Palladium nanoparticles modified electrospun CoFe2O4 nanotubes with enhanced peroxidase-like activity for colorimetric detection of hydrogen peroxide

Herein, we report a simple procedure to decorate small palladium nanoparticles (Pd NPs) on the surface of CoFe₂O₄ nanotubes; the decorated nanotubes possess intrinsic peroxidase-like activity for the sensitive detection of H₂O₂.

Metal–organic redox vehicles to encapsulate organic dyes for photocatalytic protons and carbon dioxide reduction

By encapsulation of an organic dye, a supramolecular nickel–organic macrocycle for the photocatalytic reduction of protons and CO₂ has been reported.

Cyclo[6]aramide-Tropylium Charge Transfer Complex as a Colorimetric Chemosensor for Differentiation of Intimate and Loose Ion Pairs

Shape-persistent iso-C16-cyclo[6]aramide (1) was found to form a charge-transfer (CT) complex with aromatic carbonium tropylium (Tr(+)). The resulting CT complex was evidenced by both experimental results and theoretical calculations. Particularly, dibutylammonium salt with PF6(-) as the counterion can extrude Tr(+) from the CT complex, but it cannot do so with Cl(-), thereby offering a visual approach to identify organic intimate ion pairs and loose ion pairs.

Transition metal catalysis in confined spaces

Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has recently been shown to be a viable method to induce new selectivity and activity in transition metal catalysis. In this review we focus on supramolecular strategies to encapsulate transition metal complexes with the aim of controlling the selectivity via the second coordination sphere. As we will discuss, catalyst confinement can result in selective processes that are impossible or difficult to achieve by traditional methods. We will describe the template-ligand approach as well as the host-guest approach to arrive at such supramolecular systems and discuss how the performance of the catalyst is enhanced by confining it in a molecular container.

Construction of a smart microgel glutathione peroxidase mimic based on supramolecular self-assembly

In an effort to construct smart artificial glutathione peroxidase (GPx) featuring high catalytic activity in an efficient preparation process, an artificial microgel GPx (PPAM-ADA-Te) has been prepared using a supramolecular host-guest self-assembly technique. Herein, 6,6'-telluro-bis(6-deoxy-β-cyclodextrin) (CD-Te-CD) was selected as a tellurium-containing host molecule, which also served as the crosslinker for the scaffold of the supramolecular microgel. And an adamantane-containing block copolymer (PPAM-ADA) was designed and synthesized as a guest building block copolymer. Subsequently, PPAM-ADA-Te was constructed through the self-assembly of CD-Te-CD and PPAM-ADA. The formation of this self-assembled construct was confirmed by dynamic light scattering, NMR, SEM and TEM. Notably, PPAM-ADA-Te not only exhibits a significant temperature responsive catalytic activity, but also features the characteristic saturation kinetics behaviour similar to that of a natural enzyme catalyst. We demonstrate in this paper that both the hydrophobic microenvironment and the crosslinker in this supramolecular microgel network played significant roles in enhancing and altering the temperature responsive catalytic behaviour. The successful construction of PPAM-ADA-Te not only provides a novel method for the preparation of microgel artificial GPx with high catalytic activity but also provides properties suitable for the future development of intelligent antioxidant drugs.

Tailoring of the desired selectivity and the turn-on detection range in a self-assembly-based fluorescence sensory system

This study demonstrates how to control the selectivity and the turn-on detection range toward the tailoring of an assembly-based fluorescence (FL) sensory system. Assembly-based FL chemosensors composed of oligophenylenevinylene with a varied number of guanidinium receptors (G2, G4 and G6) were newly developed, and their FL response to nucleotides (AMP, ADP and ATP) was investigated. Indeed, G6 exhibited FL emission via self-assembly with ATP. More importantly, the FL response of G6 showed markedly improved selectivity for ATP over ADP and a broadly extended detection range of ATP concentration under adjusted salt conditions. The salt effect on the FL response revealed the competitive binding interactions affecting the subsequent self-assembly process. These studies have unveiled the pivotal binding mechanisms operating in the self-assembly process, which tailor the performance level of the assembly-based sensory system. We believe that this study offers a new design principle of an assembly-based FL chemosensor with high selectivity and the appropriate detection range, being different from the conventional key-and-lock system.

Self-assembly of cricoid proteins induced by "soft nanoparticles": an approach to design multienzyme-cooperative antioxidative systems

A strategy to construct high-ordered protein nanowires by electrostatic assembly of cricoid proteins and "soft nanoparticles" was developed. Poly(amido amine) (PAMAM) dendrimers on high generation that have been shown to be near-globular macromolecules with all of the amino groups distributing throughout the surface were ideal electropositive "soft nanoparticles" to induce electrostatic assembly of electronegative cricoid proteins. Atomic force microscopy and transmission electron microscopy all showed that one "soft nanoparticle" (generation 5 PAMAM, PD5) could electrostatically interact with two cricoid proteins (stable protein one, SP1) in an opposite orientation to form sandwich structure, further leading to self-assembled protein nanowires. The designed nanostructures could act as versatile scaffolds to develop multienzyme-cooperative antioxidative systems. By means of inducing catalytic selenocysteine and manganese porphyrin to SP1 and PD5, respectively, we successfully designed antioxidative protein nanowires with both excellent glutathione peroxidase and superoxide dismutase activities. Also, the introduction of selenocysteine and manganese porphyrin did not affect the assembly morphologies. Moreover, this multienzyme-cooperative antioxidative system exhibited excellent biological effect and low cell cytotoxicity.

Bifunctionalized mesoporous silica-supported gold nanoparticles: intrinsic oxidase and peroxidase catalytic activities for antibacterial applications

Bifunctionalized mesoporous silica-supported gold nanoparticles as oxidase and peroxidase mimics for antibacterial applications are demonstrated. For the first time, these mesoporous silica-supported gold nanoparticles are applied as oxidase and peroxidase mimics. Taking advantage of their prominent enzyme activities, the MSN-AuNPs show excellent antibacterial properties against both Gram-negative and Gram-positive bacteria. Furthermore, MSN-AuNPs also exhibit outstanding performance in biofilm elimination .

Nanodevices for the immobilization of therapeutic enzymes

Therapeutic enzymes are one of the most promising applications of this century in the field of pharmaceutics. Biocatalyst properties can be improved by enzyme immobilization on nano-objects, thereby increasing stability and reusability and also enhancing the targeting to specific tissues and cells. Therapeutic biocatalyst-nanodevice complexes will provide new tools for the diagnosis and treatment of old and newly emerging pathologies. Among the advantages of this approach are the wide span and diverse range of possible materials and biocatalysts that promise to make the matrix-enzyme combination a unique modality for therapeutic delivery. This review focuses on the most significant techniques and nanomaterials used for enzyme immobilization such as metallic superparamagnetic, silica, and polymeric and single-enzyme nanoparticles. Finally, a review of the application of these nanodevices to different pathologies and modes of administration is presented. In short, since therapeutic enzymes constitute a highly promising alternative for treating a variety of pathologies more effectively, this review is aimed at providing the comprehensive summary needed to understand and improve this burgeoning area.

Gas-phase chemistry of molecular containers

The use of mass spectrometry for the investigation of supramolecular capsules and containers in solution and the gas-phase is reviewed.

Strongly fluorescent organogels and self-assembled nanostructures from pyrene coupled coumarin derivatives: application in cell imaging

The present work reports facile synthesis of pyrene coupled coumarin derivatives which could form self-assembled molecular gel and nano-flakes. The nanomaterials obtained via a self-assembly process could be potentially used in fluorescence imaging applications.

Reversible pH-controlled switching of an artificial antioxidant selenoenzyme based on pseudorotaxane formation and dissociation

A conceptual smart GPx model that showed a response to pH stimuli was developed by using a simple selenium-containing compound and a cucurbit[6]uril-pseudorotaxane-based molecular switch.

Copper and zinc complexes of a diaza-crown ether as artificial nucleases for the efficient hydrolytic cleavage of DNA

Copper and zinc complexes of a diaza-crown ether, serving as artificial nucleases, exhibited high nuclease activities towards the hydrolytic cleavage of DNA.

Gold(I) catalysis at extreme concentrations inside self-assembled nanospheres

Homogeneous transition-metal catalysis is a crucial technology for the sustainable preparation of valuable chemicals. The catalyst concentration is usually kept as low as possible, typically at mM or μM levels, and the effect of high catalyst concentration is hardly exploited because of solubility issues and the inherent unfavorable catalyst/substrate ratio. Herein, a self-assembly strategy is reported which leads to local catalyst concentrations ranging from 0.05 M to 1.1 M, inside well-defined nanospheres, whilst the overall catalyst concentration in solution remains at the conventional mM levels. We disclose that only at this high concentration, the gold(I) chloride is reactive and shows high selectivity in intramolecular CO and CC bond-forming cyclization reactions.

Novel chiral (salen)Mn(III) complexes containing a calix[4]arene unit in 1,3-alternate conformation as catalysts for enantioselective epoxidation reactions of (Z)-aryl alkenes

Two new chiral calix[4]arene-salen ligands 1a,b, based on calix[4]arene platforms in 1,3-alternate conformation, have been prepared by a new general synthetic pathway. Their Mn(III) complexes, 3a,b have shown fairly good efficiency in the asymmetric epoxidation of styrene and substituted styrenes, whereas excellent catalytic activity and selectivity were observed with rigid bicyclic alkenes, namely 1,2-dihydro-naphthalene and substituted 2,2'-dimethyl-chromene. The higher catalytic properties of 3a may be ascribed to the more rigid and inherently chiral structure as proved by molecular modelling, NMR spectroscopy and X-ray data of the similarly structured UO2 complexes 2a,b.

Reaction mediated artificial cell termination: control of vesicle viability using Rh(I)-catalyzed hydrogenation

Methods for artificial cell control by applying catalytic processes are receiving increasing attention as a basis for artificial control of cellular functions. Here we have developed a Rh(I)-based catalytic hydrogenation reaction of unsaturated bonds of lipids that make up vesicles contained in aqueous media. The reduction reaction was applied to vesicles revealing that oleate vesicles collapse following catalytic reduction with H2 and a Rh(I) catalyst, while the distribution of EggPC liposomes was increased following the reaction. Proliferation and size of the vesicles could thus be controlled by catalysis based on variations in fluidity of the vesicle membrane. This process is applicable for use in artificial cells and/or even living cellular systems.

The peroxidase/catalase-like activities of MFe₂O₄ (M=Mg, Ni, Cu) MNPs and their application in colorimetric biosensing of glucose

MFe2O4 (M=Mg, Ni, Cu) magnetic nanoparticles (MNPs) were found to have catalytic activities similar to those of biological enzymes such as catalase and peroxidase. These nanomaterials, as bifunctional catalase/peroxidases (KatGs), not only could catalyze H2O2 to produce hydroxyl radicals, which oxidized peroxidase substrate to produce color, but also could catalyze the decomposition reaction of H2O2 into water and oxygen directly in the same condition through the catalase-like activity. And it was also found that the amount of generated hydroxyl radicals and oxygen was related to the concentration of MFe2O4 (M=Mg, Ni, Cu) MNPs. The peroxidase-like catalytic behavior of MFe2O4 MNPs was analyzed in detail. Under the optimized conditions, NiFe2O4 MNPs were used as a colorimetric biosensor for the detection of 9.4×10(-7)-2.5×10(-5) mol L(-1) glucose with a limit of detection (LOD) of 4.5×10(-7) mol L(-1). The sensor was successfully applied to glucose detection in urine sample.

Nano-gold as artificial enzymes: hidden talents

Creating artificial enzymes that mimic the complexity and function of natural systems has been a great challenge for the past two decades. In this Progress Report, the focus is on recently discovered "hidden talents" of gold nanomaterials in artificial enzymes, including mimicking of nuclease, esterase, silicatein, glucose oxidase, peroxidase, catalase, and superoxide dismutase. These unexpected enzyme-like activities can be ascribed to nano-gold itself or the functional groups present on surrounding monolayer. Along with introducing the mechanisms of the various enzyme-like activities, the design and development of gold-based biomimetic catalysts, the search for efficient modulators, and their potential applications in bionics, biosensing, and biomedical sciences are highlighted. Eventually, it is expected that the rapidly growing interest in gold-based nanozymes will certainly fuel the excitement and stimulate research in this highly active field.

A supramolecular microgel glutathione peroxidase mimic with temperature responsive activity

Glutathione peroxidase (GPx) protects cells from oxidative damage by scavenging surplus reactive oxygen species (ROS). Commonly, an appropriate amount of ROS acts as a signal molecule in the metabolism. A smart artificial GPx exhibits adjustable catalytic activity, which can potentially reduce the amount of ROS to an appropriate degree and maintain its important physiological functions in metabolism. To construct an optimum and excellent smart artificial GPx, a novel supramolecular microgel artificial GPx (SM-Te) was prepared based on the supramolecular host-guest interaction employing the tellurium-containing guest molecule (ADA-Te-ADA) and the cyclodextrin-containing host block copolymer (poly(N-isopropylacrylamide)-b-[polyacrylamides-co-poly(6-o-(triethylene glycol monoacrylate ether)-β-cyclodextrin)], PPAM-CD) as building blocks. Subsequently, based on these building blocks, SM-Te was constructed and the formation of its self-assembled structure was confirmed by dynamic light scattering, NMR, SEM, TEM, etc. Typically, benefitting from the temperature responsive properties of the PNIPAM scaffold, SM-Te also exhibited similar temperature responsive behaviour. Importantly, the GPx catalytic rates of SM-Te displayed a noticeable temperature responsive characteristic. Moreover, SM-Te exhibited the typical saturation kinetics behaviour of a real enzyme catalyst. It was proved that the changes of the hydrophobic microenvironment and the pore size in the supramolecular microgel network of SM-Te played significant roles in altering the temperature responsive catalytic behaviour. The successful construction of SM-Te not only overcomes the insurmountable disadvantages existing in previous covalent bond crosslinked microgel artificial GPx but also bodes well for the development of novel intelligent antioxidant drugs.

Cooperative Binding of Cyclodextrin Dimers to Isoflavone Analogues Elucidated by Free Energy Calculations

Dimerization of cyclodextrin (CD) molecules is an elementary step in the construction of CD-based nanostructured materials. Cooperative binding of CD cavities to guest molecules facilitates the dimerization process and, consequently, the overall stability and assembly of CD nanostructures. In the present study, all three dimerization modes (head-to-head, head-to-tail, and tail-to-tail) of β-CD molecules and their binding to three isoflavone drug analogues (puerarin, daidzin, and daidzein) were investigated in explicit water surrounding using molecular dynamics simulations. Total and individual contributions from the binding partners and solvent environment to the thermodynamics of these binding reactions are quantified in detail using free energy calculations. Cooperative drug binding to two CD cavities gives an enhanced binding strength for daidzin and daidzein, whereas for puerarin no obvious enhancement is observed. Head-to-head dimerization yields the most stable complexes for inclusion of the tested isoflavones (templates) and may be a promising building block for construction of template-stabilized CD nanostructures. Compared to the case of CD monomers, the desolvation of CD dimers and entropy changes upon complexation prove to be influential factors of cooperative binding. Our results shed light on key points of the design of CD-based supramolecular assemblies. We also show that structure-based calculation of binding thermodynamics can quantify stabilization caused by cooperative effects in building blocks of nanostructured materials.

Supramolecular assemblies obtained by mixing different cyclodextrins and AOT or BHDC reverse micelles

In this contribution we show the effect of the surfactant polar head and the external solvent on the incorporation of different cyclodextrins (CDs) {α-CD, β-CD, γ-CD, decenylsuccinyl-β-CD (Mod-β-CD), and hydroxypropyl-β-CD (hp-β-CD)} in different reverse micelles (RMs) {benzene/sodium 1,4-bis(2-ethylhexyl) sulfosuccinate(AOT)/water, and benzene/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/water} and compare them with previous results obtained in n-heptane/AOT/water RMs. To investigate the different systems, we have used UV-vis spectrophotometry, induced circular dichroism spectroscopy (ICD), and the achiral molecular probe methyl orange (MO). The results show dramatic differences changing the external solvent and the surfactant, which are explained by considering the differences in the RMs interface composition, the water-surfactant interaction, and the CDs' location in the different media investigated. None of the CDs were incorporated into the benzene/AOT/water RMs at any [H2O]/[surfactant] ratio studied (W0) whereas it was previously shown that Mod-β-CD and hp-β-CD could be included in n-heptane/AOT/water RMs. However, all of the CDs are incorporated in benzene/BHDC/water RMs at W0 > 10 and hp-β-CD is dissolved even at W0 = 0. Different from what was found in n-heptane/AOT RMs, in BHDC RMs MO showed ICD signals with two different CDs: Mod-β-CD and hp-β-CD. The results are explained by considering the known difference in the interfacial water structure for AOT and BHDC RMs and the electron-rich region on the secondary hydroxyl (wider side of the CDs), which helps to solubilize all CDs in BHDC. This study shows that chiral cyclodextrin could be available for a guest in an organic medium such as the RMs. Therefore we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.

Self-Assembled M₂L₄ Nanocapsules: Synthesis, Structure and Host-Guest Recognition Toward Square Planar Metal Complexes

Metallosupramolecular cages of the general formulas [M₂(L)₄][X]₄ can be self-assembled in good yields, where M = Pd, X = NO₃, L = L¹ (1a); M = Pd, X = OTf, L = L¹ (1b); M = Pt, X = OTf, L = L¹ (2); M = Pd, X = OTf, L = L² (3); L¹ = 1,3-bis(pyridin-3-ylethynyl)-5-methoxybenzene; and L² = 2,6-(pyridin-3-ylethynyl)-4-methoxyaniline, respectively. These cages have been fully characterized using ¹H, ¹³C NMR, elemental analysis, IR spectroscopy, and electrospray mass spectrometry. Additionally the molecular structure of [Pd₂(L¹)₄][OTf]₄ (1b) was confirmed using single crystal X-ray diffraction. The capacity of central cavities of M₂L₄ cages to accommodate square planar metal complexes was investigated. In particular, the tetracationic cage [Pd₂(L²)₄][OTf]₄ (3) was found to encapsulate the anionic metal complex [PtCl₄]²⁻ through electrostatic interactions and also via hydrogen bonding with the amino groups of the bridging ligand displayed by this nanocage.

A facile one-pot method to synthesize a polypyrrole/hemin nanocomposite and its application in biosensor, dye removal, and photothermal therapy

In this work, we introduced a facile method for the construction of a polypyrrole/hemin (PPy/hemin) nanocomposite via one-pot chemical oxidative polymerization. In this process, a hemin molecule serving as a dopant was entrapped in the PPy nanocomposite during chemical oxidative polymerization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and UV-visible spectroscopy results demonstrated that the PPy/hemin nanocomposite was successfully synthesized. The as-prepared nanocomposite exhibited intrinsic peroxidase-like catalytic activities, strong adsorption properties, and an excellent near-infrared (NIR) light-induced thermal effect. We utilized the nanomaterials to catalyze the oxidation of a peroxidase substrate 3,3,5,5-tetramethylbenzidine by H2O2 to the oxidized colored product which provided a colorimetric detection of glucose. As low as 50 μM glucose could be detected with a linear range from 0.05 to 8 mM. Moreover, the obtained nanocomposite also showed excellent removal efficiency for methyl orange and rhodamine B and a photothermal effect, which implied a promising application as the pollutant adsorbent and photothermal agent. The unique nature of the PPy/hemin nanocomposite makes it very promising for the fabrication of inexpensive, high-performance bioelectronic devices in the future.

Encapsulation of a catalytic imidazolium salt into avidin: towards the development of a biohybrid catalyst active in ionic liquids

Herein, we report the development of biohybrid catalysts that are capable of catalyzing the aldol reaction. The use of biotinylated imidazolium salts in combination with racemic or enantiomerically pure catalytic anions allowed us to study the adaptive and cooperative positioning of the anionic catalyst inside the protein. Supramolecular encapsulation of the biotinylated catalyst into avidin resulted in good selectivity for the aldol reaction performed in ionic liquid/water mixtures.

Self-assembling small molecules for the detection of important analytes

Self-assembling small molecules including those capable of forming hydrogels have been used to detect important analytes.

Improving the esterification activity of Pseudomonas fluorescens and Burkholderia cepacia lipases via cross-linked cyclodextrin immobilization

Improving activities: solid cross-linked β-cyclodextrin enzymes can remarkably improve thermal stability and enzyme activity as compared to commercial immobilized enzymes in esterification reactions (e.g., monostearin synthesis).

Supramolecular control of selectivity in transition-metal catalysis through substrate preorganization

The Perspective highlights possibilities to use supramolecular interactions between a substrate molecule and a (bifunctional) catalyst as a powerful tool to control the selectivity in transition-metal catalysis.

Hemin-block copolymer micelle as an artificial peroxidase and its applications in chromogenic detection and biocatalysis

Following an inspiration from the fine structure of natural peroxidases, such as horseradish peroxidase (HRP), an artificial peroxidase was constructed through the self-assembly of diblock copolymers and hemin, which formed a functional micelle with peroxidase-like activity. The pyridine moiety in block copolymer poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) can coordinate with hemin, and thus hemin is present in a five-coordinate complex with an open site for binding substrates, which mimics the microenvironment of heme in natural peroxidases. The amphiphilic core-shell structure of the micelle and the coordination interaction of the polymer to the hemin inhibit the formation of hemin μ-oxo dimers, and thereby enhance the stability of hemin in the water phase. Hemin-micelles exhibited excellent catalytic performance in the oxidation of phenolic and azo compounds by H2O2. In comparison with natural peroxidases, hemin-micelles have higher catalytic activity and better stability over wide temperature and pH ranges. Hemin-micelles can be used as a detection system for H2O2 with chromogenic substrates, and they anticipate the possibility of constructing new biocatalysts tailored to specific functions.

A smart artificial glutathione peroxidase with temperature responsive activity constructed by host–guest interaction and self-assembly

A smart supramolecular artificial glutathione peroxidase (GPx) with tunable catalytic activity was prepared based on host–guest interaction and a blending process. The change of the self-assembled structure of SGPxmax during the temperature responsive process played a significant role in altering the temperature responsive catalytic behavior.