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82
Here, M
0
is the molecular weight of the monomer.
Examples:
Polymer
Monomer
Structure
Formula
M
0
(Da)
Cellulose
Amylose
D-glucose
C
6
H
10
O
5
162
Na-Alginate D-mannuronic acid
(M) and L-guluronic
acid
C
6
H
7
O
6
Na 198
Chitin
N-acetyl-
glucosamine
C
8
H
13
O
5
N 203
Note to table: H atoms linked to carbon atoms of the ring are not shown in the
figures.
The M
0
values for linked sugars are smaller than for the corresponding free
sugars (180 Da for D-glucose) due to the loss of a water molecule upon
forming a glycosidic linkage. However, this does not apply to the terminal
sugar (reducing end). Hence for a polymer of D-glucose the exact molecular
weight becomes:
M
=
DP
⋅
M
0
+
18
Exact molecular weights can be determined experimentally using mass
spectrometry, for example.
2.1.4. Polydispersity
Another inherent property of many biopolymers is polydispersity
26
. This
means that the sample is a mixture of different chain lengths. The reason may
either be that chains of different lengths are biosynthesized by the parent
26 IUPAC has deprecated the use of the term polydispersity index having replaced it with the term dispersity (Wikipedia 2013). In this
compendium we stick to the older nomenclature.
O
HOH
2
C
OH
HO
O
O
-
OOC
OH
HO
O
Na
O
HOH
2
C
NH
HO
O
O
CH
3