Artificial selenoenzymes: designed and redesigned

Enzymes, highly evolved machinery developed by nature, catalyse reactions with formidable efficiency and specificity under mild conditions. Considerable efforts have been devoted for several decades on the development of enzyme-like catalysts with tailored properties by rationally manipulating natural and artificially synthesized host molecules. One of the great challenges is to design artificial systems with catalytic efficiencies and specificities rivalling natural components. Although most of the designed artificial enzymes present mild rate promotion, the high efficiency and specificity rivalling natural ones by artificially designed system appears. In this tutorial review, we recount the methods and strategies of design and redesign of artificial selenoenzymes on synthesized and natural hosts, with emphasis on construction of the active sites of antioxidative glutathione peroxidase (GPx) by the concept of synergy between recognition and catalysis (66 references).     

Artificial polymeric flavonoids: synthesis and applications

Flavonoids, one of the most numerous and best studied groups of plant polyphenols, are well known to exhibit various biological and pharmacological effects. Functional artificial polymeric flavonoids, flavonoid polymers and amine containing polymer-flavonoid conjugates have been developed. The acid-catalyzed polymerization of catechin and aldehydes proceeds regioselectively to produce catechin-aldehyde polycondensates. Peroxidases and laccases catalyze the oxidative coupling of flavonoids and oxidative conjugation with polyamines. The resulting polymers show much higher antioxidant activities than the flavonoid monomers. In addition, these polymeric flavonoids efficiently inhibit disease related enzymes, such as xanthine oxidase, collagenase, elastase, hyaluronidase and tyrosinase. Based on these results, the molecular design for amplification of the biological and pharmacological properties of flavonoids is proposed.     

Influence of ring position on the temporal dependence of charge movement in a switchable [2]rotaxane

Switchable mechanically interlocked molecular architectures (MIMAs) are promising candidates for the components of nanoscale devices. An example of a MIMA-based switch used in nanoscale devices is the electrochemically switchable Stoddart-Heath-type [2]rotaxane. This system's two coconformations differ in electrical conductance, a feature that has been harnessed for electronic and information storage applications. Herein we study the flow of charge in two coconformations of a bistable Stoddart-Heath-type [2]rotaxane and report statistical predictions of electron transfer times using a probabilistic approach for characterizing the timescale of quantum particle transit. The ratio of predicted transfer times for the two coconformations is consistent with the experimentally reported difference in electrical conductance. Path information offered by the probabilistic method gives insight into the influence of ring position on the mechanism of electron transit in this mechanically interlocked assembly.     

An Artificial Disc: Chemical and Biomechanical Analysis

Summary: Degeneration of intervertebral discs is the most common cause of back pain. The first phase of this degenerative process involves the nucleus pulposus. A rapid recovery of this structure can prevent further degradation of the annulus fibrosus. Guar Gum is an hydrophilic polysaccharide extracted from the seed endosperm of a plant. Through a cross-linking procedure a Guar hydrogel was synthesized. The Guar hydrogel could be injected by a syringe and it is a good candidate as a nucleus pulposus substitute. For the preparation of the artificial fibrosus annulus, commercially available polymer materials are tuned to achieve suitable mechanical properties. To achieve this peculiar behaviour, the main strategy investigated is the dispersion of hollow polymer micro spheres in a thermoplastic polymer matrix. Processing conditions and particle content are finely tuned to get the target mechanical behaviour.     

ATPase-coupled release control from polyion complex capsules encapsulating muscle proteins

In the present study, a muscle contractile protein complex, actomyosin, has been successfully encapsulated into gellan-chitosan polyion complex (PIC) capsules. The recovery of the myosin-ATPase activity is approximately 50% and the Mg2+-ATPase activity is stimulated by the presence of F-actin, which implies the formation of the actomyosin complex inside the capsule. Furthermore, encapsulation could protect the myosin, F-actin, and actomyosin inside from hydrolysis by proteases. Two small proteins, myoglobin and cytochrome c, have been used in the release tests. The release of myoglobin is not affected by the ionic strength of the external solution, while the release of cytochrome c increases with increasing ionic strength. The maximal releases are found in the external pH solution close to the isoelectric points of each protein. The Mg2+-ATP complex itself reduces the release percentages of the small proteins from the PIC capsule. The release amounts further decrease when coexisting with Mg2+-ATP and the encapsulated actomyosin, which indicates the release regulation by actomyosin. The present study suggests that the ATPase-coupled sliding motion of the myosin-F-actin filaments modifies the pore size of the polymer networks in the PIC capsule membranes.     

Artificial Photosynthesis: Mimicking Redox Asymmetry

Directional light-induced electron transfer takes place in the catenane shown schematically on the right. This catenane is similar to the photosynthetic reaction center: The two chemically identical electron acceptors (rectangles) bound to a ruthenium complex as donor have different reduction potentials because their environments are of different polarity. The electron transfer proceeds preferentially (85 %) to the external acceptor.     

Deconstructing Oligomer Distributions: Discrete Species and Artificial Distributions

The separation of an oligo(methyl acrylate) distribution, obtained from reversible addition–fragmentation chain transfer (RAFT) polymerization, in a discrete (dispersity=1) oligomeric library (degree of polymerization between 1 and 22) is presented. The properties of this library in terms of diffusivity, glass transition temperature, and viscosity are determined, filling a significant knowledge gap associated with these materials. The obtained oligomer library is used to construct artificial oligomer distributions on demand. These artificial oligomer distributions are used to highlight the potential to tailor physical properties of a material, while concomitantly demonstrating the limitations associated with size‐exclusion chromatography analysis of molecular weight and dispersity in particular.     

Palladium-catalyzed synthesis of spiro[2.4]heptanes: ligand-dependent position control in the nucleophilic attack to a pi-allylpalladium intermediate

A palladium-catalyzed intermolecular cycloaddition of gamma-methylidene-delta-valerolactones with electron-deficient olefins has been developed for the synthesis of spiro[2.4]heptanes with high selectivity through a nucleophilic ring closure to the central carbon of a pi-allylpalladium intermediate. It was found that the course of the reaction is dependent on the ligand employed, and selective [4 + 2] cycloadditions can also be achieved by the use of a bulky monophosphine ligand.     

人工海水制剂——海水晶

阐述了人工海水制剂海水晶的化学组成、发展历程、用途和不当使用的危害,并介绍了几种鉴别海水晶等假冒食盐简单可行的方法。     

人工碳循环——二氧化碳转化利用技术

纵观历史长河,从薪柴到煤炭,再到油气和新能源,每次能源的更替都极大地促进了社会生产力的发展。从化学角度看,能源革命的本质就是“减碳趋氢”的过程。本文在介绍了能源发展史后,简单阐述了能源利用的本质及不同能源的结构差异;随后从反应热力学和动力学角度,重点介绍了CO₂作为重要碳一(C₁)资源的转化利用技术及研究进展;最后展望了我国未来碳科学与技术的总旋律。     

Artificial Neural Networks in water analysis: Theory and applications

Artificial Neural Networks (ANNs) have seen an explosion of interest over the last two decades and have been successfully applied in all fields of chemistry and particularly in analytical chemistry. Inspired from biological systems and originated from the perceptron, i.e. a program unit that learns concepts, ANNs are capable of gradual learning over time and modelling extremely complex functions. In addition to the traditional multivariate chemometric techniques, ANNs are often applied for prediction, clustering, classification, modelling of a property, process control, procedural optimisation and/or regression of the obtained data. This paper aims at presenting the most common network architectures such as Multi-layer Perceptrons (MLPs), Radial Basis Function (RBF) and Kohonen's self-organisations maps (SOM). Moreover, back-propagation (BP), the most widespread algorithm used today and its modifications, such as quick-propagation (QP) and Delta-bar-Delta, are also discussed. All architectures correlate input variables to output variables through non-linear, weighted, parameterised functions, called neurons. In addition, various training algorithms have been developed in order to minimise the prediction error made by the network. The applications of ANNs in water analysis and water quality assessment are also reviewed. Most of the ANNs works are focused on modelling and parameters prediction. In the case of water quality assessment, extended predictive models are constructed and optimised, while variables correlation and significance is usually estimated in the framework of the predictive or classifier models. On the contrary, ANNs models are not frequently used for clustering/classification purposes, although they seem to be an effective tool. ANNs proved to be a powerful, yet often complementary, tool for water quality assessment, prediction and classification.     

Catalytic nanomotors: autonomous movement of striped nanorods

Rod-shaped particles, 370 nm in diameter and consisting of 1 microm long Pt and Au segments, move autonomously in aqueous hydrogen peroxide solutions by catalyzing the formation of oxygen at the Pt end. In 2-3% hydrogen peroxide solution, these rods move predominantly along their axis in the direction of the Pt end at speeds of up to 10 body lengths per second. The dimensions of the rods and their speeds are similar to those of multiflagellar bacteria. The force along the rod axis, which is on the order of 10(-14) N, is generated by the oxygen concentration gradient, which in turn produces an interfacial tension force that balances the drag force at steady state. By solving the convection-diffusion equation in the frame of the moving rod, it was found that the interfacial tension force scales approximately as SR(2)gamma/muDL, where S is the area-normalized oxygen evolution rate, gamma is the liquid-vapor interfacial tension, R is the rod radius, mu is the viscosity, D is the diffusion coefficient of oxygen, and L is the length of the rod. Experiments in ethanol-water solutions confirmed that the velocity depends linearly with the product Sgamma, and scaling experiments showed a strong dependence of the velocity on R and L. The direction of motion implies that the gold surface is hydrophobic under the conditions of the experiment. Tapping-mode AFM images of rods in air-saturated water show soft features that are not apparent in images acquired in air. These features are postulated to be nanobubbles, which if present in hydrogen peroxide solutions, would account for the observed direction of motion.     

The extracellular matrix and the control of proliferation of vascular endothelial and vascular smooth muscle cells

In this short review we describe the observations which have led us to conclude that one of the most important components involved in modulating cell proliferation in vitro, and probably in vivo as well, may be the extra-cellular matrix upon which cells rest.     

The position of the analyst as expert: Yesterday and today

The interrelation between law and analytical chemistry 150 years ago is outlined, showing that similar problems to today already existed at that time. Examples of present-day cases of judicial investigations are given and consequences for the duty of the analytical chemist are discussed. Received: 19 April 2000 / Accepted: 14 June 2000     

The position of the analyst as expert: yesterday and today

The interrelation between law and analytical chemistry 150 years ago is outlined, showing that similar problems to today already existed at that time. Examples of present-day cases of judicial investigations are given and consequences for the duty of the analytical chemist are discussed.     

A PDMS-based biochip with integrated sub-micrometre position control for TIRF microscopy of the apical cell membrane

A poly(dimethylsiloxane) (PDMS)-based biochip with an integrated pressure controlled positioning system with sub-micrometre precision was realized. The biochip was easy and cheap to manufacture and enabled positioning in a wet environment. It allowed the application of total internal reflection fluorescence (TIRF) microscopy at the dorsal cell membrane, which is not adhering to a support. Specifically, the chip enabled TIRF microscopy at the apical membrane of polarized epithelial cells. Thereby, the device allowed us for the first time to monitor individual fusion events of GPI-GFP bearing vesicles at the apical membrane in live Madin-Darby canine kidney II (MDCK II) cells. Moreover, a mapping of fusion sites became feasible and revealed that the whole apical membrane is fusion competent. In total, the biochip offers an all-in-one solution for apical TIRF microscopy and contributes a novel tool to study trafficking processes close to the apical plasma membrane in polarized epithelial cells.     

Artificial Molecular Ratchets: Tools Enabling Endergonic Processes

Non-equilibrium chemical systems underpin multiple domains of contemporary interest, including supramolecular chemistry, molecular machines, systems chemistry, prebiotic chemistry, and energy transduction. Experimental chemists are now pioneering the realization of artificial systems that can harvest energy away from equilibrium. In this tutorial Review, we provide an overview of artificial molecular ratchets: the chemical mechanisms enabling energy absorption from the environment. By focusing on the mechanism type—rather than the application domain or energy source—we offer a unifying picture of seemingly disparate phenomena, which we hope will foster progress in this fascinating domain of science.     

点石成金——人造钻石的真相

A diamond is forever, diamond is not only seen as a kind of precious stones, but also used in industry. With technology and science continuing to develop, synthetic diamond is developing rapidly. To answer readers' confusion of synthetic diamond, there is a wonderful story, which tells readers about structure and properties of graphite and diamond, the basic method and catalysis of synthetic diamond.