Why is solubility phe > tyr ?
kalonia at uconnvm.uconn.edu
Thu Jun 13 17:36:22 EST 1996
Achim Recktenwald wrote:
> I have a question concerning the solubilities of the amino acids phenylalanine and
> I had posted this message already a few weeks ago, but received no The solubility is an equilibrium quantity. The free energy of
solubilization (del G) depends on three factors. Interaction of
(solvent_solvent molecules)+ (solvent_solute)+(solute_solute).
In this case assuming water as solvent, the solvent_solute factor is same
for both Phe and Tyr. The solvent_solute is more favorable for Tyr since
it has a polar group (-OH). The third factor solute_solute is the one
that creates confusion here. This energy depends on crystal lattice.
The energy of crystallization for Tyr is much larger than that of Phe,
ie. the O..H--O interaction and stacking of the hydrophobic rings
results in stronger interaction in the solid state. Thus more energy
must be provided to move the molecules from a solid_solid state to a
solvent_solid state. Thus poor solubility for tyr.
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