Selective catalysis and nanoscience: an inseparable pair

Chiral Carbon Dots: Synthesis and Applications in Circularly Polarized Luminescence, Biosensing and Biology

Chiral carbon dots (CDs) are a novel luminescent zero-dimensional carbon-based nanomaterial with chirality. They not only have the advantages of good biocompatibility, multi-color-emission, easy functionalization, but also exhibits highly symmetrical chiral optical characteristics, which broadens their applicability to enantioselectivity of some chiral amino acids like cysteine and lysine, asymmetric catalysis as well as biomedicine in gene expression and antibiosis. In addition, the exploration of the excited state chirality of CDs has developed its excellent circularly polarized luminescence (CPL) properties, opening up a new application scenario like recognition of chiral light sources and anti-counterfeit printing with information encryption. This review mainly focuses on the mature synthesis approaches of chiral CDs, including chiral ligand method and supramolecular self-assembly method, then we consider emerging applications of chiral CDs in CPL, biosensing and biological effect. Finally, we concluded with a perspective on the potential challenges and future opportunities of such fascinating chiral CDs.

Chiral Surface and Geometry of Metal Nanocrystals

Chirality is a basic property of nature and has great importance in photonics, biochemistry, medicine, and catalysis. This importance has led to the emergence of the chiral inorganic nanostructure field in the last two decades, providing opportunities to control the chirality of light and biochemical reactions. While the facile production of 3D nanostructures has remained a major challenge, recent advances in nanocrystal synthesis have provided a new pathway for efficient control of chirality at the nanoscale by transferring molecular chirality to the geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Atomically precise alloy nanoclusters: syntheses, structures, and properties

Metal nanoclusters fill the gap between discrete atoms and plasmonic nanoparticles, providing unique opportunities for investigating the quantum effects and precise structure-property correlations at the atomic level. As a versatile strategy, alloying can largely improve the physicochemical performances compared to the corresponding homo-metal nanoclusters, and thus benefit the applications of such nanomaterials. In this review, we highlight the achievements of atomically precise alloy nanoclusters, and summarize the alloying principles and fundamentals, including the synthetic methods, site-preferences for different heteroatoms in the templates, and alloying-induced structure and property changes. First, based on various Au or Ag nanocluster templates, heteroatom doping modes are presented. The templates with electronic shell-closing configurations tend to maintain their structures during doping, while the others may undergo transformation and give rise to alloy nanoclusters with new structures. Second, alloy nanoclusters of specific magic sizes are reviewed. The arrangement of different atoms is related to the symmetry of the structures; that is, different atoms are symmetrically located in the nanoclusters of smaller sizes, and evolve into shell-by-shell structures at larger sizes. Then, we elaborate on the alloying effects in terms of optical, electrochemical, electroluminescent, magnetic and chiral properties, as well as the stability and reactivity via comparisons between the doped nanoclusters and their homo-metal counterparts. For example, central heteroatom-induced photoluminescence enhancement is emphasized. The applications of alloy nanoclusters in catalysis, chemical sensing, bio-labeling, and other fields are further discussed. Finally, we provide perspectives on existing issues and future efforts. Overall, this review provides a comprehensive synthetic toolbox and controllable doping modes so as to achieve more alloy nanoclusters with customized compositions, structures, and properties for applications. This review is based on publications available up to February 2020.

Oxalato bridged coordination polymer of manganese(iii) involving unconventional O⋯π-hole(nitrile) and antiparallel nitrile⋯nitrile contacts: antiproliferative evaluation and theoretical studies

Unconventional O⋯π-hole(nitrile) and antiparallel nitrile⋯nitrile contacts have been theoretically investigated for a Mn(iii) coordination polymer considering cytotoxicity, apoptosis, ROS generation, molecular docking and pharmacophore features.

Selectivity boost in partial hydrogenation of acetylene via atomic dispersion of platinum over ceria

High-throughput flame spray pyrolysis affords a low-loading Pt catalyst supported on cerium oxide, which is an excellent material for selective C₂H₂ semihydrogenation at 180 °C, with near-complete conversion and high selectivity towards C₂H₄ (87.1%).

ZnO powders as multi-facet single crystals

Oxides are most commonly found in divided forms with properties difficult to control since their crystallographic orientations usually escape analysis. To overcome this an appropriate model system can be provided by ZnO smoke which, obtained by combustion of Zn in air, exhibits nanoparticles with well-defined surface facets. The present work focuses on the interaction of water with ZnO smokes by combining density functional theory based simulations and infrared spectroscopy measurements with applied pressures from 10^-7 to 1 mbar. We demonstrate that the use of ultra-high vacuum allows the analysis of the very first stages of the adsorption, and report on water structures on ZnO(112[combining macron]0) for the first time. We further show that ZnO powders behave as multi-facet single crystals involving (101[combining macron]0), (112[combining macron]0), (0001), and (0001[combining macron]) surfaces with the polar orientations corresponding to 25% of the total surface area. A great deal of cross-agreements between experimental results and simulation provides a simple approach for the examination of hydroxylated/hydrated ZnO smokes and can be widely applied on other ZnO-related powders.

The chiral nano-world: chiroptically active quantum nanostructures

Chirality is one of the key factors in molecular recognition, therefore the development of new chiral nanoparticles is of great interest to many fields of scientific endeavour including chemistry, biochemistry, pharmacology and medicine. Knowledge of the fundamental concepts relevant to chirality in nanosystems is also very important for further advancement of nanoscience and nanotechnology in general. Over the past years, the use of stereospecific chiral stabilising molecules has opened a new avenue to the area of nanocrystal research. In this review article we present some recent advances in the development of various chiroptically active quantum nanostructures and discuss the latest progress in various approaches for the preparation of these nanostructures. We also consider the intrinsic chirality in quantum nanostructures due to the presence of chiral defects such as screw dislocations and discuss the structure-property relationship. Furthermore, the corresponding potential applications of these chiral nanomaterials has been analysed for key areas: sensing, cytotoxicity mediation and cell imaging, asymmetric catalysis and enantiomeric separation, circular polarised light emitting devices and spintronics. Finally, we provide an outlook for the future development of chiroptically active quantum nanostructures.

Keto-Enol Tautomeric Equilibrium of Acetylacetone Solution Confined in Extended Nanospaces

We aim to clarify the effects of size confinement, solvent, and deuterium substitution on keto-enol tautomerization of acetylacetone (AcAc) in solutions confined in 10-100 nm spaces (i.e., extended nanospaces) using (1)H NMR spectroscopy. The keto-enol equilibrium constants of AcAc (K(EQ) = [keto]/[enol]) in various solvents confined in extended nanospaces of 200-3000 nm were examined using the area ratios of -CH3 peaks in keto to enol forms. The results showed that the keto form of AcAc in hydrogen-bonded solvents such as water and ethanol increased drastically with decreasing space sizes below about 500 nm, but the size confinement did not induce equilibrium shifts in aprotic solvents such as DMSO. The magnitudes of K(EQ) enhancement were well correlated with solvent proton donicity. It followed from the determination of thermodynamic parameters that the stabilization of intermolecular interactions between protons in water and carbonyl oxygen (C═O) in the keto form of AcAc were promoted by size-confinement, and that the keto form could be energetically and structurally favored in extended nanospaces vis-à-vis the bulk space. Furthermore, the measurements of deuterium dependence of the K(EQ) values verified that the nanoconfinement-induced shifts of keto-enol tautomerization of AcAc are attributable to high proton mobility via a proton hopping mechanism of the confined water.

Enantioselective cyanosilylation of aldehydes catalyzed by a multistereogenic salen–Mn(iii) complex with a rotatable benzylic group as a helping hand

A multistereogenic salen–Mn(iii) complex bearing an aromatic pocket and two benzylic groups as helping hands was found to be efficient in the catalysis of asymmetric cyanosilylation.

Pair distribution function computed tomography

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.

A general method for artificial metalloenzyme formation through strain-promoted azide-alkyne cycloaddition

Strain-promoted azide-alkyne cycloaddition (SPAAC) can be used to generate artificial metalloenzymes (ArMs) from scaffold proteins containing a p-azido-L-phenylalanine (Az) residue and catalytically active bicyclononyne-substituted metal complexes. The high efficiency of this reaction allows rapid ArM formation when using Az residues within the scaffold protein in the presence of cysteine residues or various reactive components of cellular lysate. In general, cofactor-based ArM formation allows the use of any desired metal complex to build unique inorganic protein materials. SPAAC covalent linkage further decouples the native function of the scaffold from the installation process because it is not affected by native amino acid residues; as long as an Az residue can be incorporated, an ArM can be generated. We have demonstrated the scope of this method with respect to both the scaffold and cofactor components and established that the dirhodium ArMs generated can catalyze the decomposition of diazo compounds and both Si-H and olefin insertion reactions involving these carbene precursors.

Surface chromium single sites: open problems and recent advances

The results of decades of studies on the Phillips chromium (Cr)/silica polymerization catalyst are briefly summarized. The application of several characterization methods has allowed a detailed knowledge of the structure and reactivity of Cr centres to be obtained. In particular, many aspects of this apparently simple single-site catalyst, including the heterogeneity, the modification of the ligand sphere upon interaction with many molecules and the initiation mechanism of the ethylene polymerization reaction, have been clarified. It is shown that based on the acquired knowledge, it is now possible to proceed further towards the intelligent modification of the ligand sphere with the scope to increase the reaction rate and selectivity. It is also illustrated that, besides polymerization/oligomerization reactions, it is possible to extend the study of Cr II reactivity towards new reactions.

Pd nanoparticle assemblies--as the substitute of HRP, in their biosensing applications for H2O2 and glucose

The spherical porous Pd nanoparticle assemblies (NPAs) have been successfully synthesized by starch-assisted chemical reduction of Pd(II) species at room temperature. Such Pd NPAs are not simply used to enlarge the surface area and to promote the electron transfer. They also catalyze the reduction of H(2)O(2) which are regarded as horseradish peroxidase (HRP) substitutes in electron transfer process. By using them as electrocatalysts, as low as 6.8×10(-7) M H(2)O(2) can be detected with a linear range from 1.0×10(-6) to 8.2×10(-4) M. Moreover, through co-immobilization of such Pd NPAs and glucose oxidase (GOx), a sensitive and selective glucose biosensor is developed. The detection principle lies on measuring the increase of cathodic current by co-reduction of dissolved oxygen and the in situ generated H(2)O(2) during the enzymatic reaction. Under optimal conditions, the detection limit is down to 6.1×10(-6) M with a very wide linear range from 4.0×10(-5) to 2.2×10(-2) M. The proposed biosensor shows a fast response, good stability, high selectivity and reproducibility of serum glucose level. It provides a promising strategy to construct fast, sensitive, stable and anti-interferential amperometric biosensors for early diagnosis and prevention of diabetes.

Probing the surfaces of heterogeneous catalysts by in situ IR spectroscopy

This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with "in situ" controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H(2), CO, NO and C(2)H(4) are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some "key studies" and trying to evidence similarities and differences among surfaces and probes (572 references).

Effect of carbon concentration on changing the morphology of titanium carbide nanoparticles from cubic to cuboctahedron

Titanium carbide nanoparticles were synthesized by flowing methane through a plasma generated from an arc discharge between two titanium electrodes. Different methane concentrations were employed in studies made to investigate the effects of carbon concentration on particle morphology. Transmission electron microscopy and X-ray diffraction were used to investigate the synthesized TiC nanopowders, whereupon it was found that nanocrystalline TiC nanoparticles prefer a cubic morphology at low concentrations of methane and a cuboctahedron morphology at high concentration of methane. The change in particle morphology is attributed to carbon affecting the relative growth rates of the {111} and {100} facets on a TiC seed crystal.

Shape-controlled synthesis of metal nanocrystals: simple chemistry meets complex physics?

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.