Mutarotation


Mutarotation

Mutarotation is the change in the optical rotation that occurs by epimerization (that is the change in the equilibrium between two epimers, when the corresponding stereocenters interconvert). Cyclic sugars show mutarotation as α and β anomeric forms interconvert.[1] The optical rotation of the solution depends on the optical rotation of each anomer and their ratio in the solution.

Mutarotation was discovered by French chemist Dubrunfaut in 1846, when he noticed that the specific rotation of aqueous sugar solution changes with time.[2][3]

Contents

Measurement

The α and β anomers are diastereomers of each other and usually have different specific rotations. A solution or liquid sample of a pure α anomer will rotate plane polarised light by a different amount and/or in the opposite direction than the pure β anomer of that compound. The optical rotation of the solution depends on the optical rotation of each anomer and their ratio in the solution.

For example if a solution of β-D-glucopyranose is dissolved in water, its specific optical rotation will be +18.7. Over time, some of the β-D-glucopyranose will undergo mutarotation to become α-D-glucopyranose, which has an optical rotation of +112.2. Thus the rotation of the solution will increase from +18.7 to an equilibrium value of +52.5 as some of the β form is converted to the α form. The equilibrium mixture is actually about 64% of β-D-glucopyranose and about 36% of α-D-glucopyranose, though there are also with traces of the other forms including furanoses and open chained form.[4]

Glucoseab.png

The observed optical rotation of the sample is the weighted sum of the optical rotation of each anomer weighted by the amount of that anomer present. Therefore one can use a polarimeter to measure the rotation of a sample and then calculate the ratio of the two anomers present from the enantiomeric excess, as long as one knows the rotation of each pure anomer. One can monitor the mutarotation process over time or determine the equilibrium mixture by observing the optical rotation and how it changes.

Reaction mechanism

Reaction mechanism for the interconversion of α and β anomers

See also

References

  1. ^ IUPAC Gold Book mutarotation
  2. ^ Derek Horton (2008). "The Development of Carbohydrate Chemistry and Biology". Carbohydrate Chemistry, Biology and Medical Applications: 1–28. doi:10.1016/B978-0-08-054816-6.00001-X. 
  3. ^ Augustin-Pierre Dubrunfaut—An early sugar chemist. Hewitt G. Fletcher, J. Chem. Educ., 1940, 17 (4), p 153, DOI: 10.1021/ed017p153
  4. ^ Francis Carey (2000). Organic Chemistry (4th, McGraw-Hill Higher Education Press ed.). 

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Look at other dictionaries:

  • mutarotation — ● mutarotation nom féminin Changement du pouvoir rotatoire d une solution d un composé actif sur la lumière polarisée. (La mutarotation d une solution de glucose traduit l équilibre chimique entre les deux anomères de ce corps.) …   Encyclopédie Universelle

  • Mutarotation — Als Mutarotation (von lateinisch mutare, dt. ‚ändern‘) bezeichnet man die spontane Änderung des Drehwinkels einer Lösung eines optisch aktiven Stoffes vom Zeitpunkt des Ansetzens der Lösung bis zum Erreichen eines festen Wertes.[1] An diesem …   Deutsch Wikipedia

  • Mutarotation — La mutarotation est l évolution du pouvoir rotatoire d’une solution d’une forme pure vers le pouvoir rotatoire de la solution du mélange α+ β à l’équilibre thermodynamique. Il est décrit par le chimiste français Augustin Pierre Dubrunfaut en 1846 …   Wikipédia en Français

  • Mutarotation — Mu|ta|ro|ta|ti|on [lat. mutare = vertauschen, wechseln, verändern, versetzen; ↑ Rotation] in Lsg. mancher optisch aktiver Zucker auftretende langsame, durch Säuren, Basen oder ↑ Mutarotase beschleunigbare Änderung des optischen Drehwertes [αD],… …   Universal-Lexikon

  • mutarotation — mutarotacija statusas T sritis chemija apibrėžtis Optiškai aktyvių junginių tirpalų šviesos poliarizacijos plokštumos sukimo kampo savaiminis kitimas. atitikmenys: angl. mutarotation rus. мутаротация …   Chemijos terminų aiškinamasis žodynas

  • mutarotation — Change in optical rotation with time as an optical isomer in solution converts into other optical isomers …   Dictionary of molecular biology

  • mutarotation — /myooh teuh roh tay sheuhn/, n. Chem. a gradual change in the optical rotation of freshly prepared solutions of reducing sugars. [1895 1900; < L muta(re) to change + ROTATION] * * * …   Universalium

  • mutarotation — noun A dynamic change in the rotation of polarized light as it passes through a fresh solution of some sugars as an equilibrium mixture of anomers is formed …   Wiktionary

  • mutarotation — The process of changing specific rotation at a given wavelength; e.g., a solution of α d glucose recrystallized from its solution in acetic acid and freshly dissolved in water gives a rotation of [α] = +112.2°, but when recrystallized from a… …   Medical dictionary

  • Mutarotation — Mu|ta|ro|ta|ti|on die; , en <zu lat. mutare »(ver)ändern«> allmähliche Veränderung der Schwingungsebene von polarisiertem Licht (bei wässrigen Lösungen von einfachen Zuckern; Chem.) …   Das große Fremdwörterbuch


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