A mixed‐valence {MnII3MnIIIFeII2FeIII2} cyanide‐bridged molecular cube hosting a caesium cation, Cs⊂{Mn4Fe4}, was synthesized and structurally characterized by X‐ray diffraction. Cyclic‐voltammetry measurements show that its electronic state can be switched between five different redox states, which results in a remarkable electrochromic effect. Magnetic measurements on fresh samples point to the occurrence of a spin‐state change near room temperature, which could be ascribed to a metal‐to‐metal electron transfer converting the {FeII−CN−MnIII} pair into a {FeIII−CN−MnII} pair. This feature was only previously observed in the polymeric MnFe Prussian‐blue analogues (PBAs). Moreover, this novel switchable molecule proved to be soluble and stable in organic solvents, paving the way for its integration into advanced materials.
Antibody detection in autoimmune disorders, such as multiple sclerosis (MS) and Rett syndrome (RTT) can be achieved more efficiently using synthetic peptides. The previously developed synthetic antigenic probe CSF114(Glc), a type I' β-turn N-glucosylated peptide structure, is able to recognize antibodies in MS and RTT patients' sera as a sign of immune system derangement. We report herein the design, synthesis, conformational analysis, and immunological evaluation of a collection of glycopeptide analogs of CSF114(Glc) to characterize the specific role of secondary structures in MS and RTT antibody recognition. Therefore, we synthesized a series of linear and cyclic short glucosylated sequences, mimicking different β-turn conformations, which were evaluated in inhibition enzyme-linked immunosorbent assays (ELISA). Calculated IC50 ranking analysis allowed the selection of the candidate octapeptide containing two (S)-2-amino-4-pentynoic acid (L-Pra) residues Ac-Pra-RRN(Glc)GHT-Pra-NH2 , with an IC50 in the nanomolar range. This peptide was adequately modified for solid-phase ELISA (SP-ELISA) and surface plasmon resonance (SPR) experiments. Pra-RRN(Glc)GHT-Pra-NH2 peptide was modified with an alkyl chain linked to the N-terminus, favoring immobilization on solid phase in SP-ELISA and differentiating IgG antibody recognition between patients and healthy blood donors with a high specificity. However, this peptide displayed a loss in IgM specificity and sensitivity. Moreover, an analog was obtained after modification of the octapeptide candidate Ac-Pra-RRN(Glc)GHT-Pra-NH2 to favor immobilization on SPR sensor chips. SPR technology allowed us to determine its affinity (KD = 16.4 nM), 2.3 times lower than the affinity of the original glucopeptide CSF114(Glc) (KD = 7.1 nM).
A key challenge in the design of magnetic molecular switches is to obtain bistability at room temperature. Here, we show that application of moderate pressure makes it possible to convert a paramagnetic FeIII2CoII2 square complex into a molecular switch exhibiting a full dia‐ to paramagnetic transition: FeIICoIII ⇔ FeIIICoII. Moreover, the complex follows a rare behavior: the higher the pressure, the broader the magnetic hysteresis. Thus, the application of an adequate pressure allows inducing a magnetic bistability at room temperature with predictable hysteresis width. The structural studies at different pressures suggest that the pressure‐enhanced bistability is due to the strengthening of intermolecular interactions upon pressure increase. An original microscopic Ising‐like model including pressure effects is developed to simulate this unprecedented behavior. Overall, this study shows that FeCo complexes could be very sensitive piezo switches with potential use as sensors.
The search for chiral chromophores with efficient circularly polarized luminescence (CPL) is an on‐going hot topic in chemistry due to their potential applications in emerging fields such as spintronics and photonics. Beyond the largely exploited p‐block, 4d/5d‐block and f‐block chiral entities, chiral chromium(III) complexes have recently attracted interest because of the abundancy of chromium in the earth's crust, its kinetic inertness and its promising metal‐centered Cr(2E) and Cr(2T1) phosphorescence. The associated spin‐flip transitions could provide large dissymmetric factor (gnormallnormalunormalm ) and high luminescence quantum yields (ϕ) when six‐membered strong‐field chelate rings are coordinated to chiral six‐coordinate Cr(III) centers. In this minireview, we intend to focus our attention on the state‐of‐the‐art for the design of pseudo‐octahedral chiral mononuclear Cr(III) complexes for which chiroptical properties were investigated. The promising electronic properties of these complexes together with their low cost make these underexplored systems appealing candidates for CPL applications.
We have studied the zero-dimensional cubane molecular correspondent of a Prussian blue analogue Cs-Fe 4 Co 4 at low temperature and high magnetic field by means of Ledge X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We probe the magnetic and electronic structures of Fe and Co separately upon light irradiation, which allows us to observe directly the electron transfer coupled to a spin transition (ETCST) phenomenon within the molecular cubes and to investigate the nature of the metastable photoexcited state. From our results we estimate a lower bound for the intramolecular Fe-Co exchange coupling of with the negative sign denoting antiferromagnetic coupling. TOC GRAPHICS.
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The [Fe II (C 6 F 5 Tp) 2 ] spin-crossover complex is an atypical molecular switch, which can be converted upon annealing between two archetypal spin-crossover behaviours: from an extremely gradual spin-crossover to a broad hysteretic spin-transition (of ca. 65 K). The hysteresis shows an uncommon "rounded shape" that is reproducible upon cycling temperature. In depth structural studies reveal a first crystal phase transition, which occurs upon melting and recrystallizing at high temperature. This first irreversible transition is associated with a radical change in the crystal packing. More importantly, the "rounded and broad" hysteretic transition is shown to occur in a non-cooperative SCO system and is associated with the occurrence of a symmetry-breaking phase transition that appears when roughly ca. 50 % of the SCO complexes are switched.
Whereas dye-sensitized lanthanide-doped nanoparticles represent an unquestionable advance for pushing linear near-infrared (NIR) to visible-light upconversion within the frame of applications, analogous improvements are difficult to mimic for related but intramolecular processes induced at the molecular level in coordination complexes. Major difficulties arise from the cationic nature of the target cyanine-containing sensitizers (S), which drastically limits their thermodynamic affinities for catching the lanthanide activators (A) required for performing linear light upconversion. In this context, the rare previous design of stable dye-containing molecular SA light-upconverters required large S···A distances at the cost of the operation of only poorly efficient intramolecular S → A energy transfers and global sensitization. With the synthesis of the compact ligand [L2]+, we exploit here the benefit of using a single sulfur connector between the dye and the binding unit for counterbalancing the drastic electrostatic penalty which is expected to prevent metal complexation. Quantitative amounts of nine-coordinate [L2Er(hfac)3]+ molecular adducts could be finally prepared in solution at millimolar concentrations, while the S···A distance has been reduced by 40% to reach circa 0.7 nm. Detailed photophysical studies demonstrate the operation of a three times improved energy transfer upconversion (ETU) mechanism for molecular [L2Er(hfac)3]+ in acetonitrile at room temperature, thanks to the boosted heavy atom effect operating in the close cyanine/Er pair. NIR excitation at 801 nm can thus be upconverted into visible light (525–545 nm) with an unprecedented brightness of B up(801 nm) = 2.0(1) × 10–3 M–1·cm–1 for a molecular lanthanide complex.
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