Biomedical Engineering Reference
In-Depth Information
backbone along with free amino- and carboxylic groups in either end of the molecule. The
most favorable configuration of the peptide is with two side-chains sticking out on opposite
sides. However, when both side-chains possess hydrophobic properties, it is
thermodynamically favorable to have them both on the same side of the peptide backbone,
thereby facilitating the shielding of these hydrophobic regions. Figure 2b provides the
structure of the nanotube formed by this monomer and Figure 2c compares the position of
the monomers in the nanotubes and nanofibers.
The nanotubes are formed in solution by the addition of the peptide monomers to water,
whereas the nanofibers are grown from an amorphous peptide film on a substrate in an
aniline vapor. To form nanoparticles with this particular monomer, a tertbutoxycarbonyl
group is attached to the amino group of the dipeptide (Adler-Abramovich & Gazit, 2008).
When these modified dipeptides are emerged into a mixture of ethanol and water the
nanoparticles are formed within minutes.
Fig. 3. SEM images of the three different structures that can be obtained from dipeptide
diphenylalanine. Right) The nanotubes are formed in aqueous solution. Top) The peptide
nanofibers that are grown from an amorphous film in an aniline vapor. Left) Nanoparticles
formed from a modified version of the peptide monomer where the amino group is
protected by a Boc group. The scale bar in the images corresponds to 1 µm.
Figure 3 illustrates the structure of the nanotubes formed by the diphenylalanine dipeptides.
On the left one can see an image of how these smaller nanotubes assemble into larger
microcrystals with radii up to a couple of micrometers. Both scale bars correspond to 1 µm
and hence the single nanotube formed from diphenylalanine has a diameter around 200 nm.
The top image presents a SEM image of the peptide fibers grown from a substrate. Here, it
can be seen that the nanofibers are somewhat similar in width and length (both depend on
the condition during formation). Finally, the right image shows the nanoparticles formed
from the Boc modified diphenylalanine. The size of these spherical nanoparticles ranges
from 50 nm to hundreds of nanometers.
All of the organization processes mentioned above are driven by entropy through
hydrophobic - hydrophilic interactions and are further stabilized by hydrogen bonding
