Rod Molecules Research Articles

Design and Evaluation of a Reprocessable Bismaleimide Thermoset: Enhancing Functionality and Sustainability Compatibility.

Bismaleimide (BMI) resins are high-performance thermosets that are primarily used in aerospace because of their exceptional heat resistance and physical properties. However, their growing demand has led to significant environmentally unfriendly waste. To address this, our research proposes a reprocessable BMI system using a newly synthesized BMI vitrimer (BMIV) with functional groups that form covalent adaptable networks (CANs). To enhance the properties, a symmetrical BMI with two ester groups introduced into the rigid rod molecule was designed as a CAN component. After confirming the structure using various spectroscopic techniques, BMIV was coupled with aromatic diamines via an additional aza-Michael reaction to obtain the cured resins. Subsequently, the mechanical properties and reprocessing behavior of the thermally stable and optimized thermosetting material with the best performance were evaluated, and the evidence, mechanism, and activation energy of the topology rearrangement are reported in detail.

Size dependence of transport coefficients of thin and long asphaltene molecules as determined using a mode-coupling theory approach

Rotational diffusion coefficients (Dr) and viscosities (η) of rigid rod molecules consisting of N beads were first revisited for the situation at low density. Starting from this, the transport coefficients at high density condition were expressed in terms of different density pair correlation functions, such as intermolecular radial distribution function and structure factor. This was attained using a mode-coupling theory approach to approximate the intermolecular force–force correlation function, and thus the friction coefficient. As these density pair correlation functions are dependent on N, they determine how “entangled” the rigid rod molecules are, and therefore reproducing the crossover in the log –log plot of transport coefficients with N. It was found that there are crossovers in transport coefficients from Dr∼N−2.3 and η∼N2.3 at low N to Dr∼N−6.5 and η∼N6.5 at high N. The strength of N dependence is mainly determined by the competition between available free space and the compressibility of the system.

Structure and Conformation of Hydroxypropylmethyl Cellulose with a Wide Range of Molar Masses in Aqueous Solution─Effects of Hydroxypropyl Group Addition.

The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses (Mw) from 23 to 5000 kg mol-1, a controlled degree of substitution (DS) of 1.9 by methyl groups, and a molar substitution number (MS) of 0.25 by hydroxypropyl groups dissolved in aqueous solution was examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide angle neutron scattering (S-WANS) techniques, and intrinsic viscosity ([η]) measurements. The determined Mw and the radius of gyration (Rg) showed the relationships Rg ∝ Mw1.0 and [η] ∝ Mw1.7 in a range of Mw < 100 kg mol-1, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing Mw and reached ∼0.5 in a high Mw region, which is a typical value of flexible chain molecules for both Rg and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (lp). The ratios of the hydrodynamic radius via DLS measurements to Rg also supported semiflexible rod behavior. Particle form factors and the average lengths (L) resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of Mw < 100 kg mol-1 and semiflexible rods with lp ∼ 100 nm in Mw > 100 kg mol-1. Because the average contour length (lc) calculated from Mw is approximately twice as long as L in the Mw range < 100 kg mol-1, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the lc/L value increases gradually in the range Mw > 200 kg mol-1, where the formed HpMC particles behave as semiflexible rods. The formed particle structure was substantially different from that found in methyl cellulose samples with a similar DS value, which showed rod-like behavior over a wide Mw range. The addition of hydroxypropyl groups only at MS = 0.25 effectively changed the formed particle structure.

Research progress in molecular dynamics of high-performance PBO fibers

This article reviews the application and development of molecular dynamics in the field of poly(p-benzobisoxazole) (PBO) molecules, including the use of molecular dynamics simulations to calculate the theoretical Young’s modulus of PBO molecules and discuss them from the perspective of molecular theory Combine the rotational isomerism state theory with the long molecular dynamics simulation of small fragments to evaluate the limit length of the persistence vector a. The molecular dynamics calculation is used to study the molecular motion behavior of isolated rigid rod molecules such as PBO. Combining computer simulation technology and X-ray diffraction data collected by the imaging board system to analyze the crystal structure of the PBO fiber, and use molecular dynamics and dynamic modeling to establish the PBO/epoxy interface and study its performance.

Crowding effect on the alignment of rod molecules confined in a spherical cavity

We conduct Monte Carlo simulation for a simple model to elucidate alignments of multiple rigid rods confined within a rigid spherical cavity under crowding. For rods shorter than the cavity’s radius, depletion forces are essential. Rods distribute around cavity boundary with low orientation ordering in presence of rigid crowders. For rods longer than the cavity’s radius, they form a bundle in cavity interior and display nematic ordering by increasing crowding levels. Formation of nematic order is entropically favorable, which increases free space for crowders distributing around the cavity boundary. These findings are consistent with experimental results in the past literature.

Synthesis of Rigid Rod, Trigonal, and Tetrahedral Nucleobase-Terminated Molecules

AbstractAn efficient fragment splicing method for the construction of multiple nucleobase-terminated monomers has been developed. Conformationally fixed rod, trigonal planar and tetrahedral thymine and adenine structures were generated in moderate to good yields, which will serve as inspiring examples for exploration of nucleobases as natural hydrogen-bond components in supramolecular chemistry.

Theory of nematic ordering driven by hydrogen bonding between rods and solvent molecules

ABSTRACT A mean-field theory is introduced to describe nematic () ordering and phase separations in aqueous low-molecular-weight liquid crystalline molecules (or short rodlike molecules). We consider a physical bonding (or a hydrogen bonding) between the rod and solvent (water) molecules. Our theory predicts that the hydrogen bonds between the unlike molecules stabilise the phase and take place novel phase separations on the temperature-concentration plane. Upon increasing the number of functional groups on the rods, capable of forming the physical bond with the solvent molecule, the stable phase region is broadened on the phase diagram. We also find a miscibility window of the phase and closed-loop coexistence curves with upper and lower critical solution temperatures near the phase.

Integrin Binding Dynamics Modulate Ligand-Specific Mechanosensing in Mammary Gland Fibroblasts.

SummaryThe link between integrin activity regulation and cellular mechanosensing of tissue rigidity, especially on different extracellular matrix ligands, remains poorly understood. Here, we find that primary mouse mammary gland stromal fibroblasts (MSFs) are able to spread efficiently, generate high forces, and display nuclear YAP on soft collagen-coated substrates, resembling the soft mammary gland tissue. We describe that loss of the integrin inhibitor, SHARPIN, impedes MSF spreading specifically on soft type I collagen but not on fibronectin. Through quantitative experiments and computational modeling, we find that SHARPIN-deficient MSFs display faster force-induced unbinding of adhesions from collagen-coated beads. Faster unbinding, in turn, impairs force transmission in these cells, particularly, at the stiffness optimum observed for wild-type cells. Mechanistically, we link the impaired mechanotransduction of SHARPIN-deficient cells on collagen to reduced levels of collagen-binding integrin α11β1. Thus integrin activity regulation and α11β1 play a role in collagen-specific mechanosensing in MSFs.

Characterisation of the molecular properties of scleroglucan as an alternative rigid rod molecule to xanthan gum for oropharyngeal dysphagia

Scleroglucan, a neutral β(1–3) glucan with β(1–6) glucan branches every third residue, is being considered as an alternative rod-like, shear thinning high molecular weight β-glucan based polysaccharide to xanthan gum for the management of patients with oropharyngeal dysphagia. It is therefore important to understand more fully its hydrodynamic properties in solution, in particular heterogeneity, molecular weight distribution and its behaviour in the presence of mucin glycoproteins. A commercially purified scleroglucan preparation produced by fermentation of the filamentous fungus Sclerotium rolfsii was analysed in deionised distilled water with 0.02% added azide. Sedimentation velocity in the analytical ultracentrifuge showed the scleroglucan preparation to be unimodal at concentrations >0.75 mg/ml which resolved into two components at lower concentration and with partial reversibility between the components. Sedimentation coefficient versus concentration plots showed significant hydrodynamic non-ideality. Self-association behaviour was confirmed by sedimentation equilibrium experiments with molecular weights between ~3 × 106 g/mol to ~5 × 106 g/mol after correcting for thermodynamic non-ideality. SEC-MALS-viscosity experiments showed a transition between a rod-shape at lower molar masses to a more flexible structure at higher masses consistent with previous observations. Sedimentation velocity experiments also showed no evidence for potentially problematic interactions with submaxillary mucin.

Synthesis of Rod-coil Molecules bearing Oligo-Phenylene Vinylene Motifs: Effect of PEO Chain Lengths on the Evolution of Nanostructures Morphology and their Photophysical Properties

The applications of nano-dispersed organic conjugated active compounds or materials as well as current research is concerned mainly with optimization and control of the optical properties, by particle size and supramolecular structure of the particles. The aromatic macromolecules consisting of conjugated rigid rod segment and hydrophilic flexible chain as coil in aqueous solution can aggregate into a variety of supramolecular structures through mutual interaction between aromatic rod and hydrophilic chains of molecules and water. Here we report the synthesis of newer oligo phenylene vinylene (OPV) based rod-coil molecules with varying chain-length polyethylene oxide (PEO) repeating units (n = 8, 17, 45). Formation and photophysical properties of their nanostructures in water are studied comparatively. The nanostructures evolution of these molecules is observed with simple reprecipitation method. The stable nanostructures were formed without addition of any surfactants. The fabricated nanostructures ultimately give the materials with ‘controlled’ aggregation induced enhanced photophysical properties. The self-assembly of such OPV type rod molecules in water without adding any surfactants, therefore, can provide a strategy for the construction of well-defined and stable nanostructures with certain chemical functionalities and physical properties as advanced materials for photonic, electronic and biological applications. Copyright © VBRI Press.

Sequential Symmetry-Breaking Intercolumnar Transformations of a Conjugated Rod Molecule with a Flexible Coil

In this paper, we report distinct symmetry-breaking phase transitions in molecules based on oligo-para-phenylene rods and a poly(ethylene oxide) coil depending on the length of the aromatic rod block The observed phase transitions were characterized by differential scanning calorimetry (DSC) and X-ray scattering methods. Compound 1 with a tetra-para-phenylene rod exhibited a symmetry breaking intercolumnar transition from p2gg to p6mm symmetry. This phase transition was accompanied by an endothermic peak in the DSC profile (first-order transition), suggesting an in-plane twist of the ribbon-like rod domain. On the other hand, 2 with a longer penta-para-phenylene rod exhibited sequential symmetry breaking intercolumnar transitions from c2mm to p2gg to p6mm symmetry. In contrast with 1, the phase transitions were accompanied by no enthalpy change. Therefore, the ribbon-like rod domains were not segmented due to increased inter-rod interactions of the longer aromatic rods. The phase transitions of 2 are attributed to increased thermal motions of the coils, which vary the orientational angle of the aromatic columns in the lattice.

Active Calpain Promotes Fibrin Clot Contraction By Strengthening the Coupling of Fibrin-Bound αIIbβ3 to the Platelet Cytoskeleton

Platelet-driven blood clot contraction reduces and compacts clot volume, promoting hemostasis while restoring blood flow past otherwise obstructive thrombi. Clot contraction is driven by traction forces in the range of tens of pN per platelet that are generated by platelet non-muscle myosin IIa and actin on αIIbβ3 bound to extracellular fibrin fibers. In an analysis of the kinetics of thrombin-induced clot formation and contraction in platelet-rich plasma, we found that clot contraction has two discernable phases: an exponential initiation phase and a second exponential contraction phase. It is noteworthy that Azam et al (Mol Cell Biol21:2213-20, 2001) observed that deleting the µ-calpain gene in mice impairs platelet-mediated clot contraction. In this context, we found that inhibiting calpain activity with ALLM (N-Acetyl-Leu-Leu-Methional), a cell-permeable calpain inhibitor, significantly prolonged the duration of the initiation phase and decreased the kinetic rate constants for both the initiation and contraction phases of thrombin-stimulated platelet-mediated clot contraction, but without affecting the overall extent of contraction. The calpain inhibitor ALLN (N-acetyl-Leu-Leu-Norleu) had the same effect. Thus, these studies imply that activation of platelet calpain facilitates the transmission of traction forces from the platelet cytoskeleton to the αIIbβ3 bound to fibrin fibers. μ-Calpain is calcium-dependent cytosolic neutral cysteine protease that is activated 30-60 seconds after the onset of platelet aggregation stimulated by platelet agonists such as thrombin. To identify the calpain-cleaved protein or proteins involved in clot contraction, we incubated washed human platelets with the thrombin activation peptide TRAP in the presence or absence of calpain inhibitors and identified calpain-cleaved proteins using subtiligase-mediated biotin-labeling of nascent N-termini followed by mass spectrometry. We identified 32 proteins in the platelet cytosol that undergo calpain-mediated cleavage after TRAP stimulation. Many of these are cytoskeletal proteins, most prominently talin which connects integrins to the cytoskeleton and vinculin which is required for myosin-contractility-dependent effects on traction force and adhesion strength. Accordingly, we focused our attention on these two proteins. Talin, a 250 kD protein, is composed of a 45 kD N-terminal head domain attached via a flexible linker to a 200 kD C-terminal rod domain. The rod domain consists of 62 amphipathic α-helices organized into a series of four- and five-helix bundles. Vinculin is a 116 kD protein composed of 5 domains and has an autoinhibited structure in which domains 1-3 bind to domain 5. We detected 8 calpain-mediated cleavages in talin, 2 previously identified cleavage sites in unstructured regions and 6 others in α-helical regions known to interact with other proteins. Four of the latter are located within the first 12 talin helices, a region that contains four vinculin binding sites (VBSs). Likewise, the remaining two cleavage sites are in proximity to a VBS. A VBS is a vinculin-binding α-helix that is buried in a helical bundle due to extensive hydrophobic interactions with other amphipathic helices. Because VBS are packed into the interior of a helical bundle, a structural rearrangement is required to initiate vinculin binding. Using magnetic tweezers and atomic force microscopy, del Rio et al demonstrated that force-induced stretching of single talin rod molecules activates VBSs (Science323:638-41, 2009)), implying that stretching causes the conformational change required to expose buried VBSs. Thus, based on the location of the calpain-mediated cleavages in talin, we hypothesize that by cleaving talin in proximity to a VBS, calpain facilitates vinculin to binding talin, thereby strengthening the coupling of fibrin-bound αIIbβ3 to the platelet cytoskeleton to promote fibrin clot contraction. DisclosuresNo relevant conflicts of interest to declare.

Single chains of strong polyelectrolytes in aqueous solutions at extreme dilution: Conformation and counterion distribution.

The molecular conformation of two typical polyelectrolytes, sodium polystyrene sulfonate (NaPSS) and quarternized poly-4-vinylpyridine (QP4VP), was studied in aqueous solutions without salt addition at the single molecular level. By fluorescence correlation spectroscopy, the hydrodynamic radius (Rh) of NaPSS and QP4VP with the molecular weight ranging more than one order of magnitude was measured. The scaling analysis of Rh exhibits scaling exponent of 0.70 and 0.86 for NaPSS and QP4VP in solutions without added salts, respectively, showing the conformation is much more expanded than random coil. Numerical fittings using the model of diffusion of a rod molecule agree with the data well, indicating that the polyelectrolyte chains take the rod-like conformation under the condition without salt addition. Further investigations by determining the electric potential of single PSS- chains using the photon counting histogram technique demonstrate the enhanced counterion adsorption to the charged chain at higher molecular weight.

Finding Transition Pathways on Manifolds

We consider noise-induced transition paths in randomly perturbed dynami- cal systems on a smooth manifold. The classical Freidlin-Wentzell large devia- tion theory in Euclidean spaces is generalized and new forms of action functionals are derived in the spaces of functions and the space of curves to accommodate the intrinsic constraints associated with the manifold. Numerical meth- ods are proposed to compute the minimum action paths for the systems with constraints. The examples of conformational transition paths for a single and double rod molecules arising in polymer science are numerically investigated.

Radical Polymerization of Pendant (Meth)acrylates on a Rigid Helical Polyisocyanate Backbone Producing Poly(meth)acrylates with “Ideally” Atactic Main Chain Configuration

This study includes a topic that poly(methyl methacrylate) (PMMA) with an “ideally” atactic main chain configuration, approximately triad tacticities of mm/mr/rr = 1/2/1, has been produced in solution by the “one-dimensionally regulated” radical polymerization using rigid helical polyisocyanate as a macromolecular template. Three types of isocyanate monomers with pendant (meth)acryloxy groups, such as 2-(methacryloxy)ethyl isocyanate (MOI), 2-[2-(methacryloxy)ethoxy]ethyl isocyanate (MOI-EO), and 2-(acryloxy)ethyl isocyanate (AOI), were polymerized using a titanium alkoxide complex to produce the corresponding polyisocyanates, MOI-n, MOI-EO-n, and AOI-n, respectively, in which n represents the number-averaged degree of polymerization. From the SAXS measurements of MOI-26 in hexafluoro-2-propanol and MOI-EO-38 in tetrahydrofuran at 25 °C, the polyisocyanates were found to be considered as rigid rod molecules. The radical polymerization of the pendant (meth)acryloxy groups was performed, and the polyisocyanate template was removed by alkali hydrolysis followed by methyl esterification, eventually producing the poly[methyl (meth)acrylate]s. The diad, triad, and pentad tacicities of the products were determined by the 1H and 13C NMR spectra, and these probabilities followed those calculated based on the Bernoulli statistics. The influences of the polymerization conditions, such as polymerization temperature and monomer concentration, on the tacticity of the final polymers were clarified. The effect of the flexible spacer between the polymerizable group and polyisocynate template was also evaluated. The radical polymerizations in which the polymerizable groups are molecularly regulated on a rod-like helical polyisocyanate backbone produced vinyl polymers with inimitable tacticities even in the solution state.

Self-Organization of Bent Rod Molecules into Hexagonally Ordered Vesicular Columns

Bent-shaped rigid-core molecules with flexible chiral dendrons grafted to the outer side of the bend were synthesized and characterized by circular dichroism, differential scanning calorimetry, X-ray scatterings, and transmission electron microscopy in solution and the solid state. The bent aromatic rods based on hepta- and nonaphenylene with nitrile groups at both ends self-assemble into well-ordered hollow tubular structures in aqueous solution, while the bent rod based on heptaphenylene without nitrile groups showed no apparent aggregations in aqueous solution. In the solid state, the rigid-flexible molecules based on heptaphenylene rod without the nitrile group self-assemble into a 2D oblique columnar structure with the columnar cross-section containing two interlocked molecules. Remarkably, the rigid flexible molecules based on hepta-, nona-, and undecaphenylene with nitrile groups self-assemble into a hexagonal columnar structure with weak 3D order. A model of vesicular channel structure is proposed based on small- and wide-angle X-ray diffraction on oriented fibers, density measurement, reconstruction and simulation of electron density maps, and molecular dynamics simulation. In contrast to the hollow tubular structure found in solution, in the solid both the outside and the interior of the columns are filled by the pendant aliphatic coils. Filling of the interior of these vesicular channels is made possible by some bent rod molecules turning their obtuse apex inward. One in 7, 2 in 8, and 4 in 10 molecules are thus inverted in a column slice in compounds with hepta-, nona-, and undecaphenylene cores, respectively. These are new examples of vesicular double-segregated columnar structures recently discovered in some dendrons.

Cell Adhesion-dependent Serine 85 Phosphorylation of Paxillin Modulates Focal Adhesion Formation and Haptotactic Migration via Association with the C-terminal Tail Domain of Talin

Integrin-mediated adhesion to extracellular matrix proteins is dynamically regulated during morphological changes and cell migration. Upon cell adhesion, protein-protein interactions among molecules at focal adhesions (FAs) play major roles in the regulation of cell morphogenesis and migration. Although tyrosine phosphorylation of paxillin is critically involved in adhesion-mediated signaling, the significance of paxillin phosphorylation at Ser-85 and the mechanism by which it regulates cell migration remain unclear. In this study, we examined how Ser-85 phosphorylation of paxillin affects FA formation and cell migration. We found that paxillin phosphorylation at Ser-85 occurred during HeLa cell adhesion to collagen I and was concomitant with tyrosine phosphorylation of both focal adhesion kinase and talin. However, the non-phosphorylatable S85A mutant of paxillin impaired cell spreading, FA turnover, and migration toward collagen I but not toward serum. Furthermore, whereas the (presumably indirect) interaction between paxillin and the C-terminal tail of talin led to dynamic FAs at the cell boundary, S85A paxillin did not bind talin and caused stabilized FAs in the central region of cells. Together, these observations suggest that cell adhesion-dependent Ser-85 phosphorylation of paxillin is important for its interaction with talin and regulation of dynamic FAs and cell migration.

Spontaneous Dimerization of Titin Protein Z1Z2 Domains Induces Strong Nanomechanical Anchoring

Muscle elasticity strongly relies on the mechanical anchoring of the giant protein titin to both the sarcomere M-band and the Z-disk. Such strong attachment ensures the reversible dynamics of the stretching-relaxing cycles determining the muscle passive elasticity. Similarly, the design of biomaterials with enhanced elastic function requires experimental strategies able to secure the constituent molecules to avoid mechanical failure. Here we show that an engineered titin-mimicking protein is able to spontaneously dimerize in solution. Our observations reveal that the titin Z1Z2 domains are key to induce dimerization over a long-range distance in proteins that would otherwise remain in their monomeric form. Using single molecule force spectroscopy, we measure the threshold force that triggers the noncovalent transition from protein dimer to monomer, occurring at ∼700 piconewtons. Such extremely high mechanical stability is likely to be a natural protective mechanism that guarantees muscle integrity. We propose a simple molecular model to understand the force-induced dimer-to-monomer transition based on the geometric distribution of forces occurring within a dimeric protein under mechanical tension.

Mathematical and numerical modeling of liquid crystal elastomer phase transition and deformation

ABSTRACTLiquid crystal (in particular, nematic) elastomers consist of cross-linked flexible polymer chains with embedded stiff rod molecules that allow them to behave as a rubber and a liquid crystal. Nematic elastomers are characterized by a phase transition from isotropic to nematic past a temperature threshold. They behave as rubber at high temperature and show nematic behavior below the temperature threshold. Such transition is reversible. While in the nematic phase, the rod molecules are aligned along the direction of the ’’nematic director’’. This molecular rearrangement induces a stretch in the polymer chains and hence macroscopic spontaneous deformations. The coupling between nematic order parameter and deformation gives rise to interesting phenomena with a potential for new interesting applications. In the biological field, the ability to considerably change their length makes them very promising as artificial muscles actuators. Their tunable optical properties make them suitable, for example, as lenses for new imaging systems.We present a mathematical model able to describe the behavior of nematic elastomers and numerical simulations reproducing such peculiar behavior. We use a geometrically linear version of the Warner and Terentjev model [1] and consider cooling experiments and stretching experiments in the direction perpendicular to the one of the director at cross-linking.

Excited-state hydrogen relay along a blended-alcohol chain as a model system of a proton wire: deuterium effect on the reaction dynamics

The excited-state deuteron transfer (ESDT) of deuterated 7-hydroxyquinoline (7DQ) along a heterogeneous hydrogen (H)-bonded chain composed of two deuterated alcohol (ROD) molecules having different acidities, as a model system of a proton wire consisting of diverse amino acids, has been investigated. To understand dynamic differences between deuteron transfer and proton transfer, solvent-inventory experiments have been performed with variation of the combination as well as the composition of alcohols in a H-bonded mixed-alcohol chain. Deuteron transfer from the adjacent ROD molecule to the basic imino group of 7DQ via tunneling, which is the rate-determining step, initiates ESDT, and subsequent barrierless deuteron relay from the acidic enolic group of 7DQ to the alkoxide moiety along the H-bonded chain completes ESDT. Whereas the acceleration of the reaction has been observed in excited-state proton transfer because of the accumulated proton-donating abilities of two alcohol molecules in a H-bonded chain by a push-ahead effect, such acceleration is not observed in ESDT. Because the energy barrier of deuteron relay is much higher than that of proton relay due to the low zero-point energy of 7DQ·(ROD)(2) and a deuteron is twice as heavy as a proton, it is hard for a deuteron to pass through the barrier via tunneling. Moreover, both the H-bonding ability and the acidity of ROD molecules are so weak that their deuteron-donating abilities cannot be accumulated at the rate-determining step of ESDT. Consequently, the rate constant of ESDT is determined mostly by the acidity of the ROD molecule H-bonded directly to the imino group of 7DQ.