Search our site

Custom Search

Tuesday, 9 July 2019

When is a Strawberry No Longer a Strawberry?

You take that first bite, tearing through the cells of the red berry and allowing its fragrance to erupt. Juices ooze, coating your mouth. The sweetness, modulated with a slight bitter hint, hits your tongue and lights up your senses, and the distinctive flavour of the strawberry overflows.

Why do we love strawberries so much?


Why do we love strawberries so much? There’s something alluring about them, something intense and complex in the flavour we experience that is not matched by any other berry – its chemistry.

When we recognise a flavour – the combined experience of taste, mouth feel and (crucially) smell – we are actually recognising the aromatic chemistry of a food, the volatile molecules given off when we bring it close to our nose or after we bite into it. When we understand the molecules that make up the distinct chemical profile of a flavour, we can replicate it by creating those chemicals in a lab and stirring them together. This helps us make artificial banana flavour, artificial vanilla flavour, and artificial fresh grass smell. But strawberries are awkward. Strawberry flavour is made up of a chemical medley of many, many different molecules (more than 350), variation exists strawberry species to strawberry species, and we just don’t know how important each chemical is.

This is in direct contrast to the raspberry, a humble berry that we recognise as 4-(4-hydroxyphenyl)butan-2-one, or “raspberry ketone”. Whilst cranberries and blackberries also contain this odour, they mix it with other chemicals, whilst in the raspberry it is exclusively responsible for the raspberry profile we instantly know.

Raspberry ketone, the molecule behind the smell we know so well. © Things We Don't Know.

Wednesday, 19 June 2019

Lifetime of a Plastic Bag


450 years into the future - that’s the agreed lifetime of a uniform piece of plastic like a bag. But who’s arguing? Man-made plastics have only been around for about 50 years: we don’t know for sure how long it takes a plastic bag to decompose: so where does this number come from?

A floating plastic bag. Like so many, it has ended up in the ocean. Image credit: Andrew (Flickr).

Plastic readily breaks down into smaller and smaller pieces (microplastics) under environmental conditions: it can now be found anywhere, a splash of colour amongst sand particles viewed beneath a microscope. But this isn’t the same as biodegradation, defined as the bacteria-driven chemical transformation of a material into other compounds.

Natural plastics do exist and do biodegrade: rubber and cellulose, for example. But these don’t make a good comparison with man-made plastics: cellulose is eaten by many animals, and enzymes and microorganisms exist in nature to catalyse its break down, which normally happens by about 6 months[1]. There are some man-made plastic-eating bacteria, but these have only recently been discovered: how fast they act or what products the plastics are broken down into (and whether they are safe and useful) is still a mystery[2].

Friday, 31 May 2019

Toxic Climate: how climate change changes pollution

When it comes to climate change, contaminated land is the forgotten risk.

Climate change leaves us worrying about quite a lot of things: tropical diseases, extreme weather events, extinctions... But we don’t tend to worry about pollution outbreaks. In DEFRA’s climate change risk assessment, it doesn’t even get a mention.

But is that because we’ve forgotten the risks, or because we don’t know?

Extreme weather may affect land safety, access and use. Image © Rowena Fletcher-Wood

Lots of land is “contaminated land”. This doesn’t mean it glows yellow in the dark or is a breeding site for mutant flesh-eating bacteria. Most land is contaminated by waste from agriculture, industry, energy or medicine, and that can be anything from fertilisers that cause algal overgrowths to pharmaceuticals that make male fish feminine[1]. Humans like to concentrate chemicals to put them to use doing specific jobs. This is great when they’re where they’re supposed to be, but leftover chemicals or waste products are still relatively concentrated and can be poisonous or harmful.

Contaminants can also come from the land itself: like arsenic, which is rife in various rocks. Or radon, a radioactive gas found in granite, and especially Cornwall.

There are three main ways of dealing with chemicals in the environment:

1. Spread them out – diluting them more and more until they’re no longer at harmful concentrations
2. Concentrate them – and lock them up in a box or a landfill somewhere they can’t do any harm
Or 3. Change them. Chemical reactions can change the nature of some chemicals, such as pharmaceuticals, making potentially harmful things into harmless things.

These processes are called remediation.

Saturday, 27 April 2019

Can we power the world with HYDROGEN?

Hydrogen fuel cells

 

Hydrogen fuel cells operate by reacting hydrogen and oxygen gases together to make water. This process is exothermic – it releases usable energy. Although it uses both hydrogen and oxygen, it is called a hydrogen fuel cell because hydrogen is a fuel that’s burnt in the presence of oxygen to make water, exactly the same way that a fossil fuels burn, except that there’s no carbon dioxide made from hydrogen.

Hydrogen is considered a green fuel, and because of this it is an attractive future energy source. Scientists have envisaged a future where hydrogen gas could be a major source of everyday energy, reducing greenhouse gas emissions, reducing the problem of climate change, and letting us use our televisions and computers to our hearts' content.

The hydrogen fuel cell is a simple bit of kit. It’s lightweight, with no moving parts, so doesn't malfunction easily. To work, hydrogen loses electrons that then travel round an electrical circuit to join up with oxygen atoms, producing hydrogen ions (or protons) and oxygen ions. The hydrogen ions are small enough to travel through a semi-permeable barrier to where the oxygen is. Here, they react together to produce pure, clean drinking water.

Fuel cell. H2 is catalysed to H+ at the anode; electrons travel through the circuit to provide a direct current and meet oxygen gas at the cathode, forming O2-. H+ ions then travel through a semi-permeable membrane to combine with O2- ions and make water. Image via © TWDK.

Thursday, 21 March 2019

The Call of the Void

Apparently, I experience ‘High Place Phenomenon’.

As a climbing instructor, I’m used to people saying “I can’t go any further – I’m afraid of heights.”

And I always say, “So am I.”

Of course I am. Everyone is. We just develop strategies for managing that fear, and some manage it better than others. The first time I climb somewhere new, I can feel the fear eating away at me, like a voice in my head saying “Oh god, oh god, oh god.” My strategy is just to get to the top and get it finished – and once I’ve done that, going up again has lost its dauntingness.

It can even feel exciting. I’ve oftentimes sat on the edge of a ledge preparing to belay and realised how easily I could unclip and jump to my death. The thought of the rush of the world shooting past, the feeling of somehow having triumphed over my survival instincts and beaten nature, the sense of freedom, power, and the excitement tremble through me. I’m drugged up on adrenalin. My fingers move instinctively with the rope – and it’s a good job they do, because my mind is addled.
 
Looking down from above. Image © Thing We Don’t Know.

Does this sound familiar? 30% of people experience it at least once. The French call it l’appel du vide – the call of the void – and that is exactly what it feels like to me. A beckoning. As though someone were on my left shoulder... whispering, “Do it!”

Monday, 18 March 2019

Carbon-Based Hydrogen Bonding

Many chemists will be shocked to discover that carbon-based hydrogens can hydrogen bond. Weakly. But actually.

If you're not a chemist you're probably thinking that doesn't sound like much of a surprise... A hydrogen can hydrogen bond? Who've thunk it? And that is the first condition for hydrogen bonding – having a hydrogen.

However, until the discovery of the carbon-based hydrogen bond between acetone and halogenated hydrocarbons in 1937, it was believed that that the hydrogen could only make these bonds when attached to something very electronegative – electron-loving.

Why is this?

Electronegative atoms are electron-greedy and pull the electrons in a bond towards themselves. The electrons are shared unequally, leaving the electronegative atom a bit negative and whatever it’s bonded to a bit positive. We call this bond polar, because it has two differently charged ends, like a magnet. And, just like with two magnets, when the positive end of one comes near the negative end of the other, they bond. All polar molecules do this; we call it permanent dipole bonding. But hydrogens do it with an aggressive zeal that marks them out as unique.
Hydrogen bonds form between the slightly positive hydrogen atoms and slightly negative oxygen atoms in water molecules. Image via Wikipedia Commons.
There are three elements considered electronegative enough to polarise a hydrogen: fluorine, oxygen and nitrogen. Fluorine is the most electronegative element in the periodic table, given the Pauling electronegativity value (a made up scale we use to compare electronegativity values) 4. Oxygen is just behind it, with an electronegativity value 3.5, and nitrogen is 3. In contrast, hydrogen has an electronegativity value of 2.1, which means the difference between it and fluorine is 1.9 – considered enough to make a bond polar. But carbon is not very electronegative, and the difference between it and hydrogen is 0.4, surely too little to create polar bonds?

Apparently not.

Monday, 18 February 2019

Language of Smell

One of our five senses, it is the most complex, the most evocative, and the most mysterious sense – But we don’t know how to talk about it

Think about that for a moment – what words have you got to describe flavour except for comparing it to something else? Strong, weak, rich, complicated – there are some, but not many. Compared to the plethora of words we have to describe colour, shape, movement, sound – the flavour landscape is desolate. Most people duck away from vivid descriptions, preferring hedonic terms, like “It’s good.” And yet food is incredibly important to us; it evokes memories, creates atmospheres, is used to bond with other people and change our mood.

Smell plays a bigger role in our lives than we might realise Image credit: Public domain

Different people respond to different flavours differently, partly because of memories, and partly because of different sensitivities to flavours.

Sensitivity can be mapped: our sensitivity to bitterness is gradually lost as we age, allowing us to drink stronger tea. Strangely, this changes differently for men and women: the decline in scent and in bitterness sensitivity is gradual for men, but for women, doesn’t kick in until the menopause. This may be because many bitter things are natural poisons. Our ability to detect them directly impacts our ability to survive in the wild. It’s more important to refine this sense early so we learn lessons we remember our whole lives. Similarly, children are mad about sugar. This sensitivity to it, which we lose as we age, could be another survival tactic, encouraging children to quickly hone in on the densest sources of energy.

But different people lose sensitivity to different smells. It's possible this may depend on the pollutants and viruses you’re exposed to during your lifetime. More mysterious is the fact that by actively studying scents, you can halt sensitivity loss entirely. You can also teach yourself to like flavours or get sick of them by exposing yourself to them – adjusting your internal regulator.

Thursday, 15 November 2018

Mysterious Mo

Why is stainless steel stainless?


Iron vs Steel


Steel is made from iron, but it’s not the same thing: steel is an alloy - iron doped with other elements to engineer new, useful properties. Some of these elements have been especially selected to provide certain properties, but not all metallurgy is that well understood: some elements have simply been stuck in and performed well - and we don’t know why.