What IS a chemical?

a_chemistry_teacher_explaining_an_experiment_8d41253v

You at the back there! Get your nose out of that dictionary and pay attention!

What do we mean when we use the word “chemical”? It seems like a simple enough question, but is it, really? I write about chemicals all the time – in fact my last WhatCulture article was about just that – and I’ve mentioned lots of different definitions before. But I’ll be honest, some of them have bothered me.

I don’t often like the definitions you find in dictionaries. Lexicography and chemistry don’t seem to be common bedfellows, and dictionary compilers haven’t, generally speaking, spent their formative years being incessantly nagged by weary chemistry teachers about their choice of vocabulary.

For example, in the Cambridge Dictionary we find:
any basic substance that is used in or produced by a reaction involving changes to atoms or molecules.”

Hm. Firstly, “basic” has a specific meaning in chemistry. Obviously the definition doesn’t mean to imply that acids aren’t chemicals, but it sort of accidentally does. Then there’s the implication that a chemical reaction has to be involved. So inert substances aren’t chemicals? Admittedly, “used in” doesn’t necessarily imply reacts – it could be some sort of inert solvent, say – but, again, it’s bothersome. Finally, “atoms or molecules”. Ionic substances not chemicals either, then?

Yes, it’s picky, but chemists are picky. Be glad that we are. A misplaced word, or even letter, on a label could have serious consequences. Trust me, you do not want to mix up the methanol with the ethanol if you’re planning cocktails. Similarly, fluorine is a whole other kettle of piranhas compared to fluoride ions. This stuff, excuse the pun, matters.

Dictionary definitions have their problems.

Dictionary definitions have their problems.

Let’s look at some more definitions (of the word as a noun):

The Free Dictionary tells us that a chemical is:
“A substance with a distinct molecular composition that is produced by or used in a chemical process.”

Merriam Webster says:
“of, relating to, used in, or produced by chemistry or the phenomena of chemistry <chemical reactions>”

And Dictionary.com goes with the simple:
“a substance produced by or used in a chemical process.”

That idea that a chemical reaction must be involved somehow seems to be pervasive. It’s understandable, since that’s the way the word is mostly used, but it’s not really right. Helium, after all, is still very much a chemical, despite being stubbornly unreactive.

Possibly the best of the bunch is found in the Oxford Living Dictionary:
“A distinct compound or substance, especially one which has been artificially prepared or purified.”

Not bad. Well done Oxford. No mention of chemical reactions here – it’s just a substance. We do most often think of chemicals as things which have been “prepared” somehow. Which is fair enough, although it can lead to trouble. In particular, ridiculous references to “chemical-free” which actually mean “this alternative stuff is naturally-occurring.” (Except of course it often isn’t: see this article about baby wipes.) The implication, of course, is that thing in question is safe(r), but there are lots and lots of very nasty chemicals in nature: natural does not mean safe.

You keep using that word. I do not think it means what you think it means.

Sometimes people will go the other way and say “everything is chemicals.” We know what this means, but it has its problems, too. Light isn’t a chemical. Sound isn’t a chemical. All right, those are forms of energy. What about neutrinos, then? Or a single proton? Or a single atom? Or, going the other way, some complicated bit of living (or once living) material? In one debate about this someone suggested to me that a “chemical was anything you could put in a jar,” at which point I pedantically said, “I keep coffee in a jar. Is that a chemical?” Obviously there are chemicals in coffee, it works from the “everything is chemicals” perspective, but it’s a single substance that’s not a chemical.

Language is annoying. This is why chemists like symbols and numbers so much.

Anyway, what have we learned? Firstly, something doesn’t necessarily have to be part of a chemical reaction to be a chemical. Secondly, we need to include the idea that it’s something with a defined composition (rather than a complex, variable mixture, like coffee), thirdly that chemical implies matter – light, sound etc don’t count, and fourthly that it also implies a certain quantity of stuff (we probably wouldn’t think of a single atom as a chemical, but collect a bunch together into a sample of gas and we probably would).

So with all that in mind, I think I shall go with:

So what IS a chemical?

A chemical is…

(Drum roll please….)

Any substance made of atoms, molecules and/or ions which has a fixed composition.

I’m not entirely convinced this is perfect, but I think it more or less works.

If you have a better idea, please do comment and let me know!


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8 Things Everyone Gets Wrong About ‘Scary’ Chemicals

scaryChemicals. The word sounds a little bit scary, doesn’t it? For some it probably conjures up memories of school, and that time little Joey heated something up to “see what would happen” and you all had to evacuate the building. Which was actually good fun – what’s not to love about an unplanned fire drill during lesson time?

But for others the word has more worrying associations. What about all those lists of additives in foods, for starters? You know, the stuff that makes it all processed and bad for us. Don’t we need to get rid of all of that? And shouldn’t we be buying organic food, so we can avoid ….

….Read the rest of this article at WhatCulture Science.


This is my first article for WhatCulture Science – please do click the link and read the rest!


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The cold cure that’s 5000 years old

Could we just remove the front of my face? I think it'd be less painful....

Could we just remove the front of my face? I think it’d be less painful….

A couple of days ago I was struck down with a sinus infection. This is something I thought I’d had before, but it turns out that what I’d actually had before was an uncomfortably stuffy nose. Whereas this, on the other hand, was the sensation that someone had put my forehead in a vice and was inflating my eyeballs with a bicycle pump.

I explained this to the doctor. He nodded sympathetically and suggested a drug that’s been used, in one form or another, for five thousand years.

If you’re new to this blog, you might be wondering at this point whether, when I say ‘doctor’ I actually mean ‘naturopath’ (or some other thing that translates as ‘not a doctor’). But, no, this was a properly qualified member of the medical profession. Well, I hope he is. I mean, I haven’t looked him up on the General Medical Council’s list. I assume my surgery did that. I’m sure they did. Anyway….

207px-(+)-Pseudoephedrin

Pseudoephedrine

What was this mysterious, ancient medicine? It was pseudoephedrine, otherwise known (in the UK anyway) by the brand name Sudafed®.

It’s a drug many of us have probably taken to help with cold symptoms, and not given much thought to, but it’s actually got a pretty interesting story.

Pseudoephedrine falls under the class of amphetamines. The ‘amine’ bit of that word refers to the NH group (or it might be NH2, or even just N) and, being one of the fundamental bits in proteins, it turns up in lots of biologically active molecules. It’s in paracetamol (acetaminophen) for example, and antihistamine drugs used to treat allergies, as well as many molecules that occur naturally in the body, such as dopamine and adrenaline (epinephrine).

It’s also there in methamphetamine (commonly known as ‘crystal meth’ or just ‘meth’). In fact, pseudoephedrine and methamphetamine are chemically similar, and the latter can be synthesised from the former (I’m not recommending any of my readers try this; it’s very much frowned upon from a legal point of view). For this reason, the sale of pseudoephedrine is tightly regulated; in the UK you can only buy it over the counter in a licensed pharmacy, and then only in small blister packs. (Cold medications that you can pick up from the shelf usually contain the far less effective phenylephrine.)

800px-Ephedra_sinica_alexlomas

The Ephedra sinica plant

Where does it come from? These days, pseudoephedrine is made in a three-step process, the first of which involves yeast fermentation, but it was first isolated from plants, in particular Ephedra sinica, also known as Chinese ephedra or Ma Huang.

This is where the five thousand years comes in, because these plants have been used in Chinese medicine for millennia. In fact, Ephedra is one of the oldest known medicines. It’s described in the legendary Chinese pharmacopoeia Pen-tsao Kang-mu, and became a common part of Chinese prescriptions to treat cold symptoms, fevers and asthma.

The first substance in Ephedra plants to be used in western medicine was Ephedrine. It was isolated in 1885 by a Japanese chemist called Nagai Nagayoshi, but it was then rather forgotten about until 1920s, when it was rediscovered and became a popular treatment for asthma.

In those days, steroid inhalers had yet to be developed, and the standard treatment for asthma was adrenaline. This was problematic, because adrenaline isn’t orally stable: it had to be injected. Ephedrine, by contrast, would work if swallowed as a pill, making it much easier to use.

Ephedrine_enantiomers

Ephedrine is made up of a mixture of these two mirror-image molecules

Unfortunately, ephedrine had rather unpleasant side-effects. It caused raised blood pressure, and then there were a number of other potential problems such as dizziness, trembling, headache, irregular heartbeat and even, in some cases, heart attack and stroke. Worth the risk perhaps, if you’re in the middle of a life-threatening asthma attack, but not something you’d want to use routinely.

The story goes (although I haven’t been able to verify this by finding, say, a recorded study) that when the use of the whole Ephedra plant as a treatment was compared to the use of pure ephedrine, people noticed that the side-effects were much less severe, even though the whole plant still appeared to be an effective treatment. This caused researchers to wonder whether there was some other substance in Ephedra that had subtly different effects on the body.

Whether this observation was really made or not, it turned out there was another active molecule in the Ephedra plant. It was first separated from ephedrine in in 1927, and was given the name pseudoephedrine, literally ‘false ephedrine’. Ephedrine and pseudoephedrine are structural isomers: they have the same number and type of atoms, ordered slightly differently. This is a common theme in medicinal chemistry: switching just a couple of atoms around can make big differences to the way the human body reacts to drugs.

Like ephedrine, pseudoephedrine was an effective bronchodilator and vasoconstrictor (causing blood vessels to shrink), but its effects were less dramatic, which made it a lot safer. It doesn’t raise blood pressure nearly as much, and is far less likely to cause something really nasty like a heart attack. That said, it’s not side-effect free, and it should go without saying that anyone with an existing medical condition should speak to their doctor before using it. Likewise, don’t go messing about with Ephedra plants.

Vasoconstriction is why pseudoephedrine such a good decongestant. Less fluid leaves the shrunken blood vessels and therefore less fluid enters the throat, nose and sinus linings. This reduces inflammation mucus production, and the incessant pounding of a sinus headache eases up a bit.

Of course, pseudoephedrine doesn’t somehow know to restrict itself to your nose and lungs. Blood vessels throughout the body are affected. This can be useful – for example, pseudoephedrine can help to treat ear infections – but it can also result in other, less desirable effects. In particular, pseudoephedrine suppresses breast-milk production, and for this reason shouldn’t be used by new mothers trying to establish breastfeeding. It might also interfere with mucus membranes in the vagina, potentially causing a small reduction in fertility and, not surprisingly, a substance which is a vasoconstrictor can also aggravate erectile dysfunction. Basically, if you’re trying to make a baby this might be one to avoid, although if you’re stuffed up with a cold you might not feel like it anyway, so perhaps it doesn’t matter.

Anyway, I know what you’re all desperately wondering: But, Chronicle Flask, did it sort out your sinus infection?!

dara

“Science knows it doesn’t know everything; otherwise, it’d stop.”

Well, actually, I’m relieved to report that after taking three doses of pseudoephedrine twice a day for a couple of days the pain has eased up considerably. Of course, there’s nothing antiviral (or antibacterial) in this medicine, but it would appear that my immune system managed to take care of the infection for me, once the inflammation was reduced and the excess fluid which was causing the pressure was able to (yuck) drain away.

To quote the comedian Dara O’Briain:
“‘Oh, herbal medicine’s been around for thousands of years!’ Indeed it has, and then we tested it all, and the stuff that worked became ‘medicine’.”


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