Now available online:
Design and Analysis of a Molecular Tool for Carbon Transfer in Mechanosynthesis [PDF]
By Damian G. Allis and K. Eric Drexler
Mechanosynthesis exploits mechanical positioning to direct reactive moieties to specific reactive sites on target structures. This mechanism of control contrasts with that of conventional synthesis techniques, in which solution-phase diffusion produces undirected molecular encounters. Despite this lack of direct positional control, diffusion-based synthesis techniques can achieve considerable site specificity by seeking reaction sequences in which each distinct reactive site, at each step, differs from the rest in its reactivity.
This strategy for structural control becomes more difficult as structures grow larger and more complex, due to the proliferation of similar reactive sites. Mechanosynthetic techniques, in contrast, can perform different synthetic operations on target sites of similar reactivity that are distinguished solely by their structural position.This means of control is essentially independent of product scale and complexity and can be quite reliable.
Diffusion-based synthesis techniques have been under development for more than a century and have achieved striking results. Mechanosynthetic techniques are rudimentary today, but their further development promises to greatly expand the scale, diversity, and complexity of products made by structurally precise molecular synthesis.
Mechanosynthesis of a target class of graphene-, nanotube-, and diamond-like structures will require molecular tools capable of transferring carbon moieties to structures that have binding energies in the range of 1.105 to 1.181 aJ per atom (159 to 170 kcal mol^−1). Desirable properties for tools include exoergic transfer of moieties to these structures; good geometrical exposure of moieties; and structural, electronic, and positional stability.
This paper [PDF] introduces a novel carbon-transfer tool design (named "DC10c"), the first predicted to exhibit these properties in combination.
Also available online:
Kinematic Self-Replicating Machines
Robert A. Freitas Jr. and Ralph C. Merkle co-authored the most comprehensive review ever published about self-replicating machine systems, specifically kinematic self-replicating machines: systems in which actual physical objects, not mere patterns of information, undertake their own replication.
With 200+ illustrations and 3200+ literature references, KSRM describes all proposed and experimentally realized self-replicating systems that were publicly known as of 2004, ranging from nanoscale to macroscale systems. The book extensively describes the historical development of the field. It presents for the first time a detailed 137-dimensional map of the entire kinematic replicator design space to assist future engineering efforts. KSRM has been cited in two articles appearing in Nature this year (Zykov et al, Nature 435, 163 [12 May 2005] and Griffith et al, Nature 437, 636 [29 September 2005]) and appears well on its way to becoming the classic reference in this field.