Semi-empirical AM-1 Studies on Porphyrin - Modern Trends in Chemistry and Chemical Engineering - page 134

Table 9.4. (Continued)

Atom Mulliken Atomic ZDO Atomic

charge

Atom Mulliken Atomic

Charges

ZDO Atomic charge

Charges

9 C -0.0499 -0.0019 28 H 0.2077 0.1436

10 C 0.1044 0.0905 29 H 0.2112 0.1469

11 C -0.2314 -0.1878 30 H 0.2077 0.1436

12 C 0.0474 0.0356 31 H 0.2304 0.1615

13 N -0.2389 -0.2031 32 H 0.2304 0.1615

14 C -0.0818 -0.0865 33 H 0.2192 0.1527

15 C -0.0499 -0.0019 34 H 0.2175 0.1515

16 C -0.043 -0.058 35 H 0.2197 0.1534

17 C -0.1994 -0.1339 36 H 0.2197 0.1534

18 C -0.1994 -0.1339 37 H 0.2192 0.1527

19 C -0.2472 -0.1829 38 H 0.2175 0.1515

A look on the Table 9.3 reveals that the centers N-1, N-3, and N-7, N-13, and
C-8, C-14, and C-9, C-15, and C-5, C-11,C-17, C-18, and C-4, C-10, and C-6, C-12,
and C-2, C-16, and C-19, C-23, and C-20, C-24, and C-21, C-22 are almost equal in
their f + (r), f 0 (r), and f - (r) value. The local softnesses of the centers are also following
the similar trend of variation. A deeper study on the Table 9.3 reveals that the center
N-1, N-3 are lowest and C-5, C-11, C-17, C-18 have the highest f + (r) and s + value and
the trans pair, N-1 and N-3 have the lowest and C-2, C-16 have the highest f - (r) and
s - value.
Thus, it is clear from the above discussions that the local softness and Fukui func-
tions are not useful for the study of the bio-interaction between the donor sites of the
porphyrin ring and the metal ion. The failure of the Fukui function for the study of the
softest and hardest regions of some soft and hard molecule was reported by Torrent-
Sucarrat, Proft, Geerlings, and Ayers [43].
It is well known to us that the four coordination number of Fe (II) (in case of hemo-
globin) is satisfi ed by four N atoms of the macromolecule, which are not the maximum
reactive site according to their Fukui function and local softness values in that mol-
ecule. We found the suggestion of Mendez and Gazquez [14] where it was stated that
the interaction between two molecules will occur not necessarily through their softest
atoms but rather through those atoms whose Fukui functions are the same. Parr and
Yang [27] previously showed that the interactions between two molecules say A and B
having atoms, a 1 , a 2, and so on and b 1 , b 2 , and so on does not necessarily occur through
the softest atom of A and B (say a 1 for A and b 1 for B) but through those atom of A and
B (say a 2 for A, and b 2 for B) whose Fukui functions [say f (a 2 ) and f (b 2 )] are approxi-
mately close to each other, that is, f (a 2 ) ≈ f (b 2 ). If we consider the example of heme