Switchable Catalysis with a Light‐Responsive Cavitand

Abstract

Katalytische Gaststars: Ein Cavitand mit Azobenzolwand nimmt bei Bestrahlung mit UV‐Licht eine introvertierte Form an. Diese Konformation wurde in Lösung und im Festkörper charakterisiert und wird genutzt, um die Bindung von Gastmolekülen zu steuern. Durch Einführung eines organokatalytischen Gastes lässt sich die Geschwindigkeit der Knoevenagel‐Kondensation mittels Licht steuern.

Synthesis of coumarin-appended cyclophanes and evaluation of their complexation with myoglobin

“…Macrocyclic cyclophanes bearing polar side chains furnish hydrophobic cavities in aqueous media [1][2][3]. The cyclophanes act as a water-soluble host for incorporation of organic guest molecules [4].…”

Ultrafast Light‐Driven Substrate Expulsion from the Active Site of a Photoswitchable Catalyst

“…[4] Theu se of light to irreversibly photodissociate and thereby activate ac aged compound allows the initiation of areaction at adefined point in time.U nfortunately the process induced by the initial cleavage cannot be reversed or shut down. [7] Ap rominent example is the previously developed azobenzene (AB) based supramolecular catalyst, [8] which brings two metal centers in proximity in the active state.A nother system is al ight-responsive cavitand [9] which binds and thereby activates the catalyst. [6] Considerable efforts are being made to reversibly photoregulate catalysis, which is perhaps the most attractive function to control from ac hemistsp oint of view.…”

“…This limitation is overcome by making the activation reversible and repeatable, utilizing geometric rearrangements of the molecular structure.T his approach has been used to photoswitch biological activity of proteins [4,5] and DNAtranscription. [7] Ap rominent example is the previously developed azobenzene (AB) based supramolecular catalyst, [8] which brings two metal centers in proximity in the active state.A nother system is al ight-responsive cavitand [9] which binds and thereby activates the catalyst. [7] Ap rominent example is the previously developed azobenzene (AB) based supramolecular catalyst, [8] which brings two metal centers in proximity in the active state.A nother system is al ight-responsive cavitand [9] which binds and thereby activates the catalyst.…”

“…[6] Considerable efforts are being made to reversibly photoregulate catalysis, which is perhaps the most attractive function to control from ac hemistsp oint of view. [7] Ap rominent example is the previously developed azobenzene (AB) based supramolecular catalyst, [8] which brings two metal centers in proximity in the active state.A nother system is al ight-responsive cavitand [9] which binds and thereby activates the catalyst. Osorio-Planes et al [10] recently reported regulation of catalytic activity via photoswitchable intramolecular hydrogen bonding that inhibits the active site.N ote that photoregulated catalysis (via uncaging or photoswitching) has to be distinguished from photocatalysis, [11] where ap hotoreaction is promoted by electronic excitation.Thep reviously developed catalyst under study (Figure 1A,blue structures), [12,13] shortly called "A zocat" (derived from AB-based catalyst), is aprototype system for conformational control of reactivity.This molecule catalyzes the Henry reaction, ab ase-catalyzed addition of nitroalkanes to aldehydes or ketones,for which reversible active-site accessibility has already been shown.…”

A Toggle Nanoswitch Alternately Controlling Two Catalytic Reactions

“…[6,7] It occurred to us that the new family of triangular nanoswitches as developed by us over the past three years with their 2 nm reorganization at their switching arm [8,9] may be suitable to bring about an analogous dual alternating catalytic scenario using exclusively artificial components. At present, only a handful of nanomechanical switches are known that allow regulation of catalytic processes, for example, Rebeks light-controlled azobenzene-calixarene switch modulating a Knoevenagel condensation, [10] Mirkins weak-link-controlled Diels-Alder cycloaddition, [11] Shibasakis acylation, [12] Feringas motor [13] and Leighs rotaxane both of which catalyze a conjugate addition, [14] plus our largeamplitude ON/OFF nanoswitches controlling the catalysis of a Knoevenagel addition [8] as well as a cis-trans isomerization. [9] Herein we describe how the chemically toggled nanoswitch [Cu(1)] +[9] is able to alternately regulate two different catalyzed reactions-a Knoevenagel addition and a click reaction-depending on the respective switching state (Scheme 1).…”