NANOTECHNOLOGY—TECHNOLOGY ON A MOLECULAR SCALE - Chemistry: Notable Research and Discoveries - page 41

Instead of gravity, electromagnetic forces are the major “players”
in the nanoworld. This is a different environment, which along with the
effects of quantum mechanics, means that materials can have different
properties in nanotechnology than they have in the macroscopic world.
As discussed in the remainder of the chapter, this can have advantages
as well as disadvantages.
As in all active areas of research, there are several approaches to the
development of nanotechnology. One approach involves techniques
similar to sculpting, where one starts with a large piece of material and
cuts away what is not needed. The problem is that a lot of the material
winds up wasted on the cutting room floor. An alternative approach,
described in the following section, starts at the bottom or lower end
of the scale and builds up from there. An important feature of this ap-
proach is the bonding of molecules to make even larger, more complex
molecules—supramolecular chemistry.
SuPrAMolECulArCHEMISTry
The previous chapter discussed covalent and ionic bonds. These are
strong chemical bonds formed when atoms share electrons, in the case
of covalent bonds, or transfer electrons, as in ionic bonds. A large por-
tion of chemistry textbooks are devoted to these chemical bonds, and
rightfully so, considering their importance in the formation of many of
the compounds and materials that people use. But there are other kinds
of bonds, generally referred to as noncovalent bonds, that are weaker
and often temporary, breaking and forming repeatedly. These bonds
play a vital role in certain materials and are the primary mechanisms
involved in supramolecular chemistry.
Many biological molecules, such as proteins, are large and have
complex structures. Proteins are composed of a sequence of units,
called amino acids, which are joined by a strong covalent bond known
as a peptide bond. But proteins also fold up into a certain shape, which
is vital to their function—a protein that loses its shape cannot fulfill its
function as an enzyme or a transporter. The sequence of amino acids
determines the shape; 20 different amino acids are found in proteins,
and each one has slightly different chemical and physical properties.
For example, some amino acids are hydrophilic, readily interacting