Rodney A. Fernandes, Asim K. Chowdhury,Pullaiah Kattanguru DOI: 10.1002/ejoc.201301033 The orthoester Johnson–Claisen rearrangement, an important C–C bond forming reaction, has been used enormously in the past four decades in the synthesis of bioactive molecules, natural products, synthetic intermediates, analogues, and useful building blocks. The method has also featured in chemical modification of materials. This review covers developments in this rearrangement since 2003. Unlike many other forms of Claisen rearrangement, this reaction is generally a one-pot, one-step process. It is compatible with numerous functional groups, despite its use of acid catalysis, and offers chirality transfer to produce stereoselective products. The method also offers opportunities for rapid modifications to various functionalized compounds and building blocks for further synthetic exploration.
Shift work: The new NMR technique, instant homonuclear decoupling, which is achieved by slice-selective homo-decoupling during acquisition, yields pure-shift NMR spectra (see picture) which can be recorded like regular 1D spectra. No special data processing is necessary and this approach can also be easily adapted for the direct dimension of two- and multidimensional spectra, giving improved resolution.
Dr. N. Helge Meyer,Prof. Klaus Zangger*Angewandte Chemie International Edition
Electron Shape Measurement, Most Precise Yet, Rules Out New Physics Theories Huffington Post Scientists are unanimous that their current theory of physics is incomplete. Yet every effort to expose a deeper theory has so far disappointed.
Researchers in the group led by ICFO Prof. Romain Quidant, in collaboration with Prof. Frank Koppens at ICFO, CSIC and Macquarie University in Australia, have developed a new technique, similar to the MRI but with a much higher resolution and sensitivity, which has the ability to scan individual cells. The paper published in Nature Nanotech, and highlighted by Nature, explains how this was accomplished using artificial atoms, diamond nanoparticles doped with nitrogen impurity, to probe very weak magnetic fields such as those generated in some biological molecules.
Individual atoms are structures that are highly sensitive to their environment, with a great ability to detect nearby electromagnetic fields. The challenge these atoms present is that they are so small and volatile that in order to be manipulated, they must be cooled to temperatures near the absolute zero. This complex process requires an environment that is so restrictive that it makes individual atoms unviable for potential medical applications. Artificial atoms used by Quidant and his team are formed by a nitrogen impurity captured within a small diamond crystal. "This impurity has the same sensitivity as an individual atom but is very stable at room temperature due to its encapsulation. This diamond shell allows us to both move and rotate the nitrogen impurity. In addition, because such control is achieved in solution, our technique is compatible with measurements on a living cell" argues Dr. Quidant.
To trap and manipulate these artificial atoms, researchers use laser light. The laser works like tweezers, leading the atoms above the surface of the object to study and extract information from its tiny magnetic fields.
The emergence of this new technique could strongly benefit the field of medical imaging, providing a new class of information that could contribute to early detection of diseases, and thus a higher probability for successful treatment.
Russia has temporarily suspended upcoming launches of its Proton-M rocket in the wake of Monday's high-profile mishap, according to media reports.
An unmanned Proton-M crashed shortly after blasting off on Monday (July 1), destroying three navigation satellites worth a total of nearly $200 million. The incident marked the fifth major Proton launch failure since December 2010.
The Proton has been grounded while a Russian governmental commission investigates the causes of the crash and attempts to determine which officials bear responsibility for it, the Russian news agency Ria Novosti reported today (July 2).
Double-slit diffraction is a corner stone of quantum mechanics. It illustrates key features of quantum mechanics: interference and the particle-wave duality of matter. In 1965, Richard Feynman presented a thought experiment to show these features.
Richard Feynman described electron diffraction as a phenomenon 'which has in it the heart of quantum mechanics. In reality, it contains the only mystery'. He went on to describe a thought experiment for which he stated 'that you should not try to set up' because 'the apparatus would have to be made on an impossibly small scale to show the effects we are interested in'. He used these effects to help illustrate the phenomena of wave–particle duality, which is a postulate that all particles exhibit both wave and particle properties. The effects he described were: the relations between electron probability distributions from single- and double-slits, and observation of single particle diffraction. In this paper we report both control over the individual slits to observe probability distributions from both single- and double-slits, and the build-up of a diffraction pattern at single electron detection rates to achieve the full realization of Feynman's thought experiment. We use the term build-up to refer to the measurement of the cumulative spatial detection pattern as a function of time.
The general perception is that the electron double-slit experiment has already been performed. This is true in the sense that Jönsson demonstrated diffraction from single, double, and multiple (up to five) micro-slits, but he could not observe single particle diffraction, nor close individual slits. In two separate landmark experiments, individual electron detection was used to produce interference patterns; however, biprisms were used instead of double-slits. First, Pozzi recorded the interference patterns at varying electron beam densities. Then, Tonomura recorded the positions of individual electron detection events and used them to produce the well known build-up of an interference pattern. It is interesting to point out that the build up of a double-slit diffraction pattern has been called 'The most beautiful experiment in physics', while the build-up for a true double-slit has, up to now, never been reported.
More recently, electron diffraction was demonstrated with single- and double-slits using focused ion beam (FIB) milled nano-slits. In addition, one single slit in a double-slit was closed by FIB induced deposition. This process is not reversible, so observation of the electron probability distribution through both single-slits could not be done. Also, using a fast-readout pixel detector, electrons were recorded one at a time and stacked into a final diffraction pattern, but intermediate spatial patterns were not reported.
Feynman's original thought experiment contained two parts. The first involved observing probability distributions in three scenarios: electrons traveling through slit 1 with slit 2 closed (P1); electrons traveling through slit 2 with slit 1 closed (P2); and electrons traveling through both slits (P12). These scenarios illustrate the quantum mechanical superposition principle, i.e. the wave properties, and can be demonstrated with control of the slits (see Figure). The second part of the thought experiment was the observation of individual electrons associated with detection 'clicks'. This illustrates that a quantum mechanical electron wave cannot be thought of as comprising multiple electrons, i.e. the particle properties, which can be demonstrated with the build-up of the diffraction pattern.
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