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Next: Conclusion Up: Acetylcholine : A Previous: Constraints

Results

A plot of the results of the static and relaxed calculations may be seen in Figures 4.5 and 4.6 respectively. The conformation corresponding to the crystal structure of acetylcholine chloride is shown as a + on the plot of the static results and points corresponding to experimentally identified conformations of acetylcholine, given in Table 4.1, are marked on the plot of the relaxed calculations.

  
Figure 4.5: Results of static calculations. The point corresponding to the conformation of the acetylcholine chloride crystal is marked as a `+'.

  
Figure 4.6: Results of relaxed calculations.

  
Table 4.1: Experimentally Observed Conformations of Acetylcholine

  
Figure 4.7: Plot of energy difference between static and relaxed calculations.

A plot of the energy differences between the static and relaxed calculations can be seen in Figure 4.7. Excluding high energy regions which are conformationally unimportant the average energy difference was 297.5 kcal per mole with a standard deviation of 13 kcal per mole.

The conformation of the crystal structure of acetylcholine chloride may be seen to lie within the vicinity of the global minimum of the static conformational energy map. It must be noted however that the experimental points do not in general lie near to this minimum.

The majority of the experimental points do lie near to local minima in the map of relaxed total energy. The exceptions to this are the points F and I, which have significantly different geometries to that of acetylcholine chloride. Therefore it is likely that the insufficient iterations were performed in the relaxation to find these states.

Conformation E is not found experimentally, however a detailed study by Froimowitz and Gans [15] found this minimum to be very narrow and hence conformationally unimportant.

The minimum energy structure calculated for the minimum about the point D2=180,D3=70 may be seen in Figure 4.8. This was found to have a conformation defined by the following dihedral angles:

This conformation has a energy of -3.55 kcal/mol relative to the minimum calculated energy on the relaxed conformational energy map.

  
Figure 4.8: The calculated minimum energy conformation of acetylcholine showing electron density isosurface.



next up previous contents
Next: Conclusion Up: Acetylcholine : A Previous: Constraints



Mr. Matthew D. Segall
Fri Jul 21 15:33:30 BST 1995