Quoting Carlos Jaime <carlos.jaime.uab.es>:
> When working with fluorine compunds, we realized that averaging two
> conformers, the fluorine atoms got a charge almost zero. We checked the
> behaviour of the RESP program with individual conformations and is
> working properly, but as soon as we are using more than one conformer,
> the charges are greatly reduced and several values are finally near zero.
> We were really surprised and we started to search through the RESP code.
> We found thet RESP do not average charges but average the molecular
> electrostatic potentials. This means that the average of the meps of two
> conformers that are enantiomeric is almost null, and atomic charges are
> then also almost zero.
I calculated RESP charges (keeping the mol. orientation generated by Gaussian).
for the 2 enantiomers of:
Me
H-C~F
Br
This couple of enantio. presents as advantage that a single conf. is possible.
See below. Fitting two enantios together i.e. by considering them like
conformations seems to work...
Regards, Francois
- Enantio-1:
.<TRIPOS>MOLECULE
UNK
8 7 1 0 1
SMALL
USER_CHARGES
.<TRIPOS>ATOM
1 C1 0.403146 0.111616 0.385438 C 1 UNK 0.1555
2 H1 0.423120 0.222436 1.455812 H 1 UNK 0.1346
3 F13 0.809035 1.274305 -0.165085 F 1 UNK -0.1907
4 CL12 -1.309102 -0.142930 -0.054943 CL 1 UNK -0.1766
5 C2 1.274686 -1.014023 -0.109894 C 1 UNK -0.1588
6 H21 2.302537 -0.802990 0.163914 H 1 UNK 0.0787
7 H22 0.974964 -1.954229 0.334145 H 1 UNK 0.0787
8 H23 1.205813 -1.089714 -1.187347 H 1 UNK 0.0787
.<TRIPOS>BOND
1 1 2 1
2 1 3 1
3 1 4 1
4 1 5 1
5 5 6 1
6 5 7 1
7 5 8 1
.<TRIPOS>SUBSTRUCTURE
1 UNK 1 **** 0 **** ****
- Enantio-2:
.<TRIPOS>MOLECULE
UNK
8 7 1 0 1
SMALL
USER_CHARGES
.<TRIPOS>ATOM
1 C1 -0.403146 0.111616 0.385435 C 1 UNK 0.1590
2 H1 -0.423122 0.222437 1.455809 H 1 UNK 0.1343
3 F13 -0.809036 1.274306 -0.165084 F 1 UNK -0.1914
4 CL12 1.309104 -0.142930 -0.054942 CL 1 UNK -0.1774
5 C2 -1.274688 -1.014023 -0.109894 C 1 UNK -0.1645
6 H21 -0.974975 -1.954229 0.334154 H 1 UNK 0.0800
7 H22 -2.302541 -0.802984 0.163903 H 1 UNK 0.0800
8 H23 -1.205805 -1.089722 -1.187345 H 1 UNK 0.0800
.<TRIPOS>BOND
1 1 2 1
2 1 3 1
3 1 4 1
4 1 5 1
5 5 6 1
6 5 7 1
7 5 8 1
.<TRIPOS>SUBSTRUCTURE
1 UNK 1 **** 0 **** ****
The diff. in charge observed between the 2 enantio. come from the mol.
orientation of the opt. structure which is different in the 2 enantio. This
diff. becomes = 0 if you use the rigid body orientation algo. implemented in
R.E.D.
- Enantios-1+2:
.<TRIPOS>MOLECULE
UNK
8 7 1 0 1
SMALL
USER_CHARGES
.<TRIPOS>ATOM
1 C1 0.403146 0.111616 0.385438 C 1 UNK 0.1473
2 H1 0.423120 0.222436 1.455812 H 1 UNK 0.1375
3 F13 0.809035 1.274305 -0.165085 F 1 UNK -0.1835
4 CL12 -1.309102 -0.142930 -0.054943 CL 1 UNK -0.1794
5 C2 1.274686 -1.014023 -0.109894 C 1 UNK -0.1635
6 H21 2.302537 -0.802990 0.163914 H 1 UNK 0.0805
7 H22 0.974964 -1.954229 0.334145 H 1 UNK 0.0805
8 H23 1.205813 -1.089714 -1.187347 H 1 UNK 0.0805
.<TRIPOS>BOND
1 1 2 1
2 1 3 1
3 1 4 1
4 1 5 1
5 5 6 1
6 5 7 1
7 5 8 1
.<TRIPOS>SUBSTRUCTURE
1 UNK 1 **** 0 **** ****
.<TRIPOS>MOLECULE
UNK
8 7 1 0 1
SMALL
USER_CHARGES
.<TRIPOS>ATOM
1 C1 -0.403146 0.111616 0.385435 C 1 UNK 0.1473
2 H1 -0.423122 0.222437 1.455809 H 1 UNK 0.1375
3 F13 -0.809036 1.274306 -0.165084 F 1 UNK -0.1835
4 CL12 1.309104 -0.142930 -0.054942 CL 1 UNK -0.1794
5 C2 -1.274688 -1.014023 -0.109894 C 1 UNK -0.1635
6 H21 -0.974975 -1.954229 0.334154 H 1 UNK 0.0805
7 H22 -2.302541 -0.802984 0.163903 H 1 UNK 0.0805
8 H23 -1.205805 -1.089722 -1.187345 H 1 UNK 0.0805
.<TRIPOS>BOND
1 1 2 1
2 1 3 1
3 1 4 1
4 1 5 1
5 5 6 1
6 5 7 1
7 5 8 1
.<TRIPOS>SUBSTRUCTURE
1 UNK 1 **** 0 **** ****
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Received on Tue Dec 06 2005 - 13:53:00 PST
