This table gives selected properties of some important amino acids and closely related compounds. Compounds are listed by name in alphabetical order. The three-letter symbol is included for the 20 “standard” amino acids that are the basic constituents of proteins. Structures are given in the following table.
Column heading | Definition |
Symbol | Three-letter symbol for standard amino acids; table lists amino acids alphabetically by this symbol |
Name | Amino acid name |
Mol. form. | Molecular formula of amino acid |
Mol. wt. | Molecular weight |
tm | Melting point, in °C |
pKa, pKb, pKc, pKd | Negative of the logarithm of the acid dissociation constants for the COOH and NH2 groups (and, in some cases, other groups) in the molecule (at 25 °C) |
pI | pH at the isoelectric point |
Sol. | Solubility in water, in units of grams of compound per kilogram of water; a temperature of 25 °C is understood unless otherwise stated; when quantitative data are not available, a qualitative indication is given |
2/ cm3 mol-1 |
Partial molar volume in aqueous solution at infinite dilution at 25 °C |
Data on the enthalpy of formation of many of these compounds are included in the table “Standard Thermodynamic Properties of Chemical Substances” in Section 5 of this CRC Handbook. Absorption spectra and optical rotation data can be found in Ref. 3. Partial molar volume is taken from Ref. 5; other thermodynamic properties, including solubility as a function of temperature, are given in Refs. 3 and 5. Most of the pK values come from Refs. 1, 6, and 7.
Symbol | Name | Synonym | Mol. form. | CAS Reg. No. | Mol. wt. | tm/ºC | pKa | pKb | pKc | pKd | pI | Sol./g kg-1 | 2/ cm3 mol-1 V‾ |
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Standard amino acids | |||||||||||||
Ala | L-Alanine | 2-Aminopropanoic acid, (S)- | C3H7NO2 | 56-41-7 | 89.094 | 297 dec | 2.33 | 9.71 | 6.00 | 166.9 | 60.54 | ||
Arg | L-Arginine | C6H14N4O2 | 74-79-3 | 174.201 | 260 | 2.03 | 9.00 | 12.10 | 10.76 | 182.6 | 127.42 | ||
Asn | L-Asparagine | α-Aminosuccinamic acid | C4H8N2O3 | 70-47-3 | 132.118 | 235 | 2.16 | 8.73 | 5.41 | 25.1 | 78.0 | ||
Asp | L-Aspartic acid | L-Aminosuccinic acid | C4H7NO4 | 56-84-8 | 133.104 | 270 | 1.95 | 9.66 | 3.71 | 2.77 | 5.04 | 74.8 | |
Cys | L-Cysteine | 2-Amino-3-mercaptopropanoic acid, (R)- | C3H7NO2S | 52-90-4 | 121.159 | 240 dec | 1.91 | 10.28 | 8.14 | 5.07 | vs | 73.45 | |
Gln | L-Glutamine | 2-Aminoglutaramic acid | C5H10N2O3 | 56-85-9 | 146.144 | 182 | 2.18 | 9.00 | 5.65 | 42 | |||
Glu | L-Glutamic acid | (S)-2-Aminopentanedioic acid | C5H9NO4 | 56-86-0 | 147.130 | 160 dec | 2.16 | 9.58 | 4.15 | 3.22 | 8.6 | 89.85 | |
Gly | Glycine | Aminoacetic acid | C2H5NO2 | 56-40-6 | 75.067 | 290 dec | 2.34 | 9.58 | 5.97 | 239 | 43.26 | ||
His | L-Histidine | Glyoxaline-5-alanine | C6H9N3O2 | 71-00-1 | 155.154 | 287 dec | 1.70 | 9.09 | 6.04 | 7.59 | 43.5 | 98.3 | |
Ile | L-Isoleucine | 2-Amino-3-methylpentanoic acid | C6H13NO2 | 73-32-5 | 131.173 | 284 dec | 2.26 | 9.60 | 6.02 | 34.2 | 105.80 | ||
Leu | L-Leucine | 2-Amino-4-methylpentanoic acid | C6H13NO2 | 61-90-5 | 131.173 | 293 | 2.32 | 9.58 | 5.98 | 23.8 | 107.77 | ||
Lys | L-Lysine | 2,6-Diaminohexanoic acid, (L)- | C6H14N2O2 | 56-87-1 | 146.187 | 224 dec | 2.15 | 9.16 | 10.67 | 9.74 | 5.8 | 108.5 | |
Met | L-Methionine | C5H11NO2S | 63-68-3 | 149.212 | 281 dec | 2.16 | 9.08 | 5.74 | 56 | 105.57 | |||
Phe | L-Phenylalanine | α-Aminobenzenepropanoic acid, (S)- | C9H11NO2 | 63-91-2 | 165.189 | 283 dec | 2.18 | 9.09 | 5.48 | 27.9 | 121.5 | ||
Pro | L-Proline | 2-Pyrrolidinecarboxylic acid | C5H9NO2 | 147-85-3 | 115.131 | 221 dec | 1.95 | 10.47 | 6.30 | 1625 | 82.76 | ||
Ser | L-Serine | 2-Amino-3-hydroxypropanoic acid, (S)- | C3H7NO3 | 56-45-1 | 105.093 | 228 dec | 2.13 | 9.05 | 5.68 | 250 | 60.62 | ||
Thr | L-Threonine | 2-Amino-3-hydroxybutanoic acid, [R-(R*,S*)] | C4H9NO3 | 72-19-5 | 119.119 | 256 dec | 2.20 | 8.96 | 5.60 | 90.6 | 76.90 | ||
Trp | L-Tryptophan | α-Aminoindole-3-propanoic acid, (l)- | C11H12N2O2 | 73-22-3 | 204.225 | 289 dec | 2.38 | 9.34 | 5.89 | 13.2 | 143.8 | ||
Tyr | L-Tyrosine | 4-Hydroxy-L-phenylalanine | C9H11NO3 | 60-18-4 | 181.188 | 343 dec | 2.24 | 9.04 | 10.10 | 5.66 | 0.51 |
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