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As you have observed, the link between structure and function is vital to designs on both the macro and nanoscale. Thestructures described here do not, by any means, encompass the countless molecular structures that are required for the synthesis offunctional molecules, but serve only to provide a general idea of the types of designs involved in molecular manufacturing. With this briefintroduction to molecular manufacturing we are prepared to examine a specific example of molecular manufacturing: nanocar 1.

Design, structure, and function of nanocar system

The structure of nanocars facilitates their function. Therefore, their structure and more importantly the precise,deliberate engineering of their structure through assembly and implementation represents vital progress in nanoscale design andmolecular manufacturing. Studying the mechanics of rotors and motors from the bottom up, starting with the simplest molecules possible, theTour group engineered nanocars as the first in a series of tools to test molecular mechanics and prove the viability of moleculardesign.

Central to understanding the implications of the Tour Group research is an understanding of the structure of thenanocars—their design and their function. To best address the nanocar structure we will analyze its design and assembly in three components:the wheel, the chassis, and the surface it operates on. As it turns out, each of these aspects is equally important in determining thefunctionality of the nanocar and is therefore the best way to analyze the structure of the nanocar system.

Wheels

The driving characteristic of the wheel, if you will, is its ability to roll. Apart from this implicit necessity, the wheel must also be ofa size that can be imaged with an STM. If a molecule is too big the STM cannot resolve it. Likewise, if a molecule is too small the STMcannot discern it from its neighbors. A wheel must also be large enough to have ‘ground clearance’ whereby the wheel is of sufficientheight or radius to elevate the chassis high enough above the operating surface to avoid molecular interactions. Ease of synthesismust also be considered in the selection of a wheel. A molecular wheel must be reactive enough to bond with its chassis in order tosynthesize the molecule.

Buckminsterfullerene compared to soccer ball. The alternating pentagonal and hexagonal cyclical bond structuresform a spherical shell reminiscent of a soccer ball. The functional properties of the C60 molecule are a result of theordered bonding of the molecule.

Clearly, there are many considerations that must be taken into account when choosing a wheel. The Tour Group atRice University selected C60 as their wheel for their first nanocar. C60 is entirely composed of carbon with alternatingpentagonal and hexagonal cyclical bond structures that form a spherical shell reminiscent of a soccer ball (figure 5). Ideally, thisstructure, under the right conditions, could roll with its compact surface and spherical shape. Furthermore, it is of a height that canbe imaged with an STM and elevate the chassis to prevent interactions with the operating surface. In a subsequent section, we will learnmore about how these concepts were tested and observed by the Tour Group.

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Source:  OpenStax, Nanotechnology: content and context. OpenStax CNX. May 09, 2007 Download for free at http://cnx.org/content/col10418/1.1
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