26 Aug 2016-Angewandte Chemie (John Wiley & Sons Ltd)-Vol. 55, Iss: 36, pp 10737-10740
TL;DR: A catalytic system based on monolayer-functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported and the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu(2+) ions under controlled conditions.
Abstract: A catalytic system based on monolayer-functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported. The catalytic activity relies on the presence of metal ions (Cd2+ and Cu2+), which can be complexed by the nanoparticle-bound monolayer. This activates the system towards the catalytic cleavage of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), which can be monitored by UV/Vis spectroscopy. It is shown that Cu2+ metal ions can be delivered to the system by applying an oxidative potential to an electrode on which Cu0 was deposited. By exploiting the different affinity of Cd2+ and Cu2+ ions for the monolayer, it was also possible to upregulate the catalytic activity after releasing Cu2+ from an electrode into a solution containing Cd2+. Finally, it is shown that the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu2+ ions under controlled conditions.
TL;DR: The use of photocatalysts and catalyst-free approaches to mediate polymerization upon photoexcitation and the existing challenges in polymer chemistry that could be overcome by further development of light-mediated polymerization techniques are highlighted.
Abstract: Recently, visible-light-regulated polymerization has been gaining popularity, as it opens a range of new opportunities for the synthesis of functional polymers and materials Here, the most recent developments in this field are summarized, which is the use of photocatalysts and catalyst-free approaches to mediate polymerization upon photoexcitation These catalysts can transfer an electron or energy to activate an initiator The recent achievements in light-regulated atom-transfer radical polymerization, reversible addition-fragmentation chain-transfer polymerization, ring-opening metathesis polymerization, cobalt-mediated radical polymerization, iodine-mediated radical polymerization, and living cationic polymerization are reviewed Recent development in these fields have solved important challenges in polymer chemistry, such as the development of oxygen-tolerant polymerization, polymerization mediated by near-infrared, metal-free polymerization, and spatial-, temporal-, and sequence-controlled polymerization Some applications of these techniques will be discussed, such as adapting the current photocatalytic systems to synthesize heterogeneous photocatalysts that act as recyclable photocatalysts and novel light-mediated approaches for surface functionalization of hybrid materials and living cells Finally, the existing challenges in polymer chemistry that could be overcome by further development of light-mediated polymerization techniques are highlighted along with the future directions of this field
TL;DR: Metal coordination has a manifold of rewards, putting it primo loco in opportunities for putting nanomechanical systems into action, and its strength and dynamics can be properly modulated and fine-tuned by the choice of metal, redox state, and ligand.
Abstract: A look at the elegance and efficiency of biological machines readily reveals that Nature masters the full gamut of chemical interactions to compose masterpieces of the living world. The present analysis singles out metal coordination for the actuation of nanomechanical motion. According to our analysis, metal coordination has a manifold of rewards, putting it primo loco in opportunities for putting nanomechanical systems into action: (i) its strength and dynamics can be properly modulated and fine-tuned by the choice of metal, redox state, and ligand(s), (ii) the high directionality of the interaction allows reliable design, and (iii) the emergence of novel self-sorting algorithms allows multiple of these interactions to be working in parallel. On top of all these advantages, intermolecular metal-ion translocation is a well-known factor in biological signaling. These benefits have recently proven their usefulness in the operation of networked devices and in overcoming the limitations of traditional stand-alone molecular systems.
TL;DR: A tri-stable switchable catalyst is encoded by pH-controlled dynamic self-assembly of gold and TiO2 nanoparticles by precise adjustment of the integrated dynamic covalent and noncovalent self- assembly process.
Abstract: A tri-stable switchable catalyst is encoded by pH-controlled dynamic self-assembly of gold and TiO2 nanoparticles (NPs). Through precise adjustment of the integrated dynamic covalent and noncovalent self-assembly process of the two types of nanoparticles, the photocatalytic activity of the hybrid system is modulated by switching pH conditions between tri-stable "highly active", "active", and "inactive" states.
TL;DR: A molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions, used in an assisted tandem catalysis set up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.
Abstract: Disclosed here is a molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set-up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.
Abstract: This Digest letter aims to stimulate the readers with some recent developments in the field of artificial switchable catalysis achieved during the last couple of years. The significance of this young but burgeoning field was emphasized with the help of these latest examples.
TL;DR: A catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions is reported that not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.
Abstract: The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.
TL;DR: This review discusses various nanomaterials that have been explored to mimic different kinds of enzymes and covers their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal.
Abstract: Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).
TL;DR: Graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems and the incorporation of modulator into artificial enzymes can offer a facile but highly effective way to improve their overall catalytic performance.
Abstract: ConspectusNatural enzymes, exquisite biocatalysts mediating every biological process in living organisms, are able to accelerate the rate of chemical reactions up to 1019 times for specific substrates and reactions. However, the practical application of enzymes is often hampered by their intrinsic drawbacks, such as low operational stability, sensitivity of catalytic activity to environmental conditions, and high costs in preparation and purification. Therefore, the discovery and development of artificial enzymes is highly desired. Recently, the merging of nanotechnology with biology has ignited extensive research efforts for designing functional nanomaterials that exhibit various properties intrinsic to enzymes. As a promising candidate for artificial enzymes, catalytically active nanomaterials (nanozymes) show several advantages over natural enzymes, such as controlled synthesis in low cost, tunability in catalytic activities, as well as high stability against stringent conditions.In this Account, we fo...
TL;DR: This critical review presents a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques and discusses important nanommaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO(2) and SnO( 2), as well as lithium Mn-richMetal oxides.
Abstract: The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO2 and SnO2, as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).
Abstract: Electrochemical reduction of an exemplary ATRP catalyst, C 11 Br 2 /Me 6 TREN, is shown to be an efficient process to mediate and execute an ATRP. The onset of polymerization occurs only through passage of a cathodic current achieved under a reductive potential to form Cu 1 Br 2 /Me 6 TREN, within the reaction medium. Unprecedented control over the polymerization kinetics can be attained through electrochemical methods by modulating the magnitude of the applied potential allowing polymerization rate enhancement or retardation. Additional polymerization control is gained through electrochemical “dials” allowing polymerization rate enhancements achieved by larger applied potentials and the ability to successfully switch a polymerization “on” and “off between dormant and active states by application of multistep intermittent potentials.