Core-shell structured nanoassemblies based on β-cyclodextrin containing block copolymer and poly(β-benzyl L-aspartate) via host-guest complexation

Double hydrophilic copolymers (PEG-b-PCDs) with one PEG block and another block containing β-cyclodextrin (β-CD) units were synthesized by macromolecular substitution reaction. Via a dialysis procedure, complex assemblies with a core-shell structure were prepared using PEG-b-PCDs in the presence of a hydrophobic homopolymer poly(β-benzyl l-aspartate) (PBLA). The hydrophobic PBLA resided preferably in the cores of assemblies, while the extending PEG chains acted as the outer shell. Host-guest interaction between β-CD and hydrophobic benzyl group was found to mediate the formation of the assemblies, where PEG-b-PCD and PBLA served as the host and guest macromolecules, respectively. The particle size of the assemblies could be modulated by the composition of the host PEG-b-PCD copolymer. The molecular weight of the guest polymer also had a significant effect on the size of the assemblies. The assemblies prepared from the host and guest polymer pair were stable during a long-term storage. These assemblies could also be successfully reconstituted after freeze-drying. The assemblies may therefore be used as novel nanocarriers for the delivery of hydrophobic drugs.     

The performance of wood and tile roofing assemblies exposed to continuous firebrand assault

The performance of tile roofing assemblies as well as untreated cedar shake roofing assemblies exposed to continuous firebrand showers were compared. Specifically, experiments were conducted for two types of concrete tile roofing assemblies (flat and profiled), one type of terracotta tile roofing assembly (flat) and an untreated (without any fire retardant) cedar shake roofing assembly. The design of the roofing assemblies was based on construction guidelines in the USA. The duration of the firebrand flux was fixed at 20 min, and the wind speed was varied from 6 m/s to 9 m/s. These wind speeds were chosen to be able to compare roofing assembly performance to similar assemblies exposed to a batch‐feed firebrand generator which had limited duration of firebrand exposure (6 min). The average firebrand mass flux that arrived at the surface of the roofing assemblies was 0.3 g/m²s Results indicated that for the untreated cedar shake assemblies, ignition occurred easily from the firebrand assault, and this type of roofing assembly generated their own firebrands after ignition. To attempt to quantify the degree of penetration, the number of firebrands that penetrated the tile roofing assemblies, and deposited onto the underlayment/counter‐batten system was counted as function of wind speed for each assembly. Firebrand penetration was observed, even for the flat tile assemblies. It is believed that these are the first‐ever experiments described in the peer‐reviewed literature to expose wood and tile roofing experiments to continuous wind‐driven firebrand showers. Copyright © 2016 John Wiley & Sons, Ltd.     

Permeability characteristics of multilayer fiber reinforcements. Part I: Experimental observations

The fluid permeability characteristics of homogeneous and heterogeneous multilayer fabric assemblies were determined by a radial in-plane flow technique. The permeabilities and flow anisotropies of multilayer assemblies generally differ from those of the constituent layers. In homogeneous assemblies, the creation of interlaminar pores can increase the effective in-plane permeability. In heterogeneous assemblies, the effective in-plane permeabilities and anisotropies are governed by the high permeability layers or directions. A transverse flow mechanism contributes to filling the low permeability layers and keeping the fluid front macroscopically uniform.     

防火聚四氟乙烯软管组件的设计

设计防火聚四氟乙烯软管组件。四氟乙烯内管由两部分组成,内层掺用一定比例的导电炭黑,而外层则为纯四氟乙烯材料;金属接头采用倒刺式与多槽式复合结构;防火设计采用聚四氟乙烯软管外覆防火硅橡胶套管的形式;扣压模具设计为八瓣式。通过优化设计,提升了软管组件耐压、耐高低温、防静电、防火等性能,能够满足不同系统的使用需求。     

Dynamic Continuum of Molecular Assemblies for Controlling Cell Fates

Biological systems have evolved to create a structural and dynamic continuum of bio-macromolecular assemblies for the purpose of optimizing the system′s functions. The formation of these dynamic higher-order assemblies is precisely controlled by biological cues. However, controlling the self-assembly of synthetic molecules spatiotemporally in or on live cells is still a big challenge, especially for performing functions. This concept article introduces the use of in situ reactions as a spatiotemporal control to form assemblies of small molecules that induce cell morphogenesis or apoptosis. After briefly introducing a representative example of a natural dynamic continuum of the higher-order assemblies, we describe enzyme-instructed self-assembly (EISA) for constructing dynamic assemblies of small molecules, then discuss the use of EISA for controlling cell morphogenesis and apoptosis. Finally, we provide a brief outlook to discuss the future perspective of this exciting new research direction.     

啮合同向双螺杆挤出机中组合螺杆性能的数值研究（Ⅱ）混合特性分析

采用有限元软件POLYFLOW,对组合式啮合同向双螺杆挤出机ZSK60中不同构型的组合螺杆进行了混合分析。通过计算螺杆转过不同角度时的拟稳态流场,采用粒子示踪分析(PTA)方法,对组合螺杆中聚合物熔体的动态混合过程进行了可视化模拟;在此基础上通过对大量粒子运动轨迹的统计处理,分别采用停留时间分布、分布混合指数、分离尺度等累积混合指数表征了组合螺杆的轴向混合性能、分布混合性能以及分散混合性能。此外还研究了不同工艺条件下组合螺杆的混合特性。并将部分数值模拟结果与前人实验研究进行了对比。     

The Versatile Manipulations of Self-Assembled Proteins in Vaccine Design

Protein assemblies provide unique structural features which make them useful as carrier molecules in biomedical and chemical science. Protein assemblies can accommodate a variety of organic, inorganic and biological molecules such as small proteins and peptides and have been used in development of subunit vaccines via display parts of viral pathogens or antigens. Such subunit vaccines are much safer than traditional vaccines based on inactivated pathogens which are more likely to produce side-effects. Therefore, to tackle a pandemic and rapidly produce safer and more effective subunit vaccines based on protein assemblies, it is necessary to understand the basic structural features which drive protein self-assembly and functionalization of portions of pathogens. This review highlights recent developments and future perspectives in production of non-viral protein assemblies with essential structural features of subunit vaccines.     

Preparation and characterization of bottle‐brush polymer via host−guest self‐assembly between β‐cyclodextrin and adamantane

Supramolecular assemblies with a bottle‐brush structure are obtained by inclusion complexation between β‐cyclodextrin and adamantane. β‐cyclodextrin‐modified chitosan is synthesized via the aldimine condensation reaction between β‐cyclodextrin monoaldehyde and chitosan as the host. The guest is prepared through the esterification reaction between methoxypoly(ethylene glycol) and 1‐adamantanecarboxylic acid chloride. The supramolecular assemblies are formed through the inclusion of adamantane‐modified methoxypoly(ethylene glycol) into the β‐cyclodextrin cavity on the chitosan chain. Fourier transform infrared and ¹H NMR spectra were used to prove that the host, guest and assemblies were successfully obtained. UV?visible spectra were employed to confirm the formation of assemblies. Furthermore, the size of the particles in the assembled solution, the change before and after self‐assembly, and the effect of the addition of competitive molecules were studied by dynamic light scattering measurements. The results indicate that supramolecular assemblies have formed successfully which might be used to realize the biomimetic structure of the articular cartilage proteoglycan. © 2014 Society of Chemical Industry     

Applications of DNA-Functionalized Proteins

As an important component that constitutes all the cells and tissues of the human body, protein is involved in most of the biological processes. Inspired by natural protein systems, considerable efforts covering many discipline fields were made to design artificial protein assemblies and put them into application in recent decades. The rapid development of structural DNA nanotechnology offers significant means for protein assemblies and promotes their application. Owing to the programmability, addressability and accurate recognition ability of DNA, many protein assemblies with unprecedented structures and improved functions have been successfully fabricated, consequently creating many brand-new researching fields. In this review, we briefly introduced the DNA-based protein assemblies, and highlighted the limitations in application process and corresponding strategies in four aspects, including biological catalysis, protein detection, biomedicine treatment and other applications.     

Crystalline host-guest assemblies of steroidal and related molecules: diversity, hierarchy, and supramolecular chirality

Steroidal bile acids and over 50 of their derivatives serve as the hosts of inclusion crystals. These hosts each exhibit their own characteristic inclusion behaviors, which have been explored through more than 300 crystallographic data. The molecules with three-axial chirality combine in asymmetric fashion to form diverse assemblies, which have supramolecular properties, such as recognition and dynamics, through cooperative weak interactions. From an overview of these results, an analogy emerged: the steroidal assemblies may have hierarchical structures, such as primary, secondary, tertiary, and host-guest assemblies, similar to proteins. Accordingly, the assemblies with dimensionality bear supramolecular chirality, such as three-axial, tilt, helical, bundle, and complementary chirality. Such a concept can be extended to other organic substances, such as alkaloids and organic salts. These results move in the direction of supramolecular crystal engineering.     

Temperature/pH-induced morphological regulations of shell cross-linked graft copolymer assemblies

Shell cross-linked (SCL) assemblies are prepared from the thermally induced three-layered, onion-like micelles of graft copolymers comprising acrylic acid (AAc) and 2-methacryloylethyl acrylate (MEA) as the backbone units and poly(N-isopropylacrylamide) (PNIPAAm) and monomethoxy poly(ethylene glycol) (mPEG) as the grafts via radical polymerization of the MEA residues within the AAc-rich interfacial layers in the aqueous phase of pH 5.0 at 60 °C. The resulting nanosized SCL assemblies exhibit versatile structural regulations in a fully reversible manner in response to changes in pH and temperature. At 20 °C, SCL assemblies retain the morphology of vesicle-like hollow microspheres with pH-controlled water influx and particle size. At pH 7.0, SCL assemblies remain invariant in both vesicular structure and size irrespective of the temperature increase beyond the coil-to-globule phase transition of PNIPAAm grafts occurring primarily in a highly individual manner. When the temperature increases from 20 to 60 °C at pH 5.0, the hollow particle size is greatly reduced, accompanied by the development of hydrophobic, impermeable PNIPAAm lumens attached to the inside surfaces of the interfacial gel layers. In addition, SCL assemblies undergo a dramatic thermally induced transformation from the vesicle-like to micelle-like morphology by virtue of yielding hydrophobic PNIPAAm inner cores at pH 3.0. The thermally evolved morphology of SCL assemblies is governed by the vesicle structure in response to the effect of pH on the AAc ionization within the interfacial gel layers at ambient temperature.     

Functional molecules and assemblies in controlled environments: formation and measurements

The local environment of a functional molecule or nanoscale assembly has tremendous impact on it and thus can be used for functional control. In addition, the local environment is critical in the interface to the physical, chemical, and biological worlds beyond the assemblies that are the most common applications targeted. Functional measurements without local structural information lack key insight into both the details and the roles of the environment. This Account focuses on progress toward and challenges in the controlled assembly and measurements of functional nanostructures in well-defined environments. The study of single precise supramolecular assemblies in well-defined environments offers unique insights into both interactions and function. By designing interactions between molecules and controlling assembly conditions, we can create and place atomically precise nanostructures. The tools to test the structures targeted and to measure the function of these assemblies are just now being developed and becoming available. Advances in this field have depended on gaining access to measurements at this scale. In particular, we recognize but do not yet understand the critical role of the chemical and physical environment of the assemblies. Likewise, we are just now realizing the important role that the substrates to which the assemblies are attached play in these processes. In order to develop a predictive understanding and the ability to design and to optimize functional assemblies, we must elucidate the physical, chemical, and electronic couplings among the molecules in the assemblies and with their substrates. With a suite of atomic- and molecular-resolution analytical tools, we are able both to ascertain whether the targeted structures have been formed and to measure their function. One of the keys to our ability to determine structure and measure function has been the development and application of methods for the automated acquisition, analysis, and associations of thousands or tens of thousands of single-molecule/particle/assembly structural, dynamic, spectroscopic, and functional data points.     

A DEM study on the effective thermal conductivity of granular assemblies

A discrete element method (DEM) is developed to simulate the heat transfer in granular assemblies in vacuum with consideration of the thermal resistance of rough contact surfaces. Average heat flux is formulated by the positions and heat flow rates of particles on the boundaries of the granular assemblies. Average temperature gradient is given as a best-fit formulation, which is computed from the relative position and temperature of particles. With the thermal boundary condition imposed on the border region, the effective thermal conductivity (ETC) of granular assemblies can be calculated from the average heat flux and temperature gradient obtained from DEM simulations. Moreover, the effects of particle size, solid volume fraction and coordination number on the ETC are also investigated. Simulation results show that granular assemblies with coarse particles and under large external compression forces exhibit a better heat conduction behavior. The effects of particle size and external compression forces on the ETC are in good agreement with experiment observations.     

Performance of wood stud shear walls exposed to fire

This paper presents the results of seven full‐scale fire resistance tests conducted on load‐bearing gypsum board protected, wood stud shear wall assemblies. The experimental studies were conducted to determine the effects of placement of shear membrane and type of insulation on the fire resistance of such assemblies. Details of the results, including the temperatures and deflections measured during the fire tests, are presented. Results from the studies indicate that the placement of shear membrane and insulation type significantly influence the fire resistance of such wood stud shear wall assemblies. Copyright © 2000 Crown in the right of Canada.     

Ionic Supramolecular Assemblies

Supramolecular structures assembled via noncovalent interactions have found diverse applications in mechanical, biological, electronic, and manufacturing-related fields. Ionic interactions represent key noncovalent interactions, which can be used, for example, to create highly ordered, responsive, conductive, reversible, and/or viscoelastic supramolecular assemblies. The recent advances in the field of ionic supramolecular assemblies, including those prepared from polymers, small molecules, or a combination of the two are reviewed. The versatility and simplicity of constructing ionic supramolecular assemblies are illustrated through several examples. Finally, the outstanding issues and potential opportunities are discussed to stimulate critical discussions and encourage further discovery.     

TEMPERATURE DEPENDENCE OF POLYMER INTERACTION: RELEVANCE TO ADHESION

Acid-base interaction parameters, obtained from inverse gas chromatographic data, have been studied as function of temperature for a series of homopolymers. Acid-base functionality varies inversely with temperature, permitting the identification of a critical temperature where acid-base interaction abates, leaving dispersion forces to act at the surface. Polymer assemblies, prepared at temperatures encompassing the critical values, display a discontinuity in lap-shear bond strength. In inherently incompatible pairs, the abatement of unfavorable acid-base forces enhanced bond strength. An adverse effect was noted in assemblies containing polymers with favorable acid-base interaction. Bond strengths of assemblies joined above critical temperatures display a time-dependent reversion to equilibrium values when exposed to lower temperatures.     

Temperature dependence of polymer interaction: Relevance to adhesion

Acid-base interaction parameters, obtained from inverse gas chromatographic data, have been studied as function of temperature for a series of homopolymers. Acid-base functionality varies inversely with temperature, permitting the identification of a critical temperature where acid-base interaction abates, leaving dispersion forces to act at the surface. Polymer assemblies, prepared at temperatures encompassing the critical values, display a discontinuity in lap-shear bond strength. In inherently incompatible pairs, the abatement of unfavorable acid-base forces enhanced bond strength. An adverse effect was noted in assemblies containing polymers with favorable acid-base interaction. Bond strengths of assemblies joined above critical temperatures display a time-dependent reversion to equilibrium values when exposed to lower temperatures.     

Understanding structure ignition vulnerabilities using mock‐up sections of attached wood fencing assemblies

Firebrand production from structure combustion becomes a key factor in the magnitude of how quickly a large outdoor fire may spread. Post‐fire disaster investigations suggest that attached building components, such as wood fencing assemblies are known to be prone to ignition in these fires, and may provide pathways to structure ignition. Here, a comparison of ignition results from full‐scale fencing assembly experiments conducted using a full‐scale wind tunnel facility, to mock‐ups of full‐scale fencing assemblies using the recently developed experimental capability at the National Research Institute of Fire and Disaster (NRIFD) are discussed. In both experimental facilities, the fencing assemblies were exposed to firebrand showers using custom built continuous feed firebrand generators with size and mass distributions similar to those generated from structure combustion. Similar ignition behaviors were observed between the full‐scale fencing assemblies and the mock‐up of full‐scale fencing assemblies. Additional experiments are required for other fencing assembly types to further verify these important findings.     

Zeolite Beta nanosized assemblies

Nanosized zeolite Beta assemblies are prepared by a steam assisted conversion (SAC) method from micron-sized porous amorphous silica grains soaked in clear solutions containing the alumina source and organic template. The zeolite Beta assemblies are built of closely packed uniform nanocrystals (100 nm) and retain the size and morphological features of the primary silica grains. The crystallinity and the phase purity depend strongly on the temperature and time of SAC treatment as well as on the initial aluminum content. For comparison, colloidal zeolite Beta samples with similar Si/Al ratio were prepared by a hydrothermal treatment (HT). The Raman and NMR spectroscopic data reveal that the method of preparation (SAC or HT) does not affect the local structure of Al-rich samples, while for high-silica samples the degree of disorder is higher in the ones obtained via the SAC approach. The adsorption/desorption isotherms of zeolite Beta assemblies and colloidal Beta powders indicate the presence of both micro- and mesoporosity. The catalytic behavior of the zeolite Beta assemblies and colloidal Beta powders in pentane hydroisomerization reaction is studied.     

Thoughts and observations on fire‐endurance tests of wood‐frame assemblies protected by gypsum board

Forintek Canada Corp. participated in a series of collaborative research projects with the National Research Council Canada and other organizations to determine fire‐resistance ratings for wood‐frame assemblies used in the construction of Canadian housing and small buildings. Over the course of those studies, Forintek's scientists observed a large number of full‐scale fire‐endurance tests on walls lined on both faces with gypsum board and floor assemblies with gypsum‐board ceilings. Those observations have given Forintek's researchers unique insights into the fire performance of wood‐frame assemblies and fire‐endurance testing. Those insights are the subject of this paper. Copyright © 2002 John Wiley & Sons, Ltd.