Multicompartment Nanoparticles of Poly(4-vinylpyridine) Graft Block Terpolymer: Synthesis and Application as Scaffold for Efficient Au Nanocatalyst

Multicompartment nanoparticles (MCBNs) constructed with the brush block terpolymer of [poly­(<i>p</i>-chloromethylstyrene)-<i>graft</i>-poly­(4-vinylpyridine)]-<i>block</i>-polystyrene (PCMS-<i>g</i>-P4VP)-<i>b</i>-PS are prepared through dispersion polymerization of styrene in the methanol/water mixture mediated by the brush macro-RAFT agent of poly­(<i>p</i>-chloromethylstyrene)-<i>graft</i>-poly­(4-vinylpyridine) trithiocarbonate. During the dispersion RAFT polymerization, the molecular weight of the brush (PCMS-<i>g</i>-P4VP)-<i>b</i>-PS block terpolymer linearly increases with the monomer conversion. Ascribed to the brush (PCMS-<i>g</i>-P4VP) block, MCBNs including a PS core and discrete subdomains of (PCMS-<i>g</i>-P4VP) on the PS core dispersed in water are formed. The reasons leading to formation of MCBNs are discussed, and the immiscibility of the brush (PCMS-<i>g</i>-P4VP) block with the PS core, the low number density of the brush (PCMS-<i>g</i>-P4VP₂₅)₂₁ chains tethered on per surface area of the PS core, and the high molecular weight but the low polymerization degree of the brush (PCMS-<i>g</i>-P4VP) block are ascribed. Au nanoparticles are immobilized on the bulgy PCMS-<i>g</i>-P4VP subdomains on MCBNs and show high catalytic efficiency in the aerobic alcohol oxidation

Efficient Synthesis of Molecularly Imprinted Polymers with Enzyme Inhibition Potency by the Controlled Surface Imprinting Approach

A facile, general, and highly efficient approach to prepare uniform core–shell molecularly imprinted polymer (MIP) particles with enzyme inhibition potency is described for the first time, which involves the combined use of molecular imprinting and controlled/“living” radical polymerization (CRP) techniques as well as surface-anchoring strategy. The thickness of the enzyme-imprinted surface layers of the core–shell MIP microspheres had a significant influence on their binding properties, and only those with their thickness comparable with the diameters of the targeted enzymes could afford enzyme-MIPs with optimal specific bindings. The as-prepared enzyme-MIPs were found to have homogeneous binding sites and high template binding capacities, affinity, and selectivity, and they proved to show much higher enzyme inhibition potency than the small inhibitor by 3 orders of magnitude (i.e., the enzyme inhibition constant of every binding site of the MIP microspheres was about one-thousandth of that of the small inhibitor), mainly due to the formation of strong long-range secondary interactions between enzymes and imprinted pockets. In addition, the general applicability of our strategy was confirmed

Synthesis and Self-Assembly of Amphiphilic Janus Laponite Disks

Materials with asymmetric structures are attractive for wide applications in chemistry and materials science. Two-dimensional Janus disks or nanosheets are particularly appealing because of the unique shape and the distinctive self-assembled structures. A facile and versatile method for the synthesis of amphiphilic Janus Laponite disks is proposed in this paper. Positively charged PS spheres were prepared by ATRP emulsion polymerization. Upon addition of aqueous dispersion of negatively charged Laponite disks into PS emulsions, the nanosized disks were adsorbed onto the surface of PS particles via electrostatic interaction. One side of a Laponite disk touches the surface of a colloidal particle, and the other side faces the medium. After addition of positively charged polymeric micelles or quaternized poly­(2-(dimethylamino)­ethyl methacrylate) (q-PDMAEMA) chains into the aqueous dispersions of the colloidal particles, the micelles or polymer chains were immobilized onto the Laponite disks, and Janus disks were produced on particle templates. After centrifugation and redispersion of the colloidal particles into a good solvent, amphiphilic Janus Laponite disks with PS chains on one side and hydrophilic q-PDMAEMA or polymeric micelles on the other side were obtained. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize the Janus disks. Self-assembly of the Janus disks at liquid–liquid interface and in selective solvents was investigated. Similar to small molecular surfactants, the amphiphilic Janus disks can self-assemble at liquid–liquid interface, resulting in a decrease of the interfacial tension and emulsification of oil droplets in water. In a THF–methanol mixture at a volume ratio of 1:6, PS brushes on the Janus disks collapse forming two-layer face-to-face stacks. The distinctive self-assembled structures were analyzed by TEM and AFM

Synergy between Polyamine and Anionic Surfactant: A Bioinspired Approach for Ordered Mesoporous Silica

A novel bioinspired approach for ordered mesoporous silica was developed on the basis of the synergic coassembly between polyamine and an anionic surfactant as a template. With the help of cationic polyamine, anionic surfactant micelles could be utilized as a mesostructure template, whereas with the aid of the anionic surfactant micelles the cationic polyamine chains underwent aggregation to exert their ability to induce silica condensation. Mesoporous silicas with well-ordered mesostructure of <i>Fd</i>-3<i>m</i> symmetry and 3D hexagonal close-packed mesostructure (hcp) were fabricated. Because of the abundant types of anionic surfactants and polyamines, the synthesis approach can be regarded as a general method for anionic-surfactant-templated mesoporous silica, and new mesostructures and morphologies are expected

Thickness Dependence of Glass Transitions Measured by AC-Chip Calorimetry in Films with Controlled Interface

When most prior studies on thin polymer films have shown that glass transition temperature (<i>T</i>_g) decreases under nanoconfinement, the differential alternating current chip (ac-chip) calorimetric method shows little dependence of <i>T</i>_g on thickness for supported film. To reveal this contradiction, we have manipulated a controlled interface by spin-coating polystyrene (PS) with immiscible surfactants such as tetraoctylammonium bromide or citric acid. Since the immiscible surfactants did not show plasticizing effect for PS, there was no observable reduction of <i>T</i>_g from the bulk value ether in powdered blends or in thick films. However, the ultrathin film with thickness <i>h</i> ∼ 25 nm, consisting of 95 wt % PS and 5 wt % surfactants, showed a reduction of <i>T</i>_g by 6–7 °C, as compared to thick film with the same composition. We propose that the surfactant molecules assembled on the interface between thin film and substrate due to phase separation. The molecular mobility of molecules at the interface was dramatically increased, which was detected by ¹NMR with dipolar filter sequence. It appeared that the deviation range was not so large as that measured by other methods. But considering that we were measuring <i>T</i>_g at a high frequence (10 Hz), this amount of deviation was quite significant for ac-chip calorimetry. As a result, ac-chip calorimetry measured <i>T</i>_g data unambiguously demonstrate that thickness dependence of <i>T</i>_g is a real property of confined thin film

Reversible Interactions of Proteins with Mixed Shell Polymeric Micelles: Tuning the Surface Hydrophobic/Hydrophilic Balance toward Efficient Artificial Chaperones

Molecular chaperones can elegantly fine-tune its hydrophobic/hydrophilic balance to assist a broad spectrum of nascent polypeptide chains to fold properly. Such precious property is difficult to be achieved by chaperone mimicking materials due to limited control of their surface characteristics that dictate interactions with unfolded protein intermediates. Mixed shell polymeric micelles (MSPMs), which consist of two kinds of dissimilar polymeric chains in the micellar shell, offer a convenient way to fine-tune surface properties of polymeric nanoparticles. In the current work, we have fabricated ca. 30 kinds of MSPMs with finely tunable hydrophilic/hydrophobic surface properties. We investigated the respective roles of thermosensitive and hydrophilic polymeric chains in the thermodenaturation protection of proteins down to the molecular structure. Although the three kinds of thermosensitive polymers investigated herein can form collapsed hydrophobic domains on the micellar surface, we found distinct capability to capture and release unfolded protein intermediates, due to their respective affinity for proteins. Meanwhile, in terms of the hydrophilic polymeric chains in the micellar shell, poly­(ethylene glycol) (PEG) excels in assisting unfolded protein intermediates to refold properly via interacting with the refolding intermediates, resulting in enhanced chaperone efficiency. However, another hydrophilic polymer-poly­(2-methacryloyloxyethyl phosphorylcholine) (PMPC) severely deteriorates the chaperone efficiency of MSPMs, due to its protein-resistant properties. Judicious combination of thermosensitive and hydrophilic chains in the micellar shell lead to MSPM-based artificial chaperones with optimal efficacy

Accessing Structure and Dynamics of Mobile Phase in Organic Solids by Real-Time T_1C Filter PISEMA NMR Spectroscopy

The structure and dynamic behavior of mobile components play a significant role in determining properties of solid materials. Herein, we propose a novel real-time spectrum-editing method to extract signals of mobile components in organic solids on the basis of the polarization inversion spin exchange at magic angle (PISEMA) pulse sequence and the difference in ¹³C T₁ values of rigid and mobile components. From the dipolar splitting spectrum sliced along the heteronuclear dipolar coupling dimension of the 2D spectrum, the structural and dynamic information can be obtained, such as the distances between atoms, the dipolar coupling strength, the order parameter of the polymer backbone chain, and so on. Furthermore, our proposed method can be used to achieve the separation of overlapped NMR signals of mobile and rigid phases in the PISEMA experiment. The high efficacy of this 2D NMR method is demonstrated on organic solids, including crystalline l-alanine, semicrystalline polyamide-6, and the natural abundant silk fibroin

Confinement-Induced Deviation of Chain Mobility and Glass Transition Temperature for Polystyrene/Au Nanoparticles

The mobility and glass transition temperature (<i>T</i>_g) for polymers under nanoscale confinement differ substantially from the bulk. Whereas many studies have focused on the one-dimensional confinement, it has great significance to extend studies to higher geometries. Here, we systematically investigate the mobility by dipolar-filter sequence in solid-state NMR and <i>T</i>_g by DSC for thiolated polystyrene (PS-SH) on gold nanoparticles. The increase in <i>T</i>_g and signal suppression in NMR spectra clearly indicate that the surface confinement dominates molecular mobility as well as <i>T</i>_g. The molecular weight of PS-SH and nanoparticles size show significant influence on the immobilization and <i>T</i>_g. Our results can be fitted with a core–two shell model; the inner shell is under strong constraints while the outer shell with less confinement. This work is essential to better understand the confinement effect and also provides a step toward the ultimate desire to tailor the properties of nanomaterials

Investigation on the Mechanism of the Synthesis of Gold(I) Thiolate Complexes by NMR

In this article, we characterized the polymeric gold­(I) thiolates that precipitated from the intermediate solutions during the synthesis process of gold nanoparticles (GNPs) by the Brust–Schiffrin two-phase method and investigated the formation mechanism of the polymeric gold­(I) thiolates. The solution ¹H NMR confirmed the complete reduction from Au­(III) to Au­(I) with the addition of the first two equivalents of thiols, while only the third and fourth equivalents of thiols were found to participate in forming gold­(I) thiolates. Gold­(I) thiolates, [Au­(I)­SR]_<i>n</i>, precipitated from these solutions were further characterized by ¹H solid-state NMR spectroscopy under fast magic angle spinning (MAS), Raman spectroscopy, and thermogravimetric analysis. Further quantitative studies revealed that the composition of [Au­(I)­SR]_<i>n</i> could be controlled by changing the order of addition of the third and fourth equivalents of thiols. This work has great significance to better understand the mechanism of gold nanoparticle formation and thus to tailor the properties of the final products

Viscoelasticity and Structures in Chemically and Physically Dual-Cross-Linked Hydrogels: Insights from Rheology and Proton Multiple-Quantum NMR Spectroscopy

Hydrogels have received considerable attention as an innovative material due to their widespread applications in various fields. As a soft and wet material, its mechanical behavior is best understood in terms of the viscoelastic response to the periodic deformation, which is closely related to the microscopic chemically/physically cross-linked structures. Herein, a dual-cross-linked (DC) hydrogel, where a physically cross-linked network by ionic coordination (Fe³⁺) is imposed on a chemically cross-linked poly­(acrylamide-<i>co</i>-acrylic acid) network, was studied in detail by rheology and proton multiple-quantum (MQ) NMR spectroscopy. Rheology experiments revealed the diverse temperature- and strain-frequency-dependent viscoelastic behaviors for DC hydrogels induced by the dynamic Fe³⁺ coordination interactions, in contrast to the single chemically cross-linked (SC) hydrogels. During the shear experiment, the trivalent Fe³⁺ complex with moderate/weak binding strength might transform to those with strong binding strength and serve as permanent-like cross-linkages to resist the periodic deformation when a large strain frequency was applied. The viscoelastic behaviors of the DC hydrogels were strongly affected by the monomer ratio (<i>C</i>_AAc/<i>C</i>_AAm) and Fe³⁺ concentrations; however, the chemically cross-linked density did not change with <i>C</i>_AAc/<i>C</i>_AAm, while the physically cross-linked density was greatly enhanced with increasing Fe³⁺ concentrations. Besides, the DC hydrogels have less contents of network defects in comparison to the SC hydrogels. The heterogeneous structural evolution with increasing the Fe³⁺ concentration and monomer ratio was also quantitatively determined and elucidated by proton MQ NMR spectroscopy. In addition, the moduli (<i>G</i>′, <i>G</i>″) of DC hydrogels were almost an order magnitude higher than that of the corresponding SC hydrogels, demonstrating the significant contribution of Fe³⁺ coordination to the mechanical properties, in consistent with the high activation energy of viscoelasticity for the physically cross-linked network as obtained from the variable-temperature shear rheology experiments. The experimental findings obtained from the rheology and proton MQ NMR experiments can be correlated with and complementary to each other. Herein, a combination of rheology and proton solid-state NMR is well demonstrated as an effective and unique way for establishing the relationship between microscopic structures and macroscopic viscoelastic properties