Chemistry Reference
In-Depth Information
Figure 3.5 Dependence on pH of the second-
order rate constant (k
2
) for the hydrolysis of the
heavy (
*
; curve b) and the light (
&
; curve a)
chains of
c
-globulin catalyzed by (Sal)
3
-PEI at
50
C.
8
The Sal
3
site contains three carboxyl and three phenol groups in addition to amino
groups provided by the polyethylenimine backbone. Since such functionalities are ac-
tive groups in enzymes, they might provide a catalytic module in Sal
3
-PEI. When Sal
3
-
PEI was incubated with
c
-globulin, protein degradation was observed by SDS-PAGE
electrophoresis (Figure 3.4). Kinetic data, collected by measuring the decrease in in-
tensity of the electrophoretic band, revealed a half-life as short as 1 h at pH 7 and 50
8
C
for this
-globulin degradation. When salicylates were attached to polyethylenimine
randomly, little catalytic activity was observed, indicating that the proteolytic activity
of Sal
3
-PEI arose from collaboration among proximal salicylates. The pH dependence
of the second-order rate constant (Figure 3.5) revealed optimum activity at pH 6-7.
Since carboxyl, phenol, and amino groups can all play catalytic roles at pH 6-7,
one cannot tell which of these functional groups is responsible for the proteolysis.
In the preparation of Sal
3
-PEI, each building block of the preassembled module is
linked to polyethylenimine by a single attachment. This would allow flexibility of the
catalytic moieties incorporated into the active site. Conversely, double attachment of
the building blocks preassembled by the scaffold to the polyethylenimine framework
may better conserve the original geometry of the preassembled module.
Highly effective host molecules for metal ions have been designed with 2,9-bis(bro-
momethyl)-1,10-phenanthroline (
2
) by the cross-linkage method [37]. By the reaction
c
2
