an inconvenient admission

I've talked with classes about climate change for years but I have never watched An Inconvenient Truth. By the time the movie came out I was pretty sure that much of the science that would be discussed would be stuff I'd already heard about. Plus, anybody who knows me very well knows I'm famously impatient with movies.

Today's Al Gore-style slideshow presentation by Bill Bradbury was full of new images for me. I don't know how closely the slideshow follows the movie, but the images were moving, sometimes beautiful and of course sometimes shocking. I was pleasantly surprised at the injection of local information and our presenter's enthusiasm and interest in his audience. Nicely done, Mr. Bradbury.

But--having heard the criticisms of the movie--I was on the lookout for overgeneralizations or convenient (yet terrible) coincidences, and I have to say I thought I recognized a few instances of that. It's a dificult challenge and serious responsibility to bring these messages to people, and I hope that two things happen: 1. The integrity of the presentations will go from good to great by continual scrutiny of what gets said and shown, to be sure that no exaggeration is allowed to creep in, and 2. The message will change as the audiences hearing it become more informed and more accepting of the science, from a persuasive "this is actually happening and you should be concerned" speech into a "here's how we can make change."

de colores

The fall colors are just about gone for the year, and leaves are falling fast. I love fall. This time of year the larches in Shevlin Park have gone from green to yellow and are in the midst of dropping their needles. Big sections of the park are covered with a carpet of yellow. As always, I enjoy the scene as a regular person, thinking stuff like "gee, that's pretty!" and "wow, cool, needles falling off a conifer!" but I also can get geeky and enjoy the scene from a chemist's viewpoint. "Gee, anthocyanins!" and "what's the name of that protein that makes the leaves actually drop?!" and "why do some trees have so many reds when others in the same habitat are so yellow?"

It's delightful to think that the bright colors so noticable at the peak of fall are actually hiding behind the greens of the chlorophylls all summer long. While we don't eat tree leaves (do we?) we do hunt down highly-colored fruits and vegetables that contain pigments like lycopene and beta carotene because they are health-promoting. What do all these colored substances have in common? They're typically highly-conjugated alkenes. Lots of double bonds, large molecules, lots of resonance structures, loosely-held electrons, ready to be promoted to higher energy levels with just a minimum-energy photon: one that falls into the range of the visible. This is chemically why they are colored. For those of you who understand: small HOMO LUMO gaps.

These same double bonds make those fruits and vegetables we love susceptible to darkening from oxidation if they're left out in the air for too long. I have heard it suggested that tree leaves may contain some of these compounds to protect them from the damage of high-intensity light in the visible and uv range. That they absorb the energy of the visible light and in so doing keep other more critical molecules from being damaged. How curious.

Maestro Chem Educator Bassam Shakhashiri has a great page on fall colors here:
http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html

Here's a link to a journal article about anthocyanins, which are red and purple, as protective compounds:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=125091

And about that supposed protein I thought was involved in leaf dropping: the compound I thought responsible is abscisin.....actually abscisic acid. It's not a protein (as is suggested vaguely by the original name). And turns out Wikipedia says it's not even thought to be involved in leaf drop anymore, even though that's how it got its name.

Bill Bradbury to visit Thursday

News! Secretary of State Bill Bradbury is coming to class next Thursday! However we need to start earlier than our usual meeting time (his schedule is busier than ours, and it is of course our pleasure to host him at his convenience). He will start at 12:00, and be done by/around 1:30. If you can possibly be here on time, be here. If you come late, we'll invite you in (and he'll know the situation so you don't need to feel sheepish).

We can do our quiz later.

Tell your friends. Since Tuesday is Veteran's Day there is no way for me to deliver this message by voice to the entire class. If any of you have questions about this send me an email or leave a comment here.

cis/trans isomerism: a tasty tidbit

Do geometric stereoisomers matter? You bet. Here's one reason why:

All the things we hear about trans fats in our diets relate to the presence of trans-alkenes in the fats we eat. Nearly all (but not all) naturally occurring fats are cis. The majority of the trans fats we eat come from fats that have been manipulated by hydrogenation: an addition of hydrogen across the double bonds. If a particular alkene group does not get fully hydrogenated during this process, it can switch from the cis to trans orientation. New industrial processes are allowing us to hydrogenate fats in ways that avoid this problem.

The amount of unsaturation in dietary fats has traditionally been determined by finding the "iodine number" or "iodine value." This number is calculated by reacting iodine with the fats, until a purple color shows up. The presence of the iodine color indicates there are no more groups on the fat that will react with it. The reaction that normally consumes the iodine is an addition reaction (of X2, in this case I2) across the double bond.

Those of you lucky enough to be in Organic this fall will discuss this particular reaction type in class next Thursday. I can hardly wait!

studentdoctor.org

Interested in Medical or Dental School or Pharmacy? A former student pointed me to studentdoctor.org a while back. You may want to investigate the conversations that are out there.

Exams are graded and scores posted!

Enjoying crystallization, even on weekends

Crystals have been on my mind a lot the last week or two.

I was asked a fun question this week about the formation of snowflakes. This morning I see that the Cascades are socked in, hidden behind heavy clouds, and I'm beginning to think about snow again, as I look forward to ski season. Last Friday and the week before the Organic class was doing recrystallization in lab. I've got their reports on my desk, ready to grade. My introductory class has been learning about ions and ionic compounds, and the resulting crystals. Crystals are everywhere!

The question I was asked is about snowflake types, and whether there is a connection between snowflake type and the temperature where the snowflake forms.

I'm no expert on this stuff, and I doubt the situation is simple. I have browsed Barnes and Noble enough to know that there are field guides to weather, and that they include some neat stuff about snow, but I don't own one of these books and I haven't ever taken the time to dig very far into it. Experience tells me that cold and dry air leads to tiny and sparkly-perfect but tiny crystals (champagne powder), while wetter and warmer conditions can lead to big flakes.

I would guess that both temperature and humidity would have a dramatic effect on snow type. Other things like shearing from winds might also matter.

As I think about this now I'm trying to link the formation of snow crystals to what we see in the lab, in solutions --which may be importantly different!-- but to make big crystals in the lab we cool the solution slowly and don't disturb the flask while they form. This results in a situation where there is more opportunity for crystal growth and the nucleation events (which is when the crystals start forming) are more rare, so there are fewer, bigger crystals. If the solution is cooled rapidly, you get lots of nucleation and little chance for crystals to grow.

Wikipedia has a good and pretty technical page on snow, here.