Regular acyclic and macrocyclic [AB] oligomers by formation of push-pull chromophores in the chain-growth step

The substrate scope of the [2+2] cycloaddition-cycloreversion (CA-CR) reaction between electron-deficient (2,2-dicyanovinyl)benzene (DCVB) or (1,2,2-tricyanovinyl)benzene (TCVB) derivatives and N,N-dimethylanilino (DMA)-substituted acetylenes was investigated. The structural features of the cyanobutadiene products of these transformations were examined and the rates of selected CA-CR reactions were measured. Rate constants for reactions utilizing pentafluorinated TCVB and DCVB were found to be one to two orders of magnitude larger than those for the unsubstituted analogues. Multiple, consecutive CA-CR reactions were performed with substrates incorporating two reactive 2,2-cyanovinyl or 4-ethynylanilino sites. 1,4-Bis(2,2-dicyanovinyl)-2,3,5,6-tetrafluorobenzene and 1,4-bis[(4'-dihexylamino)phenylethynyl]benzene were selected as suitably reactive monomers for the synthesis of regular [AB] oligomers wherein the push-pull chromophores were formed in the chain-growth step. Oligomers of two types were isolated: macrocyclic [AB](n) and open-chain B[AB](n) oligomers, with n≤4.     

Cascade catalysis for the homogeneous hydrogenation of CO2 to methanol

This communication demonstrates the homogeneous hydrogenation of CO(2) to CH(3)OH via cascade catalysis. Three different homogeneous catalysts, (PMe(3))(4)Ru(Cl)(OAc), Sc(OTf)(3), and (PNN)Ru(CO)(H), operate in sequence to promote this transformation.     

Novel lanthanide-based polymeric chains and corresponding ultrafast dynamics in solution

Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl(3)·(H(2)O)(m)] with dibenzoylmethane (Ph(2)acacH) and a base. Using cesium carbonate (Cs(2)CO(3)) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph(2)acac)(4)}](n) (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl(3)·(H(2)O)(6)] with Ph(2)acacH resulted in [K{Nd(Ph(2)acac)(4)}](n) (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph(2)acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1-5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the individual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump/probe experiments with DMF solutions of 1-5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S(1) to T(1) level of the ligands. Magnetic studies show that [Cs{Dy(Ph(2)acac)(4)}](n) (4) has slow relaxation of the magnetization arising from the single Dy(3+) ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.     

New volatile strontium and barium imidazolate complexes for the deposition of group 2 metal oxides

We report the synthesis, characterization, and experimental density function theory-derived properties of new volatile strontium and barium imidazolate complexes, which under atomic layer deposition conditions using ozone as a reagent can deposit crystalline strontium oxide at 375 °C.     

Binaural speech unmasking and localization in noise with bilateral cochlear implants using envelope and fine-timing based strategies

Four adult bilateral cochlear implant users, with good open-set sentence recognition, were tested with three different sound coding strategies for binaural speech unmasking and their ability to localize 100 and 500 Hz click trains in noise. Two of the strategies tested were envelope-based strategies that are clinically widely used. The third was a research strategy that additionally preserved fine-timing cues at low frequencies. Speech reception thresholds were determined in diotic noise for diotic and interaurally time-delayed speech using direct audio input to a bilateral research processor. Localization in noise was assessed in the free field. Overall results, for both speech and localization tests, were similar with all three strategies. None provided a binaural speech unmasking advantage due to the application of 700 micros interaural time delay to the speech signal, and localization results showed similar response patterns across strategies that were well accounted for by the use of broadband interaural level cues. The data from both experiments combined indicate that, in contrast to normal hearing, timing cues available from natural head-width delays do not offer binaural advantages with present methods of electrical stimulation, even when fine-timing cues are explicitly coded.     

The oxygen-resistant [FeFe]-hydrogenase CbA5H harbors an unknown radical signal

[FeFe]-hydrogenases catalyze the reversible conversion of molecular hydrogen into protons and electrons with remarkable efficiency. However, their industrial applications are limited by their oxygen sensitivity. Recently, it was shown that the [FeFe]-hydrogenase from Clostridium beijerinckii (CbA5H) is oxygen-resistant and can be reactivated after oxygen exposure. In this work, we used multifrequency continuous wave and pulsed electron paramagnetic resonance (EPR) spectroscopy to characterize the active center of CbA5H, the H-cluster. Under oxidizing conditions, the spectra were dominated by an additional and unprecedented radical species. The generation of this radical signal depends on the presence of an intact H-cluster and a complete proton transfer pathway including the bridging azadithiolate ligand. Selective ⁵⁷Fe enrichment combined with isotope-sensitive electron-nuclear double resonance (ENDOR) spectroscopy revealed a spin density distribution that resembles an H-cluster state. Overall, we uncovered a radical species in CbA5H that is potentially involved in the redox sensing of CbA5H.

Electron paramagnetic resonance spectroscopy revealed an unprecedented radical species in the oxygen-resistant [FeFe]-hydrogenase CbA5H. Analysis of the isotope-sensitive data suggests that it is related to the active site, the H-cluster.     

Mechanical interlocking of SWNTs with N-rich macrocycles for efficient ORR electrocatalysis

Substitutional N-doping of single-walled carbon nanotubes is a common strategy to enhance their electrocatalytic properties in the oxygen-reduction reaction (ORR). Here, we explore the encapsulation of SWNTs within N-rich macrocycles as an alternative strategy to display electroactive sites on the surface of SWNTs. We design and synthesize four types of mechanically interlocked derivatives of SWNTs (MINTs) by combining two types of macrocycles and two types of SWNT samples. Comprehensive electrochemical characterization of these MINTs and their reference SWNTs allows us to establish structure–activity relationships. First, we show that all MINT samples are superior electrocatalysts compared to pristine SWNTs, which serves as general validation of our strategy. Secondly, we show that macrocycles displaying both N atoms and carbonyl groups perform better than those with N atoms only. Finally, we demonstrate that a tighter fit between macrocycles and SWNTs results in enhanced catalytic activity and stability, most likely due to a more effective charge-transfer between the SWNTs and the macrocycles. These results, focusing on the ORR as a testbed, show the possibility of understanding electrocatalytic performance of SWNTs at the molecular level and thus enable the design of more active and more stable catalysts in the future.

We present the encapsulation of SWNTs within N-rich macrocycles to enhance electrocatalytic activity towards the oxygen-reduction reaction.     

Ionically Modified Gelatin Hydrogels Maintain Murine Myogenic Cell Viability and Fusion Capacity

For tissue engineering of skeletal muscles, there is a need for biomaterials which do not only allow cell attachment, proliferation, and differentiation, but also support the physiological conditions of the tissue. Next to the chemical nature and structure of the biomaterial, its response to the application of biophysical stimuli, such as mechanical deformation or application of electrical pulses, can impact in vitro tissue culture. In this study, gelatin methacryloyl (GelMA) is modified with hydrophilic 2-acryloxyethyltrimethylammonium chloride (AETA) and 3-sulfopropyl acrylate potassium (SPA) ionic comonomers to obtain a piezoionic hydrogel. Rheology, mass swelling, gel fraction, and mechanical characteristics are determined. The piezoionic properties of the SPA and AETA-modified GelMA are confirmed by a significant increase in ionic conductivity and an electrical response as a function of mechanical stress. Murine myoblasts display a viability of >95% after 1 week on the piezoionic hydrogels, confirming their biocompatibility. The GelMA modifications do not influence the fusion capacity of the seeded myoblasts or myotube width after myotube formation. These results describe a novel functionalization providing new possibilities to exploit piezo-effects in the tissue engineering field.     

Comproportionation of CO2 and Cellulose to Formate Using a Floating Semiconductor-Enzyme Photoreforming Catalyst

Formate production via both CO₂ reduction and cellulose oxidation in a solar-driven process is achieved by a semi-artificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO₂| FDH ) producing up to 1.16±0.04 mmol_formate g ⁻¹ in 24 hours at 30 °C and 101 kPa under anaerobic conditions. Isotopic labeling experiments with ¹³C-labeled substrates support the mechanism of stoichiometric formate formation through both redox half-reactions. TiO₂| FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmol_formate per m² irradiation area after 24 hours. This work demonstrates the synergistic solar-driven valorization of solid and gaseous waste streams using a biohybrid photoreforming catalyst in aqueous solution and will thus provide inspiration for the development of future semi-artificial waste-to-chemical conversion strategies.