Single Crystals of Insoluble Porous Salicylimine Cages.

Porous organic cages (POCs) are meanwhile an established class of porous materials. Most of them are soluble to a certain extend and thus processable in or from solution. However, a few of larger salicylimine cages were reported to be insoluble in any organic solvents and thus characterized as amorphous materials. These cages were now synthesized as single-crystalline materials to get insight into packing motifs and preferred intermolecular interactions. Furthermore, the pairs of crystalline and amorphous materials for each cage allowed to compare their gas-sorption properties in both morphological states.

Microengineered Hollow Graphene Tube Systems Generate Conductive Hydrogels with Extremely Low Filler Concentration.

The fabrication of electrically conductive hydrogels is challenging as the introduction of an electrically conductive filler often changes mechanical hydrogel matrix properties. Here, we present an approach for the preparation of hydrogel composites with outstanding electrical conductivity at extremely low filler loadings (0.34 S m-1, 0.16 vol %). Exfoliated graphene and polyacrylamide are microengineered to 3D composites such that conductive graphene pathways pervade the hydrogel matrix similar to an artificial nervous system. This makes it possible to combine both the exceptional conductivity of exfoliated graphene and the adaptable mechanical properties of polyacrylamide. The demonstrated approach is highly versatile regarding porosity, filler material, as well as hydrogel system. The important difference to other approaches is that we keep the original properties of the matrix, while ensuring conductivity through graphene-coated microchannels. This novel approach of generating conductive hydrogels is very promising, with particular applications in the fields of bioelectronics and biohybrid robotics.

Functional Characterization of Cardiac Actin Mutants Causing Hypertrophic (p.A295S) and Dilated Cardiomyopathy (p.R312H and p.E361G).

Human wild type (wt) cardiac α-actin and its mutants p.A295S or p.R312H and p.E361G correlated with hypertrophic or dilated cardiomyopathy, respectively, were expressed by using the baculovirus/Sf21 insect cell system. The c-actin variants inhibited DNase I, indicating maintenance of their native state. Electron microscopy showed the formation of normal appearing actin filaments though they showed mutant specific differences in length and straightness correlating with their polymerization rates. TRITC-phalloidin staining showed that p.A295S and p.R312H exhibited reduced and the p.E361G mutant increased lengths of their formed filaments. Decoration of c-actins with cardiac tropomyosin (cTm) and troponin (cTn) conveyed Ca2+-sensitivity of the myosin-S1 ATPase stimulation, which was higher for the HCM p.A295S mutant and lower for the DCM p.R312H and p.E361G mutants than for wt c-actin. The lower Ca2+-sensitivity of myosin-S1 stimulation by both DCM actin mutants was corrected by the addition of levosimendan. Ca2+-dependency of the movement of pyrene-labeled cTm along polymerized c-actin variants decorated with cTn corresponded to the relations observed for the myosin-S1 ATPase stimulation though shifted to lower Ca2+-concentrations. The N-terminal C0C2 domain of cardiac myosin-binding protein-C increased the Ca2+-sensitivity of the pyrene-cTM movement of bovine, recombinant wt, p.A295S, and p.E361G c-actins, but not of the p.R312H mutant, suggesting decreased affinity to cTm.

De Novo Missense Mutations in TNNC1 and TNNI3 Causing Severe Infantile Cardiomyopathy Affect Myofilament Structure and Function and Are Modulated by Troponin Targeting Agents.

Rare pediatric non-compaction and restrictive cardiomyopathy are usually associated with a rapid and severe disease progression. While the non-compaction phenotype is characterized by structural defects and is correlated with systolic dysfunction, the restrictive phenotype exhibits diastolic dysfunction. The molecular mechanisms are poorly understood. Target genes encode among others, the cardiac troponin subunits forming the main regulatory protein complex of the thin filament for muscle contraction. Here, we compare the molecular effects of two infantile de novo point mutations in TNNC1 (p.cTnC-G34S) and TNNI3 (p.cTnI-D127Y) leading to severe non-compaction and restrictive phenotypes, respectively. We used skinned cardiomyocytes, skinned fibers, and reconstituted thin filaments to measure the impact of the mutations on contractile function. We investigated the interaction of these troponin variants with actin and their inter-subunit interactions, as well as the structural integrity of reconstituted thin filaments. Both mutations exhibited similar functional and structural impairments, though the patients developed different phenotypes. Furthermore, the protein quality control system was affected, as shown for TnC-G34S using patient's myocardial tissue samples. The two troponin targeting agents levosimendan and green tea extract (-)-epigallocatechin-3-gallate (EGCg) stabilized the structural integrity of reconstituted thin filaments and ameliorated contractile function in vitro in some, but not all, aspects to a similar degree for both mutations.

Chiral Self-sorting of Giant Cubic [8+12] Salicylimine Cage Compounds.

Chiral self-sorting is intricately connected to the complicated chiral processes observed in nature and no artificial systems of comparably complexity have been generated by chemists. However, only a few examples of purely organic molecules have been reported so far, where the self-sorting process could be controlled. Herein, we describe the chiral self-sorting of large cubic [8+12] salicylimine cage compounds based on a chiral TBTQ precursor. Out of 23 possible cage isomers only the enantiopure and a meso cage were observed to be formed, which have been unambiguously characterized by single crystal X-ray diffraction. Furthermore, by careful choice of solvent the formation of meso cage could be controlled. With internal diameters of din =3.3-3.5 nm these cages are among the largest organic cage compounds characterized and show very high specific surface areas up to approx. 1500 m2 g-1 after desolvation.

Luminogens for Aggregation-Induced Emission via Titanium-Mediated Double Nucleophilic Addition to 2,5-Dialkynylpyridines: Formation and Transformation of the Emitting Aggregates.

Invited for the cover of this issue are Lutz H. Gade, Claudia Backes, and co-workers at Heidelberg University. The image depicts 2-(1,2,2-triarylvinyl)-pyridines, which are luminogens for aggregation-induced emission which "light up" upon irradiation. Read the full text of the article at 10.1002/chem.201905611.

Luminogens for Aggregation-Induced Emission via Titanium-Mediated Double Nucleophilic Addition to 2,5-Dialkynylpyridines: Formation and Transformation of the Emitting Aggregates.

New luminogens for aggregation-induced emission (AIE), which are characterized by a branched cross-conjugated 2,6-bis(1,2,2-triarylvinyl)pyridine motif, have been synthesized exploiting the one-pot Ti-mediated tetraarylation of 2,6-bis(arylethynyl)pyridines. Thin layer solid-state emitters were prepared by spin-coating of the luminogens, while AIE-colloidal dispersions were investigated in terms of optical density and scattering behaviour. This has given insight into particle size distributions, time evolution of the aggregation and the influence of different functionalization patterns on the luminescence of molecular aggregates. In particular, a combination of extinction spectroscopy and dynamic light scattering is being proposed as a powerful method for investigating the dynamic aggregation process in AIE-type colloids.

The Structure of Acto-Myosin.

After several decades studying different acto-myosin complexes at lower and intermediate resolution - limited by the electron microscope instrumentation available then - recent advances in imaging technology have been crucial for obtaining a number of excellent high-resolution 3D reconstructions from cryo electron microscopy. The resolution level reached now is about 3-4 Å, which allows unambiguous model building of filamentous actin on its own as well as that of actin filaments decorated with strongly bound myosin variants. The interface between actin and the myosin motor domain can now be described in detail, and the function of parts of the interface (such as, e.g., the cardiomyopathy loop) can be understood in a mechanistical way. Most recently, reconstructions of actin filaments decorated with different myosins, which show a strongly bound acto-myosin complex also in the presence of the nucleotide ADP, have become available. The comparison of these structures with the nucleotide-free Rigor state provide the first mechanistic description of force sensing. An open question is still the initial interaction of the motor domain of myosin with the actin filament. Such weakly interacting states have so far not been the subject of microscopical studies, even though high-resolution structures would be needed to shed light on the initial steps of phosphate release and power stroke initiation.

A Robust Porous Quinoline Cage: Transformation of a [4+6] Salicylimine Cage by Povarov Cyclization.

Porous shape-persistent organic cages have become the object of interest in recent years because they are soluble and thus processable from solution. A variety of cages can be achieved by applying dynamic covalent chemistry (DCC), but they are less chemically stable. Here the transformation of a salicylimine cage into a quinoline cage by a twelve-fold Povarov reaction as the key step is described. Besides the chemical stability of the cage over a broad pH regime, it shows a unique absorption and emission depending on acid concentration. Furthermore, thin films for the vapor detection of acids were investigated, showing color switches from pale-yellow to red, and characteristic emission profiles.

The Impact of Aggregation on the Photophysics of Spiro-Bridged Heterotriangulenes.

We report on the impact of the central heteroatom on structural, electronic, and spectroscopic properties of a series of spirofluorene-bridged heterotriangulenes and provide a detailed study on their aggregates. The in-depth analysis of their molecular structure by NMR spectroscopy and X-ray crystallography was further complemented by density functional theory calculations. With the aid of extensive photophysical analysis the complex fluorescence spectra were deconvoluted showing contributions from the peripheral fluorenes and the heteroaromatic cores. Beyond the molecular scale, we examined the aggregation behavior of these heterotriangulenes in THF/H2 O mixtures and analyzed the aggregates by static and dynamic light scattering. The excited-state interactions within the aggregates were found to be similar to those found in the solid state. A plethora of morphologies and superstructures were observed by scanning electron microscopy of drop-casted dispersions.

Novel Functional TPE Polymers: Aggregation-Induced Emission, pH Response, and Solvatochromic Behavior.

Four tetraphenylethylene (TPE)-based aryleneethynylene polymers with amino or nitro groups are reported. They display strong aggregation-induced emission (AIE). The functional groups trigger acidochromic changes in the emission behavior of these polymers. Amino-substituted P1-P3 exhibit pH response through protonation of the amino groups. The position of the amino groups (on TPE or the side chains) influences the fluorescence intensity or emission wavelength as a response to different pH values. Nitro-P4 is solvatochromic due to its donor-acceptor structure. AIE, intramolecular charge transfer, and Förster resonance energy transfer define the fluorescence-based performance of the polymers. The amino-functionalized TPE polymers show excellent nitroarene-sensing performance. P4 is less effective than the amino polymers. A sensor array based on P1-P3 identifies 12 different nitroarenes in water.

Force-producing ADP state of myosin bound to actin.

Molecular motors produce force when they interact with their cellular tracks. For myosin motors, the primary force-generating state has MgADP tightly bound, whereas myosin is strongly bound to actin. We have generated an 8-Å cryoEM reconstruction of this state for myosin V and used molecular dynamics flexed fitting for model building. We compare this state to the subsequent state on actin (Rigor). The ADP-bound structure reveals that the actin-binding cleft is closed, even though MgADP is tightly bound. This state is accomplished by a previously unseen conformation of the ß-sheet underlying the nucleotide pocket. The transition from the force-generating ADP state to Rigor requires a 9.5° rotation of the myosin lever arm, coupled to a ß-sheet rearrangement. Thus, the structure reveals the detailed rearrangements underlying myosin force generation as well as the basis of strain-dependent ADP release that is essential for processive myosins, such as myosin V.

Transformation of a [4+6] Salicylbisimine Cage to Chemically Robust Amide Cages.

In recent years, interest in shape-persistent organic cage compounds has steadily increased, not least because dynamic covalent bond formation enables such structures to be made in high to excellent yields. One often used type of dynamic bond formation is the generation of an imine bond from an aldehyde and an amine. Although the reversibility of the imine bond formation is advantageous for high yields, it is disadvantageous for the chemical stability of the compounds. Amide bonds are, in contrast to imine bonds much more robust. Shape-persistent amide cages have so far been made by irreversible amide bond formations in multiple steps, very often accompanied by low yields. Here, we present an approach to shape-persistent amide cages by exploiting a high-yielding reversible cage formation in the first step, and a Pinnick oxidation as a key step to access the amide cages in just three steps. These chemically robust amide cages can be further transformed by bromination or nitration to allow post-functionalization in high yields. The impact of the substituents on the gas sorption behavior was also investigated.

Modern field emission scanning electron microscopy provides new perspectives for imaging kidney ultrastructure.

Recent progress in electron microscopy (EM) techniques has opened new pathways to study renal tissue in research and pathology. Modern field emission scanning EM may be utilized to scan thin sections of resin-embedded tissue mounted on a conductive support. Here we sought to achieve automated imaging without the typical limitations of transmission EM with equivalent or superior quality. Extended areas of tissue were either imaged in two (nanotomy) or in three dimensions (volume EM) by serial-section-based array tomography. Single-beam and fast-recording multi-beam field emission scanning EM instruments were compared using perfusion-fixed rodent kidneys. High-resolution scans produced excellent images of tissue, cells, and organelles down to macromolecular complexes. Digital stitching of image tiles in both modes allowed seamless Google Earth-like zooming from overview to regions of interest at the nanoscale. Large datasets were created that can be rapidly shared between scientists of different disciplines or pathologists using open source software. Three-dimensional array tomography of thin sections was followed by segmentation to visualize selected features in a large volume. Furthermore, correlative light-EM enabled the identification of functional information in a structural context. Thus, limitations in biomedical transmission EM can be overcome by introducing field emission scanning EM-based technology that permits high-quality, large field-of-view nanotomy, volume EM, and correlative light-EM modes. Advantages of virtual microscopy in clinical and experimental nephrology are illustrated.

Shape-Persistent [4+4] Imine Cages with a Truncated Tetrahedral Geometry.

The synthesis of shape-persistent organic cage compounds is often based on the usage of multiple dynamic covalent bond formation (such as imines) of readily available precursors. By careful choice of the precursors geometry, the geometry and size of the resulting cage can be accurately designed and indeed a number of different geometries and sizes have been realized to date. Despite of this fact, little is known about the precursors conformational rigidity and steric preorganization of reacting functional groups on the outcome of the reaction. Herein, the influence of conformational rigidity in the precursors on the formation of a [4+4] imine cage with truncated tetrahedral geometry is discussed.

Discrete Triptycene-Based Hexakis(metalsalphens): Extrinsic Soluble Porous Molecules of Isostructural Constitution.

In 2013 the concept of OMIMs (organic molecules of intrinsic microporosity) was introduced by McKeown et al. These OMIMs are constructed on the basis of rigid molecular cores such as triptycene, spirobifluorenes, and others. Like shape-persistent organic cages, these are soluble discrete molecules and therefore an interesting alternative to 3D, insoluble porous materials, such as metal-organic frameworks, covalent-organic frameworks, or zeolites. OMIMs are chemically and thermally robust because the formation of strong covalent bonds has been used for their synthesis. To date, a few OMIMs have been reported, though most of them did not contain any functional unit to enhance gas sorption properties. This work introduces an isostructural series of metal-salphene based OMIMs with different metal ions (Zn2+ , Ni2+ , Cu2+ , Pd2+ , and Pt2+ ) integrated into the backbone. The influence of the metal centers on interaction with gas molecules has been investigated by gas sorption experiments.

Shape-Persistent Tetrahedral [4+6] Boronic Ester Cages with Different Degrees of Fluoride Substitution.

In recent years the interest of shape-persistent organic cage compounds synthesized by dynamic covalent chemistry (DCC) has risen, because these cages are potentially interesting for gas sorption or -separation. One such reaction in DCC is the condensation of boronic acids with diols to form boronic esters. Most interestingly, the variety of geometries and sizes for boronic ester cages is much lower than that of, for example, imine-based cages. Here, a small series of shape-persistent [4+6] tetrahedral boronic ester cages is introduced. One cage has a high specific surface area of 511 m2 g-1 and selectively adsorbs ethane over ethylene and acetylene.

Optical Properties and Sequence Information of Tin-Centered Conjugated Microporous Polymers.

We synthesized conjugated microporous polymers (CMPs) based on tetrakis(4-ethynylphenyl)stannane and diiodobenzene as tectons, using Sonogashira couplings under different conditions. Through variation of the reaction conditions (catalysts, bases and solvents), appearance, surface area and emission properties of the formed CMPs were significantly altered. Wet-chemical, acid-mediated digestion and analysis of the resulting struts of these otherwise insoluble networks give insight into the molecular setup.

Dipole-Switchable Poly(para-phenyleneethynylene)s: Ferroelectric Conjugated Polymers.

Dipolar 2,3-difluorobenzene units are introduced into the backbone of a poly(para-phenyleneethynylene) (PPE) to generate a ferroelectric conjugated polymer. The structural features of the partially fluorinated PPE allow for the generation of a remanent polarization in the solid state; the difluorinated benzene rings behave as molecular rotors at high temperature, while at room temperature, stacking of such rings clamps down the ring orientation. The molecular dipoles can still be oriented by moderate external electrical fields at room temperature, and this PPE is then ferroelectric. The concept should be transferable to other poly(aryleneethynylene)s, and novel conjugated ferroelectric conjugated polymers will be accessible using this concept.

Cell Fixation by Light-Triggered Release of Glutaraldehyde.

Chemical fixation of living cells for microscopy is commonly achieved by crosslinking of intracellular proteins with dialdehydes prior to examination. We herein report a photocleavable protecting group for glutaraldehyde that results in a light-triggered and membrane-permeable fixative, which is nontoxic prior to photocleavage. Lipophilic ester groups allow for diffusion across the cell membrane and intracellular accumulation after enzymatic hydrolysis. Irradiation with UV light releases glutaraldehyde. The in situ generated fixative crosslinks intracellular proteins and preserves and stabilizes the cell so that it is ready for microscopy. In contrast to conventional glutaraldehyde fixation, tissue autofluorescence does not increase after fixation. Caged glutaraldehyde may in future enable functional experiments on living cells under a light microscope in which events of interest can be stopped in spatially confined volumes at defined time points. Samples with individually stopped events could then later be analyzed in ultrastructural studies.