Grinding-Induced Water Solubility Exhibited by Mechanochromic Luminescent Supramolecular Fibers.

Most mechanochromic luminescent compounds are crystalline and highly hydrophobic; however, mechanochromic luminescent molecular assemblies comprising amphiphilic molecules have rarely been explored. This study investigated mechanochromic luminescent supramolecular fibers composed of dumbbell-shaped 9,10-bis(phenylethynyl)anthracene-based amphiphiles without any tetraethylene glycol (TEG) substituents or with two TEG substituents. Both amphiphiles formed water-insoluble supramolecular fibers via linear hydrogen bond formation. Both compounds acquired water solubility when solid samples composed of supramolecular fibers are ground. Grinding induces the conversion of 1D supramolecular fibers into micellar assemblies where fluorophores can form excimers, thereby resulting in a large redshift in the fluorescence spectra. Excimer emission from the ground amphiphile without TEG chains is retained after dissolution in water. The micelles are stable in water because hydrophilic dendrons surround the hydrophobic luminophores. By contrast, when water is added to a ground amphiphile having TEG substituents, fragmented supramolecular fibers with the same molecular arrangement as the initial supramolecular fibers are observed, because fragmented fibers are thermodynamically preferable to micelles as the hydrophobic arrays of fluorophores are covered with hydrophilic TEG chains. This leads to the recovery of the initial fluorescent properties for the latter amphiphile. These supramolecular fibers can be used as practical mechanosensors to detect forces at the mesoscale.

Reconstruction of Chitosan Network Orders Using the Meniscus Splitting Method for Designing pH-Responsive Materials.

Chitosan is a product of deacetylated chitin and a natural polymer that is attractive as a functional and biocompatible material in the pursuit of alternative materials to synthetic plastics for a sustainable society. Although hierarchical architectures, from precise molecular structures to nanofibers and twisted structures, have been clarified, the expansion of the anisotropic microstructures of chitosan into millimeter-scale materials is in the process of development. In this study, a chitosan network was reconstructed from an aqueous solution by using the meniscus splitting method to form a three-dimensionally ordered microstructure. A chitosan membrane deposited on the millimeter scale formed a useful anisotropically pH-responsive hydrogel. During the evaporation of the aqueous solution from a finite space, chitosan underwent ordered deposition by capillary force to form a membrane with oriented microstructures and microlayers. Unlike the cast films formed between solid-liquid and air-liquid interfaces, this membrane formed between two air-liquid interfaces. As a result, the membranes with ordered microstructures were capable of signifying directional swelling in aqueous environments and reversible/irreversible swelling-deswelling changes by controlling the pH range. We envision that the anisotropic pH response of the chitosan network can be utilized under physiological conditions as a next-generation material.

Water Adsorption on π-Surfaces of Open-Fullerenes.

Understanding the water adsorptive behavior of fullerenes is of particular importance for their material application in aqueous media. The conventional fullerenols usually provide complex physical pictures of water adsorption due to their uncontrollable hydroxylation degree and substitution pattern. Herein, we focus on poorly hydroxylated fullerenes with well-defined structures. The water adsorptive behavior was examined by synchrotron IR spectroscopy and computational studies. As a result, three types of IR bands were observed for adsorbed water. The population of the three states was considerably altered by the orientational difference of the hydroxy groups. Nevertheless, water adsorption could not occur for 9-fluorenol and catechol. This indicates that the Lewis acidic fullerene π-surface plays a prominent role in water adsorption, while the rather Lewis basic π-surface of 9-fluorenol is unable to attract much water at a boundary with humid air.

Promotion of glyoxylic acid penetration into human hair by glycolic acid.

OBJECTIVE: Glyoxylic acid (GA) is widely used as a straight perming agent for hair care products, however, advanced GA penetration-enhancing agents are desired due to the peculiar odour and hair colour fading caused by the continuous use of GA products. Hence, it is important to develop a penetration-enhancing agent that helps minimize the GA concentration. We have found that the combined use of GA and glycolic acid (GCA) has a strong hair straightening effect. METHODS: Straightening hair test was carried out to the evaluation of the effect of additives. Liquid chromatography-mass spectrometry (LC/MS) was performed to quantify the GA penetration amount into human hair. Attenuated total reflection (ATR) Fourier transform-infrared spectroscopy (FT-IR) and FT-IR microscope were implemented to estimate the localization of GA in the hair. RESULTS: Straightening hair tests indicated that the hair straightening effect by GA was enhanced by the presence of GCA. LC/MS results showed that the addition of GCA enhanced the amount of GA that penetrated human hair by about four times. ATR FT-IR and FT-IR microscope measurements indicated that GA was localized more in the innermost region of hair (medulla) than the cortex and cuticle. The GA accumulated in the medulla disappeared after a hair straightener treatment at 180°C due to the chemical reaction. CONCLUSIONS: The GA penetration-enhancing effect of GCA is worth investigating to reduce the GA concentration in products for more comfortable use.

OBJECTIF: L'acide glyoxylique (AG) est largement utilisé en tant qu'agent de lissage pour les produits de soins capillaires. Cependant, des agents avancés améliorant la pénétration de l'AG sont souhaités en raison de l'odeur particulière et de la décoloration des cheveux causées par l'utilisation continue de produits à base d'AG. Il est donc important de mettre au point un agent améliorant la pénétration qui contribue à minimiser la concentration d'AG. Nous avons constaté que l'utilisation combinée de l'AG et de l'acide glycolique (AGC) a un fort effet lissant sur les cheveux. MÉTHODES: Un test de lissage des cheveux a été effectué pour évaluer l'effet des additifs. Une chromatographie en phase liquide avec spectrométrie de masse (liquid chromatography-mass spectrometry, LC/MS) a été réalisée pour quantifier le volume de pénétration de l'AG dans les cheveux humains. Une spectroscopie infrarouge à transformée de Fourier (Fourier transform-infrared spectroscopy, FT-IR) à réflexion totale atténuée (RTA) et un microscope FT-IR ont été adoptés pour estimer la localisation de l'AG dans les cheveux. RÉSULTATS: Les tests de lissage des cheveux ont indiqué que l'effet de lissage des cheveux de l'AG était renforcé par la présence d'AGC. Les résultats de la LC/MS ont montré que l'ajout d'AGC augmentait d'environ quatre fois la quantité d'AG pénétrant dans les cheveux humains. Les mesures de la FT-IR à RTA et du microscope FT-IR ont indiqué que l'AG était plus localisé dans la région la plus interne du cheveu (médulla) que dans le cortex et la cuticule. L'AG accumulé dans la médulla a disparu après un traitement au lisseur à cheveux à 180 °C en raison de la réaction chimique. CONCLUSIONS: L'effet d'amélioration de la pénétration de l'AG observé avec l'AGC mérite d'être étudié afin de réduire la concentration d'AG dans les produits pour une utilisation plus confortable.

Hydration Mechanism in Blood-Compatible Polymers Undergoing Phase Separation.

Interactions involving intermediate water are crucial for the design of novel blood-compatible materials. Herein, we use a combination of atomic force microscopy, quartz crystal microbalance measurements, and soft X-ray emission spectroscopy to investigate the local hydrogen-bonded configuration of water on blood-compatible poly(2-methoxyethyl acrylate) and non-blood-compatible poly(n-butyl acrylate) grafted on a gold substrate. We find that the initially incorporated water induces polymer-dependent phase separation, facilitating further water uptake. For the blood-compatible polymer, tetrahedrally coordinated water coexists with water adsorbed on C═O groups in low-density regions of the grafted polymer surface, providing a scaffold for the formation of intermediate water. The amount of intermediate water is determined by the type of functional groups, local polymer configuration, and polymer morphology. Thus, blood compatibility is governed by the complex water/polymer interactions.

Synergetic improvement in the mechanical properties of polyurethanes with movable crosslinking and hydrogen bonds.

Polyurethane (PU) materials with movable crosslinking were prepared by a typical two-step synthetic process using an acetylated γ-cyclodextrin (TAcγCD) diol compound. The soft segment of PU is polytetrahydrofuran (PTHF), and the hard segment consists of hexamethylene diisocyanate (HDI) and 1,3-propylene glycol (POD). The synthesized PU materials exhibited the typical mechanical characteristics of a movable crosslinking network, and the presence of hydrogen bonds from the urethane bonds resulted in a synergistic effect. Two kinds of noncovalent bond crosslinking increased the Young's modulus of the material without affecting its toughness. Fourier transform infrared spectroscopy and X-ray scattering measurements were performed to analyze the effect of introducing movable crosslinking on the internal hydrogen bond and the microphase separation structure of PU, and the results showed that the carbonyl groups on TAcγCD could form hydrogen bonds with the PU chains and that the introduction of movable crosslinking weakened the hydrogen bonds between the hard segments of PU. When stretched, the movable crosslinking of the PU materials suppressed the orientation of polymer chains (shish-kebab orientation) in the tensile direction. The mechanical properties of the movable crosslinked PU materials show promise for future application in the industrial field.

Mechanisms of the antiferro-electric ordering in superprotonic conductors Cs3H(SeO4)2 and Cs3D(SeO4)2.

Wide ranges of absorbance spectra were measured to elucidate a difference in the antiferro-electric (AF) ordering mechanisms below 50 and 168 K in Cs3H(SeO4)2 and Cs3D(SeO4)2, respectively. Collective excitations due to deuterons successfully observed at 610 cm-1 exhibit a remarkable isotope effect. This indicates that the transfer state in the dimer of Cs3D(SeO4)2 is dominated by a deuteron hopping in contrast to Cs3H(SeO4)2, where a proton hopping makes a tiny contribution compared to a phonon-assisted proton tunneling (PAPT) associated with 440-cm-1 defbend . The fluctuation relevant to the AF ordering in Cs3D(SeO4)2 is not driven by the conventional deuteron hopping but by the phonon-assisted deuteron hopping associated with 310-cm-1 defbend . Consequently, Cs3D(SeO4)2 has a distinct ordering mechanism from Cs3H(SeO4)2, in which quantum fluctuations toward the AF ordering are enhanced through the PAPT associated with the in-phase libration.

Temperature-Dependent Low-Frequency Vibrations of Thiamine Crystal Containing Hydrated Ions.

Low-frequency vibrations of crystalline molecules are very sensitive to the local environment in which the molecules, for example, hydrated ions captured in crystals, find themselves. We present low-temperature X-ray crystallographic measurements on the harvested thiamine crystal containing hydrated ions and its temperature-dependent terahertz spectra and synchrotron infrared microspectra. It is found from the X-ray structure that the hydrated ions and hydration water are in a similar environment to liquid, although those are captured in crystals. The vibrationally resolved THz spectra of two states in the present organic crystals containing hydrated ions are well explained by the difference in the hydrogen-bonded pattern. Peak assignments were performed based on highly accurate first-principles calculations incorporating relativistic effects and dispersion corrections. The temperature dependences are observed for the vibrations around the chloride ions and hydration water due to the loose binding of chloride ions, the bond elongation with increasing temperature, and the cleavage of weak hydrogen bonds.

Self-Assembly of Surfactin into Nanofibers with Hydrophilic Channels in Nonpolar Organic Media.

We investigated the self-assembly of surfactin (SFNa), a cyclic peptide amphiphile produced by Bacillus subtilis, in a nonpolar organic solvent, namely, cyclohexane (CHx). The CHx solution of SFNa formed a thermoreversible organogel. Transmission electron microscopy and small-angle X-ray scattering (SAXS) analyses showed that gelation of the CHx solution of SFNa was caused by physical cross-linking of SFNa nanofibers. Wide-angle X-ray diffraction and Fourier-transform infrared analyses showed that the SFNa nanofibers were formed by one-dimensional stacking of SFNa rings with a period of 0.48 nm corresponding to the length of inter-ring hydrogen bonds between amide groups. A combination of SAXS and small-angle neutron scattering investigations of CHx and deuterated CHx solutions of SFNa nanofibers containing H2O or D2O showed that the SFNa nanofibers had a hydrophilic interior and formed water channels by water incorporation in this region.

Supramolecular Biocomposite Hydrogels Formed by Cellulose and Host-Guest Polymers Assisted by Calcium Ion Complexes.

Hydrogels are biocompatible polymer networks; however, they have the disadvantage of having poor mechanical properties. Herein, the mechanical properties of host-guest hydrogels were increased by adding a filler and incorporating other noncovalent interactions. Cellulose was added as a filler to the hydrogels to afford a composite. Citric acid-modified cellulose (CAC) with many carboxyl groups was used instead of conventional cellulose. The preparation began with mixing an acrylamide-based αCD host polymer (p-αCD) and a dodecanoic acid guest polymer (p-AADA) to form supramolecular hydrogels (p-αCD/p-AADA). However, when CAC was directly added to p-αCD/p-AADA to form biocomposite hydrogels (p-αCD/p-AADA/CAC), it showed weaker mechanical properties than p-αCD/p-AADA itself. This was caused by the strong intramolecular hydrogen bonding (H-bonding) within the CAC, which prevented the CAC reinforcing p-αCD/p-AADA in p-αCD/p-AADA/CAC. Then, calcium chloride solution (CaCl2) was used to form calcium ion (Ca2+) complexes between the CAC and p-αCD/p-AADA. This approach successfully created supramolecular biocomposite hydrogels assisted by Ca2+ complexes (p-αCD/p-AADA/CAC/Ca2+) with improved mechanical properties relative to p-αCD/p-AADA hydrogels; the toughness was increased 6-fold, from 1 to 6 MJ/m3. The mechanical properties were improved because of the disruption of the intramolecular H-bonding within the CAC by Ca2+ and subsequent complex formation between the carboxyl groups of CAC and p-AADA. This mechanism is a new approach for improving the mechanical properties of hydrogels that can be broadly applied as biomaterials.

Phonon-assisted proton tunneling in the hydrogen-bonded dimeric selenates of Cs3H(SeO4)2.

In phases III and IV of Cs3H(SeO4)2, the vibrational state and intrabond transfer of the proton in the dimeric selenates are systematically studied with a wide range of absorbance spectra, a spin-lattice relaxation rate of 1H-NMR (T1 -1), and DFT calculations. The OH stretching vibrations have extremely broad absorption at around 2350 (B band) and 3050 cm-1 (A band), which originate from the 0-1 and 0-2 transitions in the asymmetric double minimum potential, respectively. The anharmonic-coupling calculation makes clear that the A band couples not only to the libration but also to the OH bending band. The vibrational state (nano-second order) is observed as the response of the proton basically localized in either of the two equivalent sites. The intrabond transfer between those sites (pico-second order) yields the protonic fluctuation reflected in T1 -1. Together with the anomalous absorption [νp2 phonon, libration, tetrahedral deformation (δ440), and 610-cm-1 band], we have demonstrated that the intrabond transfer above 70 K is dominated by the thermal hopping that is collectively excited at 610 cm-1 and the phonon-assisted proton tunneling (PAPT) relevant to the tetrahedral deformation [PAPT(def)]. Below 70 K, T1 -1 is largely enhanced toward the antiferroelectric ordering and the distinct splitting emerges in the libration, which dynamically modulates the O(2)-O'(2) distance of the dimer. The PAPT(lib) associated with the libration is confirmed to be a driving force of the AF ordering.

Effect of Charged Group Spacer Length on Hydration State in Zwitterionic Poly(sulfobetaine) Brushes.

Effect of alkyl chain spacer length between the charged groups (CSL) in zwitterionic poly(sulfobetaine) (PSB) brushes on the hydration state was investigated. PSB brushes with ethyl (PMAES), propyl (PMAPS), or butyl (PMABS) CSL were prepared by surface-initiated atom transfer radical polymerization on silicon wafers. Hydration states of the PSB brushes in aqueous solutions and/or humid vapor were investigated by contact angle measurement, infrared spectroscopy, AFM observation, and neutron reflectivity. The PSB brushes are swollen in humid air and deionized water due to the hydration of the charged groups leading to the reduction of hydrated PSB brushes/water interfacial free energy. The hydrated PSB brushes exhibit clear interface with low interfacial roughness due to networking of the PSB brush chains through association of the SBs. The hydrated PSB brushes produce diffusive swollen layer in the presence of NaCl because of the charge screening followed by SB dissociation by the bound ions. The ionic strength sensitivity in the hydration got more significant with increasing the CSL in SBs because of the augmentation in partial charge by charged group separation.

Open-[60]fullerenols with water adsorbed both inside and outside.

The water affinity on [60]fullerenols was found to be governed by surface electrostatic potential while water aggregation is initiated by the hydroxy groups attached on the carbon surface. The molecular water adsorption at the internal sphere caused a significnat inhibition of water adsorption at the external carbon surface.

Excellent capture of N2O functioning at RT and lower pressure by utilizing an NaCaA-85 zeolite.

We have found an efficient adsorption feature provided by an NaCaA-85 zeolite for N2O even at 298 K and at lower pressures: N2O adsorption capacities of 1.33 mmol g-1 and 4.69 mmol g-1 under respective pressures of 0.3 and at 100 Torr, respectively, indicating the best performance among adsorbent materials so far reported. These adsorption peculiarities will pave a new way for developing excellent materials working for adsorption/separation processes of N2O.

Hyperconfined bio-inspired Polymers in Integrative Flow-Through Systems for Highly Selective Removal of Heavy Metal Ions.

Access to clean water, hygiene, and sanitation is becoming an increasingly pressing global demand, particularly owing to rapid population growth and urbanization. Phytoremediation utilizes a highly conserved phytochelatin in plants, which captures hazardous heavy metal ions from aquatic environments and sequesters them in vacuoles. Herein, we report the design of phytochelatin-inspired copolymers containing carboxylate and thiolate moieties. Titration calorimetry results indicate that the coexistence of both moieties is essential for the excellent Cd2+ ion-capturing capacity of the copolymers. The obtained dissociation constant, KD ~ 1 nM for Cd2+ ion, is four-to-five orders of magnitude higher than that for peptides mimicking the sequence of endogenous phytochelatin. Furthermore, infrared and nuclear magnetic resonance spectroscopy results unravel the mechanism underlying complex formation at the molecular level. The grafting of 0.1 g bio-inspired copolymers onto silica microparticles and cellulose membranes helps concentrate the copolymer-coated microparticles in ≈3 mL volume to remove Cd2+ ions from 0.3 L of water within 1 h to the drinking water level (<0.03 µM). The obtained results suggest that hyperconfinement of bio-inspired polymers in flow-through systems can be applied for the highly selective removal of harmful contaminants from the environmental water.

Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change.

Novel water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles, having dibenzophenazine as the acceptor and heteroatom-bridged amphiphilic diarylamines as the donors, have been developed. The materials displayed a distinct photoluminescence color change in response to humidity in a poly(vinylalcohol) matrix.

Correction: Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change.

Correction for 'Water-dispersible donor-acceptor-donor π-conjugated bolaamphiphiles enabling a humidity-responsive luminescence color change' by Tomoya Enjou et al., Chem. Commun., 2024, https://doi.org/10.1039/d3cc05749f.

Optical conductivity measurement of a dimer Mott-insulator to charge-order phase transition in a two-dimensional quarter-filled organic salt compound.

We report a novel insulator-insulator transition arising from the internal charge degrees of freedom in the two-dimensional quarter-filled organic salt ß-(meso-DMBEDT-TTF)2PF6. The optical conductivity spectra above Tc=70 K display a prominent feature of the dimer Mott insulator, characterized by a substantial growth of a dimer peak near 0.6 eV with decreasing temperature. The dimer peak growth is rapidly quenched as soon as a peak of the charge order appears below Tc, indicating a competition between the two insulating phases. Our infrared imaging spectroscopy has further revealed a spatially competitive electronic phase far below Tc, suggesting a nature of quantum phase transition driven by material-parameter variations.

Spreading and structuring of water on superhydrophilic polyelectrolyte brush surfaces.

The wetting behavior of superhydrophilic polyelectrolyte brushes was investigated. Reflection interference contrast microscopy demonstrated that the contact angles of water on the polyelectrolyte brushes were extremely low but remained finite in the range of <3°. The presence of water molecules was evident, even outside the macroscopic water droplet. These water molecules were confined to the thin brush layers and contained a highly ordered hydrogen bond network, which was identified as structural water. The presence of the thin film and the structural water changed the surface energies, which prevented the complete wetting of the surface.

Highly Stretchable Stress-Strain Sensor from Elastomer Nanocomposites with Movable Cross-links and Ketjenblack.

Practical applications like very thin stress-strain sensors require high strength, stretchability, and conductivity, simultaneously. One of the approaches is improving the toughness of the stress-strain sensing materials. Polymeric materials with movable cross-links in which the polymer chain penetrates the cavity of cyclodextrin (CD) demonstrate enhanced strength and stretchability, simultaneously. We designed two approaches that utilize elastomer nanocomposites with movable cross-links and carbon filler (ketjenblack, KB). One approach is mixing SC (a single movable cross-network material), a linear polymer (poly(ethyl acrylate), PEA), and KB to obtain their composite. The electrical resistance increases proportionally with tensile strain, leading to the application of this composite as a stress-strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other approach is a composite made with KB and a movable cross-network elastomer for knitting dissimilar polymers (KP), where movable cross-links connect the CD-modified polystyrene (PSCD) and PEA. The obtained composite acts as a highly sensitive stress-strain sensor that exhibits an exponential increase in resistance with increasing tensile strain due to the polymer dethreading from the CD rings. The designed preparations of highly repeatable or highly responsive stress-strain sensors with good mechanical properties can help broaden their application in electrical devices.