Search

This study is aimed at booming intelligent polymers and their applications in catalysis, presenting an intelligent polymer catalyst with photo-mediated catalytic ability. This catalyst was fabricated with polymeric 2-acrylamide-2-methylpropylsulfonic acid (acidic moieties capable of catalytic hydrolysis) and photo-sensitive acrylamide-azobenzene prepared from the synthesis of 4-aminoazobenzene with acryloyl chloride. Under the radiation of ultraviolet light, this catalyst would undergo a change of cis/trans-conformation of azobenzene, causing alterable accessibility to the internal catalytic sites and as a result mediated catalytic ability. This catalyst presented significant catalytic ability at ambient conditions due to the trans-conformation of azobenzene which endorsed accessibility to the internal catalytic sites. Conversely, this catalyst showed limited catalytic ability under ultraviolet light, in response to the isomerization of the cis-conformation of azobenzene which inhibited the accessibility. In this way, this catalyst showed the photo-mediated catalytic ability. The suggestion of this polymer catalyst provides a prospect to optically modulate the catalytic proceedings, particularly for complicated processes. [ABSTRACT FROM AUTHOR]

A large number of species in nature demonstrate switchable responsiveness to external stimuli, which is essential for their adaptation to the changing environment. Inspired by the responsive properties in nature, researchers have made significant progress in the field of synthetic stimuli-responsive materials over the years, particularly in the field of smart polymer catalysts which are able to control the catalytic processes. Here, we review these bio-inspired polymer materials and their applications in self-controlled catalytic processes. Other issues involved in developing these bio-inspired polymer materials including the origin, mechanisms, switchable behaviors and merits are also discussed. [ABSTRACT FROM AUTHOR]

The study is aimed at the present challenge in tandem catalysis, addressing how to achieve tandem catalytic ability and meantime to avoid a mutual engagement between the tandem processes. This objective was met by constituting a nanoreactor with bio-inspired compartments made of core-and-shell architectures. The core-and-shell architectures allowed the nanoreactor to spatiotemporally separate the tandem catalytic processes from each other, in virtue of the restriction from mass transfer and the radial distribution of reaction loci. The shell in this nanoreactor admitted a precursor reaction while the core was responsible the following reaction. There was no mutual engagement in the tandem processes, due to the spatiotemporally-driven sequential catalysis in the nanoreactor. In this way, this nanoreactor demonstrated the "undisturbed" tandem catalytic ability. Differing from reported nanoreactors and bi-functional catalysts which often involve a mutual competition and even cross-reactions between the tandem processes, this nanoreactor may partition the tandem catalytic processes and avoid the mutual engagement. The constitution of this nanoreactor suggests a prospect to develop "undisturbed" tandem catalysts for complicated catalytic processes. [ABSTRACT FROM AUTHOR]

This study is aimed at the present challenge in tandem catalysts, addressing how to endow the catalysts with self‐controlled tandem catalytic‐ability. By borrowing the predation strategy from sundew, the objective was originally met by reporting a smart tandem catalyst which can self‐control the tandem catalytic behavior by catching, decomposing and assimilating the engaging molecules (such as 4‐nitrophenyl acetate). This catalyst was made of a unique leaf containing two functional layers where each may be responsible for one coupled process. The first layer in this catalyst was fabricated with a zipper‐like reactive polymer capable of opening and closing, which allowed the catalyst to catch and decompose 4‐nitrophenyl acetate. The second layer in this catalyst allowed, however, further access to assimilate the decomposed substrate (i. e., 4‐nitrophenol), made of an antibody‐like polymer and encapsulated metal nanoparticles. In this way, the use of this catalyst led to the occurrence of the self‐controlled tandem catalytic‐ability. This novel design suggests a new protocol for developing smart tandem catalysts, which opens new opportunities for controlled tandem catalytic processes. Copying Nature: Inspired by the predation strategy in sundews, this study presents the first case of smart tandem catalysts which can self‐control the tandem catalytic behavior by catching, decomposing and assimilating the engaging molecules (such as 4‐nitrophenyl acetate). This catalyst was fabricated with a unique leaf made of two functional layers where each may be responsible for one coupled process. This novel design opens new opportunities for controlled tandem catalytic processes. [ABSTRACT FROM AUTHOR]

This study was aimed at addressing the present challenge in self-controlled catalysts, about how to furnish the catalysts with self-governed catalytic ability in water. This objective was met by constructing a polymer composite reactor inspired from marine mussels, made of an aquatically autonomous polymer and encapsulated metal nanoparticles. The aquatically autonomous properties at the polymer support, in combination with the catalytic ability of metal nanoparticles, allowed the reactor to run catalysis with aquatically ‘autonomous’ access, which led to the occurrence of aquatically self-governed catalytic ability. This reactor showed poor catalytic reactivity in water at relatively low temperatures due to the ‘closed’ polymeric networks, which blocked access to the encapsulated metal nanoparticles. This reactor showed, however, significant reactivity in water at relatively high temperatures in response to the ‘openness’ of the access. Unlike the switchable catalysis at reported catalytic reactors which usually involved conventional hydrophilic/hydrophobic transition and the leaching of metal nanoparticles, the switchable catalysis at this reactor ran naturally with the aquatically autonomous access that did not involve any hydrophilic/hydrophobic transition and the leaching of metal nanoparticles. This protocol suggested opportunities for developing robust smart catalysts for aquatic chemical processes. [ABSTRACT FROM AUTHOR]

A self-switchable polymer reactor with a hyperbranched structure for controlled catalytic chemistry processes is reported. This polymer reactor was made of silver nanoparticles and a polymer carrier consisting of hyperbranched polyethylenimine and hydroxyethyl acrylate that behaved as thermally switchable domains. Below the transfer temperature, relatively strong catalytic reactivity was demonstrated due to the leading role of hydrophilic groups in the switchable domains, which opened access to the substrate for the packaged silver nanoparticles. In contrast, it showed weak catalysis at relatively high temperatures, reducing from the significantly increased hydrophobicity in the switchable domains. In this way, the polymer reactor displays controllable, tunable, catalytic activity based on this approach. This novel design opens up the opportunity to develop intelligent polymer reactors for controlled catalytic processes. [ABSTRACT FROM AUTHOR]

The realization of selective/nonselective-switchable catalytic ability remains a significant challenge in controlled catalytic processes. We herein report an originally-designed imprinted polymer nanoreactor capable of meeting this challenge. This nanoreactor was composed of Ag nanoparticles and a unique holothurian-inspired imprinted polymer carrier that contained mobile molecular chains. These mobile molecular chains, by motioning and lying motionless, enabled the imprinted carrier to function in an 'online/offline'-shiftable paradigm, causing switchable access to the encapsulated metal nanoparticles. This nanoreactor showed selective catalytic ability at relatively low temperatures due to the 'frozen' molecular chains, which allowed for substrate-selective access to the encapsulated metal nanoparticles (i.e., imprinted carrier's 'online' status). In contrast, this nanoreactor provided non-selective catalysis at relatively high temperatures in response to the increased mobility of these molecular chains, which resulted in dismantling the selective access (i.e., imprinted carrier's 'offline' status). Unlike reported imprinted polymer nanoreactors which simply provide selective catalysis, this novel nanoreactor allows selective/nonselective-switchable catalysis in virtue of the bio-inspired design. This study opens up opportunities to modulate catalytic selectivity for controlled chemical processes. [ABSTRACT FROM AUTHOR]

This study was aimed at addressing the present challenge of cascade reactions, namely, how to furnish the catalysts with desired and hierarchical catalytic ability. This issue was addressed by constructing a cascade-reaction nanoreactor made of a bifunctional molecularly imprinted polymer containing acidic catalytic sites and Pt nanoparticles. The acidic catalytic sites within the imprinted polymer allowed one specified reaction, whereas the encapsulated Pt nanoparticles were responsible for another coupled reaction. To that end, the unique imprinted polymer was fabricated by using two well-coupled templates, that is, 4-nitrophenyl acetate and 4-nitrophenol. The catalytic hydrolysis of the former compound at the acidic catalytic sites led to the formation of the latter compound, which was further reduced by the encapsulated Pt nanoparticles to 4-aminophenol. Therefore, this nanoreactor demonstrated a catalytic-cascade ability. This protocol opens up the opportunity to develop functional catalysts for complicated chemical processes. [ABSTRACT FROM AUTHOR]

An originally designed catalytic and shape-memory polymer reactor is reported. This reactor is made of a unique shape-switchable polymer composed of a thermosensitive control layer and an inert substrate layer. With the inert substrate layer made of poly(acrylamide), the thermosensitive control layer consists of nickel nanoparticles and a smart polymer composite of poly(1-vinylimidazole) (PVIm) and poly(acrylic acid) (PAAc) that exhibit switchable domains. The self-healing and dissociation between PVIm and PAAc induce convex/concave-switchable shapes in the resulting reactor, which cause tunable access to the encapsulated metal nanoparticles. In this way, this reactor demonstrates tunable catalytic ability. Unlike reported smart polymer reactors exhibiting tunable catalysis usually due to the thermal phase transition of poly(N-isopropylacrylamide) (PNIPAm), this novel reactor adopts the shape-switchable strategy for tunable catalysis. This novel design suggests a new protocol for the development of smart catalytic reactors, which opens new opportunities for controlled chemical processes. [ABSTRACT FROM AUTHOR]

Abstract: A large number of molecularly imprinted polymers (MIPs) have been investigated and reported over the last decade. Various templates have been successfully exploited and used, leading to significant advances in separation, adsorption, catalysis, sensing, and drug delivery. Among all the templates, small molecules have dominated in the synthesis of MIPs. In contrast, progress made in imprinting macromolecules has been slow, mainly due to the challenges presented by the size, structure and conformational fragility of biological macromolecules. In this review, we focus on discussing some key issues involved in the imprinting of macromolecules from recent publications. The similarity and difference between imprinting small molecules and macromolecules are highlighted. Other aspects relating to polymer design and function are also discussed. [Copyright &y& Elsevier]

Abstract: A novel electrochemical immunosensor capable of enzyme-free detection of alpha fetoprotein (AFP) is reported. This immunosensor was fabricated in a sandwich-like format where catalytic Au–Pd nanocrystals and highly conductive N-doped graphene sheets were incorporated. The significant catalysis by Au–Pd nanocrystals toward hydrogen peroxide, along with the increased electron transfer by graphene sheets, caused signal generation and increased sensitivity, which enables the enzyme-free detection of AFP. With a low detection limit at 0.005ngmL−1, this novel immunosensor worked well over the broad linear range of 0.05–30ngmL−1. Unlike previously reported enzyme-based electrochemical immunosensors, which often involve the complicated steps for enzyme loading and necessary treatments to keep the activity of enzyme, this novel immunosensor is simple in nature and employed catalytic Au–Pd nanoparticles and highly conductive graphene, which thus enables reliable and sensitive detection for clinic usage. [Copyright &y& Elsevier]

Abstract: ‘On/off’-switchable catalysis by a smart enzyme-like imprinted polymer is reported. This unique imprinted polymer was composed of poly(N-isopropylacrylamide)-containing p-nitrophenyl phosphate-imprinted networks that exhibited temperature-dependent hydrophilicity/hydrophobicity. At a relatively low temperature (such as 20°C), this polymer was capable of vigorous catalysis for the hydrolysis of p-nitrophenyl acetate due to its hydrophilic networks, which enabled access to the imprinted framework. On the contrary, at higher temperatures (such as 40°C), this polymer demonstrated poor catalysis resulting from its dramatically increased hydrophobicity, which inhibited access to the imprinted sites. Unlike previously reported imprinted polymers which lack adjustable networks, this novel imprinted polymer employed thermosensitive poly(N-isopropylacrylamide) networks, thus enabling the switchable catalysis. [Copyright &y& Elsevier]

In this paper, we report a novel three-layer polymer reactor capable of simple/tandem self-controlled catalysis. The top and bottom layers were composed of two different molecularly imprinted polymers respectively containing two catalytic sites (an acidic site catalyzing hydrolysis and metal nanoparticles catalyzing reduction), performing two selective tandem reactions without interference between each other. The middle layer was composed of a copolymer of poly- N -isopropylacrylamide (PNIPAM) and polyacrylamide (PAm) in different ratios, acting as a temperature-responsive switch for the tandem catalysis process. In an aqueous environment, when the temperature is lower than the Lower Critical Solution Temperature (LCST) of the copolymer, the reactor exhibited an open middle access (hydrophilic condition) of intermediate, allowing the tandem processes from hydrolysis to reduction. When the temperature is higher than the LCST, the channels of the middle layer were closed (hydrophobic condition), which obstructed the access of reactants. As a result, the reactor could only conduct simple hydrolysis processes. Therefore, with the three-layer structure, the polymer reactor has led to a self-controlled catalysis. This new multi-layer polymeric reaction concept can expand the practical use of functional catalysts by permitting the control of processes in large temperature ranges. The switchable mechanism of the three-layer polymer reactor. [Display omitted] • A three-layer polymer reactor with non-tandem/tandem self-controlled catalytic abilities was prepared. • The middle layer made of PNIPAM-PAM acts as a molecular switch to control the tandem catalysis. • Tandem catalysis without interference was obtained by using molecularly imprinted polymers as carriers. • A temperature controlled and stable smart tandem catalysis was achieved. [ABSTRACT FROM AUTHOR]

This study aimed at the present challenge in self-controlled catalysis, addressing how to furnish the catalysts with sortable catalytic ability. This objective was reached by developing a polymer catalyst made of metal nanoparticles and a unique polymer carrier containing self-assembled hierarchical access. The hierarchical access, by closing, relaxing and opening, acted as a molecular switch for providing sequenced entrance to the encapsulated metal nanoparticles. This polymer catalyst showed poor catalytic reactivity at relatively low temperatures due to the closed access, which blocked substrate from the encapsulated metal nanoparticles. This polymer catalyst showed, however, significant reactivity for small molecules of substrate at modest temperatures, arising from relaxing of the access, which allowed small molecules to gain entrance to the catalytic metal nanoparticles. This polymer catalyst further showed significant reactivity for large molecules of substrate at relatively high temperatures, in response to the opening at the access. In this way, this polymer catalyst demonstrated the sortable catalytic ability. This suggested protocol opens up the opportunity to develop smart catalysts for controlled chemical processes. [ABSTRACT FROM AUTHOR]

This study is aimed at addressing the present challenges of self-controlled processes in tandem catalysis. Inspired by the opening and closing switchable behaviors of stomata in plant leaves arose by temperature, the objective is met by originally developing a "smart" tandem catalyst capable of crossing-response properties. The catalyst consisted of two unique functional layers where each may self-govern one coupled process. The first layer was fabricated with a negatively-thermosensitive imprinted polymer and encapsulated metal nanoparticles (PDEA- co -PAM/Ag) which were responsible for a catalytic reduction process. The second layer was made of a positively-thermosensitive polymer (PVI- co -PAMPS) with acidic groups, which were capable of a catalytic hydrolysis process. At low temperatures, this catalyst would conduct only catalytic reduction because of the open channel in the first layer. In middle temperatures, the catalyst would run the tandem processes from catalytic reduction to hydrolysis because of the open channels in both the two layers. At higher temperatures, the catalyst only catalyzed hydrolysis because of the closed channel in the first layer. In this way, the smart bi-layer catalyst achieved the single/tandem/single catalysis featured with a dual temperature-responsive switch. The novel protocol not only provides a new solution to complicated catalytic processes but also inspires the further application of smart polymers in a broader spectrum of areas. The switchable mechanism of the polymer reactor. [Display omitted] • Thermo-sensitive tandem catalyst is able to adapt to the changing environment. • A "smart" tandem catalyst is capable of crossing-response properties. • The catalyst is able to conduct the single/tandem/single reactions in different temperatures. • New catalyst shares a promising prospect to the development of one-pot catalytic processes in applications. [ABSTRACT FROM AUTHOR]