Molecular Spring Research Articles

Anion-Coordination Foldamer-Based Polymer Network: from Molecular Spring to Elastomer.

Foldamer is a scaled-down version of coil spring, which can absorb and release energy by conformational change. Here, polymer networks with high-density of molecular springs were developed by employing anion-coordination-based foldamers as the monomer. The coiling of the foldamer is controlled by oligourea ligands coordinating to chloride ions; subsequently, the folding and unfolding of foldamer conformations endow the polymer network with excellent energy dissipation and toughness. The mechanical performance of the corresponding polymer network shows a dramatic increase from P-L2UCl (non-folding), P-L4UCl (a full turn) to P-L6UCl (1.5 turns), in terms of strength (2.62 MPa; 14.26 Mpa; 22.93 Mpa), elongation at break (70%; 325%; 352%), Young's modulus (2.69 MPa; 63.61 Mpa; 141.50 Mpa), and toughness (1.12 MJ/m3; 21.39 MJ/m3; 49.62 MJ/m3), respectively, which are also better than those without anion centers and the non-foldamer based counterparts.Moreover, P-L6UCl shows enhanced strength and toughness than most of the molecular-spring based polymer networks.Moreover, P-L6UCl shows enhanced strength and toughness than most of the molecular-spring based polymer networks. Thus, an effective strategy for designing high-performance anion-coordination-based materials is presented in this study.

Titin: roles in cardiac function and diseases

The giant protein titin is an essential component of muscle sarcomeres. A single titin molecule spans half a sarcomere and mediates diverse functions along its length by virtue of its unique domains. The A-band of titin functions as a molecular blueprint that defines the length of the thick filaments, the I-band constitutes a molecular spring that determines cell-based passive stiffness, and various domains, including the Z-disk, I-band, and M-line, serve as scaffolds for stretch-sensing signaling pathways that mediate mechanotransduction. This review aims to discuss recent insights into titin’s functional roles and their relationship to cardiac function. The role of titin in heart diseases, such as dilated cardiomyopathy and heart failure with preserved ejection fraction, as well as its potential as a therapeutic target, is also discussed.

Releasing a bound molecular spring with light: a visible light-triggered photosalient effect tied to polymorphism.

Here we present a study on the solid state properties of trans tetra-ortho-bromo azobenzene (4Br-Azo). Two distinct crystal polymorphs were identified: the α-phase and β-phase. Notably, only the β-phase exhibited an extraordinary photosalient effect (jumping/breaking) upon exposure to a wide range of visible light. Powder X-ray diffraction and Raman spectroscopy revealed that the β-phase is metastable and can transition to the α-phase when subjected to specific stimuli like heat and light. Furthermore, single crystal X-ray diffraction and density functional theory calculations highlighted the significance of a highly strained conformer in the β-phase, showing that the metastability of the phase potentially arises from relieving this strain. This metastability leads to a light induced phase transition, which appears to be the cause of the photosalient effect in these crystals. Interestingly the polymorphism at the core of 4Br-Azo's dynamic behavior is based on different arrangements of halogen based intermolecular interactions. It is possible that continued study on combining visible light capturing chromophores with halogen interaction-based polymorphism will lead to the discovery of even more visible light controlled dynamic crystal materials.

Liquid piston based on molecular springs for energy storage applications

Liquid piston is a method for pressure transmission used in a wide range of technologies. Currently, liquid piston is a passive element solely used to apply pressure to a working body. In this work, the concept of liquid piston based on molecular springs – an active element, which can store a considerable amount of mechanical energy, apart from its main function, which is pressure transmission is proposed. To demonstrate the concept, the {Cu2(tebpz) MOF + H2O} molecular spring was characterized by employing high-pressure intrusion-extrusion cycling, atomistic simulations, in situ neutrons scattering, scanning electron microscopy and X-ray diffraction. Using compressed air energy storage (CAES) as a case study, it is demonstrated that energy density for this technology can be enhanced ∼5 times by replacing water with a water-based molecular spring. Apart from increased energy density, liquid piston based on molecular spring improves thermal management of CAES systems, enables narrow operational pressure ranges and provides an anti-vibration feature to mitigate undesired vibrations or impacts. The liquid piston based on molecular spring concept can be useful for a broad range of technologies, where pressure transmission is implemented through fluids.

Structure determination and analysis of titin A-band fibronectin type III domains provides insights for disease-linked variants and protein oligomerisation

Titin is the largest protein found in nature and spans half a sarcomere in vertebrate striated muscle. The protein has multiple functions, including in the organisation of the thick filament and acting as a molecular spring during the muscle contraction cycle. Missense variants in titin have been linked to both cardiac and skeletal myopathies. Titin is primarily composed of tandem repeats of immunoglobulin and fibronectin type III (Fn3) domains in a variety of repeat patterns; however, the vast majority of these domains have not had their high-resolution structure determined experimentally. Here, we present the crystal structures of seven wild type titin Fn3 domains and two harbouring rare missense variants reported in hypertrophic cardiomyopathy (HCM) patients. All domains present the typical Fn3 fold, with the domains harbouring variants reported in HCM patients retaining the wild-type conformation. The effect on domain folding and stability were assessed for five rare missense variants found in HCM patients: four caused thermal destabilization of between 7 and 13 °C and one prevented the folding of its domain. The structures also allowed us to locate the positions of residues whose mutations have been linked to congenital myopathies and rationalise how they convey their deleterious effects. We find no evidence of physiological homodimer formation, excluding one hypothesised mechanism as to how titin variants could exert pathological effects.

Static and Dynamic Testing of Bag-Type Molecular Spring Vibration Isolator

Static and Dynamic Testing of Bag-Type Molecular Spring Vibration Isolator

Ultra-tough and stress-free two-way shape memory polyurethane induced by polymer segment “spring”

Two-way shape memory polymers (2WSMP) are highly desired for artificial muscles, soft actuators and sensors, while the stress-free 2WSMP greatly expands the practical potential of shape memory polymers. However, traditional 2WSMP cannot show high strength or good mechanical properties, which limited its practical application. It is important to create a new reversible polymer system in order to obtain more intricate movements, precise control and great mechanical properties. Herein, a two-way shape memory polyurethane was created using a new molecular strategy, which shows great properties, i.e., 2342% super stretch strain, 591 MPa true tensile strength, 708.04 J/kg of energy density, and 667.96 W/kg of power density. In addition, the 2WSMP could achieve a maximum 24.53% reversible transformation under 1 MPa stress, and 13.7% two-way shape change without external stress, respectively. In this polyurethane, the great mechanical properties and stress-free two-way shape memory effect are caused by the elastic polybutadiene (PB) segments, which acts as a “molecular spring.” Furthermore, this 2WSMP could simulate reversible muscle-like motion, and be employed in ligaments. Consequently, this polyurethane offers a fresh design concept for stress-free two-way performance memory polymers and has a wide range of potential applications in the field of artificial muscles, soft actuators and ligaments.

Innenrücktitelbild: Messung von Nanometerabständen in Lösung mittels 13C NMR‐Spektroskopie – Schrumpfen von Makrocyclen mit zunehmender Temperatur (Angew. Chem. 25/2023)

The determination of nanometer-scale distances in solution is an enormous challenge. In their Research Article (e202301465) Gebhard Haberhauer and co-workers demonstrate that distances in macrocycles can be measured using a molecular spring and 13C-NMR spectroscopy. The sensitivity of the method even allows the determination of thermoelasticity at the molecular level: One studied system expands at low temperatures and shrinks at high temperatures.

Inside Back Cover: Measurement of Nanometer Distances in Solution via 13C NMR Spectroscopy—Shrinking of Macrocycles with Increasing Temperature (Angew. Chem. Int. Ed. 25/2023)

The determination of nanometer-scale distances in solution is an enormous challenge. In their Research Article (e202301465) Gebhard Haberhauer and co-workers demonstrate that distances in macrocycles can be measured using a molecular spring and 13C-NMR spectroscopy. The sensitivity of the method even allows the determination of thermoelasticity at the molecular level: One studied system expands at low temperatures and shrinks at high temperatures.

Messung von Nanometerabständen in Lösung mittels 13C NMR‐Spektroskopie – Schrumpfen von Makrocyclen mit zunehmender Temperatur

AbstractBei molekularen Systemen sind Größe und Form von elementarer Bedeutung für Funktion und Eigenschaften. Daher ist die Bestimmung von Abständen innerhalb eines Moleküls elementar. Die aktuell gängigen Methoden sind jedoch nur für Abstände kleiner als 4 Å oder größer als 15 Å geeignet. Hier zeigen wir, dass wir durch den Einbau einer molekularen Feder Abstände in Makrocyclen im Bereich von 10 Å mit Hilfe der 13C NMR‐Spektroskopie messen können. Die Genauigkeit der Methode erlaubt es auch die Temperaturabhängigkeit der Abstände zu bestimmen. In einem Fall findet man bei Erwärmung ein Schrumpfen der Länge um fast 10 %. Diese Verkürzung durch Erwärmung kann als inverse Thermoelastizität auf molekularer Ebene betrachtet werden und ist ein bisher völlig vernachlässigtes Phänomen, das in Zukunft als Werkzeug zur Veränderung der Länge und damit der Funktion eines Systems genutzt werden kann.

Measurement of Nanometer Distances in Solution via 13 C NMR Spectroscopy-Shrinking of Macrocycles with Increasing Temperature.

For a molecular system, size and shape are of elementary importance for its function and properties. Therefore, the determination of distances within a molecule is essential. However, the commonly used methods are only suitable for distances smaller than 4 Å or larger than 15 Å. Here, we show that by incorporating a molecular spring, we can measure distances in macrocycles in the range of 10 Å using 13 C NMR spectroscopy. The accuracy of the method also allows to determine the temperature dependence of the distances. In one case, we find a contraction of the length by almost 10 % upon heating. This shrinking due to heating can be considered as inverse thermoelasticity at the molecular level and is a previously completely overlooked phenomenon that can be used in the future as a tool to change the length and, thus, the function of a system.

Titin activates myosin filaments in skeletal muscle by switching from an extensible spring to a mechanical rectifier

Titin is a molecular spring in parallel with myosin motors in each muscle half-sarcomere, responsible for passive force development at sarcomere length (SL) above the physiological range (>2.7 μm). The role of titin at physiological SL is unclear and is investigated here in single intact muscle cells of the frog (Rana esculenta), by combining half-sarcomere mechanics and synchrotron X-ray diffraction in the presence of 20 μM para-nitro-blebbistatin, which abolishes the activity of myosin motors and maintains them in the resting state even during activation of the cell by electrical stimulation. We show that, during cell activation at physiological SL, titin in the I-band switches from an SL-dependent extensible spring (OFF-state) to an SL-independent rectifier (ON-state) that allows free shortening while resisting stretch with an effective stiffness of ~3 pN nm-1 per half-thick filament. In this way, I-band titin efficiently transmits any load increase to the myosin filament in the A-band. Small-angle X-ray diffraction signals reveal that, with I-band titin ON, the periodic interactions of A-band titin with myosin motors alter their resting disposition in a load-dependent manner, biasing the azimuthal orientation of the motors toward actin. This work sets the stage for future investigations on scaffold and mechanosensing-based signaling functions of titin in health and disease.

Storage of mechanical energy in DNA nanorobotics using molecular torsion springs

Storage of mechanical energy in DNA nanorobotics using molecular torsion springs

Molecular torsion springs: alteration of helix curvature in frustrated tertiary folds.

The first abiotic foldamer tertiary structures have been recently reported in the form of aromatic helix-turn-helix motifs based on oligo-quinolinecarboxamides held together by intramolecular hydrogen bonds. Tertiary folds were predicted by computational modelling of the hydrogen-bonding interfaces between helices and later verified by X-ray crystallography. However, the prognosis of how the conformational preference inherent to each helix influences the tertiary structure warranted further investigation. Several new helix-turn-helix sequences were synthesised in which some hydrogen bonds have been removed. Contrary to expectations, this change did not strongly destabilise the tertiary folds. On closer inspection, a new crystal structure revealed that helices adopt their natural curvature when some hydrogen bonds are missing and undergo some spring torsion upon forming the said hydrogen bonds, thus potentially giving rise to a conformational frustration. This phenomenon sheds light on the aggregation behaviour of the helices when they are not linked by a turn unit.

Inorganic hydrogen-bonded SnO(OH)2as molecular springs boosted the piezocatalytic degradation of contaminants

SnO(OH)2is the first highly active hydrogen-bonded inorganic piezocatalyst due to its rich hydrogen bonds and high valence band.

Emulating Titin by a Multidomain DNA Structure.

Titin, a giant protein containing multiple tandem domains, is essential in maintaining the superior mechanical performance of muscle. The consecutive and reversible unfolding and refolding of the domains are crucial for titin to serve as a modular spring. Since the discovery of the mechanical features of a single titin molecule, the exploration of biomimetic materials with titin-emulating modular structures has been an active field. However, it remains a challenge to prepare these modular polymers on a large scale due to the complex synthesis process. In this study, we propose modular DNA with multiple hairpins (MH-DNA) as the fundamental block for the bottom-up design of advanced materials. By analyzing the unfolding and refolding dynamics of modular hairpins by atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS), we find that MH-DNA shows comparable stability to those of polyproteins like titin. The unique low hysteresis of modular hairpin makes it an ideal molecular spring with remarkable mechanical efficiency. On the basis of the well-established DNA synthesis techniques, we anticipate that MH-DNA can be used as a promising building block for advanced materials with a combination of superior structural stability, considerable extensibility, and high mechanical efficiency.

Conformer Ring Flip Enhances Mechanochromic Performance of ansa-Donor-Acceptor-Donor Mechanochromic Torsional Springs.

Mechanochromophores based on conformational changes of donor-acceptor-donor (DAD) springs allow sensing of forces acting on polymer chains by monotonic changes of absorbance or photoluminescence (PL) wavelength. Here, we identify a series of thiophene (D)-flanked quinoxalines (A) as molecular torsional springs for force sensing in bulk polymers at room temperature. The mode of DAD linkage to the polymer matrix and linker rigidity are key parameters that influence the efficacy of force transduction to the DAD spring and thus mechanochromic response, as probed by in situ PL spectroscopy of bulk films during stress-strain experiments. The largest shift of the PL maximum, and thus the highest sensitivity, is obtained from an ansa-DAD spring exhibiting bridged D units and a stiff A linker. Using detailed spectroscopy and density functional theory calculations, we reveal conformer redistribution in the form of a thiophene ring flip as the major part of the overall mechanochromic response. At forces as low as 27 pN at early stages of deformation, the ring flip precedes mechanically induced planarization of the ansa-DAD spring, the latter process producing a PL shift of 21 nm nN-1. Within the stress-strain diagram, the thiophene ring flip and DAD planarization are thus two separated processes that also cause irreversible and reversible mechanochromic responses, respectively, upon sample failure. As the thiophene ring flip requires much smaller forces than planarization of the DAD spring, such micromechanical motion gives access to sensing of tiny forces and expands both sensitivity and the force range of conformational mechanochromophores.

Back Cover: Helical Molecular Springs with Varying Spring Constants (Angew. Chem. Int. Ed. 50/2022)

Back Cover: Helical Molecular Springs with Varying Spring Constants (Angew. Chem. Int. Ed. 50/2022)

Rücktitelbild: Helical Molecular Springs with Varying Spring Constants (Angew. Chem. 50/2022)

Rücktitelbild: Helical Molecular Springs with Varying Spring Constants (Angew. Chem. 50/2022)

Helical Molecular Springs with Varying Spring Constants.

We report a general synthetic route toward helical ladder polymers with varying spring constants, built with chirality-assisted synthesis (CAS). Under tension and compression, these shape-persistent structures do not unfold, but rather stretch and compress akin classical Hookean springs. Our synthesis is adaptable to helices with different pitch and diameter, which allowed us to investigate how molecular flexibility in solution depends on the exact geometry of the ladder polymers. Specifically, we showed with molecular dynamic simulations and by measuring the longitudinal 1 H NMR relaxation times (T1 ) for our polymers at different Larmor frequencies, that increasing the helix diameter leads to increased flexibility. Our results present initial design rules for tuning the mechanical properties of intrinsically helical ladder polymers in solution, which will help inspire a new class of robust, spring-like molecular materials with varying mechanical properties.