You discuss the nature of C–H…O bonds and reminisce about hydrogen sulfide
The article on June Sutor (Chemistry World, August 2019, p22) brought back good memories of visiting her in her later years. By then, there was good data on protein structures that enabled us to assess whether her speculation as to ‘whether C–H…O bonds play a part in the structure of biological molecules’ could be justified.
The data demonstrated that she was on the right track: shorter-than-expected polar to apolar group distances were indeed frequent in proteins. Moreover, crystallographic data showed that polar-apolar contacts occurred with similar frequency to the polar-polar and apolar-apolar ones. Methane’s polarisability is not insubstantial, so it shouldn’t have come as a surprise that dipole-induced dipole interactions between mutually contacting polar and apolar groups could contribute to the stability of a macromolecule. Even though each interaction may be 5–10% of the average energy of a hydrogen bond, the large number of them within a protein suggests a potentially significant total effect on biomolecular stability – especially considering that the thermal stability of the protein may be equivalent to only 5–10 hydrogen bonds.
There is still disagreement on whether a hydrogen bond is purely electrostatic or involves some charge transfer, so whether the term ‘hydrogen bond’ applies to such polar-apolar interactions remains a matter of argument. But it is clear that such interactions do exist. It’s sad that June’s contribution was so controversial when the physics of such interactions was pretty clear even then.
John Finney FRSC
University College London, UK
Maureen Julian suggests misogyny as the cause of Jerry Donohue’s scathing rebuttal of June Sutor’s work on C–H…O interactions. I can, however, advance two other possible reasons for Donohue’s reaction. Firstly, Sutor’s evidence was flimsy, and her case was far from proven. This wasn’t her fault; she simply didn’t have enough good data. Secondly, Donohue did his PhD with Linus Pauling, the man who wrote the seminal account of hydrogen bonding without mentioning C-H groups. His respect for one of the greatest chemists ever may have been enough for Donohue to look with scepticism at any suggestion that his mentor had missed something.
Robin Taylor FRSC
Egg and Kipp’s
The podcast by Michael Freemantle on hydrogen sulfide (9 August) brought back many memories for me. I sat A-level chemistry in the early 1960s, and what was termed ‘semimicro qualitative analysis’ was the mainstay of the practical portion of the exam. Central to the analysis was the use of hydrogen sulfide to precipitate out sulfides of different colours. Although I did use a Kipp’s apparatus for this purpose on many occasions, it was more normal in our school to use hydrogen sulfide dissolved in acetone. This meant less exposure to hydrogen sulfide fumes, though the smell was still horrendous.
Contrary to Freemantle’s experience, my use of Kipp’s apparatus was confined to A-levels. As an undergraduate my practical analytical courses were quantitative rather than qualitative. Our lecturer used to rant and rave that if we couldn’t analyse chemicals accurately to the nearest thousandth of a gram we should pack up and go home. This was probably because until the 1960s most chemistry graduates found employment in analytical chemistry.
Zero waste is rubbish
‘Zero waste’ has a fine, crusading, rallying-call ring about it (Chemistry World, August 2019, p7.) However, scientists should bristle whenever this term is used. No practical system for producing materials or work can be ‘zero waste’, even in principle. This is an inviolable consequence of the second law of thermodynamics. Proponents of electric vehicles call them ‘zero emissions’, ignoring the emissions from producing the electricity that powers them. Even renewable sources, such as solar and wind power, are not waste and emissions-free. It should no more occur to a scientist to call a process or system zero waste than it would be to propose that we should aim for a machine that delivers perpetual motion.
Neil Winterton, FRSC
What to do with Pu?
The response to my letter about the use of radiation to break down plastic waste material (Chemistry World, July 2019, p.4) suggests a deeper interest among RSC members in measures to protect the planet from the effects of environmental pollution, one aspect of which is the problem of managing stocks of radioactive waste.
Incinerating plutonium contaminated material to reduce its volume has been tried but failed. Otherwise it can be reduced to ash using bacteria, after which chemistry can step in to recover the plutonium for use in a variety of applications, including generating hydrogen. Spent Magnox fuel cladding can be dissolved in carbonic acid and the Pu recovered. After exhausting all recycling possibilities, residual Pu can be converted into more rapidly decaying beta/gamma elements using neutron generators.
Recovery of heritage Magnox material is unlikely to be achieved for at least 50 years, when the UK government plans to move it to a geological disposal facility (GDF). To date, a suitable package to safely contain the radioactivity has not been found. Having failed to convince the public of the efficacy and practicality of GDFs, in April 2015 MPs voted to include them in the UK’s nationally significant infrastructure projects, which bypass normal planning requirements. A month ago I was alerted by the RSC’s Radiochemistry Group of a new programme of politically inspired publicity to sell the disposal concept to local authorities. Peer review is long overdue.
David Bradley FRSC
I’m sorry to see that, with your magazine wrapper, you are following the trend for futile climate-change gestures. I found the wrapper tasteless, very chewy and not very digestible. Composting it will, eventually, release carbon dioxide – or worse, methane, which will warm the climate in the short term, and degrade to carbon dioxide to warm it more long term. So I have burnt my wrapper to keep me warm – for my very own futile gesture.
Paul A Bristow FRSC