(Note: that in the presence of excess iodide ion, iodine is rapidly interconverted to triiodide ion; I2 + I- → I3-) (this is a back titration so start by finding the moles of the thiosulphate, write the 3 equations and there mole ratios)
A 64.3 mg sample of a protein (MW = 58,600) was treated with 2.00 mL of 0.0487 M
sodium periodate (NaIO4) to react all of the serine and threonine residues.
R
COOH + NH4+ + 10H → R
HO + HN3 R = H, serine R=CH3,threonine
The solution was then treated with excess iodide ion to convert the unreacted periodate
into iodine.
IO4- + 3I- + H2O → IO3- + I2 + OH-
Titration of the iodine required 823 L of 0.0988 M thiosulfate. Calculate the number of
serine plus threonine residues per molecule of protein
Avogadro's number = 6.02 x 10^23 mol^-1
2S2O3^2- + I2 → 3I^- + S4O6^2-
(Note: that in the presence of excess iodide ion, iodine is rapidly interconverted to
triiodide ion; I2 + I- → I3-)
