Archive for April, 2007

Metric Mental

April 26, 2007

It seems that it is insufficient merely to obtain funding and produce publications as an academic scientist.  One’s greatness must be somehow assessed, conjuring images of an early scene in Dead Poet’s Society where the greatness of a poem is obtained from a graph.  The Hirsch Index (h-index) was discussed when it was unveiled a while ago on many a blog and internet site.  The RSC has recently publicised a listing of 2000 living chemists based on this calculation.[1]

Hirsch Index calculations for the uninitiated:

A scientist has index h if h of his Np papers have at least h citations each, and the other (Np – h) papers have at most h citations each.[2]

So if h=100, we can expect a scientist to have 100 papers with 100 or more citations, and the remainder with less than 100 citations.  Previous metrics have involved quantifying the number of citations or publications only, this gives some measure of relative merit of papers.  There is a web program [3] available to calculate h indices if you feel so inclined.  It also allows distinction between scientists with a couple of great, highly cited papers in their careers, and those who have made broader impact with many well cited papers.

So who is on the chemistry list?[4]  Unsurprisingly the top three are:

1.  E. J. Corey, h = 132, Organic Chemistry
2.  G. M. Whitesides, h=131, Organic Chemistry
3.  M. Karplus, h=127, Theoretical

The list is a work in progress (only 2000 chemists so far, but is interesting reading).  Particularly due to the distribution of Nobel Laureates throughout the list…

 References
[1] Royal Society of Chemistry, Chemistry World News Article, Chemistry World Blog Article
[2] Wikipedia Article on h-index; Nature Article on h-index
[3] Web Program
[4] PDF of Chemistry List (from RSC Website)

Vanillin

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Stinky Lab Stuff

April 17, 2007

Following on from Dylan Style’s theme – chemicals and lab stuff that smells bad.

  • “Off” DMF
  • t-butyl mercaptan (skunk juice)
  • THF (loathsome)
  • Benzoic acid (cloying, evil smell)
  • Autoclaved stuff
  • Someone elses success (ha!)
  • Ion exchange resin (cat pee)
  • Pentenoyl chloride (cat vomit anyone?)
  • Bullshit (mainly in group meetings)

–Cryogen

Square Propellers

April 15, 2007

Polyhedral Oligomeric Silsesquioxanes are silicon-oxygen cage or ladder molecules.  The cubic form R8Si8O12 has silicons on the corners, bridged by oxygen atoms (making up the edges).  Each corner can be functionalised by a variety of groups – H, vinyl, allyl, aminopropyl etc. 

 OctaVinyl-POSS 2808 Molecule Diagram

Vinyl Silsesquioxane (these things are hard to draw!)

[Contents scheme]

Bromo-pyrene

JACS ASAP had  a very cool paper this week using octavinylsilsesquioxane and 1-bromopyrene.  Octavinylsilsesquioxane is commercaially available and was coupled to 1-bromopyrene using Heck conditions (palladium catalyst)*.  Varying the ratio of pyrene to cube created 8 to 16 subsituted molecules fo application in organic light emitting diodes.   For monosubsitution at each corner the 8-pyrene form was most abundant, for disubstitution, 14 pyrenes were most abudant, probably due to steric considerations.  Putting so many pyrene derivatives around a small silsesquioxane is hard work.

 When I printed this paper out, I was mesmerized for a few minutes – these molecules are beautiful. They have very high symmetry due to the cube structure and the 14 pyrene molecule is just elegant.  I’m not going to attempt to draw the final products. 

OLEDs were prepared using the 8- and 14- pyrene vinyl silsequioxanes.  The fluorescent efficiency was found to be good, and possibly the highest achieved to date for silsequioxane based emitters.  14-pyrene vinyl silsequioxane gave lower efficiency, probably due to the higher density of pyrene groups and subsequent quenching in the solid state.

Lo et al., JACS 2007; ASAP 

Vanillin 

*Heck reactions are palladium -catalyzed carbon carbon couplings betwene aryl or vinyl halides and alkenes, with base.

Awakenings

April 10, 2007

Crystals are the ultimate reward for hours of work synthesising new stuff.  Chemists wait with eager anticipation for the sparkling solids that may have been deposited in their flasks.  More often that not, things turn out semicrystalline – a mixture of near perfection and amorphous murk.  What is this blog about?  Well, we wanted to try this science writing/blogging thing.  We have an unhealthy fascination with both crystalline and gooey stuff.  We like the extreme ends of that spectrum, so this is our attempt to meet in the middle, find some common ground and write about stuff that is, to us, semicrystalline.