Posts Tagged ‘JACS’
This Message Will Self-Heal in 3, 2, 1…
by mitch on Feb 12 2010 (7402 Views)
Cassandra Fraser
Recently, Cassandra Fraser’s group reported on a very cool property, reversible mechanochromic luminescence, observed in an easy to make material.[JACS] The molecule of interest is the difluoroboron complex of avobenzone (BF2AVB), that UV absorbing molecule in your sunscreen minus the boron and fluorines.
In broad general language, mechanochromic luminescence describes the ability of some materials to change colors after scratching under UV light. The image below shows BF2AVB coated on weighing paper (A), a cotton swab is used to write “Light” (B), the surface is hit with a heat-gun (C), the surface is ready to be written on again with a cotton swab (D).
The image brings up all kinds of creative ways to write secret messages, especially as the letters will fade over time even without using a heat gun. But before the CIA intelligence wonks in the audience get ahead of themselves the material doesn’t seem to be completely reversible at room temperature without annealing.
…even a small mechanical perturbation, such as a slight touch with the tip of a cotton swab, changed the green-blue BF2AVB film emission to yellow. The yellow emission gradually reverted back to green again at room temperature, with much faster recovery at elevated temperature. The written regions were no longer readable after annealing.
The field has, in short order, gotten tantalizingly close to a 100% reversible mechanochromic luminescent material at room temperature. Congrats!
Link to article: Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone
Sam covered one of the first entrants to reversible mechanochromic luminescence a year ago: reversible mechanochromic luminescence is cool
Mitch
Update and Correction: Cassandra Fraser has corrected me, apparently the wording of the paper was just awkward to my ear, the material is fully reversible at room temperature!
Subscribe to the comments for this postNanoPropulsion
by mitch on Jan 16 2010 (10488 Views)
The current state of the art in nanopropulsion devices was recently reviewed by Ebbens and Howse in an article last Friday.[SoftMatter] A short summary of the nano- systems is presented below with video action shots when I could find them.
The Whitesides
Catalyst: Pt
Fuel: H2O2
Propulsion: Bubble propulsion
Terrain: Aqueous meniscus
Max Speed: 2 cm/s
Mitch’s Name: The Karl Benz (since it was the first)
Article: Autonomous Movement and Self-Assembly
The Sen-Mallouk-Crespi
Catalyst: Pt
Fuel: H2O2
Propulsion: Self electrophoresis/Interfacial tension
Terrain: Settled near boundary in aqueous solution
Max Speed: 6.6 um/s
Mitch’s Names: The Ford Mustang of nanopropulsion. (It is a hot rod, get it?)
Article: Catalytic Nanomotors: Autonomous Movement of Striped Nanorods
The Jones-Golestanian
Catalyst: Pt
Fuel: H2O2
Propulsion: Pure self diffusiophoresis
Terrain: Free aqueous solution
Max Speed: 3um/s
Mitch’s Name: The Volkswagen Beetle
Article: Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk
The Mano-Heller
Catalyst: Glucose oxidase and Biliruben oxidase
Fuel: Glucose
Propulsion: Self electrophoresis
Terrain: Aqueous meniscus
Max Speed: 1 cm/s
Mitch’s Name: The Komatsu Truck (because it is huge)
Article: Bioelectrochemical Propulsion
The Feringa
Catalyst: Synthetic catalse
Fuel: H2O2
Propulsion: Bubble/interfacial
Terrain: Acetonitrile solution
Max Speed: 35 um/s
Mitch’s Name: The F150 (has some exhaust issues)
Article: Catalytic molecular motors: fuelling autonomous movement by a surface bound synthetic manganese catalase
The Sen-Mallouk
Catalyst: Pt (CNT) (+cathodic reactions at Au)
Fuel: H2O2/N2H4
Propulsion: Self electrophoresis
Terrain: Settled near boundary in aqueous solution
Max Speed: 200 um/s
Mitch’s Names: The Ford Mustang GT (has more kick than the regular version)
Article: Bipolar Electrochemical Mechanism for the Propulsion of Catalytic Nanomotors in Hydrogen Peroxide Solutions
The Feringa v2
Catalyst: Glucose oxidase and catalse
Fuel: Glucose
Propulsion: Local oxygen bubble formation
Terrain: Free aqueous buffer solution
Max Speed: 0.2–0.8 um/s
Mitch’s Name: The Chevrolet Nova (more hot rod action)
Article: Autonomous propulsion of carbon nanotubes powered by a multienzyme ensemble
The Gibbs-Zhao
Catalyst: Pt
Fuel: H2O2
Propulsion: Bubble release mechanism
Terrain: Aqueous solution
Max Speed: 6 um/s
Mitch’s Name: The Rover
Article: Autonomously motile catalytic nanomotors by bubble propulsion
The Bibette
Engine: External magnetic field
Propulsion: Flagella
Terrain: Aqueous solution
Max Speed: unknown
Mitch’s name: The BMW Mini E (because there is no such thing as a magnetic car)
Article: Microscopic artificial swimmers
The Sagués
Engine: External magnetic field
Propulsion: Doublet rotation coupling with boundary interactions
Terrain: Settled near boundary in aqueous solution
Max Speed: 3.2 um/s
Mitch’s Name: The Smart ED
Article: Magnetically Actuated Colloidal Microswimmers
The Fischer
Engine: External magnetic field
Propulsion: Propeller drive
Terrain: Aqueous solution
Max Speed: 40 um/s
Mitch’s Name:
Article: Controlled Propulsion of Artificial Magnetic Nanostructured Propellers
The Najafi-Golestanian
Engine: Conformation changes in linking units
Propulsion: Time irreversible translations
Terrain: Free solution
Max Speed: ?
Mitch’s Name: The Eternal Concept Car
Article: Propulsion at low Reynolds number
Some devices that were not included by the authors of the review article, but should definitely be included in any list like this are below:
The Gracias
Engine: External magnetic field
Propulsion: Brute Force
Terrain: Aqueous solution
Max Speed: ?
Mitch’s Name: The Truck Cranes
Article: Tetherless thermobiochemically actuated microgrippers
Tetherless Microgrippers Grabs Tissue Sample – Watch today’s top amazing videos here
The Nelson
Engine: External electromagnetic fields
Propulsion: Flagella
Terrain: ?
Max Speed: 18 um/s
Mitch’s Name: The Tesla Roadster (simply awesome)
Article: Characterizing the Swimming Properties of Artificial Bacterial Flagella
Link to Review Article: In pursuit of propulsion at the nanoscale
Mitch
Crystals from IR Lasers
by mitch on Aug 01 2009 (5697 Views)
I was perusing Chem Feeds when this paper caught my eye with its snazzy abstract (right). The authors, Alexander et al., report crystallizing a supersatuated solution of KCl in agarose gel by using an IR laser. They are capable of crystallizing any pattern of interest by using a mask. The nice thing about using an IR laser is it won’t cause your solute to have side photochemical reactions from this process.
Although the highlight of the paper is its potential use as a 2d or 3d method of controlled crystallization, I wonder how well the general method of nonphotochemical laser induced nucleation (NPLIN) is at crystallizing stubborn molecules that normally are a pain to crystallize at the bench. Any new tricks that will decrease the time it takes to make nice crystals would be appreciated by myself and I’m sure others…
Link to Alexander et al.’s JACS paper: Spatial Control of Crystal Nucleation in Agarose Gel
Update (August 6th): Aaron Rowe covers this in C&EN — Lasers Spark Crystal Growth
Mitch
Magnetic Levitation: Because TLC Plates are so 20th Century
by mitch on Dec 14 2008 (2155 Views)Mirica et al. had an awesome JACS communication out last week. They use magnets to track the progress of reactions. A schematic is shown below.
By using a paramagnetic solution (GdCl3) and polymeric beads as their solid support, they monitor the progress of reactions as a function of their beads’ height. The setup is very sensitive to the density (g/ml) of the beads, thus as the beads are chemically modified the height changes. The beads cluster together when they are mostly all starting material or product. They spread out as different beads take different amounts of time to become fully reacted. Some images from their paper and supporting information really highlight this effect.
What else can we use magnets in the lab for, ideas anyone?
Mitch
32-electron chemistry
by mitch on Dec 07 2008 (1357 Views)We all remember learning about octets and valence electrons in school. We may also remember the first time we saw an 18-electron transition metal complex. This week Dognon et al. discuss the possibility of 32-electron organometallic complexes.[JACS] In order to reach 32-electrons, f-orbital participation is essential. Below is a picture of a hypothetical organometallic complex with 28 carbons in a cage around an actinide element.
Although these systems are not new, as the Smalley group made U@C28 in the gas-phase in ‘92,[Science] Dognon et al. examine a series of these systems for different actinides. The major conclusion is that the plutonium system is theoretically predicted to have the largest bonding energy for its Pu4+@C28 complex. Since fullerenes and the intercalation of metals often only need heat to be synthesized, I wouldn’t be surprised if these complexes have already been made but missed as impurities and byproducts.
Link to paper: A Predicted Organometallic Series Following a 32-Electron Principle: An@C28 (An = Th, Pa+, U2+, Pu4+)
Update 1: Jyllian Kemsley also covered it at C&EN — Stable Caged Actinides Proposed(subscription)
Mitch
Introducing ChemFeeds your Graphical Abstracts Portal
by mitch on Oct 22 2008 (1395 Views)Decided to make a new website, ChemFeeds, where you can view pretty graphical chemical abstracts from various sources like JACS, Angewandte, JOCS, OrgLett, and a whole host of others. It even has the Angewandte punsCBC, vis-à-vis OCB.
Feel free to roam around at the website, link is here:
http://www.chemfeeds.com/
Feedback and suggestions on how to make the website better and more useful for you, would be great.
Update 1: Permanent link can now be found in the top right header of this website. Which is an extension of the concept and scripts introduced here: Full Frontal JACS
Mitch
Problems with Aryl Enediyne Cyclizations?
by mitch on Oct 17 2008 (1424 Views)Enediynes are lovely functional groups that are famous for undergoing Bergman cyclizations as shown below.
Scheme 1. Bergman cyclization.
Vavilala et al. have found an alternate reaction pathway for thermal enediyne cyclizations when bulky aryl groups are attached to the terminal ends; they observed indene formation.
Scheme 2. Pascal cyclization anyone?
Making indenes from enediynes is an old trick, either by photochemical or some exotic initiator, the caveat with this work is it runs under thermal conditions. The reaction they ran is shown below.
Scheme 3. Thermolysis (TCP = 2,4,6-trichlorophenyl)
No Bergman cyclization products were observed. The idea being, the distance of the terminal carbons (C1-C6) is crucial in determining which type of cyclization will occur. An interesting part of the paper is Matzger gets mentioned by name as a referee and as holding a different opinion of the authors, he basically argues the results are due to transfer hydrogenations from bergman cyclization intermediates. Definately an interesting read if you have time.
Link to paper: Thermal C1-C5 Diradical Cyclization of Enediynes
Mitch
Full Frontal JACS
by mitch on Oct 09 2008 (2411 Views)The Journal of the American Chemical Society (JACS) has flirted with web 2.0 with it’s recent JACS β initiative. It has been warmly received around the blogosphere [CSB, TCB, CBC]. Although, I don’t have any complaints about the website, what I really wanted was less hand-holding and more of a shotgun approach to navigating through JACS online.
The nicest thing about thumbing through the print edition of JACS, is reading all the various chemistry that is outside your research tunnel-vision but still interesting. If you go to the JACS homepage, here, you’ll see a list of 20 of the most recent articles, but not all of them! For example, 31 papers were added to ASAP today and only the last 20 are shown on their website, hardly a dire circumstance, but the fact is you miss some by using that setup. JACS also offers a nifty RSS feed of their articles, but I’ve never come across an RSS reader that’ll nicely format an active feed, 30+ submissions a day, in a format that will ever make me want to read it.
So how does one go about designing a more attractive JACS online browsing environment? Below is my attempt, it is as busy and attractive as a conference poster, but it lets you see a huge list of the most recently added papers to JACS ASAP.
The website parses through the JACS RSS feed. I was a bit worried about incorporating the graphical abstracts, but since they are included in the RSS feed, I’m going to claim fair use. The site isn’t pretty, but it gets the job done.
Here is a link for your viewing pleasure, Full Frontal JACS: http://www.chemfeeds.com/
Comments are always welcomed, but obviously this format is not for everyone.
Edit: A link to the site has been included in the links section to the right, towards the bottom under websites, titled Full Frontal JACS.
Update 1: Improved ACIE RSS feed
Update 2: Links edited to point to ChemFeeds instead of the simple script.
Mitch
