Edible education

One subject I've had in my list to write about (once I spent the time to find some good sources) was why some leaves are edible while others aren't—completely aside from the question of toxicity, there are lots of plants that we simply can't digest. I hadn't yet got around to digging into the subject when I ran across the answer recently, along with loads of other interesting information about food chemistry.

A few weeks ago I discovered a free, online course offered by McGill University via edX, on the subject of food and nutrition. Despite being offered by the chemistry department there, it doesn't require more than high school chemistry and the ability to use a 4-function calculator as prerequisites, and I'm not even sure if it needs high school chemistry. You should probably know the difference between an atom and a molecule, and at least recognize the Periodic Table of the Elements.

I was too late to sign up for the credit version, where the assignment deadlines are enforced, but there is a non-credit, audit version (which I'm doing) where you still have access to all the video lectures, discussions, and mini-quizzes.

So back to edible vs. non-edible leaves.

In the lesson on carbohydrates, (week 4, lesson 1) they showed the chemical structure of starch vs. cellulose (video 8). Both are long strings of glucose connected by oxygen atoms, but the way they're strung together is different—and that's it. That's the difference between plants we can digest and plants we can't. (Plants we can digest still have cellulose in them and we pass that through our system no problem—but we don't get any nutrition out of it.)

(Screenshot from Food for Thought, week 4/lesson 1/video 8. Requires free course registration to view.)

They look very similar at first glance, but if you look closely, they have an important difference: every second glucose segment is upside down in the cellulose chain.

We have the enzymes necessary to digest starch. We don't, but cows and other ruminants do, have the enzymes necessary to digest cellulose.

Enzymes are complicated things which have a very specific shape, and can fit around molecules of a very specific shape. So, an enzyme that fits the shape of starch in order to cut it down to its component glucose molecules will simply not fit the different shape of cellulose, even though the components are all the same.

So that was short and sweet. Also, check out the course, it's fascinating. (Keep in mind you can adjust the playback speed of the videos. I found my attention wandering because the instructors speak kind of slowly; running them at 1.5x speed makes it easier for me to keep from wandering. You can also back up and repeat sections if you don't catch it the first time through, or pause to look at the diagrams, because it's a video.)

Unnatural or Natural

Something I've been thinking about for a while, even since before I did the greenwashing article series, is: what makes a thing "natural" or "unnatural"?

Many people would say that "natural" things are things which come from nature with minimal processing. It sounds like a reasonable definition at first glance, but when I try to get specific, I start running into trouble with the definitions of the words used to define "natural". They seem to be a bit fuzzy themselves, which makes the term "natural" hard to pin down.

So my first question is, what is meant, exactly, by "from nature"?

Chilly chemical properties

Because it's the middle of winter here in Canada, I think today is a good day to talk about refrigeration.

Just kidding. Actually it's because the ISS had to replace a piece of its refrigeration system last week, and I thought that was a good excuse to talk about refrigeration.

Most modern refrigeration involves the chemical property \(\Delta H_{vap}\), or enthalpy (heat) of vaporization. Every substance has a heat of vaporization, and the amount of heat energy required to vaporize a substance is independent of what temperature the substance boils at. To choose a rather extreme contrast, water boils at 100C while lead boils at 1750C, but water requires 539cal/g to convert from liquid to gas while lead only needs 208cal/g, less than half that required by water. This amount of heat does not account for how much is required to get to the boiling point, and if you remember your high school chemistry, the temperature does not change with the additional heat input while it changes from liquid to gas.

The basic principle in use here is that when a substance evaporates, it draws heat energy from its surroundings (or the more familiar form: when you add heat to a substance, it will evaporate), and when a substance condenses, it releases heat energy back to its surroundings. Put an insulated barrier between these two sides of the process, and you have refrigerators, freezers, and air conditioners which get colder "inside" and warmer "outside".

Bouncing liquids

Never mind hydrophobic, how about "omniphobic"?

A new material—or rather, a new shape of an existing material—has been made that rejects nearly every liquid thrown at it, both oils and waters, both acids and bases. The material is a plastic, one with slightly lower surface energy than the famous PTFE (Teflon), so it has very little stick to it to begin with.

In order to make the liquids not only not stick but actually bounce right off, they changed the shape at a microscopic level so it wasn't a smooth flat surface, but a textured surface that was mostly air:

Posted with permission from J. Am. Chem. Soc., 2013, 135 (2), pp 578–581. Copyright 2012 American Chemical Society.

Folded Solar

Solar electrical is pretty exciting right now, I must say. After my previous post on some of the cool stuff coming up in photovoltaics I let it slide for a while and chased other cool news, but this new thing from late December really caught my attention.

I mean, solar panel stickers? Which you can apply to fabric or paper, bend them, and have them still work?

The researchers say that this technique isn't only good for solar panels but also possibly for electronic circuits, transistors, and even LCDs as well. Maybe you really could have a solar powered, electronically active jacket, including flexible display, one day. Imagine, a self-powered jacket that could show you a map of where you are, among other things.

They tested the solar panels to a bend radius of 7mm without any damage. I don't know if it would handle a crease (if on paper) very well, or crumpled-clothes type bends. From the paper, it doesn't look like they tested its bending abilities to failure.

Greenwashing and CBC #3: T-Fal Natura frying pan

Continuing from my previous post with #3 on the CBC Marketplace "Lousy Labels" greenwashing list is T-fal Natura frying pan.

As I mentioned last week, Marketplace is a 22 minute show and they did a 10-product countdown, giving them approximately 2 minutes per product, so they had to leave a lot of information out.

So, the T-Fal website claims for the Natura line that it's made from 100% recycled aluminium and the non-stick coating is PFOA-free, lead-free, and cadmium-free.

Marketplace says that PFOA is still used in the manufacturing process, and that it always has been not present in the final product, and that it likely causes cancer as well as being widespread in the environment. Also they acknowledge that 100% recycled aluminium is a good, environmentally friendly thing.

Olympicene: just to see if we can

Not too long ago, a picture from the world's most sensitive atomic force microscope was published, which showed the internal structure of a fairly small organic molecule: a 5-ring snippet of graphene, which is currently a hot and sexy topic in carbon chemistry.

The AFM in question has a sensor "needle" made of a single carbon monoxide molecule, and it's small enough to measure the gap in the middle of a six-carbon hexagonal ring structure, of which olympicene has five.

Will olympicene be a useful compound? I don't know. It's one of a class of potentially useful compounds. Even if it turns out not to be useful itself, learning how to control the reactions to create it is useful in learning how to create other molecules, and learning how to get a clear image of it is useful in learning how to get clear images of other molecules, so we can directly see what shape they are.

And here's an interview with the people who made it:

Crystal habits

I am fascinated by crystals, particularly by their regularity. They basically consist of a unit cell that repeats over and over again, identically, across the whole span of the crystal. And if the crystal is big enough to see with the naked eye, that's a very large number of unit cells.

Very simple crystals, for example table salt (NaCl), have a tiny unit cell consisting of 4 atoms of Na and 4 atoms of Cl, arranged in alternating rows, a structure that is called face-centred cubic, because on each face of the cube, there's an atom in the centre of the same type as the atoms on the corners of the unit cell.

An interesting quirk of the simple 1:1 ratio cubic crystal structure is that you can define either Na or Cl as the corners of your unit cell, and it'll still be face-centred cubic.

Diamond's structure is also simple: every carbon atom has four links to four other carbon atoms, arranged in a tetrahedral shape around it. Because unit cells are defined as cubic or rectangular shapes, however, the diamond unit cell is less simple, even if the structure itself is simple.

Simulated Failure

Simulating normal operation is something that's been done for a while now, ever since computers got powerful enough to do it. Once validated, a model of, say, a stirred tank, will let an engineer consider where two liquids being mixed are not mixing properly, or where fragile solids are likely to be broken because the shear is high, and adjust the design accordingly before the manufacturer ever cuts metal.

I started by talking about fluid dynamics simulation because that and chemical reaction simulation are the two aspects I'm most likely to work with. Other simulations which could affect me but are outside of my field are materials and mechanical related - pipe and tank fractures, for example. The stresses and weak points of a piece of equipment are something I have to trust to a mechanical engineer, but I have to think about it at least a bit, because what's inside those tanks and pipes is sometimes hot, sometimes toxic, sometimes corrosive, or other forms of dangerous and undesirable to have present outside the equipment, and I have to know what kind of safety features and procedures I have to put in place, from sensors to detect a small leak to secondary containment to prevent a catastrophic spill from escaping and doing even more damage.