Optical lifting demonstrated for the first time w Video

center_img Explore further Citation: Optical lifting demonstrated for the first time (w/ Video) (2010, December 7) retrieved 18 August 2019 from https://phys.org/news/2010-12-optical-video.html Time-lapsed composite image (1.67 s per shot) of a semi-cylindrical rod lifting sideways from left to right near the bottom of a glass chamber, as a result of a transverse optical lift force. Image credit: Nature Photonics, doi:10.1038/nphoton.2010.266 Light has been known for some time to be capable of pushing objects and this is the principle behind the solar sail, which uses light to push vehicles along in space. Now, a new study by physicist Dr. Grover Swatzlander and colleagues of the Rochester Institute of Technology in Rochester, New York shows light is also capable of creating the more complex force of “lift,” which is the force generated by airfoils that make a plane rise upwards as it travels forward.In a paper that appeared online in Nature Photonics on December 5th, Swartzlander and colleagues describe their demonstration of light providing optical lift to tiny lightfoils. The experiment began as computer models that suggested when light is shone on tiny objects shaped like a wing a stable lift force would be created. Intrigued, the researchers decided to do physical experiments in the laboratory, and they created tiny, transparent, micrometer-sized rods that were flat on one side and rounded on the other, rather like airplane wings. They immersed the lighfoils in water and bombarded them with 130 mW ultraviolet laser light from underneath the chamber. As predicted, the lightfoils were pushed upwards by the light, but they also moved sideways in a direction perpendicular to the beam of light, in other words they were optically lifted. Symmetrical micro-spheres did not show the optical lift effect.In aerodynamic lift, which is created by an airfoil, the lift occurs because the wing shape causes air flowing under the wing to move more slowly and at higher pressure than that above the wing. In optical lift, created by a lightfoil, the lift is created within the transparent object as light shines through it and is refracted by its inner surfaces. In the lightfoil rods a greater proportion of light leaves in a direction perpendicular to the beam and this side therefore experiences a larger radiation pressure and hence, lift. © 2010 PhysOrg.com Play Videos: Nature Photonics, doi:10.1038/nphoton.2010.266 last_img read more

Using catalysts like tweezers to select single enantiomer from a mirrored pair

first_img © 2017 Phys.org Explore further (Phys.org)—A team of researchers at Harvard University has developed a catalytic technique that allows for selecting a single enantiomer (mirror-image isomers) when choosing between one of two mirrored possibilities. In their paper published in the journal Science, the group describes their technique and the possible ways it might be used. Anita Mattson with Worcester Polytechnic Institute offers a Perspective piece on the work done by the team in the same journal issue along with a discussion of why such work is important. Citation: Using catalysts like tweezers to select single enantiomer from a mirrored pair (2017, November 10) retrieved 18 August 2019 from https://phys.org/news/2017-11-catalysts-tweezers-enantiomer-mirrored-pair.html As Mattson notes, using a catalyst to synthesize desired molecules has become a vital part of modern manufacturing processes—approximately 90 percent of all such reactions rely on a catalyst, she says. As she also notes, catalytic methods for creating chiral molecules in the form of mirror image isomers has also become very important in applications such as making pharmaceutical drugs or chemicals for use in agriculture. But, as she further notes, quite often, only one of the resultant molecules from the pair is desired (because they are not normally the same, biologically speaking)—thus, researchers require a means for selecting only the one that is needed. In this new effort, the team at Harvard has developed such a technique.In their approach, the team used molecular catalysts that had two closely set nitrogen-hydrogen groups as a sort of miniature tweezers, latching (by activating a carbon middle) onto a leaving group (using double hydrogen bonding) to pluck them away, leaving behind undesired material. The result was an ion pair that was biased to favor the one that was desired based on the shape of the catalyst. The group reports that they used their technique to set off a Lewis acid co-catalyst that pulled a leaving group off silicon rather than carbon. They suggest their technique is better for setting off reactions that involve weaker leaving groups on carbon. Mattson suggests that the new technique could be used by other researchers to help in the discovery of new catalyst combinations, perhaps leading to new complex molecular products. More information: Steven M. Banik et al. Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis, Science (2017). DOI: 10.1126/science.aao5894AbstractSmall-molecule dual hydrogen-bond (H-bond) donors such as ureas, thioureas, squaramides, and guanidinium ions enjoy widespread use as effective catalysts for promoting a variety of enantioselective reactions. However, these catalysts are only weakly acidic and therefore require highly reactive electrophilic substrates to be effective. We introduce here a mode of catalytic activity with chiral H-bond donors that enables enantioselective reactions of relatively unreactive electrophiles. Squaramides are shown to interact with silyl triflates by binding the triflate counterion to form a stable, yet highly Lewis acidic, complex. The silyl triflate-chiral squaramide combination promotes the generation of oxocarbenium intermediates from acetal substrates at low temperatures. Enantioselectivity in nucleophile additions to the cationic intermediates is then controlled through a network of noncovalent interactions between the squaramide catalyst and the oxocarbenium triflate.center_img Journal information: Science Banik et al. show that a compound that makes hydrogen bonds to a Lewis acid creates an active catalyst. An example of a cycloaddition reaction is depicted. Tf, triflate; t-Bu, tert-butyl; Me, methyl; R, alkyl. Credit: (c) 2017 A. Kitterman/Science Using a nickel catalyst with hydrocarbons to make fatty acids 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.last_img read more