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Journal ArticleDOI

Single-Event Spectroscopy and Unravelling Kinetics of Covalent Domains Based on Cyclobutane Mechanophores

TL;DR: In this paper, a covalent synthetic mimics of the mechanical unfolding of noncovalent “stored length” doma... is proposed to serve as a synthetic mimic of the unfolding of polymer contour length.
Abstract: Mechanochemical reactions that lead to an increase in polymer contour length have the potential to serve as covalent synthetic mimics of the mechanical unfolding of noncovalent “stored length” doma...
Citations
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Journal ArticleDOI
TL;DR: In this article, a mechanophore based on benzo[1,3]oxazine (OX) fused with a heptamethine cyanine moiety was developed and incorporated into a poly(methyl acrylate) chain to showcase the first force-induced NIR chromism in polymeric materials.
Abstract: A near-infrared (NIR) mechanophore was developed and incorporated into a poly(methyl acrylate) chain to showcase the first force-induced NIR chromism in polymeric materials. This mechanophore, based on benzo[1,3]oxazine (OX) fused with a heptamethine cyanine moiety, exhibited NIR mechanochromism in solution, thin-film, and bulk states. The mechanochemical activity was validated using UV-vis-NIR absorption/fluorescence spectroscopies, gel permeation chromatography (GPC), NMR, and DFT simulations. Our work demonstrates that NIR mechanochromic polymers have considerable potential in mechanical force sensing, damage detection, bioimaging, and biomechanics.

18 citations

Journal ArticleDOI
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.

17 citations

Journal ArticleDOI
Jingyuan Nie1, Fang Tian1, Bin Zheng1, Ziyi Wang1, Peng Zheng1 
TL;DR: It is shown that metalloprotein plays an essential role in many different biological processes and represents an indispensable protein subgroup and the knowledge of this subgroup is essential for the development of new drugs to treat cancer.
Abstract: Thanks to the binding of various metal ions, metalloprotein plays an essential role in many different biological processes and represents an indispensable protein subgroup. Thus, the knowledge of t...

7 citations

Journal ArticleDOI
TL;DR: In this article , it is shown that solely elastic environments do not change this barrier in contrast to the predictions of constraint geometry simulate external force (COGEF) strategies, which is confirmed by explicit calculations of bond rupture in a polydimethylsiloxane model.
Abstract: Abstract Bond rupture under the action of external forces is usually induced by temperature fluctuations, where the key quantity is the force dependent barrier that needs to be overcome. Using analytic potentials we find that these barriers are fully determined by the dissociation energy and the maximal force the potential can withstand. The barrier shows a simple dependence on these two quantities that allows for a re‐interpretation of the Eyring‐Zhurkov‐Bell length Δx‡ and the expressions in theories going beyond that. It is shown that solely elastic environments do not change this barrier in contrast to the predictions of constraint geometry simulate external force (COGEF) strategies. The findings are confirmed by explicit calculations of bond rupture in a polydimethylsiloxane model.

4 citations

Journal ArticleDOI
TL;DR: In this paper , the potential match between covalent polymer mechanochemistry and recent advances in polymer network chemistry, specifically, topologically controlled networks and the hierarchical material responses enabled by multi-network architectures and mechanically interlocked polymers is discussed.
Abstract: Over the past 20 years, the field of polymer mechanochemistry has amassed a toolbox of mechanophores that translate mechanical energy into a variety of functional responses ranging from color change to small-molecule release. These productive chemical changes typically occur at the length scale of a few covalent bonds (Å) but require large energy inputs and strains on the micro-to-macro scale in order to achieve even low levels of mechanophore activation. The minimal activation hinders the translation of the available chemical responses into materials and device applications. The mechanophore activation challenge inspires core questions at yet another length scale of chemical control, namely: What are the molecular-scale features of a polymeric material that determine the extent of mechanophore activation? Further, how do we marry advances in the chemistry of polymer networks with the chemistry of mechanophores to create stress-responsive materials that are well suited for an intended application? In this Perspective, we speculate as to the potential match between covalent polymer mechanochemistry and recent advances in polymer network chemistry, specifically, topologically controlled networks and the hierarchical material responses enabled by multi-network architectures and mechanically interlocked polymers. Both fundamental and applied opportunities unique to the union of these two fields are discussed.

4 citations

References
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Journal ArticleDOI
16 May 1997-Science
TL;DR: Single-molecule atomic force microscopy was used to investigate the mechanical properties of titin, the giant sarcomeric protein of striated muscle, and refolding of immunoglobulin domains was observed.
Abstract: Single-molecule atomic force microscopy (AFM) was used to investigate the mechanical properties of titin, the giant sarcomeric protein of striated muscle. Individual titin molecules were repeatedly stretched, and the applied force was recorded as a function of the elongation. At large extensions, the restoring force exhibited a sawtoothlike pattern, with a periodicity that varied between 25 and 28 nanometers. Measurements of recombinant titin immunoglobulin segments of two different lengths exhibited the same pattern and allowed attribution of the discontinuities to the unfolding of individual immunoglobulin domains. The forces required to unfold individual domains ranged from 150 to 300 piconewtons and depended on the pulling speed. Upon relaxation, refolding of immunoglobulin domains was observed.

2,959 citations

Journal ArticleDOI
15 May 1997-Nature
TL;DR: Mechanical experiments on single molecules of titin are done to determine their visco-elastic properties, showing that there are two main sources of elasticity: one deriving from the entropy of straightening the molecule; the other consistent with extension of the polypeptide chain in the PEVK region.
Abstract: The giant muscle protein titin, also called connectin, is responsible for the elasticity of relaxed striated muscle, as well as acting as the molecular scaffold for thick-filament formation. The titin molecule consists largely of tandem domains of the immunoglobulin and fibronectin-III types, together with specialized binding regions and a putative elastic region, the PEVK domain. We have done mechanical experiments on single molecules of titin to determine their visco-elastic properties, using an optical-tweezers technique. On a fast (0.1s) timescale titin is elastic and force-extension data can be fitted with standard random-coil polymer models, showing that there are two main sources of elasticity: one deriving from the entropy of straightening the molecule; the other consistent with extension of the polypeptide chain in the PEVK region. On a slower timescale and above a certain force threshold, the molecule displays stress-relaxation, which occurs in rapid steps of a few piconewtons, corresponding to yielding of internal structures by about 20 nm. This stress-relaxation probably derives from unfolding of immunoglobulin and fibronectin domains.

734 citations

Journal ArticleDOI
TL;DR: Here, different techniques that allow for the in situ measurement of the absolute value of the spring constant of the cantilevers are compared.

469 citations

Journal ArticleDOI
TL;DR: It is shown that under force-clamp conditions, an engineered titin protein elongates in steps because of the unfolding of its modules and that the waiting times to unfold are exponentially distributed.
Abstract: Here we demonstrate the implementation of a single-molecule force clamp adapted for use with an atomic force microscope. We show that under force-clamp conditions, an engineered titin protein elongates in steps because of the unfolding of its modules and that the waiting times to unfold are exponentially distributed. Force-clamp measurements directly measure the force dependence of the unfolding probability and readily captures the different mechanical stability of the I27 and I28 modules of human cardiac titin. Force-clamp spectroscopy promises to be a direct way to probe the mechanical stability of elastic proteins such as those found in muscle, the extracellular matrix, and cell adhesion.

373 citations

Journal ArticleDOI
TL;DR: The force-clamp experiments directly demonstrate that an ensemble average of ubiquitin unfolding events is well described by a two-state Markovian process that obeys the Arrhenius equation.
Abstract: We use single-molecule force spectroscopy to study the kinetics of unfolding of the small protein ubiquitin. Upon a step increase in the stretching force, a ubiquitin polyprotein extends in discrete steps of 20.3 ± 0.9 nm marking each unfolding event. An average of the time course of these unfolding events was well described by a single exponential, which is a necessary condition for a memoryless Markovian process. Similar ensemble averages done at different forces showed that the unfolding rate was exponentially dependent on the stretching force. Stretching a ubiquitin polyprotein with a force that increased at a constant rate (force-ramp) directly measured the distribution of unfolding forces. This distribution was accurately reproduced by the simple kinetics of an all-or-none unfolding process. Our force-clamp experiments directly demonstrate that an ensemble average of ubiquitin unfolding events is well described by a two-state Markovian process that obeys the Arrhenius equation. However, at the single-molecule level, deviant behavior that is not well represented in the ensemble average is readily observed. Our experiments make an important addition to protein spectroscopy by demonstrating an unambiguous method of analysis of the kinetics of protein unfolding by a stretching force.

361 citations