Section: 7 | Properties of Amino Acids |

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PROPERTIES OF AMINO ACIDS

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
t_m	Melting point, in °C
pK_a, pK_b, pK_c, pK_d	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
$\bar{V}$ 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.

References

Dawson, R. M. C., Elliott, D. C., Elliott, W. H., and Jones, K. M., Data for Biochemical Research, Third Edition, Clarendon Press, Oxford, 1986.
O’Neil, Maryadele J., Ed., The Merck Index, 15th Edition, Royal Society of Chemistry, Cambridge, 2013.
Sober, H. A., Ed., CRC Handbook of Biochemistry. Selected Data for Molecular Biology, CRC Press, Boca Raton, FL, 1968.
Voet, D., and Voet, J. G., Biochemistry, Second Edition, John Wiley & Sons, New York, 1995.
Hinz, H. J., Ed., Thermodynamic Data for Biochemistry and Biotechnology, Springer-Verlag, Heidelberg, 1986. [https://doi.org/10.1007/978-3-642-71114-5]
Fasman, G. D., Ed. Practical Handbook of Biochemistry and Molecular Biology, CRC Press, Boca Raton, FL, 1989.
Smith, R. M., and Martell, A. E., NIST Standard Reference Database 46: Critically Selected Stability Constants of Metal Complexes Database, Version 3.0, National Institute of Standards and Technology, Gaithersburg, MD, 1997.
Ramasami, P., J. Chem. Eng. Data, 47, 1164, 2002. [https://doi.org/10.1021/je025503u]

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Properties of Amino Acids

Symbol	Name	Synonym	Mol. form.	CAS Reg. No.	Mol. wt.	t_m/ºC	pK_a	pK_b	pK_c	pK_d	pI	Sol./g kg^-1	$\bar{V}$ ₂/ cm³ mol^-1 V‾
Continued on next page...
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

^slsSlightly soluble.
^sSoluble.
^vsVery soluble.
¹⁴At 14 °C.
²⁰At 20 °C.
⁴⁰At 40 °C.

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