Biomedical Engineering Reference
In-Depth Information
monomers (di-
p-
toluenesulfonic acid salts of bis-(α-amino acid) α,ω-alkylene diesters and di-
p
-nitro-
phenyl esters of diacids). The resulting functional AA-PEAs could have either free pendant -NH
2
, -OH
or -COOH, depending on the type of the new
Z
-amino acid-NCA monomer (Deng et al., 2009, 2011).
For example, if Lys is used (
Z
-Lys-NCA), the resulting AA-PEA copolymer would have pendant -NH
2
functionality. Note the difference in pendant functional group between the first and second copoly-
mer approaches even though the same Lys was used. The chemical structure of the functional AA-PEA
copolymers from the second copolymer approach (Figure 5.7) is quite different from the chemical struc-
ture of the functional AA-PEAs from the first copolymer approach. In the first copolymer approach
(Jokhadze et al., 2007), each of the two amino acids is distinctively located at two different blocks, for
example, Phe in one block and Lys in another block. In the second copolymer approach (Deng et al.,
2009, 2011), two amino acids are located in the same block and directly connected by a peptide bond,
and one of these two amino acids is also located in a separate block. Deng et al. (2009) reported that
the pendant -NH
2
group can be attached by a NHS-fluorescein, and the resulting dye-tagged AA-PEAs
exhibit fluorescence characteristic.
Glilies et al. also recently reported another method of synthesizing functional AA-PEAs with free
pendant amino groups (De Wit et al., 2008). They incorporated bis(l-lysine) R,ω-alkylene diester mono-
mer into the PEA, and the pendant amine group can be recovered after deprotection reaction. However,
the chemical structure of Glilies et al.'s functional AA-PEAs differs from that of Deng et al.'s in that the
two amino acids within the same block in the Glilies et al.'s study are separated by diacid spacer on the
AA-PEA backbone, while the two amino acids in the same block in the Deng et al.'s study are directly
connected via a peptide bond.
An effort to integrate saturated AA-SPEAs with unsaturated AA-UPEAs into one single entity was
recently reported and an example is shown in Figure 5.8 (Guo and Chu, 2007a), and the major advantage
of such an integration is to combine the merits of both saturated and unsaturated AA-PEAs into one sin-
gle entity via chemical linkages so that a wide range of physical, chemical, thermal, and biological prop-
erties could be obtained by simply changing the composition ratio of saturated to unsaturated AA-PEAs.
Beside ester and amide linkages in AA-PEAs, Guo and Chu (2007b, 2008, 2010) reported the addition
of ether linkage into AA-PEAs as shown in Figure 5.9. The resulting poly(ether ester amide) (AA-PEEA)
O
CH
2
O
CH
2
O
O
O
O
O
NH
4
m
NH
NH
NH
O
NH
O
4
n
-
m
2
2
O
O
O
CH
2
O
CH
2
NH
2
FIGURE 5.7
Chemical structure of the repeating unit of functional AA-PEAs synthesized via
ε-(benzyloxycarbonyl)-amino acid-
N
-carboxyanhydride (
Z
-amino acid-NCA) route (the second copolymer
approach as described above) (Deng et al., 2010).
O
O
O
CH
2
Ph
O
CH
2
Ph
O
NH
NH
O
O
NH
x
O
NH
O
O
O
O
CH
2
Ph
m
CH
2
Ph
n
FIGURE 5.8
The chemical structure of the repeating unit of saturated and unsaturated amino acid-based
poly(ester amide)s. (Adapted from Guo, K. and Chu, C.C., 2007a.
J. Polym. Sci. Polym. Chem. Ed
., 45: 1595-1606.)
