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Reinhard Maurer
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A Program to Calculate the Steric Size of Molecules about a Point in terms of their Cone Angles and Solid Angles, as well as their total Volumes and Projected Areas.
This program was originally written to calculate the solid angle represented by a molecule as seen from a point perspective according to a semi-analytical algorithm developed by White et al. (1993). Since then, not only has the semi-analytical algorithm undergone major changes (Taverner (1996)) to incorporate atomic overlaps of order greater than two, but several other calculations have been added. The original Cone Angle concept by Tolman has been incorporated. Vertex angle and Solid angle of bonded and non-bonded regions of overlap have been included. A fully numerical Solid angle can also be calculated, together with a fully numerical molecular volume. The molecular volume is not the only parameter, however, that is not dependent on a point of perspective. The new fully analytical molecular projection area is not dependant on a point perspective, but is dependant on a directional perspective. All the other calculations are applicable only to situations where the steric size of the molecule about a point is of interest.
Examples of such situations are:
Ligands about a metal atom.
Comparisons of different reaction sites in catalysts and small enzymes.
Steric effects in reaction rates for point reactions.
Steric effects in stereoselective synthesis.
Examples where the molecular volume is of interest:
Steric effects in molecular packing in the solid state.
Order-disorder phase transitions in crystals.
Host-Guest Inclusion Compounds.
Examples where the molecular orthogonal projection area is of interest:
Molecule-Surface interactions.
pi-Stacking interactions.
Further extensions to the above calculations were added with the radial profile calculation and the conformer average calculation. The radial profile calculation calculates the solid angle (or alternative steric parameter) of the intersection between the molecule and a sphere of a particular radius about the point of perspective. This is performed for a range of radii normally encompassing the entire molecule.
http://hobbes.gh.wits.ac.za/craig/steric/
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