As always in science, traditional groupings of concepts are never sharply defined and are commonly present to support the teaching and the intellectual development of the subject. As a subject matures, the barriers between regions of activity often dissolve and great fecundity is found where activities that were once isolated begin to mingle. All that is certainly true of chemistry.
Indeed, the current vigorous development of the subject is springing from the merging of disciplines and focusing on materials of ever greater subtlety built by collaborations across traditional borders. These materials will enhance our technological, medical, and everyday worlds. They will range from the large-scale materials, essential to construction, to the intricate molecules that will modify the processes of life.
However, for organisation reasons, and for teaching, it is often convenient to start an account of the contributions of chemistry from the traditional regions of the subject and this is how I shall proceed here.
The theoretical branch of physical chemistry is currently almost wholly centred on computation, and as the power of computers has increased, so has physical chemistry’s reliance on them.
A liveliness has come to computational chemistry, and the exposition of chemistry as a whole, as the graphical display of the results of computations has become more sophisticated. Before long, computational chemists will be able to produce detailed three-dimensional animations of reactions in progress in solution. They can already do something similar for reactions in gases where there are no solvent molecules, but it is a much more demanding task to do analogous computations for reactions in condensed phases, especially in that most intricate but important solvent, water.
Potential and actual pharmaceuticals already figure large in computational chemistry, and pharmaceutical chemists can make reasonably authoritative predictions about the pharmacological activities of potential drugs and thereby contribute hugely to cost-cutting in the target phase. That aspect will certainly flourish.
Physical chemistry will continue to contribute to the search for and development of alternative modes of energy, particularly in the field of electrochemistry. Energy, heat, work, and their interconversion, the domain of thermodynamics, have always been central to modern chemistry, but the deployment of heat to achieve work is intrinsically wasteful. A collaboration between photochemistry and electrochemistry could save civilisation and deflect it from its abuse of its fossil reserves. Both subjects are a part of physical chemistry, and work currently under way in the development of photovoltaics, synthetic photosynthetic techniques, and electrode materials will be a central focus of physical chemistry in the coming decades.
One major contribution of physical chemistry to experimental chemistry is its provision and interpretation of increasingly subtle spectroscopic techniques, especially to the development of single-molecule studies, the investigation of oligoatomic clusters, and the information that comes from synchrotron sources. These techniques increasingly depend on sophisticated applications of quantum mechanics and are revealing details about the most intimate moments of chemical reactions. The techniques being developed will play a role in the realisation of quantum computing and, in other applications, need to be extended to the observation of reactions taking place in condensed phases.
The role of organic chemistry is not merely to emulate Nature but to surpass, or at least modify, her. This aspect of the subject is coming ever more important as natural products are discovered that have pharmacological potency but cannot be harvested in abundance. Organic chemists are in the business of tweaking such molecules to take them out of Nature’s ponderous and undirected evolutionary path and render them more potent for the tasks that mankind might have in mind for them.
Organic chemistry is responsible for the development of new materials for construction and for human, animal, and plant health. This role will expand, especially as the genetic roots of disease become understood in greater detail and can be counteracted more effectively, in some cases by genetic intervention or accommodation to an individual’s genotype. Here the issue of complexity arises, for the genome does not send a simple message to the organism, and intervention at a molecular level will need to be developed with extraordinary care to avoid a cascade of catastrophe. By implication, one hugely important future for chemistry is the development of its capacity to deal, perhaps computationally, with complexity.
Organic chemistry has been responsible for developing materials that have enormously enhanced our ability to construct, fabricate, and clothe. The development of such materials, currently mostly simple plastics, is moving towards ever more elaborate composite and biomimetic materials that might replace metals, until the oil from which they are made is exhausted, at least. The shift of emphasis, and of responsibility, will be perhaps from biodegradability, to protect the environment, to recyclability, to protect our resources.
Intricacy is the lair of information. Organic chemists are beginning to devise substances capable, in principle, of being hugely dense information stores and switches. Perhaps in the future it will be possible to grow computers under the guidance of the equivalent of DNA rather than fabricating them directly. Although silicon has long been regarded as the likely displacer of carbon as natural intelligence is replaced by artificial intelligence, the boot may be on the other foot, and that most self-effacing of elements, carbon, might reassert its primacy.
By using the techniques of combinatorial chemistry, organic chemists are not always clear what it is that has been synthesised until they identify an unusual property that needs them to take its identity seriously. The next step is not to bother to do the synthesis at all, but let a computer do a series of virtual syntheses, predict a variety of properties, and only then advise the chemist to proceed with a real synthesis, albeit under the computer’s direction. At the other extreme, where there is a specific and possibly elaborate molecule in mind, laboratory syntheses may give rise to microbial syntheses and such chemicals will be milked from genetically modified herds.
The material world
There are currently two principal drivers of inorganic chemistry. One is its long-established alliance with organic chemistry to generate organometallic compounds. These compounds have subtle properties, which is generally the case where carbon is involved, and are responsible for the development of highly specific and effective catalysts.
The other driving force is nanotechnology, which is already the focus of huge intellectual investment worldwide. Although some of the interest in nanotechnology and its infrastructure, nanomaterials, is likely to turn out to be technological giga-hype, there can be little doubt that materials of extraordinary usefulness will emerge, and the current investment is almost certainly money, time, and effort well spent. Lurking in the background of this endeavour is, yet again, carbon and the potential, and perhaps not yet over-hyped, properties and promise of carbon nanotubes and graphene.
Not wholly unrelated to its contribution to nanoscience is inorganic chemistry’s contribution to that other hypothecated saviour of civilisation, high-temperature superconductivity. One of the successes of 21st century science, this time a collaboration between theoretical solid-state physicists, who will provide the explanations, and inorganic chemists, who will provide the materials, will be the resolution of the mechanism and the realisation of the technological dream of widespread superconducting networks. Ceramics in general are also a developing promise, with the prospect of modern versions of these age-old materials displacing the relative newcomer metal, with an effective reversion to a new Stone Age offering savings of weight and greater efficiency in engines that can run at higher temperatures.
As in the case of high-temperature superconductors – recognised by the 1987 Nobel Prize in physics – it is always engaging to monitor the excitement of a new discovery or an old one newly recognised by a Nobel Prize, and to note whether the enthusiastic promise was fulfilled.
We have seen a little of that with the fullerenes, acknowledged in 1996, still waiting in the wings for their widescale deployment; we are watching graphene, acknowledged in 2010, once again for physics, but clearly on chemistry’s turf, to see whether it is a star or merely a passing star. And what of quasicrystals, acknowledged in 2011? Academic excitement is warranted when ground-breaking discoveries are made, but often decades pass before the hopes and the hypes are fulfilled. The laser is an example from physics; maybe fullerenes, graphene, and quasicrystals will be – perhaps in some form of subtle collaboration – examples in chemistry.
Another realm where inorganic chemistry is currently playing a vital role is in the inorganic chemistry of life. Here great promise lies in biomimicry and the emulation of processes vital to life and taking place on inorganic atoms embedded in organic frameworks. These include artificial blood, making use of iron and emulating haemoglobin; the synthesis of ammonia, making use of iron and molybdenum and emulating nitrogenase; and artificial achievement of photosynthesis emulating magnesium in its host chlorophyll. Here lies a triple point of collaboration, between inorganic chemists, organic chemists, and biologists.
Analytic chemistry has always been central to the practice of chemistry and depends on close collaboration with chemists from all the traditional disciplines, especially spectroscopists and those who inhabit reciprocal space, crystallographers. In the middle of the 19th century, the founder of sociology, Auguste Comte asserted, with all the confidence of the under-informed, that mankind would never be able to establish the temperature or composition of a star. How far we have come! Now it is possible to do exactly that and, even more impressively, to determine the composition of a rock on Mars by looking at it from a distance of several metres. Perhaps the problem with analytical chemistry is that, in its forensic and environmental applications, it is just too sensitive, being able to detect anything anywhere. It is surely better, though, to be over- than under-informed.
In conclusion, it seems to me that the preceding 200 years of chemistry have been the preparation for a surge forward into extraordinary achievement in the synthesis of amazing materials. Through those apprentice years, chemists assembled and refined their tools and understanding by crafting simple molecules and thinking productively about their structures and properties. Now, with their apprenticeship over, they are ready to graduate into the synthesis of ever more complex matter and to take on the task of dealing quantitatively with complexity. No one can predict what new kinds of matter will emerge, be it from flask or microbe, but there can be no doubt that whatever it is will provide the infrastructure for technological and medical advance and thereby, let us hope, enhance the pleasure of being alive.