162 research outputs found
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Direct introduction of nitrogen and oxygen functionality with spatial control using copper catalysis.
Synthetic chemists have spent considerable effort optimizing the synthesis of nitrogen and oxygen containing compounds through a number of methods; however, direct introduction of N- and O-functionality remains challenging. Presented herein is a general method to allow for the simultaneous installation of N- and O-functionality to construct unexplored N-O heterocyclic and amino-alcohol scaffolds. This transformation uses earth abundant copper salts to facilitate the formation of a carbon-centered radical and subsequent carbon-nitrogen bond formation. The intermediate aminoxyl radical is terminated by an intramolecularly appended carbon-centered radical. We have exploited this methodology to also access amino-alcohols with a range of aliphatic and aromatic linkers
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Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)
Photoisomerization of azobenzene in polymer matrices is a powerful method to convert photon energy into mechanical work. While most previous studies have focused on incorporating azobenzene within amorphous or liquid crystalline materials, the limited extents of molecular ordering and correspondingly modest enthalpy changes upon switching in such systems has limited the achievable energy densities. In this work, we introduce a semicrystalline main-chain poly(azobenzene), where photoisomerization is capable of reversibly triggering melting and recrystallization under essentially isothermal conditions. These materials can be drawn into aligned fibers, yielding optically driven two-way shape memory actuators capable of reversible bending
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Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement.
An enantioselective aza-Piancatelli rearrangement has been developed using a chiral Brønsted acid based on pentacarboxycyclopentadiene (PCCP). This reaction provides rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks from readily available starting material and is operationally simple
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Multiaddressable Photochromic Architectures: From Molecules to Materials
Multiaddressable architectures comprising lightâresponsive photochromic molecules and different stimuliâresponsive components are appealing platforms for intelligent materials because of not only the potential diversity of components and corresponding properties, but also the functions resulting from their synergistic interactions. A variety of multiaddressable photochromic architectures are being designed to meet the demands of applications in different areas ranging from molecular machines to smart materials. This review highlights exciting recent advances in the field of multiaddressable systems that employ photoswitching molecules, specifically with regard to photoâ/chemicalâaddressable, photoâ/pHâaddressable, photoâ/thermalâaddressable, photoâ/redoxâaddressable, and multiâphotoaddressable architectures. Design concepts, crosstalk between different components, and photoswitch integration in these multiaddressable systems are discussed
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Promoting the Furan Ring-Opening Reaction to Access New Donor-Acceptor Stenhouse Adducts with Hexafluoroisoproponal
Donorâacceptor Stenhouse adducts (DASAs) are visibleâlightâresponsive photoswitches with a variety of emerging applications in photoresponsive materials. Their twoâstep modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3âhexafluoroâ2âpropanol (HFIP) promotes the ringâopening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASAâbased photoswitches and DASAâpolymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1Hâ
NMR and UV/Vis spectroscopy. The use of sterically hindered, electronâpoor amines enabled the dark equilibrium to be decoupled from closedâisomer halfâlives for the first time
Promoting the furan ring opening reaction to access new donorâacceptor stenhouse adducts with hexafluoroisopropanol
Donorâacceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two-step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) promotes the ring-opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA-based photoswitches and DASAâpolymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer half-lives for the first time
Molecular-scale substrate anisotropy and crowding drive long-range nematic order of cell monolayers
The ability of cells to reorganize in response to external stimuli is
important in areas ranging from morphogenesis to tissue engineering. Elongated
cells can co-align due to steric effects, forming states with local order. We
show that molecular-scale substrate anisotropy can direct cell organization,
resulting in the emergence of nematic order on tissue scales. To quantitatively
examine the disorder-order transition, we developed a high-throughput imaging
platform to analyze velocity and orientational correlations for several
thousand cells over days. The establishment of global, seemingly long-ranged
order is facilitated by enhanced cell division along the substrate's nematic
axis, and associated extensile stresses that restructure the cells' actomyosin
networks. Our work, which connects to a class of systems known as active dry
nematics, provides a new understanding of the dynamics of cellular remodeling
and organization in weakly interacting cell collectives. This enables
data-driven discovery of cell-cell interactions and points to strategies for
tissue engineering.Comment: 29 pages, 7 figure
Visible light-responsive materials : the (photo)chemistry and applications of donorâacceptor Stenhouse adducts in polymer science
Donorâacceptor Stenhouse adduct (DASA) photoswitches have gained a lot of attention since their discovery in 2014. Their negative photochromism, visible light absorbance, synthetic tunability, and the large property changes between their photoisomers make them attractive candidates over other commonly used photoswitches for use in materials with responsive or adaptive properties. The development of such materials and their translation into advanced technologies continues to widely impact forefront materials research, and DASAs have thus attracted considerable interest in the field of visible-light responsive molecular switches and dynamic materials. Despite this interest, there have been challenges in understanding their complex behavior in the context of both small molecule studies and materials. Moreover, incorporation of DASAs into polymers can be challenging due to their incompatibility with the conditions for most common polymerization techniques. In this review, therefore, we examine and critically discuss the recent developments and challenges in the field of DASA-containing polymers, aiming at providing a better understanding of the interplay between the properties of both constituents (matrix and photoswitch). The first part summarizes current understanding of DASA design and switching properties. The second section discusses strategies of incorporation of DASAs into polymers, properties of DASA-containing materials, and methods for studying switching of DASAs in materials. We also discuss emerging applications for DASA photoswitches in polymeric materials, ranging from light-responsive drug delivery systems, to photothermal actuators, sensors and photoswitchable surfaces. Last, we summarize the current challenges in the field and venture on the steps required to explore novel systems and expand both the functional properties and the application opportunities of DASA-containing polymers
Photoswitchable gating of non-equilibrium enzymatic feedback in chemically communicating polymersome nanoreactors
The circadian rhythm generates out-of-equilibrium metabolite oscillations that are controlled by feedback loops under light/dark cycles. Here we describe a non-equilibrium nanosystem comprising a binary population of enzyme-containing polymersomes capable of light-gated chemical communication, controllable feedback and coupling to macroscopic oscillations. The populations consist of esterase-containing polymersomes functionalized with photo-responsive donor-acceptor Stenhouse adducts (DASA) and light-insensitive semipermeable urease-loaded polymersomes. The DASA-polymersome membrane becomes permeable under green light, switching on esterase activity and decreasing the pH, which in turn initiates the production of alkali in the urease-containing population. A pH-sensitive pigment that absorbs green light when protonated provides a negative feedback loop for deactivating the DASA-polymersomes. Simultaneously, increased alkali production deprotonates the pigment, reactivating esterase activity by opening the membrane gate. We utilize light-mediated fluctuations of pH to perform non-equilibrium communication between the nanoreactors and use the feedback loops to induce work as chemomechanical swelling/deswelling oscillations in a crosslinked hydrogel. We envision possible applications in artificial organelles, protocells and soft robotics
Visible light-responsive DASA-polymer conjugates
A modular synthesis of Donor-Acceptor Stenhouse Adduct (DASA) polymer conjugates is described. Pentafluorophenyl-ester chemistry is employed to incorporate aromatic amines into acrylate and methacrylate copolymers, which are subsequently coupled with activated furans to generate polymers bearing a range of DASA units in a modular manner. The effect of polymer glass transition temperature on switching kinetics is studied, showing dramatic rate enhancements in going from a glassy to a rubbery matrix. Moreover, tuning the DASA absorption profile allows for selective switching, as demonstrated by ternary photopatterning, with potential applications in rewriteable data storage
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