Solvent-Responsive Nonporous Adaptive Crystals Derived from Pyridinium Hydrochloride and the Application in Iodine Adsorption.

Nonporous adaptive crystals (NACs) are crystalline nonporous materials that can undergo a structural adaptive phase transformation to accommodate specific guest via porous cavity or lattice voids. Most of the NACs are based on pillararenes because of their flexible backbone and intrinsic porous structure. Here a readily prepared organic hydrochloride of 4-(4-(diphenylamino)phenyl)pyridin-1-ium chloride (TPAPyH), exhibiting the solvent dimension-dependent adaptive crystallinity is reported. Wherein it forms a nonporous α crystal in a solvent with larger dimensions, while forming two porous ß and γ crystals capable of accommodating solvent molecules in solvent with small size. Furthermore, the thermal-induced single-crystal-to-single-crystal (SCSC) transition from the ß to α phase can be initiated. Upon exposure to iodine vapor or immersion in aqueous solution, the nonporous α phase transforms to porous ß phase by adsorbing iodine molecules. Owing to the formation of trihalide anion I2Cl- within the crystal cavity, TPAPyH exhibits remarkable performance in iodine storage, with a high uptaking capacity of 1.27 g g-1 and elevated iodine desorption temperature of up to 110 and 82 °C following the first and second adsorption stage. The unexpected adaptivity of TPAPyH inspires the design of NACs for selective adsorption and separation of volatile compound from organic small molecules.

Controlled Molecular Arrangement of Cinnamic Acid in Layered Double Hydroxide through pi-pi Interaction for Controlled Release.

Cinnamic acid (CA) was successfully incorporated into Zn-Al layered double hydroxide (LDH) through coprecipitation. The CA moiety was stabilized in the interlayer space through not only electrostatic interaction but also intermolecular π-π interaction. It was noteworthy that the CA arrangement was fairly independent of the charge density of LDH, showing the important role of the layer-CA and CA-CA interactions in molecular stabilization. Computer simulations using the Monte Carlo method as well as analytical approaches including infrared, UV-vis spectroscopy, and differential scanning calorimetry showed the existence of intermolecular interaction. In order to reinforce molecular stabilization, a neutral derivative of CA, cinnamaldehyde (CAD), was additionally incorporated into LDH. It was clearly shown that CAD played a role as a π-π interaction mediator to enhance the stabilization of CA. The time-dependent release of CA from LDH was first governed by the layer charge density of LDH; however, the existence of CAD provided additional stabilization to the CA arrangement to slow down the release kinetics.

Controlled molecular arrangement of easily aggregated deoxycholate with layered double hydroxide.

Deoxycholate (DA) is a natural emulsifying agent involved in the absorption of dietary lipids. Due to the facial distribution of hydrophobic-hydrophilic region, DA easily aggregates under ambient conditions, and this property hinders the practical application of DA in clinical applications. In this study, we found that the molecular arrangement of DA molecules could be controlled by using layered double hydroxide (LDH) under a specific reaction condition. The effect of reaction methods such as co-precipitation, ion exchange and reconstruction on the molecular arrangement of DA was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, high-resolution transmission electron microscopy and differential scanning calorimetry. It was demonstrated that the self-aggregation of DA molecules could be suppressed by the oriented arrangement of DA between the gallery space of LDH. The DA moiety was well stabilized in the LDH layers due to the electrostatic interaction between DA molecules and LDH layers. The most ordered arrangement of DA molecules was observed when DA was incorporated into LDH via a reconstruction method. The DA molecules arranged in LDH via reconstruction did not show significant exothermic or endothermic behaviour up to 400°C, showing that the DA moiety lost its intermolecular attraction in between LDH layers.

Control of parallel versus antiparallel molecular arrangements in crystalline assemblies of alkyl ß-cellulosides.

HYPOTHESIS: The precise control of parallel versus antiparallel molecular arrangements in synthetic assemblies of biorelated molecules is an attractive research focus from both scientific and technological viewpoints. However, little is known about cellulose-based synthetic assemblies. We hypothesized the existence of potential parameters, such as temperature, salt concentration, salt species, and solvent species, for controlling the molecular arrangement in assemblies of alkyl ß-cellulosides with different alkyl chain lengths. EXPERIMENTAL: The self-assembly of alkyl ß-cellulosides was triggered by neutralization-induced water insolubilization. The crystal structures of the cellulose moieties in the assemblies were characterized by attenuated total reflection-Fourier transform infrared absorption spectroscopy and wide-angle X-ray diffraction measurements. The morphologies of the assemblies were also characterized by scanning electron, atomic force, and transmission electron microscopy. FINDINGS: The temperature for the self-assembly, the concentration and species of inorganic salt in the self-assembly solution, and the solvent species (namely, the addition of water-miscible organic solvents into the self-assembly solution) strongly affected the molecular arrangement of the assemblies. The observations suggested that hydrophobic effects between the alkyl groups of the alkyl ß-cellulosides and/or interactions of the alkyl ß-cellulosides with solvent species were potential factors for controlling the molecular arrangement.

En Route Towards the Control of Luminescent, Optically-Active 3D Architectures.

π-Extended systems are key components for the development of future organic electronic technologies. While conceiving molecules with improved properties is fundamental for the evolution of materials science, keeping control over the 3D arrangement of molecules represents an ever-expanding challenge. Herein, a synthetic protocol to replace carbon atoms of π-systems by dissymmetric phosphorus atoms is reported; in particular, it allowed for conceiving new fused phosphapyrene derivatives with improved properties. The presence of dissymmetric phosphorus atoms precluded the formation of excimers. X-ray diffraction revealed that, meanwhile, strong intermolecular interactions are taking place in the solid state. The phosphapyrenes photoluminesce in the visible region with high quantum yields; importantly, they are CD-active. In addition, the unique non-planar features of phosphorus atoms allowed for the control of the 3D arrangement of molecules, rendering lemniscate-like structures. Based on our discoveries, we envisage the possibility to construct higher-order, chiral 3D architectures from larger phosphorus-containing π-systems.

Molecular Dynamic Investigations on the Adhesion Behaviors of Asphalt Mastic-Aggregate Interface.

The asphalt mastic-aggregate interface plays an essential role in determining the service performance of asphalt mixtures. The objective of this paper was to investigate the adhesion behaviors and mechanism between asphalt mastic and aggregate based on molecular dynamic (MD) simulations. First, the asphalt mastic model considering the actual mass ratio of filler to asphalt (F/A) condition was established and validated in terms of thermodynamic properties. Second, the molecular arrangement characteristics of polar components on the aggregate substrate were analyzed by radial distribution function (RDF), relative concentration (RC), and mean square displacement (MSD). Third, the interfacial adhesion ability between asphalt and aggregate was quantitively evaluated based on the work of adhesion. Finally, the coupling effect of moisture and temperature on interfacial adhesion behaviors was investigated to explore the adhesion failure characteristics of the asphalt-aggregate interface. The results demonstrate that the thermodynamic properties could be employed to validate the reliability of the asphalt mastic model. The self-aggregation degree of polar components in base asphalt could be significantly increased with the addition of silica particles, exhibiting a change of configuration from "parallel arrangement" into "stack distribution" due to the high polarity of silica particles. The polar components in asphalt mastic exhibit a more uniform distribution state and lower mobility capability than base asphalt owing to the adsorption effect of silica particles. Silica particles with amounts of residual charges could significantly increase the electrostatic energy of the asphalt mastic-aggregate interface, contributing to an improvement of the adhesion between asphalt mastic and aggregate. The increase of temperature enhances the work of adhesion of the asphalt mastic-aggregate interface, which is opposite to that of the base asphalt-aggregate interface. The asphalt mastic exhibits a greater sensitivity to interfacial moisture damage than base asphalt. The findings would provide insights into a better understanding on the micro adhesion mechanism of the asphalt mastic-aggregate interface.

Interfacial properties and micellization of triblock poly(ethylene glycol)-poly(ε-caprolactone)-polyethyleneimine copolymers.

This study aimed to explore the link between block copolymers' interfacial properties and nanoscale carrier formation and found out the influence of length ratio on these characters to optimize drug delivery system. A library of diblock copolymers of PEG-PCL and triblock copolymers with additional PEI (PEG-PCL-PEI) were synthesized. Subsequently, a systematic isothermal investigation was performed to explore molecular arrangements of copolymers at air/water interface. Then, structural properties and drug encapsulation in self-assembly were investigated with DLS, SLS and TEM. We found the additional hydrogen bond in the PEG-PCL-PEI contributes to film stability upon the hydrophobic interaction compared with PEG-PCL. PEG-PCL-PEI assemble into smaller micelle-like (such as PEG-PCL4006-PEI) or particle-like structure (such as PEG-PCL8636-PEI) determined by their hydrophilic and hydrophobic block ratio. The distinct structural architectures of copolymer are consistent between interface and self-assembly. Despite the disparity of constituent ratio, we discovered the arrangement of both chains guarantees balanced hydrophilic-hydrophobic ratio in self-assembly to form stable construction. Meanwhile, the structural differences were found to have significant influence on model drugs incorporation including docetaxel and siRNA. Taken together, these findings indicate the correlation between molecular arrangement and self-assembly and inspire us to tune block compositions to achieve desired nanostructure and drug loading.

Hydrophobicity-Modulated Small Antibacterial Molecule Eradicates Biofilm with Potent Efficacy against Skin Infections.

The role of molecular arrangement of hydrophobic and hydrophilic groups for designing membrane-active molecules remains largely ambiguous. To explore this aspect, herein we report a series of membrane-active small molecules by varying the spatial distribution of hydrophobic groups. The two terminal amino groups of linear triamines such as diethylene triamine, bis(trimethylene)triamine, and bis(hexamethylene)triamine were conjugated with cationic amino acids bearing variable side chain hydrophobicity (such as diaminobutyric acid, ornithine, and lysine). The hydrophobicity was also modulated through conjugation of different long chain fatty acids with the central secondary amino group of the triamine. Molecules with constant backbone hydrophobicity displayed an enhanced antibacterial activity and decreased hemolytic activity upon increasing the side chain hydrophobicity of amino acids. On the other hand, increased hydrophobicity in the backbone introduced a slight hemolytic activity but a higher increment in antibacterial activity, resulting in better selective antibacterial compounds. The optimized lead compound derived from structure-activity-relationship (SAR) studies was the dodecanoyl analogue of a lysine series of compounds consisting of bis(hexamethylene)triamine as the backbone. This compound was active against various Gram-positive and Gram-negative bacteria at a low concentration (MIC ranged between 3.1 and 6.3 µg/mL) and displayed low toxicity toward mammalian cells (HC50 = 890 µg/mL and EC50 against HEK = 85 µg/mL). Additionally, it was able to kill metabolically inactive bacterial cells and eradicate preformed biofilms of MRSA. This compound showed excellent activity in a mouse model of skin infection with reduction of ∼4 log MRSA burden at 40 mg/kg dose without any sign of skin toxicity even at 200 mg/kg. More importantly, it revealed potent efficacy in an ex vivo model of human skin infection (with reduction of 85% MRSA burden at 50 µg/mL), which indicates great potential of the compound as an antibacterial agent to treat skin infections.

Adsorption behavior of acetone solvent at the HMX crystal faces: A molecular dynamics study.

Molecular dynamics simulations have been performed to understand the adsorption behavior of acetone (AC) solvent at the three surfaces of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctan (HMX) crystal, i.e. (011), (110), and (020) faces. The simulation results show that the structural features and electrostatic potentials of crystal faces are determined by the HMX molecular packing, inducing distinct mass density distribution, dipole orientation, and diffusion of solvent molecules in the interfacial regions. The solvent adsorption is mainly governed by the van der Waals forces, and the crystal-solvent interaction energies among three systems are ranked as (020)≈(110)>(011). The adsorption sites for solvent incorporation at the crystal surface were found and visualized with the aid of occupancy analysis. A uniform arrangement of adsorption sites is observed at the rough (020) surface as a result of ordered adsorption motif.

Physicochemical Property Variation in Spider Silk: Ecology, Evolution, and Synthetic Production.

The unique combination of great stiffness, strength, and extensibility makes spider major ampullate (MA) silk desirable for various biomimetic and synthetic applications. Intensive research on the genetics, biochemistry, and biomechanics of this material has facilitated a thorough understanding of its properties at various levels. Nevertheless, methods such as cloning, recombination, and electrospinning have not successfully produced materials with properties as impressive as those of spider silk. It is nevertheless becoming clear that silk properties are a consequence of whole-organism interactions with the environment in addition to genetic expression, gland biochemistry, and spinning processes. Here we assimilate the research done and assess the techniques used to determine distinct forms of spider silk chemical and physical property variability. We suggest that more research should focus on testing hypotheses that explain spider silk property variations in ecological and evolutionary contexts.

Polymer Encapsulation of an Amorphous Pharmaceutical by initiated Chemical Vapor Deposition for Enhanced Stability.

The usage of amorphous solids in practical applications, such as in medication, is commonly limited by the poor long-term stability of this state, because unwanted crystalline transitions occur. In this study, three different polymeric coatings are investigated for their ability to stabilize amorphous films of the model drug clotrimazole and to protect against thermally induced transitions. For this, drop cast films of clotrimazole are encapsulated by initiated chemical vapor deposition (iCVD), using perfluorodecyl acrylate (PFDA), hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA). The iCVD technique operates under solvent-free conditions at low temperatures, thus leaving the solid state of the encapsulated layer unaffected. Optical microscopy and X-ray diffraction data reveal that at ambient conditions of about 22 °C, any of these iCVD layers extends the lifetime of the amorphous state significantly. At higher temperatures (50 or 70 °C), the p-PFDA coating is unable to provide protection, while the p-HEMA and p-MAA strongly reduce the crystallization rate. Furthermore, p-HEMA and p-MAA selectively facilitate a preferential alignment of clotrimazole and, interestingly, even suppress crystallization upon a temporary, rapid temperature increase (3 °C/min, up to 150 °C). The results of this study demonstrate how a polymeric coating, synthesized directly on top of an amorphous phase, can act as a stabilizing agent against crystalline transitions, which makes this approach interesting for a variety of applications.

Competition between Hexagonal and Tetragonal Hexabromobenzene Packing on Au(111).

Low-temperature scanning tunneling microscope investigations reveal that hexabromobenzene (HBB) molecules arrange in either hexagonally closely packed (hcp) [Formula: see text] or tetragonal [Formula: see text] structure on Au(111) dependent on a small substrate temperature difference around 300 K. The underlying mechanism is investigated by density functional theory calculations, which reveal that substrate-mediated intermolecular noncovalent C-Br···Br-C attractions induce hcp HBB islands, keeping the well-known Au(111)-22×√3 reconstruction intact. Upon deposition at 330 K, HBB molecules trap freely diffusing Au adatoms to form tetragonal islands. This enhances the attraction between HBB and Au(111) but partially reduces the intermolecular C-Br···Br-C attractions, altering the Au(111)-22×√3 reconstruction. In both cases, the HBB molecule adsorbs on a bridge site, forming a ∼15° angle between the C-Br direction and [112̅]Au, indicating the site-specific molecule-substrate interactions. We show that the competition between intermolecular and molecule-substrate interactions determines molecule packing at the subnanometer scale, which will be helpful for crystal engineering, functional materials, and organic electronics.

The Acanthamoeba shikimate pathway has a unique molecular arrangement and is essential for aromatic amino acid biosynthesis.

The shikimate pathway is the only known biosynthetic route for de novo synthesis of aromatic compounds. It is described as an ancient eukaryotic innovation that has been retained in a subset of eukaryotes, replaced in plants through the acquisition of the chloroplast, but lost in many including humans. Herein, we demonstrate that Acanthamoeba castellanii possesses the shikimate pathway by biochemical and a combination of bioinformatics and molecular biological methods. The growth of A. castellanii (Neff strain and a recently isolated clinical specimen, both T4 genotypes) is inhibited by glyphosate [N-(phosphonomethyl) glycine], an inhibitor of EPSP synthase and the addition of phenylalanine and tryptophan, which are dependent on the shikimate pathway, rescued A. castellanii from glyphosate indicating that glyphosate was specific in action. A. castellanii has a novel complement of shikimate pathway enzymes including unique gene fusions, two Type I and one Type II DAHP synthases (for which their likely sensitivities to feedback inhibition by phenylalanine, tyrosine and tryptophan has been modelled) and a canonical chorismate synthase. The shikimate pathway in A. castellanii therefore has a novel molecular arrangement, is required for amino acid biosynthesis and represents an attractive target for antimicrobials.