New Vistas in N‐Heterocyclic Silylene (NHSi) Transition‐Metal Coordination Chemistry: Syntheses,Structures and Reactivity towards Activation of Small Molecules

This account is a review on the synthesis and transition‐metal coordination chemistry of N‐heterocyclic silylenes (NHSi’s) over the last 20 years till the present time (2012). Recently, fascinating and novel synthetic methods have been developed to access transition‐metal–NHSi complexes as an emerging class of compounds with a wealth of intriguing reactivity patterns. The striking influence of coordinating NHSi’s to transition‐metal complex fragments affording different reactivities to the “free” NHSi is a connecting theme (“leitmotif”) throughout the review, and highlights the potential of these compounds which lie at the interface of contemporary main‐group and classical organometallic chemistry towards new molecular catalysts for small‐molecule activation.     

Organized molecular assemblies: Creation and investigation of their functional properties

One of the most important problems of modern chemistry, both preparative and theoretical one, is the creation of organized atomic - molecular assemblies i.e., atoms and molecules bound in a definite manner and interacting with each other, as a jointly, they become able to behave like an assembly, a single mechanism, to perform some functions, for example, to recognize separate molecules of environment (receptors), to transform an electromagnetic signal to electric field (photosynthetic), to memorize (memory cell), catalyze function and others. The chemistry of preceding period had been developing as the science of properties and transformations of individual compounds and substances. At present the progress in the notion of the nature of chemical bonds, a new level of understanding of the chemical reactions mechanism, the knowledge of the regularities of nonstationary states in reactive media and the data on the at processes interfaces have determined the up to day problem of organized molecular assemblies with a required functionality. Thermal oxidation of silicon crystals which is the key process in the technology of integral circuits production can be represented, in its main features, by the mechanism of semiconductor dissolving in the condensed phase. A characteristic feature of silicon oxidation is that the silicon activation energy of the limiting stage is lower than that of the formation of gas - phase monoxide, difference being the energy of siloxane net reorganization in silicon dioxide. The analysis shows that within the row of possible systems semiconductor - dielectric, it is silicon - silicon dioxide that is distinguished by a maximum self - organizing effect. This is one of the main reasons why only silicon could be chosen among large number of semiconductor substances for use in the technology of integral circuits. A molecular system of amphiphilic long - chain molecules, obtained according to the Langmuir - Blodgett method is an example of simplest assembly on the basis of which the elements of gas sensors can be prepared, as well as the systems of quantum dots, the objects of the low - dimension physics. We have investigated assemblies constructed from multimolecular compositions using the Langmuir - Blodgett technique and thin - layer systems based on glassy and amorphous silica films with fragments of organic molecules introduced into the matrix. Molecular engineering is a new level of the modern preparative chemistry; moreover, it is a system of concepts introducing a new culture in technology. In this sense, it is most important to realize the evolution principle in the strategy of science research.     

Selective Host Molecules Obtained by Dynamic Adaptive Chemistry

Up till 20 years ago, in order to endow molecules with function there were two mainstream lines of thought. One was to rationally design the positioning of chemical functionalities within candidate molecules, followed by an iterative synthesis–optimization process. The second was the use of a “brutal force” approach of combinatorial chemistry coupled with advanced screening for function. Although both methods provided important results, “rational design” often resulted in time‐consuming efforts of modeling and synthesis only to find that the candidate molecule was not performing the designed job. “Combinatorial chemistry” suffered from a fundamental limitation related to the focusing of the libraries employed, often using lead compounds that limit its scope. Dynamic constitutional chemistry has developed as a combination of the two approaches above. Through the rational use of reversible chemical bonds together with a large plethora of precursor libraries, one is now able to build functional structures, ranging from quite simple molecules up to large polymeric structures. Thus, by introduction of the dynamic component within the molecular recognition processes, a new perspective of deciphering the world of the molecular events has aroused together with a new field of chemistry. Since its birth dynamic constitutional chemistry has continuously gained attention, in particular due to its ability to easily create from scratch outstanding molecular structures as well as the addition of adaptive features. The fundamental concepts defining the dynamic constitutional chemistry have been continuously extended to currently place it at the intersection between the supramolecular chemistry and newly defined adaptive chemistry, a pivotal feature towards evolutive chemistry.     

Supramolecular Inorganic Chemistry: Small Guests in Small and Large Hosts

A key reaction in the biological and material world is the controlled linking of simple (molecular) building blocks, a reaction with which one can create mesoscopic structures, which, for example, contain cavities and display specifically desired properties, but also compounds that exhibit typical solid-state structures. The best example in this context is the chemistry of host–guest interactions, which spans the entire range from three- and two-dimensional to one- and “zero-dimensional”, discrete host structures. Members of the class of multidimensional compounds have been classified as such for a long time, for example, clathrates and intercalation compounds. Thus far, however, there are no classifications for discrete inorganic host–guest compounds. The first systematic approach can be applied to novel polyoxometalates, a class of compounds which has only recently become known. Molecular recognition; tailor-made, molecular engineering; control of fragment linkage of spin organization and crystallization; cryptands and coronands as “cages” for cations, anions or anion–cation aggregates as sections of ionic lattices; anions within anions, receptors; host–guest interactions; complementarity, as well as the dialectic terms reduction and emergence are important terms and concepts of supramolecular inorganic chemistry. Of particular importance for future research is the comprehension of the mesoscopic area (molècular assemblies)—that between individual molecules and solids (“substances”)—which acts in the biological world as carrier of function and information and for which interesting material properties are expected. This area is accessible through certain variations of “controlled” self-organization processes, which can be demonstrated by using examples from the chemistry of polyoxometalates. The comprehension of the laws that rule the linking of simple polyhedra to give complex systems enables one to deal with numerous interdisciplinary areas of research: crystal physics and chemistry, heterogeneous catalysis, bioinorganic chemistry (biomineralization), and materials science. In addition, conservative self-organization processes, for example template-directed syntheses, are of importance for natural philosophy in the context of the question about the inherent properties of material systems.     

Starburst Dendrimers: Molecular-Level Control of Size,Shape, Surface Chemistry,Topology, and Flexibility from Atoms to Macroscopic Matter

Starburst dendrimers are three-dimensional, highly ordered oligomeric and polymeric compounds formed by reiterative reaction sequences starting from smaller molecules—“initiator cores” such as ammonia or pentaerythritol. Protecting group strategies are crucial in these syntheses, which proceed via discrete “Aufbau” stages referred to as generations. Critical molecular design parameters (CMDPs) such as size, shape, and surface chemistry may be controlled by the reactions and synthetic building blocks used. Starburst dendrimers can mimic certain properties of micelles and liposomes and even those of biomolecules and the still more complicated, but highly organized, building blocks of biological systems. Numerous applications of these compounds are conceivable, particularly in mimicking the functions of large biomolecules as drug carriers and immunogens. This new branch of “supramolecular chemistry” should spark new developments in both organic and macromolecular chemistry.     

The structural theory and physical organic chemistry

Woolley's revolutionary proposal that quantum mechanics does not sanction the concept of “molecular structure”—which is but only a “metaphor”—has fundamental implications for physical organic chemistry. On the one hand, the Uncertainty Principle limits the precision with which transition state structures may be defined; on the other, extension of the structure concept to the transition state may be unviable. Attempts to define transition states have indeed caused controversy. Consequences for molecular recognition, and a mechanistic classification, are also discussed.     

What's Hot,What's Not: The Trends of the Past 20 Years in the Chemistry of Odorants

This review is the sequel to the 2000 report on the recent advances in the chemistry of odorants and it summarizes the developments in fragrance chemistry over the past 20 years. Following the olfactory spectrum set out in that report, trendsetting so‐called captive odorants (patent‐protected ingredients unavailable to the market) are presented according to the main odor families: “fruity”, “marine”, “green”, “floral”, “spicy”, “woody”, “amber”, and “musky”. The design of odorants, their chemical synthesis, and their use in modern perfumery are illustrated with prominent examples. Featured are new fruity odorants that provide signature in the top note, as well as precursor technology. In the green domain, focus is on leafy notes and green pear. New benzodioxepines and benzodioxoles have modernized the marine family and required a revision of the existing olfactophore models. The replacement of Lilial and Lyral kept the industry busy in the floral domain with a plethora of new “muguets”. There was continued activity in the domain of rose odorants, especially in the area of rose ketones. Biotechnology became significant, for example, with Clearwood and Ambrofix, and the principal odorants of vetiver oil in the woody family have been found. Fourth and fifth families of musk odorants were also discovered and populated. Thus, new avenues for further explorations into fragrance chemistry have been opened.     

理论化学与下世纪“化学学科重组”前瞻

本文展望了理论化学的发展趋势并预言了下个世纪“化学学科的重组”。作者建议了现代化学的定义：化学是研究从原子,分子片,分子,超分子,生物大分子到分子的各种不同尺度和不同程度的聚集态的合成和反应,分离和分析,结构和形态,物理性能和生物活性及其规律和应用的科学． 根据这个定义,从化学的研究对象不同,在２１ 世纪化学分支学科可能发生重组,因此化学可以划分为如下八个层次：１） 原子层次的化学; ２） 分子片层次的化学; ３） 分子层次的化学; ４） 超分子层次的化学; ５）生物与分子层次的化学; ６） 宏观聚集态化学; ７） 介观聚集态化学和８） 复杂分子体系的化学     

The History and the Current Revival of the Oxo Chemistry of Iron in its Highest Oxidation States: FeVI – FeVIII

The history of the oxo compounds of iron in its highest oxidation states is reviewed and modern activities in this long neglected area of inorganic chemistry are highlighted. The chemistry of ferrates(VI) is the most rapidly advancing branch owing to several potential applications in diverse fields such as environmental chemistry and energy storage. Convenient and high‐yield preparations of ferrates(VI) in high purity are presented, followed by a coverage of the analytical, spectroscopic, and structural characterization in the solid and in solution, with a focus on the stability of these compounds, which had long been under‐estimated. Particular attention has been paid to the fascinating mechanisms that have been proposed for the intriguing “self‐decay” of the [FeO₄]^2– dianion. Redox processes with inorganic and organic substrates are summarized including fresh and waste water treatment on the one hand and “super‐iron batteries” on the other. Recent advances in the experimental and computational approach to ferrates(VII) [FeO₄]^– and the elusive “iron tetroxide” [FeO₄] are described.     

Analysis of Low Molecular Weight Homologues of Fiber-Forming Polycondensates

Oligomers belong to the gray area between low molecular weight chemistry and macromolecular chemistry. Although they represent an undesirable “natural impurity” in fiber-forming polycondensates, they serve as useful model compounds for the corresponding polymers in fundamental research. Whereas for many years new classes of oligomers were being made preparatively accessible and the isolation of higher oligomers in pure form was being pursued, at the present time the emphasis is on analysis. By a combination of classical chemical and instrumental methods of analysis from polymer and organic chemistry, the identification of oligomers of unknown structure, the analytical control of their synthesis and the determination of their content in technical polymers has meanwhile become a routine task.     

Electrospray Mass Spectrometry of Biomacromolecular Complexes with Noncovalent Interactions—New Analytical Perspectives for Supramolecular Chemistry and Molecular Recognition Processes

The development of “soft” ionization methods in recent years has enabled substantial progress in the mass spectrometric characterization of macromolecules, in particular important biopolymers such as proteins and nucleic acids. In contrast to the still existing limitations for the determination of molecular weights by other ionization methods such as fast atom bombardment and plasma desorption, electrospray ionization (ESI) and matrix-assisted laser desorption have provided a breakthrough to macromolecules larger than 100 kDa. Whereas these methods have been successfully applied to determine the molecular weight and primary structure of biopolymers, the recently discovered direct characterization by ESI-MS of complexes containing noncovalent interactions (“noncovalent complexes”) opens new perspectives for supramolecular chemistry and analytical biochemistry. Unlike other ionization methods ESI-MS can be performed in homogeneous solution and under nearly physiological conditions of pH, concentration, and temperature. ESI mass spectra of biopolymers, particularly proteins, exhibit series of multiply charged macromolecular ions with charge states and distributions (“charge structures”) characteristic of structural states in solution, which enable a differentiation between native and denatured tertiary structures. In the first part of this article, fundamental principles, the present knowledge about ion formation mechanism(s) of ESI-MS, the relations between tertiary structures in solution and charge structures of macro-ions in the gas phase, and experimental preconditions for the identification of noncovalent complexes are described. The hitherto successful applications to the identification of enzyme–substrate and –inhibitor complexes, supramolecular protein–and protein–nucleotide complexes, double-stranded polynucleotides, as well as synthetic self-assembled complexes demonstrate broad potential for the direct analysis of specific noncovalent interactions. The present results suggest new applications for the characterization of supramolecular structures and molecular recognition processes that previously have not been amenable to mass spectrometry; for example, the sequence-specific oligomerization of polypeptides, antigen–antibody complexes, enzyme–and receptor–ligand interactions, and the evaluation of molecular specificity in combinatorial syntheses and self-assembled systems.     

Molecular Tweezers: Concepts and Applications

Taken to the molecular level, the concept of “tweezers” opens a rich and fascinating field at the convergence of molecular recognition, biomimetic chemistry and nanomachines. Composed of a spacer bridging two interaction sites, the behaviour of molecular tweezers is strongly influenced by the flexibility of their spacer. Operating through an “induced‐fit” recognition mechanism, flexible molecular tweezers select the conformation(s) most appropriate for substrate binding. Their adaptability allows them to be used in a variety of binding modes and they have found applications in chirality signalling. Rigid spacers, on the contrary, display a limited number of binding states, which lead to selective and strong substrate binding following a “lock and key” model. Exquisite selectivity may be expressed with substrates as varied as C₆₀, nanotubes and natural cofactors, and applications to molecular electronics and enzyme inhibition are emerging. At the crossroad between flexible and rigid spacers, stimulus‐responsive molecular tweezers controlled by ionic, redox or light triggers belong to the realm of molecular machines, and, applied to molecular tweezing, open doors to the selective binding, transport and release of their cargo. Applications to controlled drug delivery are already appearing. The past 30 years have seen the birth of molecular tweezers; the next many years to come will surely see them blooming in exciting applications.     

The Pyrolysis of Azides in the Gas Phase

The chemistry of the non-metallic elements has in recent years passed through a period of rapid development, often referred to as its “renaissance”. To emphasize just one of the key facets: numerous short-lived molecules containing multiple bonds to elements of the third and higher periods have been discovered, often accompanied by the planned synthesis of derivatives which are sterically shielded by bulky groups and thus kinetically stabilized. Thus today molecules such as silabenzenes H₆C_6?nSi_n and silaethenes H₂Si?CH₂ or R₂Si?CR₂, disilenes R₂Si?SiR₂ and diphosphenes RP?PR, silaphenylisonitrile H₅C₆? N?Si, or methylidyne-phosphanes R? C?P, are all well-known species. Sandwich compounds with P₆ rings or silicon centers demonstrate that there are now hardly any barriers to impede the imagination of the non-metal chemist. In sharp contrast is our lack of knowledge regarding the “microscopic” pathways of chemical reactions: thus apart from information provided for example by molecular beam experiments, or from exact numerical calculations involving species consisting of only a few atoms, it remains largely unknown from which directions medium-sized molecules must approach each other to successfully collide and form a “reaction complex”, in which way their structures are changed in such a process or which role is played by molecular dynamics in the energy transfer.–The pyrolysis of azides X? N₃, i.e. compounds which tend to explode violently when ignited in the condensed phase but can be heated in low-pressure gas flow systems without much risk, illustrates that studies of reactive intermediates are of interest not only because novel molecules may be discovered and isolated, and thereby possibilities for synthesis expanded. Moreover, some aspects of the “microscopic” pathways of these azide pyrolyses can be described satisfactorily on the basis of calculated energy hypersurfaces, and the influence of molecular dynamics becomes experimentally visible in the “chemical activation” of intermediates which leads to their “thermal explosion”.     

Perspectives in Metabolic Engineering: Understanding Cellular Regulation Towards the Control of Metabolic Routes

Metabolic engineering seeks to redirect metabolic pathways through the modification of specific biochemical reactions or the introduction of new ones with the use of recombinant technology. Many of the chemicals synthesized via introduction of product-specific enzymes or the reconstruction of entire metabolic pathways into engineered hosts that can sustain production and can synthesize high yields of the desired product as yields of natural product-derived compounds are frequently low, and chemical processes can be both energy and material expensive; current endeavors have focused on using biologically derived processes as alternatives to chemical synthesis. Such economically favorable manufacturing processes pursue goals related to sustainable development and “green chemistry”. Metabolic engineering is a multidisciplinary approach, involving chemical engineering, molecular biology, biochemistry, and analytical chemistry. Recent advances in molecular biology, genome-scale models, theoretical understanding, and kinetic modeling has increased interest in using metabolic engineering to redirect metabolic fluxes for industrial and therapeutic purposes. The use of metabolic engineering has increased the productivity of industrially pertinent small molecules, alcohol-based biofuels, and biodiesel. Here, we highlight developments in the practical and theoretical strategies and technologies available for the metabolic engineering of simple systems and address current limitations.     

Chemical Syntheses and Chemical Biology of Carboxyl Polyether Ionophores: Recent Highlights

A central goal of chemical biology is to develop molecular probes that enable fundamental studies of cellular systems. In the hierarchy of bioactive molecules, the so‐called ionophore class occupies an unflattering position in the lower branches, with typical labels being “non‐specific” and “toxic”. In fact, the mere possibility that a candidate molecule possesses “ionophore activity” typically prompts its removal from further studies; ionophores—from a chemical genetics perspective—are molecular outlaws. In stark contrast to this overall poor reputation of ionophores, synthetic chemistry owes some of its most amazing achievements to studies of ionophore natural products, in particular the carboxyl polyethers renowned for their intricate molecular structures. These compounds have for decades been academic battlegrounds where new synthetic methodology is tested and retrosynthetic tactics perfected. Herein, we review the most exciting recent advances in carboxyl polyether ionophore (CPI) synthesis and in addition discuss the burgeoning field of CPI chemical biology.     

核心素养视角下人教版新旧教材中“硫及其化合物”的对比分析*

选取人教版新旧必修化学教材中的“硫及其化合物”单元作为研究对象,基于新课标中化学学科核心素养的培养视角,明确了新课标对“硫及其化合物”的素养定位后,对新旧教材中该单元的引言、正文、栏目和插图进行对比分析。对比分析结果显示,新教材“硫及其化合物”的内容侧重“证据推理与模型认知”素养的培养,其次是“宏观辨识与微观探析”“科学态度与社会责任”素养,而在素养水平上则侧重水平1和2维度的培养,符合新课标对该主题单元的学业要求和素养定位。     

Pyramidal Carbocations

Pyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a “side-on” or an “end-on” ligand.     

Rhenium and technetium complexes with N-heterocyclic carbenes – A review

The coordination chemistry of technetium and rhenium with N-heterocyclic carbenes of the dimethylimidazol-2-ylidene and 1,2,4-triazol-5-ylidene types is reviewed. Compounds containing the metals in the oxidation states “+7”, “+5” and “+1” are introduced. General trends and differences in the chemical behaviour of the complexes, particularly between the different metal cores (oxo, nitrido, imido) of Tc(V) and Re(V) compounds, are discussed. The influence of electronic and steric factors for the stabilisation of the metal complexes is explored.     

Preparative Solid-State Chemistry with High-Power CO2 Lasers

The establishment of solid state chemistry as an independent field, which also has had a stimulating effect on material sciences, is a consequence of the experimental skill of chemists. The development of new methods led to an abundance of new compounds, the characteristic properties of which are linked with the solid state. The reaction temperature plays an important role in the synthesis of solid compounds; therefore, it is not surprising that a large number of the newly developed experimental techniques involve methods which can produce high temperatures on the openended temperature scale. Since the development of the CO₂ laser, the solidstate chemist has an excellent heat source available, and with the power available today the range of high temperatures possible has been extended considerably. A way is now open for producing metastable, “entropy-supported” high-temperature compounds and substances with anomalous oxidation states and with macroscopic defects.