Subject: MOPAC Cu Complex questions

From: Eric Billings <[email-masked]>
Date: Tue, 15 Nov 1994 14:40:19 -0500 (EST)

Hello fellow netters:

We have been using MOPAC (AM1 hamiltonian) to generate partial
charges on a tetradentate dinegative ligand that has a metal
binding site and a separate protonation site (an amine).  The
ligand has one plane of symmetry.  We have used sparkles to
mimic the charge polarization of the metal center since we have
been unable to locate parameters for copper (I and II).

                /CH2-C=O
      +    CH2-NH    O
    H3N \ /     \   /
         C       Cu(I/II)
    H3C / \     /   \
           CH2-NH    O
                \CH2-C=O

We have two questions:
1. Are there MOPAC parameters for Cu I and II available ?
2. Can anyone help explain why MOPAC is able to converge in
   three of the four cases below - but fail on the fourth.

We have found the following:
1. When the ++ sparkle is used, and the protonation site is
protonated (-NH3+) the set of partial charges obtained reflects
the symmetry of the ligand. (Total molecular charge: +1)

2. When the ++ sparkle is used, and the protonation site is
unprotonated (-NH2) the set of partial charges obtained reflects
the symmetry of the ligand. (Total molecular charge: 0)

3.When a + sparkle is used, and the protonation site is protonated,
a set of charges is obtained which also properly reflects ligand
symmetry. (Total molecular charge: 0)

4. However, when a + sparkle and no protonation is used, MOPAC
cannot converge with a total molecular charge: -1.  However, if
CHARGE=-0.999 is used, convergence is achieved with questionable
results.  Specifically, the partial charges do not reflect the
symmetry of the molecule.  This result appears to be chemically
unreasonable.

In addition, the assymetry of the partial charges in (4) can be
reversed simply by rotating the -NH2 group around its C-N axis.
We would appreciate suggestions about any fixes for this problem,
or  discussion about the result.

Please respond to me directly and I'll summarize if folks are
interested.  We've included the input file for the difficult
case below.
 Thanks !!!   - Eric

Eric Billings
Biophysics Grad Student
UCONN
[email-masked]

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Here's the file that converges with CHARGE=-0.999 (but not -1)
and produces the asymmetric charges.
-------------------------------------------------------------------
GRAPH UHF CHARGE=-0.999 AM1 1SCF
INSIGHT generated AMPAC/MOPAC input file
DATE: Fri Nov  4 15:19:28 1994
 +    0.000000 0    0.000000 0    0.000000 0  0  0  0
 O    3.945394 0    0.000000 0    0.000000 0  1  0  0
 N    1.988805 0   63.980175 0    0.000000 0  1  2  0
 C    1.243780 0   21.286814 0   11.840311 0  2  3  1
 C    2.483390 0   95.464783 0  177.089172 0  3  1  4
 C    2.741488 0  155.718201 0  172.258453 0  1  3  4
 O    2.069859 0   98.706131 0  -90.481331 0  1  3  4
 O    1.959568 0   83.935295 0   97.237152 0  1  3  7
 O    1.954638 0  172.158951 0   76.167824 0  1  3  8
 O    1.222477 0  123.999367 0  178.865356 0  6  9  1
 N    1.998371 0   95.456062 0  166.698486 0  1  3  8
 N    1.512800 0  138.539734 0 -136.269485 0  5  3  1
 C    1.476681 0  104.733261 0 -164.992844 0  3  1 11
 C    1.468735 0  117.143456 0  -38.470036 0  3  1 11
 C    1.529775 0  112.715981 0  -70.285004 0  5 14  3
 C    1.519738 0  116.683731 0   -1.443380 0  6  9  1
 C    1.516491 0  112.850174 0   59.862339 0  5 14  3
 H    0.847857 0  105.924355 0   85.132477 0  3  1 11
 H    0.852142 0  104.861160 0  -84.707642 0 11  1  3
 H    0.971031 0  110.465836 0  -54.648548 0 12  5 14
 H    0.898043 0  112.369568 0 -179.796890 0 12  5 14
 H    0.939738 0  109.942955 0   74.964302 0 13  3  1
 H    0.869576 0  109.047089 0 -157.552032 0 13  3  1
 H    0.983221 0  107.203888 0  -61.799381 0 14  3  1
 H    0.912557 0  110.428726 0  176.152573 0 14  3  1
 H    0.931023 0  109.966446 0  -49.515186 0 15  5 14
 H    0.900946 0  110.653557 0 -169.862305 0 15  5 14
 H    0.944812 0  109.929031 0  -90.911400 0 16 11  1
 H    0.881151 0  109.577477 0  148.162247 0 16 11  1
 H    0.930954 0  112.317932 0  -61.163052 0 17  5 14
 H    0.964762 0  109.814117 0   55.678158 0 17  5 14
 H    1.001573 0  109.777176 0  175.788788 0 17  5 14
 H    0.942113 0  106.874374 0 -179.980927 0  7  1  3
 H    1.210611 0  104.268616 0   69.931961 0  7  1  3
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