Letters: October 2024

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Readers celebrate an MSc course, manufacturing and multi-dimensional space

Glycolysis takes TLC

I was interested to read the article ‘Glycolysis method breaks down mixed textiles for recycling’, which brought back memories of my MSc course at the University of Bristol, UK, in 1967–8, supervised by Graham Nickless. After six months of lectures followed by exams, we then had a further six months to undertake a project and produce a thesis type report for assessment. In my case I was given 17 different samples of polyurethane as chips, sheets or foams, and my task was to determine the chemicals used for their formulation.

For the depolymerisation, I devised a process of heating small samples with water in sealed glass tubes in an autoclave, which I optimised for two hours at 200°C, close to the 210°C described in the above article. For identification and semi-quantitative analysis, I used thin layer chromatography (TLC) and needed four systems – dicarboxylic acids, the aliphatic and aromatic diamines and the polyvalent alcohols. In an article earlier this year, Derek Lowe describes his early experiences of TLC. My work was over a decade before his and at that time we had to prepare our own stationary phases and layer the plates, an art which took much practice, even using the Desaga apparatus. (I’m guessing that Andrea Sella has one of these archived in his stores).

Using a double system of ion exchange, anion for the acids and cation for the amines, with the polyvalent alcohols passing straight through, it was possible to use gas chromatography systems for quantitative results. Some of the samples and depolymerisation products were also examined by IR and NMR analyses.

Patrick Knowles FRSC
Via email

Manufacturing growth

I was encouraged to read the positive feelings among many stakeholders and interested parties about the opportunities that the change of government may bring to the research and development (R&D) community in the UK (Chemistry World, August 2024, p8).

It is true, and has been for a very long time, that, as the article states, ‘Science, engineering and broader R&D are huge assets for the UK’s ability to innovate and produce economic growth’. But economic growth does not come from such assets alone, as the last 40–50 years of de-industrialisation in the UK has clearly demonstrated. Yes, patent portfolios can be sold or licensed and income made from royalties or sharing sales revenue. Startups can be enabled. But this is usually small beer without manufacturing.

The world’s power economies – Great Britain, the United States, Japan and China – were born out of industrialisation and manufacturing not tourism and service industries. It will be very important that the fruits of R&D are exploited by manufacturing here in the UK through a sustainable programme of re-industrialisation. In this way we will truly ‘make the most of the opportunities ahead for R&D to improve the lives and livelihoods of people across the UK’.

Michael Hawkins MRSC
Bolsover, UK

Dimensional analysis

Chemists interested in crystallographically restricted crystals were not perturbed by three-dimensional space. In a world of Cartesian coordinates they could readily see that if you had 27 identical cubes C(1) you could easily arrange them 3x3x3 to get a bigger cube, C(2). And so on isotropically, so that C(x+1) = 3³ C(x), x => 1. And then adorn the vertices – corner, edge, facial or internalised – with molecular fragments as required. Space-filling, regarded as contiguous, reduced the total number of vertices commensurate with face-sharing.

Following Roger Penrose it was then recognised in this 3D world that instead of a multiplier of 27, pairs of successive Fibonacci numbers could be applied to golden rhombohedra, both prolate and oblate: species R₁(x) and R₂(x), which correspond to the two unlike Penrose tiles in 2D. (The cube is a special case of the rhombohedron, a 3D space-filler; however, it is not golden.)

But today we seem to inhabit an increasingly two-dimensional world: graphical displays; spreadsheets, charts and so on (despite less use of paper); even graphene! It’s now that we see the classic decagonal picture to exemplify ‘the irregular habits of crystals’. Yet even here 3D remains as important as ever. Exactly 20 of the prolate species may join at a central point to form a crystal shape of icosahedral symmetry, the rhombic hexecontahedron: a Great Stella stellation.

Perhaps what we learn then, from Dan Shechtman’s heroic resolve, is not only that 2π/5 rotation is just as ‘crystalline’ as translation; more than that, it’s that we may invoke as few or as many dimensions as we need to solve the problem of interest. To explain what he observed in aluminium manganese, for example, Shechtman needed six: the six-dimensional cube, that projected into his diffraction pattern.

Or so it seems to me.

Alan Hare MRSC
Via email

Davy decoded

Barry Knight and Derek Martin were quite correct with their reading of the handwritten words in Humphry Davy’s notebook.

I was aware that Davy experimented with phosphine and drew the wrong conclusion when trying to decipher the handwriting in the printed version of the article.

I can see that the online version of Chemistry World would have helped in that situation (magnification of image), and there are of course other benefits with this option.

Robert Haresnape
Via email

Correction

Thank you to the reader who pointed out the error in the September 2024 coronene puzzle. In the ‘A’ grid of the puzzle it was not possible to spell the word ‘Resend’ with the element symbols provided – we have provided an alternative solution below. In addition to this, the crossword grid had a small error; the number ‘14’ should have been printed in the box to the right. Apologies for any confusion caused.