Solid Complex Formation of Oxalic Acid with a-Amino Acids

Abstract

SOIid complex formation of oxal ie acid with several a-ami no acids was studied by usi ng an X-ray diffractometer, a R i ltfrared spectrometer and a differential thermobalance a Ralyser.
Oxalic acid forms enly o ne ki nd of complex with dlnt-ala nine, dl-nerleucine or dl-leucine i n a molar ratio of 1:1, while it ferms two kinds of complexes with glyei qe, dl-a-ami Robutylic aeid, dl-val i ne. dl-norvaline o r dl-isoleuci ne i n molar ratios of 1:1 a nd 1:2. lt was presurned that the formation of the cemplexes was promoted by proten-transfer from the carboxyl group in oxalic aeid to the ca rboxyl ion of amino aeid i n t he case of 1:1 complex and by the intermolecular hydrogeR bond between two hydregen atoms of t h e carboxyl groups i R oxalic acid a nd t he carboxyl ions ef t wo molecules of ami no acid i lt t he case of 1:2 complex.
The difference i n com plex formatioA amoRg a-ami nO acids is suppostxl to resu l t from the steric request of a-ami no acid, although it can hardly be explai ned enly by the size of the alkyi group at a-position.