Modified Chemistry of Siloxanes under Tensile Stress:  Interaction with Environment

Lupton, Elizabeth M.; Achenbach, Frank; Weis, Johann; Bräuchle, Christoph; Frank, Irmgard

doi:10.1021/jp0607059

Cited by 25 publications

(52 citation statements)

References 30 publications

(45 reference statements)

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“…Simulations at constant distance were performed, for example, in Ref. [13]. Our experience is that the different simulation modes do not affect the observed chemistry unless velocities beyond the velocity of sound are reached, which may lead to fragmentation of the chains.…”

Section: Resultsmentioning

confidence: 99%

“…In the past we used the CPMD approach to simulate the mechanically induced cleavage of polymer chains 11. 12, 13, 14 The observed reactions could be classified as homolytic or heterolytic reactions, that is, either two unpaired electrons were formed upon bond rupture or all electrons remained paired. The homolytic reactions simply lead to radical fragments.…”

Section: Introductionmentioning

confidence: 99%

“…In several systems, reactions with the solvent were observed leading to hydrolysis of the expanded polymer. [12,13] In the present study we investigate a mechanically induced redox reaction, namely, the breaking of a disulfide bond in the presence of a reducing agent.…”

Section: Introductionmentioning

confidence: 99%

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Disulfide Bond Cleavage: A Redox Reaction Without Electron Transfer

Hofbauer

Frank

2010

Chemistry A European J

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By using Car-Parrinello molecular dynamics (CPMD) simulations we have simulated a mechanically induced redox reaction. Previous single-molecule atomic force microscopy (AFM) experiments demonstrated that the reduction of disulfide bonds in proteins with the weak reducing agent dithiothreitol depends on a mechanical destabilization of the breaking bond. With reactive molecular dynamics simulations the single steps of the reaction mechanism can be elucidated and the motion of the electrons can be monitored. The simulations show that the redox reaction consists of the heterolytic cleavage of the S--S bond followed by a sequence of proton transfers.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Disulfide Bond Cleavage: A Redox Reaction Without Electron Transfer

Hofbauer

Frank

2010

Chemistry A European J

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“…As is often the case, water acts differently than alcohols, as it converts -(CH 3 ) 2 Si + and -(CH 3 ) 2 SiO À into -(CH 3 ) 2 SiOH by hydrolysis [21] thus annihilating the surface charges. [15] In fact, when water is added to the prepared conductive PDMS-ES pieces, it protonates the -(CH 3 ) 2 SiO À ions and reacts with -(CH 3 ) 2 Si + to form -(CH 3 ) 2 SiOH (Figure 4 b).…”

Section: Methodsmentioning

confidence: 99%

Mechanically Driven Activation of Polyaniline into Its Conductive Form

Baytekin

Grzybowski

2014

Angewandte Chemie

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Mechanical treatment of polymers produces surface cations and anions which, as demonstrated here for the first time, can drive chemical reactions. In particular, it is shown that such a mechanical treatment transforms nonconductive polyaniline into its conductive form. These results provide a mechanical means of patterning conductive polymers and also coating small polymer objects with conductive polyaniline films preventing accumulation of static electricity.Recent research on polymer mechanochemistry [1] -which aims to break or modify chemical bonds in polymers by mechanical stimuli-has demonstrated a range of mechanically driven reactions using both synthetic [2] and biological polymers [3] and sometimes displaying new reaction pathways. [4] In one exciting example, mechanochemical treatment of polymers incorporating trans and cis isomers of a 1,2disubstituted benzocyclobutene unit enabled electrocyclic ring opening, which, according to the Woodward-Hoffmann orbital symmetry rules, [5,6] should not be possible. In another work, 1,3-dipolar cycloreversions (reverse "click" chemistry), which are not possible under moderate thermal treatment, were made possible by mechanical input. These and several other reactions were enabled by incorporating into the polymers the so-called mechanophores, [6,7] which are functional groups designed to undergo a desired transformation. [8] Moreover, we [9] and others [10] have recently shown that it is also possible to drive mechanochemical reactions without the presence of mechanophores, using common polymers. In these systems, mechanical deformation of a polymer causes homolytic bond scission creating radicals, which then react with the surrounding solvent to yield hydrogen peroxide in quantities sufficient to synthesize nanoparticles, bleach dyes, or even turn on fluorescence visible to a naked eye.Homolytic cleavage is, of course, not the only pathway by which polymer bonds can break upon mechanical treatment. The bonds can also break heterolytically, forming surfacebound cations and anions, which form (+ /À) "mosaics" (Scheme 1) of surface charges of both polarities. [11a] In a recent series of publications, we [11] and others [12] have shown how these processes relate to the accumulation of static electricity which is a technologically useful process (e.g., in xerography) but also a source of shocks, explosions, and damage to electronic equipment. However, despite early reports [13] -which, were later refuted [11d, 14] -it has so far proven impossible to use these mechanochemically created surface charges in chemical applications, largely because the charges are rapidly annihilated in aqueous solutions. [15] Here we show, for the first time, that in non-aqueous but protic environments, these mechanoions can drive chemical reactions at material interfaces. In particular, we demonstrate that they can transform the non-conductive form of polyaniline (PANI) into its conductive salt. With spatially localized activation, our mechanical treatment allows for imprinting con...

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“…These studies have focused primarily on simulating molecular systems exposed to external forces by treating the system as though it moves on a force-modified potential energy surface that incorporates the work performed on a chemical system as it undergoes structural changes in the presence of an external force. These studies have examined the rupture forces of bonds [32], the reactivities of molecules subjected to tensile stresses and strains [38][39][40][41], the effects of strains on pericyclic reactions [14, 29-31, 33, 34, 42-44], the differences between thermochemistry and mechanochemistry [45], and the effects of chain length on the transduction of external forces at atomic levels [46,47].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity

Kochhar

Heverly‐Coulson

Mosey

2015

Topics in Current Chemistry

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The use of mechanical stresses to induce chemical reactions has attracted significant interest in recent years. Computational modeling can play a significant role in developing a comprehensive understanding of the interplay between stresses and chemical reactivity. In this review, we discuss techniques for simulating chemical reactions occurring under mechanochemical conditions. The methods described are broadly divided into techniques that are appropriate for studying molecular mechanochemistry and those suited to modeling bulk mechanochemistry. In both cases, several different approaches are described and compared. Methods for examining molecular mechanochemistry are based on exploring the force-modified potential energy surface on which a molecule subjected to an external force moves. Meanwhile, it is suggested that condensed phase simulation methods typically used to study tribochemical reactions, i.e., those occurring in sliding contacts, can be adapted to study bulk mechanochemistry.

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Modified Chemistry of Siloxanes under Tensile Stress: Interaction with Environment

Cited by 25 publications

References 30 publications

Disulfide Bond Cleavage: A Redox Reaction Without Electron Transfer

Disulfide Bond Cleavage: A Redox Reaction Without Electron Transfer

Mechanically Driven Activation of Polyaniline into Its Conductive Form

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity

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