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| Cardea Fellows Program : Publications since January 2023List all publications in the database. :chronological alphabetical combined listing:%% Baker, Lee D. @article{fds373890, Author = {Baker, LD}, Title = {The Gamble and the Game: Reflections on Writing From Savage to Negro}, Journal = {Transforming Anthropology}, Volume = {31}, Number = {2}, Pages = {96-99}, Year = {2023}, Month = {October}, url = {http://dx.doi.org/10.1111/traa.12258}, Doi = {10.1111/traa.12258}, Key = {fds373890} } %% Craig, Stephen L @article{fds370028, Author = {Wang, J and Kouznetsova, TB and Xia, J and Ángeles, FJ and de la Cruz, MO and Craig, SL}, Title = {A polyelectrolyte handle for single-molecule force spectroscopy}, Journal = {Journal of Polymer Science}, Volume = {62}, Number = {7}, Pages = {1277-1286}, Year = {2024}, Month = {April}, url = {http://dx.doi.org/10.1002/pol.20230051}, Abstract = {Single-molecule force spectroscopy is a powerful tool for the quantitative investigation of the biophysics, polymer physics and mechanochemistry of individual polymer strands. One limitation of this technique is that the attachment between the tip of the atomic force microscope and the covalent or noncovalent analyte in a given pull is typically not strong enough to sustain the force at which the event of interest occurs, which makes the experiments time-consuming and inhibits throughput. Here we report a polyelectrolyte handle for single-molecule force spectroscopy that offers a combination of high (several hundred pN) attachment forces, good (~4%) success in obtaining a high-force (>200 pN) attachment, a non-fouling detachment process that allows for repetition, and specific attachment locations along the polymer analyte.}, Doi = {10.1002/pol.20230051}, Key = {fds370028} } @article{fds376825, Author = {Sun, Y and Neary, WJ and Huang, X and Kouznetsova, TB and Ouchi, T and Kevlishvili, I and Wang, K and Chen, Y and Kulik, HJ and Craig, SL and Moore, JS}, Title = {A Thermally Stable SO2-Releasing Mechanophore: Facile Activation, Single-Event Spectroscopy, and Molecular Dynamic Simulations.}, Journal = {Journal of the American Chemical Society}, Year = {2024}, Month = {April}, url = {http://dx.doi.org/10.1021/jacs.4c02139}, Abstract = {Polymers that release small molecules in response to mechanical force are promising candidates as next-generation on-demand delivery systems. Despite advancements in the development of mechanophores for releasing diverse payloads through careful molecular design, the availability of scaffolds capable of discharging biomedically significant cargos in substantial quantities remains scarce. In this report, we detail a nonscissile mechanophore built from an 8-thiabicyclo[3.2.1]octane 8,8-dioxide (<b>TBO</b>) motif that releases one equivalent of sulfur dioxide (SO<sub>2</sub>) from each repeat unit. The <b>TBO</b> mechanophore exhibits high thermal stability but is activated mechanochemically using solution ultrasonication in either organic solvent or aqueous media with up to 63% efficiency, equating to 206 molecules of SO<sub>2</sub> released per 143.3 kDa chain. We quantified the mechanochemical reactivity of <b>TBO</b> by single-molecule force spectroscopy and resolved its single-event activation. The force-coupled rate constant for <b>TBO</b> opening reaches ∼9.0 s<sup>-1</sup> at ∼1520 pN, and each reaction of a single <b>TBO</b> domain releases a stored length of ∼0.68 nm. We investigated the mechanism of <b>TBO</b> activation using ab initio steered molecular dynamic simulations and rationalized the observed stereoselectivity. These comprehensive studies of the <b>TBO</b> mechanophore provide a mechanically coupled mechanism of multi-SO<sub>2</sub> release from one polymer chain, facilitating the translation of polymer mechanochemistry to potential biomedical applications.}, Doi = {10.1021/jacs.4c02139}, Key = {fds376825} } @article{fds376826, Author = {Hu, Y and Wang, L and Kevlishvili, I and Wang, S and Chiou, C-Y and Shieh, P and Lin, Y and Kulik, HJ and Johnson, JA and Craig, SL}, Title = {Self-Amplified HF Release and Polymer Deconstruction Cascades Triggered by Mechanical Force.}, Journal = {Journal of the American Chemical Society}, Volume = {146}, Number = {14}, Pages = {10115-10123}, Year = {2024}, Month = {April}, url = {http://dx.doi.org/10.1021/jacs.4c01402}, Abstract = {Hydrogen fluoride (HF) is a versatile reagent for material transformation, with applications in self-immolative polymers, remodeled siloxanes, and degradable polymers. The responsive <i>in situ</i> generation of HF in materials therefore holds promise for new classes of adaptive material systems. Here, we report the mechanochemically coupled generation of HF from alkoxy-<i>gem</i>-difluorocyclopropane (<i>g</i>DFC) mechanophores derived from the addition of difluorocarbene to enol ethers. Production of HF involves an initial mechanochemically assisted rearrangement of <i>g</i>DFC mechanophore to α-fluoro allyl ether whose regiochemistry involves preferential migration of fluoride to the alkoxy-substituted carbon, and ab initio steered molecular dynamics simulations reproduce the observed selectivity and offer insights into the mechanism. When the alkoxy <i>g</i>DFC mechanophore is derived from poly(dihydrofuran), the α-fluoro allyl ether undergoes subsequent hydrolysis to generate 1 equiv of HF and cleave the polymer chain. The hydrolysis is accelerated via acid catalysis, leading to self-amplifying HF generation and concomitant polymer degradation. The mechanically generated HF can be used in combination with fluoride indicators to generate an optical response and to degrade polybutadiene with embedded HF-cleavable silyl ethers (11 mol %). The alkoxy-<i>g</i>DFC mechanophore thus provides a mechanically coupled mechanism of releasing HF for polymer remodeling pathways that complements previous thermally driven mechanisms.}, Doi = {10.1021/jacs.4c01402}, Key = {fds376826} } @article{fds375389, Author = {Duan, C and Malek, JC and Craig, SL and Widenhoefer, RA}, Title = {Modulating Transition Metal Reactivity with Force}, Journal = {ChemCatChem}, Volume = {16}, Number = {5}, Year = {2024}, Month = {March}, url = {http://dx.doi.org/10.1002/cctc.202301479}, Abstract = {The reactivity and selectivity of a transition metal catalyst is intimately related to its ligand-sphere geometry, and, in many cases, the ideal ligand geometry for one step of a catalytic cycle is poorly matched to the ideal ligand geometry for another. For this reason, methods for reversibly modulating ligand geometry on the time scale of catalytic turnover or monomer enchainment are highly desirable. Mechanical force represents a heretofore untapped approach to modulate catalyst geometry and/or reactivity, with the potential to do so on the timescale of catalytic turnover or monomer enchainment. Macroscopic mechanical forces are large, directional and localized to an extent that differentiates them from other forms of energy input such as heat or light. In this Concept, we describe our efforts to address the fundamental challenges associated with force-modulated transition metal catalysis by employing molecular force probe ligands comprising a stiff stilbene photoswitch tethered to rotationally flexible biaryl bisphosphine ligand. Our efforts to date include the modulation of catalytic activity through force-mediated ligand perturbations, quantification of the force-coupled ligand effects on the energetics of elementary organometallic transformations, and evaluation of the mechanisms of force transduction in these systems.}, Doi = {10.1002/cctc.202301479}, Key = {fds375389} } @article{fds375839, Author = {Wu, Z and Bayón, JL and Kouznetsova, TB and Ouchi, T and Barkovich, KJ and Hsu, SK and Craig, SL and Steinmetz, NF}, Title = {Virus-like Particles Armored by an Endoskeleton.}, Journal = {Nano letters}, Volume = {24}, Number = {10}, Pages = {2989-2997}, Year = {2024}, Month = {March}, url = {http://dx.doi.org/10.1021/acs.nanolett.3c03806}, Abstract = {Many virus-like particles (VLPs) have good chemical, thermal, and mechanical stabilities compared to those of other biologics. However, their stability needs to be improved for the commercialization and use in translation of VLP-based materials. We developed an endoskeleton-armored strategy for enhancing VLP stability. Specifically, the VLPs of physalis mottle virus (PhMV) and Qβ were used to demonstrate this concept. We built an internal polymer "backbone" using a maleimide-PEG<sub>15</sub>-maleimide cross-linker to covalently interlink viral coat proteins inside the capsid cavity, while the native VLPs are held together by only noncovalent bonding between subunits. Endoskeleton-armored VLPs exhibited significantly improved thermal stability (95 °C for 15 min), increased resistance to denaturants (i.e., surfactants, pHs, chemical denaturants, and organic solvents), and enhanced mechanical performance. Single-molecule force spectroscopy demonstrated a 6-fold increase in rupture distance and a 1.9-fold increase in rupture force of endoskeleton-armored PhMV. Overall, this endoskeleton-armored strategy provides more opportunities for the development and applications of materials.}, Doi = {10.1021/acs.nanolett.3c03806}, Key = {fds375839} } @article{fds375324, Author = {Hu, Y and Lin, Y and Craig, SL}, Title = {Mechanically Triggered Polymer Deconstruction through Mechanoacid Generation and Catalytic Enol Ether Hydrolysis.}, Journal = {Journal of the American Chemical Society}, Volume = {146}, Number = {5}, Pages = {2876-2881}, Year = {2024}, Month = {February}, url = {http://dx.doi.org/10.1021/jacs.3c10153}, Abstract = {Polymers that amplify a transient external stimulus into changes in their morphology, physical state, or properties continue to be desirable targets for a range of applications. Here, we report a polymer comprising an acid-sensitive, hydrolytically unstable enol ether backbone onto which is embedded <i>gem</i>-dichlorocyclopropane (<i>g</i>DCC) mechanophores through a single postsynthetic modification. The <i>g</i>DCC mechanophore releases HCl in response to large forces of tension along the polymer backbone, and the acid subsequently catalyzes polymer deconstruction at the enol ether sites. Pulsed sonication of a 61 kDa PDHF with 77% <i>g</i>DCC on the backbone in THF with 100 mM H<sub>2</sub>O for 10 min triggers the subsequent degradation of the polymer to a final molecular weight of less than 3 kDa after 24 h of standing, whereas controls lacking either the <i>g</i>DCC or the enol ether reach final molecular weights of 38 and 27 kDa, respectively. The process of sonication, along with the presence of water and the existence of <i>g</i>DCC on the backbone, significantly accelerates the rate of polymer chain deconstruction. Both acid generation and the resulting triggered polymer deconstruction are translated to bulk, cross-linked polymer networks. Networks formed via thiol-ene cross-linking and subjected to unconstrained quasi-static uniaxial compression dissolve on time scales that are at least 3 times faster than controls where the mechanophore is not covalently coupled to the network. We anticipate that this concept can be extended to other acid-sensitive polymer networks for the stress-responsive deconstruction of gels and solvent-free elastomers.}, Doi = {10.1021/jacs.3c10153}, Key = {fds375324} } @article{fds375838, Author = {Lin, Y and Kouznetsova, TB and Foret, AG and Craig, SL}, Title = {Solvent Polarity Effects on the Mechanochemistry of Spiropyran Ring Opening.}, Journal = {Journal of the American Chemical Society}, Volume = {146}, Number = {6}, Pages = {3920-3925}, Year = {2024}, Month = {February}, url = {http://dx.doi.org/10.1021/jacs.3c11621}, Abstract = {The spiropyran mechanophore (SP) is employed as a reporter of molecular tension in a wide range of polymer matrices, but the influence of surrounding environment on the force-coupled kinetics of its ring opening has not been quantified. Here, we report single-molecule force spectroscopy studies of SP ring opening in five solvents that span normalized Reichardt solvent polarity factors (<i>E</i><sub>T</sub><sup>N</sup>) of 0.1-0.59. Individual multimechanophore polymers were activated under increasing tension at constant 300 nm s<sup>-1</sup> displacement in an atomic force microscope. The extension results in a plateau in the force-extension curve, whose midpoint occurs at a transition force <i>f</i>* that corresponds to the force required to increase the rate constant of SP activation to approximately 30 s<sup>-1</sup>. More polar solvents lead to mechanochemical reactions that are easier to trigger; <i>f</i>* decreases across the series of solvents, from a high of 415 ± 13 pN in toluene to a low of 234 ± 9 pN in <i>n</i>-butanol. The trend in mechanochemical reactivity is consistent with the developing zwitterionic character on going from SP to the ring-opened merocyanine product. The force dependence of the rate constant (Δ<i>x</i><sup>‡</sup>) was calculated for all solvent cases and found to increase with <i>E</i><sub>T</sub><sup>N</sup>, which is interpreted to reflect a shift in the transition state to a later and more productlike position. The inferred shift in the transition state position is consistent with a double-well (two-step) reaction potential energy surface, in which the second step is rate determining, and the intermediate is more polar than the product.}, Doi = {10.1021/jacs.3c11621}, Key = {fds375838} } @article{fds374905, Author = {Horst, M and Meisner, J and Yang, J and Kouznetsova, TB and Craig, SL and Martínez, TJ and Xia, Y}, Title = {Mechanochemistry of Pterodactylane.}, Journal = {Journal of the American Chemical Society}, Volume = {146}, Number = {1}, Pages = {884-891}, Year = {2024}, Month = {January}, url = {http://dx.doi.org/10.1021/jacs.3c11293}, Abstract = {Pterodactylane is a [4]-ladderane with substituents on the central rung. Comparing the mechanochemistry of the [4]-ladderane structure when pulled from the central rung versus the end rung revealed a striking difference in the threshold force of mechanoactivation: the threshold force is dramatically lowered from 1.9 nN when pulled on the end rung to 0.7 nN when pulled on the central rung. We investigated the bicyclic products formed from the mechanochemical activation of pterodactylane experimentally and computationally, which are distinct from the mechanochemical products of ladderanes being activated from the end rung. We compared the products of pterodactylane's mechanochemical and thermal activation to reveal differences and similarities in the mechanochemical and thermal pathways of pterodactylane transformation. Interestingly, we also discovered the presence of elementary steps that are accelerated or suppressed by force within the same mechanochemical reaction of pterodactylane, suggesting rich mechanochemical manifolds of multicyclic structures. We rationalized the greatly enhanced mechanochemical reactivity of the central rung of pterodactylane and discovered force-free ground state bond length to be a good low-cost predictor of the threshold force for cyclobutane-based mechanophores. These findings advance our understanding of mechanochemical reactivities and pathways, and they will guide future designs of mechanophores with low threshold forces to facilitate their applications in force-responsive materials.}, Doi = {10.1021/jacs.3c11293}, Key = {fds374905} } @article{fds375520, Author = {Barrat, JL and Del Gado and E and Egelhaaf, SU and Mao, X and Dijkstra, M and Pine, DJ and Kumar, SK and Bishop, K and Gang, O and Obermeyer, A and Papadakis, CM and Tsitsilianis, C and Smalyukh, II and Hourlier-Fargette, A and Andrieux, S and Drenckhan, W and Wagner, N and Murphy, RP and Weeks, ER and Cerbino, R and Han, Y and Cipelletti, L and Ramos, L and Poon, WCK and Richards, JA and Cohen, I and Furst, EM and Nelson, A and Craig, SL and Ganapathy, R and Sood, AK and Sciortino, F and Mungan, M and Sastry, S and Scheibner, C and Fruchart, M and Vitelli, V and Ridout, SA and Stern, M and Tah, I and Zhang, G and Liu, AJ and Osuji, CO and Xu, Y and Shewan, HM and Stokes, JR and Merkel, M and Ronceray, P and Rupprecht, JF and Matsarskaia, O and Schreiber, F and Roosen-Runge, F and Aubin-Tam, ME and Koenderink, GH and Espinosa-Marzal, RM and Yus, J and Kwon, J}, Title = {Soft matter roadmap}, Journal = {JPhys Materials}, Volume = {7}, Number = {1}, Year = {2024}, Month = {January}, url = {http://dx.doi.org/10.1088/2515-7639/ad06cc}, Abstract = {Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts.}, Doi = {10.1088/2515-7639/ad06cc}, Key = {fds375520} } @article{fds374348, Author = {Beech, HK and Wang, S and Sen, D and Rota, D and Kouznetsova, TB and Arora, A and Rubinstein, M and Craig, SL and Olsen, BD}, Title = {Reactivity-Guided Depercolation Processes Determine Fracture Behavior in End-Linked Polymer Networks.}, Journal = {ACS macro letters}, Volume = {12}, Number = {12}, Pages = {1685-1691}, Year = {2023}, Month = {December}, url = {http://dx.doi.org/10.1021/acsmacrolett.3c00559}, Abstract = {The fracture of polymer networks is tied to the molecular behavior of strands within the network, yet the specific molecular-level processes that determine the mechanical limits of a network remain elusive. Here, the question of reactivity-guided fracture is explored in otherwise indistinguishable end-linked networks by tuning the relative composition of strands with two different mechanochemical reactivities. Increasing the substitution of less mechanochemically reactive ("strong") strands into a network comprising more reactive ("weak") strands has a negligible impact on the fracture energy until the strong strand content reaches approximately 45%, at which point the fracture energy sharply increases with strong strand content. This aligns with the measured strong strand percolation threshold of 48 ± 3%, revealing that depercolation, or the loss of a percolated network structure, is a necessary criterion for crack propagation in a polymer network. Coarse-grained fracture simulations agree closely with the tearing energy trend observed experimentally, confirming that weak strand scissions dominate the failure until the strong strands approach percolation. The simulations further show that twice as many strands break in a mixture than in a pure network.}, Doi = {10.1021/acsmacrolett.3c00559}, Key = {fds374348} } @article{fds371955, Author = {Ritter, VC and McDonald, SM and Dobrynin, AV and Craig, SL and Becker, ML}, Title = {Mechanochromism and Strain-Induced Crystallization in Thiol-yne-Derived Stereoelastomers.}, Journal = {Advanced materials (Deerfield Beach, Fla.)}, Volume = {35}, Number = {41}, Pages = {e2302163}, Year = {2023}, Month = {October}, url = {http://dx.doi.org/10.1002/adma.202302163}, Abstract = {Most elastomers undergo strain-induced crystallization (SIC) under tension; as individual chains are held rigidly in a fixed position by an applied strain, their alignment along the strain field results in a shift from strain-hardening (SH) to SIC. A similar degree of stretching is associated with the tension necessary to accelerate mechanically coupled, covalent chemical responses of mechanophores in overstretched chains, raising the possibility of an interplay between the macroscopic response of SIC and the molecular response of mechanophore activation. Here, thiol-yne-derived stereoelastomers doped covalently with a dipropiolate-derivatized spiropyran (SP) mechanophore (0.25-0.38 mol%) are reported. The material properties of SP-containing films are consistent with undoped controls, indicating that the SP is a reporter of the mechanical state of the polymer. Uniaxial tensile tests reveal correlations between mechanochromism and SIC, which are strain-rate-dependent. When mechanochromic films are stretched slowly to the point of mechanophore activation, the covalently tethered mechanophore remains trapped in a force-activated state, even after the applied stress is removed. Mechanophore reversion kinetics correlate with the applied strain rate, resulting in highly tunable decoloration rates. Because these polymers are not covalently crosslinked, they are recyclable by melt-pressing into new films, increasing their potential range of strain-sensing, morphology-sensing, and shape-memory applications.}, Doi = {10.1002/adma.202302163}, Key = {fds371955} } @article{fds372950, Author = {Zhao, J and Bobylev, EO and Lundberg, DJ and Oldenhuis, NJ and Wang, H and Kevlishvili, I and Craig, SL and Kulik, HJ and Li, X and Johnson, JA}, Title = {Polymer Networks with Cubic, Mixed Pd(II) and Pt(II) M6L12 Metal-Organic Cage Junctions: Synthesis and Stress Relaxation Behavior.}, Journal = {Journal of the American Chemical Society}, Volume = {145}, Number = {40}, Pages = {21879-21885}, Year = {2023}, Month = {October}, url = {http://dx.doi.org/10.1021/jacs.3c06029}, Abstract = {Metal-organic cages/polyhedra (MOCs) are versatile building blocks for advanced polymer networks with properties that synergistically blend those of traditional polymers and crystalline frameworks. Nevertheless, constructing polyMOCs from very stable Pt(II)-based MOCs or mixtures of metal ions such as Pd(II) and Pt(II) has not, to our knowledge, been demonstrated, nor has exploration of how the dynamics of metal-ligand exchange at the MOC level may impact bulk polyMOC energy dissipation. Here, we introduce a new class of polymer metal-organic cage (polyMOC) gels featuring polyethylene glycol (PEG) strands of varied length cross-linked through bis-pyridyl-carbazole-based M<sub>6</sub>L<sub>12</sub> cubes, where M is Pd(II), Pt(II), or mixtures thereof. We show that, while polyMOCs with varied Pd(II) content have similar network structures, their average stress-relaxation rates are tunable over 3 orders of magnitude due to differences in Pd(II)- and Pt(II)-ligand exchange rates at the M<sub>6</sub>L<sub>12</sub> junction level. Moreover, mixed-metal polyMOCs display relaxation times indicative of intrajunction cooperative interactions, which stands in contrast to previous materials based on point metal junctions. Altogether, this work (1) introduces a novel MOC architecture for polyMOC design, (2) shows that polyMOCs can be prepared from mixtures of Pd(II)/Pt(II), and (3) demonstrates that polyMOCs display unique relaxation behavior due to their multivalent junctions, offering a strategy for controlling polyMOC properties independently of their polymer components.}, Doi = {10.1021/jacs.3c06029}, Key = {fds372950} } @article{fds372653, Author = {Wentz, KE and Yao, Y and Kevlishvili, I and Kouznetsova, TB and Mediavilla, BA and Kulik, HJ and Craig, SL and Klausen, RS}, Title = {Systematic Investigation of Silicon Substitution on Single Macromolecule Mechanics}, Journal = {Macromolecules}, Volume = {56}, Number = {17}, Pages = {6776-6782}, Year = {2023}, Month = {September}, url = {http://dx.doi.org/10.1021/acs.macromol.3c01066}, Abstract = {Four unsaturated poly(carbooligosilane)s (P1-P4) were prepared via acyclic diene metathesis polycondensation of new oligosilane diene monomers (1-4). These novel polymers with varying main-chain Si incorporation have high trans internal olefin stereochemistry (ca. 80%) and molecular weights (9500-21,700 g mol-1). Postpolymerization epoxidation converted all alkene moieties to epoxides and rendered the polymers (P5-P8) more electrophilic, which allowed for single-molecule force spectroscopy studies via a modified atomic force microscope setup with a silicon tip and cantilever. The single-chain elasticity of the polycarbooligosilanes decreased with increasing numbers of Si-Si bonds, a finding reproduced by quantum chemical calculations.}, Doi = {10.1021/acs.macromol.3c01066}, Key = {fds372653} } @article{fds371593, Author = {Duan, C and Zheng, X and Craig, SL and Widenhoefer, RA}, Title = {Force-Modulated C-C Reductive Elimination from Nickel Bis(polyfluorophenyl) Complexes}, Journal = {Organometallics}, Volume = {42}, Number = {15}, Pages = {1918-1926}, Publisher = {American Chemical Society (ACS)}, Year = {2023}, Month = {August}, url = {http://dx.doi.org/10.1021/acs.organomet.3c00168}, Abstract = {We have analyzed the rate of C(sp2)-C(sp2) reductive elimination from nickel(II) bis(2,4,6-trifluorophenyl) complexes (P-P)Ni(2,4,6-C6H2F3)2 containing either MeOBiPhep (3a) or a macrocyclic bisphosphine ligand (3b-3e) as a function of force applied to the biaryl backbone of these ligands through intramolecular tension generated by a molecular force probe. Nickel complexes 3 were isolated in 22-60% yield from the reaction of bisphosphine with the bis(tetrahydrofuranyl) complex (THF)2Ni(2,4,6-C6H2F3)2 followed by chromatography. Thermolysis of complexes 3 in C6D6 at 68 °C leads to first-order decay through >3 half-lives to the form 2,2′,4,4′,6,6′-hexafluorobiphenyl as the exclusive fluorine-containing product in ≥93% yield. Whereas compressive forces up to −65 pN have no significant effect on the rate of reductive elimination, extension forces increase the rate of reductive elimination by a factor of 3 over an ∼230 pN range of restoring forces relative to the strain-free MeOBiphep complex. The rate response of reductive elimination from nickel(II) bis(trifluorophenyl) complexes as a function of extension force is similar to the previously reported 2.8-fold increase in the rate of reductive elimination from platinum diaryl complexes (P-P)Pt(4-C6H4NMe2)2 over the same range of forces.}, Doi = {10.1021/acs.organomet.3c00168}, Key = {fds371593} } @article{fds372356, Author = {Yu, Y and O'Neill, RT and Boulatov, R and Widenhoefer, RA and Craig, SL}, Title = {Allosteric control of olefin isomerization kinetics via remote metal binding and its mechanochemical analysis.}, Journal = {Nature communications}, Volume = {14}, Number = {1}, Pages = {5074}, Year = {2023}, Month = {August}, url = {http://dx.doi.org/10.1038/s41467-023-40842-5}, Abstract = {Allosteric control of reaction thermodynamics is well understood, but the mechanisms by which changes in local geometries of receptor sites lower activation reaction barriers in electronically uncoupled, remote reaction moieties remain relatively unexplored. Here we report a molecular scaffold in which the rate of thermal E-to-Z isomerization of an alkene increases by a factor of as much as 10<sup>4</sup> in response to fast binding of a metal ion to a remote receptor site. A mechanochemical model of the olefin coupled to a compressive harmonic spring reproduces the observed acceleration quantitatively, adding the studied isomerization to the very few reactions demonstrated to be sensitive to extrinsic compressive force. The work validates experimentally the generalization of mechanochemical kinetics to compressive loads and demonstrates that the formalism of force-coupled reactivity offers a productive framework for the quantitative analysis of the molecular basis of allosteric control of reaction kinetics. Important differences in the effects of compressive vs. tensile force on the kinetic stabilities of molecules are discussed.}, Doi = {10.1038/s41467-023-40842-5}, Key = {fds372356} } @article{fds375521, Author = {Caballero, RM and González-Gamboa, I and Craig, SL and Steinmetz, NF}, Title = {Linear and multivalent PEGylation of the tobacco mosaic virus and the effects on its biological properties}, Journal = {Frontiers in Virology}, Volume = {3}, Publisher = {Frontiers Media SA}, Year = {2023}, Month = {June}, url = {http://dx.doi.org/10.3389/fviro.2023.1184095}, Abstract = {<jats:p>Plant virus-based nanoparticles (VNPs) offer a bioinspired approach to the delivery of drugs and imaging agents. The chemical addressability, biocompatibility, and scalable manufacturability of VNPs make them a promising alternative to synthetic delivery platforms. However, VNPs, just like other proteinaceous or synthetic nanoparticles (NPs), are readily recognized and cleared by the immune system and mechanisms such as opsonization and phagocytosis. Shielding strategies, such as PEGylation, are commonly used to mitigate premature NP clearance. Here, we investigated polyethylene glycol (PEG) coatings on the tobacco mosaic virus (TMV), which was used as a model nanocarrier system. Specifically, we evaluated the effects of linear and multivalent PEG coatings at varying chain lengths on serum protein adsorption, antibody recognition, and macrophage uptake. Linear and multivalent PEGs of molecular weights 2,000 and 5,000 Da were successfully grafted onto the TMV at ≈ 20%–60% conjugation efficiencies, and the degree of cross-linking as a function of PEG valency and length was determined. PEGylation resulted in the modulation of TMV–macrophage interactions and reduced corona formation as well as antibody recognition. Linear and multivalent PEG 5,000 formulations (but not PEG 2,000 formulations) reduced α-TMV antibody recognition, whereas shorter, multivalent PEG coatings significantly reduced α-PEG recognition—this highlights an interesting interplay between the NP and the PEG itself in potential antigenicity and should be an important consideration in PEGylation strategies. This work provides insight into the PEGylation of VNPs, which may improve the possibility of their implementation in clinical applications.</jats:p>}, Doi = {10.3389/fviro.2023.1184095}, Key = {fds375521} } @article{fds371309, Author = {Wang, S and Hu, Y and Kouznetsova, TB and Sapir, L and Chen, D and Herzog-Arbeitman, A and Johnson, JA and Rubinstein, M and Craig, SL}, Title = {Facile mechanochemical cycloreversion of polymer cross-linkers enhances tear resistance.}, Journal = {Science (New York, N.Y.)}, Volume = {380}, Number = {6651}, Pages = {1248-1252}, Year = {2023}, Month = {June}, url = {http://dx.doi.org/10.1126/science.adg3229}, Abstract = {The mechanical properties of covalent polymer networks often arise from the permanent end-linking or cross-linking of polymer strands, and molecular linkers that break more easily would likely produce materials that require less energy to tear. We report that cyclobutane-based mechanophore cross-linkers that break through force-triggered cycloreversion lead to networks that are up to nine times as tough as conventional analogs. The response is attributed to a combination of long, strong primary polymer strands and cross-linker scission forces that are approximately fivefold smaller than control cross-linkers at the same timescales. The enhanced toughness comes without the hysteresis associated with noncovalent cross-linking, and it is observed in two different acrylate elastomers, in fatigue as well as constant displacement rate tension, and in a gel as well as elastomers.}, Doi = {10.1126/science.adg3229}, Key = {fds371309} } @article{fds370191, Author = {Wakefield, H and Kevlishvili, I and Wentz, KE and Yao, Y and Kouznetsova, TB and Melvin, SJ and Ambrosius, EG and Herzog-Arbeitman, A and Siegler, MA and Johnson, JA and Craig, SL and Kulik, HJ and Klausen, RS}, Title = {Synthesis and Ring-Opening Metathesis Polymerization of a Strained trans-Silacycloheptene and Single-Molecule Mechanics of Its Polymer.}, Journal = {Journal of the American Chemical Society}, Volume = {145}, Number = {18}, Pages = {10187-10196}, Year = {2023}, Month = {May}, url = {http://dx.doi.org/10.1021/jacs.3c01004}, Abstract = {The <i>cis</i>- and <i>trans</i>-isomers of a silacycloheptene were selectively synthesized by the alkylation of a silyl dianion, a novel approach to strained cycloalkenes. The <i>trans</i>-silacycloheptene (<i>trans</i>-SiCH) was significantly more strained than the <i>cis</i> isomer, as predicted by quantum chemical calculations and confirmed by crystallographic signatures of a twisted alkene. Each isomer exhibited distinct reactivity toward ring-opening metathesis polymerization (ROMP), where only <i>trans</i>-SiCH afforded high-molar-mass polymer under enthalpy-driven ROMP. Hypothesizing that the introduction of silicon might result in increased molecular compliance at large extensions, we compared poly(<i>trans</i>-SiCH) to organic polymers by single-molecule force spectroscopy (SMFS). Force-extension curves from SMFS showed that poly(<i>trans</i>-SiCH) is more easily overstretched than two carbon-based analogues, polycyclooctene and polybutadiene, with stretching constants that agree well with the results of computational simulations.}, Doi = {10.1021/jacs.3c01004}, Key = {fds370191} } @article{fds370029, Author = {Wang, S and Panyukov, S and Craig, SL and Rubinstein, M}, Title = {Contribution of Unbroken Strands to the Fracture of Polymer Networks}, Journal = {Macromolecules}, Volume = {56}, Number = {6}, Pages = {2309-2318}, Year = {2023}, Month = {March}, url = {http://dx.doi.org/10.1021/acs.macromol.2c02139}, Abstract = {We present a modified Lake-Thomas theory that accounts for the molecular details of network connectivity upon crack propagation in polymer networks. This theory includes not only the energy stored in the breaking network strands (bridging strands) but also the energy stored in the tree-like structure of the strands connecting the bridging strands to the network continuum, which remains intact as the crack propagates. The energy stored in each of the generations of this tree depends nonmonotonically on the generation index due to the nonlinear elasticity of the stretched network strands. Further, the energy required to break a single bridging strand is not necessarily dominated by the energy stored in the bridging strand itself but in the higher generations of the tree. We describe the effect of mechanophores with stored length on the energy stored in the tree-like structure. In comparison with the “strong” mechanophores that can only be activated in the bridging strand, “weak” mechanophores that can be activated both in the bridging strand and in other generations could provide more energy dissipation due to their larger contribution to higher generations of the tree.}, Doi = {10.1021/acs.macromol.2c02139}, Key = {fds370029} } @article{fds370192, Author = {Ouchi, T and Wang, W and Silverstein, BE and Johnson, JA and Craig, SL}, Title = {Effect of strand molecular length on mechanochemical transduction in elastomers probed with uniform force sensors}, Journal = {Polymer Chemistry}, Volume = {14}, Number = {14}, Pages = {1646-1655}, Year = {2023}, Month = {March}, url = {http://dx.doi.org/10.1039/d3py00065f}, Abstract = {The mechanical properties of a polymer network reflect the collective behavior of all of the constituent strands within the network. These strands comprise a distribution of states, and a central question is how the deformation and tension experienced by a strand is influenced by strand length. Here, we address this question through the use of mechanophore force probes with discrete molecular weights. Probe strands, each bearing a mechanochromic spiropyran (SP), were prepared through an iterative synthetic strategy, providing uniform PDMS-functionalized SP force probes with molecular weights of 578, 1170, and 2356 g mol−1. The probes were each doped (9 mM) into the same silicone elastomer matrix. Upon stretching, the materials change color, consistent with the expected conversion of SP to merocyanine (MC). The critical strain at which measurable mechanochromism is observed is correlated with the strain hardening of the matrix, but it is independent of the molecular length of the probe strand. When a network with activated strands is relaxed, the color dissipates, and the rate of decoloration varies as a function of the relaxing strain (= r); faster decoloration occurs at lower r. The dependence of decoloration rate on r is taken to reflect the effect of residual tension in the once-activated strands on the reversion reaction of MC to SP, and the effect of that residual tension is indistinguishable across the three molecular lengths examined. The combination of discrete strand synthesis and mechanochromism provides a foundation to further test and develop molecular-based theories of elasticity and fracture in polymer networks.}, Doi = {10.1039/d3py00065f}, Key = {fds370192} } @article{fds369053, Author = {Ozer, I and Slezak, A and Sirohi, P and Li, X and Zakharov, N and Yao, Y and Everitt, JI and Spasojevic, I and Craig, SL and Collier, JH and Campbell, JE and D'Alessio, DA and Chilkoti, A}, Title = {An injectable PEG-like conjugate forms a subcutaneous depot and enables sustained delivery of a peptide drug.}, Journal = {Biomaterials}, Volume = {294}, Pages = {121985}, Year = {2023}, Month = {March}, url = {http://dx.doi.org/10.1016/j.biomaterials.2022.121985}, Abstract = {Many biologics have a short plasma half-life, and their conjugation to polyethylene glycol (PEG) is commonly used to solve this problem. However, the improvement in the plasma half-life of PEGylated drugs' is at an asymptote because the development of branched PEG has only had a modest impact on pharmacokinetics and pharmacodynamics. Here, we developed an injectable PEG-like conjugate that forms a subcutaneous depot for the sustained delivery of biologics. The PEG-like conjugate consists of poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) conjugated to exendin, a peptide drug used in the clinic to treat type 2 diabetes. The depot-forming exendin-POEGMA conjugate showed greater efficacy than a PEG conjugate of exendin as well as Bydureon, a clinically approved sustained-release formulation of exendin. The injectable depot-forming exendin-POEGMA conjugate did not elicit an immune response against the polymer, so that it remained effective and safe for long-term management of type 2 diabetes upon chronic administration. In contrast, the PEG conjugate induced an anti-PEG immune response, leading to early clearance and loss of efficacy upon repeat dosing. The exendin-POEGMA depot also showed superior long-term efficacy compared to Bydureon. Collectively, these results suggest that an injectable POEGMA conjugate of biologic drugs that forms a drug depot under the skin, providing favorable pharmacokinetic properties and sustained efficacy while remaining non-immunogenic, offers significant advantages over other commonly used drug delivery technologies.}, Doi = {10.1016/j.biomaterials.2022.121985}, Key = {fds369053} } @article{fds368039, Author = {Ouchi, T and Bowser, BH and Kouznetsova, TB and Zheng, X and Craig, SL}, Title = {Strain-triggered acidification in a double-network hydrogel enabled by multi-functional transduction of molecular mechanochemistry.}, Journal = {Materials horizons}, Volume = {10}, Number = {2}, Pages = {585-593}, Year = {2023}, Month = {February}, url = {http://dx.doi.org/10.1039/d2mh01105k}, Abstract = {Recent work has demonstrated that force-triggered mechanochemical reactions within a polymeric material are capable of inducing measurable changes in macroscopic material properties, but examples of bulk property changes without irreversible changes in shape or structure are rare. Here, we report a double-network hydrogel that undergoes order-of-magnitude increases in acidity when strained, while recovering its initial shape after large deformation. The enabling mechanophore design is a 2-methoxy-<i>gem</i>-dichlorocyclopropane mechanoacid that is gated within a fused methyl methoxycyclobutene carboxylate mechanophore structure. This gated mechanoacid is incorporated <i>via</i> radical co-polymerization into linear and network polymers. Sonication experiments confirm the mechanical release of HCl, and single-molecule force spectroscopy reveals enhanced single-molecular toughness in the covalent strand. These mechanochemical functions are incorporated into a double-network hydrogel, leading to mechanically robust and thermally stable materials that undergo strain-triggered acid release. Both quasi-static stretching and high strain rate uniaxial compression result in substantial acidification of the hydrogel, from pH ∼ 7 to ∼5.}, Doi = {10.1039/d2mh01105k}, Key = {fds368039} } @article{fds368041, Author = {Craig, SL}, Title = {Concluding remarks: Fundamentals, applications and future of mechanochemistry.}, Journal = {Faraday discussions}, Volume = {241}, Pages = {485-491}, Year = {2023}, Month = {January}, url = {http://dx.doi.org/10.1039/d2fd00141a}, Abstract = {This paper provides a summary of the <i>Faraday Discussions</i> meeting on "Mechanochemistry: fundamentals, applications, and future" in the context of broad themes whose exploration might contribute to a unified framework of mechanochemical phenomena.}, Doi = {10.1039/d2fd00141a}, Key = {fds368041} } @article{fds368878, Author = {Lloyd, EM and Vakil, JR and Yao, Y and Sottos, NR and Craig, SL}, Title = {Covalent Mechanochemistry and Contemporary Polymer Network Chemistry: A Marriage in the Making.}, Journal = {Journal of the American Chemical Society}, Volume = {145}, Number = {2}, Pages = {751-768}, Year = {2023}, Month = {January}, url = {http://dx.doi.org/10.1021/jacs.2c09623}, 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.}, Doi = {10.1021/jacs.2c09623}, Key = {fds368878} } @article{fds372763, Author = {Johnson, PN and Yao, Y and Huang, X and Kevlishvili, I and Schrettl, S and Weder, C and Kulik, HJ and Craig, SL}, Title = {Metal identity effects in the fracture behavior of coordinatively crosslinked elastomers}, Journal = {POLYMER}, Volume = {285}, Year = {2023}, url = {http://dx.doi.org/10.1016/j.polymer.2023.126337}, Abstract = {Polymers comprising polybutadiene backbones with 2,6-bis(1′-methyl-benzimidazolyl)pyridine (MeBip) sidechains were crosslinked by complexation with two different metal salts, either with copper(II) trifluoromethanosulfonate or with iron(II) trifluoromethanosulfonate. Dynamic mechanical analysis (DMA) and small-angle X-ray scattering (SAXS) data indicate that the crosslinking density and topology of the two materials are the same. The material crosslinked with copper ions, however, exhibits a higher extensibility and fracture energy than the polymer crosslinked with iron. These differences are attributed to differing mechanochemical responses of the metal complexes to applied stress. Computational results further indicate that the copper complexes are more labile, both in the stress-free state as well as upon application of force, and that the “open” complex in which only one MeBip ligand coordinates copper binds fewer counter-ions than the iron-coordinated analog. Both these factors enable easier re-binding of a second MeBip ligand. The computations further suggest that mechanochemically coupled spin-crossover behavior must be considered to fully understand the response of these metal-ligand complexes to mechanical stimuli. The data presented here furthers the facile manipulation of a material's strain response via metal species modulation, and the results offer a way to understand the relationship between bulk and molecular strain response.}, Doi = {10.1016/j.polymer.2023.126337}, Key = {fds372763} } | |
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