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-Original Message-
From: Jacob Keller
Sender: CCP4 bulletin board
Date: Tue, 24 Jul 2012 12:55:31
To:
Reply-To: Jacob Keller
Subject: Re: [ccp4bb] How to identify unknow heavy atom??
Perhaps also exafs should be mentioned--I believe the various ion species,
redox states, and even binding geometry can be determined.
JPK
On Tue, Jul 24, 2012 at 12:37 PM, Roberts, Sue A - (suer) <
s...@email.arizona.edu> wrote:
> Hello
>
> Actually, if the home source uses a copper tube, neither copper nor zinc
> have much of an anomalous signal at that wavelength (the energy is below
> the absorption edge for both).
> The best way is to check the location of the absorption edge at the
> synchrotron. Cu+ and Cu++ can be distinguished this way, but make sure the
> absorption scan is done before you collect data since copper(II) can be
> photoreduced to copper(I) in the synchrotron x-ray beam. Whether or not
> you can get a clue from geometry depends upon the resolution of the
> structure.
>
> Sue
>
> On Jul 24, 2012, at 10:22 AM, Nat Echols wrote:
>
> > On Tue, Jul 24, 2012 at 10:14 AM, Haytham Wahba
> wrote:
> >> 1- if i have anomalous peak of unknown heavy atom, How can i identify
> this
> >> heavy atom in general. (different methods)
> >>
> >> 2- in my case, i see anomalous peak in heavy atom binding site (without
> any
> >> soaking). preliminary i did mass spec. i got Zn++ and Cu, How can i know
> >> which one give the anomalous peak in my protein.
> >>
> >> 3- there is way to know if i have Cu+ or Cu++.
> >
> > You may be able to identify the element based on the coordination
> > geometry - I'm assuming (perhaps incorrectly) that it is actually
> > different for Cu and Zn. Marjorie Harding has written extensively on
> > the geometry of ion binding:
> >
> > http://tanna.bch.ed.ac.uk/
> >
> > The only way to be certain crystallographically, if you have easy
> > access to a synchrotron, is to collect data above and below the K edge
> > of any candidate element, and compare the difference maps. (For
> > monovalent ions it is more complicated, since they don't have
> > accessible K edges.) On a home source, Cu should have a larger
> > anomalous map peak, but I'm not sure if this will be enough to
> > identify it conclusively.
> >
> > -Nat
>
> Dr. Sue A. Roberts
> Dept. of Chemistry and Biochemistry
> University of Arizona
> 1041 E. Lowell St., Tucson, AZ 85721
> Phone: 520 621 8171 or 520 621 4168
> s...@email.arizona.edu
> http://www.cbc.arizona.edu/xray or
> http://www.cbc.arizona.edu/facilities/x-ray_diffraction
>
--
***
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
email: j-kell...@northwestern.edu
***
