The Chronicles of the Chronicle Flask: 2021

In January I wrote about a nasal spray that could prevent COVID-19 infections

It’s Christmas 2021, everyone. Can you believe it? It feels like it’s been 2020 for about five years now, doesn’t it? Anyway, regular followers will know that each year in December I write a ‘Chronicles’ post summing up everything I’ve written about over the year.

But before I get into my time machine and set the dial for January 2021 (the sacrifices I make in the name of science communication, honestly), a quick reminder to check out the #272Sci tag on Twitter for tiny science updates and, for Christmas, #272SciXmas. As I write this, I’ve just done eggnog – yum! Oh, and one more thing, if you’re looking for something to keep the children, and yourself, occupied over the holiday break, why not download some STEM Heroes colouring pages, courtesy of Dr Kit Chapman?

So, without further ado, let’s talk about January! Covid-19 was, and of course is, still very much on everyone’s minds, and this post featured talk of a nasal spray designed to be used regularly to prevent infection. What happened to that, you ask? Well, it hasn’t disappeared! It looks as though some countries are now at the stage of approving sales of the spray, so it may begin to become available sometime in 2022…

February featured light, vision and carrots, which is a less idiosyncratic combination than you might imagine. The Crash Course Organic Chemistry episode that I’d been working on at the time has also just made its way into the world. Check it out!

In March, following some online debate about Covid-19 vaccine ingredients, I took a look at chemical names. Lots of chemicals have similar-sounding names, and there are good reasons for that, but it doesn’t mean they have the same properties. Be wary of anyone trying to imply otherwise…

April was a fragrant tale, with gratuitous butterfly pics

This brings us to April, which is when the Viburnum carlesii bush outside my front door always flowers, bringing its gorgeous scent with it. This was one of my favourite sorts of posts, where chemistry turns out to be a path between umpteen topics – in this case, flowers, butterflies, fragrance molecules, an anaesthetic used to help Covid patients, history, and back to chemical names again. And it gave me an excuse to include lots of butterfly photos, too!

Continuing the nature theme, in May my Dad came across some swarming bees, so it was time to talk about them. Do you know why it might be unwise to eat bananas around bees? You will if you read this!

In June I was a little pushed for time, and so it ended up being a summary of things I’d written recently for The Skeptic, Chemistry World, Crash Course Organic Chemistry and DK Super Science. It’s awesome to see projects out in the wild.

It was back to COVID-19 science in July, as I (along with Mark Lorch) took a look at lateral flow tests, and reports of teenagers finding ways to get fake positive results…

For August I wrote about something I was surprised I hadn’t covered before – neem oil. My orchids are doing rather well, since you ask 😉 One of them is just about to flower again!

Following a little Twitter spat (always a good source of inspiration) September became about how chemists identify molecules, and the skill involved in putting the pieces of these chemical jigsaws together. To mash together a few different quotes: just because you don’t know how it’s done, doesn’t mean someone else is using nefarious magic.

October felt like the time for something light-hearted, so I turned the spotlight on ‘dog rocks’. Can putting rocks in your dog’s water bowl protect your lawn? Short answer: no. But it was fun pulling this one apart. Oh, and as I mentioned at the start, October was also when I started #272Sci – if you’re a Twitter user, check that out!

No, it’s not some sort of weird Guinea pig: it’s ice. But why, and how, does it look like this? Well…

Which brings us to November, back to nature, and what might just be one of my all-time favourites: freezing fungal farts! Have a read – I really enjoyed this one.

And now it’s December! Along with Andy Brunning of Compound Interest I’ve been making daily advent-themed science tweets. As I said in the November post, I intend to wind up the regular monthly blog posts this year. Life has got busy, but it’s all good – I’m excited to see what 2022 will bring. Speaking of which, please do consider supporting the Great Explanations book project here!

But I’m not quite done, because after this I’ll be on post 150, and that seems like a milestone I shouldn’t miss. So, for New Year, I’ll be back with a ‘all time most popular’ post. Watch this space.

In the meantime, I wish you a lovely, and peaceful, Christmas!


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Vibrant Viburnum: the fascinating chemistry of fragrant flowers

There’s a Viburnum carlesii bush (sometimes called Koreanspice) near my front door and, right now, it smells amazing. It only flowers for a relatively short time each year and otherwise isn’t that spectacular – especially in the autumn when it drops its leaves all over the doorstop, and I’m constantly brushing them out of the house.

But it’s all worth it for these few weeks in April, when everyone who has any reason to come anywhere near our door says, ‘ooh, what is that smell? It’s gorgeous!’ We also rear butterflies at this time of year, and they love the flowers once they’ve emerged from their chrysalids. (No, of course this isn’t an excuse to include all my butterfly photos in a post. Painted lady, since you ask.)

But let’s talk chemistry – what is in the Viburnum carlesii’s fragrance? Well, it’s a bit complicated. Fragrances, as you might imagine, often are. We detect smells when volatile (things that vaporise easily) compounds find their way to our noses which are, believe it or not, great chemical detectors.

Well, I say great, many animals have far better smell detection: dogs, of course, are particularly known for it. Their noses have some 300 million scent receptors*, while humans “only” have 5-6 million but, and this is the really fantastic part, by some estimates we’re still able to detect a trillion or so smells. We (and other animals) inhale air that contains odour molecules, and those molecules bind to the receptors in our noses, triggering electrical impulses that our brains interpret as smell.

Most scents aren’t just one molecule, but are actually complex mixtures. Our brains learn to recognise combinations and to associate them with certain, familiar things. It’s not that different from recognising patterns of sound as speech, or patterns of light as images, it’s just that we often don’t think of smell in quite the same way.

Viburnum carlesii flowers have a fragrance often described as sweet and spicy.

So my Viburnum bush – and the flowers I’ve cut and put on my desk – is actually pumping out loads of different molecules right now. After a bit of hunting around, I tracked them down to (brace yourself for a list of chemical names) isoeugenol, eugenol, methyleugenol, 4-allylsyringol, vinyl-guaiacol and methyl nicotinate, plus the old favourites methyl salicylate (this stuff turns up everywhere), methyl benzoate (so does this), indole, cinnamic aldehyde and vanillin, and then some isovaleraldehyde, acetoin, hexanal, (Z)-3-hexen-1-ol and methional.

Phew.

Don’t worry, I’m not going to talk about the chemistry of all of those. But just for a moment consider how wondrous it is that our noses and brains work together to detect all of those molecules, in their relevant quantities, and then send the thought to our conscious mind that oh, hey, the Viburnum is flowering! (It’s also pretty astonishing that, in 2021, I can just plug all those names into a search engine and, with only a couple of exceptions, get all sorts of information about them in seconds – back in the old days when I was studying chemistry, you had to use a book index, and half the time the name you wanted wasn’t there. You kids don’t know how good you’ve got it, I’m telling you.)

Anyway, if you glance at those names, you’ll see eugenol popping up quite a bit, so let’s talk about that. It’s a benzene ring with a few other groups attached, and lots of chemicals like this have distinctive smells. In fact, we refer to molecules with these sorts of ring structures as “aromatic” for this exact, historical reason – when early chemists first isolated them, they noticed their distinctive scents.

Eugenol is an aromatic compound, both in terms of chemistry and fragrance (image source)

In fact there are several groups of molecules in chemistry that we tend to think of as particularly fragrant. There are esters (think nail polish and pear drops), linear terpenes (citrus, floral), cyclic terpenes (minty, woody), amines (fishy, rot) and the aromatics I’ve just mentioned.

But back to eugenol: it’s a yellowish, oily liquid that can be extracted from plants such as nutmeg, cloves, cinnamon, basil and bay leaves. This might give you an idea of its scent, which is usually described as “spicy” and “clove-like”.

Not surprisingly, it turns up in perfumes, and also flavourings, since smell and flavour are closely linked. It’s also a local antiseptic and anaesthetic – you may have used some sort of eugenol-based paste, or perhaps just clove oil, if you’ve ever had a tooth extracted.

Plants, of course, don’t go to the trouble and biological expense of making these chemicals just so that humans can walk past and say, “ooh, that smells nice!” No, the benefit for the plant is in attracting insects, which (hopefully) help with pollination. Which explains why my butterflies like the flowers so much. (Another butterfly pic? Oh well, since you insist.) Eugenol, it turns out, is particularly attractive to various species of orchid bee, which use it to synthesise their own pheromones. Nature’s clever, isn’t she?

By the way, notice I mentioned anaesthetics back there? Eugenol turns out to be too toxic to use for this in large quantities, but the study of it did lead to the development of the widely-used drug propofol which, sadly, is pretty important right now – it’s used to sedate mechanically ventilated patients, such as those with severe COVID-19 symptoms. You may have seen some things in the news earlier this year about anaesthetic supply issues, precisely for this reason.

Isoeugenol has the same “backbone” as eugenol, with just a difference to the position of the C=C bond on the right. (image source)

Back in that list of chemical names, you’ll see “eugenol” forming parts of other names, for example isoeugenol. This points back to a time when chemicals tended to be named based on their origins. Eugenol took its name from the tree from which we get oil of cloves, Eugenia, which was in turn named after Prince Eugene of Savoy – a field marshal in the army of the Holy Roman Empire. And then other molecules with the same “backbone” were given the same name with prefixes and suffixes added on to describe their differences. As I said in my last post, this sort of naming system it was eventually replaced with more consistent rules, but a lot of these older substances have held onto their original names.

Still, regardless of what we call the chemicals, the flowers smell delightful. I’m off to replenish the vase on my desk while I still can. Roll on May, vaccines and (hopefully) lockdown easing!

Take care and stay safe.


*it’s even been suggested dogs’ super-powered sense of smell might be able to detect COVID-19 infections.


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