Chemistry Reference
In-Depth Information
Fig. 9 Electrostatic potentials of AMCHA as computed in the indicated surroundings. All
geometries were optimized in the respective environment
arises whether such differences can be measured experimentally. According to
Luger, the experimental uncertainties are about 0.1 e/
˚
3
for EDs and 4-5 e/
˚
5
for Laplacians [
24
]. In the calculations, the largest absolute differences are found
for the
l
3
curvature of the C-O2 bond. The computations predict 25.3 e/
˚
5
for the
p/p environment, while 29.7 e/
˚
5
is computed for c/c. This difference is just as
large as the experimental error bars. Taking into account that the determination
of EDs in protein crystals is substantially more difficult, it is obvious that this
difference is presently much too small to be detected experimentally. Note that all
other differences are even smaller. In summary, experimental EDs of the reversible
inhibitor-enzyme complex between AMCHA and K1
Pg
and of the AMCHA-crystal
are predicted to be virtually identical. This is also seen if the contour plots (Figs.
7
and
8
) and the ESPs (Figs.
9
and
10
) of the c/c and the p/p situation are compared.
While the c/c and p/p situations are essentially identical, larger differences are
seen if both datasets are compared with pure gas phase results (g/g). Let us
concentrate on the C-O1 bond that forms two salt bridges within crystal and protein
environments. The
l
3
values obtained for the p/p and the g/g situation differ by
about 20% (Table
9
). If the ED is computed at the protein geometry for a gas phase
