures, [*] Prof. J.-P. Collin, Dr. F. Durola, J. Lux, Prof. J.-P. Sauvage Laboratoire de Chimie Organo-Min rale, Institut de Chimie, LC3 UMR 7177 du CNRS Universit de Strasbourg 4 rue Blaise Pascal, 67070 Strasbourg Cedex (France) Fax: (+ 33)3-9024-1368 E-mail: sauvage@chimie.u-strasbg.fr Homepage: http://www-chimie.u-strasbg.fr/~ lcom/

Near-infrared-induced heating of confined water in polymeric particles for efficient payload release.

Near-infrared (NIR) light-triggered release from polymeric capsules could make a major impact on biological research by enabling remote and spatiotemporal control over the release of encapsulated cargo. The few existing mechanisms for NIR-triggered release have not been widely applied because they require custom synthesis of designer polymers, high-powered lasers to drive inefficient two-photon processes, and/or coencapsulation of bulky inorganic particles. In search of a simpler mechanism, we found that exposure to laser light resonant with the vibrational absorption of water (980 nm) in the NIR region can induce release of payloads encapsulated in particles made from inherently non-photo-responsive polymers. We hypothesize that confined water pockets present in hydrated polymer particles absorb electromagnetic energy and transfer it to the polymer matrix, inducing a thermal phase change. In this study, we show that this simple and highly universal strategy enables instantaneous and controlled release of payloads in aqueous environments as well as in living cells using both pulsed and continuous wavelength lasers without significant heating of the surrounding aqueous solution.

Light-responsive nanoparticle depot to control release of a small molecule angiogenesis inhibitor in the posterior segment of the eye

Therapies for macular degeneration and diabetic retinopathy require intravitreal injections every 4-8 weeks. Injections are uncomfortable, time-consuming, and carry risks of infection and retinal damage. However, drug delivery via noninvasive methods to the posterior segment of the eye has been a major challenge due to the eyes unique anatomy and physiology. Here we present a novel nanoparticle depot platform for on-demand drug delivery using a far ultraviolet (UV) light-degradable polymer, which allows noninvasively triggered drug release using brief, low-power light exposure. Nanoparticles stably retain encapsulated molecules in the vitreous, and can release cargo in response to UV exposure up to 30 weeks post-injection. Light-triggered release of nintedanib (BIBF 1120), a small molecule angiogenesis inhibitor, 10 weeks post-injection suppresses choroidal neovascularization (CNV) in rats. Light-sensitive nanoparticles are biocompatible and cause no adverse effects on the eye as assessed by electroretinograms (ERG), corneal and retinal tomography, and histology.

Layered hydrogels accelerate iPSC-derived neuronal maturation and reveal migration defects caused by MeCP2 dysfunction

Significance Three-dimensional systems enable the formation of tissue-mimetic architectures and promote more realistic physiological responses than conventional 2D systems. Here we report a previously unidentified layered 3D culture system to assay migration and maturation of human induced pluripotent stem cell (iPSC)-derived neural progenitor cells (NPCs) and reveal a genotype-specific effect of methyl-CpG-binding protein-2 (MeCP2) dysfunction on iPSC-derived neuronal migration and maturation in 3D layered hydrogels. Using this platform, we identified a migration defect in MeCP2-mutant iPSC-derived NPCs and confirmed previous observations that neurons derived from these cells have reduced neurite outgrowth and fewer synapses. Meanwhile, 3D hydrogel culture accelerates neuronal differentiation of iPSC-derived NPCs. Probing a wide range of cellular phenotypes in neurodevelopmental disorders using patient-derived neural progenitor cells (NPCs) can be facilitated by 3D assays, as 2D systems cannot entirely recapitulate the arrangement of cells in the brain. Here, we developed a previously unidentified 3D migration and differentiation assay in layered hydrogels to examine how these processes are affected in neurodevelopmental disorders, such as Rett syndrome. Our soft 3D system mimics the brain environment and accelerates maturation of neurons from human induced pluripotent stem cell (iPSC)-derived NPCs, yielding electrophysiologically active neurons within just 3 wk. Using this platform, we revealed a genotype-specific effect of methyl-CpG-binding protein-2 (MeCP2) dysfunction on iPSC-derived neuronal migration and maturation (reduced neurite outgrowth and fewer synapses) in 3D layered hydrogels. Thus, this 3D system expands the range of neural phenotypes that can be studied in vitro to include those influenced by physical and mechanical stimuli or requiring specific arrangements of multiple cell types.

A copper-based shuttling [2]rotaxane with two bidentate chelates in the axis: steric control of the motion

Contrary to most of the other molecular machines based on copper-complexed catenanes or rotaxanes made and investigated in Strasbourg, the present report is dealing with a molecular shuttle for which the copper centre is complexed to two bidentate chelates, regardless of the state of the shuttle. In other words, the axis contains a sterically hindering bidentate chelate, namely a 2,9-diphenyl-1,10-phenanthroline (dpp) derivative, and another but less hindering bidentate chelate, 2,2′-bipyridine (bipy). The synthesis of the [2]rotaxane involves 15 individual chemical steps, excluding the preparation of the macrocyclic component of the [2]rotaxane. The threaded macrocycle is a 39-membered ring which incorporates an endocyclic but non sterically hindering chelate of the 8,8′-diphenyl-3,3′-biisoquinoline family (dpbiiq). The electrochemically-induced gliding motion of the copper-complexed ring from the dpp “station” to the bipy “station” and vice versa is fast on the cyclic voltammetry timescale (milliseconds). The copper(I) state is preferably located on the dpp unit whereas, by oxidising the copper(I) centre to its divalent state, the translation motion takes place to afford the thermodynamically most stable state now involving the bipy chelate.

Nanogels from metal-chelating crosslinkers as versatile platforms applied to copper-64 PET imaging of tumors and metastases

Metals are essential in medicine for both therapy and diagnosis. We recently created the first metal-chelating nanogel imaging agent, which employed versatile, reproducible chemistry that maximizes chelation stability. Here we demonstrate that our metal chelating crosslinked nanogel technology is a powerful platform by incorporating 64Cu to obtain PET radiotracers. Polyacrylamide-based nanogels were crosslinked with three different polydentate ligands (DTPA, DOTA, NOTA). NOTA-based nanogels stably retained 64Cu in mouse serum and accumulated in tumors in vivo as detected by PET/CT imaging. Measurement of radioactivity in major organs ex vivo confirmed this pattern, revealing a high accumulation (12.3% ID/g and 16.6% ID/g) in tumors at 24 and 48 h following administration, with lower accumulation in the liver (8.5% ID/g at 24 h) and spleen (5.5% ID/g). Nanogels accumulated even more efficiently in metastases (29.9% and 30.4% ID/g at 24 and 48 h). These metal-chelating nanogels hold great promise for future application as bimodal PET/MRI agents; chelation of β-emitting radionuclides could enable radiation therapy.

Metal Chelating Crosslinkers Form Nanogels with High Chelation Stability.

We present a series of hydrogel nanoparticles (nanogels) incorporating either acyclic or cyclic metal chelates as crosslinkers. These crosslinkers are used to formulate polyacrylamide-based nanogels (diameter 50 to 85 nm) yielding contrast agents with enhanced relaxivities (up to 6-fold greater than Dotarem®), because this nanogel structure slows the chelators tumbling frequency and allows fast water exchange. Importantly, these nanogels also stabilize Gd3+ within the chelator thermodynamically and kinetically against metal displacement through transmetallation, which should reduce toxicity associated with release of free Gd3+. This chelation stability suggests that the chelate crosslinker strategy may prove useful for other applications of metal-chelating nanoparticles in medicine, including other imaging modalities and radiotherapy.

Long-Lasting and Efficient Tumor Imaging Using a High Relaxivity Polysaccharide Nanogel Magnetic Resonance Imaging Contrast Agent.

Clinically approved small-molecule magnetic resonance imaging (MRI) contrast agents are all rapidly cleared from the body and offer weak signal enhancement. To avoid repeated administration of contrast agent and improve signal-to-noise ratios, agents with stronger signal enhancement and better retention in tumors are needed. Therefore, we focused on hydrogels because of their excellent water accessibility and biodegradability. Gadolinium (Gd)-chelating cross-linkers were incorporated into self-assembled pullulan nanogels to both impart magnetic properties and to stabilize this material that has been extensively studied for medical applications. We show that these Gd-chelating pullulan nanogels (Gd-CHPOA) have the highest reported relaxivity for any hydrogel-based particles and accumulate in the 4T1 tumors in mice at high levels 4 h after injection. This combination offers high signal enhancement and lasts up to 7 days to delineate the tumor clearly for longer imaging time scales. Importantly, this long-term accumulation does not cause any damage or toxicity in major organs up to three months after injection. Our work highlights the clinical potential of Gd-CHPOA as a tumor-imaging MRI contrast agent, permitting tumor identification and assessment with a high signal-to-background ratio.

Malachite Green Derivatives for Two-Photon RNA Detection

The design, preparation and characterisation of a library of malachite green (MG) derivatives for two‐photon RNA labelling is described. Some of these MG derivatives exhibit an increased affinity for an MG‐aptamer, as well as improved two‐photon sensitivity when compared to the classical malachite green chloride. The underlying mechanisms and potential benefits for in vivo RNA visualisation are discussed.

Short Soluble Coumarin Crosslinkers for Light-Controlled Release of Cells and Proteins from Hydrogels

Materials that degrade or dissociate in response to low power light promise to enable on-demand, precisely localized delivery of drugs or bioactive molecules in living systems. Such applications remain elusive because few materials respond to wavelengths that appreciably penetrate tissues. The photocage bromohydroxycoumarin (Bhc) is efficiently cleaved upon low-power ultraviolet (UV) and near-infrared (NIR) irradiation through one- or two-photon excitation, respectively. We have designed and synthesized a short Bhc-bearing crosslinker to create light-degradable hydrogels and nanogels. Our crosslinker breaks by intramolecular cyclization in a manner inspired by the naturally occurring ornithine lactamization, in response to UV and NIR light, enabling rapid degradation of polyacrylamide gels and release of small hydrophilic payloads such as an ∼10 nm model protein and murine mesenchymal stem cells, with no background leakage.