2D Plasmonic Molecules via Hydrogen Bond Interaction between Polymer-Grafted Nanoparticles.

The use of macromolecular design features to regulate non-covalent bonding on the nanoscale is a young and emerging fabrication strategy for advanced nanostructures. For the first time, we describe a self-assembly method to create a series of 2D plasmonic molecules (PMs) using hydrogen-bond interaction between a pair of polymer-capped gold nanoparticles (hydrogen-bond donor and acceptor). Due to the nature of hydrogen-bond interaction, we found that polymer interaction and solvation compete with each other during the self-assembly process, which turns out to be the most important condition for controlling the coordination number of PMs. We have conducted an extensive study on the solvent effect, which has helped us to design and fabricate a series of precise PMs with high symmetry.

Near-Infrared-Triggered Photothermal Aggregation of Polymer-Grafted Gold Nanorods in a Simulated Blood Fluid.

Gold nanorods were decorated with thermoresponsive copolymers of tailored architecture and constructed from N-isopropyl acrylamide and acrylamide. The copolymers were prepared via reversible addition-fragmentation chain transfer polymerization (RAFT) and immobilized on the gold nanorod surface taking advantage of the aurophilicity of its inherently formed trithiocarbonate groups. The topology as well as the average molecular weight of the copolymers was altered using either a monofunctional or 3-arm star RAFT agent. Two-dimensional arrays of the self-assembled core-shell nanostructures were fabricated by drop-casting showing tunable interparticle spacings. In a simulated blood fluid, the lower critical solution temperature of the nanohybrids could be modified over a significant temperature range around body temperature by adjusting the copolymer composition, the architecture, and/or the size of the polymer. The intrinsic photothermal properties of the gold nanorods were utilized to trigger particle aggregation by irradiation at 808 nm in the optical window of human tissues. In effect, a new nanohybrid system with remotely controllable aggregation via an external NIR-light stimulus for nanomedical applications was developed.

Macroscalar Helices Co-Assembled from Chirality-Transferring Temperature-Responsive Carbohydrate-Based Bolaamphiphiles and 1,4-Benzenediboronic Acid.

We present the first example of macroscalar helices co-assembled from temperature-responsive carbohydrate-based bolaamphiphiles (CHO-Bolas) and 1,4-benzenediboronic acid (BDBA). The CHO-Bolas contained hydrophilic glucose or mannose moieties and a hydrophobic coumarin dimer. They showed temperature-responsive reversible micelle-to-vesicle transition (MVT) in aqueous solutions. After the binding of carbohydrate moieties with boronic acids of BDBA in their alkaline solutions, right-handed helices were formed via the temperature-driven chirality transfer of d-glucose or d-mannose from the molecular to supramolecular level. These helices were co-assembled by unreacted BDBA, boronate esters (B-O-C bonds) between CHO-Bolas and BDBA, as well as boroxine anhydrides (B-O-B bonds) of self-condensed BDBA. After heating at 300 °C under nitrogen, the helices displayed excellent morphological stability. Moreover, they emitted bright blue luminescence caused by strong self-condensation of BDBA and decomposition of coumarin dimers.

Supramolecular Self-Assembly of ß3 -Peptides Mediated by Janus-Type Recognition Units.

To gain mechanistic insights, natural systems with biochemical relevance are inspiring for the creation of new biomimetics with unique properties and functions. Despite progress in rational design and protein engineering, folding and intramolecular organization of individual components into supramolecular structures remains challenging and requires controlled methods. Foldamers, such as ß-peptides, are structurally well defined with rigid conformations and suitable for the specific arrangement of recognition units. Herein, we show the molecular arrangement and aggregation of ß3 -peptides into a hexameric helix bundle. For this purpose, ß-amino acid side chains were modified with cyanuric acid and triamino-s-triazine as complementary recognition units. The pre-organization of the ß3 -peptides leads these Janus molecule pairs into a hexameric arrangement and a defined rosette nanotube by stacking. The helical conformation of the subunits was indicated by circular dichroism spectroscopy, while the supramolecular arrangement was detected by dynamic light scattering and confirmed by high-resolution electrospray ionization mass spectrometry (ESI-HRMS).

Prediction of Kinetically Stable Nanotheranostic Superstructures: Integral of First-Passage Times from Constrained Simulations.

The kinetics of forming multifunctional nanostructures, such as nanotheranostic superstructures, is often highly protracted, involving macroscopic time scales and resulting in nanostructures that correspond to kinetically stable states rather than thermodynamic equilibrium. Predicting such kinetically stable nanostructures becomes a great challenge due to the widely different, relevant time scales that are implicated in the formation kinetics of nano-objects. We develop a methodology, integral of first-passage times from constrained simulations (IFS), to predict kinetically stable, planet-satellite nanotheranostic superstructures. The simulation results are consistent with our experimental observations. The developed methodology enables the exploration of time scales from molecular vibrations of 10-3 ns toward macroscopic scales, 1010 ns, which permits the rational design and prediction of kinetically stable nanotheranostic superstructures for applications in nanomedicine.

Micellar Catalysis for Ruthenium(II)-Catalyzed C-H Arylation: Weak-Coordination-Enabled C-H Activation in H2 O.

Chemoselective C-H arylations were accomplished through micellar catalysis by a versatile single-component ruthenium catalyst. The strategy provided expedient access to C-H-arylated ferrocenes with wide functional-group tolerance and ample scope through weak chelation assistance. The sustainability of the C-H arylation was demonstrated by outstanding atom-economy and recycling studies. Detailed computational studies provided support for a facile C-H activation through thioketone assistance.

Silica-Coated Magnetite Nanoparticles Carrying a High-Density Polymer Brush Shell of Hydrophilic Polymer.

Integrating the properties of magnetite nanoparticles (MNPs) and high-density polymer brushes in one structure requires sophisticated synthetic designs and effective chemical approaches. A simple and versatile strategy for the fabrication of hydrophilic-polymer-capped magnetite-core-silica-shell nanohybrids with well-defined structure employing reverse microemulsion technique and reversible addition-fragmentation chain transfer (RAFT) polymerization is presented. The high-density polymer brush allows precise patterning of the magnetic nanohybrids with a tunable interparticle distance ranging from 20 nm to 80 nm by controlling the polymer size. The high structural precision provides a near stand-alone state of the MNPs in the nanohybrids with effectively inhibited magnetic interaction, as shown by superconducting quantum interference device (SQUID) measurements.

Thermosensitive Cation-Selective Mesochannels: PNIPAM-Capped Mesoporous Thin Films as Bioinspired Interfacial Architectures with Concerted Functions.

Rational design and elaborate modular construction of interfacial architectures in which molecular transport is mediated by responsive/adaptive nanostructures has become a growing and fertile field of research in supramolecular materials chemistry. This work presents, for the first time, the use of PNIPAM-capped mesoporous silica thin films as thermosensitive cation-selective mesochannels. Thus far, this feature has only been observed in thermosensitive biological channels. The interfacial architecture created here accomplishes its specific functions through the concerted or simultaneous action of spatially addressed subunits with temperature response and ion exclusion capabilities. The thermo-perm-selectivity effect stems from the synergistic interplay between the pH-dependent electrostatic characteristics of the silica scaffold and the thermo-controlled steric effects introduced by the capping brush layer. It is hoped that the "nanoarchitectonic" approach presented here will provide new routes toward the generation of heterosupramolecular nanosystems displaying addressable transport properties similar to those encountered in biological ion channels.

Uniform Distance Scaling Behavior of Planet-Satellite Nanostructures Made by Star Polymers.

Planet-satellite nanostructures from RAFT star polymers and larger (planet) as well as smaller (satellite) gold nanoparticles are analyzed in experiments and computer simulations regarding the influence of arm number of star polymers. A uniform scaling behavior of planet-satellite distances as a function of arm length was found both in the dried state (via transmission electron microscopy) after casting the nanostructures on surfaces and in the colloidally dispersed state (via simulations and small-angle X-ray scattering) when 2-, 3-, and 6-arm star polymers were employed. This indicates that the planet-satellite distances are mainly determined by the arm length of star polymers. The observed discrepancy between TEM and simulated distances can be attributed to the difference of polymer configurations in dried and dispersed state. Our results also show that these distances are controlled by the density of star polymers end groups, and the number of grabbed satellite particles is determined by the magnitude of the corresponding density. These findings demonstrate the feasibility to precisely control the planet-satellite structures at the nanoscale.

Functionalization of Planet-Satellite Nanostructures Revealed by Nanoscopic Localization of Distinct Macromolecular Species.

The development of a straightforward method is reported to form hybrid polymer/gold planet-satellite nanostructures (PlSNs) with functional polymer. Polyacrylate type polymer with benzyl chloride in its backbone as a macromolecular tracer is synthesized to study its localization within PlSNs by analyzing the elemental distribution of chlorine. The functionalized nanohybrid structures are analyzed by scanning transmission electron microscopy, electron energy loss spectroscopy, and spectrum imaging. The results show that the RAFT (reversible addition-fragmentation chain transfer) polymers' sulfur containing end groups are colocalized at the gold cores, both within nanohybrids of simple core-shell morphology and within higher order PlSNs, providing microscopic evidence for the affinity of the RAFT group toward gold surfaces.

The Structure of Gold-Nanoparticle Networks Cross-Linked by Di- and Multifunctional RAFT Oligomers.

Gold nanoparticle (AuNP) network structures featuring particles from the two-phase Brust-Schiffrin synthesis and linear RAFT oligomers of styrene with two and multiple trithiocarbonate (TTC) groups along their backbone have been investigated in detail. Insights into the internal structures of these particle networks could be obtained from small-angle X-ray scattering experiments, showing that primary AuNPs are cross-linked by the employed molecular linker. The extent of AuNP network formation was investigated by means of dynamic light scattering and UV/visible extinction spectroscopy, showing an abrupt attenuation of network formation after a critical degree of polymerization of the cross-linker is exceeded. Analysis of transmission electron micrographs indicated a three-dimensional shape of the particle superstructures, which is evenly filled with the primary AuNPs. From the results obtained in this study, guidelines for the fabrication of nanoparticle networks from the self-assembly with macromolecular cross-linkers are suggested.

Planet-satellite nanostructures made to order by RAFT star polymers.

The investigation and application of complex nanostructures requires the hierarchical arrangement of distinct domains on a small scale. Herein, we report a method to prepare planet-satellite arrangements using RAFT polymers. Our approach is based on star polymers decorated with trithiocarbonate groups on their outer periphery that attach to gold surfaces and thus provide the polymer with the ability to connect (larger) gold nanoparticle planets with (smaller) gold nanoparticle satellites. By adjusting the molecular weight of the polymeric linker, nanostructures with tailored planet-satellite distances, as evidenced by transmission electron microscopy, are obtained. This strategy offers a straightforward way to prepare gold nanoparticle scaffolds with multiple reactive functionalities at defined distances from the central core.

Dehydration regulates structural reorganization of dynamic hydrogels.

The dehydration process is widely recognized as a significant phenomenon in nature. Hydrogels, which are important functional materials with high water content and crosslinked networks, encounter the issue of dehydration in their practical applications. Here, we report the distinctive anisotropic dehydration modality of dynamic hydrogels, which is fundamentally different from the more commonly observed isotropic dehydration of covalent hydrogels. Xerogels derived from dynamic hydrogel dehydration will fully cover a curved substrate surface and exhibit hollow structures with internal knots, in contrast to the bulk xerogels produced by covalent hydrogel dehydration. Depending on the competing cohesion of polymer chains and the adhesion at the hydrogel-substrate interface, the previously overlooked reorganization of polymer networks within dynamic hydrogels, triggered by dehydration-induced stress, has been discovered to regulate such macroscopic structural reconstruction for dynamic hydrogel dehydration. With the attached hydrogel-substrate interface, the surface microstructures of substrates can also be engraved onto xerogels with high resolution and on a large scale. This work will greatly enhance our understanding of the soft matter dehydration process and broaden the applications of dehydration technologies using water-containing materials.

Free-Radical Propagation Rate Coefficients of Diethyl Itaconate and Di-n-Propyl Itaconate Obtained via PLP-SEC.

The propagation step is one of the key reactions in radical polymerization and knowledge about its kinetics is often vital for understanding and designing polymerization processes leading to new materials or optimizing technical processes. Arrhenius expressions for the propagation step in free-radical polymerization of diethyl itaconate (DEI) as well as di-n-propyl itaconate (DnPI) in bulk, for which propagation kinetics was yet unexplored, were thus determined via pulsed-laser polymerization in conjunction with size-exclusion chromatography (PLP-SEC) experiments in the temperature range of 20 to 70 °C. For DEI, the experimental data was complemented by quantum chemical calculation. The obtained Arrhenius parameters are A = 1.1 L·mol-1·s-1 and Ea = 17.5 kJ·mol-1 for DEI and A = 1.0 L·mol-1·s-1 and Ea = 17.5 kJ·mol-1 for DnPI.

One-pot RAFT/"click" chemistry via isocyanates: efficient synthesis of α-end-functionalized polymers.

A new methodology has been developed for preparing α-functional polymers in a one-pot simultaneous polymerization/isocyanate "click" reaction. Our original synthetic strategy is based on the preparation of a carbonyl-azide chain transfer agent (CTA) precursor that undergoes the Curtius rearrangement in situ during reversible addition-fragmentation chain transfer (RAFT) polymerization yielding well-controlled α-isocyanate modified polymers. This strategy overcomes numerous difficulties associated with the synthesis of a polymerization mediator bearing an isocyanate at the R group and with the handling of such a reactive functionality. This new carbonyl-azide CTA can control the polymerization of a wide range of monomers, including (meth)acrylates, acrylamides, and styrenes (M(n) = 2-30 kDa; D = 1.16-1.38). We also show that this carbonyl-azide CTA can be used as a universal platform for the synthesis of α-end-functionalized polymers in a one-pot RAFT polymerization/isocyanate "click" procedure.

Functional binary micropattern of hyperbranched poly(ether amine) (hPEA-AN) network and poly(ether amine) (PEA) brush for recognition of guest molecules.

A binary micropattern of anthracene-contained hyperbranched poly(ether amine) (hPEA-AN) network and poly(ether amine) (PEA) brush on gold surface was developed and explored. First, a micropatterned hPEA-AN network array on gold surface was fabricated by photolithography via photodimerization of anthracene moieties, and a PEA brush was subsequently immobilized on the remaining free gold surface areas by chemical adsorption of thiol groups. The patterned hPEA-AN network exhibits selectivity with respect to the adsorption of hydrophilic dyes: Methyl orange is strongly adsorbed, but rhodamine 6G is not, as indicated by the fluorescence response. The PEA brush domain exhibits excellent protein adsorption repellency, whereas the hPEA-AN network layer readily adsorbs protein. These characteristics make the binary hPEA-AN network and PEA brush array sensitive to different kinds of dyes and proteins, which open up pathways to potential applications as microsensors, biochips, and bioassays.

Gold nanoparticle ring arrays from core-satellite nanostructures made to order by hydrogen bond interactions.

Polyethylene glycol-grafted gold nanoparticles are attached to silica nanoparticle cores via hydrogen bonding in a controlled fashion, forming well-defined core-satellite structures in colloidal solution. For separating these complex structures effectively from the parental nanoparticles, a straightforward and easy protocol using glass beads has been developed. The attached gold nanoparticles show unique surface mobility on the silica core surface, which allows for nanoparticle rearrangement into a 2D ring pattern surrounding the silica nanoparticle template when the core-satellite structures are cast to a planar surface. When etching away the silica core under conditions in which the polymer shell fixes the satellites to the substrate, highly ordered ring-shaped patterns of gold nanoparticles are formed. By variation of the size of the parental particles - 13 to 28 nm for gold nanoparticles and 39 to 62 nm for silica nanoparticles - a great library of different ring-structures regarding size and particle number is accessible with relative ease. The proposed protocol is low-cost and can easily be scaled up. It moreover demonstrates the power of hydrogen bonds in polymers as a dynamic anchoring tool for creating nanoclusters with rearrangement ability. We believe that this concept constitutes a powerful strategy for the development of new and innovative nanostructures.

Efficacy of occlusive wraps used for delivery room care.

BACKGROUND: Guidelines advise for more than 20 years to use occlusive plastic wraps for temperature management during delivery room care but data on efficacy of different types of wrap are still scarce. METHODS: A random sample of seven different types of plastic wrap was tested using prewarmed aluminium blocks. RESULTS: The most effective wrap increased the time to cool by 2°C by one-third for the core and by 100% for the surface whereas the least effective wrap led to even faster heat loss compared with no wrap at all. The least effective wrap concerning all capacities tested was made from polyurethane that contains potentially toxic and narcotic monomers. Heat and water retention did not correlate to wrap thickness. DISCUSSION: Large differences in heat and water retention capacity warrant a careful choice of the type of wrap as some might be counterproductive. Wraps containing polyurethane should not be used.

Increasing the Gas Barrier Properties of Polyethylene Foils by Coating with Poly(methyl acrylate)-Grafted Montmorillonite Nanosheets.

Low-density polyethylene (LDPE) foils were coated with a thin film of polymer-grafted Montmorillonite (MMT) nanosheets, which form a barrier against gas diffusion due to their unique brick-and-mortar arrangement. The MMT nanosheets were grafted with poly(methyl acrylate) (PMA), a soft and flexible polymer. Already very thin films of this nanocomposite could reduce gas permeability significantly. The impact of the topology of the surface-grafted polymer on gas permeability was also studied. It was found that grafting MMT nanosheets with a mixture of star-shaped and linear PMA and with PMA that is cross-linked via hydrogen bonds further decrease gas permeability. The presented strategy is quick and simple and allows for the easy formation of effective gas barrier coatings for LDPE foils, as used in food packaging.

Self-Compounded Nanocomposites: toward Multifunctional Membranes with Superior Mechanical, Gas/Oil Barrier, UV-Shielding, and Photothermal Conversion Properties.

Nanocomposites combine multiple favorable properties to achieve intriguing functionalities, but the formation of nanocomposites with only one constituent with the inclusion of multiple superior properties is still not known. Herein, novel self-compounded nanocomposite membranes from one single polymer-cellulose cinnamate (CCi)-with multiple outstanding properties are reported. The self-compounded membranes contain two distinct morphologies as CCi nanoparticles (CCi-NPs) and a CCi polymer matrix, while CCi-NPs are either firmly embedded in the CCi matrix or fused with adjacent CCi-NPs. The unique self-compounded nanostructure endows the membranes with a tensile strength of 94 MPa and Young's modulus of 3.1 GPa. The water vapor permeability, oxygen permeability, and oil permeability reach as low as (0.94 ± 0.03) × 10-11 g m-1 s-1 Pa-1, (8.48 ± 2.39) ×10-13 cm3·cm/cm2·s·cmHg, and 0.008 ± 0.003 g mm m-2 day-1, respectively. Moreover, self-compounded CCi nanocomposite membranes also demonstrate UV-shielding and photothermal conversion properties. UVB and UVC light are entirely blocked, while UVA light is partly blocked. The temperature increases from room temperature to 120 °C within 1 min under UV irradiation. In addition, CCi membranes also show remarkable thermal and humidity resistance. Based on these outstanding properties, CCi membranes are applied as food packaging materials. This work offers a new avenue to construct nanocomposites with multiple superior properties from one constituent, which is promising for diverse applications.