Svedberg

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A laboratory ultracentrifuge. Beckman-Coulter ultracentrifuge XL-100K -01.jpg
A laboratory ultracentrifuge.

In chemistry, a Svedberg unit or svedberg (symbol S, sometimes Sv [lower-alpha 1] ) is a non-SI metric unit for sedimentation coefficients. The Svedberg unit offers a measure of a particle's size indirectly based on its sedimentation rate under acceleration (i.e. how fast a particle of given size and shape settles out of suspension). [1] The svedberg is a measure of time, defined as exactly 10−13 seconds (100  fs).

Contents

For biological macromolecules and cell organelles like ribosomes, the sedimentation rate is typically measured as the rate of travel in a centrifuge tube subjected to high g-force. [1]

The svedberg (S) is distinct from the SI unit sievert or the non-SI unit sverdrup, which also use the symbol Sv, and to the SI unit Siemens which uses the symbol S too.

Naming

The unit is named after the Swedish chemist Theodor Svedberg (1884–1971), winner of the 1926 Nobel Prize [2] in chemistry for his work on disperse systems, colloids and his invention of the ultracentrifuge. [3]

Factors

The Svedberg coefficient is a nonlinear function. [1] A particle's mass, density, and shape will determine its S value. The S value depends on the frictional forces retarding its movement, which, in turn, are related to the average cross-sectional area of the particle. [1]

The sedimentation coefficient is the ratio of the speed of a substance in a centrifuge to its acceleration in comparable units. A substance with a sedimentation coefficient of 26S (26×10−13 s) will travel at 26 micrometers per second (26×10−6 m/s) under the influence of an acceleration of a million gravities (107 m/s2). [lower-alpha 2] Centrifugal acceleration is given as rω2; where r is the radial distance from the rotation axis and ω is the angular velocity in radians per second.

Bigger particles tend to sediment faster and so have higher Svedberg values.

Svedberg units are not directly additive since they represent a rate of sedimentation, not weight. [1]

Use

In centrifugation of small biochemical species, a convention has developed in which sedimentation coefficients are expressed in the Svedberg units.

See also

Footnotes

  1. ↑ Please note that there is an SI unit with the same Sv abbreviation, the sievert.
  2. ↑ 1 G=9.8 m/s2, i.e. approx 10 m/s2; A million G = 106 x 10 m/s2 = 107 m/s2

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References

  1. 1 2 3 4 5 6 7 Slonczewski, Joan; Foster, John Watkins (2009). Microbiology: An Evolving Science. New York: W.W. Norton. ISBN   9780393978575.
  2. ↑ "The Nobel Prize in Chemistry 1926".
  3. ↑ Koehler, Christopher S. W. (2003). "Developing the Ultracentrifuge" (PDF). Archived from the original (PDF) on 2 October 2023.
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