ACID–BASE PROPERTIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 56

TABLE 2.1. Structure and Dissociation Constants of Amino Acids at 25°C at Zero Ionic
Strength

Type of
Side
Chain

Abbreviated
Name (One
Letter) Name Structure of the Side Chain p K a1 p K a2 p K a3

Aliphatic Glycine Gly (G) ——H 2.43 a 9.60 a -

Alanine Ala (A) ——Me 2.55 b 10.08 b -

Valine Val (V) 2.28 c 9.54 c - Me

CH

Me

Leucine Leu (L) Me 2.58 b 9.93 b -

CH 2 CH

Me

Isoleucine Ile (I) 2.32 d 9.76 d -

Me

CH

Et

Alcohols Serine Ser (S) ——CH 2 OH 2.09 e 9.05 e -

Threonine Thr (T) 2.45 b 9.28 b -

OH

CH

Me

Acids Aspartic acid Asp (D) ——CH 2 CO 2 H 2.10 c 3.86 c 9.82 c

2.19 f 4.45 f 10.1 f Glutamic acid Glu (E) ——CH 2 CH 2 CO 2 H

Amides Asparagine Asn (N) ——CH 2 CONH 2 2.16 g 8.73 g -

Glutamine Gln (Q) ——CH 2 CH 2 CONH 2 2.18 g 9.00 g -

1.85 f 9.42 f 11.18 f Bases Lysine Lys (K) ——CH 2 CH 2 CH 2 CH 2 NH 2

Arginine Arg (R) CH 2 CH 2 CH 2 NH C NH 2 1.97 f 9.05 f 11.94 f

NH

Histidine His (H) 1.56 f 6.00 f 9.25 f

H 2 C

HN N

Thiol Cysteine Cys (C) ——CH 2 SH 2.14 h 8.18 h 10.21 h

Sulfide Methionine Met (M) ——CH 2 CH 2 S——Me 2.14 i 9.61 i -

Aromatic Tryptophan Trp (W) 2.37 f 9.36 f -

H 2 C

N
H

Tyrosine Tyr (Y)

2.04 f 9.09 f 10.69 f

CH 2 OH