From: Nikolay Igorovich Rodionov <nirodion@syr.edu>

Date: May 21, 2012 12:43:34 PM PDT

To: Eric Pettersen <pett@cgl.ucsf.edu>

Subject: RE: [Chimera-users] ESP calculations

Thank you both,

Can either of you tell me how the information in a volume data set is organized? I am looking at a .dx file that I created using APBS which I would assume to be very similar to the volumetric data sets created by Chimera. What does each column of data represent? Is there any way for me to sort the ESP data based on position using Excel or Matlab? I am only concerned with ESP data for one region of molecule.  If you could point me in the direction of some good documentation on this file type it would be great.

Thanks again,
Nikolay Rodionov

-----Original Message-----
From: Eric Pettersen [mailto:pett@cgl.ucsf.edu]
Sent: Monday, May 21, 2012 2:57 PM
To: chimera-users@cgl.ucsf.edu BB
Cc: Nikolay Igorovich Rodionov
Subject: Re: [Chimera-users] ESP calculations

Also, if you compute a volume, you can use the "Values at Atom Positions" tool to, um, get the values at atom positions (say, a ligand), if that's relevant to what you're doing.

--Eric

On May 21, 2012, at 9:09 AM, Elaine Meng wrote:

Hi Nikolay,

You can generate a grid of values with the "Compute grid" option of

Coulombic Surface Coloring (or corresponding option of the "coulombic"

command).  The grid is a volume data set, and when it is generated the

Volume Viewer  and Surface Color dialogs will automatically appear.

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/coulombic/co

ulombic.html

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/coulombic/co

ulombic.html#volume

You can save the grid to a file with the FIle menu of Volume Viewer.

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/volumeviewer

/framevolumeviewer.html

As for the values at each point of the surface, I don't know of a way

to write these all to a file, but in Surface Color if you click the

Options button and then turn on the option to "Report value at mouse

position" it will report the values in the status line at the bottom

of the Chimera window when you click into the graphics window and then

mouse over the surface. I just noticed that to make this work it is

necessary to recolor the surface first by clicking the Color button on

this dialog, which may be a bug, but that's the workaround!

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/surfcolor/su

rfcolor.html

If you have the grid file saved you can reopen it in Chimera later and

use it in Surface Color without rerunning the ESP calculation.

However, keep in mind that Coulombic ESP is more for qualitative

purposes of visualization or making comparisons between related

structures than for absolute quantitative accuracy.  For example, you

could easily make all the ESP values half as large simply by doubling

the dielectric constant used in their calculation, as shown in the

equation in the Coulombic Surface Coloring manual page.

I hope this helps,

Elaine

----------

Elaine C. Meng, Ph.D.

UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab Department

of Pharmaceutical Chemistry University of California, San Francisco

On May 21, 2012, at 8:05 AM, Nikolay Igorovich Rodionov wrote:

Hi all,

I was wondering if there was a way to get an output data file

regarding ESP coloring and calculations based on Coulomb's law. The

visualization is great but I would also like to quantify the data.

Thank you,

Nikolay Rodionov

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