Studies On The Fluorescence Properties Of Several Non-aromatic Amino Acids And Their Influencing Factors

In recent years, some amino-group-containing organic compounds, without traditional fluorophores, were found to emit strong fluorescence, which has attracted great attentions. In contrast to common fluorescent organic materials, amino-group-containing organic compounds not only possesse excellent biocompatibility and high water solubility, but also simple to prepare and easy to functionally modify. The above advantages will make the novel fluorescent compounds have applications in many fields in future, such as in green luminescent and biomedical fields. However, these studies are still in preliminary stage, and the luminescenct mechanism has not been well understood. Amino acids belong to the kind of amino-group-containing compounds, nevertheless,so far, aromatic amino acids(eg: tyrosine, tryptophan, phenylalanine) are the only natural amino acids which are reported to emit fluorescence. In this paper, we selected four kinds of non-aromatic amino acids, including L-lysine, L-lysine hydrochloride, L-glycine, and L-arginine, to study their fluorescenct phenonmena.In our experiments, on one hand, the effects of several influencing factors on the fluorescenct properties of amino acid substances were studied. First, from the perspective of the temperature, all of the above four kinds of amino acids were carried out in a way of heat treatment. Then, from the perspective of concentration, we studied the changes in fluorescence properties of L- lysine and L- lysine hydrochloride in the process of varying concentrations. Then, from the viewpoint of oxidation, L-lysine hydrochloride emitted fluorescence after oxidation. Finally, from the perspective that the impact of metal ions on fluorescence properties of L-lysine, we found that there have little effects(eg: NaCl) on the fluorescent properties; meanwhile, the effect of p H on fluorescence properties of L-lysine and L-lysine hydrochloride were also studied, which showed that L-lysine got its maximum fluorescence intensity in the near-neutral environment. In addition, the aging effects on fluorescence properties of L-lysine and L-lysine hydrochloride were investigated. On the other hand, we used MS and LC techniques to get more informations on the fluorescence emission mechanism, which confirmed the significant impacts of aggregation on fluorescence properties. Meanwhile, the fluorescent stability of Llysine was investigated, which exhibited their special photosensitive properties. The test of fluorescence quantum yields was also carried out.The experimental results in this paper show that, after suitable heat treatment or oxidation, L- lysine can emit strong fluorescence, which have the typical fluorescent properties of amino-group-containing organic compounds. Importantly, the fluorescent non-aromatic amino acids will find great applications in many fields, due to their optical and biologic advantages.