1
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A Photoswitchable Macrocycle Controls Anion-Templated Pseudorotaxane Formation and Axle Relocalization. Angew Chem Int Ed Engl 2024; 63:e202316628. [PMID: 38059917 DOI: 10.1002/anie.202316628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 12/01/2023] [Accepted: 12/06/2023] [Indexed: 12/08/2023]
Abstract
Important biological processes, such as signaling and transport, are regulated by dynamic binding events. The development of artificial supramolecular systems in which binding between different components is controlled could help emulate such processes. Herein, we describe stiff-stilbene-containing macrocycles that can be switched between (Z)- and (E)-isomers by light, as demonstrated by UV/Vis and 1 H NMR spectroscopy. The (Z)-isomers can be effectively threaded by pyridinium halide axles to give pseudorotaxane complexes, as confirmed by 1 H NMR titration studies and single-crystal X-ray crystallography. The overall stability of these complexes can be tuned by varying the templating counteranion. However, upon light-induced isomerization to the (E)-isomer, the threading capability is drastically reduced. The axle component, in addition, can form a heterodimeric complex with a secondary isophthalamide host. Therefore, when all components are combined, light irradiation triggers axle exchange between the macrocycle and this secondary host, which has been monitored by 1 H NMR spectroscopy and simulated computationally.
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2
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Abstract
Photoisomerization of retinal is pivotal to ion translocation across the bacterial membrane and has served as an inspiration for the development of artificial molecular switches and machines. Light-driven synthetic systems in which a macrocyclic component transits along a nonsymmetric axle in a specific direction have been reported; however, unidirectional and repetitive translocation of protons has not been achieved. Herein, we describe a unique protonation-controlled isomerization behavior for hemi-indigo dyes bearing N-heterocycles, featuring intramolecular hydrogen bonds. Light-induced isomerization from the Z to E isomer is unlocked when protonated, while reverse E → Z photoisomerization occurs in the neutral state. As a consequence, associated protons are displaced in a preferred direction with respect to the photoswitchable scaffold. These results will prove to be critical in developing artificial systems in which concentration gradients can be effectively generated using (solar) light energy.
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3
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Photoswitchable Bis(amidopyrroles): Modulating Anion Transport Activity Independent of Binding Affinity. J Org Chem 2023; 88:11328-11334. [PMID: 37440304 PMCID: PMC10407928 DOI: 10.1021/acs.joc.3c01018] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Indexed: 07/14/2023]
Abstract
Toward photocontrol of anion transport across the bilayer membrane, stiff-stilbene, which has dimethyl substituents in the five-membered rings, is functionalized with amidopyrrole units. UV-vis and 1H NMR studies show high photostability and photoconversion yields. Where the photoaddressable (E)- and (Z)-isomers exhibit comparable binding affinities, as determined by 1H NMR titrations, fluorescence-based transport assays reveal significantly higher transport activity for the (Z)-isomers. Changing the binding affinity is thus not a necessity for modulating transport. Additionally, transport can be triggered in situ by light.
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4
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Abstract
Anionic species are omnipresent and involved in many important biological processes. A large number of artificial anion receptors has therefore been developed. Some of these are capable of mediating transmembrane transport. However, where transport proteins can respond to stimuli in their surroundings, creation of synthetic receptors with stimuli-responsive functions poses a major challenge. Herein, we give a full overview of the stimulus-controlled anion receptors that have been developed thus far, including their application in membrane transport. In addition to their potential operation as membrane carriers, the use of anion recognition motifs in forming responsive membrane-spanning channels is discussed. With this review article, we intend to increase interest in transmembrane transport among scientists working on host-guest complexes and dynamic functional systems in order to stimulate further developments.
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5
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Photoswitching of halide-binding affinity and selectivity in dithienylethene-strapped calix[4]pyrrole. Chem Commun (Camb) 2023. [PMID: 37345527 DOI: 10.1039/d3cc02264a] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/23/2023]
Abstract
Dithienylethene-strapped calix[4]pyrrole is isomerized by 300/630 nm light between ring-open and -closed isomers, which affects the size of the anion binding site. Where for chloride this results in only a small change in affinity, that of the larger bromide and iodide ions is majorly affected, resulting in altered selectivity.
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6
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Photoswitchable molecular tweezers: isomerization to control substrate binding, and what about vice versa? Chem Commun (Camb) 2022; 58:11045-11058. [PMID: 36106956 PMCID: PMC9531670 DOI: 10.1039/d2cc04329g] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 08/31/2022] [Indexed: 11/21/2022]
Abstract
The linkage of two identical binding motifs by a molecular photoswitch has proven to be a straightforward and versatile strategy to control substrate binding affinity by light. Stimulus control of binding properties in artificial receptors is partly inspired by the dynamic behavior of proteins and is highly attractive as it could, for example, improve extraction processes and allow (de)activation of membrane transport on demand. This feature article summarizes the development and design principles of molecular tweezers containing a molecular photoswitch as the core unit. Besides the control of binding affinity by isomerization, the effect of substrate binding on the isomerization behavior is discussed where data is available. While the latter often receives less attention, it could be of benefit in the future creation of multi-stimuli-controlled molecular switching and machine-like systems.
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7
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Anion-Induced Reversible Actuation of Squaramide-Crosslinked Polymer Gels. ACS APPLIED MATERIALS & INTERFACES 2022; 14:43711-43718. [PMID: 36099444 PMCID: PMC9523616 DOI: 10.1021/acsami.2c11136] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 09/06/2022] [Indexed: 06/15/2023]
Abstract
Supramolecular anion binding to squaramide crosslinkers in poly(N,N-dimethylacrylamide) gel networks enhances swelling and allows reversible chemically driven actuation. The volume swelling ratio of the gels is shown to depend on both the type of anion and its concentration. 1H NMR and UV-vis titrations with the squaramide crosslinkers reveal a relationship between anion binding affinity and the concentration-dependent swelling behavior. Gel swelling is shown to be reversible, and by embedding a solid support into rod-shaped gels, soft actuators are fabricated that undergo forward and backward bending motion in response to changing anion concentration. The swelling and bending process, which is accompanied by intense green coloration of the gel, is achieved by using only low amounts of crosslinker. This macroscopic actuation achieved by anion binding to specific molecular entities in the polymer network will open new opportunities in the field of chemically responsive materials.
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8
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Photomodulation of Transmembrane Transport and Potential by Stiff-Stilbene Based Bis(thio)ureas. J Am Chem Soc 2022; 144:331-338. [PMID: 34932344 PMCID: PMC8759083 DOI: 10.1021/jacs.1c10034] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Indexed: 12/14/2022]
Abstract
Membrane transport proteins fulfill important regulatory functions in biology with a common trait being their ability to respond to stimuli in the environment. Various small-molecule receptors, capable of mediating transmembrane transport, have been successfully developed. However, to confer stimuli-responsiveness on them poses a fundamental challenge. Here we demonstrate photocontrol of transmembrane transport and electric potential using bis(thio)ureas derived from stiff-stilbene. UV-vis and 1H NMR spectroscopy are used to monitor E-Z photoisomerization of these bis(thio)ureas and 1H NMR titrations reveal stronger binding of chloride to the (Z)-form than to the (E)-form. Additional insight into the binding properties is provided by single crystal X-ray crystallographic analysis and DFT geometry optimization. Importantly, the (Z)-isomers are much more active in transmembrane transport than the respective (E)-isomers as shown through various assays. As a result, both membrane transport and depolarization can be modulated upon irradiation, opening up new prospects toward light-based therapeutics as well as physiological and optopharmacological tools for studying anion transport-associated diseases and to stimulate neuronal activity, respectively.
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9
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Push-Pull Stiff-Stilbene: Proton-Gated Visible-Light Photoswitching and Acid-Catalyzed Isomerization. Chemistry 2021; 27:17346-17350. [PMID: 34605565 PMCID: PMC9298359 DOI: 10.1002/chem.202103052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Indexed: 01/03/2023]
Abstract
Donor‐acceptor substituted stiff‐stilbene is shown to undergo isomerization induced by visible light avoiding the need for harmful UV light. This visible‐light photoswitching is inhibited by protonation of the dimethylamino‐donor unit, disrupting the push‐pull character and thus, gating of the photochromic properties is allowed by acid/base addition. Remarkably, the addition of a mild acid also triggers fast thermal back‐isomerization, which is unprecedented for stiff‐stilbene photoswitches usually having a very high energy barrier for this process. These combined features offer unique orthogonal control over switching behavior by light and protonation, which is investigated in detail by 1H NMR and UV/Vis spectroscopy. In addition, TD‐DFT calculations are used to gain further insight into the absorption properties. Our results will help elevating the level of control over dynamic behavior in stiff‐stilbene applications.
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10
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Abstract
Controlling supramolecular polymerization by external stimuli holds great potential toward the development of responsive soft materials and manipulating self-assembly at the nanoscale. Photochemical switching offers the prospect of regulating the structure and properties of systems in a noninvasive and reversible manner with spatial and temporal control. In addition, this approach will enhance our understanding of supramolecular polymerization mechanisms; however, the control of molecular assembly by light remains challenging. Here we present photoresponsive stiff-stilbene-based bis-urea monomers whose trans isomers readily form supramolecular polymers in a wide range of organic solvents, enabling fast light-triggered depolymerization-polymerization and reversible gel formation. Due to the stability of the cis isomers and the high photostationary states (PSS) of the cis-trans isomerization, precise control over supramolecular polymerization and in situ gelation could be achieved with short response times. A detailed study on the temperature-dependent and photoinduced supramolecular polymerization in organic solvents revealed a kinetically controlled nucleation-elongation mechanism. By application of a Volta phase plate to enhance the phase-contrast method in cryo-EM, unprecedented for nonaqueous solutions, uniform nanofibers were observed in organic solvents.
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A photoswitchable strapped calix[4]pyrrole receptor: highly effective chloride binding and release. Chem Sci 2021; 12:3188-3193. [PMID: 34164086 PMCID: PMC8179391 DOI: 10.1039/d0sc06686a] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A stiff-stilbene strapped calix[4]pyrrole receptor can be reversibly switched by light between a strong chloride-binding Z-isomer and a very weakly binding E-isomer. The light-induced switching process is monitored by UV-Vis and 1H NMR spectroscopy and chloride binding is studied in detail using both 1H NMR and ITC titrations in DMSO and MeCN. In DMSO, at millimolar concentrations, switching from a fully bound to an almost fully unbound state can be triggered. Quantification of the binding constants in MeCN reveals an extraordinary 8000-fold affinity difference between the Z- and E-isomer. Single crystal X-ray crystallographic analysis gives insight into the structure of the photogenerated E-isomer and the geometry of the chloride-bound receptors is optimized by DFT calculations. The highly effective control of binding affinity demonstrated in this work opens up new prospects for on demand binding and release in extractions and photocontrol of membrane transport processes, among other applications.
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12
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Tuning of Morphology by Chirality in Self-Assembled Structures of Bis(Urea) Amphiphiles in Water. Chemistry 2021; 27:326-330. [PMID: 32785999 PMCID: PMC7839493 DOI: 10.1002/chem.202003403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 08/10/2020] [Indexed: 12/12/2022]
Abstract
We present the synthesis and self‐assembly of a chiral bis(urea) amphiphile and show that chirality offers a remarkable level of control towards different morphologies. Upon self‐assembly in water, the molecular‐scale chiral information is translated to the mesoscopic level. Both enantiomers of the amphiphile self‐assemble into chiral twisted ribbons with opposite handedness, as supported by Cryo‐TEM and circular dichroism (CD) measurements. The system presents thermo‐responsive aggregation behavior and combined transmittance measurements, temperature‐dependent UV, CD, TEM, and micro‐differential scanning calorimetry (DSC) show that a ribbon‐to‐vesicles transition occurs upon heating. Remarkably, chirality allows easy control of morphology as the self‐assembly into distinct aggregates can be tuned by varying the enantiomeric excess of the amphiphile, giving access to flat sheets, helical ribbons, and twisted ribbons.
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13
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Controlled Diffusion of Photoswitchable Receptors by Binding Anti-electrostatic Hydrogen-Bonded Phosphate Oligomers. J Am Chem Soc 2020; 142:20014-20020. [PMID: 33180496 PMCID: PMC7735709 DOI: 10.1021/jacs.0c09072] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Indexed: 12/12/2022]
Abstract
Dihydrogen phosphate anions are found to spontaneously associate into anti-electrostatic oligomers via hydrogen bonding interactions at millimolar concentrations in DMSO. Diffusion NMR measurements supported formation of these oligomers, which can be bound by photoswitchable anion receptors to form large bridged assemblies of approximately three times the volume of the unbound receptor. Photoisomerization of the oligomer-bound receptor causes a decrease in diffusion coefficient of up to 16%, corresponding to a 70% increase in effective volume. This new approach to external control of diffusion opens prospects in controlling molecular transport using light.
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14
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Abstract
Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.
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16
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Stiff‐Stilbene Photoswitches: From Fundamental Studies to Emergent Applications. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202001031] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Supramolecular control of unidirectional rotary motion in a sterically overcrowded photoswitchable receptor. Org Chem Front 2020. [DOI: 10.1039/d0qo01154a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The induction of unidirectional rotary motion in an achiral, sterically overcrowded, photoswitchable receptor by binding of a chiral guest molecule is unequivocally established.
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18
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Light-Modulated Self-Blockage of a Urea Binding Site in a Stiff-Stilbene Based Anion Receptor. Chemphyschem 2019; 20:3306-3310. [PMID: 31622003 PMCID: PMC6972635 DOI: 10.1002/cphc.201900917] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 10/14/2019] [Indexed: 12/16/2022]
Abstract
Anion binding to a receptor based on stiff-stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and 1 H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors.
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19
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A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes. Beilstein J Org Chem 2019; 15:2767-2773. [PMID: 31807210 PMCID: PMC6880828 DOI: 10.3762/bjoc.15.268] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Accepted: 10/11/2019] [Indexed: 12/13/2022] Open
Abstract
In recent years, increasing efforts have been devoted to designing new functional stimuli-responsive supramolecular assemblies. Here, we present three isomeric supramolecular coordination complexes consisting of a Pd2L4 stoichiometry. As shown by NMR, CD and X-ray studies, as well as DFT calculations, these complexes form cage-like structures by chiral self-sorting. Photochromic ligands derived from first generation molecular motors enable light-driven interconversion between the three isomers. Two of the isomers were able to form host–guest complexes opening up new prospects toward stimuli-controlled substrate binding and release.
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20
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Salen‐Based Amphiphiles: Directing Self‐Assembly in Water by Metal Complexation. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201908010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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21
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Salen-Based Amphiphiles: Directing Self-Assembly in Water by Metal Complexation. Angew Chem Int Ed Engl 2019; 58:14935-14939. [PMID: 31389650 PMCID: PMC6899911 DOI: 10.1002/anie.201908010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 08/05/2019] [Indexed: 11/09/2022]
Abstract
Tuning morphologies of self-assembled structures in water is a major challenge. Herein we present a salen-based amphiphile which, using complexation with distinct transition metal ions, allows to control effectively the self-assembly morphology in water, as observed by Cryo-TEM and confirmed by DLS measurements. Applying this strategy with various metal ions gives a broad spectrum of self-assembled structures starting from the same amphiphilic ligand (from cubic structures to vesicles and micelles). Thermogravimetric analysis and electric conductivity measurements reveal a key role for water coordination apparently being responsible for the distinct assembly behavior.
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22
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Unidirectional rotary motion in a metal-organic framework. NATURE NANOTECHNOLOGY 2019; 14:488-494. [PMID: 30886378 DOI: 10.1038/s41565-019-0401-6] [Citation(s) in RCA: 127] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 02/06/2019] [Indexed: 05/20/2023]
Abstract
Overcrowded alkene-based light-driven molecular motors are able to perform large-amplitude repetitive unidirectional rotations. Their behaviour is well understood in solution. However, Brownian motion precludes the precise positioning at the nanoscale needed to harness cooperative action. Here, we demonstrate molecular motors organized in crystalline metal-organic frameworks (MOFs). The motor unit becomes a part of the organic linker (or strut), and its spatial arrangement is elucidated through powder and single-crystal X-ray analyses and polarized optical and Raman microscopies. We confirm that the light-driven unidirectional rotation of the motor units is retained in the MOF framework and that the motors can operate in the solid state with similar rotary speed (rate of thermal helix inversion) to that in solution. These 'moto-MOFs' could in the future be used to control dynamic function in crystalline materials.
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Abstract
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Molecular rotary
motors based on oxindole which can be driven by
visible light are presented. This novel class of motors can be easily
synthesized via a Knoevenagel condensation, and the choice of different
upper halves allows for the facile tuning of their rotational speed.
The four-step rotational cycle was explored using DFT calculations,
and the expected photochemical and thermal isomerization behavior
was confirmed by NMR, UV/vis, and CD spectroscopy. These oxindole
motors offer attractive prospects for functional materials responsive
to light.
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25
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Light‐Gated Rotation in a Molecular Motor Functionalized with a Dithienylethene Switch. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201802392] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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Light-Gated Rotation in a Molecular Motor Functionalized with a Dithienylethene Switch. Angew Chem Int Ed Engl 2018; 57:10515-10519. [PMID: 29806875 PMCID: PMC6099277 DOI: 10.1002/anie.201802392] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 05/14/2018] [Indexed: 02/01/2023]
Abstract
A multiphotochromic hybrid system is presented in which a light-driven overcrowded alkene-based molecular rotary motor is connected to a dithienylethene photoswitch. Ring closing of the dithienylethene moiety, using an irradiation wavelength different from the wavelength applied to operate the molecular motor, results in inhibition of the rotary motion as is demonstrated by detailed 1 H-NMR and UV/Vis experiments. For the first time, a light-gated molecular motor is thus obtained. Furthermore, the excitation wavelength of the molecular motor is red-shifted from the UV into the visible-light region upon attachment of the dithienylethene switch.
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Abstract
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The
design and synthesis of an overcrowded-alkene based molecular
motor featuring a crown ether integrated in its stator structure has
been accomplished. The photostationary state ratios and rotational
speed of this motor can be modulated by cation coordination to the
crown ether moiety, which can be reversed upon the addition of a competing
chelating agent, thus achieving a dynamic control over the rotational
behavior of the motor.
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Highly Efficient and Robust Enantioselective Liquid-Liquid Extraction of 1,2-Amino Alcohols utilizing VAPOL- and VANOL-based Phosphoric Acid Hosts. CHEMSUSCHEM 2018; 11:178-184. [PMID: 29092103 DOI: 10.1002/cssc.201701896] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 10/30/2017] [Indexed: 06/07/2023]
Abstract
The large-scale production of enantiopure compounds in a cost-effective and environmentally friendly manner remains one of the major challenges of modern-day chemistry. The resolution of racemates through enantioselective liquid-liquid extraction was developed as a suitable solution but has remained largely underused, owing to a lack of highly efficient and robust chiral hosts to mediate the process. This paucity of hosts can in part be attributed to a poor understanding of the underlying principles behind these processes hindering the design of more efficient selectors. A previously untested class of hosts, VAPOL and VANOL derived phosphoric acids, has been studied in depth for the efficient enantioselective liquid-liquid extraction of 1,2-amino alcohols. A systematic investigation of extraction parameters was conducted, revealing many key interactions and DFT calculations illustrate the binding modes for the 1:1 complexes that are involved in chiral recognition. The resulting, now-optimized, procedures are highly robust and easy to implement. They are also easily scalable, as demonstrated by U-tube experiments.
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29
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Braking of a Light-Driven Molecular Rotary Motor by Chemical Stimuli. Chemistry 2017; 24:81-84. [DOI: 10.1002/chem.201704747] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2017] [Indexed: 12/26/2022]
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30
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31
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Abstract
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The enantiomeric
homogeneity of light-driven molecular motors based
on overcrowded alkenes is crucial in their application as either unidirectional
rotors or as chiral multistate switches. It was challenging to obtain
these compounds as single enantiomers via the established synthetic
procedures due to loss of optical purity in the key step, i.e., the
Barton–Kellogg olefination reaction. Searching for strategies
to avoid racemization, a new class of light-driven molecular motors
was designed, synthesized, and studied. The stereochemical integrity
was fully preserved throughout the synthesis, and on the basis of
photochemical and kinetic studies using UV/vis, CD, and 1H NMR spectroscopy, it was established that they still function properly
as unidirectional molecular motors.
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32
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Abstract
Exploring routes to visible-light-driven rotary motors, the possibility of red-shifting the excitation wavelength of molecular motors by extension of the aromatic core is studied. Introducing a dibenzofluorenyl moiety in a standard molecular motor resulted in red-shifting of the absorption spectrum. UV/vis and 1H NMR spectroscopy showed that these motors could be isomerized with light of wavelengths up to 490 nm and that the structural modification did not impair the anticipated rotary behavior. Extension of the aromatic core is therefore a suitable strategy to apply in pursuit of visible-light-driven molecular motors.
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33
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Abstract
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Toward
the development of photoresponsive anion receptors, a stiff-stilbene
photoswitch has been equipped with two urea anion-binding motifs.
Photoinduced E/Z isomerization has
been studied in detail by UV–vis and NMR spectroscopy. Titration
experiments (1H NMR) reveal strong binding of acetate and
phosphate to the (Z)-isomer, in which the urea groups
are closely together. Isomerization to the (E)-form
separates the urea motifs, resulting in much weaker binding. Additionally,
geometry optimizations by density functional theory (DFT) illustrate
that oxo-anion binding to the (Z)-form involves four
hydrogen bonds.
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34
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In situ control of polymer helicity with a non-covalently bound photoresponsive molecular motor dopant. Chem Commun (Camb) 2017; 53:6393-6396. [DOI: 10.1039/c7cc03188b] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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35
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Abstract
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The
rotational speed of an overcrowded alkene-based molecular rotary
motor, having an integrated 4,5-diazafluorenyl coordination motif,
can be regulated allosterically via the binding of metal ions. DFT
calculations have been used to predict the relative speed of rotation
of three different (i.e., zinc, palladium, and platinum) metal dichloride
complexes. The photochemical and thermal isomerization behavior of
these complexes has been studied in detail using UV–vis and 1H NMR spectroscopy. Our results confirm that metal coordination
induces a contraction of the diazafluorenyl lower half, resulting
in a reduction of the steric hindrance in the “fjord”
region of the molecule, which causes an increase of the rotational
speed. Importantly, metal complexation can be accomplished in situ and is found to be reversible upon the addition
of a competing ligand. Consequently, the rotational behavior of these
molecular motors can be dynamically controlled with chemical additives.
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Reversible gel-sol photoswitching with an overcrowded alkene-based bis-urea supergelator. Chem Sci 2016; 7:4341-4346. [PMID: 30155080 PMCID: PMC6013809 DOI: 10.1039/c6sc00659k] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 03/22/2016] [Indexed: 01/06/2023] Open
Abstract
A new type of low-molecular-weight gelator (LMWG), i.e. overcrowded alkene-based bis-ureas, can be switched effectively between cis and trans isomers using light as demonstrated by 1H NMR and UV-Vis spectroscopy. Gelation studies reveal that one of the synthesized trans compounds forms stable gels in aromatic hydrocarbon solvents down to a critical concentration of 0.4 mg mL-1. Transmission electron microscopy (TEM) shows that this gel consists of an entangled fibrous network. For the trans isomer of this LMWG intermolecular urea hydrogen bonding is observed in the solid state, whereas density functional theory (DFT) geometry optimization of the cis isomer indicates the possible formation of an intramolecular hydrogen bond. Irradiation of the gel triggers trans-to-cis isomerization and consequently, a gel-sol phase transition. This process can be fully reversed by altering the irradiation wavelength.
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Intramolecular transport of small-molecule cargo in a nanoscale device operated by light. Chem Commun (Camb) 2016; 52:6765-8. [DOI: 10.1039/c6cc02382g] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
A light-operated molecular nanodevice is able to transport an acetyl cargo intramolecularly over a distance of about 2 nm.
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Dynamic Inversion of Stereoselective Phosphate Binding to a Bisurea Receptor Controlled by Light and Heat. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201509479] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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Dynamic Inversion of Stereoselective Phosphate Binding to a Bisurea Receptor Controlled by Light and Heat. Angew Chem Int Ed Engl 2015; 55:1001-4. [DOI: 10.1002/anie.201509479] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Indexed: 11/08/2022]
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Visible‐Light‐Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex. Angew Chem Int Ed Engl 2015; 54:11457-61. [DOI: 10.1002/anie.201505781] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Indexed: 12/20/2022]
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Visible-Light-Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201505781] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Multi-State Regulation of the Dihydrogen Phosphate Binding Affinity to a Light- and Heat-Responsive Bis-Urea Receptor. J Am Chem Soc 2014; 136:16784-7. [DOI: 10.1021/ja510700j] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Light-harvesting and ultrafast energy migration in porphyrin-based metal-organic frameworks. J Am Chem Soc 2013; 135:862-9. [PMID: 23249338 DOI: 10.1021/ja310596a] [Citation(s) in RCA: 375] [Impact Index Per Article: 34.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal-organic frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts [5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinato]zinc(II) and [5,15-bis[4-(pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ~45 porphyrin struts within its lifetime in DA-MOF (but only ~3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.
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Effective cholesteric liquid crystal inducers based on axially chiral alleno-acetylenes. RSC Adv 2013. [DOI: 10.1039/c3ra44883e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Extremely strong self-assembly of a bimetallic salen complex visualized at the single-molecule level. J Am Chem Soc 2012; 134:7186-92. [PMID: 22475214 DOI: 10.1021/ja3030802] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A bis-Zn(salphen) structure shows extremely strong self-assembly both in solution as well as at the solid-liquid interface as evidenced by scanning tunneling microscopy, competitive UV-vis and fluorescence titrations, dynamic light scattering, and transmission electron microscopy. Density functional theory analysis on the Zn(2) complex rationalizes the very high stability of the self-assembled structures provoked by unusual oligomeric (Zn-O)(n) coordination motifs within the assembly. This coordination mode is strikingly different when compared with mononuclear Zn(salphen) analogues that form dimeric structures having a typical Zn(2)O(2) central unit. The high stability of the multinuclear structure therefore holds great promise for the development of stable self-assembled monolayers with potential for new opto-electronic materials.
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Self-assembly of Zn(salphen) complexes: steric regulation, stability studies and crystallographic analysis revealing an unexpected dimeric 3,3'-t-Bu-substituted Zn(salphen) complex. Dalton Trans 2011; 39:4541-50. [PMID: 20372698 DOI: 10.1039/b925560e] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The self-assembly features of a series of (non)symmetrical Zn(salphen) complexes have been studied in detail by X-ray crystallography, NMR and UV-vis techniques. The combined data demonstrate that the stability of these dimeric assemblies and the relative position of each monomeric unit within the dinuclear structure depend on the location and combination of the aromatic ring substituents.
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Rücktitelbild: Effective Chirogenesis in a Bis(metallosalphen) Complex through Host-Guest Binding with Carboxylic Acids (Angew. Chem. 3/2011). Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201006805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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