Molecular engineering is any means of manufacturing molecules or
creating new manufacturing materials using them. It may be used to create, on
an extremely small scale, most typically one at a time, new molecules which may
not exist in nature, or be stable beyond a very narrow range of conditions.
Today this is an extremely difficult process, requiring
manual manipulation of molecules using such devices as a scanning tunneling microscope.
Eventually it is expected to exploit lifelike self-replicating 'helper
molecules' that are themselves engineered. Thus the field can be seen as a
precision form of chemical engineering that includes protein engineering, the creation of protein
molecules, a process that occurs naturally in biochemistry,
e.g., prion
reproduction. However, it provides far more control than genetic modification of an existing genome, which must
rely strictly on existing biochemistry to express genes as proteins, and has
little power to produce any non-proteins.
Molecular engineering is an important part of pharmaceutical
research and materials science.
Emergence of scanning tunneling microscopes and picosecond-burst
lasers in the 1990s, plus discovery of new carbon
nanotube applications to motivate mass production of these custom
molecules, drove the field forward to commercial reality in the 2000s.
As it matures, it is seeming to converge with mechanical engineering, since the molecules
being designed often resemble small machines. A general theory of molecular mechanosynthesis
to parallel that of photosynthesis and chemosynthesis
(both used by living things) is the ultimate goal of the field. This may lead
to a molecular assembler, according to some, such as
K.
Eric Drexler, Ralph Merkle, and Robert
Freitas, and of the potential for integrating vast numbers of assemblers
into a kg-scale nanofactory.
Molecular engineering is sometimes called generically
"nanotechnology", in reference to the nanometre
scale at which its basic processes must operate. That term is considered to be
vague, however, due to misappropriation of the word in association with other
techniques, such as X-ray lithography, that are not used to create new
free-floating ions or molecules.
Future developments in molecular engineering hold out the
promise of great benefits, as well as great risks. See the nanotechnology
article for an extensive discussion of the more speculative aspects of the
technology. Of these, the one that sparks the most controversy is that of the molecular assembler.
A 2013 paper published in the journal Science details a new method of synthesizing
a peptide in a sequence-specific manner by using an artificial molecular
machine that is guided by a molecular strand. This functions in the same way as
a ribosome building proteins by assembling amino acids according to a messenger
RNA blueprint. The structure of the machine is based on a rotaxane, which
is a molecular ring sliding along a molecular axle. The ring carries a thiolate group
which removes amino acids in sequence from the axle, transferring them to a
peptide assembly site.
In two dimensions
The study and fabrication of molecular-precise
architectures confined at interfaces (i.e., molecular thick architectures) has
rapidly emerged as a scientific approach towards supramolecular and molecular
engineering. The fabrication step of such architectures (often referred as molecular self-assembly depending on the
deposition process and interactions involved) relies in the use of solid
interfaces to create adsorbed monolayers. Just recently, have such
two-dimensional (or "on-surface") chemistry and physics yielded
large-scale molecular-precise structures of technological relevance. Albeit
spatial control and working devices remain to be evidenced in the field,
predictive (computational) models[5]
as well as advances in the thermo- and photo- chemical physics of monolayers
are expected to bring the field to technology within the next 10 years.
It is worth noting that the ansatz of a molecular assembler or STM manipulation
experiments aim at achieving atom-by-atom fabrication, i.e. fabrication with
resolutions of ca. 3Åx3Åx3Å. On the other hand (2D) on-surface molecular
engineering will be intrinsically limited to the size of the molecules which
are capable of encoding complex physico-chemical information. This might be
considered a technique having a maximum resolution of ca. 20Åx20Åx3Å. In
contrast, state-of-the art lithography methods, a form of less-precise
molecular engineering, is expected to achieve a resolution of 50Åx50Åx50Å by
2016.
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