Wednesday, March 28, 2007

Alphabet Soup

Image from Carlos J. Hernandez/Thomas G. Mason, UCLA Chemistry. This image is published in the Journal of Physical Chemistry C.

"Colloidal Alphabet Soup: Monodisperse Dispersions of Shape-Designed LithoParticles" by the Mason group at UCLA is the cover article for the Journal of Physical Chemistry C this week. Although this article was brought to my attention by my husband (a physical chemist of course), I found it interesting nonetheless. Taking advantage of high-throughput automated stepper lithography, graduate student Hernandez literally generated a soup of three-dimensional colloidal particles--including letters of the alphabet, crosses capable of alignment and formation of columnar structures, donut particles that can aggregate to form tubes as well as various combinations of the above. Lithioparticles, as the authors call these miniature polymeric colloids, range in size from micron to submicron units and can be colored through the incorporation of green, red, or blue fluorescent dyes.

So what exactly is "stepper lithography"? First, both a sacrificial layer and a polymeric photoresist layer are placed on top of a silicon wafer through a process known as spin coating. Using the "stepper," or a fully automated lithiographic projection exposure system, UV light is shined through a stencil-like "mask"and through the stepper's lens onto the photoresist layer. This step crosslinks the part of the photoresist that was exposed to UV light (the part not covered by the "mask"). Exposure to an organic developing solvent removes the unexposed photoresist, while leaving behind both the sacrificial layer and crosslinked LithoParticles. Finally the sacrificial layer is dissolved in water, and the alphabet soup is lifted off the surface of the silicon wafer into an aqueous solution. Once they are in solution, the particles are relatively stable, and the aqueous solvent can be exchanged for something organic.

For me the final paragraphs of the article were the most exciting part to read, as the authors discussed possible applications of designed Lithoparticles. By incorporating fluorescent molecules or other probes such as DNA or charged molecules, Lithioparticles might be useful for studying microstructures inside of cells. Tiny tweezers made out of lasers can be used to move letters of the "alphabet soup," (which is nicely illustrated by the UCLA below) and in this fashion cells could be identified with a unique symbol. Could it be possible to use this technology to mark cancer cells with a "X" and thus facilitate their elimination?

Well, with this technology, that dream might be one step closer to reality.

DOI: 10.1021/jp0672095

Monday, March 26, 2007

Review: Molecular Modeling Kits

Check out this review of 4 of the most common molecular modeling kits out there (in German):

Molecular Modeling Kits

As a chemist can never have too many molecule building kits, I actually own kits number 1, 2, & 4 as they are presented in the link.

Beware of the Portugese Man-of-War

Since I'll be traveling at the end of this week (unfortunately not to the ACS meeting), I decided to post something relevant to my destination. According to the people I'm visiting, there is currently an infestation of Portugese Men-of-War on the beaches and in the surrounding water of this sunny locale. As I consider myself equal parts organic chemist and chemical biologist, I thought that this might make for an informative post. Interestingly, the Portugese Man-of-War is a siphonophora; thus, it is a colonial species, made up of four different types of polyps. While each is an individual, they are completely integrated with each other and the colony is often mistaken for one large jellyfish. Its tentacles can be up to 50 meters long! Although I couldn't find much information about the chemical composition of Physalia physalis venom, I did learn that it consists of ATPase, RNase, AMPase, and nonspecific aminoesterases [1], most of which work to degrade cellular content, producing extreme pain in the process. 28% of the venom protein consists of physalitoxin, which is a large heterotrimeric glycoprotein that hemolyses mammalian erythrocytes. Cells treated with man-of-war poison generally release histamine. Research has shown that the venom itself creates pores in the cell membrane, allowing for the free transport of mono- and divalent cations [2], which has a major impact on the cardiac system of poisoned animals. Usually man-of-war stings are not fatal to humans, unless one is stung while swimming in extremely deep water. According to many websites, treatment with either hot or cold water best relieves pain from stings, while vinegar may cause the tentacles to release more venom, and should be avoided.

Also, I shouldn't fail to mention that Richet won the Nobel Prize for his work with the Portugese Man-of-War, in which he discovered and characterized anaphylaxis (an extreme allergic reaction).

Can anyone guess where I am headed?

photo taken from: Lilactree

Friday, March 23, 2007

Mechanophores: a force to be reckoned with

The concept is logical and easy to follow--if reactions can be triggered by light, heat, pressure, or electrical potential, then why can't mechanical force also be harnessed to distort molecules in a way that promotes reaction? Actually, using molecules appropriately termed mechanophores, the Moore group has succeeded in employing the mechanical forces generated from ultrasound to promote and influence chemical reaction pathways. Although ultrasound generally has no effect on small molecules, the collapse of cavitation bubbles produced during sonication can agitate polymers in solution, generating friction, otherwise known as mechanical force. By incorporating small molecule mechanophores (either trans- or cis-1,2- dimethoxybenzocyclobutenes, BCBs) into a larger polymer, researchers were able to take advantage of this force and promote ring opening. According to the Woodward-Hoffmann rules, in a reaction promoted through light energy, both cis- and trans- BCBs undergo a disrotatory ring opening, while thermal activation produces conrotatory products. On the other hand, computational studies indicated that under mechanical influences, the cis-BCB would produce the disrotatory product, but the trans-BSB would generate the conrotatory product.

In order to test this hypothesis, the BCB-containing polymer was sonicated at 6-9 degrees C with an excess of a pyrene functionalized maleimide, which was meant to function as a a dienophile trap. Indeed, the mechanophore did behave as predicted; by distorting bond lengths and angles sonication produced the trans-BCB through a conrotatory process, while the mechanical force worked to reduce the energy barrier for a disrotatory reaction pathway for the cis-BCB. As the article title indicates, reactions can certainly be biased through the use of mechanical force.

So what will the next mechanophore be?

Thursday, March 22, 2007

Earlier this week I saw a list of "10 suggestions for becoming a more pretentious graduate student." As much as we hate to admit it, chemists can be a little overbearing at times, and this list just describes graduate school struggles soooo accurately. I thought it was hilarious, so I wanted to share it: