Clever molecules

A particularly interested case of clever molecule is the very simple and well-known metal complex, [Ru(bpy)3]2+ (bpy = 2,2 -bipyridine), which was found to perform as both an encoder and a decoder of a combination of electronic and photonic inputs and outputs [31]. 

This model of Cro binding to DNA was arrived at by intuition and clever model building. Its validity was considerably strengthened when the same features were subsequently found in the DNA-binding domains of the lambda-repressor molecule. The helix-turn-helix motif with a recognition helix is present in the repressor, and moreover the repressor DNA-binding domains dimerize in the crystals in such a way that the recognition helices are separated by 34 A as in Cro. 

When water undergoes self-ionization, a range of cationic species are formed, the simplest of which is the hydronium ion, HjO (Clever, 1963). This ion has been detected experimentally by a range of techniques including mass spectrometry (Cunningham, Payzant Kebarle, 1972), as have ions of the type H+ (HaO) with values of n up to 8. Monte-Carlo calculations show that HjO ions exist in hydrated clusters surrounded by three or four water molecules in the hydration shell (Kochanski, 1985). These ions have only a short lifetime, since the proton is highly mobile and may be readily transferred from one water molecule to another. The time taken for such a transfer is typically of the order of 10 s provided that the receiving molecule of water is correctly oriented. 

Ideally, those molecules that are involved in the catalytic reaction should be the best characterizers of catalytic sites. Indeed, the path of the development of organic reaction mechanisms is paved with clever examples of stereochemistry and isotopic substitution that reveal the nature of activated complexes and intermediates and allow the unambiguous interpretation of the stereorelations... 

Finally, we note a very clever isotope experiment done by Tatsuo Matsushima (2 4). The results are summarized in Figure 14 and show that when 1JC0 is preadsorbed on Pt and then a mixture of - - C0 and O2 is introduced into the gas phase, the product CO2 molecules initially formed all are labelled with - C. In fact the experiment is not quite so simple. An initial 002/ C02 ratio is measured (unity in... 

A number of clever syntheses have employed this strategy. Entry 8 in Scheme 6.5 shows the final steps in the synthesis of the alkaloid pseudotropine. The proper stereochemical orientation of the hydroxyl group is ensured by the structure of the isoxazoline from which it is formed by reduction. Entry 9 portrays the early stages of a synthesis of the biologically important molecule biotin. 

The CIP system evolved in four steps by a combination of logical reasoning and a pragmatic trial and error approach. The evolution was driven by the practical necessity to describe the vast number of known molecules and an impressive array of brain-teasers proposed by clever chemists. 

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