Dear Eleanor,
We can tune the wavelength over a large range (lambda = 1.2 – 6 A). This allows collecting data above and below the absorption edges of Ca, K, Cl, S and even P. Crystal, solvent and loop absorption are of course a problem for the longest wavelengths, but so far we have done quite a fair amount of studies around these absorption edges with strong signal above the edge and obviously no signal below. Resolution in our setup is limited to around 3.2 A at 5 A wavelength, but for anomalous difference fourier maps this is sufficient. I have attached an example for a disulphide bridge which should illustrate it better.
Best regards,
Armin
[cid:image001.png@01D42A41.AE0B8B60]
From: Eleanor Dodson <[log in to unmask]>
Date: Wednesday, 1 August 2018 at 19:09
To: Armin Wagner <[log in to unmask]>
Cc: "[log in to unmask]" <[log in to unmask]>
Subject: Re: [ccp4bb] Sulphate or phosphate?
I am not sure if you gave your wave length but it is always worth doing an anomalous map, and looking at relativr peak heights for your known S positions and the putative sulphate or phosphate.
There are small differences in the expected f" at most wavelengths.
Chemical arguments are doubtless better of Course!
Eleanor
On 1 August 2018 at 16:54, [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Dear David,
The long-wavelength beamline I23 at Diamond (http://www.diamond.ac.uk/Instruments/Mx/I23.html) can go all way down to the phosphorous edge. While data quality will be obviously compromised by absorption effects (we are working on this), for a reasonably well diffracting crystal like yours we should be able to get anomalous difference fourier maps from data collected above and below the sulphur edge (lambda ~5 A) to answer your question.
We’ve published some test crystal work around the sulphur edge a while ago, you might want to have a look here:
https://doi.org/10.1016/j.nimb.2016.12.005
The beamline is currently in an advanced commissioning phase accepting a limited number of projects. So, please get into touch if you are interested. We are currently sorting out a few more hardware and software aspects before we can run the beamline as a standard user facility, but we have made a lot of progress over the past months. There will be more details here on the bulletin board ahead of the next call for proposals in autumn.
Best regards,
Armin
Postdoc position for long-wavelength crystallography:
https://vacancies.diamond.ac.uk/vacancy/post-doctoral-research-associate-355285.html
On 31/07/2018, 14:38, "CCP4 bulletin board on behalf of David Schuller" <[log in to unmask]<mailto:[log in to unmask]> on behalf of [log in to unmask]<mailto:[log in to unmask]>> wrote:
How can one distinguish between a sulphate or phosphate in an electron
density map? Both are present in the mother liquor, and resolution is in
the range of 1.75 - 2.25 A
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All Things Serve the Beam
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David J. Schuller
modern man in a post-modern world
MacCHESS, Cornell University
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