Chemistry Reference
In-Depth Information
faced by humanity. Such practices not only produce a positive return on the investment
that society has made to chemistry research but also prompt chemists to seek a deeper
understanding of how their molecules/materials behave in “real environments” as
opposed to modeled environments such as a homogenous solution in a beaker.
In much of the last two decades of foldamer chemistry, chemists spent their time look-
ing for different ways to generate synthetic analogues of biofoldamers [1-7]. It is
extremely exciting to see that chemists, using their imagination and creativity, can prepare
abiotic molecules that resemble proteins and nucleic acids in conformational order.
Ifnaturecanuse20aminoacidsandfournucleotide bases to create the exquisite and
essentially limitless structures and functions with biofoldamers, what vast potential have
chemists when the genetic and biological constraints are removed? Helices, single and
multiple strands, turns, and sheets have all been realized in synthetic foldamers in this
quest [1-7]. Foldamers with quaternary structures have been made via the bottom-up
approach [8-10]. As the quest continues, however, chemists are no longer satisfied with
mere new foldameric structures. Instead, the question of increasing importance becomes
“what can the new foldamer do?” Numerous chemists have answered to such challenges
and created many useful materials out of foldamers, including antimicrobial materials
[11-15], protein surface-binders and inhibitors [16-19], vesicles [20], organogellators
[20], and enantioselective catalysts [21].
It is natural for a curious reader to wonder at this point what benefits foldamers can
offer as a class of materials, in terms of both structure and function. According to one
advanced organic text, “conformations are the different shapes that a molecule can attain
without breaking any covalent bonds [22].” These shapes, of course, are the results of
many rotations around the s bonds within the molecule. IUPAC puts it another way: con-
formations are “the spatial arrangement of the atoms affording distinction between stereo-
isomers which can be interconverted by rotations about formally single bonds [23].” To a
chemist, both definitions are illuminating, as the shape of a molecule can strongly influ-
ence its physical properties, and the spatial arrangement of the atoms in a molecule deter-
mines its three-dimensional distribution of functional groups and, in turn, the chemical
and physical properties of the molecule. Clearly, if chemists can master the skill to control
the conformation of a molecule, they can unlock the secrets in “taming” the molecule and
potentially can regulate its physical and chemical behavior on demand. Moreover, since
the interconversion between different conformers is often strongly influenced by their
environment, conformational control serves as a rational way to design environmentally
responsive materials. Cells rely on such responsiveness of proteins and nucleic acids to
survive and adapt, whether to temperature, pH, nutrients, or specific signal molecules.
Chemists collectively have just begun to design such functions through the approach of
conformational control.
What do metal ions bring to this picture? We may catch a glimpse of the answer by
looking into the metalloproteins, nature's examples of metallofoldamers. The earlier
chapters of this topic have extensive discussionsonthistopic.Inbrief,metalionscan
bring profound influence to both the structure and the function of a foldamer. Metal ions
tend to have their preferred coordination patterns. Because of the potentially strong
metal-ligand interactions, metal ions may overwhelm other factors or at least play a sig-
nificant role in determining the conformation of a foldamer. Moreover, metal ions can
possess electronic, photonic, or catalytic properties not found in the organic backbone of
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