Liel Sapir

• PostDoc Position at Duke University

Both polymer size and chain elasticity depend on long-range bond correlations. These correlations are gradually cut off for higher externally applied force thus increasing chain stiffness. We develop a theory for tension-dependent elasticity and validate it with simulations. Our model explains the higher stiffness measured in single-molecule force...

Extending polymer chains results in a positive chain tension, fch, primarily due to conformational restrictions. At the level of individual bonds, however, tension, fb, is either negative or positive and depends on both chain tension and bulk pressure. Typically, the chain and bond tension are assumed to be directly related. In specific systems, ho...

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 cyclorever...

Slide-ring gels are polymer networks with cross-links that can slide along the chains. In contrast to conventional unentangled networks with cross-links fixed along the chains, the slide-ring networks are strain-softening and distribute tension much more uniformly between their strands due to the so-called "pulley effect". The sliding of cross-link...

Cells are crowded, but proteins are almost always studied in dilute aqueous buffer. We review the experimental evidence that crowding affects the equilibrium thermodynamics of protein stability and protein association and discuss the theories employed to explain these observations. In doing so, we highlight differences between synthetic polymers an...

Polymer networks are complex systems consisting of molecular components. Whereas the properties of the individual components are typically well understood by most chemists, translating that chemical insight into polymer networks themselves is limited by the statistical and poorly defined nature of network structures. As a result, it is challenging,...

Deep eutectic mixtures are a promising sustainable and diverse class of tunable solvents that hold great promise for various green chemical and technological processes. Many deep eutectic solvents (DES) are hygroscopic and find use in applications with varying extents of hydration, hence urging a profound understanding of changes in the nanostructu...

Trehalose is a naturally occurring disaccharide known to remarkably stabilize biomacromolecules in the biologically active state. The stabilizing effect is typically observed over a large concentration range and affects many macromolecules including proteins, lipids, and DNA. Of special interest is the transition from aqueous solution to the dense...

Proprioception requires the transduction of muscle-generated deformations into sensory neuronal impulses. In proprioceptive organs, the mechanical coupling between the sensory neuron and the muscle is mediated by a connective structure composed of accessory cells and an extracellular matrix (ECM). Here, we use the fly chordotonal organ (ChO) to inv...

Video S1. Bead Displacements Generated by Beating of a Pair of Mechanically Coupled Cardiac Cells, Related to Figure 1 Time lapse imaging of the deformation field generated by a pair of beating cardiac cell on a flexible substrate. Mechanical deformations are detected by following movements of 0.2-μm fluorescent beads embedded within the gel. The...

Data S1. Cardiac Cell as a Calcium Oscillator – Theoretical Model for Enzyme-Mediated Noise Reduction

Video S2: Strain Field Generated by Beating of a Pair of Mechanically Coupled Cardiac Cells, Related to Figure 1 Strain map along the y axis (ɛyy) for a pair of spontaneously beating cardiac cells cultured on a flexible substrate, 20 μm apart. The strain was calculated using the time lapse imaging of the fluorescent beads shown in Video S1. The be...

Cells can communicate mechanically by responding to mechanical deformations generated by their neighbors. Here, we describe a new role for mechanical communication by demonstrating that mechanical coupling between cells acts as a signaling cue that reduces intrinsic noise in the interacting cells. We measure mechanical interaction between beating c...

On a hot summer’s day you decide to cool off in the neighborhood swimming pool. The pool is jam packed with others trying to do the same, but you venture to go in, anyway. The stress and crowded feeling is (more or less) what a macromolecule would feel inside a living cell. The third or so dry mass of an average cell translates in the pool analogy...

The communication between cells enables them to coordinate their activity and is key for the differentiation, development, and function of tissues and multicellular organisms. Cell-cell communication is discussed almost exclusively as having a chemical or electrical origin. Only recently, a new mode of cell communication was elucidated: mechanical...

In processes involving aqueous solutions and in almost every biomolecular interaction, hydrogen bonds play important roles. Though weak compared to the covalent bond, hydrogen bonds modify the stability and conformation of numerous small and large molecules and modulate their intermolecular interactions. We propose a simple methodology for extracti...

The riddle of anomalous polar behavior of the centrosymmetric crystal of α-glycine is resolved by the discovery of a polar, several hundred-nanometer thick hydrated layer, created at the {010} faces during crystal growth. This layer was detected by two independent pyroelectric analytical methods: (i) periodic temperature change technique (Chynoweth...

Deep eutectic solvents (DES) are mixtures of two or more components with high melting temperatures, which form a liquid at room temperature. These DES hold great promise as green solvents for chemical processes, as they are inexpensive and environmentally friendly. Specifically, they present a unique solvating environment to polymers that is differ...

From colloidal dispersions to solvated polymers or proteins, solution composition is known to strongly influence the stable state of the bathing macromolecules. Mixed solvents containing species with different affinity to specific macromolecular states can shift equilibrium towards the thermodynamically preferred state with lower free energy, even...

Stabilizing osmolytes are known to impact the process of amyloid aggregation, often altering aggregation kinetics. Recent evidence further suggests that osmolytes modify the peptide conformational dynamics, as well as change the physical characteristics of assembling amyloid fibrils. To resolve how these variations emerge on the molecular level, we...

We propose a mean field theory to account for the experimentally determined temperature dependence of protein stabilization that emerges in solutions crowded by preferentially excluded cosolutes. Based on regular solution theory and employing the Flory-Huggins approximation, our model describes cosolutes in terms of their size, and two temperature-...

Cosolutes excluded from macromolecules create effective attractions between the excluding macromolecules, and promote their self-association. This “depletion force” serves an important stabilizing role in many biological and technological processes. Specifically, many osmolytes and polymeric crowders that are excluded from protein surfaces stabiliz...

Solutes excluded from macromolecules or colloids are known to drive depletion attractions. The established Asakura−Oosawa model, as well as subsequent theories aimed at explaining the effects of macromolecular crowding, attribute depletion forces to diminished hard-core excluded volume upon compaction, and hence predict depletion forces dominated by...

Solutes added to solutions often dramatically impact molecular processes ranging from the suspension or precipitation of colloids to biomolecular associations and protein folding. Here we revisit the origins of the effective attractive interactions that emerge between and within macromolecules immersed in solutions containing cosolutes that are pre...

Numerous cellular cosolutes significantly impact the way that proteins and other biomacromolecules act and interact. We have followed the thermodynamic effect of several cosolute classes, including polymers, cellular osmolytes, and inorganic salts, on the stability of biomolecular folding and complexation. By comparing changes in free energy, entha...

On the molecular level, life is established through the specific interaction between and within macromolecules in an aqueous environment. It is increasingly realized, however, that even modest changes in solution conditions, brought on by the presence of many cellular cosolutes, can profoundly affect the balance of forces underlying the specificity...

In aqueous solutions, trehalose possesses a high propensity to form hydrogen bonds with water as well as other trehalose molecules. This hydrogen bonding not only affects water structure but also promotes extensive concentration dependent aggregation of trehalose molecules, which may impact trehalose's role as a protective cosolute to biomacromolec...

Using molecular dynamics simulations, we study the effect of polyalcohols on water structuring in concentrated solutions, comparing six different polyols that vary in the number of hydroxyl groups and internal structure. For all polyols, we find that the hydrogen bond network order, as assessed by changes in the tetrahedral order parameter, is dist...