Transcript Acid-Base Properties of Amino Acids What are amino acids?  Amino acids are the building blocks of proteins.  In the body, they.

Acid-Base Properties of Amino
Acids
What are amino acids?
 Amino acids are the building blocks of proteins.
 In the body, they exist as zwitterions.
 Zwitterions can behave as both an acid or a base.
Today we will:
 Study the acid-base properties
of amino acids, We will perform
a simple titration.
 Start the titration with the
amino acid in acidic form. As
we slowly increase the pH we
should be able to plot a graph
similar to the one on the right.
3
2
pH
1
mL NaOH
Remember from Chem 103L…
HCl + NaOH
NaCl + H2O
pH vs. NaOH Volume, mL
14
12
10
8
pH
Z
6
X
4
2
0
0
2
4
pKa = - log Ka
Ka = X-pKa
6
8
NaOH Volume, mL
10
12
At point Z…?
At point X…?
Henderson-Hasselbalch
[OH ]
pH  pKa  log 
[H ]
The titration curve points…
 1 – where half of the original
acidic amino acid had been
titrated and became a
zwitterion.
 2 - where the amino acid is
entirely in the zwitterion form.
 3 – where half of the amino acid
is in the zwitterion form and
half is in the basic form.
3
pH
2
1
Volume NaOH, mL
What does each point mean?
 The pH of the midpoint of the first
leg (1) is the pK value of the
carboxylic acid group.
 The midpoint of the second leg (2)
is known as the isoelectric point. All
the amino acids are in zwitterion
form at this point.
 The pH of the midpoint of the third
leg (3) is equal to the pK of the –
NH3+
3
pH
2
1
Volume NaOH, mL
Today we will…
 Titrate our amino acid solution with NaOH to see the pH
curve as it relates to the amount of NaOH added.
 Use pH meters to monitor pH changes during our titration.
 Construct a graph of pH vs. Volume, mL of NaOH added.
Caution!
Be sure to monitor your buret carefully as to not put too much
base into your amino acid solution at once.
Potential Health Concerns
 Inhalation: irritation, burns, coughing, corrosion, sneezing, choking,




sore throat, runny nose, pneumonitis, inflammation of the upper
respiratory system, pulmonary edema, circulatory failure and death
Ingestion: large oral doses may result in nausea, corrosion, pain and
burns of the mouth, throat, esophagus and gastrointestinal tract,
vomiting, scarring of tissue, bleeding, diarrhea, low blood pressure,
and death
Skin contact: corrosion, redness, pain, burns, scarring, ulcers and
discoloration of the skin
Eye contact: irritation, tearing, pain, redness, corrosion, soreness,
burns, impaired vision, permanent eye damage and blindness
Tumorigen, mutagen and reproductive effector