Chain Asymmetry Research Articles

Quasi‐elastic neutron scattering study on dynamically asymmetric polymer blends

AbstractCompatibility between polymers with different glass transition temperatures controls the thermomechanical properties of blends. This work explores the segmental dynamics of poly(methyl acrylate) (PMA) chains when they are blended with polymers of different rigidities and miscibility. Inspired by the intriguing dynamic asymmetry of chains within the interfacial layer of nanoparticles, this study aims to understand dynamic heterogeneity in dynamically asymmetric blends of PMA/poly(methyl methacrylate) (PMMA), PMA/polystyrene (PS), and PMA/poly(ethylene oxide) (PEO) using the differential scanning calorimetry (DSC) and quasi‐elastic neutron scattering (QENS) measurements below and above the glass transition temperature of PMMA or PS. Results revealed that the segmental jump distance of PMA increased on blending due to volume enhancement. The reduced effective diffusivity of PMA in PMMA is attributed to PMMA's enhanced flexibility (lower characteristic ratio, ) and superior interaction (lower ) when compared with the PS environment. The results demonstrate that the chain rigidity and miscibility affect the free volume, interchain cooperativity, and segmental dynamics in dynamically asymmetric blends.

High-Density Packing of Spherical Microdomains from A(AB3)3 Dendron-like Miktoarm Star Copolymer.

An A(AB3)3 dendron-like miktoarm star copolymer consisting of polystyrene (PS, A) and poly(2-vinylpyridine) (P2VP, B) was synthesized using a series of anionic polymerization, atom-transfer radical polymerization (ATRP), and click reaction. The morphology of A(AB3)3 changed greatly depending on the volume fraction of A and the chain asymmetry. Interestingly, a body-centered cubic spherical phase was found even at fA = 0.51 because the chain architecture of A(AB3)3 stabilizes the large interfacial curvature toward A domains. On the other hand, when the length difference between the end and middle A blocks decreased, a hexagonally packed cylindrical phase was formed at fA = 0.50. This is attributed to the fact that the middle A chains are arranged in a more relaxed way, resulting in a milder interfacial curvature toward A domains. The experimental observations are well-consistent with the predictions based on self-consistent-field theory.

Effects of interdigitation on the biophysical properties of lipid bilayers: A molecular dynamics study of chain asymmetric lipids.

Plasma membranes (PMs) are composed of hundreds of different lipids varying in structure and chemical properties. A major challenge in membrane biophysics is to determine how different classes of lipids contribute to the physical properties of the PM. One particularly interesting type of lipid is characterized by a different number of carbons in its two hydrocarbon chains. These chain asymmetric lipids are thought to have a higher propensity for interdigitation with lipids in the opposing leaflet and thus, to have a unique effect on interleaflet coupling. We have used molecular dynamics (MD) simulations to systematically examine fluid-phase bilayers composed of fully saturated PC lipids, each with a total of 32 acyl chain carbons, but increasing asymmetry ranging from zero to four carbons difference between the two chains. We quantified interdigitation in these bilayers using three novel methods and compared the results to standard approaches; we found general agreement in the trends, namely that increasing chain asymmetry results in increased interdigitation. We hypothesized that a greater extent of interdigitation should result in stiffer bilayers and thus, higher values of the bending modulus. To test this hypothesis, we measured various structural and mechanical properties of the simulated bilayers including thickness, lipid packing, and bending and compressibility moduli. Surprisingly, we found that the bilayers with the greatest extent of interdigitation are also the softest at a common temperature of 50°C. These results provide new insights into the structural and mechanical effects of lipid chain asymmetry and open up further questions about the nature of the coupling between lipid chain interdigitation and membrane biophysical properties.

Unsynchronous conformational transitions induced by the asymmetric adsorption-response of an active diblock copolymer in an inert brush.

To exploit the chemical asymmetry of diblock copolymer chains on the design of high-performance switch sensors, we propose an analytically tractable model system which contains an adsorption-responsive diblock copolymer in an otherwise inert brush, and study its phase transitions by using both analytical theory and self-consistent field calculations. The copolymer chain is chemically asymmetric in the sense that the two blocks assume different adsorption strengths, which is characterized by the defined adsorption ratio. We found that the conformation states, the number of stable phases, and transition types are mainly controlled by the length of each block and the adsorption ratio. In particular, when the length of the ungrafted block is longer than the brush chains, and the adsorption ratio is smaller than a critical value, the copolymer chain shows three thermodynamically stable states, and undergoes two unsynchronous transitions, where the two blocks respond to the adsorption in a different manner, when the adsorption changes from weak to sufficiently strong. For this kind of three-state transition, the transition point, transition barrier, and transition width are evaluated by using the self-consistent field method, and their scaling relationship with respect to the system parameters is extracted, which matches reasonably well with the predictions from the analytical theory. The self-consistent field calculations also indicate that the conformational transitions involved in the three-state transition process are sharp with a low energy barrier, and interestingly, barrier-free transitions are observed. Our finding shows that the three-state transitions not only specify a region where high performance unsynchronous switch sensors can be exploited, but may also provide a useful model understanding the unsynchronous biological processes.

(Digital Presentation) Dielectric and Vibrational Spectroscopic Study on Asymmetric Quaternary Phosphonium-Based Ionic Liquids

Ionic liquids (IL) have a great potential of applications in electrochemical devices such as electrolytes for fuel cells. In particular, quaternary phosphonium cation-based ionic liquids (P-ILs) is much suitable due to lower viscosity and better ionic conductivity compared with corresponding quaternary ammonium cation-based ionic liquids (A-ILs). Over the past decade, fundamental properties of P-ILs have been investigated by viscometry, calorimetry, spectroscopy, calculation, and so on. However, little is known about molecular mechanism for such better potential of P-ILs. The present study aimed to reveal the relationship between molecular structure and macroscopic material properties of P-ILs in terms of alkyl chain asymmetry. The P-ILs used in this study were prepared by quadrification of trialkylphosphine followed by ion exchange with bis(trifluoromethanesulfonyl)imide (TFSA) anions. We named P-ILs based on the number of alkyl chain length. For example, P2225 means triethyl(penta)phosphonium cation. In this study, we used P2225-TFSA, P2228-TFSA, and P222(12)-TFSA. We conducted temperature-variable broadband dielectric spectroscopy between 20 Hz and 100 MHz. We also carried out Raman spectroscopy (laser excitation at 532 nm) and THz spectroscopy. The obtained complex dielectric spectra were dominated by (i) electrode polarization, (ii) ionic conduction, and (iii) reorientational relaxation, depending on the frequency and temperature. The spectra at the frequency regions between ionic conduction and reorientational relaxation were well-fitted with a Havriliak-Negami dielectric relaxation function, superimposed with a conductivity term. Thus, we determined both ionic conductivity (σdc) and relaxation time for structural relaxation (τHN) of ionic liquids. Although the σdc for all of the P-ILs used in this study exhibited similar Vogel-Fulcher-Tamman-type temperature dependence, the σdc slightly decreased with increasing the asymmetric alkyl chain length. Such temperature dependence was also observed in τHN, meaning that translational dynamics partly coupled with segmental dynamics. This result is consistent with that internal motion of the alkyl chains should depend on the chain length. Raman and THz spectroscopy provided an information on molecular structure (such as conformation) and inter- and intra-molecular interaction between anions and cations. In the presentation, we will describe the relationship of charge carrier transportation with ion conformations and intermolecular structures.

Phase Behavior of PS-(PS-b-P2VP)3 Miktoarm Star Copolymer

We synthesized polystyrene-[polystyrene-b-poly(2-vinylpyridine)]3 miktoarm star copolymer [PSL-(PSS-b-P2VP)3], where PSL and PSS are long and short PS chains, respectively, by the combination of anionic polymerization, atom transfer radical polymerization (ATRP), and click reaction. We changed the volume fraction of the PS block (fPS) and the chain asymmetry of the PS chain τ = fPS,L/(fPS,L + fPS,S). Phase behavior of PS-(PS-b-P2VP)3 was investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Inverted gyroids consisting of PS chains were formed at fPS = 0.64 and τ = 0.65, while asymmetric lamellae were observed at fPS = 0.81 and τ = 0.79. Because a long PS chain (PSL) and three short PSS-b-P2VP copolymer chains are linked at a single junction point, a huge configurational entropy penalty was expected, resulting in distorting the original phase boundaries observed for conventional AB diblock copolymer. PSS-b-P2VP chains are mainly located at the interface between PS and P2VP microdomains, whereas PSL chains fill the regions far from the interface, which causes a radial distribution to form interfacial curvature. Interestingly, the phase behavior was greatly affected by τ at a fixed fPS. For instance, at a fixed fPS (0.64), an inverted gyroid structure was formed at τ = 0.65, while a lamellar structure was observed at τ = 0.46. With the decrease in τ (or the difference of molecular weight between PSL and PSS becomes smaller), the interfacial curvature is not expected because all PSS-b-P2VP chains have no need to be arranged in the same direction. The experimental results are consistent with the predictions based on self-consistent field theory (SCFT).

Design and synthesis of HFCA‐based plasticizers with asymmetrical alkyl chains for poly(vinyl chloride)

AbstractA series of bio‐based diester plasticizers with various alkyl chain asymmetry and the same molecular weight were designed and synthesized, using renewable 5‐hydroxymethyl‐2‐furancarboxylic acid (HFCA) as the raw material. The chemical structures of the HFCA‐based plasticizers were characterized by Fourier transform infrared and nuclear magnetic resonance (1H NMR and 13C NMR). Besides, the influence of alkyl chain asymmetry on plasticization properties of the HFCA‐based plasticizers in poly(vinyl chloride) (PVC) blends was also investigated. It was found that increasing the alkyl chain asymmetry of the diester plasticizer and keeping the molecular weight unchanged simultaneously could further improve its plasticizing efficiency, without sacrificing its volatility resistance and exudation resistance. The results showed that this study provided a new approach for further optimizing the overall properties of the asymmetric diester plasticizers.

Differential flexibility leading to crucial microelastic properties of asymmetric lipid vesicles for cellular transfection: A combined spectroscopic and atomic force microscopy studies

The role of microscopic elasticity of nano-carriers in cellular uptake is an important aspect in biomedical research. Herein we have used AFM nano-indentation force spectroscopy and Förster resonance energy transfer (FRET) measurements to probe microelastic properties of three novel cationic liposomes based on di-alkyl dihydroxy ethyl ammonium chloride based lipids having asymmetry in their hydrophobic chains (Lip1818, Lip1814 and Lip1810). AFM data reveals that symmetry in hydrophobic chains of a cationic lipid (Lip1818) imparts higher rigidity to the resulting liposomes than those based on asymmetric lipids (Lip1814 and Lip1810). The stiffness of the cationic liposomes is found to decrease with increasing asymmetry in the hydrophobic lipid chains in the order of Lip1818 > Lip1814 > lip1810. FRET measurements between Coumarin 500 (Donor) and Merocyanine 540 (Acceptor) have revealed that full width at half-maxima (hw) of the probability distribution (P(r)) of donor-acceptor distance (r), increases in an order Lip1818 < Lip1814 < Lip1810 with increasing asymmetry of the hydrophobic lipid chains. This increase in width (hw) of the donor-acceptor distance distributions is reflective of increasing flexibility of the liposomes with increasing asymmetry of their constituent lipids. Thus, the results from AFM and FRET studies are complementary to each other and indicates that an increase in asymmetry of the hydrophobic lipid chains increases elasticity and or flexibility of the corresponding liposomes. Cell biology experiments confirm that liposomal flexibility or rigidity directly influences their cellular transfection efficiency, where Lip1814 is found to be superior than the other two liposomes manifesting that a critical balance between flexibility and rigidity of the cationic liposomes is key to efficient cellular uptake. Taken together, our studies reveal how asymmetry in the molecular architecture of the hydrophobic lipid chains influences the microelastic properties of the liposomes, and hence, their cellular uptake efficiency.

Thermal rectifiers based on asymmetric interaction of molecular chains, carbon nanoribbons, and nanotubes with thermostats

The model of thermal rectifier based on the asymmetry of interaction of the molecular chain ends with thermostats is proposed in this work. The rectification mechanism is not related to the chain asymmetry, but to the asymmetry of the interaction of chain ends with thermostats, for instance, due to different lengths of the end thermostats. The chain can be homogeneous, it is only important that the thermal conductivity of the chain should depend on temperature strict monotonically. The effect is maximal when convergence of the thermal conductivity with increasing length just begins to manifest itself. In this case, the efficiency of thermal rectification can reach 25%. These conditions are met for carbon nanoribbons and nanotubes. Therefore, they can be ideal objects for the construction of thermal rectifiers based on the asymmetric interaction with thermostats. Numerical simulation of heat transfer shows that the rectification of heat transfer can reach 14% for nanoribbons and 22% for nanotubes.

Poly(9‐undecyl‐9‐methyl‐fluorene) and poly(9‐pentadecyl‐9‐methyl‐fluorene): Synthesis, solution structure, and effect of side chain asymmetry on aggregation behavior

ABSTRACTWe report on solution aggregates and backbone conformation of poly(9‐undecyl‐9‐methyl‐fluorene) (PF1‐11) and poly(9‐pentadecyl‐9‐methyl‐fluorene) (PF1‐15), having two different side chains compared with poly(9,9‐dihexylfluorene) (PF6) and poly(9,9‐dioctylfluorene) (PF8) with two identical side chains. In the poor solvent methylcyclohexane (MCH), X‐ray scattering indicates that PF1‐11 and PF1‐15 appear as three‐dimensional aggregates (5–10 nm wide and thick), forming ribbon‐like agglomerates (correlation lengths of 100 nm). PF6 and PF8 appear as two‐dimensional aggregates (&gt;10 nm wide and 2–3 nm thick) involving ribbon‐like agglomerates (correlation lengths much greater than 100 nm). Upon heating, all aggregates undergo a gel–sol transition which occurs at lower temperatures for PF1‐11 and PF1‐15 (&lt;60°C) than for PF6 and PF8 (&gt;80°C). In the good solvent toluene, PF1‐11 and PF1‐15 form networks of cylindrical particles. The mesh size and the cylinder radius are smaller in 24°C toluene (60 nm, 0.5 nm) than in 60°C MCH (300 nm, 1–2 nm). Nuclear magnetic resonance spectra in toluene‐d8 together with density functional theory calculations suggest higher torsion angles between polymer repeat units for PF6, PF8, and PF1‐11 (less planar conformation) and a gauche arrangement of the dihedral angles between the bridge carbon atom and the side chain methylene groups in PF1‐15. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 826–837

Supply chain coordination with inventory and pricing decisions

In this study, we conduct a comprehensive literature review on the inventory and pricing decisions under the supply chain coordination. To be specific, we review the publications from 1997 to 2017 and divide the papers into six areas for discussion, they are: decisions under integrated supply chain, supply contract, capital-constrained, competition, risk aversion, and information asymmetry. After reviewing the literature, we identify three major future research directions. First, we propose to explore different real world industrial supply contracts and the forms of demand function. Second, limited studies consider risk aversion behaviour of the supply chain members; hence, we also propose to examine the inventory and pricing decisions under supply chain coordination with risk-averse retailer and risk-averse supplier, respectively. Finally, it is also interesting to investigate different types of information asymmetry.

Asymmetric cationic gemini surfactants: an improved synthetic procedure and the micellar and surface properties of a homologous series in the presence of simple salts

The micellar and morphological properties of symmetric, cationic gemini surfactants have been well studied in the literature as a function of nature and type of the spacer group and the length and type of hydrophobic chain. In this paper, we have examined the effects of tail asymmetry on the properties of a series of cationic surfactants, the N-alkyl-1-N′-alkyl-2-N,N,N′,N′-tetramethyldiammonium dibromide. A novel synthetic method is used to prepare a series of these surfactants and the consequences of asymmetry on micellar properties are presented. This new method has been shown to be more efficient, with higher yields of the asymmetric surfactants than the yields of the accepted literature method. The critical micelle concentration values and the micelle sizes of the asymmetric gemini surfactants, 12-4-12, 12-4-10, 12-4-8, and 12-4-6 gemini surfactants, were obtained from conductivity and dynamic light scattering. With increasing chain asymmetry, the size of the micelle increased due to the formation of loose micelles. The addition of NaCl and Na2SO4 to the surfactant solutions increased the aggregate size, and this effect was more pronounced with increasing salt concentrations. These results are interpreted in terms of the effect these ions have on the “compactness” of the micelle structure.

Acyl chain asymmetry and polyunsaturation of brain phospholipids facilitate membrane vesiculation without leakage

Phospholipid membranes form cellular barriers but need to be flexible enough to divide by fission. Phospholipids generally contain a saturated fatty acid (FA) at position sn1 whereas the sn2-FA is saturated, monounsaturated or polyunsaturated. Our understanding of the impact of phospholipid unsaturation on membrane flexibility and fission is fragmentary. Here, we provide a comprehensive view of the effects of the FA profile of phospholipids on membrane vesiculation by dynamin and endophilin. Coupled to simulations, this analysis indicates that: (i) phospholipids with two polyunsaturated FAs make membranes prone to vesiculation but highly permeable; (ii) asymmetric sn1-saturated-sn2-polyunsaturated phospholipids provide a tradeoff between efficient membrane vesiculation and low membrane permeability; (iii) When incorporated into phospholipids, docosahexaenoic acid (DHA; omega-3) makes membranes more deformable than arachidonic acid (omega-6). These results suggest an explanation for the abundance of sn1-saturated-sn2-DHA phospholipids in synaptic membranes and for the importance of the omega-6/omega-3 ratio on neuronal functions.

Pricing and Benefit of Decentralization for Competing Supply Chains With Fixed Costs

This paper develops two duopoly game models to explore price decisions and the channel benefit of decentralization for two supply chains, and investigates the channel structure decisions in the presence of fixed marketing and manufacturing costs. We give the price decisions and discuss price distortion. Under the downward decentralization model, our analysis reveals that first, symmetric decentralization improves supply chain profit only when the fixed marketing costs are high or product substitutability is high; second, decentralization improves channel profit, and symmetric decentralization (i.e., both manufacturers use decentralization) is an equilibrium if the fixed marketing (or unit production) costs are sufficiently high and the market scales are sufficiently small; and third, the presence of fixed marketing costs and asymmetry of supply chains support the existence of asymmetric equilibrium. Under the upward decentralization model, we find that symmetric outsourcing emerges when the fixed manufacturing cost or the unit production cost is low while both market scale and product substitutability are large in the supplier-led setting, the channel profit under downward decentralization is higher than that under symmetric outsourcing only if product substitutability is high, and the sourcing strategy largely depends on the specific game sequence.

Morphology Reentry with a Change in Degree of Chain Asymmetry in Neat Asymmetric Linear A1BA2 Triblock Copolymers

We report experimental results on relationship between polymer chain architecture and morphology of microdomains of asymmetric linear triblock copolymers, S1BS2 (S: polystyrene; B: polybutadiene). For this purpose, we synthesized various asymmetric triblock copolymers having different lengths of two end-blocks. The morphology was examined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Although total molecular weight, composition, and thermal annealing temperature were kept constant, the morphology was found to change with a degree of chain asymmetry. One typical example exhibits a morphological change as cylinder → lamella → cylinder with a decrease in length of the shorter S2 end-block chains, while keeping the total molecular weight and the total polystyrene composition constant. This curious morphological behavior exhibiting a re-entrant type change is qualitatively in accord with the self-consistent field theory (SCFT) results by Matsen [J. Chem. Phys. 2000, 113, 55...

Polystyrene-block-poly(ethylene oxide) Bottlebrush Block Copolymer Morphology Transitions: Influence of Side Chain Length and Volume Fraction

A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction (fPEO) from 22% to 81%. A series of PS-b-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO–norbornene (PEO-NB) (Mn ∼ 0.75, 2.0, or 5.0 kg/mol) and PS–norbornene (PS-NB) (Mn ∼ 3.5 kg/mol) macromonomers (MM). A map of fPEO versus side chain asymmetry (Mn(PEO-NB)/Mn(PS-NB)) was constructed to describe the BBCP phase behavior. Symmetric and asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of fPEO from 28% to 72%. At high fPEO, crystallization of PEO was evident. Temperature-controlled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature TMST was observed over a temperature range of 150–180...

Membrane Lipid Asymmetry, a Key Property of the Mammalian Plasma Membrane, Alters the Insertion of the pHLIP Peptide

The plasma membrane has an asymmetric distribution of lipids between the inner and outer leaflets of the bilayer. Two types of phospholipid asymmetry can occur between the leaflets: head group asymmetry and acyl chain asymmetry. One lipid head group of interest is phosphatidylserine (PS), which carries a net negative charge. In healthy cells, PS is actively sequestered to the inner leaflet of the membrane but can redistribute to the outer leaflet in situations such as apoptosis and cancer. Not only do membranes contain lipids, they also contain proteins. Marginally hydrophobic membrane proteins can contain acidic residues in their transmembrane sequence and can have topological transitions after membrane association. What is unclear is how lipid asymmetry affects these topological transitions. Here, we propose to use the pH low insertion peptide (pHLIP) as a model to study topological transitions in relation to membrane head group asymmetry in free floating asymmetric phosphatidylcholine (PC)/PS vesicles. Based on environmental pH, pHLIP undergoes a topological reorientation and inserts into the membrane. The inclusion of PS in symmetric vesicles affects the insertion process by lowering the pH midpoint of insertio n. However, we do not know how PS asymmetry will affect insertion. We propose that having an asymmetric distribution of PS (more in the inner leaflet) will affect the insertion of pHLIP. Fluorescence spectroscopy data show that the pH midpoint of pHLIP insertion into asymmetr ic vesicles is higher compared to symmetric vesicles containing PS. Acrylamide quenching data show that the two tryptophans in pHLIP are more solvent exposed in the presence of asymmetry. We hypothesize that pHLIP insertion is affected by a change in the transmembrane potential induced by the asymmetric distribution of charged lipids between the leaflets.

Interplay between alkyl chain asymmetry and cholesterol addition in the rigid ion pair amphiphile bilayer systems.

Ion pair amphiphile (IPA), a molecular complex composed of a pair of cationic and anionic surfactants, has been proposed as a novel phospholipid substitute. Controlling the physical stability of IPA vesicles is important for its application developments such as cosmetic and drug deliveries. To investigate the effects of IPA alkyl chain combinations and the cholesterol additive on the structural and mechanical properties of IPA vesicular bilayers, we conducted a series of molecular dynamics studies on the hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS) and dodecyltrimethylammonium-hexadecylsulfate (DTMA-HS) IPA bilayers with cholesterol. We found that both IPA bilayers are in the gel phase at 298 K, consistent with experimental observations. Compared with the HTMA-DS system, the DTMA-HS bilayer has more disordered alkyl chains in the hydrophobic region. When adding cholesterol, it induces alkyl chain ordering around its rigid sterol ring. Yet, cholesterol increases the molecular areas for all species and disturbs the molecular packing near the hydrophilic region and the bilayer core. Cholesterol also promotes the alkyl chain mismatch between the IPA moieties, especially for the DTMA-HS bilayer. The combined effects lead to non-monotonically enhancement of the membrane mechanical moduli for both IPA-cholesterol systems. Furthermore, cholesterol can form H-bonds with the alkylsulfate and thus enhance the contribution of alkylsulfate to the overall mechanical moduli. Combined results provide valuable molecular insights into the roles of each IPA component and the cholesterol on modulating the IPA bilayer properties.

Introduction to provocative questions in left-right asymmetry.

Left-right asymmetry is a phenomenon that has a broad appeal-to anatomists, developmental biologists and evolutionary biologists-because it is a morphological feature of organisms that spans scales of size and levels of organization, from unicellular protists, to vertebrate organs, to social behaviour. Here, we highlight a number of important aspects of asymmetry that encompass several areas of biology-cell-level, physiological, genetic, anatomical and evolutionary components-and that are based on research conducted in diverse model systems, ranging from single cells to invertebrates to human developmental disorders. Together, the contributions in this issue reveal a heretofore-unsuspected variety in asymmetry mechanisms, including ancient chirality elements that could underlie a much more universal basis to asymmetry development, and provide much fodder for thought with far reaching implications in biomedical, developmental, evolutionary and synthetic biology. The new emerging theme of binary cell-fate choice, promoted by asymmetric cell division of a deterministic cell, has focused on investigating asymmetry mechanisms functioning at the single cell level. These include cytoskeleton and DNA chain asymmetry-mechanisms that are amplified and coordinated with those employed for the determination of the anterior-posterior and dorsal-ventral axes of the embryo.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Dynamic and mechanical properties of supported lipid bilayers.

Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh(2) and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts.