Depth-Resolved Characterization of Perylenediimide Side-Chain Polymer Thin Film Structure Using Grazing-Incidence Wide-Angle X-ray Diffraction with Tender X-rays

Polymers with a perylenediimide (PDI) side chain (PAc12PDI) consist of two kinds of crystalline structures with various types of orientations in a thin film. Understanding the population of the microcrystalline structure and its orientation along the thickness is strongly desired. Grazing-incidence wide-angle X-ray diffraction (GIWAXD) measurements with hard X-rays, which are generally chosen as λ = 0.1 nm, are a powerful tool to evaluate the molecular aggregation structure in thin films. A depth-resolved analysis for the outermost surface of the polymeric materials using conventional GIWAXD measurements, however, has limitations on depth resolution because the X-ray penetration depth dramatically increases above the critical angle. Meanwhile, tender X-rays (λ = 0.5 nm) have the potential advantage that the penetration depth gradually increases above the critical angle, leading to precise characterization for the population of crystallite distribution along the thickness. The population of the microcrystalline states in the PAc12PDI thin film was precisely characterized utilizing GIWAXD measurements using tender X-rays. The outermost surface of the PAc12PDI thin film is occupied by a monoclinic lattice with a = 2.38 nm, b = 0.74 nm, c = 5.98 nm, and β = 108.13°, while maintaining the c-axis perpendicular to the substrate surface. Additionally, the presence of solid substrate controls the formation of the crystallite with unidirectional orientation.

Preparation of High-Density Polymer Brushes with a Multihelical Structure

It is well-known that a mixture of isotactic and syndiotactic polymethyl methacrylate (PMMA) forms a stereocomplex consisting of a multihelical structure in which an isotactic chain is surrounded by a syndiotactic chain. Here, we report the basic structure of the stereocomplex formed when the syndiotactic PMMA chains are tethered to a silicon substrate and form a high-density polymer brush. The influence of geometric confinement was investigated by preparing the high-density polymer brushes on a flat and spherical substrate. In both cases, mixing the untethered isotactic PMMA with the grafted syndiotactic PMMA led to the formation of a stereocomplex with a multihelical structure. Static contact angle measurements showed a hindered surface mobility at the outermost surface of the polymer brush, indicating that the stereocomplex forms a crystalline structure. A syndiotactic polymer brush with substituted fluoroalkyl groups was prepared to increase the contrast for grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements. The GIWAXD results verified that the stereocomplex forms a crystalline structure oriented perpendicular to the substrate with a relatively low degree of orientation.

Design of High-Density Helical Polymer Brush on Silica Nanoparticles for the Size Recognition of Fullerene Molecules

High-density syndiotactic poly(methyl methacrylate) (st-PMMA) brushes form a helical structure and encapsulate fullerene molecules in their helical cavities, leading to a PMMA brush/fullerene inclusion complex. The brushes recognize the size of guest molecules and spontaneously adapt their helical diameter to the guest molecules. Both polymer brush/C₆₀ and polymer brush/C₇₀ inclusion complex on the flat substrate were characterized on the basis of grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements, and it is revealed that the main chains oriented perpendicular to the substrate. Moreover, high-density st-PMMA brushes grafted onto nanoparticles efficiently separate C₇₀ molecules from the mixture of C₆₀ and C₇₀ solution. Even after 5× repeating process, the selectivity for C₇₀ molecules remains at 99%.

X-Ray diffraction and resonance shear measurement of nano-confined ionic liquids

The X-ray diffraction and resonance shear measurement (RSM) demonstrated the relation between the structure and lubrication properties of ionic liquid ([C₄mim][NTf₂], [C₄mim][BF₄]) films of nanometer thickness confined between silica surfaces.

Transformation of Coiled α-Helices into Cross-β-Sheets Superstructure

The fibrous silk produced by bees, wasps, ants, or hornets is known to form a four-strand α-helical coiled coil superstructure. We have succeeded in showing the formation of this coiled coil structure not only in natural fibers, but also in artificial films made of regenerated silk of the hornet Vespa simillima xanthoptera using wide- and small-angle X-ray scatterings and polarized Fourier transform infrared spectroscopy. On the basis of time-resolved simultaneous synchrotron X-ray scattering observations for in situ monitoring of the structural changes in regenerated silk material during tensile deformation, we have shown that the application of tensile force under appropriate conditions induces a transition from the coiled α-helices to a cross-β-sheet superstructure. The four-stranded tertiary superstructure remains unchanged during this process. It has also been shown that the amorphous protein chains in the regenerated silk material are transformed into conventional β-sheet arrangements with varying orientation.

Molecular Interaction between Intercellular Lipids in the Stratum Corneum and l-Menthol, as Analyzed by Synchrotron X-Ray Diffraction

l-Menthol increases drug partitioning on the surface of skin, diffusion of drugs in the skin, and lipid fluidity in the stratum corneum and alters the rigidly arranged lipid structure of intercellular lipids. However, l-menthol is a solid at room temperature, and it is difficult to determine the effects of l-menthol alone. In this study, we vaporized l-menthol in order to avoid the effects of solvents. The vaporized l-menthol was applied to the stratum corneum or lipid models comprising composed of ceramides (CER) [EOS], the longest lipid acyl chain of the ceramides in the stratum corneum lipids that is associated with the barrier function of the skin; CER [NS], the shorter lipid acyl chain of the ceramides, and the most components in the stratum corneum of the intercellular lipids that is associated with water retention in the intercellular lipid structure of the stratum corneum; cholesterol; and palmitic acid. Synchrotron X-ray diffraction, differential scanning calorimetry, and attenuated total reflection Fourier transform infrared spectroscopy analyses revealed that the lipid models were composed of hexagonal packing and orthorhombic packing structures of different lamellar periods. Taken together, our results revealed that l-menthol strongly affected the lipid model composed of CER [EOS]. Therefore, l-menthol facilitated the permeation of drugs through the skin by liquid crystallization of the longer lamellar structure. Importantly, these simple lipid models are useful for investigating microstructure of the intercellular lipids in the stratum corneum.

Platonic Micelles: Monodisperse Micelles with Discrete Aggregation Numbers Corresponding to Regular Polyhedra

The concept of micelles was first proposed in 1913 by McBain and has rationalized numerous experimental results of the self-aggregation of surfactants. It is generally agreed that the aggregation number (Nagg) for spherical micelles has no exact value and a certain distribution. However, our studies of calix[4]arene surfactants showed that they were monodisperse with a defined Nagg whose values are chosen from 6, 8, 12, 20, and 32. Interestingly, some of these numbers coincide with the face numbers of Platonic solids, thus we named them "Platonic micelles". The preferred Nagg values were explained in relation to the mathematical Tammes problem: how to obtain the best coverage of a sphere surface with multiple identical circles. The coverage ratio D(N) can be calculated and produces maxima at N = 6, 12, 20, and 32, coinciding with the observed Nagg values. We presume that this "Platonic nature" may hold for any spherical micelles when Nagg is sufficiently small.

Elastomers built up through the π–π stacking association of polycyclic planar aromatic diimides

Polymers composed of polycyclic aromatic planar diimide (PCAD) units and flexible rubbery poly(propylene glycol) (PPG) chains were synthesized, and the morphology and viscoelasticity were investigated.

Effect of Nerolidol and/or Levulinic Acid on the Thermotropic Behavior of Lipid Lamellar Structures in the Stratum Corneum

Permeation enhancers are required to deliver drugs through the skin efficiently and maintain effective blood concentrations. Studies of the barrier function of the stratum corneum using l-menthol, a monocyclic monoterpene widely used in medicines and foods, have revealed an interaction between characteristic intercellular lipid structures in the stratum corneum and permeation enhancers. The variety of permeation enhancers that can be used to contribute to transdermal delivery systems beyond l-menthol is increasing. In this study, we focused on nerolidol and levulinic acid and investigated their influence on stratum corneum lipid structures. Nerolidol, a sesquiterpene, has been reported to enhance the permeation of various drugs. Levulinic acid is reported to enhance the permeability of buprenorphine and is used as a component of the buprenorphine^® patch. Synchrotron X-ray diffraction and attenuated total reflectance Fourier transform IR spectroscopy measurements revealed that nerolidol disturbs the rigidly arranged lipid structure and increases lipid fluidity. Levulinic acid had a smaller effect on stratum corneum lipid structures, but did increase lipid fluidity when co-administered with nerolidol or heat. We found that nerolidol has an effect on stratum corneum lipids similar to that of l-menthol, and levulinic acid had an effect similar to that of oleic acid.

Identification of a Plasmid-Mediated Quinolone Resistance Gene in Salmonella Isolates from Texas Dairy Farm Environmental Samples

A recent increase in plasmid-mediated quinolone resistance (PMQR) has been detected among Salmonella isolated from humans in the United States, and it is necessary to determine the sources of human infection. We had previously isolated Salmonella from dairy farm environmental samples collected in Texas, and isolates were tested for anti-microbial susceptibility. Two isolates, serotyped as Salmonella Muenster, showed the discordant pattern of nalidixic acid susceptibility and intermediate susceptibility to ciprofloxacin. For this project, whole-genome sequencing of both isolates was performed to detect genes associated with quinolone resistance. The plasmid-mediated qnrB19 gene and IncR plasmid type were identified in both isolates. To our knowledge, this is the first report of PMQR in Salmonella isolated from food animals or agricultural environments in the United States.

Two Distinct Cylinder Arrangements in Monodomains of a Lyotropic Liquid Crystalline Hexagonal II Phase: Monodomains with Straight Cylinders and Ringed Cylinders in Capillaries

We report a method to produce two different monodomains of an inverse hexagonal II (HII) phase in capillaries. Capillaries filled with glyceryl monooleyl ether (GME) in an inverted micellar phase were soaked in water. After a week, a monodomain of the HII phase with straight cylinders was observed in a capillary with a diameter of 1.0 mm. The axis of the straight cylinders was almost parallel to the capillary axis, and the cylinders were slightly undulated. The lattice constant of the HII phase was 5.85 nm, which indicated the monodomain was fully hydrated. Another monodomain with ringed cylinders was observed in a 0.2 mm diameter capillary. The ringed cylinders aligned to the round capillary wall, where one of the ⟨10⟩ directions in the hexagonal lattice always faced the wall. The lattice constant was 4.89 nm, from which the estimated water content of the monodomain was almost the lowest reported for the HII phase. The monodomain with ringed cylinders is stabilized by the capillary wall and the low water content. This method to produce specific monodomains is expected to be of benefit for basic and applied research on the HII phase.

In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts

A molded film of single-component polymer-grafted nanoparticles (SPNP), consisting of a spherical silica core and densely grafted polymer chains bearing hydrogen-bonding side groups capable of physical crosslinking, was investigated by in situ ultra-small-angle X-ray scattering (USAXS) measurement during a uniaxial stretching process. Static USAXS revealed that the molded SPNP formed a highly oriented twinned face-centered cubic (f.c.c.) lattice structure with the [11-1] plane aligned nearly parallel to the film surface in the initial state. Structural analysis of in situ USAXS using a model of uniaxial deformation induced by rearrangement of the nanoparticles revealed that the f.c.c. lattice was distorted in the stretching direction in proportion to the macroscopic strain until the strain reached 35%, and subsequently changed into other f.c.c. lattices with different orientations. The lattice distortion and structural transition behavior corresponded well to the elastic and plastic deformation regimes, respectively, observed in the stress-strain curve. The attractive interaction of the hydrogen bond is considered to form only at the top surface of the shell and then plays an effective role in cross-linking between nanoparticles. The rearrangement mechanism of the nanoparticles is well accounted for by a strong repulsive interaction between the densely grafted polymer shells of neighboring particles.

Molecular Orientation Enhancement of Silk by the Hot-Stretching-Induced Transition from α-Helix-HFIP Complex to β-Sheet

Enhancing the molecular orientation of the regenerated silk fibroin (RF) up to a level comparable to the native silk is highly challenging. Our novel and promising strategy for the poststretching process is (1) creating at first an α-helix-HFIP complex with a hexagonal packing as an intermediate state and then (2) stretching it at a high temperature to induce the helix-to-sheet structural phase transition. Here we show for the first time the significantly high stretching efficiency of the proposed technique compared with the conventional wet-stretching techniques and the successful achievement of higher crystalline orientation and higher Young's modulus compared even with the native silk. The detailed structural analysis based on the time-resolved simultaneous measurement of stress-strain curve, synchrotron X-ray scatterings, and FTIR has revealed the structural transition mechanism from the hexagonally packed α-helix-HFIP complex to the highly oriented β-sheet crystalline state as well as the critical level of crystal orientation needed for the helix-to-sheet transition.