Chemistry Reference
In-Depth Information
Figure 3.7 pH profile of k
o
for the hydrolysis
of albumin (S
o
= 1.50
10
-6
M
)by
[Im
C
]
22
PCD
MeO
at 25
8
C(C
o
= 0.115
M
: hereafter,
C
o
for a heterogeneous catalyst represents the
total concentration of the catalytic center or the
catalytic module attainable when the catalyst is
assumed to be dissolved).
Polymer [Im
C
]
22
PCD was effective in hydrolyzing albumin, manifesting optimum
activity at pH 7-9 (Figure 3.7). The highest k
o
shown in Figure 3.7 corresponds to a
half-life of 20 min at pH 7 and 25
8
C. Proteolytic activity was reduced markedly (Figure
3.8) when the imidazole content attached via C-2 is lowered from 22 to 5 residue mol%
or when imidazole was attached via the N atom. This indicates that the active site on
[Im
C
]
22
PCD
MeO
contains two or more imidazole moieties. Eq. (7) presents a mechan-
ism consistent with the catalytic action of two imidazoles with unalkylated N atoms
and with the pH profile of Figure 3.7.
ð
7
Þ
Figure 3.8 Comparison of k
o
for the hydrolysis of
albumin (S
o
= 1.50
10
-6
M
) by [Im
C
]
22
PCD
MeO
(C-
22), [Im
C
]
5
PCD
MeO
(C-5), [Im
N
]
16
PCD
MeO
(N-16),
and [Im
N
]
63
PCD
MeO
(N-63) (C
o
= 0.115
M
)atpH
7.00 and 25
8
C. In the nomenclature of the cata-
lysts, superscript C or N indicates that imidazole
was attached via the C or N atom, respectively, and
the subscript is the residue mol% content of
imidazole attached to PCD.
