Understanding the Mechanochemistry of Ladder-Type Cyclobutane Mechanophores by Single Molecule Force Spectroscopy.
26 Jul 2021-Journal of the American Chemical Society (American Chemical Society (ACS))-Vol. 143, Iss: 31, pp 12328-12334
TL;DR: In this paper, a series of ladder-type cyclobutane mechanophores, polymers of which can transform from nonconjugated structures to conjugated structures and change many properties at once, are reported.
Abstract: We have recently reported a series of ladder-type cyclobutane mechanophores, polymers of which can transform from nonconjugated structures to conjugated structures and change many properties at once. These multicyclic mechanophores, namely, exo-ladderane/ene, endo-benzoladderene, and exo-bicyclohexene-peri-naphthalene, have different ring structures fused to the first cyclobutane, significantly different free energy changes for ring-opening, and different stereochemistry. To better understand their mechanochemistry, we used single molecule force spectroscopy (SMFS) to characterize their force-extension behavior and measure the threshold forces. The threshold forces correlate with the activation energy of the first bond, but not with the strain of the fused rings distal to the polymer main chain, suggesting that the activation of these ladder-type mechanophores occurs with similar early transition states, which is supported by force-modified potential energy surface calculations. We further determined the stereochemistry of the mechanically generated dienes and observed significant and variable contour length elongation for these mechanophores both experimentally and computationally. The fundamental understanding of ladder-type mechanophores will facilitate future design of multicyclic mechanophores with amplified force-response and their applications as mechanically responsive materials.
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TL;DR: In this article , a conformationally flexible dual-fluorescence force probe with a theoretically estimated threshold of approximately 100 pN was presented, which enables ratiometric analysis of the distribution of local forces in a stretched polymer chain network.
Abstract: Understanding the transmission of nanoscale forces in the pico-to-nanonewton range is important in polymer physics. While physical approaches have limitations in analyzing the local force distribution in condensed environments, chemical analysis using force probes is promising. However, there are stringent requirements for probing the local forces generated before structural damage. The magnitude of those forces corresponds to the range below covalent bond scission (from 200 pN to several nN) and above thermal fluctuation (several pN). Here, we report a conformationally flexible dual-fluorescence force probe with a theoretically estimated threshold of approximately 100 pN. This probe enables ratiometric analysis of the distribution of local forces in a stretched polymer chain network. Without changing the intrinsic properties of the polymer, the force distribution was reversibly monitored in real time. Chemical control of the probe location demonstrated that the local stress concentration is twice as biased at crosslinkers than at main chains, particularly in a strain-hardening region. Due to the high sensitivity, the percentage of the stressed force probes was estimated to be more than 1000 times higher than the activation rate of a conventional mechanophore.
21 citations
TL;DR: This review summarizes the recent advances in this research field combining the viewpoints of polymer and trituration mechanochemistry, and highlighted mechanochemical transformations include π‐conjugated materials as optical force probes, the force‐induced release of small dye molecules, and the mechanochemical synthesis of polyacetylene, carbon allotropic materials.
Abstract: Mechanochemistry uses mechanical force to break, form, and manipulate chemical bonds to achieve functional transformations and syntheses. Over the last years, many innovative applications of mechanochemistry have been developed. Specifically for the synthesis and activation of carbon‐rich π‐conjugated materials, mechanochemistry offers reaction pathways that either are inaccessible with other stimuli, such as light and heat, or improve reaction yields, energy consumption, and substrate scope. Therefore, this review summarizes the recent advances in this research field combining the viewpoints of polymer and trituration mechanochemistry. The highlighted mechanochemical transformations include π‐conjugated materials as optical force probes, the force‐induced release of small dye molecules, and the mechanochemical synthesis of polyacetylene, carbon allotropes, and other π‐conjugated materials.
15 citations
TL;DR: Nanoarch architectonics approaches for mechanically responding materials are discussed as mechano‐nanoarchitectonics in this review article and Pioneering approaches on cell fate regulations at liquid–liquid interfaces are discussed in addition to well‐known mechanobiology.
Abstract: Mechanical stimuli have rather ambiguous and less‐specific features among various physical stimuli, but most materials exhibit a certain level of responses upon mechanical inputs. Unexplored sciences remain in mechanical responding systems as one of the frontiers of materials science. Nanoarchitectonics approaches for mechanically responding materials are discussed as mechano‐nanoarchitectonics in this review article. Recent approaches on molecular and materials systems with mechanical response capabilities are first exemplified with two viewpoints: i) mechanical control of supramolecular assemblies and materials and ii) mechanical control and evaluation of atom/molecular level structures. In the following sections, special attentions on interfacial environments for mechano‐nanoarchitectonics are emphasized. The section entitled iii) Mechanical Control of Molecular System at Dynamic Interface describes coupling of macroscopic mechanical forces and molecular‐level phenomena. Delicate mechanical forces can be applied to functional molecules embedded at the air–water interface where operation of molecular machines and tuning of molecular receptors upon macroscopic mechanical actions are discussed. Finally, the important role of the interfacial media are further extended to the control of living cells as described in the section entitled iv) Mechanical Control of Biosystems. Pioneering approaches on cell fate regulations at liquid–liquid interfaces are discussed in addition to well‐known mechanobiology.
12 citations
TL;DR: In this article , the authors summarize some recent researches in ultrasound induced mechanoluminescence that use various materials design strategies based on the molecular conformational changes and cycloreversion reaction.
4 citations
TL;DR: A cyclophane-based supramolecular mechanophore that contains a 1,6-bis(phenylethynyl)pyrene luminophore and a pyromellitic diimide quencher is reported, which displays orange emission in the absence of force and the ratio of the two emission intensities correlates with the applied stress.
Abstract: Abstract Mechanochromic mechanophores are reporter molecules that indicate mechanical events through changes of their photophysical properties. Supramolecular mechanophores in which the activation is based on the rearrangement of luminophores and/or quenchers without any covalent bond scission, remain less well investigated. Here, we report a cyclophane‐based supramolecular mechanophore that contains a 1,6‐bis(phenylethynyl)pyrene luminophore and a pyromellitic diimide quencher. In solution, the blue monomer emission of the luminophore is largely quenched and a faint reddish‐orange emission originating from a charge‐transfer (CT) complex is observed. A polyurethane elastomer containing the mechanophore displays orange emission in the absence of force, which is dominated by the CT‐emission. Mechanical deformation causes a decrease of the CT‐emission and an increase of blue monomer emission, due to the spatial separation between the luminophore and quencher. The ratio of the two emission intensities correlates with the applied stress.
4 citations
References
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TL;DR: The purpose of this review is to broadly survey the mechanical to chemical relationships between synthetic polymers, and to consider the I-O relationship as an energy transduction process for designing stimuli-responsive materials.
Abstract: Engineering applications of synthetic polymers are widespread due to their availability, processability, low density, and diversity of mechanical properties (Figure 1a). Despite their ubiquitous nature, modern polymers are evolving into multifunctional systems with highly sophisticated behavior. These emergent functions are commonly described as “smart” characteristics whereby “intelligence” is rooted in a specific response elicited from a particular stimulus. Materials that exhibit stimuli-responsive functions thus achieve a desired output (O, the response) upon being subjected to a specific input (I, the stimulus). Given that mechanical loading is inevitable, coupled with the wide range of mechanical properties for synthetic polymers, it is not surprising that mechanoresponsive polymers are an especially attractive class of smart materials. To design materials with stimuli-responsive functions, it is helpful to consider the I-O relationship as an energy transduction process. Achieving the desired I-O linkage thus becomes a problem in finding how to transform energy from the stimulus into energy that executes the desired response. The underlying mechanism that forms this I-O coupling need not be a direct, one-step transduction event; rather, the overall process may proceed through a sequence of energy transduction steps. In this regard, the network of energy transduction pathways is a useful roadmap for designing stimuli-responsive materials (Figure 1b). It is the purpose of this review to broadly survey the mechanical to chemical * To whom correspondence should be addressed. Phone: 217-244-4024. Fax: 217-244-8024. E-mail: jsmoore@illinois.edu. † Department of Chemistry and Beckman Institute. ‡ Department of Materials Science and Engineering and Beckman Institute. § Department of Aerospace Engineering and Beckman Institute. Chem. Rev. XXXX, xxx, 000–000 A
1,081 citations
TL;DR: It is shown that mechanically sensitive chemical groups make it possible to harness the mechanical forces generated when exposing polymer solutions to ultrasound, and that this allows us to accelerate rearrangement reactions and bias reaction pathways to yield products not obtainable from purely thermal or light-induced reactions.
Abstract: For most chemical reactions to proceed the reactants need to surmount an energy barrier. The energy required is usually provided as heat, light, pressure or electrical potential. Now mechanical force can be added to that list: to the surprise of many a chemist, a reaction can literally be given a shove. In specially designed polymers subjected to ultrasound, rearrangement reactions are accelerated and reaction pathways can be biased to yield products not obtainable from heat- or light-induced reactions. The polymers contain a mechanophore positioned at a site where forces from extensional flow are greatest. Besides offering new ways of controlling chemical reactions, this work may also lead to mechanically adaptable materials, polymers that might generate a signal to warn of impending damage, undergo structure modification to slow the rate of damage, or even self-repair. Carefully designed 'mechanophores' can tame the 'brute force' approach needed for breaking chemical bonds in reactions. If incorporated into polymers and activated by mechanical forces, the mechanophores undergo rearrangement reactions to selectively form new molecules. The effect might result in mechanically responsive polymers that warn of impending structural failures, can slow damage or even self-repair. During the course of chemical reactions, reactant molecules need to surmount an energy barrier to allow their transformation into products. The energy needed for this process is usually provided by heat, light, pressure or electrical potential, which act either by changing the distribution of the reactants on their ground-state potential energy surface or by moving them onto an excited-state potential energy surface and thereby facilitate movement over the energy barrier. A fundamentally different way of initiating or accelerating a reaction is the use of force to deform reacting molecules along a specific direction of the reaction coordinate. Mechanical force has indeed been shown to activate covalent bonds in polymers, but the usual result is chain scission1. Here we show that mechanically sensitive chemical groups make it possible to harness the mechanical forces generated when exposing polymer solutions to ultrasound2, and that this allows us to accelerate rearrangement reactions and bias reaction pathways to yield products not obtainable from purely thermal or light-induced reactions. We find that when placed within long polymer strands, the trans and cis isomers of a 1,2-disubstituted benzocyclobutene undergo an ultrasound-induced electrocyclic ring opening in a formally conrotatory and formally disrotatory process, respectively, that yield identical products. This contrasts with reaction initiation by light or heat alone3, in which case the isomers follow mutually exclusive pathways to different products. Mechanical forces associated with ultrasound can thus clearly alter the shape of potential energy surfaces4 so that otherwise forbidden or slow processes proceed under mild conditions, with the directionally specific nature of mechanical forces providing a reaction control that is fundamentally different from that achieved by adjusting chemical or physical parameters. Because rearrangement in our system occurs before chain scission, the effect we describe might allow the development of materials that are activated by mechanical stress fields.
695 citations
TL;DR: The insights provided by in silico experiments are illustrated here through a review of recent research in three areas of protein mechanics: elasticity of the muscle protein titin and the extracellular matrix protein fibronectin; linker-mediated elasticness of the cytoskeleton protein spectrin; and elasticityOf ankyrin repeats, a protein module found ubiquitously in cells but with an as-yet unclear function.
Abstract: Single-molecule force experiments in vitro enable the characterization of the mechanical response of biological matter at the nanometer scale. However, they do not reveal the molecular mechanisms underlying mechanical function. These can only be readily studied through molecular dynamics simulations of atomic structural models: "in silico" (by computer analysis) single-molecule experiments. Steered molecular dynamics simulations, in which external forces are used to explore the response and function of macromolecules, have become a powerful tool complementing and guiding in vitro single-molecule experiments. The insights provided by in silico experiments are illustrated here through a review of recent research in three areas of protein mechanics: elasticity of the muscle protein titin and the extracellular matrix protein fibronectin; linker-mediated elasticity of the cytoskeleton protein spectrin; and elasticity of ankyrin repeats, a protein module found ubiquitously in cells but with an as-yet unclear function.
536 citations
TL;DR: In this paper, the rupture forces of covalent bonds in a polymer as a function of bond lifetime are calculated with an Arrhenius kinetics model based on high-level density functional theory calculations.
Abstract: The rupture forces of covalent bonds in a polymer as a function of bond lifetime are calculated with an Arrhenius kinetics model based on high-level density functional theory calculations. Relaxed potential energy surface scans of small model molecules yield potential functions that account for the deformations and hybridizations caused by the application of force. Morse potentials chosen to exhibit the same well depth and maximum force are used as an analytic representation of an individual bond in an infinitely long one-dimensional polymer. Application of force deforms the potential, and the activation energy for the bond rupture event together with the frequency of an optical phonon in the one-dimensional polymer are the two Arrhenius parameters. Rupture forces of the bonds C–C, C–N, C–O, Si–C, Si–N, Si–O, and Si–Si are reported as a function of the lifetime of the bond.
344 citations
TL;DR: The time is ripe: A general theoretical framework based on force-transformed potential energy surfaces rationalizes the intriguing results of recent experiments in the emerging field of covalent mechanochemistry.
Abstract: The time is ripe: A general theoretical framework based on force-transformed potential energy surfaces rationalizes the intriguing results of recent experiments in the emerging field of covalent mechanochemistry.
222 citations