(a) What percentage of arginine side chains are protonated at a pH value of 11.5? (b)...
(a) What percentage of arginine side chains are protonated at a pH value of 11.5? (b) What is the average charge of the side chain of arginine at this pH? (pKa = 12)
Homework Answers
a)
pH= pKa + log [A-] /[HA]
11.5-12 = log [A-] /[HA]
[A-] /[HA] = 0.316
[HA]/ [A-] = 3.16; That means 31.6 percent is protonated.
b)
When pH≠pKa we determine the mole fraction, for each charged species.
χCOO−=1/ (1+10pKa−pH) = 0.240269, this charge is negative ; remember this
χNH3+=1/(1+10pH−pKa) = 0.7597469
Net charge is their sum = 0.519477
Plugging in the numbers, we get:
χCOO−≈0.999981χCOO−≈0.999981
χNH+3≈0.993872
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