cesium chloride - (Jun/03/2006 )

hi all,

does any one know why after centrifuging CsCl we get Self-generating CsCl density gradients
I mean one of the specificities of solutions is not to sediment, does any one know physical basis for this phenomenon?
thanx,

Hi.
The quick answer is "Magic".
For those not satisfied with this, my understanding is as follows.

Consider a protein solution that is tested by analytical ultracentrifugation. It starts off a single density, but after 24 hrs at 32,000 rpm, the protein will have concentrated at the end of the cell (to varying degrees) depending on its multimeric state. This actually represents a gradient of protein through the cell. Same thing happens with CsCL, only, instead of large protein molecules, you have ions (ions being affected by the laws of physics).

Now, I assume you're talking about using CsCl to purify DNA. After a run has completed, you have is a continuous concentration gradient of CsCl through the tube, and the genomic DNA just happens to sit at a particular point along that gradient.