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Amino Acid : Ionization and Environment
contain at least^ two^ Ionizable^ protons,^ each^ with^ its^ own^ pKa
no / The^ carboxylic^
acid has^ an^ acidic^ pKa and^ will^ be^ protonated at^ an^ acidic^ (low^ )^ pH :
AAAA- gpq-g.gg
- cootie> (^) ooo - + ti /The amino (^) group has a basic^ pKa and^ will^ be^ protonated^ until^ basic^ pH^
(high) is^ achieved^ :
ANAP
+ H^ "
Environmental Effects A- (^) carboxy group is^ much^
more acidic^ than^ in^ carboxylic^
acids
A- amino group Is^ slightly^ less^
basic than in^ amines
Due to^ intramolecular^
interactions 7-The^ normal^ pKa^
for a
PKa (^2) μ
carboxyl group^ is^ about^
Methyl -^ substituted^ amino^ group^ is^ about^10 :b """" """"°^ " """""" ""
""""^ """^ "
groups (^) CH ,^ -^ COOH^ CH,^ -^ COO
II
+ Acetic acid
H+
1MHz
carboxyl and H -^ c-^ "°" "
¥ 3 H - C - coo -
amino groups
↓' H+ H -
,
in glycine a-^ Amino^ Acid^ 1919cme) at!Am, acid (glycine)
I t
Thetprotonated amino^9 ᵗ°4P^ Electronegative oxygen atoms
withdraws electrons^ from^ the^ in^ the^ carboxyl^ group^ withdraw carboxyl group ,^ lowering^ Its^ pKa^ electrons^ from^
the amino group,
lowering it^ pKa
Ionization and^ Titration^ curves
low pH →amino^ acid^ exists^
in a positively charged^ form^ ;^ cation
high pH^
→am 10h^ acid^ exists^ in^ a^ negatively charged^ form;^ anion
Between the^ pKa^ for^ each^ group^ ,^ the^ amino^ acid^ exists^ in^ azwitterion
form , in which^ a^ single^ molecule^
has both^ a^ positive and^ negative^ charge
cation → Zwitterion - →^ Anion^ ZWItter
/ ON Nit (^) Has
13 PK^ , predominate at^ pH^ values^ between^ the^ pKa values^ of
4+2 %!^1 the^ amino^ and^ carboxyl^ groups
Glycine amino^ acids^ without^ ionizable side^ chains^ , the^ Isoelectric = (^). _÷:÷ :
-. Point (equivalence point.pl)^ IS^ :
7- Net^ charge^ __^0
- I - AA is^ least^ soluble^ in^ water
Pks.ae
/ - AA does not migrate in^ electric^ field
- : 0 ,#,!g 2 basic^ acidic group 1-1 (^) group
OH
( equivalents)
↓ I ↓ f'
Han - g
- (^) COOH +1-1, - (^) c- coolI R amino acid^ twitter10h
+ NH
}
PK ,^ I^ pkz R -
g
- (^) COO R - ¢ -^ COOH^ →^ R^ -^ C^ -^ COO
H ←^ I H
CEoE→_→aOEgoaE6o-Ey
low (^) pH pH ,=%%agyg
high pH
