Chemistry Reference
In-Depth Information
Table 2 Glass transition temperatures of selected anhydrous and aqueous,
maximally freeze-concentrated excipients
T
g
(1C)
T
g
(anhydrous) (1C)
Glycerol
93
100
Ribose
10
47
Xylose
10
47
Arabinose
2
43
Sorbitol
3
Mannitol
11 (?)
28
Fructose
13
42
Glucose
39
43
Galactose
71
42
Sucrose
70
32
Maltose.H
2
O
70
29
Lactose
Cryst.
28
a,a-trehalose (anhydrous)
106
28
b,b-trehalose (anhydrous)
109
Raffinose (anhydrous)
109
26
24
Maltotriose
95
Stachyose (anhydrous)
132
24
Dextran
81
w
14
Byco A
a
113
14
Byco C
a
116
12
Byco O
a
139
15
12
b
Hydroxyethyl starch
39
b
Inulin
Hcit (anhydrous)
11
53
Hcit.H
2
O
25
Proline
68
Glycine betaine
98
Data from several sources.
a
Non-gelling gelatin fractions, as commercially supplied (Croda Chemicals Ltd.), without addi-
tional drying.
b
As commercially supplied, without additional drying.
temperatures, whereas the addition of glycerol (T
g
ΒΌ
1001C) may lower
the glass temperature to below the operating range of any condenser used
in commercially available freeze-driers.
As regards the reliability of the entries in Table 2, reasonable agree-
ment now exists between T
g
values reported in different publications. By
contrast, T
g
is often claimed to refer to a glass transition of the (implied)
anhydrous substance. In practice, this presents problems mainly arising
from residual water. The pre-1990 literature contains T
g
data that suffer
from more serious problems, arising from the water content of crystal-
line hydrates. Thus, trehalose is commercially supplied as a crystalline
dihydrate. When melted and rapidly quenched, it does not recrystallise,
but vitrifies. The reported T
g
of the glass, 701C, was for several years
cited as the glass transition of trehalose, although it was actually the
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