In this case, would there be a higher rate of radiation damage since there are two absorbing species?
Mohamed
On Fri, 5 Feb 2016 14:07:40 -0600, James Phillips <[log in to unmask]> wrote:
>I agree with George, especially about better phases.
>
>An individual heavy atom contributes to some reflection highly and to some
>very weakly, depending on it (or their) position in the cell. These latter
>are not phased well no matter how strong F'' is. With two anom. scatterers
>in different positions in the cell you have fewer reflections poorly phased.
>
>
>On Fri, Feb 5, 2016 at 6:42 AM, George M. Sheldrick <
>[log in to unmask]> wrote:
>
>> Dear Patrick,
>>
>> I see no problem for SAD phasing of your mixed I3C/SeMet crystals with
>> shelxc/d/e (i.e.using hkl2map or the new ccp4i2 gui). Just to the high
>> energy side of the Se edge at about 0.98A, f" for Se is about 3.8 and
>> for I about 3.2, so you would see both. On the low energy side of the
>> edge f" for I will still be about 3.2 but for Se it is much lower (about
>> 0.5) so you might only see iodine. So if you collect data at these two
>> wavelengths and analyse both as SAD you get some useful extra
>> information. In practice the Se/I ratio could be higher if the I3C is
>> not fully occupied or the Se is partly oxidized and you hit a 'white line'.
>>
>> Taking the different elements into account rigorously with
>> multi-wavelength data is more complicated, but should give even better
>> phases. This is usually performed using the program SHARP.
>>
>> Best wishes, George
>>
>>
>>
>> On 02/05/2016 10:27 AM, Patrick Pausch wrote:
>> > Hey folks,
>> >
>> > I’m currently working on a complex which shows increased crystallization
>> and diffraction when co-crystallized with I3C (Iodine ligand). This is also
>> true for the Se-methionine labeled variant. The iodine signal is usually
>> accesible using CuKa radiation. I’m wondering if the anomalous signal of
>> iodine (peak should be around 20 keV) will impede data processing after
>> measuring selenium peak at synchrotron radiation source.
>> >
>> > Many thanks in advance!
>> >
>> > Patrick Pausch
>>
>> --
>> Prof. George M. Sheldrick FRS
>> Dept. Structural Chemistry,
>> University of Goettingen,
>> Tammannstr. 4,
>> D37077 Goettingen, Germany
>> Tel. +49-551-39-33021 or -33068
>> Fax. +49-551-39-22582
>>
>
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