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All you need to know about

extraction of enzymesusing reverse micelles!

M.V.N. UMA MAHESH

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Surfactants , Micelles and

Reverse Micelles

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Surface active agents , commonlydesignated as surfactants , areamphiphilic molecules containing non-polar and polar parts capable ofinteracting with surfaces. An exampleis given by the anionic surfactantAOT{bis(2-ethylhexyl)sulfosuccinate .

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The term micelleis used to describethe aggregates of amphiphilicmoleculesin aqueoussolutions andrefers to soluble aggregate,spontaneouslyandreversiblyformedfrom amphiphiles or ions.

Thesurfactant molecules'self-aggregation occurs onlyabove thecriticalmicelleconcentration (CMC)whichinpracticalsensemeans that thesurfactant has to be added of amount

exceeding itssolubility

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Reversedmicellesolventsrepresent nanometer-sized aqueousdropletsstabilizedbysurfactantsinside thebulk organicsolvents.

Thestructure of a reversemicelleconsists of a an aqueousmicro-

domain facing thepolarheads of thesurfactant that surrounds thiscoreinteracting with thebulk organicsolvent (non-polar) through

hydrophobicchains

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Understanding Reverse Micelles

Formation ofreversemicelles.

Reversemicelleshape andsize.

Reversemicelleinterface.

Organicsolvent,co-solvent,co-surfactant.

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A ternarysystemcontaining two

immiscibleliquids (ex. water andhydrocarbon)and an amphiphile formdifferent types ofmicro emulsionsystems out of whichstable water-in-oilmicro emulsionrepresents thereversedmiceller structure

Itsstructure involves a nanometer-sized aqueousdroplet embracedbythehydrophilicheads of thesurfactantmolecules andstabilizedinside a bulkorganicsolvent throughinteractionswith thesurfactant chains.

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At constant temperature, the aqueousdroplet sizeis afunction onlyof theparameter W0 (=mol[water] /mol[surfactant]), a measure of thehydrationdegree.

Thereversedmicellesizeislinearlyproportional to theratioW0 above thevalueneeded forhydration of thesurfactant polarheadgroups.

Theradius of the aqueouscore of thereversedmicellesisgivenconsidering simplespherical geometryand assumingthat all thesurfactant is aggregatedin a micelle form(Regalado et al., 1994):

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Forward Extraction( Solubilization )

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Back Extraction( Desolubilization )

Electrostaticinteractions-pH effect-Ionic Strengtheffect

Othereffects-Alcohol-Temperature-CounterIonic Detergent

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A Model for Estimation