The reactivity of OPA with amines is widely used since many years in the determination of amino acids [1] and in application of OPA as a biocide [2]. In the literature related to these applications the mechanism of reaction of OPA with amines is not completely understood. The present study was made in order to describe the detailed mechanism of OPA with primary amines using DC- and DP-polarography and UV/Vis spectrophotometry. The experiments were performed in aqueous buffered solutions of different pH, in non-aqueous acetonitrile and in mixed acetonitrile/H2O media with aqueous or non-aqueous stock solution of OPA. It has been observed that at pH between 7.5 and 10.5, OPA is reduced in three waves of reduction instead of two as mostly mentioned in the literature [3,4]. Its reduction is strongly influenced by pH-dependent hydration. It was found that there is a significant difference in reaction pattern, when using hydrated or non-hydrated form of OPA, respectively. Although the dialdehydic form was always considered as the species reacting with amines [5,6], the experiments showed that the reactivity of OPA with amines is directly related to the hydrated form of OPA, while the non-hydrated OPA undergoes hydration reaction prior the reaction with amines. It was also found that the reaction rate of OPA with primary amines is strongly influenced by the number of H-atoms at the α–carbon atom which may reflect the steric hindrance.
Acknowledgement: The material support from the grant GACR No. 13-21704S and the institutional support RVO 61388955 are acknowledged.
References
(1) Norton, D. R.; Howell, N. Analytical Chemistry 1954, 26, 1116-1119.
(2) Simoes, M.; Simoes, L. Journal of Basic Microbiology 2007, 47, 230-242.
(3) Norton, D. R.; Mann, C. K. Analytical Chemistry 1954, 26, 1111-1115.
(4) Zuman, P.; Salem, N.; Kulla, E. Electroanalysis 2009, 21, 645-649.
(5) Kulla, E.; Zuman, P. Organic & Biomolecular Chemistry 2008, 6, 3771-3780.