Tag: 巴中桑拿

Chemists discover new type of molecular bond near white dwarf stars

first_imgImage of Sirius A and Sirius B taken by the Hubble Space Telescope. Sirius B, which is a white dwarf, can be seen as a faint pinprick of light to the lower left of the much brighter Sirius A. Image: NASA, ESA (Phys.org) — Most any chemistry student when asked, will say that there are just two ways atoms bond to make molecules: covalent and ionic. In the former, atoms are bonded together by sharing electrons, in the latter it’s due to the transfer of electrons from one atom to another leading to a Coulombic attraction between the ions. Now however, it appears there is a third kind of bond, though it doesn’t exist here on Earth. E. I. Tellgren, Kai K. Lange, T. Helgaker and M. R. Hoffmann from the University of Oslo, Norway and the University of North Dakota in the US have found that some molecules can form and hold together due to extremely high magnetic fields. As they write in their paper published in the journal Science, their calculations suggest that such molecules likely exist near white dwarf stars. Explore further More information: A Paramagnetic Bonding Mechanism for Diatomics in Strong Magnetic Fields, Science 20 July 2012: Vol. 337 no. 6092 pp. 327-331. DOI: 10.1126/science.1219703ABSTRACTElementary chemistry distinguishes two kinds of strong bonds between atoms in molecules: the covalent bond, where bonding arises from valence electron pairs shared between neighboring atoms, and the ionic bond, where transfer of electrons from one atom to another leads to Coulombic attraction between the resulting ions. We present a third, distinct bonding mechanism: perpendicular paramagnetic bonding, generated by the stabilization of antibonding orbitals in their perpendicular orientation relative to an external magnetic field. In strong fields such as those present in the atmospheres of white dwarfs (on the order of 105 teslas) and other stellar objects, our calculations suggest that this mechanism underlies the strong bonding of H2 in the triplet state and of He2 in the singlet state, as well as their preferred perpendicular orientation in the external field. Citation: Chemists discover new type of molecular bond near white dwarf stars (2012, July 20) retrieved 18 August 2019 from https://phys.org/news/2012-07-chemists-molecular-bond-white-dwarf.html German team finds a way to link boron atoms with a triple bondcenter_img Journal information: Science This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Because it’s impossible, at least at this time, to create a magnetic field anywhere near as strong as that found near a white dwarf star, the researchers turned to quantum chemical simulations (full configuration-interaction) focusing on hydrogen atoms and the simple hydrogen molecule H2. At extremely hot temperatures, such as would exist near a white dwarf, the covalent bond that normally holds the molecule together wouldn’t survive and the molecule would come apart. But if there were a strong enough magnetic field (such as exists near a white dwarf) the spin states of the two atoms could align with the magnetic field (rather than exist as opposed) the molecule could bond and continue to stay that way. And that’s exactly what the team’s calculations showed, they’re calling it – perpendicular paramagnetic bonding.To further test their ideas, the team also ran helium through the simulations and found that they too could form perpendicular paramagnetic bonding of He2 molecules, though they were less stable.The researchers note that because of the different characteristics of hydrogen or helium molecules bonded together through magnetic forces near white dwarf stars, their spectrum should be different as well, which means that they should be detectable using telescopes tuned properly, assuming they exist in sufficient numbers.And just because such a strong magnetic field cannot currently be created in the lab, it doesn’t mean it can’t ever happen. If it does become possible, not only would magnetically bonded molecules be observable, but they might also be controllable by adjusting the amount of magnetism, paving the way perhaps to a quantum memory computer. © 2012 Phys.orglast_img read more

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Researchers develop a library of elastinlike proteins to help in creating synthetic

first_img(Phys.org)—A pair of researchers at Duke University has built a library of protein data that outlines the specific amino acid sequences that control changes of many elastin proteins. In their paper published in the journal Nature Materials, Felipe García Quiroz and Ashutosh Chilkoti describe their research, the making of their library, and their belief that what they have created will help in the development of new synthetic designs for possible use in medical applications. Citation: Researchers develop a library of elastin-like proteins to help in creating synthetic designs (2015, September 23) retrieved 18 August 2019 from https://phys.org/news/2015-09-library-elastin-like-proteins-synthetic.html Proteins assemble and disassemble on command This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: Sequence heuristics to encode phase behaviour in intrinsically disordered protein polymers, Nature Materials (2015) DOI: 10.1038/nmat4418AbstractProteins and synthetic polymers that undergo aqueous phase transitions mediate self-assembly in nature and in man-made material systems. Yet little is known about how the phase behaviour of a protein is encoded in its amino acid sequence. Here, by synthesizing intrinsically disordered, repeat proteins to test motifs that we hypothesized would encode phase behaviour, we show that the proteins can be designed to exhibit tunable lower or upper critical solution temperature (LCST and UCST, respectively) transitions in physiological solutions. We also show that mutation of key residues at the repeat level abolishes phase behaviour or encodes an orthogonal transition. Furthermore, we provide heuristics to identify, at the proteome level, proteins that might exhibit phase behaviour and to design novel protein polymers consisting of biologically active peptide repeats that exhibit LCST or UCST transitions. These findings set the foundation for the prediction and encoding of phase behaviour at the sequence level. Journal information: Nature Materials © 2015 Phys.org Explore further Proteins are organic compounds essential to all living organisms, they are especially prevalent in components that have structure, such as muscle, skin, hair, etc. They provide structure by self-forming into different shapes under different conditions, two of which are solubility and temperature. Proteins are made of sequences of amino acids—the order and type of which drive the shape of the protein when certain conditions are met. Scientists still do not quite understand how proteins self assemble into the specific 3D shapes they take, nor which amino acids lead to which shapes, or indeed, how the order in which they exist contributes to those shapes. To help provide a better understanding of how it all works, Quiroz and Chilkoti set about building a library of all the known elastin-like proteins, along with the shapes they take under different conditions. They based it on the sequences of five key amino acids found in the fibrous protein typically found in connective tissue, such as muscles. They then set about testing each entry in the library by growing samples of E. coli engineered to produce proteins that folded into different shapes under different conditions. Most specifically noted was under which conditions the proteins shifted from being soluble to non-soluble and vice-versa. That work led them to developing a set of rules that loosely defined which amino acid sequences would result in which shapes under which conditions.The research duo acknowledge that their rules are more like guidelines, but suggest the basis of what they have built can not only be made stronger with more research by them and others, but can be used to assist in creating synthetic proteins for use in developing targeted drugs. One example would be protein capsules that remain insoluble inside the body until a certain condition is met, at which point, a medication would be released.last_img read more

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