Chemistry Reference
In-Depth Information
F
F
n-Pr
0.719
0.731
B
O
N
1.287
1.563
1.405
Ph
1.197
S
Me
FIGURE 4.3
Nonmetallic organic complex.
calculated to be 0.657 and the calculated value of the net charges for the nitrogen
atoms was −0.26. Lacking carbon atoms (see also Table 4.1), cisplatin is considered
here an inorganic-metallic
complex.
In (hypothetical?) double-hydrated [(H
2
O)
2
M]
+n
cations, one computes B
=
0.258
for the Ca-O bond (
n
=
+
2), B
=
0.253 for the Cu-O bond (
n
=
+
1) and B
=
0.599
for the Fe-O bond (
n
=
+
2). According to Table 4.1, these species are also
inorganic- metallic
complexes.
Figure 4.3 shows a structure that was recently synthesized (Zhang et al. 2009).
This figure presents the calculated values of the bond orders of the planar chemical
bonds in cycle. We note the existence of both coordinative and aromatic bonds. The
nitrogen, boron, oxygen, fluorine, and sulfur-containing compound in Figure 4.3 is
lacking metal atoms; therefore, it is considered here an organic complex.
4.3 EXAMPLES OF DESCRIPTORS
The number of molecular characteristics that can be calculated (descriptors) is huge,
and the number of formula and calculation procedures (methods) that are developed
is growing fast. In the last 60 years, the number of descriptors in the “whole mol-
ecule” category has grown by 1 per month on average, and the number of descriptors
in the “topological indices” category has grown by 1 per week on average. Even the
number of categories (classes) of descriptors is large; there are tens of descriptor
classes today.
There are many works that present a large number of descriptor categories
(Rekker and Mannhold 1992; Karelson 2000; Tarko 2008b; Verma et al. 2010). The
Sections 4.3.5, 4.3.6, 4.3.7, 4.3.8, 4.3.11, 4.3.13, 4.3.14 and 4.3.16 include formulas
and paragraphs reproduced from Tarko 2008b. A very useful source of information
is the documentation of programs for QSPR/QSAR computations. The appendix of
this chapter lists almost 400 whole molecule descriptors computed by the PRECLAV
software (Tarko 2005). COmprehensive DEscriptors for Structural and Statistical
Analysis (CODESSA) computes about 1000 whole molecule descriptors (Murugan
et al. 1994). DRAGON
®
is one of the best-known applications for the calculation of
molecular descriptors. The latest version, 6.0, calculates 4885 descriptors and can
work both in graphical and command-line interfaces (for batch processing of large
datasets). The extension for the KNIME platform (
http://www.knime.org
)
is now
available, so that DRAGON can be easily used inside complex workflows. DRAGON
