All Eyes on Visible-Light Peroxyoxalate Chemiluminescence Read-Out Systems

Chemiluminescence (CL) reactions have been widely employed and explored over the past 50 years because they offer unique light emission upon a defined chemical stimulus. In this Minireview, we focus on peroxyoxalate (PO) compounds because they feature very high quantum yields tuneable over the entire visible spectrum, allowing for visible-light detection by the naked eye without the necessity for expensive analytical instruments. Although analytical methods have been extensively described, PO-CL read-out is a strongly emerging field with ample industrial potential. The state-of-the-art PO-CL detection read-out systems for various key analytes is here explored. In particular, structural requirements, recent developments of PO-CL read-out probes and current limitations of selected examples are detailed. Furthermore, innovative approaches and synthetic routes to push the boundaries of PO-CL reactions into biological systems are highlighted. Underpinned by recent contributions, we share perspectives on embedding PO-CL molecules into polymeric materials, which they consider the next step in designing high performance solid-phase read-out systems.     

Catalysts for new tasks: preparation and applications of tunable ruthenium catalysts for olefin metathesis

A continuous survey across structures, made over the past decades, has led to the development of highly active olefin metathesis catalysts for sophisticated synthetic tasks and for polymer technology. In this paper, our efforts toward novel and improved ruthenium complexes with even better performance in olefin metathesis are described. Oxygen ether derivatives 3, pioneered by Hoveyda, exhibit high activity and possess excellent functional group tolerance. We have successfully fine-tuned catalyst 3b to increase its activity and applicability by the introduction of electron-withdrawing groups to diminish the donor properties of the oxygen atom. As a result, the stable and easily accessible nitro-substituted catalyst 6 has found a number of successful applications in various research and industrial laboratories. We were intrigued by the possibility to further fine-tune the Hoveyda-type catalysts by combining two activating effects-steric and electronic-in a single catalyst. This was possible to achieve in so-called scorpio carbenes, which are currently under investigation in our laboratory. These modifications can be used not only to control the catalyst activity, but also to alter its physical-chemical properties, such as solubility in a given medium or an affinity to silica gel. An example of immobilization strategy based on this concept is presented.     

Elements, Principles and the Narrative of Affinity

In the 18th century, the concept of ‘affinity’, ‘principle’ and ‘element’ dominated chemical discourse, both inside and outside the laboratory. Although much work has been done on these terms and the methodological commitments which guided their usage, most studies over the past two centuries have concentrated on their application as relevant to Lavoisier's oxygen theory and the new nomenclature. Kim's affinity challenges this historiographical trajectory by looking at several French chemists in the light of their private thoughts, public disputations and communal networks. In doing so, she tells a complex story which points to the methodological and practical importance of industrial and medical chemistry. The following review highlights the advantages and snares of such an approach and makes a few historiographical points along the way. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photocontrollable analyte-responsive fluorescent probes: a photocaged copper-responsive fluorescence turn-on probe

Analyte-responsive fluorescent probes are valuable chemical tools for dissecting complex living systems. However, the major shortcoming of fluorescent probes is that once they enter the cells, control over them is basically lost. It is critical to regulate fluorescent probes in a spatial and temporal manner, as functions of biomolecules are spatiotemporal. On the other hand, light can be manipulated in time and in the application site, so the photocaging technique allows researchers to control the biomolecules of interest in a temporal and spatial fashion. Herein, we propose for the first time the combination of the merits of sensing and photocaging technologies, which may afford the caging version of analyte-responsive fluorescent probes, referred to as photocontrollable analyte-responsive fluorescent probes (PCAFPs). These "smart" fluorescent probes apparently have the intrinsic advantage of spatiotemporal control when compared to traditional fluorescent probes, as the "sensing activity" of PCAFPs is photocontrollable. This should enable biologists to interrogate complex biological systems in a spatial and temporal manner with an innovative chemical tool. In this work, for proof of concept, we report the rational design, synthesis, photocontrollable sensing in solution and in living cells, and mechanistic studies of a molecular prototype of PCAFP for copper as the first paradigm of this new class of smart fluorescent probes. We believe that PCAFPs represent a substantial breakthrough in the sensing and photocaging fields, and that the general concept of PCAFPs should be broadly applicable for a wide variety of biologically relevant species.     

Biomimetic photoelectric conversion systems based on artificial membranes

Biological light-driven proton pumps which could transfer light energy to electrical energy have aroused intense interest in the past years.Many related researches have been conducted to mimic this process in vitro because of its potential significant applications.This review describes the progress in biomimetic photoelectric conversion systems based on different kinds of promising artificial membranes.Both biological bacteriorhodopsin and the photosensitive chemical molecules which could be used to achieve...     

Quantification of Zinc Atoms in a Surface Alloy on Copper in an Industrial‐Type Methanol Synthesis Catalyst

Methanol has recently attracted renewed interest because of its potential importance as a solar fuel. 1 Methanol is also an important bulk chemical that is most efficiently formed over the industrial Cu/ZnO/Al₂O₃ catalyst. The identity of the active site and, in particular, the role of ZnO as a promoter for this type of catalyst is still under intense debate. 2 Structural changes that are strongly dependent on the pretreatment method have now been observed for an industrial‐type methanol synthesis catalyst. A combination of chemisorption, reaction, and spectroscopic techniques provides a consistent picture of surface alloying between copper and zinc. This analysis enables a reinterpretation of the methods that have been used for the determination of the Cu surface area and provides an opportunity to independently quantify the specific Cu and Zn areas. This method may also be applied to other systems where metal–support interactions are important, and this work generally addresses the role of the carrier and the nature of the interactions between carrier and metal in heterogeneous catalysts.     

Understanding chemical reactivity: the case for atom, proton and methyl transfers

The concept of "chemical reactivity" assumes that atoms and molecules contain the necessary information to describe their evolution over time as they transform from reactants to products. This concept was useful in the past to rationalize reactivity trends and predict the behavior of new systems. Free-energy relationships have played a central role in this field. However, electronic effects often counter the energetic effects and give rise to "anomalies" or separate correlations. We discuss a quantification of the concept of "chemical reactivity", emphasizing the role of molecular and electronic factors in chemistry.     

Benchmarking Catalysts for Formic Acid/Formate Electrooxidation

Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO₂ emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field.     

Light‐Induced Click Reactions

Spatial and temporal control over chemical and biological processes, both in terms of “tuning” products and providing site‐specific control, is one of the most exciting and rapidly developing areas of modern science. For synthetic chemists, the challenge is to discover and develop selective and efficient reactions capable of generating useful molecules in a variety of matrices. In recent studies, light has been recognized as a valuable method for determining where, when, and to what extent a process is started or stopped. Accordingly, this Minireview will present the fundamental aspects of light‐induced click reactions, highlight the applications of these reactions to diverse fields of study, and discuss the potential for this methodology to be applied to the study of biomolecular systems.     

Tubular Structures of Calcium Carbonate: Formation,Characterization, and Implications in Natural Mineral Environments

Chemical gardens are self-assembled tubular precipitates formed by a combination of osmosis, buoyancy, and chemical reaction, and thought to be capable of catalyzing prebiotic condensation reactions. In many cases, the tube wall is a bilayer structure with the properties of a diaphragm and/or a membrane. The interest in silica gardens as microreactors for materials science has increased over the past decade because of their ability to create long-lasting electrochemical potential. In this study, we have grown single macroscopic tubes based on calcium carbonate and monitored their time-dependent behavior by in situ measurements of pH, ionic concentrations inside and outside the tubular membranes, and electrochemical potential differences. Furthermore, we have characterized the composition and structure of the tubular membranes by using ex situ X-ray diffraction, infrared and Raman spectroscopy, as well as scanning electron microscopy. Based on the collected data, we propose a physicochemical mechanism for the formation and ripening of these peculiar CaCO₃ structures and compare the results to those of other chemical garden systems. We find that the wall of the macroscopic calcium carbonate tubes is a bilayer of texturally distinct but compositionally similar calcite showing high crystallinity. The resulting high density of the material prevents macroscopic calcium carbonate gardens from developing significant electrochemical potential differences. In the light of these observations, possible implications in materials science and prebiotic (geo)chemistry are discussed.     

New trends in polyoxometalate photoredox chemistry: from photosensitisation to water oxidation catalysis

Molecular metal oxide clusters, so-called polyoxometalates (POM) have been extensively used as homogeneous photocatalysts in various photoredox reactions such as the oxidation of alkanes, alkenes and alcohols as well as the light-induced mineralisation of various organic and inorganic pollutants. The more general application of POMs as photoactive compounds, in particular in solar energy harnessing, has been hampered as the clusters typically absorb light in the UV-region only. Over the past decade, concepts have been put forward on how the reactivity of this class of compounds can be optimised to improve their overall photoactivity, and a particular focus has been on the design of photocatalytic processes which allow the conversion of solar light into useful chemical reactivity. This perspective gives a brief overview of general aspects of POM photochemistry and critically discusses the advantages and challenges of a range of POM-based systems for photooxidations and photoreductions with a focus on the development of sustainable solar light conversion systems.     

Polymer Blends

The concept of appropriately combining two or more different polymers to obtain a new material system with the desirable features of its constituents is not new. Over the years, numerous systems based on the chemical combination of different monomers through random, block, and graft copolymerization methods have been developed with this goal in mind. For similar reasons, the coatings and rubber industries have long blended together different polymers, and particularly over the last decade the interest in polymer blend systems as a way to meet new market applications with minimum development cost has rapidly increased. This approach has not been without its difficulties and has not developed as rapidly as it might have, in part because most physical blends of different high molecular weight polymers prove to be immiscible. That is, when mixed together, the blend components are likely to separate into phases containing predominantly their own kind. This characteristic, combined with the often low physical attraction forces across the phase boundaries, usually causes immiscible blend systems to have poor mechanical properties. Despite this difficulty, a number of physical blend systems have been commercialized, and some of these are discussed later. However, there are ways around this problem of compatibility. Much research has shown that there are many truly miscible polymer pairs that can lead to significant opportunities for new products. Even for immiscible pairs, proper control of phase morphology during processing and/or the addition of “compatibilizing” agents can improve the interfacial situation mentioned above.     

Recent Advances in the Deoxydehydration of Vicinal Diols and Polyols

Deoxydehydration (DODH) is one of the most promising tools to reduce the oxygen content of biomass (sugars and polyols) and provide analogues of platform chemicals that are derived from fossil resources. This reaction converts a vicinal diol into an alkene and is typically catalyzed by high‐oxidation‐state metal‐oxo compounds in the presence of a stoichiometric reductant, with examples of both homogeneous and heterogeneous systems. This minireview will highlight the developments in this field over the past 5 years and focus on efforts to solve the problems that currently prevent DODH being performed on a commercial scale, including the nature of the reductant, substrate scope and selectivity, and catalyst recovery and expense.     

Computational Bioluminescence

Bioluminescence (BL) is an amazing natural phenomenon whose visible light is produced by living organisms. Due to its high sensitivity, high selectivity and high signal‐to‐noise ratio, BL has been applied broadly in biotechnology and biomedical fields. However, for centuries, we can only receive some sporadic and static information from experimental observations, the mechanism of most BL is unknown. In the past 14 years, we have been performing theoretical study on all kinds of bioluminescent systems, and have uncovered the mechanism and details of several BLs. Here as an example, we qualitatively introduce our theoretical study of firefly BL in this account.     

Hard X-ray Spectroscopic Nano-Imaging of Hierarchical Functional Materials at Work

Heterogeneous catalysts often consist of an active metal (oxide) in close contact with a support material and various promoter elements. Although macroscopic properties, such as activity, selectivity and stability, can be assessed with catalyst performance testing, the development of relevant, preferably quantitative structure–performance relationships require the use of advanced characterisation methods. Spectroscopic imaging in the hard X-ray region with nanometer-scale resolution has very recently emerged as a powerful approach to elucidate the hierarchical structure and related chemistry of catalytic solids in action under realistic reaction conditions. This X-ray-based chemical imaging method benefits from the combination of high resolution (∼30 nm) with large X-ray penetration and depth of focus, and the possibility for probing large areas with mosaic imaging. These capabilities make it possible to obtain spatial and temporal information on chemical changes in catalytic solids as well as a wide variety of other functional materials, such as fuel cells and batteries, in their full complexity and integrity. In this concept article we provide details on the method and setup of full-field hard X-ray spectroscopic imaging, illustrate its potential for spatiotemporal chemical imaging by making use of recent showcases, outline the pros and cons of this experimental approach and discuss some future directions for hierarchical functional materials research.     

Recent advances in surface-enhanced Raman scattering detection technology for microfluidic chips

Microfluidic chip devices and their application to sensitive chemical and biological analyses have attracted significant attention over the past decade. The miniaturization of reaction systems offers practical advantages over conventional benchtop systems. In this case, however, a highly sensitive on-chip detection method is important for the monitoring of chemical reactions as well as for the detection of analytes inside the channel because the detection volume in a micrometer-size channel is extremely small. Recently, a surface-enhanced Raman scattering (SERS) technique is being regarded as a potential candidate for the highly sensitive detection of analytes in a microfluidic chip. This review provides a general survey and an in-depth look at recent developments in SERS techniques for the biological/environmental analysis of minute analytes in a microfluidic chip.     

Polymers from carbon dioxide: Polycarbonates,polyurethanes

The world polymer industry claims over 2 million tons per year, though most synthetic polymers use petroleum feedstocks, there is a growing effort to prepare polymers from renewable raw materials concerning the depleting fossil fuel resources. In this short review, we would like to emphasize the potential that CO₂ based polymers, polycarbonates and polyurethanes from copolymerization of CO₂ and epoxides, have to mitigate the above concerns, where the newly developed metal catalyst systems allow not only their high efficient synthesis, significant advances have been achieved in stereo-controlled copolymerization. It is also noteworthy that the physical and chemical properties of CO₂ based polymers may be tailored, which help to pave the way from their lab curiosities to practical application, as new applications have been realized such as biodegradable disposal bags, and hydrolysis and oxidation resistant water borne adhesives.     

不对称自催化反应

不对称自催化反应是指由不对称反应生成的手性产物自身作为催化剂的反应过程。不对称自催化具有手性自动放大、反应活性较高、产物处理较易、反应体系连续等特点,是不对称化学的一个新的领域。不对称自催化反应结合手性放大作用,使人们对手性起源有了新的认识。自1990年代以来该方面的探索和研究取得令人注目的重大突破。本文综述了近年来不对称自催化反应的新进展。     

Asymmetric catalysis by chiral hydrogen-bond donors

Hydrogen bonding is responsible for the structure of much of the world around us. The unusual and complex properties of bulk water, the ability of proteins to fold into stable three-dimensional structures, the fidelity of DNA base pairing, and the binding of ligands to receptors are among the manifestations of this ubiquitous noncovalent interaction. In addition to its primacy as a structural determinant, hydrogen bonding plays a crucial functional role in catalysis. Hydrogen bonding to an electrophile serves to decrease the electron density of this species, activating it toward nucleophilic attack. This principle is employed frequently by Nature's catalysts, enzymes, for the acceleration of a wide range of chemical processes. Recently, organic chemists have begun to appreciate the tremendous potential offered by hydrogen bonding as a mechanism for electrophile activation in small-molecule, synthetic catalyst systems. In particular, chiral hydrogen-bond donors have emerged as a broadly applicable class of catalysts for enantioselective synthesis. This review documents these advances, emphasizing the structural and mechanistic features that contribute to high enantioselectivity in hydrogen-bond-mediated catalytic processes.     

Evolution of polyhydroxyalkanoate (PHA) production system by "enzyme evolution": successful case studies of directed evolution

Biotechnological studies towards the biosynthesis of polyhydroxyalkanoates (PHAs) biopolyesters have extensively progressed through the development of various metabolic engineering strategies. Historically, efficient PHA production has been achieved using the fermentation technology of naturally occurring PHA-producing bacteria based on external substrate manipulation (1st generation), and subsequent reinforcement with recombinant gene technology (2nd generation). More recently, "enzyme evolution" is becoming the 3rd generation approach for PHA production. A break-through in the chemical synthesis of macromolecules with desirable properties was achieved by the development of prominent chemical catalysts via "catalyst evolution", as represented by a series of Ziegler-Natta catalysts. Thus, one can easily accept the concept that the molecular evolution of the biocatalysts (enzymes) relevant to PHA synthesis will provide us with a chance to create novel PHA materials with high performance. The first trial of an in vitro enzyme evolution in PHA biosynthesis was reported by our group in 2001. The following literature data, as well as our own experimental results devoted to this new approach, have been accumulated over a short time. This review article focuses specifically on the concept and current case studies of the application of "enzyme evolution" to PHA biosynthesis.