-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Francis,
ad [1]: if you are going for neutron diffraction, you probably want the ligand to have its hydrogens replaced with deuteria, rather than a 'heavy atom derivative' of your ligand. The scattering power for neutrons does not correlate with the weight of the nucleus und deuterium scatters as strongly as O,C, ... (see ITCr, Vol. C, Chapter 4.4) In that case you also do not need a difference map against the X-ray data because the scattering of X-rays by hydrogens can be neglected. ad [1b]: see [1]; remark: since we are doing science as opposed to math or philosophy, there is no 'unambiguity'. There is only a model for the experimental data which - depending on your means of validation - fits the data more or less well. ad [2]: That probably depends on whether your ligand site is fully occupied and whether the ligand is disordered or not. Cheers, Tim On 09/13/2011 09:01 PM, Francis E Reyes wrote: > Hi all > > Suppose you have a high resolution xtal structure (from usual x-ray > diffraction) and you wanted to verify the location of a ligand. You can > purchase a heavy atom isotope version of the ligand. > > [1] Is it possible to do a neutron diffraction difference map (where you > simply calculated Fobs(heavy) - Fobs(light) to verify the location of the > ligand? > > [1b] Suppose you couldn't measure the diffraction of the light version of the > ligand. Can the x-ray data be combined with the neutron diffraction of the > heavy atom isotope to unambiguously assign the ligand site? > > [2] What would be the minimum resolution required from the neutron > diffraction? (This is particularly important as you may be unable to grow > high diffracting crystals or large crystals) > > > Note that you don't necessarily want to solve the structure of the structure > from neutron diffraction from scratch, but rather you want to use it as a > tool to verify the location of a ligand binding site. > > > Thanks! > > F > > > > --------------------------------------------- > Francis E. Reyes M.Sc. > 215 UCB > University of Colorado at Boulder > - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFOcGZNUxlJ7aRr7hoRAgY1AKC7nvHVe3RwwWnIWHzm9tjbkZcsTgCcCAmW /RGhWn+QQTJ2ZQtTdozVY4E= =XmDf -----END PGP SIGNATURE-----
