Page 568 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Reactions on Polymers 531

Considering only Lewis acid–base or donor–acceptor interactions we can envision a hydrogen
bond donor site such as an alcohol, acid, thiol, or amine and an acceptor site such as a carbonyl oxy-
gen on another molecule or part of the molecule. These components will bind with one another, act-
ing to bind either the molecules containing the two differing bonding sites or if the two sites are on
the same molecule attempt to contort, twist the molecule allowing the preferred bonding to occur.
Synthetic shapes are generally limited to sheets and polyhedral structures. Yet nature produces a
much wider variety of shapes, including curves, spirals, ripples, bowls, pores, tunnels, spheres, and
circles. We are beginning to master such shapes. We are beginning to make these shapes based on
especially “grown” shapes that act as templates for further growth. For instance, Geofreey Ozin and
coworkers mixed together alumina, phosphoric, and decylamine in an aqueous solution of tetraeth-
ylene glocol. After a few days, millimeter-sized aluminophosphate solid spheres and hollow shells
were formed with the surfaces sculpted into patterns of pores, meshes, ripples, bowls, and so on. A
decylammonium dihydrogenphosphate liquid–crystal phase was formed and this surfactant, along
with the glycol, was forming bilayer vesicles. The vesicles acted in different ways with some fusing
to one another, others splitting apart or collapsing giving a variety of structures. Thus, appropriate
conditions can be selected that favor certain template structures producing an array of geometric
structures. Further, the templates themselves can be used to make selective separations. In a related
study, the group employed a silica precursor, tetraethyl orthosilicate. Here the orthosilicate units
assembled together forming micelles that in turn acted as liquid-seed crystals growing other assem-
blies with varying shapes. Rapid growth in the axial direction produces rope-like structures that can
be made to form circles and loops through application of external forces. Other structures included
egg shapes, disks, spirals, knots, and spheres.
Metal coordination is another important bonding opportunity with respect to self-assembly. This
is important in many natural molecules such as hemoglobin and chlorophyll where the metal atom
acts as both the site of activity and as a “centralizing” agent with respect to shape and thus acts as
a nucleating agent for self-assembly.
Numerous metal chelating designs can be envisioned. Structure 16.19 is one made by Daniel
Funeriu and coworkers. The end structure is dependent upon the nature of the metal. For instance, a
wreath-shaped double-helical complex is formed when FeCl is added with each wreath containing
2
five iron ions with each iron having three bonding sites. Further, the wreath size is such that it will

selectively bind the chloride or other similarly sized ions because the source of the iron is the iron
chloride. The ratio of reactants is also important and by varying the ratio different structures can be
formed, including wire and tape-like structures. Again, it is up to the researcher to utilize informa-
tion at hand to construct these self-assemblies.

R
R
N
N N
O
O

N
N
(16.19)
N
N

O
O
N N N N

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