[RASMB] 3mm centerpieces

[Peter Schuck]

Kristian,
we've actually made these spacers and systematically compared data quality 
and boundary shapes observed with the 3 mm centerpieces in different 
positions.  In our hands, our conclusion was that for most cases there was 
no difference in data quality or information.  We will make this data 
available soon.
Peter



At 09:34 AM 9/18/2006, you wrote:
>Hi-
>Yes you can calculate (or measure) the correct 2/3rds position for the 
>centerpiece, make unequal spacers and drill the cell housing holes at that 
>level. Be aware that the 2/3 position is not the mechanical location, but 
>the optical. These positions differ by a mm or more, and are different for 
>sapphire and quartz window. Those cells would be useful for the 
>interference optics, so it would be best to determine the 2/3 position for 
>sapphire windows. The absorbance optics are focused at the midpoint, so 
>the new housings would not be helpful for them.
>Best wishes,
>Tom
>
>Kristian Schilling wrote:
>>Tom and Borries,
>>
>>I am wondering whether we might modify cell housings to overcome that 
>>problem. There is no other need for equal spacers but to align the 
>>centerpiece with the filling holes, so we might just drill the filling 
>>holes at a modified position. Of course that would mean that these 
>>housings can be used only with 3-mm-cps, but the first question is: can 
>>we match the ideal position for the centerpiece and enhance data quality?
>>
>>Kristian
>>
>>At 01:07 15.09.2006 -0400, you wrote:
>>>Hi-
>>>The spacers for the 3 mm centerpieces place the centerpiece at the 
>>>mid-point of the cell, which is out of focus for the interference 
>>>system, which is focused at the 2/3 plane of a 12-mm centerpiece, with 
>>>sapphire windows and a solvent refractive index of water. Mis-focusing 
>>>will lead to mis-registration of the true radial position with the 
>>>apparent radial position in regions of the image with steep gradients in 
>>>the concentration (1). For the 3 mm centerpieces, the focal plane is 
>>>below the sample 2/3 plane, causing steeper fringes than might be 
>>>expected... i.e. analysis will reveal what appears to be a weak 
>>>association or a heterogeneous system. This problem would also affect 
>>>the absorbance system, but the absorbance optics cannot trace a steep 
>>>enough gradient.
>>>So long as you keep gradients low enough (as I recall, about 50 fringes 
>>>displacement per mm), your data will be OK.
>>>Best wishes,
>>>Tom
>>>
>>>(1)   D. A. Yphantis. Equilibrium Ultracentrifugation of Dilute 
>>>Solutions. Biochemistry 3:297-317, 1964.
>>>
>>>Borries Demeler wrote:
>>>>Question about 3 mm centerpieces - the spacers that come with them seem
>>>>to take it out of the focal plane for the interference system, at least
>>>>we cannot get 3 mm CPs to work in interference mode. Are there spacers
>>>>that will correct this issue, or is there something else we should try?
>>>>
>>>>thanks, -Borries
>>>>_______________________________________________
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>>>>
>>>
>>>--
>>>Department of Biochemistry and Molecular Biology
>>>University of New Hampshire
>>>Rudman Hall 379
>>>46 College Road
>>>Durham, NH 03824-3544
>>>Phone: 603-862-2459
>>>FAX:  603-862-0031
>>>www.camis.unh.edu
>>>www.bitc.unh.edu
>>>
>>>
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>>>http://rasmb.bbri.org/mailman/listinfo/rasmb
>>
>>
>>
>>=================================
>>Nanolytics
>>Gesellschaft fuer Kolloidanalytik mbH
>>Dr. Kristian Schilling
>>
>>Hauptstr. 20
>>D-14624 Dallgow
>>
>>Tel.:       +49 3322 24200-5
>>Fax:       +49 3322 24200-6
>>e-mail:   schilling at nanolytics.de
>>Internet:   www.nanolytics.de
>>
>>
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>>http://rasmb.bbri.org/mailman/listinfo/rasmb
>
>--
>Department of Biochemistry and Molecular Biology
>University of New Hampshire
>Durham, NH 03824-3544
>Phone: 603-862-2459
>FAX:  603-862-0031
>E-mail: Tom.Laue at unh.edu
>www.bitc.unh.edu
>www.camis.unh.edu
>
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