The Treasures of Urine

Michelle Clement's post on What can urine tell us? has arrived at an opportune time. I am reading John Emsley's The Shocking History of Phosphorus and much of the first chapter is about the discovery of phosphorus from urine.

Alchemists of the day were desperately and highly secretively searching for the philosopher's stone. Henning Brandt, the discoverer of phosphorus, thought because urine is golden there must be something in it which make is to golden. Possibly gold?

In his attempts to isolate gold out of urine, Brandt evaporate urine to a paste and heated the residues hard to find shining vapours rising from it. When condensed he found that the shining liquid burst into flames if brought in contact with air. So he started collecting the vapours under water instead. The waxy, white solid that formed at the bottom was phosphorus.

So why phosphorus from urine? We tend to eat a lot more phosphorus than is needed by our body. So most of it is excreted.

A typical sample of urine from an adult male contains (per litre) - 52 g creatine, 21 g urea, 6.5 g chloride, 4 g sodium, 2.2 g potassium, 2.3 g amino acids, 1.4 g phosphorus, 0.7 g ammonia and  0.3 g magnesium.

Although Brandt had discovered this light-giving element in 1669, he did not divulge the method of obtaining phosphorus until 1678, by which Johann Kunckel, professor at the University of Wittenberg, had succeeded to isolate phosphorus and was touring the  European royal courts showing off the element and claiming to be its discoverer.

For many years it was thought that Kunckel discovered phosphorus, until papers from Leibniz (yes, the same calculus guy!) revealed that he had conversed with Brandt's wife about the discovery of phosphorus and which finally gave credit to the its true discoverer.

It seems that for at least a hundred after its discovery, urine remained the only source to obtain elemental phosphorus. Even today 3 million tonnes (worth ~$1 billion) of phosphorus is obtained from human excreta. Such are the treasures of urine.

Healing Polymers by Light

Polymers that can be healed could extend the lifetime of materials in so many applications. Chemists from the US and Switzerland have for the first time developed polymers that can be healed by exposure to ultraviolet light alone.

In the recent years, many strategies have been developed for healing polymers. In many cases, they are healed by heating to the glass transition temperature which transforms the polymer from its hard state into a molten state enabling the polymer chains to reform. Unfortunately, this technique is slow and difficult to use in practice. To overcome the problem, a method was needed to manipulate polymeric structure at the molecular level.

Burnworth et al. used supramolecular polymers which are lower molecular mass polymer units held together in long chains by metal-ligand bonds. These non-covalent bonds are weaker than the bonds that hold hydrogen and oxygen atoms in a water molecule but strong enough to enable the new material to possess polymer-like properties.

Healed by UV light

Metal atoms have special affinity to electron rich ligands. This allows metal atoms to form metal-ligand bonds in a polymer with ligand groups present in it its structure.

More importantly, working with these metal-ligand bonds has enabled the researchers to manipulate the bonds at the molecular level with light energy. A polymer sheet deliberately cut to 50% of the film thickness was exposed to UV light in the range of 330 – 390 nm. It was observed (as seen in the picture) that the polymer ‘healed’ by filling up the cut that was made earlier.

Metal-ligand bonds of the kind present in this polymer allow for the conversion of light energy into heat. In this case, the light energy causes the surface of the polymer to rapidly heat up to 220 °C in a very short time. The healing occurs in this state when polymer is allowed to flow and re-arrange. The advantage of using light energy lies in its specificity. Unlike heat energy, it is possible to direct light energy to precisely those areas which require repair.

Also because different metal-ligand complexes absorb light at different wavelengths it should be possible to tune the wavelength of light needed for healing. Thus, one can imagine that it may be possible to heal a broken mobile phone case just by keeping it in sunlight.

Reference: Mark Burnworth et al., Nature, 472, 334.