Synthesis of Perdeuterated Alkyl Amines/Amides with Pt/C as Catalyst under Mild Conditions.

A convenient method for the synthesis of perdeuterated alkyl amides/amines is disclosed. Perdeuterated acetyl amides can be achieved by a hydrogen-deuterium (H/D) exchange protocol with Pt/C as a catalyst and D2O as a deuterium source under mild conditions. After removal or reduction of the acetyl group, this protocol can provide perdeuterated primary, secondary, and tertiary amines, which are difficult to achieve via other methods.

Analysis of the Thermal Aging Kinetics of Tallow, Chicken Oil, Lard, and Sheep Oil.

Understanding the thermal aging kinetics of animal oils is of vital importance in the storage and applications of animal oils. In this work, we use four different techniques, including UV-Vis spectrometry, viscometry, impedance spectroscopy, and acid-base titration, to study the thermal aging kinetics of tallow, chicken oil, lard, and sheep oil in the temperature range from 120 °C to 180 °C. The evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration are discussed with the defect kinetics. The evolutions of the color centers, defects for dynamic viscosity, and electric dipoles follow second-order, first-order, and zero-order kinetics, respectively. The temperature dependence of rate constants for the evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration satisfies the Arrhenius equation with the same activation energy for individual animal oils. The activation energies are ~43.1, ~23.8, ~39.1, and ~37.5 kJ/mol for tallow, chicken oil, lard, and sheep oil, respectively. The thermal aging kinetics of the animal oils are attributed to the oxidation of triglycerides.

Tailored Solid-State Carbohydrate Nanostructures Based on Star-Shaped Discrete Block Co-Oligomers.

Carbohydrates are key building blocks for advanced functional materials owing to their biological functions and unique material properties. Here, we propose a star-shaped discrete block co-oligomer (BCO) platform to access carbohydrate nanostructures in bulk and thin-film states via the microphase separation of immiscible carbohydrate and hydrophobic blocks (maltooligosaccharides with 1-4 glucose units and solanesol, respectively). BCOs with various star-shaped architectures and saccharide volume fractions were synthesized using a modular approach. In the bulk, the BCOs self-assembled into common lamellar, cylindrical, and spherical carbohydrate microdomains as well as double gyroid, hexagonally perforated lamellar, and Fddd network morphologies with domain spacings of ∼7 nm. In thin films, long-range-ordered periodic carbohydrate microdomains were fabricated via spin coating. Such controlled spatial arrangements of functional carbohydrate moieties on the nanoscale have great application potential in biomedical and nanofabrication fields.

Small angle scattering of diblock copolymers profiled by machine learning.

We outline a machine learning strategy for quantitively determining the conformation of AB-type diblock copolymers with excluded volume effects using small angle scattering. Complemented by computer simulations, a correlation matrix connecting conformations of different copolymers according to their scattering features is established on the mathematical framework of a Gaussian process, a multivariate extension of the familiar univariate Gaussian distribution. We show that the relevant conformational characteristics of copolymers can be probabilistically inferred from their coherent scattering cross sections without any restriction imposed by model assumptions. This work not only facilitates the quantitative structural analysis of copolymer solutions but also provides the reliable benchmarking for the related theoretical development of scattering functions.

Superhelical DNA liquid crystals from dendrimer-induced DNA compaction.

Electrostatic compaction of double stranded DNA induced by a positively charged poly(amidoamine) (PAMAM) dendrimer of generation four (G4) was found to produce two unique types of DNA mesophases, in which the DNA bent into superhelices packed in a tetragonal or hexagonal lattice. The structure formed at a lower dendrimer charge density was three-dimensionally (3D) ordered, as characterized by the P41212 space group with a 41 screw axis in a tetragonal arrangement, showing that the weakly bent DNA superhelices with a pitch length of ca. 5.0 nm possessed both identical handedness and phase conservation. The 3D ordered structure transformed into a 2D mesophase at a higher dendrimer charge density, wherein the strongly bent superhelices with a pitch length of ca. 4.0 nm organized in a hexagonal lattice without lateral coherence of helical trajectory. The counterion valency of the protonic acid that is used to charge the dendrimer was found to influence the phase diagram. Under a given dendrimer charge density, the complex with a multivalent acid-protonated dendrimer tended to form structures with less curved DNA, attesting that the driving force of charge matching was reduced by increasing the counterion valency of the dendrimer.

Dendrimer-mediated columnar mesophase of surfactants.

The columnar mesophase, in which the molecular or supramolecular building blocks with rod-like geometry pack into two-dimensional (2D) lattices, is an important class of mesomorphic structure having been found in various liquid crystalline materials for practical applications. The cylindrical micelles assembled by amphiphilic surfactants may also form columnar mesophases with the micelle packing symmetry being tunable by the molecular characteristics of the surfactants. In this study, we demonstrate that a positively charged tree-like polymer, poly(amidoamine) (PAMAM) G4 dendrimer, acted as an effective structure-directing agent for the columnar mesophase of a common anionic surfactant, sodium dodecyl sulfate (SDS), via their electrostatic interaction. By adjusting the dendrimer charge density and the nominal binding ratio (Xn) of SDS to dendrimer, the electrostatic complexes self-assembled to form a body-centered cubic (BCC) sphere phase, wherein the dendrimers were staggered between the interspaces of the SDS spherical micelles packed in the BCC lattice. Four types of 2D columnar mesophase composed of SDS cylindrical micelles and dendrimers were accommodated within the interstitial tunnels, including the hexagonal columnar phase (Colhex), simple rectangular columnar phase (Colsr), oblique columnar phase (Colob) and centered rectangular columnar phase (Colcr). A detailed analysis of the geometry of the dendrimer in the columnar mesophases revealed that the structural transition was governed by the interplay among the lateral and axial deformations of the dendrimer, and the deformation of the SDS micelle cross section for achieving effective charge matching and accommodation of the dendrimer. The present study demonstrated the power of the dendrimer in directing the long-range ordered packing of oppositely charged cylinders to yield a rich structural polymorphism of the columnar mesophase that may be exploited for the development of functional materials.

Biomimetic Engineering of a Scavenger-Free Nitric Oxide-Generating/Delivering System to Enhance Radiation Therapy.

Nitric oxide (NO) is a potent tumor-cell radiosensitizer but it can be readily scavenged by hemoglobin (Hb) in vivo. A biomimetic incubator that can generate and deliver NO in a scavenger (Hb)-free environment to enhance its radiosensitizing effect to maximize its efficacy in radiotherapy is proposed. This NO incubator comprises a poly(lactic-co-glycolic acid) (PLGA) hollow microsphere (HM) that contains an NO donor (NONOate) and a surfactant molecule (sodium caprate, SC) in its aqueous core. In acidic tumorous environments, the PLGA shell of the HM allows the penetration of protons from the outside, activating the hydrolytic cleavage of NONOate, spontaneously generating NO bubbles, which are immediately trapped/stabilized by SC. The SC-stabilized NO bubbles in the HM are then squeezed through the spaces of its PLGA matrices by the elevated internal pressure. Upon leaving the HM, the entrapped NO molecules may passively diffuse through their SC-stabilized/protected layer gradually to the tumor site, having a long-lasting radiosensitizing effect and inhibiting tumor growth. The entire process of NO generation and delivery is conducted in a scavenger (Hb)-free environment, mimicking the development of young ovoviviparous fish inside their mothers' bodies in the absence of predators before birth.

Resolving solution conformations of the model semi-flexible polyelectrolyte homogalacturonan using molecular dynamics simulations and small-angle x-ray scattering.

The conformation of polyelectrolytes in the solution state has long been of interest in polymer science. Herein we utilize all atom molecular dynamics simulations (MD) and small-angle x-ray scattering experiments (SAXS) to elucidate the molecular structure of the model polyelectrolyte homogalacturonan. Several degrees of polymerization were studied and in addition partial methylesterification of the otherwise charge-carrying carboxyl groups was used in order to generate samples with varying intra-chain charge distributions. It is shown that at length scales above around 1nm the conformation of isolated chains has surprisingly little dependence on the charge distribution or the concentration of attendant monovalent salts, reflective of the intrinsic stiffness of the saccharide rings and the dynamical constraints of the glycosidic linkage. Indeed the conformation of isolated chains over all accessible length scales is well described by the atomic coordinates available from fibre diffraction studies. Furthermore, in more concentrated systems it is shown that, after careful analysis of the SAXS data, the form of the inter-particle effects heralded by the emergence of a so-called polyelectrolyte peak, can be extracted, and that this phenomena can be reproduced by multiple chain MD simulations.

Crystal orientation of PEO confined within the nanorod templated by AAO nanochannels.

The orientation of poly(ethylene oxide) (PEO) crystallites developed in the nanochannels of anodic aluminum oxide (AAO) membrane has been investigated. PEO was filled homogeneously into the nanochannels in the melt state, and the crystallization confined within the PEO nanorod thus formed was allowed to take place subsequently at different temperatures. The effects of PEO molecular weight (MPEO), crystallization temperature (Tc) and AAO channel diameter (DAAO) on the crystal orientation attained in the nanorod were revealed by 2-D wide angle X-ray scattering (WAXS) patterns. In the nanochannels with DAAO = 23 nm, the crystallites formed from PEO with the lowest MPEO (= 3400 g mol-1) were found to adopt a predominantly perpendicular orientation with the crystalline stems aligning normal to the channel axis irrespective of Tc (ranging from -40 to 20 °C). Increasing MPEO or decreasing Tc tended to induce the development of the tilt orientation characterized by the tilt of the (120) plane by 45° from the channel axis. In the case of the highest MPEO (= 95 000 g mol-1) studied, both perpendicular and tilt orientations coexisted irrespective of Tc. Coexistent orientation was always observed in the channels with a larger diameter (DAAO = 89 nm) irrespective of MPEO and Tc. Compared with the previous results of the crystal orientation attained in nanotubes templated by the preferential wetting of the channel walls by PEO, the window of the perpendicular crystal orientation in the nanorod was much narrower due to its weaker confinement effect imposed on the crystal growth than that set by the nanotube.

The effect of linker DNA on the structure and interaction of nucleosome core particles.

In eukaryotes, the compaction of chromatin fibers composed of nucleosome core particles (NCPs) connected by a linker DNA into chromosomes is highly efficient; however, the underlying folding mechanisms remain elusive. We used small angle X-ray scattering (SAXS) to investigate the influence of linker DNA length on the local structure and the interparticle interactions of the NCPs. In the presence of the linker DNA of 30 bp or less in length, the results suggest partial unwrapping of nucleosomal DNA on the NCP irrespective of the linker DNA length. Moreover, the presence of 15 bp linker DNA alleviated the electrostatic repulsion between the NCPs and prevented the formation of an ordered columnar hexagonal phase, demonstrating that the linker DNA plays an active role in chromatin folding.

In Situ Nanoreactor for Photosynthesizing H2 Gas To Mitigate Oxidative Stress in Tissue Inflammation.

Hydrogen gas can reduce cytotoxic reactive oxygen species (ROS) that are produced in inflamed tissues. Inspired by natural photosynthesis, this work proposes a multicomponent nanoreactor (NR) that comprises chlorophyll a, l-ascorbic acid, and gold nanoparticles that are encapsulated in a liposomal (Lip) system that can produce H2 gas in situ upon photon absorption to mitigate inflammatory responses. Unlike a bulk system that contains free reacting molecules, this Lip NR system provides an optimal reaction environment, facilitating rapid activation of the photosynthesis of H2 gas, locally providing a high therapeutic concentration thereof. The photodriven NR system reduces the degrees of overproduction of ROS and pro-inflammatory cytokines both in vitro in RAW264.7 cells and in vivo in mice with paw inflammation that is induced by lipopolysaccharide (LPS). Histological examinations of tissue sections confirm the ability of the NR system to reduce LPS-induced inflammation. Experimental results indicate that the Lip NR system that can photosynthesize H2 gas has great potential for mitigating oxidative stress in tissue inflammation.

Crystallization behavior of crystalline/crystalline polymer blends under confinement in electrospun nanofibers of polystyrene/poly(ethylene oxide)/poly(ε-caprolactone) ternary mixtures.

We have studied the crystallization behavior of crystalline/crystalline blends of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) in electrospun nanofibers fabricated from ternary blends of polystyrene (PS), PEO, and PCL, where PS was present as the majority component. It was demonstrated previously that PEO in PS/PEO binary blend nanofibers with a low PEO weight fraction (≦0.2) crystallized predominantly through homogenous nucleation due to the small PEO domain size which excluded the presence of heterogeneities (Soft Matter, 2016, 12, 5110). Here, it was found that PCL in PS/PCL binary blend nanofibers exhibited similar behavior, but at a much lower weight fraction of PCL (≦0.1) due to the presence of an inherently higher concentration of heterogeneities in the PCL homopolymer. In the PS/PEO/PCL ternary blend nanofibers, where the combined weight fraction of PEO and PCL was kept at 0.2 or less, the crystallization of the two components took place separately through both heterogeneous and homogenous nucleation mechanisms. The phase segregated crystallization behavior was further confirmed by the melting behavior of the blend nanofibers and wide angle X-ray diffraction (WAXD) measurements. Most significantly, the homogenous nucleation of both PEO and PCL was suppressed whereas the heterogeneous nucleation was enhanced in the ternary blend nanofibers even at very low weight fraction of PEO or PCL. This was plausibly attributed to the coupling between the crystallization and the liquid-liquid phase separation (LLPS) of the PEO/PCL mixture dispersed in the PS matrix during non-isothermal cooling of the blend nanofibers. Furthermore, it was observed that thermal treatment of the PS/PEO/PCL blend nanofibers above the glass transition temperature of PS further promoted the heterogeneous nucleation-initiated crystallization of PEO because of a complex interplay between Plateau-Rayleigh instability-induced domain breakup and its further coalescence and demixing within the PEO/PCL domains embedded in the PS matrix.

Ligand displacement induced morphologies in block copolymer/quantum dot hybrids and formation of core-shell hybrid nanoobjects.

We investigate the self-assembly of a cylinder-forming polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) mixed with trioctylphosphine oxide (TOPO) capped cadmium selenide (CdSe) quantum dots (QDs). The QDs were found to be enthalpically compatible with the P4VP chains via ligand displacement of TOPO from the QD surface. However, the QDs were found to localize preferentially at the PS/P4VP interphase plausibly to gain translational entropy in order to further lower the energetics of the self-assembled structure. Interestingly, the morphological transformation observed with increasing weight fraction of the QDs in the BCP/QD composite was driven by the migration of the displaced TOPO from the QD surface to the PS phase, effectively increasing its total volume fraction. Hence, the PS-b-P4VP BCP with PS as the minority block displayed lamellar morphology in its composite with QDs. Furthermore, the preferred localization of the QDs at the PS/P4VP interface led to the formation of a trilayer lamellar morphology which was deduced from the suppression of the primary scattering peak, relative to higher order peaks in the SAXS data. The morphological transformation was accompanied by a significant increase in the domain spacing due to excessive stretching of the longer P4VP chains of the asymmetric block copolymer. However, in the PS-b-P4VP/CdSe composites with P4VP as the minority block, cylindrical morphology was retained and the domain spacing decreased due to dominance of the co-surfactant effect as well as interfacial localization of CdSe QDs. We also demonstrate that these PS-b-P4VP/CdSe self-assembled hybrid materials could further be used to obtain isolated core-shell nanoobjects, such as nanofibers and nanosheets, containing CdSe QDs. The nanoobjects so obtained exhibited photoluminescence properties typical of CdSe quantum dots. These photoluminescent polymer nanoobjects could have potential applications in biological targeting and fluorescence labeling.

Crystallization behaviour of poly(ethylene oxide) under confinement in the electrospun nanofibers of polystyrene/poly(ethylene oxide) blends.

We have studied the confined crystallization behaviour of poly(ethylene oxide) (PEO) in the electrospun nanofibers of the phase-separated blends of polystyrene (PS) and PEO, where PS was present as the major component. The size and shape of PEO domains in the nanofibers were considerably different from those in the cast films, presumably because of the nano-dimensions of the nanofibers and the extensional forces experienced by the polymer solution during electrospinning. The phase-separated morphology in turn influenced the crystallization behaviour of PEO in the blend nanofibers. At a PEO weight fraction of ≥0.3, crystallization occurred through a heterogeneous nucleation mechanism similar to that in cast blend films. However, as the PEO weight fraction in the blend nanofibers was reduced from 0.3 to 0.2, an abrupt transformation of the nucleation mechanism from the heterogeneous to predominantly homogenous type was observed. The change in the nucleation mechanism implied a drastic reduction of the spatial continuity of PEO domains in the nanofibers, which was not encountered in the cast film. The melting temperature and crystallinity of the PEO crystallites developed in the nanofibers were also significantly lower than those in the corresponding cast films. The phenomena observed were reconciled by the morphological observation, which revealed that the phase separation under the radial constraint of the nanofibers led to the formation of small-sized fibrillar PEO domains with limited spatial connectivity. The thermal treatment of the PS/PEO blend nanofibers above the glass transition temperature of PS induced an even stronger confinement effect on PEO crystallization.

Zooming in: Structural Investigations of Rheologically Characterized Hydrogen-Bonded Low-Methoxyl Pectin Networks.

Self-assembled hydrogen-bonded networks of the polysaccharide pectin, a mechanically functional component of plant cell walls, have been of recent interest as biomimetic exemplars of physical gels, and the microrheological and strain-stiffening behaviors have been previously investigated. Despite this detailed rheological characterization of preformed gels, little is known about the fundamental arrangement of the polymers into cross-linking junction zones, the size of these bonded regions, and the resultant network architecture in these hydrogen-bonded materials, especially in contrast to the plethora of such information available for their well-known calcium-assembled counterparts. In this work, in concert with pertinent rheological measurements, an in-depth structural study of the hydrogen-bond-mediated gelation of pectins is provided. Gels were realized by using glucona-delta-lactone to decrease the pH of solutions of pectic polymers that had a (blockwise) low degree of methylesterification. Small-angle X-ray scattering and transmission electron microscopy were utilized to access structural information on length scales on the order of nanometers to hundreds of nanometers, while complementary mechanical properties were measured predominantly using small amplitude oscillatory shear rheology.

Hierarchical self-assembly of nanoparticles in polymer matrix and the nature of the interparticle interaction.

Using small angle X-ray scattering (SAXS), we elucidated the spatial organization of palladium (Pd) nanoparticles (NPs) in the polymer matrix of poly(2-vinylpyridine) (P2VP) and the nature of inter-nanoparticle interactions, where the NPs were synthesized in the presence of P2VP by the reduction of palladium acetylacetonate (Pd(acac)2). The experimental SAXS profiles were analysed on the basis of a hierarchical structure model considering the following two types of interparticle potential: (i) hard-core repulsion only (i.e., the hard-sphere interaction) and (ii) hard-core repulsion together with an attractive potential well (i.e., the sticky hard-sphere interaction). The corresponding theoretical scattering functions, which were used for analysing the experimental SAXS profiles, were obtained within the context of the Percus-Yevick closure and the Ornstein-Zernike equation in the fundamental liquid theory. The analyses revealed that existence of the attractive potential well is indispensable to account for the experimental SAXS profiles. Moreover, the morphology of the hybrids was found to be characterized by a hierarchical structure with three levels, where about six primary NPs with the diameter of ca. 1.8 nm (level one) formed local clusters (level two), and these clusters aggregated to build up a large-scale mass-fractal structure (level three) with the fractal dimension of ca. 2.3. The scattering function developed here is of general use for quantitatively characterizing the morphological structures of polymer/NP hybrids and, in particular, for exploring the interaction potential of the NPs on the basis of the fundamental liquid theory.

Hierarchical structure and crystal orientation in poly(ethylene oxide)/clay nanocomposite films.

Water-cast nanocomposite films formed by poly(ethylene oxide) (PEO) and Laponite clay were found to display three characteristic levels of structure with large-scale orientation. The first level with the length scale of ca. 30-50 nm was the clay lamellar bundles, which tended to stack perpendicularly to the film surface. The second level with the characteristic length of 1.8 nm was associated with the alternating stacking of the silicate layers and the PEO chains sandwiched between them. The preferred orientations of these two levels of structure were independent of clay content, solvent removal rate for the film preparation, and the crystallization temperature of the PEO chains situating outside the clay bundles. The third level of structure was characterized by the preferred orientation of the PEO crystalline stems with respect to the surface of the silicate layers. Perpendicular orientation always dominated in the nanocomposite films prepared by slow solvent removal irrespective of crystallization temperature. In the films prepared by fast solvent removal, however, parallel crystal orientation set in as the clay concentration exceeded ca. 33 wt %. The preferred crystal orientation was ascribed to the confinement effect imposed by the clay bundles to the crystallization of the PEO chains situating in the interbundle region. In the films cast by slow solvent removal, the weaker confinement associated with the larger interbundle distance led to perpendicular crystal orientation. When the interbundle distance was reduced to ca. 30 nm in the films prepared by rapid solvent evaporation, the strong confinement directed the crystals to form parallel orientation.

PEGylation site-dependent structural heterogeneity study of monoPEGylated human parathyroid hormone fragment hPTH(1-34).

The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1-34) as well as their unmodified counterparts, poly(ethylene glycol) (PEG) and hPTH(1-34), have been studied by small-angle neutron scattering (SANS). The scattering results show that free hPTH(1-34) in 100 mM phosphate buffer (pH 7.4) aggregates into clusters. After conjugation with PEG, the PEG-peptide conjugates self-assemble into a supramolecular core-shell structure with a cylindrical shape. The PEG chains form a shell around the hPTH(1-34) core to shield hPTH(1-34) from the solvent. The detailed structural information on the self-assembled structures is extracted from SANS using a model of the cylindrical core with a shell of Gaussian chains attached to the core surface. On the basis of the data, because of the charge-dipole interactions between the conjugated PEG chain and the peptide, the conjugated PEG chain forms a more collapsed conformation compared to free PEG. Moreover, the size of the self-assembled structures formed by the C-terminally monoPEGylated hPTH(1-34) is about 3 times larger than that of the N-terminally monoPEGylated hPTH(1-34). The different aggregation numbers of the self-assembled structures, triggered by different PEGylation sites, are reported. These size discrepancies because of different PEGylation sites could potentially affect the pharmacokinetics of the hPTH(1-34) drug.

Helical packing of nanoparticles confined in cylindrical domains of a self-assembled block copolymer structure.

Theoretical models predict that a variety of self-assembled structures of closely packed spherical particles may result when they are confined in a cylindrical domain. In the present work we demonstrate for the first time that the polymer-coated nanoparticles confined in the self-assembled cylindrical domains of a block copolymer pack in helical morphology, where we can isolate individual fibers filled with helically arranged nanoparticles. This finding provides unique possibilities for fundamental as well as application-oriented research in similar directions.

Harnessing HfO2 Nanoparticles for Wearable Tumor Monitoring and Sonodynamic Therapy in Advancing Cancer Care.

Addressing the critical requirement for real-time monitoring of tumor progression in cancer care, this study introduces an innovative wearable platform. This platform employs a thermoplastic polyurethane (TPU) film embedded with hafnium oxide nanoparticles (HfO2 NPs) to facilitate dynamic tracking of tumor growth and regression in real time. Significantly, the synthesized HfO2 NPs exhibit promising characteristics as effective sonosensitizers, holding the potential to efficiently eliminate cancer cells through ultrasound irradiation. The TPU-HfO2 film, acting as a dielectric elastomer (DE) strain sensor, undergoes proportional deformation in response to changes in the tumor volume, thereby influencing its electrical impedance. This distinctive behavior empowers the DE strain sensor to continuously and accurately monitor alterations in tumor volume, determining the optimal timing for initiating HfO2 NP treatment, optimizing dosages, and assessing treatment effectiveness. Seamless integration with a wireless system allows instant transmission of detected electrical impedances to a smartphone for real-time data processing and visualization, enabling immediate patient monitoring and timely intervention by remote medical staff. By combining the dynamic tumor monitoring capabilities of the TPU-HfO2 film with the sonosensitizer potential of HfO2 NPs, this approach propels cancer care into the realm of telemedicine, representing a significant advancement in patient treatment.