Pinpointing Mechanochemical Bond Rupture by Embedding the Mechanophore into a Macrocycle

Schütze, Doreen; Holz, Katharina; Müller, Julian; Beyer, Martin K.; Lüning, Ulrich; Hartke, Bernd

doi:10.1002/anie.201409691

Cited by 54 publications

(65 citation statements)

References 48 publications

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“…These parameters (Figure S1 and Tables S1, S2 in the Supporting Information) were subsequently used in as tandard Arrhenius-type model to describe the thermally activated and mechanically assisted bond rupture process.A pplying bond rupture probability theory,t he most probable rupture forces were calculated as afunction of the externally applied force for ag iven loading rate.T om imic the conditions used in ultrasound polymer mechanochemistry, [18] al oading rate of 10 8 nN s À1 was used (see the Supporting Information for details). In contrast, the triazoles 1s, 3s,and 5s rupture at forces F s(I) > 7nN, as can be seen when pulling on the internal anchor atoms.F or 1s, 3s, and 5s,l inker rupture is significantly more likely (F 1s(T) = 4.09 nN;F 3s(T) = 4.96 nN;F 5s(T) = 5.01 nN) and cycloreversion appears experimentally impossible.T his result is in line with previous DFT simulations [5] and single-molecule force spectroscopy experiments of 1s, [12] which suggest that mechan- In contrast, the triazoles 1s, 3s,and 5s rupture at forces F s(I) > 7nN, as can be seen when pulling on the internal anchor atoms.F or 1s, 3s, and 5s,l inker rupture is significantly more likely (F 1s(T) = 4.09 nN;F 3s(T) = 4.96 nN;F 5s(T) = 5.01 nN) and cycloreversion appears experimentally impossible.T his result is in line with previous DFT simulations [5] and single-molecule force spectroscopy experiments of 1s, [12] which suggest that mechan- …”

supporting

confidence: 89%

Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Jacobs¹,

Schneider

Blank

2016

Angew Chem Int Ed

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Mechanophores, that is, molecules that show a defined response to force, are crucial building blocks of mechanoresponsive materials. The possibility of mechanically induced cycloreversion for a series of triazoles formed via strain-promoted azide-alkyne cycloaddition reactions was investigated by density functional theory calculations, and these triazoles were compared to the 1,4- and 1,5-regioisomers formed in the reaction of an azide with a terminal alkyne. We show that cycloreversion is in principal possible and that the pulling geometry is the most important parameter that determines the probability of cycloreversion. We further compared triazole stability to the mechanical stability of polymers that are frequently used as force transducers in mechanochemical experiments and identified DIBAC (azadibenzylcyclooctyne) as a promising mechanophore for future applications.

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supporting

confidence: 89%

Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Jacobs¹,

Schneider

Blank

2016

Angew Chem Int Ed

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“…This conclusion is corroborated by independent calculations [17,18] where,m oreover,i th as been shown that simple CÀCb ond rupture [17] in the force-transducing chains attached to the mechanophore becomes energetically preferred over cycloreversion even at about 1nN. Furthermore,r ecent singlemolecule force spectroscopy experiments "cannot determine whether it was really mechanochemicallyi nduced retro-click reactions of the 1,2,3-triazole ring that took place or merely bond rupture next to it" [19] ,which leaves the case open.…”

mentioning

confidence: 91%

Unclicking the Click: Metal‐Assisted Mechanochemical Cycloreversion of Triazoles Is Possible

2017

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The mechanochemical cycloreversion of 1,2,3triazole compounds,w hich serve as unusually stable building blocks in materials and biomolecular chemistry as ar esult of mild "click chemistry", remains puzzling.W es how that the hitherto discussed straight-forwardr etro-clickm echanismo f the 1,4-disubstituted isomer,even if Cu I catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways.Instark contrast, the 1,5-regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owingtoits favorable response to the external force in conjunction with standardRu II catalysis.Supportinginformation (details on the computational methods, pertinentr eferences,a dditional analyses, and stationary point structures) for this article can be found under: https://doi.

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“…A follow‐up paper by a different research group using an atomic force microscope (AFM) single molecule force spectroscopy technique suggested that the chance for selective triazole rupture in the presence of C−Si bond is low. In several thousands of events, only three showed potential triazole rupture, but there was no suitable method to differentiate triazole rupture from other bond rupture . Earlier density functional theory calculation indicated force‐induced selective triazole rupture is unlikely .…”

Section: Introductionmentioning

confidence: 99%

Evidence of Splitting 1,2,3‐Triazole into an Alkyne and Azide by Low Mechanical Force in the Presence of Other Covalent Bonds

Khanal

Long

Cao

et al. 2016

Chemistry A European J

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The cycloaddition reaction of an alkyne and azide to form a 1,2,3-triazole is widely used in many areas. However, the stability of the triazole moiety under mechanical stress is unclear. To see if a triazole could be selectively split into an alkyne and azide in the presence of other typical covalent bonds, a mica surface functionalized with a molecule containing a triazole moiety in the middle and an activated ester at the end was prepared. An atomic force microscope (AFM) tip with amino groups on its surface was ramped over the mica surface at predefined locations, which could temporarily link the tip to the surface through amide bond formation. During retraction, the triazole or another bond in the linkage broke, and a force was recorded. The forces varied widely at different ramps from close to 0 pN to 860 pN due to nonspecific adhesions and to the inherent inconsistency of single bond rupture. If some of the forces were from triazole cycloreversion, there would be alkynes at the predefined ramping locations. The surface was reacted with an azide carboxylic acid followed by labeling with amino Au nanoparticles (AuNPs). AFM imaging revealed AuNPs at the predicted locations, which provided evidence that under certain conditions triazole could be split selectively in the presence of other bonds at forces below 860 pN.

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Pinpointing Mechanochemical Bond Rupture by Embedding the Mechanophore into a Macrocycle

Cited by 54 publications

References 48 publications

Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Unclicking the Click: Metal‐Assisted Mechanochemical Cycloreversion of Triazoles Is Possible

Evidence of Splitting 1,2,3‐Triazole into an Alkyne and Azide by Low Mechanical Force in the Presence of Other Covalent Bonds

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