# Sedimentation

Mécanique

22 févr. 2014 (il y a 4 années et 2 mois)

68 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