Morphologies Of Assemblies Research Articles

3D-measurement of particles and particulate assemblies - A review of the paradigm shift in describing anisotropic particles

The goal of seeking advanced solutions to the descriptions of particle shape, packing and tomographic measurement were key areas promoted by Professor Reg Davies. In this paper we review and reflect on the revolution that has taken place over the last 30 years in our ability to describe and measure particle shape going beyond simple shape factors to their real morphologies of complex particles and particulate assemblies. The paper presents a comprehensive review of how shape has been described and some critical analyses in the form of extended tabulations. We show how digital approaches to particle descriptions can be used to predict the properties of particles and assemblies and their use in simulations of particle processing. We note the current status and prospects for the continued development of microtomographic systems to enable the measurement of particle shape in 3D and also the 3D imaging of complex particulate structures to enable property and processing predictions. Examples of these developments and critical appraisal of their utility will be given.

Chain Architecture as an Orthogonal Parameter to Tune Morphologies of Polymer Assemblies: Efficient Synthesis and Self-Assembly of Linear-Branched Block Copolymers via RAFT Dispersion Polymerization

Chain Architecture as an Orthogonal Parameter to Tune Morphologies of Polymer Assemblies: Efficient Synthesis and Self-Assembly of Linear-Branched Block Copolymers via RAFT Dispersion Polymerization

Comparative analysis of planar and capsule morphologies of bacterial microcompartment shell protein assemblies

Comparative analysis of planar and capsule morphologies of bacterial microcompartment shell protein assemblies

A Subtle Change in the Flexible Achiral Spacer Does Matter in Supramolecular Chirality: Two‐Fold Odd‐Even Effect in Polymer Assemblies

AbstractPrecise control over the chirality and morphologies of polymer assemblies, a remaining challenge for both chemists and materials scientists, is receiving ever‐increasing attention in the recent years. Herein, we report the subtle manipulation of the achiral spacers from the chiral stereocenter to the azobenzene (Azo) unit, of which the chiroptical consistency or chiroptical inversion of self‐assemblies could be successfully controlled and present “two‐fold” odd‐even effect. Furthermore, morphological transitions from 0D spherical micelles, 1D worms, and nanowires to 3D vesicles, spindle‐ and dumbbell‐shaped vesicles were also unexpectedly found to exhibit odd‐even correlations. These observations were collectively elucidated by mesomorphic properties, stacking modes, chiroptical dynamics, and stimuli‐responsive behaviors. Negligible modifications to the spacer structures can enable remarkable modulation of supramolecular chirality and anisotropic topologies in polymer assemblies, which is of great significance for the design of complex chiral functional polymers.

A Subtle Change in the Flexible Achiral Spacer Does Matter in Supramolecular Chirality: Two-Fold Odd-Even Effect in Polymer Assemblies.

Precise control over the chirality and morphologies of polymer assemblies, a remaining challenge for both chemists and materials scientists, is receiving ever-increasing attention in the recent years. Herein, we report the subtle manipulation of the achiral spacers from the chiral stereocenter to the azobenzene (Azo) unit, of which the chiroptical consistency or chiroptical inversion of self-assemblies could be successfully controlled and present "two-fold" odd-even effect. Furthermore, morphological transitions from 0D spherical micelles, 1D worms, and nanowires to 3D vesicles, spindle- and dumbbell-shaped vesicles were also unexpectedly found to exhibit odd-even correlations. These observations were collectively elucidated by mesomorphic properties, stacking modes, chiroptical dynamics, and stimuli-responsive behaviors. Negligible modifications to the spacer structures can enable remarkable modulation of supramolecular chirality and anisotropic topologies in polymer assemblies, which is of great significance for the design of complex chiral functional polymers.

Designing sequence-defined peptoids for fibrillar self-assembly and silicification

In the biological environment, mineral crystals exquisitely controlled by biomacromolecules often show intricate hierarchical structures and superior mechanical properties. Among these biominerals, spicules, hybrid silica/protein superstructures serving as skeletal elements in demosponges, represent an excellent example for motivating the synthesis of silica materials. Herein, by designing sequence-defined peptoids containing side chains with a strong binding to silica, we demonstrated that self-assembly of these peptoids into fiber structures enables the mimicking of both biocatalytic and templating functions of silicatein filaments for the formation of silica fibers at near-neutral pH and ambient temperature. We further showed that the presence of amino groups is significant for the nucleation of silica on self-assembled peptoid nanofibers. Molecular dynamics simulation further confirmed that having silica-binding of amino side chains is critical for self-assembled peptoid fibers in triggering silica formation. We demonstrated that tuning inter-peptoid interactions by varying carboxyl and amino side chains significantly influences the assembly kinetics and final morphologies of peptoid assemblies as scaffolds for directing silica mineralization to form silica spheres, fibers, and sheets. The formation of silica shell on peptoid fibers increased the mechanical property of peptoid hydrogel materials by nearly 1000-fold, highlighting the great potential of using silicification to enhance the mechanical property of hydrogel materials for applications including tissue engineering. Since peptoids are highly robust and programmable, we expect that self-assembly of peptoids containing solid-binding side chains into hierarchical materials opens new opportunities in the design and synthesis of highly tunable scaffolds that direct the formation of composite nanomaterials.

Polymerization-induced self-assembly of side-chain liquid crystalline copolymers by dissipative particle dynamics simulation

Side-chain liquid crystal copolymers can self-assemble into dispersed assemblies effectively with the polymerization-induced self-assembly (PISA) technique. However, the synergy of polymerization and self-assembly result in undefined self-assembly behavior and polymerization kinetics. We explored the PISA behavior of side-chain liquid crystal copolymers in selective solvents by combining dissipative particle dynamics simulation and a probability-based reaction model. It was found that the morphologies of assemblies depend on the PISA time, copolymer concentrations, and various structural parameters. The polymerization exhibits three stages with different reaction constants during the PISA, achieving low polydispersity of the produced copolymers. The comparison with experiments demonstrated that the simulation could capture the essential characteristics of PISA. This study can help fundamentally understand the PISA behavior of side-chain liquid crystal copolymers.

Exploring the topological effect of linear and cyclic macroCTAs during polymerization-induced self-assembly (PISA)

Polymerization-induced self-assembly (PISA) is a robust strategy for the syntheses of block copolymer nano-objects with various morphologies. Although PISA has been extensively studied, the use of cyclic macromolecular chain transfer agents (macroCTAs) as the hydrophilic block has not been reported. We explored the effects of macroCTA topology on the polymerization kinetics and morphologies of block copolymer assemblies during reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization. To this end, linear and cyclic poly (ethylene oxide) (PEO) with 4-(4-cyanopentanoic acid) dithiobenzoate (CPADB) groups were synthesized and used as CTAs to mediate the RAFT polymerization of benzyl methacrylate (BzMA) and 2,3,4,5,6-pentafluorostyrene (PFSt) under PISA formulation. Interestingly, the nucleation period of the linear PEO is slightly shorter than that of its cyclic analog, and the cyclic hydrophilic segment leads to a delayed morphological transition during PISA.

Morphology Transformation of Foldamer Assemblies Triggered by Single Oxygen Atom on Critical Residue Switch (Small 36/2021)

Morphology Transformation The molecular-level information installed in a given foldamer is coherently transmitted to the morphologies of the foldamer morphology transformation assemblies at the micrometer scale. In article number 2102525, Hee-Seung Lee and co-workers demonstrate a stepwise morphology transformation, from the molar-tooth shape to gels via rectangular and truncated tilted prism shapes, to create biofunctional assemblies with nonspherical shapes.

Gelation of a Pentapeptide in Alcohols.

Properties of solvents such as polarity and H-bond-forming ability are critical for the formation of an organogel and have a significant impact on the gel behavior, as solvents are the majority of organogel systems. However, so far, there is still a lack of systematic studies regarding the effects of molecular structures of solvents on the characteristics of organogels. Motivated by revealing such a relationship, in this paper, we studied the morphologies of assemblies, gelation behaviors, and secondary structures of a pentapeptide termed EAF-5 in a wide variety of alcohols. The side chains and lengths of carbon chains of the solvent molecules were found to play a critical role in the self-assembly and gelation of EAF-5. EAF-5 was capable of self-assembling into fibers and entangling into a network in alcohols including ethanol, propanol, butanol, n-pentanol, and n-hexanol, which further immobilized the corresponding alcohols to form gels. In these organogels, increasing β-sheet secondary structures of the peptides were formed by introducing side chains and extending the length of primary alcohol molecules. We hypothesized that alcohol molecules with extended lengths and side chains reduced the gelator-solvent interactions and promoted the gelator-gelator interactions, resulting in the self-assembly of EAF-5 into fibril structures and development of gels. These findings provide a new sight into the interactions between gelators and solvents and are helpful for designing peptide-based organogelators.

Gas-Induced Phase Transition of Dipeptide Supramolecular Assembly

Gas-Induced Phase Transition of Dipeptide Supramolecular Assembly

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...

R-RAFT or Z-RAFT? Well-Defined Star Block Copolymer Nano-Objects Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) has served as a versatile platform for the large-scale preparation of block copolymer nano-objects with a diverse set of morphologies. However, almost all PISA formulations are focused on the syntheses of linear block copolymers rather than star block copolymers. Owing to the asymmetrical structure of the RAFT agent, herein, we report a direct comparison between Z-RAFT (the nonfragmenting group attached to the core) and R-RAFT (the fragmenting group attached to the core) strategies for preparing well-defined star block copolymer nano-objects via RAFT-mediated PISA. We showed that the Z-RAFT strategy is a more suitable strategy for the preparation of star block copolymer nano-objects without compromising the control over the molecular weight and morphology. A binary mixture of Z-type and R-type tetrafunctional macro-RAFT agents was used to control the morphologies of star block copolymer assemblies. The effect of numbers of the RAFT group on polymerization kinetics and morphologies of block copolymer nano-objects was also investigated in detail. Finally, (ABC)4 four-arm star triblock copolymer vesicles were prepared by seeded RAFT dispersion polymerization of solvophobic and solvophilic monomers using (AB)4 four-arm star diblock copolymer vesicles as seeds. This research not only expands the scope for preparing well-defined star block copolymer nano-objects but also provides important insights into the effect of the polymer architecture on RAFT-mediated PISA.

Synthesis and properties of penta-responsive ABC star quaterpolymers

The controlled synthesis of smart multicomponent copolymers can afford new insight into structure-property correlations. Given the lack of CO2 and O2 dual-gas-responsive star polymers, this study is focused on the facile synthesis and properties of multiresponsive ABC star quaterpolymers. The “core-first” strategy was adopted to generate P(ATL-co-NIPAM)-arm-PCL-arm-PDPA stars, followed by tandem amine-thiol-ene conjugation to construct the desired stars bearing O2-/oxidation-responsive and hydrogen bond-switchable Y junctions. Upon composition change, pH switching, gas bubbling and oxidation, the copolymer solution tended to show different cloud points. Furthermore, the sizes and morphologies of copolymer assemblies were strongly dependent on chemical composition and thermal, pH, CO2, O2 and oxidative stimuli, and abundant morphologies such as large compound micelles, hyperbranched micelles, disk-like micelles, spindle-like micelles, ellipsoidal micelles, and multicompartment vesicles could be formed under distinct conditions. Our study affords a promising yet straightforward approach to construct multicomponent miktoarm star polymer, and the composition-/stimuli-dependent thermoresponsive and aggregation behaviors of these polymers pave the way for multipurpose applications. By virtue of “core first” method, ABC star quaterpolymers were controllably synthesized by combination of controlled polymerization and thiolactone chemistry. The miktoarm stars were responsive to temperature, pH, CO2, O2 and oxidation, and thus the phase transition temperature, size and morphology of copolymer assemblies could be efficiently tuned via adopting a single stimulus or combined stimuli.

Nonionic Amphiphilic Linear Dendritic Block Copolymers. Solvent-Induced Self-Assembly and Morphology Tuning

In this article, we report the solution self-assembly of a series of amphiphilic linear–dendritic block copolymers (LDBCs), which are composed of hydrophilic dendritic poly(ether-ester), PEE, blocks based on 2,2-bis(hydroxymethyl)propionic acid and hydrophobic linear poly(styrene), PSt, blocks. The investigated LDBCs have narrow dispersity with three PEE generations (1–3) and a broad range of PSt molecular masses and are produced by dendron-initiated atom transfer radical polymerization of styrene followed by deprotection of the peripheral dendron hydroxyl groups. The solution self-assembly of the copolymers is performed by slowly adding water to the polymer solution in tetrahydrofuran (THF) as the common solvent for both blocks of the copolymers. The morphologies of the supramolecular assemblies are preserved either by diluting their dispersion by excess of water or by THF evaporation. It is found that the micellar morphology (sphere, wormlike, and/or vesicle) depends on the hydrophilic block fraction (F...

Tau Inclusions in Alzheimer's, Chronic Traumatic Encephalopathy and Pick's Disease. A Speculation on How Differences in Backbone Polarization Underlie Divergent Pathways of Tau Aggregation.

Tau-related dementias appear to involve specific to each disease aggregation pathways and morphologies of filamentous tau assemblies. To understand etiology of these differences, here we elucidate molecular mechanism of formation of tau PHFs based on the PMO theory of misfolding and aggregation of pleiomorphic proteins associated with neurodegenerative diseases. In this model, fibrillization of tau is initiated by the coupled binding and folding of the MTB domains that yields antiparallel homodimers, in analogy to folding of split inteins. The free energy of binding is minimized when the antiparallel alignment brings about backbone-backbone H-bonding between the MTBD segments of similar “strand” propensities. To assess these propensities, a function of the NMR shielding tensors of the Cα atoms is introduced as the folding potential function FPi; the Cα tensors are obtained by the quantum mechanical modeling of protein secondary structure (GIAO//B3LYP/D95**). The calculated FPi plots show that the “strand” propensities of the MBTD segments, and hence the homodimer's register, can be affected by the relatively small changes in the environment's pH, as a result of protonation of MBTD's conserved histidines. The assembly of the antiparallel tau dimers into granular aggregates and their subsequent conversion into the parallel cross-β structure of paired helical filaments is expected to follow the same path as the previously described fibrillization of Aβ. Consequently, the core structure of the nascent tau fibril is determined by the register of the tau homodimer. This model accounts for the reported differences in (i) fibril-core structure of in vivo and in vitro filaments, (ii) cross-seeding of isoforms, (iii) effects of reducing/non-reducing conditions, (iv) effects of PHF6 mutations, and (v) homologs' aggregation properties. The proposed model also suggests that in contrast to Alzheimer's and chronic traumatic encephalopathy disease, the assembly of tau prions in Pick's disease would be facilitated by a moderate drop in pH that accompanies e.g., transit in the endosomal system, inflammation response or an ischemic injury.

Accelerated Recombination of Lophyl Radicals with Self-Assembled Amphiphilic Lophine Dimer.

This report focuses on acceleration of the recombination of lophyl radicals with a lophine dimer derivative by forming molecular assemblies. A newly synthesized cationic amphiphilic lophine dimer formed molecular assemblies with a diameter of ~220 nm in an aqueous medium. When the molecular assemblies were formed, the rate of recombination of lophyl radicals, produced by ultraviolet light irradiation, was accelerated 50,000-fold compared to that in an organic solvent. The rate enhancement is likely derived from the short diffusion distance of the lophyl radicals in the molecular assemblies. These results revealed that accumulation of the lophine dimers via self-assembly remarkably accelerated the recombination of lophyl radicals. This novel photoisomerization system could rapidly control the interfacial properties or morphologies of molecular assemblies when used for applications, such as efficient delivery of drugs or active components.

Development of self-assembled phytosterol based nanoassemblies as vehicles for enhanced uptake of doxorubicin to HeLa cells

Nanoscale supramolecular systems have been increasingly gaining importance as drug release vehicles due to their ability to target tumor cells. In this work, we have developed a new class of nanoassemblies derived from the phytosterol 24-EpiBrassinolide (EpiB) for the development of nanocarriers for the anticancer drug Doxorubicin (DOX). EpiB is a biocompatible cholesterol mimic, and has inherent apoptotic properties toward cancer cells. Thus, by encapsulating DOX within a nanocarrier with innate anticancer ability we have developed a targeting system that can enhance the uptake and efficacy of DOX in tumor cells. The nanocarriers were formed by self-assembly of EpiB. The morphologies of assemblies formed were dependent upon the concentration of EpiB used. While at low concentrations, spherical nanoassemblies were formed, at higher concentration, lamellar aggregates with birefringence properties were observed. Our results indicated that the drug loaded nanocarriers showed diffusion controlled release of the drug, and demonstrated antiproliferative effects, cellular uptake and were apoptotic against HeLa cervical cancer cells. Furthermore, EpiB loaded DOX enhanced both apoptosis and uptake into the cell's nuclei. These supramolecular assemblies may have potential applications for enhancing efficacy of chemotherapeutic drugs through passive targeting.

UV-Responsive Behavior of Multistate and Multiscale Self-Assemblies Constructed by Gemini Surfactant 12-3-12·2Br- and trans- o-Methoxy-cinnamate.

Photoresponsive systems with adjustable self-assembly morphologies and tunable rheological properties have aroused widespread concern of researchers in recent years because of their prospect applications in controlled release, microfluidics, sensors, and so forth. In this paper, we combine a cationic Gemini surfactant 12-3-12·2Br- and trans-2-methoxy-cinnamate ( trans-OMCA) together to create a representative UV-responsive self-assembly system. The system displays abundant self-assembly behaviors, and the self-assemblies with different states and different scales including wormlike micelles, vesicles, and lyotropic liquid crystals (LCs) as well as an aqueous two-phase system (ATPS) are observed even at lower surfactant concentration. The UV-responsive behavior of the formed self-assemblies is investigated systematically. The results have shown that the photoisomerization of OMCA from trans form to cis form under UV light irradiation alters the hydrophobicity and steric hindrance effect of OMCA and thus affects the molecular packing at the micellar interface and further leads to the transformation of assembly morphologies. The long wormlike micelles can gradually transform into much shorter rodlike micelles under UV irradiation and companied by the decrease of solution viscosity by 2 orders of magnitude. In addition, the vesicles can evolve into multistate self-assembly structures including the ATPS, wormlike micelles, rod-like micelles, and small spherical micelles depending on the UV irradiation time. The ATPS and its adjacent anisotropic LC phase can respectively combine into a single phase and separate into ATPS under UV irradiation. The morphologies of assemblies in the 12-3-12·2Br-/ trans-OMCA mixed system can be tailored by adjusting the system composition and duration of UV light irradiation on purpose. The photoresponsive system with abundant self-assembly behaviors and tunable rheological properties has wide application prospect in numerous fields such as drug delivery, materials science, smart fluids, and so forth, and the macroscopic phase separation and combination provide novel strategies for effective separation and purification of certain substances.

Effects of constant load operations on platinum bands formation and cathode degradation in high-temperature polymer electrolyte fuel cells

In this paper, Pt bands and cathode degradation are investigated in polybenzimidazole (PBI) membrane-based high-temperature polymer electrolyte fuel cells (HT-PEFC). A focused ion beam/scanning electron microscopy (FIB/SEM) system was used to characterize the cross-section morphologies of membrane electrode assemblies (MEA). A Pt band is observed in the FIB/SEM images of the MEA activated by a common break-in procedure (at 200 mA cm−2 for 70 h). Then, an identical MEA was subjected to an aging process that included static holding at 200 mA cm−2 for 100 h and an open circuit voltage (OCV) operation for another 100 h. FIB/SEM images of the aged MEA show that the band formed during the break-in procedure is strengthened. Moreover, a second Pt band is observed closer to the membrane/cathode interface, which is due to the increase of hydrogen crossover caused by membrane thinning during the OCV hold test. In situ electrochemical measurements show that the cell’s performance loss due to the formation of the Pt band during cell operation at 200 mA cm−2 is negligible. The decrease of cell performance is mainly attributed to the loss of electrochemically active surface area and membrane degradation during the OCV hold test.