[Chimera-users] calculation of volume

[Navnit Kumar Mishra]

Dear Tom;

Thank you very much for your reply and pointing out the overlap van der 
waals issue. One thing how much the issue is concerned if I am using one 
receptor against a series of small ligand. I am intrested to estimate 
the entropy by using the ratio between total molecular volume to van der 
Waals volume.

As you suggested to measure the compactness which would give the 
compactness of surface protein, it would not estimate the changes in the 
inside of the protein. I would be thankful for any help.

with regards,
Navnit



Tom Goddard wrote:

> Hi Navnit,
>
>  Not sure what you mean by "vdw volume".  I guess you mean the volume 
> within the vdw surface.  That's not just the sum of the spherical atom 
> volumes since those atom spheres overlap, so the calculation is not 
> trivial.
>
>  Perhaps the following will serve as a useful measure of 
> "compactness".  Divide the solvent excluded surface enclosed volume by 
> the solvent excluded surface area.  This gives a value with units of 
> distance, a kind of mean radius quantifying the curvature of the 
> surface.  For a given volume a sphere will give the largest value, 
> while a shape with many protrusions will give a smaller value.  The 
> larger the value the more sphere-like (globular) the shape.
>
>    Tom
>