Kilogram, pterin, selenium

I really enjoyed the latest issue of Chemistry International. Did you know that pterin is called “pterin” because it was first isolated from butterfly wings, and folic acid is “folic” because it was first found in leafy vegetables (from Latin folium)? I just learned that from Edward Taylor’s illuminating article on Alimta [1].

Next, two papers on kilogram in the “New SI”. Currently, kilogram is defined as a unit of mass equal to mass of the international prototype kilogram (IPK), which is a cylinder made of 90% platinum—10% iridium alloy kept at the International Bureau of Weights and Measures in France. The problem is, IPK is losing mass! But even if it did not, it is still not good that one of SI base units is linked to an artifact rather than to something more fundamental. The chemist in me prefers the definition of kilo based on carbon-12 mass [2] to the one based on Planck constant [3].

Finally, essay by Jan Trofast on discovery of selenium [4]. I didn’t know that Swedes discovered so many elements!

1. Taylor, E.C. (2011) From the wings of butterflies: The discovery and synthesis of Alimta. Chemistry International 33, 4—8.
2. Censullo, A.C., Hill, T.P. and Miller, J. (2011) Part I — From the current “kilogram problem” to a proposed definition. Chemistry International 33, 9—12.
3. Mills, I. (2011) Part II — Explicit-constant definitions for the kilogram and for the mole. Chemistry International 33, 12—15.
4. Trofast, J. (2011) Berzelius’ discovery of selenium. Chemistry International 33, 16—19.

Copper butterfly

In a recent paper, I came across this rather poetic description:

Each of the Cu(I) centers is trigonally coordinated by three S atoms, and each of the six dithiophosphate ligands is connected to a Cu₄ butterfly, where the hinge positions are occupied by two copper atoms situated at the vertex of the central tetrahedron and the wingtips are two capping Cu atoms.

However, to understand what they are talking about, one really should see one of these beautiful structures in 3D. I used this CIF file and Mercury program to create the image below.

The enigmatic Metallosia

True, there is a lot of stuff on the web, but this is not remotely enough. Take, for example, Metallosia. The very short Wikipedia entry says:

Metallosia is a genus of moth in the family Arctiidae.

According to this taxonomy page,

There are approximately 3 species in this genus: M. chrysotis · M. nidens · M. nitens

(I wonder what “approximately 3 species” could possibly mean. Could it be that M. nidens and M. nitens is actually one species plus one typo? Can one say that 2 is approximately 3?) I also can find Metallosia mentioned in the Natural History Museum catalogue but not much factual information either. On the other hand, it is not listed in the NCBI taxonomy database, which indicates that no sequence data from these moths are available (and which makes it non-existent for bioinformatics). Internet, I am disappointed. Where can I see Metallosia? How can I recognise it if I see it? And most importantly, does it have anything to do with metals?