(part of Steps Toward Molecular Manufacturing)

MBB Conclusions:

To construct molecular machine components, it is necessary to put emphasis on building extended, three-dimensional lattices with arbitrary and irregular sequences of MBBs, yet adhering to regular overall rasters for easy designability. Once this is routinely achievable, it is then easy to design and obtain isolated components by introducing special surface-MBBs, which terminate the ability for lattice-extension at appropriate locations and provide the desirable surface structure. Conceptually speaking, the individual components are cut out from an infinitely extended lattice, and the dangling bonds at the boundaries have to be satisfied with capping-MBBs.

A complication arises through the need for positional control while assembling lattices with idiosyncratic stacking patterns. A modified AFM suitable for the task seems within short term experimental reach, but has not yet been demonstrated. Avoiding the necessity of introducing positional control can only be accomplished if the MBBs carry a sufficient amount of encoded distinguishing-information with them, implemented as surface patterns of functional groups. This could allow preprogrammed, structure-directed self-assembly to take place.

Obviously, the amount of information which can be encoded depends on the surface area available, which strongly favors large MBBs. Also through large surface areas, the strength of intermolecular interactions with neighbouring MBBs can be made suitably high, if one does not want to rely on covalent links. (Arguably the largest link-strength per cross-sectional area can be obtained by covalent bonds.) To obtain a feel for how large the area of contact between a pair of MBBs should be for good strength and specificity, one can imagine unfolding and flattening out the convoluted surface of an enzymatic binding site that recognizes a small molecule. The unfolded surface area is uncomfortably large. Trying to devise MBBs in this size range causes a lot of problems in terms of structural rigidity and very complex syntheses.

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last updated Oct. 5 1996
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