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DOI： 10.1021/acs.macromol.3c00444

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DOI： 10.1002/marc.202200936

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

An amphiphilic diblock copolymer (PChM-PNIPAM), composed of poly(cholesteryl 6-methacryloyloxy hexanoate) (PChM) and poly(N-isopropyl acrylamide) (PNIPAM) blocks, was prepared via reversible addition-fragmentation chain transfer radical polymerization. The PChM and PNIPAM blocks exhibited liquid crystalline behavior and a lower critical solution temperature (LCST), respectively. PChM-PNIPAM formed water-soluble polymer micelles in water below the LCST because of hydrophobic interactions of the PChM blocks. The PChM and PNIPAM blocks formed the core and hydrophilic shell of the micelles, respectively. With increasing temperature, the molecular motion of the pendant cholesteryl groups increased, and a liquid crystalline phase transition occurred from an amorphous state in the core. With further increases in temperature, the PNIPAM block in the shell exhibited the LCST and dehydrated. Hydrophobic interactions of the PNIPAM shells resulted in inter-micellar aggregation above the LCST.

DOI： 10.3390/polym15030770

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

Polyion complex (PIC) micelles having a hydrodynamic radius of approximately 20 nm were prepared in water by simply mixing a pair of double hydrophilic oppositely charged diblock copolymers composed of a first block containing pendant phos-phobetaine groups and a second cationic or anionic styrene -based polyelectrolyte block. The PIC micelles were stable under high salt concentration because the formation of the PIC micelles was driven by both electrostatic and hydrophobic interactions.

DOI： 10.1246/cl.220241

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.macromol.2c00485

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.macromol.1c02210

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DOI： 10.1021/acs.langmuir.1c01917

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcb.1c01864

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DOI： 10.1002/marc.202000585

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/marc.202000585

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

N-(2-Hydroxypropyl)methacrylamide (HPMA)-based statistical copolymers bearing anticancer drugs have attracted attention for their efficacy in cancer treatments. However, controlling the size and morphology of aggregates of this type of polymer has been challenging and is far from being understood. In this study, small-angle X-ray scattering and asymmetric-flow field-flow fractionation with multiangle light scattering were used to investigate the structure of aggregates formed in aqueous solutions of HPMA-based statistical copolymers of different molecular weights with the model drug pyrene borne in different amounts. The analysis revealed that spherical objects (flower micelles) were formed by the assembly of pyrene moieties in low-molecular-weight copolymers, and the flower micelles connected linearly to form string-of-pearls assemblies (flower necklaces) in high-molecular-weight copolymers. The number of pyrene moieties per polymer chain likely dominates the size and morphology of the copolymer micelles. This study shows how to alter the aggregate structure by changing the molecular weight and composition of copolymers.

DOI： 10.1021/acs.langmuir.0c02032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Recent studies show that calix[4]arene-based micelles are monodisperse with defined N-agg values chosen from 4, 6, 8, 12, 20, and 32. Interestingly, all these numbers coincide with the face numbers of Platonic solids, so they are called "Platonic micelles." As long as a certain geometric condition is fulfilled, any amphiphilic molecule can form a Platonic micelle. The preferred N-agg values are explained in relation to the mathematical Tammes problem, namely, how to obtain the best coverage of a sphere's surface with multiple identical circles. The coverage ratio can be calculated and produces maxima at 4, 6, 12, 20, and 32, coinciding with the observed N-agg values. In this feature article, Platonic micelles as well as their morphological transition by controlling pH, salt, temperature, and electrostatic interactions are summarized.

DOI： 10.1002/marc.202000227

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC FIBER SCIENCE TECHNOLOGY  

Poly[N-(2-Hydroxypropyl)methacrylamide] (PHPMA) shows excellent biocompatibility and thus is expected to be used as a carrier in a drug delivery system. In this study, we investigated how the difference in the monomer structure influences the sequence in copolymers composed of HPMA and monomers (MA-ahNHNH-Boc and MA-NHNH-Boc); the size of MA-ah-NHNH-Boc is larger than that of MA-NHNH-Boc by the alkyl chain (CH2)5 spacer. Because the obtained copolymers showed a phase separation behavior upon heating,we also investigated this phase separation behavior by turbidimetry and the molecular dimension in dilute aqueous solution by small-angle X-ray scattering (SAXS). Consequently, we found that the difference between the monomers (MA-ah-NHNH-Boc or MA-NHNH-Boc) significantly influences the monomer sequence in copolymer chains, the cloud point temperature, and the chain dimension in aqueous solution.

DOI： 10.2115/fiberst.2020-0033

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By introducing strong directed hydrogen bonds to an amphiphilic polymer, we demonstrate that phase transitions from spherical to cylindrical morphologies in aqueous solutions can significantly be shifted to favor the assembly of supramolecular polymer bottlebrushes. In water, a forced self-assembly of polymers into cylindrical structures remains a challenge as the often required hydrophobic shielding induces forces, which tend to minimize the surface area. The herein presented novel benzene trisureas can overcome these limitations due to strong hydrogen bonds and alter the morphology to cylinders despite an unfavorable packing parameter, which dominated the previously reported trisamide analogues. The systematic variation of composition and architecture revealed that a transition to spherical morphologies still occurs, but the phase-transition boundaries appear to be shifted to tolerate larger hydrophilic polymer chains. The strength of the directing interactions appears to be decisive for the shift, though we additionally observed that any restrictions of lateral aggregation can diminish the effect of the directing hydrogen bonds. Overall, the straightforward synthesis and versatile design render the presented systems an interesting blueprint for the development of more advanced supramolecular polymer bottlebrushes and multifunctional nanostructures.

DOI： 10.1021/acs.macromol.0c01361

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For designing nanoparticles as drug carriers, a covalently crosslinked structure is necessary for the structural stability in vivo. In this study, we prepared core crosslinked nanoparticles through the formation of nanoemulsions stabilized by poly(ethylene glycol) (PEG)-bearing surfactants. The structural characteristics of these particles were carefully evaluated using small-angle scattering techniques including dynamic, static, X-ray, and neutron scattering. The particles demonstrated high stability even in vivo, with the suppression of premature drug release owing to the crosslinked structure. Interestingly, the ability to retain encapsulated molecules was dependent on the molecular weight of PEG in vivo, presumably due to the difference in the crowding density of PEG chains at the outermost surface. This suggests that conferring structural stability via a core crosslinked structure is surely important, but we also need to consider controlling the crowding density of the hydrophilic polymer chains in the particle shell when designing drug carriers.

DOI： 10.1016/j.jconrel.2020.05.035

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Small-angle scattering is a powerful tool to investigate micellar structure, and a model form factor proposed by Pedersen and Gerstenberg [Pedersen, J. S.; Gerstenberg, M. Macromolecules 1996, 29, 1363-1365] has been used quite frequently to analyze experimentally obtained scattering data of block copolymer micelles. Their model consists of a spherical core and the Gaussian corona chains attached to the core surface; the corona chains are considered to be approximately continuously (evenly) distributed on the core surface. In this paper, we present a micellar form factor model in which the corona chains are discretely distributed on the core surface. Our proposed discrete model was found to deviate from the Pedersen-Gerstenberg model as well as another model [Svaneborg, C.; Pedersen, J. S. Phys. Rev. E 2001, 64, R01802.], which incorporates the approximate interference effect between the corona chains, in conditions in which the scattering from the corona chains is stronger than that from a core with lower number density of the corona chains.

DOI： 10.1021/acs.jpcb.0c04120

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Reinforcement of the in vivo structural stability of polymer-based nanoparticles such as polymeric micelles has been achieved via covalently crosslinked structures. Herein, we report new core crosslinked nano-particles prepared via an o/w nano-emulsion composed of difunctional polymerizable oil monomers stabilized by a poly(ethylene glycol) (PEG)-bearing surfactant. The obtained PEG-tethered core crosslinked nanoparticles are named furry nanoparticles (f-NPs). The f-NPs structure was evaluated using light scattering (LS; both static SLS and dynamic DLS), small-angle X-ray scattering, and transmission electron microscopy. The f-NPs' size could be easily controlled by changing the amount of oil monomer, which also affected dye loading and releasing behavior. Employing a disulfide-based oil monomer, we could endow the f-NPs with sensitivity to reduction, demonstrating destabilization in a reducing environment with a high glutathione level matching that in tumors. The structural stability of f-NPs in vivo was very high compared with that of a micellar system, resulting in prolonged circulation in the bloodstream. Interestingly, the in vivo stability might depend on the crowding density of PEG chains at the outermost surface, even though the structural stability was guaranteed by the crosslinked structure. This study demonstrates the promising synthesis of core crosslinked nanoparticles and their potential as drug carriers.

DOI： 10.1039/d0py00610f

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Polymeric micelles have been extensively studied as nanoscale drug carriers. Knowing how the encapsulation of drugs alters the micellar structure is one of the most important issues for the biomedical application of amphiphilic block copolymers. However, little is known so far about the structural changes that micelles undergo upon loading with water-insoluble guests. Herein, we investigate the micellar morphology of ABC triblock terpolymers after loading with various water-insoluble molecules (naphthalene and its derivatives as drug-equivalent model molecules). The triblock terpolymer features a poly(ethylene oxide) (PEO) block, a poly(allyl glycidyl ether) segment which has been functionalized with carboxylic acid moieties (PAGE(COOH)), and poly(tert-butyl glycidyl ether) (PtBGE) as a hydrophobic block. Structural analysis by small-angle X-ray scattering (SAXS) and cryogenic and conventional transmission electron microscopy (TEM) found that a morphological transition from spherical micelles to vesicles (polymersomes) was induced by loading the guest molecules at pH 4, whilst the spherical and prolate morphologies remained unchanged upon loading at pH 6 and 8. This study highlights the dynamics and morphological changes of polymeric micelles upon loading with guest molecules.

DOI： 10.1039/d0py00426j

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Ureido-modified poly(L-citrulline) (L-ornithine-co-L-citrulline denoted by PLOC) shows UCST-type phase separation behavior even under physiologically relevant conditions, which forms an alpha-helix structure above its phase separation temperature (T-p) but transforms into a solid-like aggregation composed of regular hexagonal packed cylinders below the T-p. This morphological transformation is characteristic of the phase separation behavior, but the mechanism behind it has remained incompletely understood. Here, we studied the phase separation behavior using small-angle X-ray scattering (SAXS) measurements. To analyze the SAXS data, we employed the modified unified model proposed previously, which decomposes the scattering profile into each structural element, such as the alpha-helices and their aggregation formed via hydrogen-bonding interactions between the ureido groups. The aggregation level is dependent on the temperature (T) and grouped into three classes: (1) mass-fractal aggregation composed of the alpha-helix (T > T-p), (2) spherical aggregation composed of the hexagonal packed cylinder (T < T-p), and (3) micro-order agglomeration formed by mutual fusion of the spherical aggregation, which appears as a solid-like aggregation. The SAXS analysis suggested that the transformation from the dispersed state as the alpha-helix to the agglomeration containing hierarchical structures occurs in a stepwise manner when the temperature falls below the T-p, which might also be transition behavior similar to the process of protein folding through folding intermediates.

DOI： 10.1021/acs.jpcb.0c00934

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

alpha-Mangostin (MGS), an anti-cancer compound, is a xanthone derivative and is extracted from the pericarps of mangosteen. MGS exhibits a variety of bioactivities, such as antioxidant, cytotoxic, anti-inflammatory, and antibacterial effects, as well as anticancer activity. However, MGS has not been approved for clinical use because of its poor bioavailability. There have been many efforts to solve this problem by use of drug carriers. Cyclodextrins (CDs) are well known as nontoxic and biodegradable drug carriers and can encapsulate MGS. In this study, we prepared CD-based nanoparticles (CDNPs) by a polyaddition reaction using epichlorohydrin and characterized them by dynamic light scattering and static light scattering coupled with fractionation. The encapsulation of MGS into CDNPs was examined, and we found that the loading ratio of MGS for CDNPs is much higher than that for CDs themselves. The cytotoxicity of the CDNP/MGS complex was examined, indicating the potential of CDNP as a carrier of MGS.

DOI： 10.1038/s41428-019-0296-y

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Upon extending a hydrophobic polymer chain from the end of a preceding hydrophilic chain in aqueous solutions, the resultant block copolymers may eventually undergo self-assembly. Further chain propagation continues in the newly formed hydrophobic polymer rich domain. This process is often referred to as polymerization-induced self-assembly (PISA). Its kinetics are determined by the polymerization and the micelle formation/growth, which may influence each other, possibly leading to a highly complex process of structural development. In this study, we examined PISA in aqueous solution on the reversible addition fragmentation chain transfer (RAFT) dispersion polymerization of poly(N-acryloylmorpholine)-b-poly(N-acryloylthiomorpholine). Using in situ small-angle X-ray scattering (SAXS) and nuclear magnetic resonance spectroscopy (NMR), the polymerization and micelle formation were observed. In the analysis, because the time scale of the micelle formation/growth is much shorter than that of the polymerization, the polymerization and micelle fomarion/growth can be decoupled. Thus, these were separately analyzed in depth, and a combination of the kinetics of RAFT polymerization and the simple scaling theory of the micellar structures can quantitatively describe the overall micellar structural development during PISA. This study provides an unprecedented insight into the processes underlying PISA and deepens our quantitative understanding of it.

DOI： 10.1039/c9py01810g

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DOI： 10.1021/acs.langmuir.0c00861

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DOI： 10.1039/d0py01185a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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When the micellar aggregation number (N-agg) is sufficiently small (N-agg o 30), the micelle shows an abnormal aggregation behavior: monodispersity without any distribution in N-agg, whose values coincide with the vertex number of a regular polyhedral structure, i.e., they are termed Platonic solids. Micelles with these characteristics are named "Platonic micelles''. In this study, we investigated the aggregation behavior of calixarene-based micelles bearing primary amines-the first example of Platonic micelles-with increasing alkyl chain length by small-angle X-ray scattering, asymmetrical flow field flow fractionation coupled with multiangle light scattering, and analytical ultracentrifugation measurements. Morphological transition of the micelles from spherical to cylindrical was observed when the alkyl chain length was increased in this calixarene-based micellar system, which is similar to the case of conventional systems and is acceptable in terms of the packing parameter principle. However, although the micellar N-agg normally increases with an increase in the alkyl chain length, the structure of calixarene-based Platonic micelles bearing butyl (C4), heptyl (C5), and hexyl (C6) chains remains at 12-mer. This is presumably due to the relationship between the thermodynamic stability of the Platonic micelles and the coverage ratio defined by the Tammes problem.

DOI： 10.1039/c9sm00076c

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Rationally designed bolaamphiphiles are known to self-assemble into nanotube structures. Herein, we report the formation of an inclusion complex between a nanotube and bovine serum albumin (BSA). This complex formation was confirmed by ultraviolet (UV) absorbance and electrophoretic light scattering (ELS). The structure for different mixing ratios of BSA to the nanotube was also investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The structural analysis with our proposed model has revealed that the BSA molecules were contained within the internal space of the nanotube with maintenance of its tubular structure.

DOI： 10.1021/acsabm.9b00047

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Micelles with perfect monodispersity in terms of the aggregation number (N-agg) have recently been discovered, whose values of N-agg interestingly always coincide with the vertex or face number of regular polyhedral structures (i.e., Platonic solids). Owing to the monodispersity of the micelles, named Platonic micelles, we could expect them to exhibit unprecedented aggregation behavior. In this study, the effects of alkyl chain length on micellar aggregation behavior were characterized using small-angle scattering techniques such as small-angle X-ray scattering and asymmetrical flow field-flow fractionation coupled with multi-angle light scattering, as well as analytical ultracentrifugation measurements. The N-agg of Platonic micelles discretely and discontinuously increased when increasing the alkyl chain length, which differs markedly from the findings for conventional micelles. This aggregation behavior could be reasonably explained by the relationship between the thermodynamic stability of the micelles and the coverage density defined by one of the unsolved mathematical problems: the Tammes problem.

DOI： 10.1021/acs.langmuir.8b04204

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

We recently identified completely monodisperse micelles whose aggregation number (N-agg) coincides with the vertex number of regular polyhedra, named Platonic micelles. The combination of both the micellar properties and controlling their structures by external stimuli could be promising for producing precisely controlled self-assembled structures. From this perspective, we newly synthesized a calix[4] arene-based amphiphile bearing disaccharides, cellobioses. The crowded and bulky structure in the hydrophilic group could provide a novel stimuli-responsiveness of disaccharides in amphiphiles. The aggregation behavior such as the morphologies and the aggregation number of the calix[4]arene-based micelle was characterized using small angle scattering techniques and analytical ultracentrifugation measurements. Owing to hydrogen bonding among the disaccharide, the head volume became smaller than expected, resulting in the formation of cylindrical ones. However, cleaving the hydrogen bond by controlling temperature or pH induced morphological transition of the micellar structure from cylindrical to spherical. The dual-stimuli (temperature and pH) generated smaller micelles with N-agg of 12. Interestingly, when the amphiphile formed spherical micelles at various conditions, the N-agg matched the Platonic number, and the change of N-agg in response to the external stimuli was non-continuous, which is consistent with the concept of Platonic micelles. (C) 2018 Published by Elsevier Inc.

DOI： 10.1016/j.jcis.2018.09.044

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The mixture ratios were used as a factor for aggregation number (N-agg) determination in binary mixtures of calix[4]arene surfactants. Platonic micelles having different N-agg were prepared by adjusting the ratio of oppositely charged compounds.

DOI： 10.1039/c8cc09621j

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Among the many studies on micelles, dating back more than 100 years, we first found a series of monodisperse micelles: spherical micelles made from calix[4]arene surfactants exhibited monodispersity in aggregation number (N-agg) with values of 4, 6, 8, 12, and 20. We named these Platonic micelles because these values coincided with the face numbers of the Platonic solids. The preferred N-agg values were explained in relation to the mathematical Tammes problem: how to obtain the best coverage of a sphere surface with multiple identical circles. In this paper, we synthesized poly(ethylene glycol)-attached surfactants and carried out small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) to determine the N-agg. We found that these polymeric surfactants also formed monodispersed micelles and N-agg discontinuously increased from 20 to 24, and then 32 with increasing the alkyl carbon numbers from 9 to 11 continuously. The determined N-agg was greater than 20 and the Platonic solid numbers. We assumed that the preferred N-agg values could be explained in relation to the Tammes problem as well.

DOI： 10.1039/c9sm00943d

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We investigated the formation kinetics of a single monolayer nanotube from bolaamphiphiles (consisting of a sugar residue, an alkyl chain, and an amino group) in solution. In this bolaamphiphile, a transition from a monomerically dispersed state to the nanotube takes place by changing the solvent condition. This transition was induced by fast mixing with a stopped-flow apparatus. From just after the mixing, this transition process was monitored in situ by time-resolved small-angle X-ray scattering. In this manner, we were able to derive the direct structural information as a function of time during the nanotube formation. The results revealed that disklike aggregates initially formed, which then grew and closed to produce a tubular structure.

DOI： 10.1021/acs.jpcb.9b01746

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC POLYMER SCIENCE JAPAN  

We overview both theoretical and experimental studies on the following kinetics of block copolymer micelles formed in a selective solvent reported so far: 1) the exchange kinetics of block copolymer chains among micelles was investigated by time-resolved small-angle neutron scattering for deuterated block copolymer micelles mixed with corresponding non-labeled micelles; 2) the growth of the micelles after a temperature jump was studied by time-resolved light scattering; 3) the nucleation-growth kinetics of the block copolymer micelles in solution was investigated by light and small-angle X-ray scattering using a stopped flow apparatus; 4) the morphology transition kinetics from cylindrical micelles to spherical micelles of block copolymers was studied by transmittance electron microscopy and time-resolved small-angle X-ray scattering.

DOI： 10.1295/koron.2018-0052

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When a negatively charged sulfonic or a positively charged amine group is attached to calix[4]arene surfactants, denoted as SCal7 and QACal7, respectively, each system forms monodispersed spherical micelles with a defined aggregation number. We postulated that these defined monodisperse aggregations can be adjusted in terms of the coverage, that is, how efficiently can a spherical surface (, hydrophobic domain) be covered with identical caps (hydrophilic headgroup). We carried out small-angle X-ray scattering (SAXS), as well as titration calorimetry and dynamic light scattering (DLS), to observe the morphologies of the mixtures of these two components. The calorimetry showed a 1:1 stoichiometric exothermic reaction with a rather large binding constant. This means that, once the twin is formed from QACaI7 and SCal7, these components hardly separate. SAXS showed that the spherical micelles changed to cylindrical ones and then to vesicle shapes as the composition reached a ratio of 1:1. At some intermediate compositions, mixtures of cylinders and plates (or spheres) were observed, which were confirmed by dynamic light scattering. We assume that the twin has a larger packing parameter than the individuals because of the cancellation of the charges between the sulfonic and the amine groups, and thus, the increase of the twin composition induces the entire morphology change, as expected from the packing parameter principle. In the present case, the coverage may be a secondary factor determining the morphology.

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Core-shell-corona micelles featuring a pH-responsive shell have been characterized in dilute aqueous solution at different pH values (4-8) by using dynamic light scattering (DLS), field-flow fractionation coupled with multiangle light scattering detector (FFF-MALS), steady-state fluorescence, small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). The micelles are formed by self-assembly of a polyether-based triblock terpolymer consisting of a hydrophobic poly(tert-butyl glycidyl ether) block (PtBGE), a pH-responsive modified poly(allyl glycidyl ether) segment (PAGE(COOH)), and a neutral hydrophilic poly(ethylene oxide) block (PEO). Because of the side-chain carboxylic acids in the middle block, the micellar structure and size depends on the solution pH. Hereby, we show that an increase in pH induces a decrease in the aggregation number (N-agg). In addition, the combination of the above measurements revealed an unexpected morphological change from spherical to ellipsoidal micelles by increasing pH.

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This study is concerned with the morphological transition kinetics of polyelectrolyte complex micelles formed from an anionic-neutral block copolymer and a cationic-neutral block copolymer in aqueous NaCl solution. The transformation was induced by changing the mixing ratio of the anionic and cationic monomer units in the copolymers. The kinetics of the morphological transition was directly tracked by time-resolved (ultra) small-angle X-ray scattering coupled with rapid mixing of the block copolymer components by a stopped flow apparatus. The transformation from cylindrical to spherical micelles upon changing the mixing ratio of the copolymers was reversible, and the process occurred via the random scission of the cylindrical micelles along their contours. The reverse transition from spherical to cylindrical micelles was found to be a slow process with high activation energy.

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When the micellar aggregation number (N-agg) is small enough (<30), the N-agg matches the value of vertexes of a regular polyhedron: Platonic solids, and demonstrates perfect monodispersity. These micelles are named Platonic micelles and are particularly found in the system of calix[4]arene-based micelles due to the rigid structure of the backbone molecule. Although sulfonatocalix[4]arene-based micelles are among the most studied host molecules in supramolecular chemistry, their micellar properties as Platonic micelles have thus far been overlooked. In this study, we prepared various sulfonatocalix[4]arene-based amphiphiles bearing alkyl chains with different lengths and investigated their aggregation behavior. When the amphiphiles formed spherical micelles, they demonstrated monodispersity in terms of N-agg, whose value changed from 4 to 17, and then to 24, upon increasing the carbon number in each alkyl chain from CS to C6, and then to C7, respectively. Although the numbers 17 and 24 do not match the vertices of regular polyhedra, these values can be reasonably explained by the Thomson problem, which considers the Coulomb potential for calculating the best packing on a sphere with multiple identical spherical caps. This study describes rediscovery of the monodispersity of sulfonatocalix[4]arene-based micelles, which is consistent with the idea of Platonic micelles.

DOI： 10.1021/acs.langmuir.8b00802

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In this paper, we describe the construction of tetramer micelles based on the idea of "Platonic micelles'' whose aggregation number (N-agg) matches the vertex number of regular polyhedra and exhibits the monodispersity and discreteness in the N-agg.

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DOI： 10.1039/c8sm90014k

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We investigated the cross-sectional structure of amolecular monolayer nanotube self-assembled from asymmetric bolaamphiphiles having two different hydrophilic headgroups. Small-angle X-ray scattering measurements clarified that the glucose and amino headgroups form the exterior and interior surfaces of the nanotube, respectively.

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Other Link： http://orcid.org/0000-0003-2168-9436

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The aggregation number of classical micelles exhibits a certain distribution, which is a recognizable feature of conventional micelles. However, we recently identified perfectly monodisperse calix[4]arene-based micelles whose aggregation numbers agree with the vertex numbers of regular polyhedra, that is, Platonic solids, and thus they are named Platonic micelles. Regarding our hypothesis of the formation mechanism of Platonic micelles, both repulsive interactions including steric hindrance and electrostatic repulsions among the headgroups are important for determining their aggregation number; however, neither of these is necessarily needed to consider. In this study, we employed polyethylene glycols (PEGs) as the nonionic headgroup of calix[4]arene-based amphiphiles to study the effects of only repulsive interactions caused by steric hindrance on the formation of Platonic micelles. The amphiphiles containing relatively low-molecular-weight PEGs (550 or 1000 g mol(-1)) form dodecamer or octamer micelles, respectively, with no variation in the aggregation number. However, relatively high-molecular-weight PEGs (2000 g mol(-1)) produce polydispersed micelles with a range of aggregation number. PEG 2000 exhibits a greater affinity for water than PEG 550 and 1000, resulting in fewer hydrophobic interactions in micelle formation, as indicated by the drastic increase of the critical micelle concentration (CMC) value in the PEG 2000 system. The instability of the structure of PEG(2k)CaL5 micelles might contribute to the higher mobility of PEG in the micellar shell, resulting in a non-Platonic aggregation number with polydispersity.

DOI： 10.1021/acs.langmuir.7b02196

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Other Link： http://orcid.org/0000-0003-2168-9436

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Calix[4]arene-derived surfactants form monodisperse micelles witha well-defined aggregation number (N-agg) of 4, 6, 8, 12, or 20, corresponding to the Platonic solids. This feature is in strong contrast to conventional micelles. In this study, a transition from a dodecamer (N-agg = 12) to an icosamer (N-agg = 20) was induced by a rapid increase in the NaCl concentration (CNaCl) using a stopped-flow device and directly observed by time-resolved small-angle X-ray scattering. The N-agg remained unchanged during the first 60 s after the increase in CNaCl, and then abruptly increased to 20. This feature resembles phase transitions in supersaturated or supercooled states, or highly cooperative phenomena. We surmise that this finding may be due to the fact that only a few N-agg values are thermodynamically allowed when N-agg is sufficiently small. This is the first observation of such an induction time in micellar aggregation.

DOI： 10.1002/anie.201702260

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Other Link： http://orcid.org/0000-0003-2168-9436

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We have investigated the morphology of a micelle consisting of a calix[4]arene-derivative surfactant under various NaCl concentrations CS by small-angle X-ray scattering (SAXS) and estimated the molar mass dispersity index (D) over tilde of the micelles by field flow fractionation (FFF). We found the sphere-to-cylinder morphology transition induced by increasing C-S. Although (D) over tilde was very low in the spherical morphology, (D) over tilde increased when the morphology became cylindrical.

DOI： 10.1246/cl.170032

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Other Link： http://orcid.org/0000-0003-2168-9436

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have prepared a new calix[4]arene-based lipid containing glutamic acid as the hydrophilic group. The alpha- amine and the gamma-carboxylic acid groups of the glutamic acid moiety allowed a continuous change in the state of the headgroup from cationic to zwitterionic and then to anionic with increasing pH. Accompanying this headgroup change, micelles of the lipid underwent a morphological transformation from spherical to cylindrical and again to spherical. The morphological transition was ascribed to the change in the lipid conformation corresponding to the pH conditions. Interestingly, at acidic and basic pH, the spherical micelles demonstrated monodispersity in terms of the aggregation number, Which agreed with the vertex numbers of Platonic solids, indicating the formation of Platonic micelles. At acidic and basic pH, the lipid conformations were almost identical, but there was a slight difference in the hydrophilic volume, which might affect the packing behavior of the lipid in micelles and account for the difference in the aggregation number. This Study clearly demonstrates the precise pH-controllable aggregation number of micelles, which belong to the Platonic micelle systems.

DOI： 10.1021/acs.langmuir.7b00603

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Other Link： http://orcid.org/0000-0003-2168-9436

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Aqueous solutions of the doubly thermosensitive block copolymer poly(2-isopropyl-2-oxazoline)-b-poly(2-ethyl-2-oxazoline) heated to 50 degrees C underwent a macroscopic liquid/liquid phase separation. The small-angle X-ray scattering intensity recorded from the concentrated phase settled on the bottom of a sample indicated that this phase was in the disordered state without any microphase separation, although the block copolymer was amphiphilic in water at 50 degrees C. It was also confirmed that the contribution to the scattering intensities of individual copolymer chains and their aggregates existing in the coexisting concentrated phase was very small, compared with the total scattering intensity of the phase-separated solution, when the concentrated phase was suspended in the form of colloidal droplets in the lean phase.

DOI： 10.1038/pj.2016.124

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Other Link： http://orcid.org/0000-0003-2168-9436

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have monitored the kinetic process of polyelectrolyte complex formation between sodium polyacrylate (SPA) and polyallylamine hydrochrolide (PAH) in aqueous NaCI solution by time-resolved ultra-small-angle X-ray scattering (TR-USAXS) combined with rapid mixing. SPA and PAH with different NaCI concentrations from 0 to 1 M were rapidly mixed in equimolar concentration of the monomer units using a stopped-flow apparatus with a dead time of about 2.5 ms. Within the dead time, percolated aggregate-like structures were observed suggesting that the initially formed small charge neutral aggregates further assembled to form higher order agglomerates. The early stage time evolution of the molar mass of the global structure in the presence of NaCI was found to be comparable to the Brownian-coagulation rate.

DOI： 10.1021/acs.jpclett.6b02957

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Other Link： http://orcid.org/0000-0003-2168-9436

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

We have formulated the mixing Gibbs energy density for the micelle phase of an amphiphilic block copolymer solution using mean-field lattice theory. We have found a transition between the micellization and the liquid-liquid phase separation in this solution by comparing the mixing Gibbs energy density for the micelle phase with that for the homogeneous phase. Micellization is preferred over the liquid-liquid phase separation not only at a higher amphiphilicity of the block copolymer chain but also at a higher degree of polymerization of the copolymer.

DOI： 10.1038/pj.2016.110

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

We investigated the local and global conformations of flower micelles and flower necklaces formed by the amphiphilic alternating copolymer of sodium maleate and dodecyl vinyl ether, P(MAL/C12), in an aqueous solution using small-angle X-ray scattering (SAXS) and light scattering. SAXS profiles obtained for seven P(MAL/C12) samples with different degrees of polymerization N-01 showed sharp minima characteristic to the hydrophobic core formed by dodecyl groups with a low electron density. Both the SAXS profile I(k) and hydrodynamic radius R-H for P(MAL/C12) samples with N-01 &lt; 300 are consistently explained by the flower micelle model with minimum-sized loops, while I(k) for micelles formed by P(MAL/C12) samples with N-01&gt;300 is explained in terms of the flower necklace model, of which hydrophobic core size determined from I(k) was slightly larger than that from R-H. The size distribution of the hydrophobic core is narrower for the flower necklace than for the flower micelle.

DOI： 10.1038/pj.2016.49

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The mixing ratio dependence of the morphology of a polyion complex micelle formed of an anionic neutral double-hydrophilic block copolymer (AP) and a cationic-neutral double-hydrophilic block copolymer (MP) in 0.1 M aqueous NaCl solution was investigated by using small-angle X-ray scattering (SAXS), electrophoretic light scattering (ELS), and isothermal titration calorimetry (ITC), under the condition that the anionic and cationic block chains are much longer than the neutral block chains. When the anionic and cationic monomer units in the solution are nearly equimolar, the net charge of the polyion complex micelle is close to zero, and the bilayer vesicle is formed. However, when the anionic or cationic monomer units in the solution are richer than the other, the polyion complex micelle is charged by including the excess block copolymer component to form the smaller spherical micelle. The morphology transition between the vesicle and spherical micelle can take place reversibly by simply adding AP or MP into the micellar solutions. The electrostatic energy of the micelle may induce the morphology transition.

DOI： 10.1021/acs.macromol.6b00308

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have investigated the self-assembly in dilute aqueous solutions of a mixture of an anionic-neutral block copolymer (AP) and a cationic-neutral block copolymer (MP) by changing the added sodium chloride (NaCl) concentration C-S or electrostatic interactions among oppositely charged blocks, by direct observation, optical and electron microscopies, and small-angle X-ray scattering. The ratio of the charged to neutral block chain lengths was ca. 10., and the total copolymer concentration and the mixing ratio (the mole fraction of the MP charge unit in the total charge units) of AP and MP were fixed to be 0.005 g/cm(3) and 0.6, respectively. With decreasing C-S from 2 to 0 M, we have found reentrant one-phase, two-phase, one-phase transitions in the aqueous solution of the AP-MP mixture. The two-phase to one-phase transition at C-S similar to 0.5 M arises from the competition between the macroscopic phase transition and micellization, which is the first observation in dilute block copolymer solutions. Moreover, we have found a micelle morphology transition from the bilayer vesicle to the cylindrical micelle with further decreasing C-S from 0.5 M to lower than 0.05 M.

DOI： 10.1021/acs.macromol.5b01368

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The dehydration and self-association of a novel thermosensitive diblock copolymer consisting of poly(2-isopropyl-2-oxazoline) and poly(N-isopropylacrylamide) (PIPOZ-b-PNIPAM) upon heating were studied in water and water methanol (MeOH) mixtures by differential scanning calorimetry (DSC), turbidimetry, small-angle X-ray scattering (SAXS), and fluorescence depolarization. Although the difference of the phase-separation temperatures of the PIPOZ and PNIPAM homopolymers solutions was enhanced as the MeOH content in the mixed solvent increases, the DSC thermograms of PIPOZ-b-PNIPAM in water MeOH mixtures were not bimodal, which indicates that the dehydration of each block does not occur independently. As a result, the amphiphilicity of this copolymer is weaker in the amphiphilic condition than that of the related thermosensitive block copolymer of PIPOZ and poly(2-ethyl-2-oxazoline) (PIPOZ-b-PEOZ) examined previously, which undergoes phase separation in hot water under the same conditions. Both PIPOZ-b-PNIPAM and PIPOZ-b-PEOZ solutions undergo a temperature-induced liquid liquid phase separation, but the formation of the spherical micelle in the coexisting dilute phase is more difficult in the former solution. The colloidal stability of the coexisting concentrated phase depends on the mixed solvent composition. The colloids flocculate in conditions for which the copolymer is of intermediate amphiphilicity, as observed previously also in the PIPOZ-b-PEOZ solution, possibly due to the viscoelastic effect experienced by colloidal particles bearing on their interface chains of a more hydrophilic block.

DOI： 10.1021/ma501538t

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The self-association behavior of a thermosensitive amphiphilic block copolymer, poly(N-isopropylacrylamide)-b-poly(N-vinyl-2-pyrrolidone) (PNIPAM-b-PNVP) in water upon heating was investigated by static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), and pulsed field gradient NMR (PFG-NMR). Combining SLS and DLS with SAXS and PFG-NMR, we conclude that above 40 degrees C, the unimer or a few arms star micelle of the copolymer coexists with large spherical particles of uniform density, which should be regarded as concentrated-phase droplets produced by a liquid liquid phase separation. The spherical particles of PNIPAM-b-PNVP samples with the PNIPAM content less than 0.32 became smaller with increasing temperature. This temperature dependence was explained in terms of the packing parameter for amphiphiles.

DOI： 10.1021/ma3020992

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have investigated the heat-induced self-association in water of a block copolymer (PIPOZ-b-PEOZ) comprising two thermosensitive blocks: a poly(2-isopropyl-2-oxazoline) block (degree of polymerization 71) and a poly(2-ethyl-2-oxazoline) block (degree of polymerization 38) using differential scanning calorimetry (DSC), static light scattering (SLS), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) together with visual observation on the macroscopic and microscopic scales. The dehydration temperatures of the PIPOZ and PEOZ blocks in water are 43 and 54 degrees C, respectively. When heated abruptly to 50 degrees C where PIPOZ-b-PEOZ is amphiphilic, the copolymer first forms star micelles that further aggregate to form large concentrated phase droplets, and finally the droplets coalesce into a bulk liquid phase, having a copolymer concentration as high as 0.8 g/cm(3). When heated abruptly to 70 degrees C, where both blocks are hydrophobic, the copolymer solution also separates into two liquid phases, consisting of phase-separated polymer-rich micrometer or submicrometer size droplets dispersed in a polymer-poor liquid phase, but the droplets do not coalesce into a liquid bulk phase. We discuss the role of the more hydrophilic PEOZ block in the macroscopic phase separation behavior. No microphase separation takes place in the concentrated phase of the aqueous PIPOZ-b-PEOZ block copolymer solution.

DOI： 10.1021/ma300969w

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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Language：English   Presentation type：Oral presentation (general)  

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