Letters: October 2005

From Bill George

In his article entitled Claiming Einstein for chemistry (Chemistry World, September 2005, p38) Philip Ball admits to talking ’somewhat with tongue in cheek’. The claimed contribution of special relativity in 1905 to chemistry as practised and generally understood is tenuous. 

Ball is misleading by crediting Einstein with much of our understanding of the quantisation of light and energy. The vast majority of measurements by IR spectroscopy, particularly on organic materials, are interpreted as classical vibrations either as qualitative fingerprint-type patterns or as group frequencies attributed to vibrating functional groups. This is normally linked to some understanding based on chemical principles of spectral changes from the effect of adjacent or other interacting groups or phase change. Such interpretations rest on the classical ball and spring model of harmonic vibrations that follow the 17th century law of Robert Hooke. 

Superficially, vibrational spectra can be widely understood in classical terms but more detailed measurements in particular cases point at anomalies better explained by quantum theory. More generally, other spectroscopic methods (eg electronic, microwave, NMR, EPR) are only explicable by quantum theory which Einstein helped us to understand.

In connection with the current centenary celebrations, Einstein’s equation E = mc²  is often described as the most important of modern times. More widely used is the Schrödinger wave equation, HΨ = EΨ. This equation relates to the earlier question of the description of systems at the atomic or molecular level in either classical or quantum terms and allows sub-atomic entities (protons, neutrons, electrons and photons) to be treated as both waves and particles. It has many applications in physics and chemistry and its solution for molecules of significant size was pioneered by John Pople, an English mathematician who shared the 1998 Nobel prize for chemistry.  

This work permits, ab initio, the determination of the many molecular properties by Hamiltonian operations (H) on approximate wave functions (Ψ) of estimated molecular models after refinement by successive iterations to stable minimum energy (E) states.  

A computer search of the scientific literature of papers including ab initio in the title, abstract or key words shows a growth over 14 years from around 1500 in 1991 to around 5500 in 2004 which may be compared with the total number of identified scientific publications from 898 000 to 1 241 000 per annum over this period.  

In the last three complete years of this period, approximately one in every 230 scientific publications has reported one or more ab initio calculations either in a theoretical context or in association with experimental work. This information on molecular science provides incentive for associated experimental measurements and processes, leading to much better understanding of the molecular basis of the natural world with implications for the future policy directions of research and teaching at many levels.  

Should Einstein defer to Schrödinger in their relative contributions to chemistry?

W O George CChem FRSC 
Swansea, UK 

 

From Philip Judson

In her article entitled Sunshine slows immune response to allergens (Chemistry World, August 2005, p27), Vikki Allen quotes Joanna Narbutt as saying that volunteers exposed to direct sunlight showed reduced allergic responses to a well-known allergen, which meant that their immune systems were suppressed. She said that this indicated the necessity of using sunscreens every day during exposure - presumably inferring from the experiment that normal immune response to infection may be jeopardised. 

My understanding is that allergy is due to over-response of the immune system to a stimulant and that one factor is the failure of the counter-mechanism that normally limits response to the right level. So rather than suggesting that sunshine is damaging and that we need to shield ourselves from every golden ray, this study could be interpreted as evidence that sunshine is beneficial. 

Might our obsession with hiding our children in the shadows and coating them from head to foot in sunscreen if they have cause to venture out even be the cause of the rising incidence of allergic diseases? Probably not, but it is arguably a more reasonable conclusion to draw from Narbutt’s experiment than the assumption that solar irradiation threatens normal immune function.

P N Judson CChem FRSC
Harrogate, UK

 

From Bill Newton

Henry Nicholls writes a very interesting article showing how chemical analysis plays a key role in archaeology (Chemistry World, September 2005, p44). 

It is unfortunate that he omitted to mention the provenance of artefacts. The most common artefacts used for provenance studies are pottery shards, which are generally the most abundant find in an archaeological dig.

There are several analytical techniques used, one of which - neutron activation analysis (NAA) - is celebrating 50 years of use in archaeology. The University of Missouri, US, is coordinating a publication to recognise the fact that in those 50 years, NAA has been used to analyse thousands of samples across the world, with over 6000 in the UK.

The technique can answer many interesting archaeological questions such as: where was an artefact made? Who built a pyramid? Who traded where and with whom? There are large numbers of examples in the literature.

G W A Newton CChem FRSC
Wrightington, Lancashire, UK

 

From David Bellamy and Jack Barrett

The news item about the Royal Society’s document, Ocean acidification due to increasing carbon dioxide,  is somewhat misleading (Chemistry World, August 2005, p6). 

The statement that ’the average pH of the oceans will fall by up to 0.5 units by 2100 if global emissions continue to rise at present rates’ refers to the very unlikely scenario in which the atmospheric concentration of carbon dioxide rises to 1680ppmv from the present day value of 380ppmv. 

If the level of the greenhouse gas reaches double that of the pre-industrial value (ie, 560ppmv), the pH of the oceans would be expected to fall by as little as 0.15 units. At current rates of emission and loss of carbon dioxide to the major sinks of photosynthesis and dissolution in the oceans, about 766 gigatonnes of carbon would have to be produced by burning fossil fuels to achieve an atmospheric concentration of 560ppmv of carbon dioxide. 

The reserves of gas, oil and coal are known to contain 320, 150 and 840 gigatonnes of carbon respectively, and burning sufficient to cause the carbon dioxide concentration to reach 560ppmv would deplete them considerably. To achieve the threatening level posed by the Royal Society report is clearly impossible.

D Bellamy
Conservation Foundation, London, UK
J Barrett, CChem MRSC
London, UK

John Raven, chair of the Royal Society working group on ocean acidification, responds: 

David Bellamy and Jack Barrett have used the wrong baseline for their calculations. 

Our assertion that ’the average pH of the oceans will fall up to 0.5 units by 2100 if global emissions continue to rise at present rates’ is relative to pre-industrial pH values - not those of today.

This pH value change is based on a simulation using the Intergovernmental panel on climate change (IPCC) A2 scenario which could produce an atmospheric carbon dioxide concentration of 1000ppm in 2100. Our report shows that such a shift from pre-industrial atmospheric concentrations of 280ppm would lead to a corresponding change in pH of 0.5 units.

Furthermore, Bellamy and Barrett, in only taking into account known reserves, underestimate how much oil, coal and gas we could burn. The IPCC, in contrast, estimates potential resources of fossil fuels to be 5000 gigatonnes of C (GtC). And after we have used up all recognised resources we might dig into other hydrocarbons which are, as yet, technically difficult and uneconomic to extract to get perhaps 20 000 GtC or more. It is simply naive to suggest that available fossil fuels will be largely depleted by the time atmospheric CO₂ reaches twice its pre-industrial concentration.

We will not simply burn ourselves out of our addiction to fossil fuels. We need decisive action to cut emissions of carbon dioxide. Failure to do so may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today. 

 

From Sally Anderson

It is true that Alexander Fleming won the Nobel prize for medicine for the discovery of penicillin’s antibiotic potential (Chemistry World, August 2005, p72) but Fleming was unable to isolate penicillin.

It was the pioneering work of Howard Florey, Ernst Chain and Norman Heatley (Oxford University, UK) that provided the quantities of penicillin needed to explore its therapeutic properties in humans [see Reviews, p55]. Chain and Florey shared the Nobel prize with Fleming but their contribution is often forgotten. 

S Anderson MRSC 
Oxford, UK

 

From John Holman

As Brian Malpass says, thermodynamics underpins everything (Chemistry World, August 2005, p72). It can be made engaging provided the lecturer follows a simple rule: start with what is familiar and interesting. 

This may mean reversing the traditional order of teaching. Historically, statistical thermodynamics and Boltzmann’s S=klnW  came after classical thermodynamics, yet it makes more intuitive sense than Clausius’ abstract laws. Use the idea of probability and numbers of ways of arranging quanta to introduce entropy, and the idea quickly makes sense. This may shock purists, but it has been shown to work, both in the Salters’ advanced chemistry course and in the Thermodynamics in context programme which has been successfully used with UK undergraduates at the universities of York and Leeds.

Here’s another heresy. Traditional courses introduce the idea of internal energy change, ΔU, before enthalpy change, ΔH. This makes sense to lecturers but not to students, who are familiar with ΔH from A level studies. Starting with the familiar ΔH, then introducing ΔU will make much more sense. 

Thermodynamics underpins everything, so there is an unlimited supply of demonstrations and contexts to increase its appeal. Start your treatment of entropy with a few demonstrations of spontaneous changes (explosions, combustion, diffusion of dyes), endothermic reactions and spectacular crystallisation and I challenge you to make it dull. 

And then there are unlimited fascinating examples of thermodynamics in everyday use: car air bags, the explosion of nitroglycerine, refrigerators and why hot water freezes faster than cold. Biochemistry is full of fascinating applications of thermodynamics, from the molecular motors that drive muscles to the protein folding that triggers BSE. Brian Malpass is right. Thermodynamics is fascinating and easily brought alive by teaching it in context. 

J Holman CChem FRSC, 
Centre director, National Science Learning Centre, York, UK