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=== Physical properties of α-amino acids due to zwitterions ===

=== Physical properties of α-amino acids due to zwitterions ===

The formation of zwitterions dramatically affects the physical properties of amino acids.  The zwitterion is the predominant form in the [[solid phase]] and aqueous [[solution]].  Due to the two charges on zwitterions, there is a much stronger intermolecular attraction between the ions, raising the melting point of an amino acid far above the melting point of organic compounds with similar [[molecular mass]] and numbers of [[electron|electrons]].  For example, the amino acid [[glycine]] decomposes at 262°C (without melting) where propanoic acid melts at -21°C<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref>.

The formation of zwitterions dramatically affects the physical properties of amino acids.  The zwitterion is the predominant form in the [[solid phase]] and aqueous [[solution]].  Due to the two charges on zwitterions, there is a much stronger intermolecular attraction between the ions, raising the melting point of an amino acid far above the melting point of organic compounds with similar [[molecular mass]] and numbers of [[electron|electrons]].  For example, the amino acid [[glycine]] decomposes at 262°C (without melting) where propanoic acid melts at -21°C<ref>Chemistry 2, Ratcliff B. & Eccles H., 2001, Cambridge University Press, ISBN 0-521-79882-5</ref>.

== Optical isomerism of amino acids ==

== Optical isomerism of amino acids ==