[RASMB] sediments, floats

[Ariel Lustig]

Dear colleagues, dear Holger,
in my long working period (now I'm anymore practical active and also  I will not appear in Uppsula since  my 
historical talk Darwin/Svedbergcoudn't  find a place in the programm) several times I was confrontated with 
the phenomena of sedimentation and floatating components-particles of the same sample. In my cases 
"clients" were interessted to  caracterize molecular  msses in aqueous solutions and also to detemie the positive-sedimenting and the negative sedimenting/floatating particles and even to test, if  partly exist  a complex of  both  components that  are assembled with an average density, that in certain  cases will either sediment or floated , total-standstill ! This  systems to analyse you  need to invest  a lot of runs in several mixed solvents.
I used  the  following  proceedure. In case of analysing the  sample in  D2O buffer you need  use  a10 fold
concentated  buffer and a 10fold concentrated sample, so you get at the end an 80% D2O solution density
with  your desiered end concentration. this procedure you must  repeat at several smaller D2O concentrations
to show  graphically the  extrapolated particle-density of  your  desiered particle [A method of  S0 (0=  viscosity) versus ? at  several  D2O / H2O  concentrations described  1971  Huang  et  al. (.ref: C H  Huang and J Charlton  (JBC 1971  vol 216  8  April] and used for the determination of ? of  vesicles)
 A similar proceedure is also possible to make   by using  precise sucrose concentrations, only in  that  case the  precise viscosity of  each  solution ( S0 ) is hard ,  unknown is also if  the  sucrose dose  not
influence biochemically  the  particles.
Knowing  the real  particle density solves  the main obstacle to  determine such sedimenting/floating
components in  one  solution.   Yours...ariel
ariel.lustig at bluewin.ch
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