Biomedical Engineering Reference
In-Depth Information
Table 2. Continued
Form of poly(
γ
-glutamic acid)
a
Instrumental analysis
H
+
Na
+
K
+
NH
4
+
Ca
2+
Mg
2+
34.01
39.74
39.68
39.60
γ CH
2
CO
182.21
182.11
182.16
182.12
COO
-
182.69
185.46
185.82
185.16
FT-IR absorption (KBr), cm
-1
C=O, stretch
1739
Amide I, N-H bending
1643
1643
1622
1654
Amide II, stretch
1585
C=O, symmetric stretch
1454
1402
1395
1412
1411
C-N, stretch
1162
1131
1139
1116
1089
N-H, oop bending
698
707
685
669
616
O-H, stretch
3449
3436
3443
3415
3402
Thermal analysis:
Hydrated water (%)
0
10
42
20
40
Dehydration temp. (°C)
109
139
110
122
Melting point (°C) 206 160 193, 238 219 160
Decomposition temp. (
°
C)
209.8 340 341 223 335.7 331.8
a
Molecular weight (kDa) of H-form=1.23 x 10
6
, Na-form=1.23 x 10
6
, K-form=0.98 x 10
6
, NH
4
-form=0.89 x
10
6
, Ca-form=0.49 x 10
6
, Mg-form=0.89 x 10
6
.
2.3. Structural Characteristics
The monomer glutamic acid in γ-PGA possesses three chemically-active functional
groups in the following order of reactivity: α-NH
2
> α-COOH > γ-COOH. In a chemical-
catalyzed polymerization of glutamic acid, the condensation occurs between the α-COOH
and α-NH
2
groups, resulting in the formation of poly(α-glutamic acid) through α-peptide
linkages. However, in the submerged fermentation process, a portion of L-glutamic acid is
enzymatically racemized to D-glutamic acid and eventually both D- and L- glutamic acids
are co-polymerized through a novel γ-peptide bonding between a less reactive γ-COOH and
α-NH
2
groups to form poly(γ-D,L-glutamic acid). An α-peptide bond, which is normally
found in protein structures, can be easily decomposed by most of the protease enzymes,
whereas γ-peptide bond can be hydrolyzed only by a rarely available γ-
glutamyltranspeptidase and γ-PGA is thus considerably resistant to microbial attack
[5,14,15]. Likewise, poly(γ-glutamic acid) contains four intramolecular hydrogen bonds
