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Molecular Machines - Design the Nano-Scale Handling of Biological Antetypes the Artificial Mimics

Final Report Summary - BIOMACH (Molecular Machines - Design and Nano-Scale Handling of Biological Antetypes and Artificial Mimics)

A human body has more than 10 to the power of 27 molecules with about one hundred thousand different shapes and functions. Interactions between molecules determine our structure and keep us alive. Researchers at the Max Planck Institute for Solid State Research in Stuttgart in collaboration with scientists from the Fraunhofer Institute in Freiburg and the King's College London have followed the interaction of only two individual molecules to show the basic mechanism underlying recognition of dipeptides. By means of scanning tunnelling microscopy movies and theoretical simulations they have shown how dynamic interactions induce the molecular fit needed for the transfer of structural information to higher levels of complexity.

Probably one of the most exciting mysteries of Nature is why the building blocks of life, i.e. amino acids (the building blocks of proteins) are exclusively present in the chiral L form and sugars (which constitute DNA) are all in the D form. Once more, the reason for this preference is 'historical', but this time goes back millions of years till the origins of the biological world. Scientists believe that current life forms could not exist without the uniform chirality ('homochirality') of these blocks, because biological processes need the efficiency in recognition achieved with homochiral substances. In other words, the separation of molecules by chirality was the crucial process during the Archean Era when life first emerged. Researchers of the Max Planck Institute for Solid State Research have now used the 'nanoscopic eye' of a scanning tunnelling microscope to make movies following how two adsorbed molecules (diphenylalanine, the core recognition motif of Alzheimer amyloid polypeptide) of the same chirality can form structures (pairs, chains) while molecules of different chirality discriminate and cannot form stable structures.

As it occurs when you shake the hand of your friend, the fact that the two homochiral hands are complementary by shape is not enough, you both have to dynamically adapt and adjust your hands to reach a better fit, a comfortable situation. By a combination with theoretical simulations done at Kings College London, the researchers have shown for the first time this dynamic mechanism of how two molecules 'shake hands' and recognise each other by mutually induced conformational changes at the single molecule level.

We live in houses, wear clothes and read books made of chiral cellulose. Most of the molecules that mediate the processes of life like hormones, antibodies and receptors are chiral. Fifty of the top hundred best-selling drugs worldwide are chiral. With this contribution to the basic mechanism of chiral recognition, the researchers have not only tracked back to the very first steps in the evolution of living matter but have also shed light on our understanding and control of synthetic (man-made) materials of increasing complexity.

In the last few years, several examples of molecular machines and motors have been designed and constructed. Although the solution studies of chemical systems as complex as molecular machines are of fundamental importance, it seems reasonable that, before functional supramolecular assemblies can find applications as machines at the molecular level, they have to be interfaced with the macroscopic world by ordering them in some way. The next generation of molecular machines and motors will need to be organized at interfaces, deposited on surfaces, or immobilised into membranes or porous materials so that they can behave coherently. Indeed, the preparation of modified electrodes represent one of the most promising ways to achieve this goal. Solid-state electronic devices based on functional rotaxanes and catenanes have already been developed. Furthermore, addressing a single molecular-scale device by instruments working at the nanometre level is no longer a dream.

Apart from more or less futuristic applications, the extension of the concept of a machine to the molecular level is of interest not only for the development of nanotechnology, but also for the growth of basic research. Looking at supramolecular chemistry from the viewpoint of functions with references to devices of the macroscopic world is indeed a very interesting exercise which introduces novel concepts into chemistry as a scientific discipline.