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Kibdelone C

27 July 2011 - Part I

Kibdelone C Porco I  Two Kibdelone C syntheses were published in a recent JACS issue with the publication-received dates just 12 days apart: the first one from Boston University (DOI) and the second one from the University of Texas (DOI). Research groups are usually aware of each other doings so the effort must have involved lots of (unpayed) overtime and stress. Here are some of the highlights from the Sloman / Bacon /Porco synthesis.

One of the key steps was an intramolecular halo-Michael aldol reaction of Aldehyde 1 to form alcohol 2. The excess reagent in this reaction was magnesium iodide and in the most favorable cyclic transition state magnesium can chelate three oxygen atoms and not just two which explains the observed diastereoselectivity.

After a round of deprotection-protection 2 returned as 3 in a oxa-Michael reaction / dehydrohalogenation with phenol 4 in DMSO with tripotassium phosphate to form tetracycle 5. A dozen other bases failed in this particular reaction and workup was problematic due to the acid-labile carbonate groups.

The next step was a formal intramolecular Friedel-Crafts acylation of 5 (after saponification) to hexcycle 6. Again the regular FC reagents failed and recourse was taken to the rather obscure cyanuric acid. Although the original protocol also listed aluminum chloride, Sloman et al. found out it was not really needed and hence they came up with a reaction mechanism involving electrocyclization / re-aromatization around an intermediate ketene (the chemical literature is rife with protocols demanding reagents that serve no purpose).

The final stretch should be uneventfull but again problems were reported: how difficult can a demethylation be? Difficult when you want to demethylate just one of the methoxy groups present and difficult when you can also oxidize other parts of the compound. In the end the reaction yielded kibdelone C 7 with Ceric ammonium nitrate / acetic acid.


Graphene for your loudspeakers

12 July 2011 - Nanotech

graphene loudspeakers.gifGraphene for your loudspeakers is just one potential graphene application under investigation and Keun-Young Shin and colleagues of the oddly sounding World Class University have devised a way to make it possible (DOI). Graphene is a great electron conductor. It is also potentially cheap to use in electronics if only you find a way to deposit the material in the right positions with the right thickness. The Keun-Young Shin solution: an inkjet printer and the concept is demonstrated in a loudspeaker application.

Here is the recipe: take a 100 mm by 100 mm piece of transparent (60 micron) polyvinylidene fluoride (piezoelectric!) and modify its surface energy by an oxygen plasma flow to match that of the ink to be employed. Then take a solution of exfoliated graphene oxide flakes in water and and use a commercial inkjet printer to print a specific pattern onto the PVDF film at two sides. Repeat printing multiple times to get complete coverage. The reduce the GO to graphene at 90°C with hydrazine and ammonia. The two graphene layers are also transparent making the whole loudspeaker sheet transparent as well.

The real interest in this venture is of course not the loudspeaker but the quality of the graphene film. The TEM image speaks for itself: complete coverage with patches of bilayers and trilayers.

Walking with actuators

08 July 2011 - Making it move V

walking with actuators.gifOnce in a while chemists get the urge to take any small object, devise a way to make it move in some direction by an external force (so far so good) and publish about it (hey!). This blog made this apparently futile branch of applied chemistry into a regular topic so now months after the macroswimmers now : the walking actuator brought to you by Yung Ma and colleagues of Jilin University (DOI).

The walking device is all about a multilayered piece of plastic. The first layer (2 micron) is in itself a crosslinked multilayer (30) of polyacrylic acid and polyallylamine hydrochloride produced in a layer by layer technique and deposited on a silicon wafer covered with PolyDADMAC. This layer is spincoated by NOA63 (10 micron), a UV-curable polyester and then cured. The multilayer film is then released from the silicon by an aqueous acid solution. To complete the walking actuator two pieces of PET are added to either side as legs with the multilayer piece serving a the hip.

The multilayer part can absorb a lot of water and with modest humidity (10%) the contraption is flat but with 40% humidity as the multilayer expands more than the NOA63 layer, it bends upwards as in an arch. By alternating between 10 and 40% percent humidity the contraption can stretch and bend but where does the moving motion come from? It can do so by walking on a terrace (think rice) that acts as a ratchet. In each cycle only the front leg can move forward on stretching and only the hind leg can move on contraction! The science team also investigated cargo transportation as a possible application and report the device can carry 120 times its weight. Movie!

Chandross on organic solar cells

04 July 2011 - Reality check

In this weeks journal Science Edwin A. Chandross (co-inventor of the light stick) is commenting on a news analysis by staff writer Robert Service on organic solar cells in an April issue of the same journal (Link). Service interviewed several specialists for the report and observes that solar cell efficiency has increased from 3 to 9% in the last two years (commercial inorganic cells do 15 to 20%). Compared to organic cells, inorganic cells suffer from global metal scarcity and inorganic cells require expensive clean-room technology. Several companies are in the process of launching commercial products, one of them Heliatek (www.heliatek.com) and hence the happy headline: Outlook Brightens for Plastic Solar Cells.

But Chandross, a veteran of Bell Laboratories where the photovoltaic cell was invented, is not impressed. He calculates that recharging a cellphone at midday in Phoenix (sunniest place in the US) would require more than one hour with 30 by 45 cm of industrial organic solar cell. He also doubts if the organic cells are as resistant to oxidation as the inorganic ones considering that these cells should last up to 30 years and hence the somewhat grumpy headline Not-So-Sunny Outlook for Organic Photovoltaics.



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