Microphase separation of star-diblock copolymer melts studied by dissipative particle dynamics simulation

The microphase-separation behaviors of two types of star-diblock copolymers (A)₄(B)₄ and (AB)₄ are investigated through the dissipative particle dynamics (DPD). The simulated phase diagrams show similar ordered mesostructures as those of corresponding linear and cyclic ones, such as lamellas (LAM), perforated lamellas (PL), hexagonal (HEX) cylinders and body-centered-cubic (BCC) spheres, besides, a series of gyroid (GR) morphologies predicted by theoretical research have been identified. In the regions between the totally ordered and disordered phases, we have found some melted morphologies that can be thought as locally ordered, such as micelles (M), liquid rods (LR) and random network (RN), which have not been identified in relevant theoretical predictions. The simulated threshold for a totally ordered mesostructure to appear is higher than theoretical predictions, which can be ascribed mainly to the increasing fluctuation with finite chain length, and the star architecture can facilitate microphase separation, which is in agreement with the theoretical predictions. In addition, it is easier for the (A) _n (B) _n copolymers than for corresponding (AB) _n ones to trigger microphase separation under the same conditions. The relations between the root-mean-square radius of gyration (RMSGR) and the composition f _A in the two types of star copolymers are almost contrary, which can be attributed to the differences in their structural characteristics.     

Engineering soft nanostructured functional materials via orthogonal chemistry

Nanostructured amphiphilic block copolymers, graft copolymers, polymeric thermally responsive molecular brushes and polymer stars are only few examples of macromolecular architectures accessible either via controlled/living radical polymerization (CLRP) techniques or the combination of CLRP mechanisms with efficient post-polymerization routes including click chemistry. Precise control over the composition, molecular weight and functionalities is a prerequisite for soft polymeric materials to self-organize into ordered morphologies. This contribution describes novel orthogonal chemical routes for the synthesis of macromolecular architectures and self-assembly of functional soft polymeric materials. Emerging potential applications of well-defined block and graft copolymers are outlined as well.     

Syntheses, characterization, and in vitro degradation of ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) copolymers by sequential ring-opening polymerization

Well-defined ethyl cellulose-graft-poly(epsilon-caprolactone) (EC-g-PCL) graft copolymers were successfully synthesized via ring-opening polymerization (ROP) of epsilon-caprolactone (CL) with an ethyl cellulose (EC) initiator and a tin 2-ethylhexanoate (Sn(Oct)2) catalyst in xylene at 120 degrees C. Then, novel ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) (EC-g-PCL-b-PLLA) graft-block copolymers were prepared by ROP of L-lactide (L-LA) with a hydroxyl-terminated EC-g-PCL macroinitiator and Sn(Oct)2 catalyst in bulk at 120 degrees C. Various graft and block lengths of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were obtained by adjusting the molar ratios of CL monomer to EC and the L-LA monomer to CL. The thermal properties and crystalline morphologies of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were different from those of linear PCL. The in vitro degradation rate of EC-g-PCL-b-PLLA was faster than those of linear PCL and EC-g-PCL due to the presence of PLLA blocks.     

Kinetically controlled nanostructure formation in self-assembled globular protein-polymer diblock copolymers

Aqueous processing of globular protein-polymer diblock copolymers into solid-state materials and subsequent solvent annealing enables kinetic and thermodynamic control of nanostructure formation to produce block copolymer morphologies that maintain a high degree of protein fold and function. When model diblock copolymers composed of mCherry-b-poly(N-isopropylacrylamide) are used, orthogonal control over solubility of the protein block through changes in pH and the polymer block through changes in temperature is demonstrated during casting and solvent annealing. Hexagonal cylinders, perforated lamellae, lamellae, or hexagonal and disordered micellar phases are observed, depending on the coil fraction of the block copolymer and the kinetic pathway used for self-assembly. Good solvents for the polymer block produce ordered structures reminiscent of coil-coil diblock copolymers, while an unfavorable solvent results in kinetically trapped micellar structures. Decreasing solvent quality for the protein improves long-range ordering, suggesting that the strength of protein interactions influences nanostructure formation. Subsequent solvent annealing results in evolution of the nanostructures, with the best ordering and the highest protein function observed when annealing in a good solvent for both blocks. While protein secondary structure was found to be almost entirely preserved for all processing pathways, UV-vis spectroscopy of solid-state films indicates that using a good solvent for the protein block enables up to 70% of the protein to be retained in its functional form.     

Effects of nanoparticles on the compatibility of PEO-PMMA block copolymers

The compatibility of six kinds of designed poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) copolymers was studied at 270, 298 and 400 K via mesoscopic modeling. The values of the order parameters depended on both the structures of the block copolymers and the simulation temperature, while the values of the order parameters of the long chains were higher than those of the short ones; temperature had a more obvious effect on long chains than on the short ones. Plain copolymers doped with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) homopolymer showed different order parameter values. When a triblock copolymer had the same component at both ends and was doped with one of its component polymers as a homopolymer (such as A5B6A5 doped with B6 or A5 homopolymer), the value of its order parameter depended on the simulation temperature. The highest order parameter values were observed for A5B6A5 doped with B6 at 400 K and for A5B6A5 doped with A5 at 270 K. A study of copolymers doped with nanoparticles showed that the mesoscopic phase was influenced by not only the properties of the nanoparticles, such as the size and density, but also the compositions of the copolymers. Increasing the size of the nanoparticles used as a dopant had the most significant effect on the phase morphologies of the copolymers.     

Synthesis of hierarchical materials

A major goal of material science is to produce hierarchical materials that are ordered on all length scales, from the molecular (1-100 A) via the nano (10-100 nm) to the meso (1-100 microm). In these materials, the larger-scale properties can be controlled by choosing molecular characteristics. Methods developed to produce three-dimensional, bulk-like hierarchical structures include biomimetic methods, which use polypeptides as building blocks, and amphiphile and colloidal templating, which use amphiphilic or colloidal mesophases as templates for inorganic mesoporous materials. Designing finite mesostructures with a given geometry still remains a challenge.     

Rare earth and yttrium elements (REY) patterns of mesostructures of Miaolingian (Cambrian) thrombolites at Jiulongshan,Shandong Province,China

The relationship between the thrombolitic mesostructures and their depositional environments is still poorly understood due to inconsistent results by sedimentary investigation. Rare earth elements plus yttrium (REY) in ancient microbialites have been extensively applied to paleoenvironmental studies owing to their fractionation in different depositional environments. In order to investigate the environmental controls on thrombolitic mesostructures, we present the REY concentrations and patterns of four types of mesostructures of the Miaolingian (Cambrian) thrombolites in the Changhia Formation at the Jiulongshan section, Shandong Province, China. The REY compositions of those thrombolites show two distinctive groups: (1) light REY depleted patterns with negative Ce anomalies in spotted (SM) and layered mesostructures (LM) of thrombolites; and (2) flat patterns with weak Ce anomalies in dendritic (DM) and meshed mesostructures (MM) of thrombolites. Controlling factors analysis reveals that terrigenous detritus inputs have stronger influence on REY in SM and LM. In contrast, early diagenetic porewaters from underlying sediments have more serious impacts on REY concentrations and patterns in DM and MM. Our results clearly indicate that SM and LM were formed under oxic marine settings with minor terrigenous inputs, whereas DM and MM formed under suboxic marine settings suffered from early diagenetic porewater from underlying sediments. This new geochemical evidence suggests that thrombolitic mesostructures were strongly influenced by paleoenvironment, and REY of thrombolites with controlling factors analysis can be utilized as effective proxies for paleoenvironments.     

Analysis of several biomechanical models for the simulation of lamb liver behaviour using similarity coefficients from medical image

In this study, six biomechanical models for simulating lamb liver behaviour are presented. They are validated using similarity coefficients from Medical Image on reconstructed volumes from computerised tomography images. In particular, the Jaccard and Hausdorff coefficients are used. Loads of 20 and 40 g are applied to the livers and their deformation is simulated by means of the finite element method. The models used are a linear elastic model, a neo-Hookean model, a Mooney–Rivlin model, an Ogden model, a linear viscoelastic model and a viscohyperelastic model. The model that provided a behaviour that is closest to reality was the viscohyperelastic model, where the hyperelastic part was modelled with an Ogden model.     

Thick Film Polymer Solar Cells Based on Naphtho[1,2‐c:5,6‐c]bis[1,2,5]thiadiazole Conjugated Polymers with Efficiency over 11%

Two novel narrow bandgap π‐conjugated polymers based on naphtho[1,2‐c:5,6‐c′]bis([1,2,5]thiadiazole) (NT) unit are developed, which contain the thiophene or benzodithiophene flanked with alkylthiophene as the electron‐donating segment. Both copolymers exhibit strong aggregations both in solution and as thin films. The resulting copolymers with higher molecular weight show higher photovoltaic performance by virtue of the enhanced short‐circuit current densities and fill factors, which can be attributed to their higher absorptivity and formation of more favorable film morphologies. Polymer solar cells (PSCs) fabricated with the copolymer PNTT achieve remarkable power conversion efficiencies (PCEs) > 11% based on both conventional and inverted structures at the photoactive layer thickness of 280 nm, which is the highest value so far observed from NT‐based copolymers. Of particular interest is that the device performances are insensitive to the thickness of the photoactive layer, for which the PCEs > 10% can be achieved with film thickness ranging from 150 to 660 nm, and the PCE remains >9% at the thickness over 1 µm. These findings demonstrate that these NT‐based copolymers can be promising candidates for the construction of thick film PSCs toward low‐cost roll‐to‐roll processing technology.     

Protein-based block copolymers

Advances in genetic engineering have led to the synthesis of protein-based block copolymers with control of chemistry and molecular weight, resulting in unique physical and biological properties. The benefits from incorporating peptide blocks into copolymer designs arise from the fundamental properties of proteins to adopt ordered conformations and to undergo self-assembly, providing control over structure formation at various length scales when compared to conventional block copolymers. This review covers the synthesis, structure, assembly, properties, and applications of protein-based block copolymers.     

Mechanics of cranial sutures during simulated cyclic loading

Previous computational and experimental analyses revealed that cranial sutures, fibrous joints between the bones, can reduce the strain experienced by the surrounding skull bones during mastication. This damping effect reflects the importance of including sutures in finite element (FE) analyses of the skull. Using the FE method, the behaviour of three suture morphologies of increasing complexity (butt-ended, moderate interdigitated, and complex interdigitated) during static loading was recently investigated, and the sutures were assumed to have linear elastic properties. In the current study, viscoelastic properties, derived from published experimental results of the nasofrontal suture of young pigs (Sus scrofa), are applied to the three idealised bone-suture models. The effects of suture viscoelasticity on the stress, strain, and strain energy in the models were computed for three different frequencies (corresponding to periods of 1, 10, and 100s) and compared to the results of a static, linear elastic analysis. The range of applied frequencies broadly represents different physiological activities, with the highest frequency simulating mastication and the lowest frequency simulating growth and pressure of the surrounding tissues. Comparing across all three suture morphologies, strain energy and strain in the suture decreased with the increase in suture complexity. For each suture model, the magnitude of strain decreased with an increase in frequency, and the magnitudes were similar for both the elastic and 1s frequency analyses. In addition, a viscous response is less apparent in the higher frequency analyses, indicating that viscous properties are less important to the behaviour of the suture during those analyses. The FE results suggest that implementation of viscoelastic properties may not be necessary for computational studies of skull behaviour during masticatory loading but instead might be more relevant for studies examining lower frequency physiological activities.     

Glucagon Fibril Polymorphism Reflects Differences in Protofilament Backbone Structure

Amyloid fibrils formed by the 29-residue peptide hormone glucagon at different concentrations have strikingly different morphologies when observed by transmission electron microscopy. Fibrils formed at low concentration (0.25 mg/mL) consist of two or more protofilaments with a regular twist, while fibrils at high concentration (8 mg/mL) consist of two straight protofilaments. Here, we explore the structural differences underlying glucagon polymorphism using proteolytic degradation, linear and circular dichroism, Fourier transform infrared spectroscopy (FTIR), and X-ray fiber diffraction. Morphological differences are perpetuated at all structural levels, indicating that the two fibril classes differ in terms of protofilament backbone regions, secondary structure, chromophore alignment along the fibril axis, and fibril superstructure. Straight fibrils show a conventional β-sheet-rich far-UV circular dichroism spectrum whereas that of twisted fibrils is dominated by contributions from β-turns. Fourier transform infrared spectroscopy confirms this and also indicates a more dense backbone with weaker hydrogen bonding for the twisted morphology. According to linear dichroism, the secondary structural elements and the aromatic side chains in the straight fibrils are more highly ordered with respect to the alignment axis than the twisted fibrils. A series of highly periodical reflections in the diffractogram of the straight fibrils can be fitted to the diffraction pattern expected from a cylinder. Thus, the highly integrated structural organization in the straight fibril leads to a compact and highly uniform fibril with a well-defined edge. Prolonged proteolytic digestion confirmed that the straight fibrils are very compact and stable, while parts of the twisted fibril backbone are much more readily degraded. Differences in the digest patterns of the two morphologies correlate with predictions from two algorithms, suggesting that the polymorphism is inherent in the glucagon sequence. Glucagon provides a striking illustration of how the same short sequence can be folded into two remarkably different fibrillar structures.     

Chromatin models. Thermal denaturation studies of (Lysx, Leuy)n-and (Lys)n(Leu)m-DNA complexes.

The structural transitions of (Lysx, Leuy)n-DNA and (Lysx)n(Leuy)m-DNA complexes have been studied by thermal denaturation utilizing simultaneous absorption and circular dichroism (CD) measurements [R. Mandel and G.D. Fasman (1974), Biochem. Biophys. Res. Commun. 59, 672]. These complexes are used as models for nucleohistones. At amino acid/nucleotide ratios r less than 1, the copolymers bind to DNA in a ratio of one amino acid residue per nucleotide, and such binding stabilizes the DNA double helix against thermal denaturation relative to the unbound regions. The leucine residues in the copolymers stabilize the bound portion of the complex against thermal denaturation but to a lesser degree than does poly(L-lysine). This study confirms the hypothesis that absorption melting profiles reflect only the change in secondary structure (helix-coil transition) of DNA. It was found that, in the absence of a higher ordered structure (condensed), the CD melting profile also reflects this same conformational transition, and the melting temperatures, Tm, in CD are equal to those in absorption. However, when a higher ordered structure (tertiary) exists in the complex, then the CD melting profile will be dominated by the structural transitions related to the melting of the higher ordered asymmetric structure in the condensed state, followed by the melting of the secondary structure. Under such circumstances, the Tm obtained from absorption may be slightly different from that of the CD, since only the secondary structural changes are being reflected in absorption. The relevance of these studies to the structure of chromatin is discussed.     

Effect of Immobilization on the Kinetic and Stability Properties of O-Acetyl-L-Serine Sulfhydrylase from: Chlamydomonas reinhardtii

The O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) from Chlamydomonas reinhardtii has been immobilized either by ionic binding to DEAE-cellulose or by covalent bonding to alkylamine silica and to vinyl acetate-divinylethylene urea copolymers. The immobilized enzyme had improved stability and showed sigmoidal kinetic behaviour with respect to O-acetyl-L-serine, but without major alterations in the corresponding apparent Km value or in the inhibitory effects of this substrate observed with the enzyme in solution. In addition, significant changes in optimum pH and reaction temperature for O-acetyl-L-serine sulfhydrylase activity were observed.     

Synthesis and properties of horseradish peroxidase copolymers

Conditions for copolymerization of native and sodium periodate-oxidized horseradish peroxidase (HTP; EC 1.11.1.7) have been optimized. Copolymerization products have been characterized electrophoretically, spectrally, and kinetically. Copolymers containing 2-3, 4, 5-7, and 9-10 molecules of the enzyme were found among the products of polymerization. The copolymers had lower values of D403/D280 than HRP. The copolymers had more ordered structures than the original HRP. Comparison of the thermal stability and kinetic characteristics of the fractions differing in the ratio of copolymers to the monomeric enzyme demonstrated that the polymeric products were more stable than HRP (in terms of resistance to high temperature or inhibitory effects of H202), but their kinetic activity was, on the whole, lower than that of the original enzyme.     

Molecular dynamics study of polyethylene chain non-isothermal crystallisation: effects of chain length and branch structure

The molecular dynamics simulations in this work were aimed to provide a molecular insight into chain structure effects on non-isothermal crystallisation of polyethylene (PE) chains. The crystallisation behaviours were influenced by chain length and cooling rate in linear PE chain crystallisation: C100 and C150 were unable to fold into crystals. From C1000 to C3000, crystallisation abilities became stronger as chain length increased. From C5000 to C14000, chain length had no influence on crystallisation abilities. Final morphologies changed from rotator phase to single crystal domain, and to multi crystal domains as chain length increased. The formation of multi crystal domains with longer chain was easier than with the shorter chain in identical conditions. Branch content influenced not only the crystallisation kinetics but also final morphologies in non-isothermal crystallisation. The branches were defective in nucleation process, which was reflected in the crystal growth process. Crystallisation temperature, rate and crystallinity decreased, and the morphologies became disordered as branch content increased. Changes of final morphologies from single crystal domain to multi crystal domains were found under the influence of branch content and cooling rate. Trans-rich phenomenon was observed, and the trans-state population increment was prior to crystallinity increment. Crystallisation processes began at different crystallisation temperature when the trans-state populations reached a critical value which was independent of branch content.     

Mapping DNA by stochastic relaxation: schedule for optimal annealing.

The analysis of the various cooling schedules for the simulated annealing algorithm is made towards the restriction map construction. Algorithm behaviour under control of three different cost functions is considered and the discrete cost function is found to handle successfully experimental data with realistic error sizes. A program using this function has been derived from the algorithm to construct linear and circular DNA maps.     

Characterization of the spontaneously forming hydrogels composed of water-soluble phospholipid polymers

Spontaneously forming hydrogels composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymers, poly(MPC-co-methacrylic acid) (PMA), and poly(MPC-co-n-butyl methacrylate) (PMB) were examined. The MPC copolymer hydrogel was observed to have a spontaneous gelation property. To determine the properties of the hydrogels and why the gelation takes place, we have studied the properties of the hydrogels by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC). The morphologies of the hydrogels were spongelike with a homogeneous structure. By XPS analysis in terms of the molecular distributions in the hydrogels, it was observed that a stabilization time was required for the hydrogel to undergo chain rearrangement. DSC thermograms of the hydrogels were different from their components, PMA and PMB. For the hydrogel, a crystallization peak around -30 degrees C was observed. This result indicated that some ordered structures existed in the hydrogels. To determine the role of the MPC groups, aqueous solutions of poly(methacrylic acid) (PMAc) and PMB were mixed. The mixture of PMAc-PMB turned into a sol state, and the sol state remained for a week. When the mixture was cooled, a very weak hydrogel was prepared. This result suggested that the MPC groups were the dominant unit for spontaneously forming the hydrogels.     

Molecular dynamics simulation study on the high-pressure behaviour of an AK16 peptide

While most proteins unfold under high-pressure conditions, some high-pressure experiments suggest that an AK16 peptide forms more helical structures. In order to understand this abnormality, molecular dynamics simulations with the simulated tempering method for the isobaric–isothermal ensemble were performed in a wide pressure range from 0.1 MPa to 1.4 GPa. It was found that the fraction of the folded state decreases once and increases after that with increasing pressure. The partial molar volume change from the folded state to unfolded state increases monotonically from a negative value to a positive value with pressure. The behaviour under high-pressure conditions is consistent with the experimental results. The radius of gyration of highly helical structures decreases with increasing pressure. Moreover, interatomic distances of AK16 become shorter at high pressure than at low pressure. These behaviours indicate that the helical structures are squeezed by high pressure.     

Great apes' risk-taking strategies in a decision making task

We investigate decision-making behaviour in all four non-human great ape species. Apes chose between a safe and a risky option across trials of varying expected values. All species chose the safe option more often with decreasing probability of success. While all species were risk-seeking, orangutans and chimpanzees chose the risky option more often than gorillas and bonobos. Hence all four species' preferences were ordered in a manner consistent with normative dictates of expected value, but varied predictably in their willingness to take risks.