There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

The fascinating story of olefin (or alkene) metathesis (eq
1) began almost five decades ago, when Anderson and
Merckling reported the first carbon-carbon double-bond
rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.

https://core.ac.uk/download/pdf/4884240.pdf

Ruthenium-based heterocyclic carbene-coordinated olefin metathesis catalysts.

The Golden Age of Transfer Hydrogenation

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions serve, inter alia, as key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. The present chapter is aiming at illustrating the great synthetic potential of metathesis reactions. Shortcomings, such as the control of olefin geometry and the unpredictable effect of substituents on the reacting olefins, will also be addressed. Examples to be presented include epothilones, amphidinolides, spirofungin A, and archazolid. Synthetic approaches involving silicon-tethered ring-closing metathesis, relay ring-closing metathesis, sequential reactions, domino as well as tandem metathesis reactions will also be illustrated.

Recent Applications of Alkene Metathesis in Fine Chemical Synthesis

Publisher Summary This chapter explores the way nitroxide spin probes employed to study the permeability of halobacterial envelope vesicle and erythrocyte membranes to spin-labeled weakly polar molecules, ions, amines, and weak acids Membrane proton pumps, such as bacteriorhodopsin, generate electrochemical potentials that can be measured with a combination of probes responsive to transmembrane electrical and pH gradients Weakly polar spin probes with fewer than two hydrogen-bonding residues permeate most membranes too rapidly to measure with available stop-flow electron spin resonance (ESR) techniques One of the nitroxides, 4-oxo-2,2,6,6,-tetramethylpiperidine- N -oxyl (TEMPONE), is used to measure volume changes in many envelope and cell preparations and permeates at least one cell appreciably more rapidly than water does Improved biophysical techniques are needed that will give higher resolution in space and time of the initial cascade of energy-conserving reactions or structural changes The spin-probe approach for improving the kinetics and spatial resolution of the measurements of electrochemical potentials across biological membranes is discussed in the chapter It also discusses the volume measurement technique, proton gradients, and electrical potentials Phosphonium probes, which excessively slow diffusion, invariably distort measurements The syntheses of other hydrophobic spin-labeled ions with the goal of improving the permeability constants, and thus reducing errors are required

[55] Measurement of transmembrane proton movements with nitroxide spin probes

Over the last two decades, olefin metathesis has emerged as a new avenue in the design of new routes for the synthesis of natural products and active pharmaceutical ingredients. In many cases, syntheses based on olefin metathesis strategies provide significant routes in terms of increasing the overall yields, improving the synthesis scope, and decreasing the number of steps. On the other hand, over the last decade, microwave-assisted chemistry has experienced an incredible development, which rapidly opened new areas in organic synthesis and in homogeneous catalysis. In this review article, we highlight applications of microwaveheated olefin metathesis reactions as pivotal steps in the total synthesis of biologically active compounds. By drawing selected examples from the recent literature, we aim to illustrate the great synthetic power and variety of metathesis reactions, as well as the beneficial effects of microwave irradiation over conventional heating sources. The majority of the selected applications of microwave-assisted olefin metathesis cover the synthesis of medium-ring cycles, macrocycles, and peptidomimetics by means of ring-closing metathesis (RCM) and crossmetathesis (CM) routes.

Microwave-assisted Olefin Metathesis as Pivotal Step in the Synthesis of Bioactive Compounds.

A series of Ni/SiO2 catalysts with different Ni content were prepared by sol-gel method for application in the synthesis of 2- methyltetrahydrofuran (2-MTHF) by hydrogenation of 2-methylfuran (2-MF). The catalyst structure was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR). It is found that structures and catalytic performance of the catalysts were highly affected by the Ni content. The catalyst with a 25% Ni content had an appropriate size of the Ni species and larger BET surface area and produced a higher 2-MF conversion with enhanced selectivity in 2-MTHF.

/pdf/synthesis-and-catalytic-performance-of-ni-sio-2-for-4gniin0owx.pdf

Synthesis and catalytic performance of Ni/SiO 2 for hydrogenation of 2-methylfuran to 2-methyltetrahydrofuran

Aiming at improving catalyst activity, ten ruthenium promoters have been investigated in carbenoid transfer from ethyl diazoacetate to styrene as a model substrate. Optimal selectivity in cyclopropanation has been attained with the new NHC–Ru complex 10, as well as with the Fischer carbene 7. The surprising non-metathetical behavior of the Grubbs’ first-generation catalyst in this multifaceted process is highlighted. Copyright © 2014 John Wiley & Sons, Ltd.

Ileana Dragutan

Papers

Recent Applications of Alkene Metathesis in Fine Chemical Synthesis

[55] Measurement of transmembrane proton movements with nitroxide spin probes

Microwave-assisted Olefin Metathesis as Pivotal Step in the Synthesis of Bioactive Compounds.

Synthesis and catalytic performance of Ni/SiO 2 for hydrogenation of 2-methylfuran to 2-methyltetrahydrofuran

Carbenoid transfer in competing reactions catalyzed by ruthenium complexes