аЯрЁБс>ўџ 24ўџџџ1џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџьЅС%` №ПbjbjЎѕЎѕ 7 ЬŸЬŸџџџџџџЄЈЈЈЈЈЈЈМ„„„„˜ Мh ААААААААч щ щ щ щ щ щ $n hж ь ЈѓААѓѓ ЈЈАА" У У У ѓ‚ЈАЈАч У ѓч У У ЈЈУ АЄ АодЦ№Ш„u "У ч 8 0h У Т— ТУ ТЈУ $АZ @У J4~uААА ­ АААh ѓѓѓѓМММd dМММ МММЈЈЈЈЈЈџџџџ The Second Annual Wynne-Jones Chemistry Lecture, Newcastle University 24 October 2008 Professor Ronald Breslow Mapping Chemical Reactions: Mountains or Molehills? Extending Nature with Biomimetic Chemistry Since earliest times, humans have observed some features of the natural world with admiration and envy. As one example, people saw the ability of birds and insects to fly while we were earth-bound, and wanted to imitate this ability. We quickly learned that we needed to imitate the principles of natural flight, not necessarily its details. Wings would help, we learned from Nature, but not necessarily wings that we power by flapping. As Philip Ball has observed, a jumbo jet is not just a scaled up pigeon. Chemists have also been filled with admiration and envy when we consider the chemistry that living things perform, in fields now called biochemistry and molecular biology. In particular, the enzymes natural catalysts involved in essentially every biochemical process are in general able to perform chemical reactions with speeds and selectivities that are not generally possible yet in the chemical processes and catalysts that chemists have invented. When a catalyst performs a reaction with increased speed, we say that a reaction that is normally slow since it has to climb over a high energy barrier the mountain becomes much faster when the catalyst produces a new pathway that avoids the mountain and instead climbs over a smaller barrier the molehill. Thus a particular field of chemistry has arisen, which we have called Biomimetic Chemistry, to try to create catalysts that will perform in this way as well as do the enzymes of Nature. As one example, we have created novel catalysts that bind a substrate, as enzymes do, and use the geometry of the resulting complexes to perform selective chemical reactions where the geometry of the complex dominates, producing products that would not be formed without the use of these artificial enzymes. Such catalysts can produce products that natural enzymes do not, so the idea behind natural enzymatic catalysis has been generalized. Chemists have also seen that most biochemistry is performed in water, not in the chemical solvents that are normally used in chemistry. Water has huge environmental advantages, and in addition it can promote selectivities and rates with enzymes and artificial enzymes by causing molecules to bind to the catalysts using what is called the Hydrophobic Effect. We have used this effect in our artificial enzymes, and have also studied it in simpler reactions where two molecules simply react by colliding. For many chemical reactions, such collisions occur more often in water. The environmentally preferred solvent water is also the one that promotes rates and selectivities. When molecules are at the top of the energy mountain or molehill we say that they are in the transition state, where they can easily slide down the energy hill to form the products. The time in the transition state is so short that we cannot directly see a species there, but information about its structure is critical in designing catalysts to lower its energy. With appropriate controls to account for other polarity effects, we find that modifiers of the Hydrophobic Effect can be used to determine the transition state geometries for a number of fundamental processes. Thus studies of Biomimetic Chemistry have for the first time afforded a new tool to let chemists understand their reactions in greater and important detail. R. Breslow, ed., Artificial Enzymes , Wiley-VCH, Weinheim, Germany, 2005. 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