[RASMB] lipid particle

[Ariel Lustig]

Dear  Ronald  Toth, dear  all,
to your  question, there  is   a very simple  answer: first of  all, if the  particle  you  want to  sediment  is   equal to  one in 
water, it will  not  sediment but  distribute all over  the  cell, so you  can't  identify any  gradient near  the  cell meniscus or bottom.
Usually  lipid particles (if they are homogen in  density but usually  they  are  not ) at  the density  range of  ro± ...1
-0.1 or more  then +1.0 in buffers. To identify them you  should  use   schlieren  optics since   usually they  do not  absorb!
if they are  not  coloured.
To determine the true  density of the  lipid  you have  to add to your solvent/buffer    a certain percent  of
D2O  to the  solution. You  have  to  perform several  sed. velocity runs at  different D2O concentrations  until  you  can  detect  a  band/ peak  that has  a  negative  sed.value,= that   floatats. If you add  too much D2O it will exceed the  mid  of the  radial  direction of the  cell and  be close to  the  meniscus.
In any  case  do  not  use  for  your   sed. runs  the density that  you   have  determined  with the advised  upper predetermined runs . To calculate a true  sedimentation you  need  to  calculate  the  density of  the  particle.
For  Mw =sed. equilibrium you  need to  do the  same  proceedure…yours …ariel. A retired   UC user
ariel.lustig at bluewin.ch