What Gives Summer That Distinct Smell?
As summer approaches us of the southern hemisphere we look forward to the sunny afternoons, the days at the beach and the smell of freshly mown grass - but what is that smell and why is it so relaxing?
When grass is cut, fats and phospholipids are broken down into long chain fatty acids, eg. linoelic acid, these fatty acids are then oxidised and chopped up by enzymes to form an end product that is either a six or twelve carbon chain. The six carbon chain molecule is the one responsible for the smell of grass so we shall focus on it. The molecules have a carbonyl group on the end and a double bond three carbons in from the end, and thus using some high school chemistry we can determine that the name of the organic molecule is cis-3-hexanal. Our noses are fantastic tools for discovering molecules and are particularly good at detecting this one; humans can detect cis-3-hexanal at 0.25 parts per billion. Cis-3-hexanal is very unstable and quickly mutates from a cis to trans - a molecule which is known as trans-2-hexanal. This molecule is known as the ‘leaf aldehyde’ and in part of what makes up commercial odours as ‘green odour’.
Cis-3-hexanal plays a role in many other aspects of life other than the smell of freshly mown grass - is it also important in the smell of strawberries, in the recovery of plants when they are damaged by pests and surprisingly in medicine. Studies have shown that molecules very similar to cis-3-hexanal can have a positive healing effect on the psychological damage caused by stress by activating blood flow in the primary olfactory cortex. So, maybe next time you’re having a rough day, go mow the lawn and spend some time sun bathing on your freshly trimmed grass.
How dare this be on my dashboard as winter approacheth!!
Let us dream hexanal dreams, though.
So why does chemistry’s role in accidents get highlighted, and whose fault is it that people are so scared of chemicals?
Simple - mine. It’s my fault, and my grandfather’s. We are responsible for chemophobia. Why? Well, grandfather’s sodium demo certainly fuelled my enthusiasm for chemistry. But it didn’t spark it - that happened somewhere else. And sparking an interest is what he should have done and what I should be doing.
Pouring fuel onto the flames of enthusiasm is easy, especially with chemistry. The theatre is easy, too - the bangs, the flames, the explosions, the pops, the whizzes, the smoke and the rockets are fabulously entertaining. I love it, and I love the whoops and cries and applause from the audience.
But at the end of the day, what did the audience remember? Just those bangs - and not a jot of chemistry. Explosive, flaming chemistry demos do nothing to show what chemistry can build and everything to highlight what it can destroy. And in the process, they blow out any flickering interest in chemistry and replace it with fear.
Chemistry classes should be cooking classes. Because who doesn’t love food? And what cooking isn’t chemistry?
Although I should add that, in addition to growing up cooking, I blew all kinds of stuff up in lab and made every kind of bang, whizz, and whoosh reaction I could, and I fell in love with science.
You don’t know scientific beauty until you light an entire ribbon of magnesium and watch its blinding glow.
But anyway, more cooking = more chemistry.
A Better Thanksgiving Through Chemistry
Win Thanksgiving this year, with a heaping helping of science. Cooking is basically controlled chemistry, and chances are your table will feature plenty of it this year … if you know where to look.
From brining turkeys (osmosis magic, and the secret to my turkey) to antioxidants (cranberry sauce) to volatile flavor compounds (spices!) to uuggghhhhhh I ate too much, I need an antacid.
If that certain uncle insists on making everyone uncomfortable by bringing up Obama’s healthcare plan during dessert, offer up these interesting tidbits instead.
(Video by BytesizeScience, from the American Chemical Society)
I needed a cover for my chemistry binder. So I made this. You’re welcome.
Don’t play with liquid nitrogen, kids.
Unless your teacher isn’t looking, then by all means play with it because it’s super-fun. Just don’t put it in your eyes or your friends’ eyes.
Seasons Come and Seasons Glow
We’ve all eaten more than our fill, especially during this time of year. Did you know plants can get full, too?
The elaborate process of converting sunlight into usable energy (the so-called “light reactions” or “magic”) is essentially a big chain where one protein hands off electrons to the next in order to break apart water and build up a bunch of hydrogen ions that can be used to power the ATP factory:
It’s a bit like someone carrying buckets of water upriver in order to power the water wheel at the old mill. The thing is, any a given chloroplast can only hold and process so much sun energy at one time. In order to prevent damage to the leaf factory, the plant gets rid of the excess, either via heat or by giving off light.
That’s right, plants can glow! Or more accurately, chlorophyll can fluoresce. And they do it just about any time they are undergoing photosynthesis, it’s just that we can’t see it. But NASA can. Their Earth-observing satellites can detect this excess plant energy and use it to check how active and healthy our planet’s vegetation is.
The above visualization from NASA shows four years worth of plant fluorescence, averaged into one complete seasonal cycle. Winter turns to spring, spring to summer, and autumn leaves fall, played out in waves of glowing pink.
Previously: The world viewed through Kodak’s Aerochrome film … pink plants everywhere!
Our bodies are comprised of a vast array of elements, with oxygen, carbon, hydrogen, and nitrogen remaining the most abundant. But there are many other chemical elements present! The figure above lists each element that has been isolated from the human body in the order of decreasing mass.
This chart is based on the work of Ed Uthman, who derived the data from The Elements, by John Emsley.
Ever wonder why we are made up of the particular ratio of elements that we happen to be made up of? The answer may be very simple. Perhaps we are that way because the universe is that way.
First, head over to Wikipedia to check out the full list of the elements that compose the human body. You can sort each by the percent of all the atoms in the body it makes up, which I think is a better way to look at it. Here’s most of you:
Next, look at this chart of how abundant each element is in the universe, organized by percent (larger here):
We are made of pretty much the same stuff that universe is made up of, and in the pretty much the same proportions. Things like hydrogen and oxygen score highly because we are made up of so much water, of course, while in the universe at large hydrogen exists as the fuel for stars and oxygen is an overreactive nuisance.
There are some exceptions, like there always are. Helium for instance, is abundant in the universe as a product of hydrogen fusion, but its nonreactive chemistry is pretty useless to us. Same with neon, great for lights, useless for biology. And iron, for instance, falls a bit further down the list of “living elements” than it does the “universal list”, mostly because we only have use for its +3 oxidation state in biochemical reactions (sorry 2+!). And many of the low scoring elements in our body are just random tag-alongs from our food and environment, and would be toxic at higher levels.
Our experience with life is limited to one place: Earth. I wonder if the elemental composition of living things would follow this pattern, should we find it elsewhere? I think that it would. Biochemistry seems to write its recipes using what it has on hand, and the pantry of elements is stocked in a very particular way.
Do you agree? Are we that way because the universe is that way?