Directed evolution: From a staphylococcal lipase to a phospholipase

The lipase of Staphylococcus aureus (SAL) is able to degrade lipids and p‐nitrophenylesters but is not active on phospholipid substrates. Interestingly, the homologous lipase from Staphylococcus hyicus is highly active on phospholipids. In order to investigate the molecular basis for this difference in substrate specificity, phospholipase activity was introduced into SAL by directed evolution strategy. In this approach, sequential rounds of error‐prone PCR were performed in combination with a screening of the resulting mutant libraries. The screening was based on a high‐throughput plate assay and a subsequent chromogenic assay in 96‐well plate format to accurately determine the enzymatic activities in cell lysates of a selected number of clones. After 4 rounds of error‐prone PCR, two products were obtained, displaying a 7.8‐ and 9.2‐fold increase in absolute phospholipase activity and a 5.9‐ and 6.9‐fold increase in phospholipase/ lipase activity ratio. A final round of DNA shuffling with these two products and wildtype (WT)‐SAL was performed to combine beneficial mutations and to eliminate neutral or deleterious mutations. This procedure yielded a best variant containing 6 amino acid mutations displaying a 11.6‐fold increase in absolute phospholipase activity and a 11.5‐fold increase in phospholipase/lipase ratio as compared to the starting point. The character of the mutations and their possible effects on substrate specificity are discussed.     

From a Racemate to a Single Enantiomer: Deracemization by Stereoinversion

The stereoinversion of one enantiomer into its mirror‐image counterpart within a racemate furnishes a single stereoisomeric product in 100 % theoretical yield. This extremely efficient type of deracemization, whereby substrate and product possess an identical chemical structure, can be achieved by using bio‐ or chemo‐catalysts or combinations thereof and is applicable to secondary alcohols, amines and α‐substituted carboxylic acids. Special emphasis is devoted to the theoretical background of the one‐pot, single‐step deracemization of sec‐alcohols.     

From a chiral switch to a ligand portfolio for asymmetric catalysis

This Account is divided into two sections. In the first section, the development of an enantioselective manufacturing process for ( S)-metolachlor, the active ingredient of the grass herbicide Dual Magnum, is described. This is today's largest application of asymmetric catalysis, and the Ir-Xyliphos hydrogenation catalyst achieves unprecedented 2 millions turnovers. The development started in 1982 and ended when the first production batch was run in November 1996. The strategies and approaches used for attaining the elusive goal are described, and the lessons learned are discussed. In the second section, the development and performance of a portfolio of chiral diphosphines for industrial asymmetric applications are described. Central to the portfolio is the idea of modular ligand families, i.e., diphosphines with the same backbone, where steric and electronic properties are easily tuned by the choice of the substituents at the phosphorous atoms.     

From Crystalline to Low-cost Silicon-based Solar Cells: a Review

Silicon - Renewable energy has become an auspicious alternative to fossil fuel resources due to its sustainability and renewability. In this respect, Photovoltaics (PV) technology is one of the...     

从厨房到餐桌的距离

餐馆的诱惑:“在饭馆就餐有服务员跑前跑后,你只要当好“上帝“就行了,而在家下厨从备料到上桌要忙上几个小时不说,再碰到一位懒丈夫,弄不好还要生一肚子的气,不如随便到外面吃点利索.“……     

From sustainability to sustainizability

Following the recent introduction of the Sustainability over Sets (SOS) concept as a sustainability analysis tool with broad flexibility in incorporating human input, in this work, the concepts of Sustainizability (SIZ) and Sustainizability over Sets (SIZOS) are introduced, as novel frameworks for sustainable system synthesis. Springing off the conceptual foundation of sustainability, SIZ (and SIZOS) refers to the existence of allowable external actions, and/or design changes that can render sustainable (sustainable over a set) an unsustainable (unsustainable over a set) system. Utilizing earlier mathematical results for SOS, rigorous necessary and sufficient conditions for SIZOS are presented. Two case studies, on a two-dimensional biological waste treatment system, and a three-dimensional food chain system, are then presented to illustrate the developed necessary and sufficient conditions for SIZOS.     

From Rings to Polymers

A short review of the origins and development of my research program at the University of Vermont in the area of inorganic polymers is presented. The topics include the discovery of a class of hybrid polymers and copolymers in which an inorganic ring such as a cyclophosphazene or cycloborazine system is a substituent on a carbon polymer chain. The subsequent elucidation of the electronic and chemical reactivity factors which control the formation of these materials allowed for design of successive generations of improved materials. Additional topic includes work in polyphosphazenes which have substituents with exploitable organic functionality.     

From silicon to carbon

Based on the professional experience of the author, the paper describes the main differences between the elements silicon and carbon which are neighbours in the periodic system of elements. The advantageous formation of SiO₂-protective layers by oxidation of silicon and silicides on one hand and the outstanding high temperature properties of graphite and its low resistance against oxidation on the other, stimulate the development of composite materials made from these elements. The paper describes in a comprehensive survey the efforts of the author in industry and at the university, not only to extend the understanding of carbons, but also to develop the basics of preparation of new high temperature materials, composed of carbon and silicon.     

整体煤气化联合循环动力岛及系统特性研究

动力岛是整体煤气化联合循环（IGCC）中复杂的关键单元,其中燃气轮机变工况性能的变化对蒸汽底循环及整个系统的影响较大。采用thermoflex软件建立IGCC系统模型,对200MW级IGCC系统的技术方案进行了探讨,从系统的角度详细分析了IGV可调等T3调节及空分整体化系数Xas和氮气回注系数Xgn对动力岛及整个系统的影响。结果表明：在采用IGV可调等乃调节时,在80％负荷时系统各参数出现转折点;随着Xas的增加,系统供电效率略有上升,但是系统总功下降;在Xas为30％时,随着氮气回注系数Xgn的变化,系统的各参数在Xgn为70％时出现峰值。     

From mechanism to mouse: a tale of two bioorthogonal reactions

Bioorthogonal reactions are chemical reactions that neither interact with nor interfere with a biological system. The participating functional groups must be inert to biological moieties, must selectively reactive with each other under biocompatible conditions, and, for in vivo applications, must be nontoxic to cells and organisms. Additionally, it is helpful if one reactive group is small and therefore minimally perturbing of a biomolecule into which it has been introduced either chemically or biosynthetically. Examples from the past decade suggest that a promising strategy for bioorthogonal reaction development begins with an analysis of functional group and reactivity space outside those defined by Nature. Issues such as stability of reactants and products (particularly in water), kinetics, and unwanted side reactivity with biofunctionalities must be addressed, ideally guided by detailed mechanistic studies. Finally, the reaction must be tested in a variety of environments, escalating from aqueous media to biomolecule solutions to cultured cells and, for the most optimized transformations, to live organisms. Work in our laboratory led to the development of two bioorthogonal transformations that exploit the azide as a small, abiotic, and bioinert reaction partner: the Staudinger ligation and strain-promoted azide-alkyne cycloaddition. The Staudinger ligation is based on the classic Staudinger reduction of azides with triarylphosphines first reported in 1919. In the ligation reaction, the intermediate aza-ylide undergoes intramolecular reaction with an ester, forming an amide bond faster than aza-ylide hydrolysis would otherwise occur in water. The Staudinger ligation is highly selective and reliably forms its product in environs as demanding as live mice. However, the Staudinger ligation has some liabilities, such as the propensity of phosphine reagents to undergo air oxidation and the relatively slow kinetics of the reaction. The Staudinger ligation takes advantage of the electrophilicity of the azide; however, the azide can also participate in cycloaddition reactions. In 1961, Wittig and Krebs noted that the strained, cyclic alkyne cyclooctyne reacts violently when combined neat with phenyl azide, forming a triazole product by 1,3-dipolar cycloaddition. This observation stood in stark contrast to the slow kinetics associated with 1,3-dipolar cycloaddition of azides with unstrained, linear alkynes, the conventional Huisgen process. Notably, the reaction of azides with terminal alkynes can be accelerated dramatically by copper catalysis (this highly popular Cu-catalyzed azide-alkyne cycloaddition (CuAAC) is a quintessential "click" reaction). However, the copper catalysts are too cytotoxic for long-term exposure with live cells or organisms. Thus, for applications of bioorthogonal chemistry in living systems, we built upon Wittig and Krebs' observation with the design of cyclooctyne reagents that react rapidly and selectively with biomolecule-associated azides. This strain-promoted azide-alkyne cycloaddition is often referred to as "Cu-free click chemistry". Mechanistic and theoretical studies inspired the design of a series of cyclooctyne compounds bearing fluorine substituents, fused rings, and judiciously situated heteroatoms, with the goals of optimizing azide cycloaddition kinetics, stability, solubility, and pharmacokinetic properties. Cyclooctyne reagents have now been used for labeling azide-modified biomolecules on cultured cells and in live Caenorhabditis elegans, zebrafish, and mice. As this special issue testifies, the field of bioorthogonal chemistry is firmly established as a challenging frontier of reaction methodology and an important new instrument for biological discovery. The above reactions, as well as several newcomers with bioorthogonal attributes, have enabled the high-precision chemical modification of biomolecules in vitro, as well as real-time visualization of molecules and processes in cells and live organisms. The consequence is an impressive body of new knowledge and technology, amassed using a relatively small bioorthogonal reaction compendium. Expansion of this toolkit, an effort that is already well underway, is an important objective for chemists and biologists alike.     

From a library of MAG antagonists to nanomolar CD22 ligands

Siglec-2, also known as CD22, is involved in the regulation and survival of B-cells and has been successfully targeted in cell depletion therapies with antibody-based approaches. Sialic acid derivatives, already known to bind with high affinity to myelin-associated glycoprotein (MAG, Siglec-4), were screened for their binding affinity for CD22 by surface plasmon resonance. The best compound identified was further modified with various hydrophobic substituents at the 2-, 5-, and 9-positions of the sialic acid scaffold, leading to nanomolar derivatives, of which ligand 17 b shows the most promising pharmacodynamic and pharmacokinetic profiles. Isothermal titration calorimetry measurements demonstrate that the binding is enthalpy driven. Interestingly, the thermodynamic fingerprints reveal an excellent correlation between gains in enthalpy and compensation by increased entropy costs. Moreover, 17 b exhibits a residence time in the range of a few seconds, clearly prolonged relative to residence times typically observed for carbohydrate-lectin interactions. Finally, initial tests regarding drug-like properties of 17 b demonstrate the required high plasma protein binding yet a lack of oral availability, although its distribution coefficient (log D) is in the required range.     

From surface science to nanotechnology

This overview sketches the historical development of surface science through nanoscience toward nanotechnology. It spans about 50 years of evolution and emphasizes the multidisciplinary nature of this field, as well as its closely-knit interactions with technology, scientific disciplines, phenomena and techniques. A series of examples is given, drawn mainly from work performed in Berkeley, to highlight various stages in the field: surfaces, interfaces, clusters, thin films, superlattices, nanostructures and “bionano”.     

From Extraction-Pyrolytic to Extraction-Additive Technology

Theoretical Foundations of Chemical Engineering - A brief review of studies of the extraction-pyrolytic method to produce inorganic materials of various purposes is presented. The potential to use...     

从化学反应到生命

通过化学进化生成的蛋白质、脂质、三磷酸苷、核糖核酸等,在脂质组成的球膜内,形成具有能量转换、物质传递、并具有遗传性能的个体,是生命最初的形式。作者并指出：弄清楚化学反应的机理。是进一步认识化学进化,生命起源的基础;并将由此引起一场新的工业革命。     

From British Standards to CEN

The Society has played a major role over the years in the development and implementation of standards for textile testing. John Morris gives an account of the relationship between the SDC and the various national and international bodies involved in the setting of standards in the testing area.     

From a laboratory to a pilot scale production of natural rubber grafted with PMMA

Graft copolymers of natural rubber and poly (methyl methacrylate) (NR‐g‐PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.5 l. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50°C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR‐g‐PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and ¹H‐NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of ¹H‐NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009