Kodchakorn Kanchanok, Nimmanpipug Piyarat, Phongtamrug Suttinun, Tashiro Kohji
Department of Chemistry, Faculty of Science and Center of Excellence for Innovation in Analytical Science and Technology, Chiang Mai University Chiang Mai 50200 Thailand
Doctor of Philosophy Program in Chemistry, Faculty of Science, Chiang Mai University Chiang Mai 50200 Thailand.
RSC Adv. 2019 Jun 20;9(34):19375-19389. doi: 10.1039/c9ra03418h. eCollection 2019 Jun 19.
Histamine is one of the most basic biogenic amino-compounds, which is composed of imidazole and a flexible ethylamine side chain moiety. Histamine is known to take the form of various types of cations, free base, monocation and dication form, where its conformational change is highly sensitively to the pH conditions. The details of these changes are still controversial due to a lack of detailed information on its crystal structures. Thus, in this study, the molecular packing structures of histidine at various pH were analyzed X-ray diffraction in combination with vibrational spectroscopy and energy calculations. A variety of molecular conformations including the tautomeric phenomenon was found to be intimately related with intra- and intermolecular hydrogen bonds. The role of the hydrogen bonds was studied also to check the possibility of high proton conductivity of histamine, as predicted by computer simulation. Consequently, the thus-predicted proton conductivity was confirmed for the first time experimentally. During the heating process, the conductivity showed the relatively high maximum value of 10 S cm at around 60 °C, which is related to the effective proton transfer between the amino NH group of one histamine unit and the imidazole ring of another.
组胺是最基本的生物源性氨基化合物之一，由咪唑和一个柔性乙胺侧链部分组成。已知组胺以各种类型的阳离子、游离碱、单阳离子和双阳离子形式存在，其构象变化对pH条件高度敏感。由于缺乏关于其晶体结构的详细信息，这些变化的细节仍存在争议。因此，在本研究中，结合振动光谱和能量计算，通过X射线衍射分析了不同pH值下组胺的分子堆积结构。发现包括互变异构现象在内的多种分子构象与分子内和分子间氢键密切相关。还研究了氢键的作用，以检验计算机模拟预测的组胺高质子传导性的可能性。因此，首次通过实验证实了预测的质子传导性。在加热过程中，电导率在60℃左右显示出相对较高的最大值10 S/cm，这与一个组胺单元的氨基NH基团与另一个组胺单元的咪唑环之间的有效质子转移有关。
