Photoswitchable basicity through the use of azoheteroarenes

Weston, Claire E.; Richardson, Robert D.; Fuchter, Matthew J.

doi:10.1039/c5cc10380k

Cited by 64 publications

(77 citation statements)

References 35 publications

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“…Reversible pK a changes exceeding seven units are obtained-to our best knowledge, a significantly larger value than those reported so far for synthetic reversible stimuli-responsive pK a modulators (38)(39)(40)(41)(42)(43). This observation is of general interest because, in principle, pH-sensitive sites with made-to-order pK a values can be rationally designed using the very same functional group (in the present case, a secondary ammonium) and adjusting the interaction between the ring and a second pH-insensitive site.…”

Section: Discussionmentioning

confidence: 88%

Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery

Ragazzon

Schäfer

Franchi

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Allosteric control, one of Nature's most effective ways to regulate functions in biomolecular machinery, involves the transfer of information between distant sites. The mechanistic details of such a transfer are still an object of intensive investigation and debate, and the idea that intramolecular communication could be enabled by dynamic processes is gaining attention as a complement to traditional explanations. Mechanically interlocked molecules, owing to the particular kind of connection between their components and the resulting dynamic behavior, are attractive systems to investigate allosteric mechanisms and exploit them to develop functionalities with artificial species. We show that the pK a of an ammonium site located on the axle component of a [2]rotaxane can be reversibly modulated by changing the affinity of a remote recognition site for the interlocked crown ether ring through electrochemical stimulation. The use of a reversible ternary redox switch enables us to set the pK a to three different values, encompassing more than seven units. Our results demonstrate that in the axle the two sites do not communicate, and that in the rotaxane the transfer of information between them is made possible by the shuttling of the ring, that is, by a dynamic intramolecular process. The investigated coupling of electron-and proton-transfer reactions is reminiscent of the operation of the protein complex I of the respiratory chain.acid-base processes | electrochemistry | free energy change | molecular machine | molecular switch A llostery-the process by which a chemical transformation at one site causes a change at a distant site within the same molecule or molecular assembly-is a key phenomenon for the regulation of biological activity (1, 2). A most important example is the long-range coupling of redox-active and acid-basesensitive sites, a crucial element of electron transport chains, as exemplified by the respiratory complex I (3). Although allosteric effects are usually described in terms of conformational changes induced by binding at one site directly affecting the affinity of the other site (4), the idea that the transmission of information at the basis of allostery could take place through dynamic mechanisms is receiving increasing attention (5-7). Indeed, despite its importance for life, allosteric regulation remains an elusive biochemical phenomenon.Mechanically interlocked molecules (MIMs) (8) such as rotaxanes and catenanes, because of the lack of strong chemical bonds between their molecular parts, are characterized by a rich dynamic behavior that involves changes of the relative position of the components (co-conformation). Indeed, in appropriately designed MIMs co-conformational rearrangements can be precisely controlled by modulating the noncovalent intercomponent interactions through external stimulation (9, 10). For these reasons, MIMs can be regarded as appealing systems for investigating allosteric communication mechanisms and implementing them within synthetic species to achieve functions (11)....

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Section: Discussionmentioning

confidence: 88%

Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery

Ragazzon

Schäfer

Franchi

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…They are frequently employed in the context of photopharmacology, as many typical pharmacophores contain aromatic heterocycles . Moreover, azoheteroarenes allow for light modulation of molecular properties such as magnetism, luminescence, and p K a . Arylazopyrazoles, a class of azoheteroarenes, can undergo light‐driven bidirectional switching between the E and Z isomers and display some of the longest thermal half‐lives ( t 1/2 ) for the Z → E isomerization of azo derivative photoswitches ( t 1/2 =1000 d) .…”

Section: Introductionmentioning

confidence: 99%

“… Literature azobenzene‐type photochromic molecules and compounds 1 – 3 prepared in this study. n.r.=not reported.…”

Section: Introductionmentioning

confidence: 99%

“…Azobis(2‐imidazole) (Figure ), a symmetric azoheteroarene reported by the Fuchter group, absorbs blue light and is protonated preferentially on the imidazole nitrogen leading to a redshift in absorption and an increase in thermal half‐life (from 16 to 352 s in H 2 O). An intramolecular hydrogen bond stabilizes the protonated Z isomer and leads to a significant difference in proton affinity between the two isomers (p K a values in water: E 4.7; Z 6.0), which can be used to reversibly modulate the pH of a solution …”

Section: Introductionmentioning

confidence: 99%

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Visible‐Light Photoswitching by Azobenzazoles

Kennedy

Sandler

Andréasson

et al. 2020

Chemistry A European J

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Three visible-light responsive photoswitches are reported, azobis(1-methyl-benzimidazole) (1), azobis(benzoxazole) (2)a nd azobis(benzothiazole) (3). Photostationaryd istributions are obtained upon irradiation with visible light comprising approximately8 0% of the thermally unstable isomer,with thermalhalf-lives up to 8min and are mostly invariant to solvent. On protonation, compound 1H + has absorption extendingb eyond 600 nm, allowing switching with yellow light, and at hermal half-life just under 5minutes.The two isomersh ave significantly different pK a values, offering potential as ap Hs witch. The absorption spectra of 2 and 3 are insensitive to acid, although changes in the thermal half-life of 3 indicatem ore basic intermediates that significantly influence the thermal barrier to isomerization. These findings are supported by high-level ab initio calculations, which validate that protonation occurs on the ring nitrogen and that the Z isomer is more basic in all cases.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.Figure 9. a) Photoswitching of 1-3H + showing the proposed intramolecular hydrogen bond in the Z isomer.b)Optimized geometry for Z-1H + in acetonitrile [M06-2X/6-31 + G(d,p)] showing the proposedh ydrogen-bonding interactionand the resulting planarity of the molecule.

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“…These materials respond to small changes of stimuli (pH, magnetic fields, temperature, light, etc.) with a change in their physical or chemical properties, often reversibly . Photochromic materials, in particular, are of considerable interest as the regulation of their activity using light allows both spatial and temporal control without any physical contact.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Electronic Mobility of a One‐Dimensional Coordination Polymeric Molecular Wire with Light

Saha

Chatterjee

Hossain

et al. 2019

Chemistry An Asian Journal

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Metal ions often influence the photoswitching efficiency of ap hotochromic system.T his article reports ao nedimensional polymer having cyclic azobenzenes coordinated to silver ions that are bridged by nitrates. The coordination polymer (CP-2)d isplays ap hotoresponsive behavior.T he switching ability in the polymer form was faster compared to the parenta zobenzene ligand withoutt he metal ions. Azobenzenes are reported to be poorlyc onducting. Here, although the azobenzene ligand does not show significant electronic mobility,t he coordination polymer (CP-2)d isplays am odest conductivity.T he conductance in the cis form of the polymer is significantly higher compared to the trans form. Upon exposure to visible light, the cis form undergoes photoisomerization to the trans form with ad rastic drop in the electronic mobility.T he trans form can be reverted to the cis form thermally or by using UV light.Thus,t his system offers ar eversible control of the conductivity using light.

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Photoswitchable basicity through the use of azoheteroarenes

Cited by 64 publications

References 35 publications

Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery

Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery

Visible‐Light Photoswitching by Azobenzazoles

Modulation of Electronic Mobility of a One‐Dimensional Coordination Polymeric Molecular Wire with Light

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Photoswitchable basicity through the use of azoheteroarenes

Cited by 64 publications

References 35 publications

Remote electrochemical modulation of pK a in a rotaxane by co-conformational allostery

Remote electrochemical modulation of pK a in a rotaxane by co-conformational allostery

Visible‐Light Photoswitching by Azobenzazoles

Modulation of Electronic Mobility of a One‐Dimensional Coordination Polymeric Molecular Wire with Light

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Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery

Remote electrochemical modulation of pK _a in a rotaxane by co-conformational allostery