Recognition-Mediated Unfolding of a Self-Assembled Polymeric Globule

Droplet evaporation on super liquid-repellent surfaces: A controllable approach for supraparticle fabrication

Supraparticles are agglomerates of nano- and/or microparticles with sizes ranging from tens to hundreds of microns, making them more accessible for handling and recovery than the building blocks. Supraparticles not only inherit the properties and functions of primary particles but also exhibit characteristics such as high porosity, large specific surface area, and improved functionalities, which can be attributed to the synergism, coupling, and co-localization among the constituents. Therefore, supraparticles hold promising applications in catalysis, drug delivery, sensing, etc. Among the various synthesizing strategies, evaporating droplets on a liquid-repellent surface is proposed as an effective approach to fabricate supraparticles with unique structural features and functions. The boundary conditions of such droplet-confinement methods significantly drive the formation of supraparticles by reducing or avoiding the use of solvents or processing liquids, which further accelerates the development and utilization of supraparticles. This paper presents an overview of recent developments in the fabrication of supraparticles by evaporating droplets on liquid-repellent surfaces. The review focuses on the evaporation processes on lubricant and superhydrophobic surfaces, structural regulation, and applications of supraparticles. Finally, an outlook on the future directions of evaporation on liquid-repellent surfaces mediated supraparticle fabrication is presented.

Nanotechnology Impact on Chemical-Enhanced Oil Recovery: A Review and Bibliometric Analysis of Recent Developments

Oil and gas are only two industries that could change because of nanotechnology, a rapidly growing field. The chemical-enhanced oil recovery (CEOR) method uses chemicals to accelerate oil flow from reservoirs. New and enhanced CEOR compounds that are more efficient and eco-friendly can be created using nanotechnology. One of the main research areas is creating novel nanomaterials that can transfer EOR chemicals to the reservoir more effectively. It was creating nanoparticles that can be used to change the viscosity and surface tension of reservoir fluids and constructing nanoparticles that can be utilized to improve the efficiency of the EOR compounds that are already in use. The assessment also identifies some difficulties that must be overcome before nanotechnology-based EOR can become widely used in industry. These difficulties include the requirement for creating mass-producible, cost-effective nanomaterials. There is a need to create strategies for supplying nanomaterials to the reservoir without endangering the formation of the reservoir. The requirement is to evaluate the environmental effects of CEOR compounds based on nanotechnology. The advantages of nanotechnology-based EOR are substantial despite the difficulties. Nanotechnology could make oil production more effective, profitable, and less environmentally harmful. An extensive overview of the most current advancements in nanotechnology-based EOR is provided in this paper. It is a useful resource for researchers and business people interested in this area. This review's analysis of current advancements in nanotechnology-based EOR shows that this area is attracting more and more attention. There have been a lot more publications on this subject in recent years, and a lot of research is being done on many facets of nanotechnology-based EOR. The scientometric investigation discovered serious inadequacies in earlier studies on adopting EOR and its potential benefits for a sustainable future. Research partnerships, joint ventures, and cutting-edge technology that consider assessing current changes and advances in oil output can all benefit from the results of our scientometric analysis.

Tuning the Porosity of Supraparticles

Supraparticles consisting of nano- or microparticles have potential applications as, for example, photonic crystals, drug carriers, or heterogeneous catalysts. To avoid the use of solvent or processing liquid, one can make supraparticles by evaporating droplets of aqueous suspensions from super-liquid-repellent surfaces. Herein, a method to adjust the porosity of supraparticles is described; a high porosity is desired, for example, in catalysis. To prepare highly porous TiO₂ supraparticles, polymer nanoparticles are co-dispersed in the suspension. Supraparticles are formed through evaporation of aqueous suspension droplets on superamphiphobic surfaces followed by calcination of the sacrificial polymer particles. The increase of porosity of up to 92% resulted in enhanced photocatalytic activity while maintaining sufficient mechanical stability.

Supramolecular Single-Chain Polymeric Nanoparticles

Nature has unparalleled control over the conformation and dynamics of its folded macromolecular structures. Nature’s ability to arrange amino acids into a precise spatial organization by way of folding allows proteins to fulfill specific functions in an extremely efficient manner. Chemists and materials scientists have used the delicate structure–function relationships observed in proteins to elucidate nature’s design principles. These insights have led to the development of various revolutionary macromolecular architectures, mimicking the structural features of proteins. In this review, we focus on the folding of single polymer chains into well-defined nanoparticles using supramolecular interactions and their possible use as enzyme mimics.

Effect of Intra- versus Intermolecular Cross-Linking on the Supramolecular Folding of a Polymer Chain

Anfinsen's famous experiment showed that the restoration of catalytic activity of a completely unfolded ribonuclease A is only possible when the correct order of events is followed during the refolding process. Inspired by this work, the effect of structural constraints induced by covalent cross-links on the folding of a synthetic polymer chain via hydrogen-bonding interactions is investigated. Hereto, methacrylate-based monomers comprising either benzene-1,3,5-tricarboxamide (BTA)-based or coumarin-based pendants are copolymerized with n-butyl methacrylate in various ratios via reversible addition-fragmentation chain-transfer (RAFT) polymerization. To assess whether the folding and single-chain polymeric nanoparticle (SCPN) formation depend on the order of events, we compare two folding pathways. In the one case, we first covalently cross-link the coumarin pendants within the polymers in a solvent that prevents hydrogen bonding, after which hydrogen bonding is activated, inducing folding of the polymer. In the other case, we induce hydrogen-bonding interactions between tethered BTAs prior to covalent cross-linking of the coumarin pendants. A combination of circular dichroism (CD) spectroscopy, UV-vis spectroscopy, size-exclusion chromatography (SEC), and dynamic light scattering (DLS) is employed to understand the effect of the structural constraints on the folding behavior of these synthetic polymers. The results show that like in ribonuclease A, the order of events matters greatly and determines the outcome. Importantly, a hydrogen-bond-promoting solvent prevents the formation of SCPNs upon covalent cross-linking and results in multichain aggregates. In contrast, covalently cross-linking the polymer when no hydrogen bonds are present followed by inducing hydrogen bonding favors the formation of SCPNs above the UCST of the methacrylate-based polymer. To our surprise, the two systems show a fundamentally different response to changes in temperature, indicating that also in synthetic polymers differences in the folding pathway induce differences in the properties of the resultant nanostructures.

Single-chain polymer nanoparticles in controlled drug delivery and targeted imaging

As a relatively new class of materials, single-chain polymer nanoparticles (SCNPs) just entered the field of (biomedical) applications, with recent advances in polymer science enabling the formation of bio-inspired nanosized architectures. Exclusive intramolecular collapse of individual polymer chains results in individual nanoparticles. With sizes an order of magnitude smaller than conventional polymer nanoparticles, SCNPs are in the size regime of many proteins and viruses (1-20 nm). Multifaceted syntheses and design strategies give access to a wide set of highly modular SCNP materials. This review describes how SCNPs have been rendered water-soluble and highlights ongoing research efforts towards biocompatible SCNPs with tunable properties for controlled drug delivery, targeted imaging and protein mimicry.

Improving the Folding of Supramolecular Copolymers by Controlling the Assembly Pathway Complexity

A family of amphiphilic, heterograft copolymers containing hydrophilic, hydrophobic, and supramolecular units based on Jeffamine M-1000, dodecylamine, and benzene-1,3,5-tricarboxamide (BTA) motifs, respectively, was prepared via a postfunctionalization approach. The folding of the copolymers in water into nanometer-sized particles was analyzed by a combination of dynamic and static light scattering, circular dichroism spectroscopy, and small-angle neutron scattering. The sample preparation protocol was crucial for obtaining reproducible and consistent results, showing that only full control over the structure and pathway complexity will afford the desired folded structure, a phenomenon similar to protein folding. The results revealed that relatively small changes in the polymer’s graft composition strongly affected the intra- versus intermolecular assembly processes. Depending on the amount of the hydrophobic grafts based on either dodecyl or BTA groups, pronounced behavioral differences were observed for copolymers that comprise similar degrees of hydrophobic content. A high number of BTA grafts (>10%) resulted in the formation of multichain aggregates comprising around six polymer chains. In contrast, for copolymers comprising up to 10% BTA grafts the folding results in nanoparticles that adopt open, sparse conformations and comprise one to two polymer chains. Interestingly, predominantly single-chain polymeric nanoparticles were formed when the copolymer comprised only Jeffamine or Jeffamine and dodecyl grafts. In addition, replacing part of the BTA grafts by hydrophobic dodecyl grafts while keeping the hydrophobic content constant promoted single-chain folding and resulted in the formation of a compact, globular nanoparticle with a more structured interior. Thus, the intra- and intermolecular self-assembly pathways can be directed by carefully tuning the polymer’s hydrophilic–hydrophobic balance in combination with the number of supramolecular grafts.

Supramolecular engineering polyesters: endgroup functionalization of glycol modified PET with ureidopyrimidinone

We report the first supramolecular engineering polymer with melt viscosity suitable for non-degradative processing plus enhanced thermal and mechanical properties.

Templated polymerizations on solid supports mediated by complementary nucleoside interactions

The preparation of immobilized poly(methacryloyl nucleosides) and their abilities for template polymerizations is discussed.

Molecular recognition with 2,4-diaminotriazine-functionalized colloids

New polymeric colloids functionalized with 2,4-diaminotriazine residues have been prepared. The functionalities provide a triple hydrogen bond motif with a donor-acceptor-donor (DAD) pattern. The colloids are based on cross-linked poly-4-methoxymethyl styrene and are polymerized by means of surfactant-free emulsion polymerization. The reaction pathway including five steps was successfully tracked and verified via (13)C CP/MAS solid-state NMR. Characterization of the colloids was done by combined static and dynamic light scattering and indicates a compact spherical particle shape. In solvents with the appropriate polarity, intercolloidal hydrogen bonding was enabled, including colloidal aggregation. In highly dilute solutions of THF, this aggregation was recordable by means of time-resolved static light scattering experiments. If THF was saturated with uracil, then aggregation could be completely inhibited. Uracil bears a triple hydrogen bond motif of the form acceptor-donor-acceptor (ADA) and is a direct antagonist of 2,4-diaminotriazine. The charging of the colloids with uracil via hydrogen bond formation as a typical molecular recognition mechanism could be confirmed by IR spectroscopy.

Recognition-mediated assembly of quantum dot polymer conjugates with controlled morphology

We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly.

pH and temperature responsive polymeric micelles and polymersomes by self-assembly of poly[2-(dimethylamino)ethyl methacrylate]-b-poly(glutamic acid) double hydrophilic block copolymers

The aqueous solution behavior of novel polypeptide-based double hydrophilic block copolymers (DHBCs), namely, poly[2-(dimethylamino)ethyl methacrylate]-b-poly(glutamic acid) (PDMAEMA-b-PGA), exhibiting pH- and temperature-responsiveness is presented using a combination of scattering techniques (light and neutron) and transmission electron microscopy. Close to the isoelectric point (IEP), direct or inverse electrostatic polymersomes are generated by electrostatic interactions developing between the two charged blocks and driving the formation of the hydrophobic membrane of the polymersomes, with the latter being stabilized in water by uncompensated charges. Under basic conditions, that is, when PDMAEMA is uncharged, the thermosensitivity of the DHBCs relates to the lower critical solution temperature (LCST) behavior of PDMAEMA around 40 degrees C. As a consequence, at pH = 11 and below this LCST, free chains of DHBC unimers are evidenced, while above the LCST the hydrophobicity of PDMAEMA drives the self-assembly of the DHBCs in a reversible manner. In this case, spherical polymeric micelles or polymersomes are obtained, depending on the PGA block length. These possibilities of variation in size and shape of morphologies that can be achieved as a function of temperature and/or pH variations open new routes in the development of multiresponsive nanocarriers for biomedical applications.

Modular and dynamic functionalization of polymeric scaffolds

The design and synthesis of multifunctionalized, architecturally controlled polymers is a prerequisite for a variety of future applications of polymeric materials. On the basis of Nature's use of self-assembly in the creation of biomaterials, this Account describes concepts that were developed over the past 5 years that utilize noncovalent interactions such as hydrogen bonding, ionic interactions, electrostatic interactions, metal coordination, and pi-pi stacking in modification of copolymer side-chains to obtain multifunctional polymeric materials, induce polymer morphology changes, and influence bulk-polymer properties.

Self-Assembly of Silver Nanoparticles: Synthesis, Stabilization, Optical Properties, and Application in Surface-Enhanced Raman Scattering

Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate.

Formation of Ordered Arrays of Oriented Polyaniline Nanoparticle Nanorods

We report the preparation of ordered polyaniline (PANI) nanorod arrays in an aqueous medium. The oriented PANI nanorods (80-400 nm in diameter and 8-15 mum in length) were synthesized in the presence of hydrophilic Allura Red AC (ARAC) as the structure-directing agent and ammonium persulfate as an oxidant in HCl solution. The morphologies of the oriented PANI nanoparticle nanorods were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy images, and the effect of reaction conditions on the morphology of PANI nanostructures was also studied. On the basis of the result obtained from small-angle X-ray scattering, we propose that rodlike micelle arrays of ARAC-aniline are responsible for directing the formation of oriented PANI nanoparticle nanorods. SEM images and the data analysis of static and dynamic light scattering give supportive evidence to the formation of the PANI nanoparticle nanorods by an elongation process. The chemical and electronic structures of the PANI nanorods were also studied by Fourier transform IR and UV-vis spectrometries, respectively.