M Eeff2 q M Eeff2

]T [((Pi • Eeff)2)o - pi • EeS)l and also introduced a constraint factor C that accounts for the reduction of the freedom of individual dipoles

So, finally we have that:

As seen above, by measuring the dielectric constant of a tubulin solution at various concentrations (and incident frequencies) one can experimentally deduce the dipole moment of the free tubulin dimer. This is not straightforward since even though an ideal dielectric contains no free charge, parts of its constituent units (individual molecules, polymer filaments, etc.) can suffer a localized separation of charge as a result of application of an external electric field. By using a solution with above-critical concentration it is also possible to monitor the changes in the dipole moment as tubulin dimers polymerize into MTs. At high frequencies where only ae will contribute, one can use the Clausius-Mossotti equation with the substitution k = n2 and by measuring the refractive index of the solution arrive at the value of |pave |.

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