Sedimentation (24.7)

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# Sedimentation (24.7) - PowerPoint PPT Presentation

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

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Presentation Transcript
Sedimentation (24.7)
• When macromolecules move in solution, their motion is dictated by the forces they feel
• Gravitational force (Fg) is opposed by frictional (Ffr) and buoyant (Fb) forces
• Specific volume of the solute is the change in solution volume upon addition of a given amount of solvent (measure in cm3/g)
• When all forces sum to zero, terminal velocity is achieved (vter)
• 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 = mNA) of the macromolecule if we know the frictional coefficient
• We can get this from a diffusion experiment