This work presents several metallosupramolecular coordination polyelectrolytes (MEPEs) self-assembled from rigid, pi-conjugated, pyridine ring functionalized bisterpyridines and metal ions. The MEPEs are water-soluble and display different colors spanning the entire visible regions. Optical, electrochemical, and electrochromic properties of the obtained MEPEs are presented. The results show that the properties are profoundly affected by the nature of the substituents at the peripheral pyridine rings. Namely, MEPEs assembled from the electron-rich OMe group modified ligands exhibit high switching reversibility and stability and show a lower switching potential than the unsubstituted and electron-deficient Br-substituted analogues. The response times can be tuned either by the design of the ligands or by the choice of the metal ions to cover a broad time scale from under 1 s to several minutes. The optical memory is enhanced from 30 s to longer than 15 min as a comparison of unsubstituted and substituted MEPEs shows. Thus, the significantly enhanced stability and the ease of tuning the properties render this type of supramolecular assembly attractive as electrochromic materials for applications in a large variety of areas. Most importantly, we presented the structure-property relationships of MEPEs, which lays the groundwork for further design of new bisterpyridine-based metallosupramolecular functional materials.

Since the first report on electrochromism, [1] rapidly growing interest has been paid to electrochromic materials (ECMs) as molecular switches for optical and electronic applications.[2]So far, conducting polymers (CPs), [3] molecular dyes, and metal oxides [2a,4] have been extensively investigated as three major classes of ECMs. Only few examples of metallo-supramolecular assemblies were reported, [5] however, these first researches indicate that the components are potential candidates for the next generation of single-layer, multi-color, lowvoltage ECMs. Metallo-supramolecular assemblies feature transition metal centered sites with redox dependent metalto-ligand charge transfer (MLCT), intervalence CT and intraligand transitions giving rise to strong optical contrast.[6] The electrochromic response is readily tuned by the choice of the metal ions as well as by the design of the ligands. [7] For the development of ECMs, ditopic bis-terpyridine based metallo-supramolecular coordination polyelectrolytes (MEPEs) are very attractive. Terpyridines have a rich coordination chemistry and generally high binding constants giving rise to macromolecular assemblies with distinct electrochemical properties.[8] The modularity of self-assembly permits introducing different metal ions and ligands as well as rapid fabrication of material libraries with a large range of properties. The resulting MEPEs are readily processed from aqueous media in various device architectures including thin films.[9] Additionally, MEPEs are also available as liquid crystalline phases that are readily processed as nanostructure, [10] thin films, [11] and mesophases.[12]In our research, we focus on pyridine-ring functionalized bis-terpyridines coupled with rigid, linear spacers, as contrasted to the unsubstituted analogues reported in previous reports.[ 8] We reasoned that a functional group at the pyridine periphery close to the metal ion will influence through steric or electronic effects the ligand field stabilization energy and, thus, affecting the properties of the MEPEs. A linear rigid-rod type structure affords a loose, uncongested polymer morphology facilitating unhindered counter ion transport, thereby leading to rapid response times. [3c,5d] Accordingly, four new MEPEs, Poly-FeL 2 ∼ Poly-FeL 5 , were self-assembled using Fe(II) and ligands L 2 ∼ L 5 , which have different substitutents and spacers (Fig. 1) in addition to the well-known Poly-FeL 1 as a reference. Here, we propose the first structure-property relationships for these materials, which are needed, but not available to date, to serve for the de novo design and fabrication of new materials. Most importantly, our results reveal that the substituents at the pyridine periphery of the ligands significantly affect the electrochromic properties of the resulting MEPEs. Consequently, MEPEs functionalized with electron-donating groups (OMe) display high stability, low switching potential, high reversibility, fast switching rates, and enhanced optical memory (defined here as the abil...

Both reactive oxygen species (ROS) and Forkhead box O (FOXO) family transcription factors are involved in the regulation of adipogenic differentiation of preadipocytes and stem cells. While FOXO has a pivotal role in maintaining cellular redox homeostasis, the interactions between ROS and FOXO during adipogenesis are not clear. Here we examined how ROS and FOXO regulate adipogenesis in human adipose-derived stem cells (hASC). The identity of isolated cells was confirmed by their surface marker expression pattern typical for human mesenchymal stem cells (positive for CD29, CD44, CD73, CD90, and CD105, negative for CD45 and CD31). Using a standard adipogenic cocktail consisting of insulin, dexamethasone, indomethacin, and 3-Isobutyl-1-methylanxthine (IDII), adipogenesis was induced in hASC, which was accompanied by ROS generation. Scavenging ROS production with N-acetyl-L-cysteine or EUK-8, a catalytic mimetic of superoxide dismutase (SOD) and catalase, inhibited IDII-induced adipogenesis. We then mimicked IDII-induced oxidative stress through a lentiviral overexpression of Nox4 and an exogenous application of hydrogen peroxide in hASC and both manipulations significantly enhanced adipogenesis without changing the adipogenic differentiation rate. These data suggest that ROS promoted lipid accumulation in hASC undergoing adipogenesis. Antioxidant enzymes, including SOD2, catalase, and glutathione peroxidase were upregulated by IDII during adipogenesis, and these effects were blunted by FOXO1 silencing, which also suppressed significantly IDII-induced adipogenesis. Our findings demonstrated a balance of ROS generation and endogenous antioxidants in cells undergoing adipogenesis. Approaches targeting ROS and/or FOXO1 in adipocytes may bring new strategies to prevent and treat obesity and metabolic syndrome.