Future directions
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
ص778-779
2025-10-28
62
Future directions
Key points: Biological metals and metalloproteins have important futures in medicine, energy production, green synthesis, and nanotechnology. The pioneering studies of the structures and mechanism of ion channels mentioned in Section 27.3 are providing important new leads in neurophysiology, including the rational design of drugs that can block or modify their action in some way. New functions for Ca are continually emerging, and one intriguing aspect is its role in determining the left–right asymmetry of higher organisms, a prime example being the specific placements of heart and liver in the body cavity. The so-called Notch signalling pathway in embryonic cells depends on transient extracellular bursts of Ca2 that are dependent in some way on the activity of an H/K-ATPase. There is also a growing awareness of the role of Zn and Zn transport proteins in control of cellular activity, and also of neural transmission. Indeed, the term metalloneurochemistry has been coined to describe the study of metal-ion function in the brain and nervous system at the molecular level. An important challenge is to map out the distribution and flow of Zn in tissue such as brain, and advances are being made in the design of fluorescent ligands that will bind Zn selectively at cellular levels and report on its transport across different zones, for example the synaptic junctions. Metal ions are involved in protein folding, and it is believed that Cu, in particular, may have an important role in fatal neurodegenerative disorders. These roles include controlling the behaviour of prions involved in transmittable diseases such as spongiform encephalopathy (Creuzfeldt–Jakob disease, the human form of ‘mad cow’ disease) as well as amyloid peptides that are implicated in Alzheimer’s disease. In many regions of the world, rice is the staple food but this commodity is low in Fe. Thus transgenic techniques are being used to improve Fe content. The object is to produce better plant siderophores and improve Fe storage (by enhanced expression of the ferritin gene). Enzymes tend to show much higher catalytic rates and far higher selectivity than syn thetic catalysts, leading naturally to greater efficiency and lower energy costs. The principal disadvantages of using enzymes as industrial catalysts are their lower thermal stability, limitations on solvent and pH conditions, and a large mass per active unit. There is much interest in achieving enzyme-like catalytic performance with small synthetic molecules, a concept that is known as ‘bioinspired catalyses. The idea is to reproduce, using all the tools of synthetic chemistry, the properties of an enzyme trimmed down to its smallest fully functional component. Examples of bioinspired catalysts have already been described: areas of particular interest for industrial production are the conversion of methane to methanol (Section 27.10), activation of N2 to produce cheap fertilizers, and production of hydrogen. In the not-so-distant future, when fossil fuels have been depleted, H2 will become an important energy carrier, used either directly or indirectly (after conversion into fuels such as alcohol) to power vehicles of all kinds. One of the scientific challenges is how to obtain efficient electrolytic production of H2 from water, given that electricity will be widely available from a variety of sources. This process requires demanding conditions of temperature and overpotential (Section 10.4), or catalysts that are currently based on Pt and other precious metals. However, Nature has already shown us that rapid hydrogen cycling is possible under mild conditions by using just the common metals Fe and Ni. A related challenge is the synthesis of efficient electrocatalysts that can convert water to O2 without requiring a large overpotential, not because there is a need for O2 itself, but because it is an essential byproduct of electrolytic or photolytic H2 production (see Box 10.3). Once again, we can turn to the biosphere for inspiration because by elucidating the mechanism of the Mn catalyst, we might synthesize new catalysts that are both cheap and durable. We have seen the exquisite structures of materials that are produced by organisms. This understanding is now leading to new directions in nanotechnology (Chapter 25). For ex ample, sponge-like single crystals of calcite, having intricate morphological features, have been produced on polymer membranes formed by templating the skeletal plates of the sea urchin. Another recent development is the production of Pd nanoclusters by hydrogen oxidizing bacteria, the action of hydrogenases making available controlled electron flow to effect the electroplating of Pd on to microscopic sites.
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