Search

Contrary to sulfides, sulfoxides or sulfones, sulfoximines have been mostly neglected in the design of fluorescent probes until recently. In this study, we elaborate systematically on sulfoximine acceptors in fluorescent flipper probes. Fluorescent flippers have been introduced as mechanosensitive probes to image membrane order and tension. They consist of twisted dithienothiophene dimers with sulfide and sulfone bridges to produce the essential primary dipole of the coupled push‐pull system. The objective of this study was to replace the sulfone acceptor by a series of sulfoximines. This is intriguing as a synthetic challenge and worthwhile because the extra nitrogen substituent offers a variability that is attractive to understand and control the performance of the probes. The new sulfoximine flippers provide corroborative evidence for the importance of the primary dipole of the planarizable push‐pull probe. Partitioning into differently ordered membranes and positioning within these different membranes is shown to correlate directly and dramatically with fluorescence lifetimes and mechanosensitivity. Sufficient partitioning into ordered membranes is confirmed as particularly important to image membrane tension by probe compression in the ground state. Compared to the conventional sulfone homolog, the best sulfoximine flipper has more red‐shifted absorption and emission maxima, longer fluorescence lifetime in cell membranes, and larger difference in lifetime upon application of membrane tension. [ABSTRACT FROM AUTHOR]

Mechanosensitive flipper probes are attracting interest as fluorescent reporters of membrane order and tension in biological systems. We introduce PhotoFlippers, which contain a photocleavable linker and an ultralong tether between mechanophore and various targeting motifs. Upon irradiation, the original probe is released and labels the most ordered membrane that is accessible by intermembrane transfer. Spatiotemporal control from photocleavable flippers is essential to access open, dynamic or elusive membrane motifs without chemical or physical interference. For instance, fast release with light is shown to place the original small‐molecule probes into the innermost leaflet of the nuclear envelope to image changes in membrane tension, at specific points in time of membrane trafficking along the secretory pathway, or in the inner leaflet of the plasma membrane to explore membrane asymmetry. These results identify PhotoFlippers as useful chemistry tools to enable research in biology. [ABSTRACT FROM AUTHOR]

Mechanosensitive flipper probes are attracting interest as fluorescent reporters of membrane order and tension in biological systems. We introduce PhotoFlippers, which contain a photocleavable linker and an ultralong tether between mechanophore and various targeting motifs. Upon irradiation, the original probe is released and labels the most ordered membrane that is accessible by intermembrane transfer. Spatiotemporal control from photocleavable flippers is essential to access open, dynamic or elusive membrane motifs without chemical or physical interference. For instance, fast release with light is shown to place the original small‐molecule probes into the innermost leaflet of the nuclear envelope to image changes in membrane tension, at specific points in time of membrane trafficking along the secretory pathway, or in the inner leaflet of the plasma membrane to explore membrane asymmetry. These results identify PhotoFlippers as useful chemistry tools to enable research in biology. [ABSTRACT FROM AUTHOR]

Despite their growing popularity in biology to image membrane tension, central design principles of flipper probes have never been validated. Here we report that upon deletion of their primary dipole, from electron-poor and electron-rich dithienothiophenes, absorptions blue-shift, lifetimes shorten dramatically, and mechanosensitivity in cells vanishes not partially, but completely. [ABSTRACT FROM AUTHOR]

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e. induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes. [ABSTRACT FROM AUTHOR]

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e. induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes. [ABSTRACT FROM AUTHOR]

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e. induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes. [ABSTRACT FROM AUTHOR]

Cyclic oligochalcogenides (COCs) are emerging as promising systems to penetrate cells. Clearly better than and different to the reported diselenolanes and epidithiodiketopiperazines, we introduce the benzopolysulfanes (BPS), which show efficient delivery, insensitivity to inhibitors of endocytosis, and compatibility with substrates as large as proteins. This high activity coincides with high reactivity, selectively toward thiols, exceeding exchange rates of disulfides under tension. The result is a dynamic‐covalent network of extreme sulfur species, including cyclic oligomers, from dimers to heptamers, with up to nineteen sulfurs in the ring. Selection from this unfolding adaptive network then yields the reactivities and selectivities needed to access new uptake pathways. Contrary to other COCs, BPS show high retention on thiol affinity columns. The identification of new modes of cell penetration is important because they promise new solutions to challenges in delivery and beyond. [ABSTRACT FROM AUTHOR]

Cyclic oligochalcogenides (COCs) are emerging as promising systems to penetrate cells. Clearly better than and different to the reported diselenolanes and epidithiodiketopiperazines, we introduce the benzopolysulfanes (BPS), which show efficient delivery, insensitivity to inhibitors of endocytosis, and compatibility with substrates as large as proteins. This high activity coincides with high reactivity, selectively toward thiols, exceeding exchange rates of disulfides under tension. The result is a dynamic‐covalent network of extreme sulfur species, including cyclic oligomers, from dimers to heptamers, with up to nineteen sulfurs in the ring. Selection from this unfolding adaptive network then yields the reactivities and selectivities needed to access new uptake pathways. Contrary to other COCs, BPS show high retention on thiol affinity columns. The identification of new modes of cell penetration is important because they promise new solutions to challenges in delivery and beyond. [ABSTRACT FROM AUTHOR]

Abstract: The design, synthesis and evaluation of catalytic triads composed of a central C60 fullerene with an amine base on one side and polarizability enhancers on the other side are reported. According to an enolate addition benchmark reaction, fullerene–fullerene–amine triads display the highest selectivity in anion–π catalysis observed so far, whereas NDI–fullerene–amine triads are not much better than fullerene–amine controls (NDI=naphthalenediimide). These large differences in activity are in conflict with the small differences in intrinsic π acidity, that is, LUMO energy levels and π holes on the central fullerene. However, they are in agreement with the high polarizability of fullerene–fullerene–amine triads. Activation and deactivation of the fullerene‐centered triads by intercalators and computational data on anion binding further indicate that for functional relevance, intrinsic π acidity is less important than induced π acidity, that is, the size of the oriented macrodipole of polarizable π systems that emerges only in response to the interaction with anions and anionic transition states. The resulting transformation is thus self‐induced, the anionic intermediates and transition states create their own anion–π catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The design, synthesis and evaluation of catalytic triads composed of a central C60 fullerene with an amine base on one side and polarizability enhancers on the other side are reported. According to an enolate addition benchmark reaction, fullerene–fullerene–amine triads display the highest selectivity in anion–π catalysis observed so far, whereas NDI–fullerene–amine triads are not much better than fullerene–amine controls (NDI=naphthalenediimide). These large differences in activity are in conflict with the small differences in intrinsic π acidity, that is, LUMO energy levels and π holes on the central fullerene. However, they are in agreement with the high polarizability of fullerene–fullerene–amine triads. Activation and deactivation of the fullerene‐centered triads by intercalators and computational data on anion binding further indicate that for functional relevance, intrinsic π acidity is less important than induced π acidity, that is, the size of the oriented macrodipole of polarizable π systems that emerges only in response to the interaction with anions and anionic transition states. The resulting transformation is thus self‐induced, the anionic intermediates and transition states create their own anion–π catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The development of sophisticated ordered functional materials is one of the important challenges in current science. One of the keys to enhance the properties of these materials is the control of the organization and morphology at different scales. This work presents a novel bioinspired methodology to achieve highly ordered donor/acceptor bio‐nanohybrids using a designed repeat protein as scaffold, endowed with photoactive and electron donating porphyrin (P) units, to efficiently wrap around electron accepting single wall carbon nanotubes (SWCNT). A systematic experimental and theoretical study to evaluate the effect of the length of the protein reveals that longer proteins wrap around the SWCNT in a more efficient manner due to the stronger supramolecular interaction existing between the inner concave surface of the protein (namely Trp and His residues) and the convex surface of the (7,6)‐SWCNT. Interestingly, spectroscopy and X‐ray diffraction data further confirm that the so‐called protein‐P–SWCNT donor–acceptor bio‐nanohybrids retain the original protein structure. Finally, the new bio‐nanohybrids show a remarkable enhancement on the photoconductivity values by flash‐photolysis microwave conductivity (FP‐TRMC technique) demonstrating that the major charge carriers of electrons are injected into the SWCNTs and move along the 1D‐structures. [ABSTRACT FROM AUTHOR]

Abstract: Supramolecular chemistry has evolved from the traditional focus on thermodynamic on‐pathways to the complex study of kinetic off‐pathways, which are strongly dependent on environmental conditions. Moreover, the control over pathway complexity allows nanostructures to be obtained that are inaccessible through spontaneous thermodynamic processes. Herein, we present a family of peptide‐based π‐extended tetrathiafulvalene (exTTF) molecules that show two self‐assembly pathways leading to two distinct J‐aggregates, namely metastable (M) and thermodynamic (T), with different spectroscopic, chiroptical, and electrochemical behavior. Moreover, cryo‐transmission electron microscopy (cryo‐TEM) reveals a different morphology for both aggregates and a direct observation of the morphological transformations from tapes to twisted ribbons. [ABSTRACT FROM AUTHOR]

Anion‐π interactions have been recently introduced to catalysis with the idea to stabilize anionic intermediates on π‐acidic surfaces. Realized examples include enolate, enamine and iminium chemistry, domino processes and Diels–Alder reactions. Moving on from the formation of contiguous stereogenic centers on π‐acidic surfaces, herein we report the first asymmetric anion‐π catalysis of cascade reactions that afford nonadjacent stereocenters. Conjugate addition‐protonation of achiral disubstituted enolate donors to 2‐chloroacrylonitrile generates 1,3‐nonadjacent stereocenters with moderate enantioselectivity and diastereoselectivity. The explored catalysts operate with complementary naphthalenediimide and fullerene surfaces with highly positive quadrupole moments and high polarizability, respectively, and proximal amine bases. We find that anion‐π catalysts can increase the diastereoselectivity of the reaction beyond the maximal 1:4.0 dr with conventional catalysts to maximal 5.3:1 dr on the large fullerene surfaces. The enantioselectivity of anion‐π catalysts, best on the confined naphthalenediimide surfaces with strong quadrupole moment, exceed the performance of conventional catalysts except for comparable results with a new, most compact, surprisingly powerful bifunctional control catalyst. Simultaneously increased rates and stereoselectivities compared to control catalysts without π‐acidic surface support that contributions of anion‐π interactions to the catalytic cascade process are significant. [ABSTRACT FROM AUTHOR]

Herein, we introduce catalysts that operate with chalcogen bonds. Compared to conventional hydrogen bonds, chalcogen bonds are similar in strength but more directional and hydrophobic, thus ideal for precision catalysis in apolar solvents. For the transfer hydrogenation of quinolines and imines, rate enhancements well beyond a factor of 1000 are obtained with chalcogen bonds. Better activities with deeper σ holes and wider bite angles, chloride inhibition and correlation with computed anion binding energies are consistent with operational chalcogen bonds. Comparable to classics, such as 2,2′-bipyrroles or 2,2′-bipyridines, dithieno[3,2-b;2′,3′-d]thiophenes (DTTs), particularly their diimides, but also wide-angle cyclopentadithiazole-4-ones are identified as privileged motifs to stabilize transition states in the focal point of the σ holes on their two co-facial endocyclic sulfur atoms. [ABSTRACT FROM AUTHOR]

Herein, we introduce catalysts that operate with chalcogen bonds. Compared to conventional hydrogen bonds, chalcogen bonds are similar in strength but more directional and hydrophobic, thus ideal for precision catalysis in apolar solvents. For the transfer hydrogenation of quinolines and imines, rate enhancements well beyond a factor of 1000 are obtained with chalcogen bonds. Better activities with deeper σ holes and wider bite angles, chloride inhibition and correlation with computed anion binding energies are consistent with operational chalcogen bonds. Comparable to classics, such as 2,2′-bipyrroles or 2,2′-bipyridines, dithieno[3,2-b;2′,3′-d]thiophenes (DTTs), particularly their diimides, but also wide-angle cyclopentadithiazole-4-ones are identified as privileged motifs to stabilize transition states in the focal point of the σ holes on their two co-facial endocyclic sulfur atoms. [ABSTRACT FROM AUTHOR]

The development of synthetic methods to build complex functional systems is a central and current challenge in organic chemistry. This goal is important because supramolecular architectures of highest sophistication account for function in nature, and synthetic organic chemistry, contrary to high standards with small molecules, fails to deliver functional systems of similar complexity. In this report, we introduce a collection of fullerenes that is compatible with the construction of multicomponent charge-transfer cascades and can be placed in triple-channel architectures next to stacks of oligothiophenes and naphthalenediimides. For the creation of this collection, modern fullerene chemistry-methanofullerenes and 1,4-diarylfullerenes-is combined with classical Nierengarten-Diederich-Bingel approaches. [ABSTRACT FROM AUTHOR]

The development of synthetic methods to build complex functional systems is a central and current challenge in organic chemistry. This goal is important because supramolecular architectures of highest sophistication account for function in nature, and synthetic organic chemistry, contrary to high standards with small molecules, fails to deliver functional systems of similar complexity. In this report, we introduce a collection of fullerenes that is compatible with the construction of multicomponent charge-transfer cascades and can be placed in triple-channel architectures next to stacks of oligothiophenes and naphthalenediimides. For the creation of this collection, modern fullerene chemistry-methanofullerenes and 1,4-diarylfullerenes-is combined with classical Nierengarten-Diederich-Bingel approaches. [ABSTRACT FROM AUTHOR]

Von der Nano ‐ zur Makroskala: Die Immobilisierung eines photo ‐ und redoxaktiven 9,10 ‐ Di(1,3 ‐ dithiol ‐ 2 ‐ yliden) ‐ 9,10 ‐ dihydroanthracen ‐ basierten Dipeptids (1) auf einwandigen Kohlenstoffnanoröhren (SWCNTs) liefert eine hohe Selbstausrichtung der 1/SWCNTs (siehe Bild). Die Anordnung der 1/SWCNTs ist der Schlüssel zur Stabilisierung langlebiger, ladungsgetrennter Zustände, die sich nach Photoanregung der SWCNTs bilden. [ABSTRACT FROM AUTHOR]

From nano‐ to macroscale: The immobilization of photo‐ and redox‐active 9,10‐di(1,3‐dithiol‐2‐ylidene)‐9,10‐dihydroanthracene‐based dipeptide 1 onto SWCNTs resulted in a high order of self‐alignment among 1/SWCNTs (see picture). The assembly of the 1/SWCNTs is the key for stabilizing long‐lived charge‐separated states that are formed upon photoexcitation of the SWCNTs. [ABSTRACT FROM AUTHOR]

Fullerenes of increasing electron deficiency are designed, synthesized and evaluated in multicomponent surface architectures to ultimately build gradients in LUMO levels with nine components over 350 meV down to −4.22 eV. [ABSTRACT FROM AUTHOR]