Amino acid based diamides are widely used as a substructure in supramolecular polymers and are also key components of polypeptides that help to understand protein folding. The interplay of folding ...and aggregation of a diamide was used to achieve seed‐initiated supramolecular polymerization. For that purpose, a pyrene‐substituted diamide was synthesized in which pyrene is used as a tracer to monitor the supramolecular polymerization. Thermodynamics and time‐dependent studies revealed that the folding of the diamide moiety, via the formation of intramolecular hydrogen bonds, effectively prevents a spontaneous nucleation that leads to supramolecular polymerization. Under such out‐of‐equilibrium conditions, the addition of seeds successfully initiates the supramolecular polymerization. These results demonstrate the utility of such amino acid based diamides in programmable supramolecular polymerizations.
Seeded polymerization: The hydrogen‐bond‐directed folding of a diamide group effectively prevents the spontaneous nucleation in the supramolecular polymerization of extended diamides. The seeded polymerization of pyrene, as an example of luminescent π‐conjugated systems, was accomplished under out‐of‐equilibrium conditions in these coupled equilibria.
Stimulation emission depletion (STED) microscopy enables ultrastructural imaging of organelle dynamics with a high spatiotemporal resolution in living cells. For the visualization of the ...mitochondrial membrane dynamics in STED microscopy, rationally designed mitochondrial fluorescent markers with enhanced photostability are required. Herein, we report the development of a superphotostable fluorescent labeling reagent with long fluorescence lifetime, whose design is based on a structurally reinforced naphthophosphole fluorophore that is conjugated with an electron-donating diphenylamino group. The combination of long-lived fluorescence and superphotostable features of the fluorophore allowed us to selectively capture the ultrastructures of the mitochondrial cristae with a resolution of ∼60 nm when depleted at 660 nm. This chemical tool provides morphological information of the cristae, which has so far only been observed in fixed cells using electron microscopy. Moreover, this method gives information about the dynamic ultrastructures such as the intermembrane fusion in different mitochondria as well as the intercristae mergence in a single mitochondrion during the apoptosis-like mitochondrial swelling process.
Bora-fluoresceins (
BF
s), fluorescein analogues containing a tricoordinate boron atom instead of an oxygen atom at the 10-position of the fluorescein skeleton, were synthesized as a new family of ...fluorescein analogues. The deprotonated
BF
s exhibited absorption and fluorescence in the near-infrared region, which were significantly red-shifted relative to those of hitherto-known heteroatom-substituted fluorescein analogues on account of the orbital interaction between the tricoordinate boron atom and the fluorescein skeleton.
BF
s also showed multi-stage changes resulting from a Lewis acid-base equilibrium at the boron center in combination with a Brønsted acid-base equilibrium at the phenolic hydroxy group.
Tricoordinate boron imparts near-infrared absorption/emission and unusual multi-stage changes in the photophysical properties to fluorescein dyes.
Boron is a unique element in terms of electron deficiency and Lewis acidity. Incorporation of boron atoms into an aromatic carbon framework offers a wide variety of functionality. However, the ...intrinsic instability of organoboron compounds against moisture and oxygen has delayed the development. Here, we present boron-doped graphene nanoribbons (B-GNRs) of widths of N=7, 14 and 21 by on-surface chemical reactions with an employed organoboron precursor. The location of the boron dopant is well defined in the centre of the B-GNR, corresponding to 4.8 atom%, as programmed. The chemical reactivity of B-GNRs is probed by the adsorption of nitric oxide (NO), which is most effectively trapped by the boron sites, demonstrating the Lewis acid character. Structural properties and the chemical nature of the NO-reacted B-GNR are determined by a combination of scanning tunnelling microscopy, high-resolution atomic force microscopy with a CO tip, and density functional and classical computations.
Understanding the transmission of nanoscale forces in the pico-to-nanonewton range is important in polymer physics. While physical approaches have limitations in analyzing the local force ...distribution in condensed environments, chemical analysis using force probes is promising. However, there are stringent requirements for probing the local forces generated before structural damage. The magnitude of those forces corresponds to the range below covalent bond scission (from 200 pN to several nN) and above thermal fluctuation (several pN). Here, we report a conformationally flexible dual-fluorescence force probe with a theoretically estimated threshold of approximately 100 pN. This probe enables ratiometric analysis of the distribution of local forces in a stretched polymer chain network. Without changing the intrinsic properties of the polymer, the force distribution was reversibly monitored in real time. Chemical control of the probe location demonstrated that the local stress concentration is twice as biased at crosslinkers than at main chains, particularly in a strain-hardening region. Due to the high sensitivity, the percentage of the stressed force probes was estimated to be more than 1000 times higher than the activation rate of a conventional mechanophore.
Chemical reduction of the structurally constrained triphenylborane 1 with K produced a radical anion. EPR analysis demonstrated the delocalization of the unpaired electron spin density over the ...entire π skeleton to a greater extent than is the case for a nonconstrained Ph3B radical anion. DFT calculations indicated that the coplanarization of the benzene rings with the boron plane and the shortening of the B–C bond lengths by the structural constraint are responsible for the spin delocalization. The geometry optimization also suggested a bowl-shaped conformation as a viable local minimum structure in addition to the planar conformation. X-ray crystal structure analysis indeed revealed the nonplanar structure of the radical anion 1 •– .
BBC news: Two boron atoms have been incorporated into a carbon nanosheet by a bottom‐up synthesis to give a “B‐doped nanographene” (see picture) with a defined structure. The experimental and ...theoretical analyses revealed the important role of the two boron atoms in producing its characteristic properties, such as broad absorption bands covering the visible region and reversible redox processes.
Metabolic distribution of fatty acid to organelles is an essential biological process for energy homeostasis as well as for the maintenance of membrane integrity, and the metabolic pathways are ...strictly regulated in response to environmental stimuli. Herein, we report a fluorescent fatty acid probe, which bears an azapyrene dye that changes its absorption and emission features depending on the microenvironment polarity of the organelle into which it is transported. Owing to the environmental sensitivity of this dye, the distribution of the metabolically incorporated probe in non-polar lipid droplets, medium-polarity membranes, and the polar aqueous regions, can be visualized in different colors. Based on density scatter plots of the fluorophore, we demonstrate that the degradation of triacylglycerols in lipid droplets occurs predominantly via lipolysis rather than lipophagy in nutrition-starved hepatocytes. This tool can thus be expected to significantly advance our understanding of the lipid metabolism in living organisms.
Luminescent mechanochromism has been intensively studied in the past few years. However, the difference in the anisotropic grinding and the isotropic compression is not clearly distinguished in many ...cases, in spite of the importance of this discrimination for the application of such mechanochromic materials. We now report the distinct luminescent responses of a new organic fluorophore, tetrathiazolylthiophene, to these stresses. The multichromism is achieved over the entire visible region using the single fluorophore. The different mechanisms of a blue shift by grinding crystals and of a red shift under hydrostatic pressure are fully investigated, which includes a high-pressure single-crystal X-ray diffraction analysis. The anisotropic and isotropic modes of mechanical loading suppress and enhance the excimer formation, respectively, in the 3D hydrogen-bond network.
Near-infrared (NIR) fluorescent molecules are of great importance for the visualisation of biological processes. Among the most promising dye scaffolds for this purpose are P&z.dbd;O-substituted ...phospha-xanthene (POX) dyes, which show NIR emission with high photostability. Their practical utility for
in vitro
and
in vivo
imaging has recently been demonstrated. Although classical modification methods have been used to produce POX-based fluorescent probes, it is still a challenge to introduce additional functional groups to control the localisation of the probe in cells. Herein, we report on the development of POXs that bear a 4-ethynylphenyl group on the phosphorus atom. These dyes can subsequently be functionalised with azide-tagged biomolecules
via
a late-stage Cu-catalysed azide/alkyne cycloaddition (CuAAC) reaction, thus achieving target-selective labelling. To demonstrate the practical utility of the functionalised POXs, we designed a sophisticated NIR probe that exhibits a bell-shaped off-on-off pH-response and is able to assess the degree of endosomal maturation.
A series of NIR-emissive phospha-xanthene dyes bearing an ethynyl group are reported. The late-stage functionalisation of the NIR dyes enables creation of multi-functionalised fluorescent probes that can be designed to target organelles of interest.
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