Sedimentation

swedishstreakMécanique

22 févr. 2014 (il y a 3 années et 7 mois)

62 vue(s)

Sedimentation (24.7)


When macromolecules move in solution, their motion is dictated by the
forces

they feel


Gravitational force (F
g
) is
opposed

by frictional (F
fr
) and buoyant (F
b
) forces


Specific volume of the solute is the change in solution volume upon addition of a given
amount of solvent (measure in cm
3
/g)




When all forces sum to zero, terminal velocity is achieved (v
ter
)






Sedimentation coefficient relates speed of sedimentation to properties of
macromolecule and solvent


Measured in units of Svedbergs (S) where 1S = 1 x 10
-
13
s


Velocity Sedimentation (24.7)


Velocity sedimentation utilizes centripetal force instead of gravity


ω is the angular velocity (i.e., speed of centrifuge) and x is the distance between the
particle and the center of rotation





Centrifugation

causes heavier particles (solute) to move away from center
of rotation


Boundary forms with one side being solution and the other side solvent


Sedimentation coefficient can be determined by monitoring motion of boundary





Sedimentation coefficients can give us molar mass (M = mN
A
) of the
macromolecule if we know the frictional coefficient


We can get this from a diffusion experiment



Sedimentation Forces

Centrifuge Cell for Velocity Sedimentation