People keep buying me t-shirts with caffeine molecules on them…
…I have no idea why that could be. Anyway. Lets’ talk about the chemistry
of caffeine, what it is, what it does, how it works, and the benefits and drawbacks.
But…before getting onto caffeine, let’s do the contextual stuff about coffee.
There’s an old legend of the dancing goats from Ethiopia, where a shepherd noticed that
whenever his goats ate particular berries, they would become hyperactive and unable to sleep.
So, the shepherd reported it to a local monastery, where the Abbott tried the berries
as a drink and was, like, “YES! THAT’S THE S**F! RIGHT THERE!”
But that’s mostly legendary and mythological.
Historically, coffee has been known for maybe a thousand or so years,
but as a drink it really became a Thing in about the 15th century,
starting in Yemen, and then spreading across the Arabian peninsula.
It slowly made its way west over the next few hundred years, having a mix of uses
from acting as a medicine, to being used as a drug to aid concentration during prayer.
Because coffee had this stimulating effect, and tended to be consumed in groups of people,
it tended to be associated with radical thinking and subversive,
independent thought… so pretty much every government or major organised religion has,
at one point or another, had a pop at banning the stuff outright.
Now, in the 20th and 21st centuries it’s been associated with… well… poverty-level wages
for the growers, who barely see a fraction of the corporate profit made from coffee,
and also with changing land use and rainforest destruction, as the natural habitats are cleared
to make way for coffee plants. It’s a problematic indulgence,
so you should try to source it as responsibly as you’re able to.
The main stimulant in coffee is caffeine. Chemically, caffeine is classified
under a number of different categories. In the broadest category, it’s an alkaloid.
These are naturally occurring organic compounds featuring basic nitrogen atoms.
Most solutions of coffee are slightly acidic, meaning that caffeine is most-likely protonated,
which also helps make it water soluble. It’s also interesting that coffee is
acidic because it tastes bitter, a taste that is normally associated with basic
solutions. Anyway, the flavour chemistry of coffee is complicated, and caffeine
doesn’t really play that big a role in it compared to many other molecules.
Caffeine is also classed as a purine. These are compounds that are heterocylic aromatic
compounds. There’s a six membered hexagonal ring with two nitrogen atoms in it, and a five-membered
pentagonal ring with another two nitrogen atoms. Put a pin in this one, we’ll come back to it soon.
Caffeine is also a xanthine, which is a modified purine – keeping up with the terms, okay? – and
specifically, a methylxanthine. So, with all the jargon
out of the way, why is that important? Well, it’s because caffeine, due to its shape
and size, is part of a large class of chemicals that will all affect your central nervous system.
One of the key parts of your nervous system to pay attention to when talking about caffeine
are the adenosine receptors. These bind to a compound called, as the name suggests, adenosine.
This molecule features an adenine attached to ribose.
Again, keeping up with the terms? There’ll be a test later.
If you stayed awake in high school biology, you’ll recognise this from adenosine triphosphate, or
ATP, which provides energy for many biochemical processes in cells. You’ll also recognise it from
DNA and RNA. Adenine, and adenosine, are integral parts of those genetic building blocks to provide
the blueprints for life… or some other… florid BBC Horizon-y Brian-Cox-y metaphor for DNA.
Anyway, it’s pretty common for biologically important molecules
to look a little bit like this. Maybe take a look at that pin you
put in purines earlier. The relationship between
adenosine and its receptors has a few functions, but they all revolve around
regulating your heart rate, blood flow, and release of neurotransmitters such as dopamine.
And if that sounds a lot like the effects of taking a big swing of extra strong black coffee,
there’s a reason for that.
When triggered, those adenosine receptors make you feel drowsy,
sleepy… and ready to yawn and go to sleep. If you’re awake and un-caffeinated, there
should be little or no adenosine in your central nervous system. So, the adenosine receptors
aren’t triggered. But you’re working,
your cells are respiring. That ATP is going to break down into ADP, then AMP then, finally,
adenosine. And it will start to hit those adenosine receptors much more. And… *yawn*…
But what if something gets in the way? Caffeine, because of its methylxanthine
structure, is just the right size and shape to interfere with adenosine receptors.
Now, a chemist might look at these two and say, “No. These are absolutely different molecules.
Look, one of them has all these extra oxygens on it, and what, one’s a primary amine and the
other is a ketone. What next, you’ll be telling me methanol, ethanol and propanol are the same!”
But, it’s roughly the same shape, the same size, and all the hydrogen bond
acceptors are in roughly the same place. So, a much squishier, and not very picky protein,
like the adenosine receptor, will be, like, “Well, you’re good enough. Come on in, petal.”
Molecules like caffeine, when working in that context, are known as antagonists. They fill
the slot in the receptor, but they don’t cause the additional knock-on effects of it. The fit
is only “good enough”, it’s still not the exact right thing the receptor is built to respond to.
And, when those receptors are all blocked up with an antagonist,
much less actual adenosine reaches them, therefore no drowsiness…
So… did you pay attention and spot what’s going on?
There’s a trick there, because the way people talk about caffeine, and what it actually does,
doesn’t really match up. People talk about caffeine perking you up, and waking you up,
and stimulating you. But it doesn’t really do that. At least, not directly.
Primarily, it _prevents_ sleepiness and tiredness.
So, you don’t necessarily need it in the morning to “wake up”,
so to speak. But, if you consume it a little later on, it will hold off some
of that sleepiness and drowsiness. Good for pulling an all-nighter, for instance.
If you happen to suffer from a lot of bad sleep inertia – which is this
feeling of tiredness that persists long, long after you’ve woken up,
often several hours – then caffeine can help clear that feeling quite
quickly by blocking the over-stimulated adenosine receptors that are causing it.
So, if you want to restore yourself with a short nap, then consuming coffee
_before_ you go to sleep will prevent that awful grogginess you might feel afterwards.
Rather interestingly, that sort of sleep inertia problem is often found alongside
attention deficit hyperactivity disorder, or ADHD.
In fact, one of the reasons we know that ADHD is a genuine neurological condition and not just – as
countless people dismiss it as – “being feckless and forgetful”, is that many people who experience
it react to stimulants, like caffeine, very differently to people without it.
Allegedly-normal people may avoid drinking tea and coffee any time after midday because
the stimulant will keep them up at night. And the idea of drinking coffee before a nap might sound
horrific to them. In which case, great, your brain chemistry is probably naturally more balanced.
But someone like me might well be able to knock back a double espresso just to feel
relaxed enough to go to bed. Because the stimulant effect brings dopamine levels
to a more comfortable range, and also fixes that sleep inertia problem just afterwards.
There are a lot of things we can also add about caffeine. There’s also how it works with other
drugs, for instance. Especially ethanol.
Contrary to popular belief, coffee will not sober you up. It removes some of the
drowsiness associated with alcohol, and can even enhance alcohol’s de-inhibiting effects,
causing you to drink more and get more rowdy in the process.
So just have the one espresso martini. I know it’s hard, it is the greatest drink
ever created, but go easy on them. It also works well with paracetamol,
having an enhancing effect, which is why it’s bundled up in some painkillers.
So that’s caffeine. There’s an… absolutely colossal rabbit hole of detail about how
caffeine binds to adenosine receptors, and how it interacts with the various types of receptor,
and all sorts of additional molecular biology that’s… well,
I’m a physical chemist with a (coffee) drinking problem, so I’ll leave it there for now.