Crystal Structure and Tautomerism Study of the Mono-protonated Metformin Salt

Bulletin of the Korean chemical society

Caifeng Bi¹  Xia Zhang¹  Yuhua Fan¹  Xin Li¹  Xingchen Yan¹  Xiaodan Wei¹ 

关键词: Metformin;    Crystal structure;    Theoretical calculation;    Tautomerism;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

A novel crystal, the mono-protonated metformin acetate (1), was obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. It was found that one of the imino group in the metformin cation was protonated along with the proton transfer from the secondary amino group to the other imino group. Its crystal structure was then compared with the previously reported diprotonated metformin oxalate (2). The difference between them is that the mono-protonated metformin cations can be linked by hydrogen bonding to form dimers while the diprotonated metformin cations cannot. Both of them are stabilized by intermolecular hydrogen bonds to assemble a 3-D supermolecular structure. The four potential tautomer of the monoprotonated metformin cation (tautomers 1a, 1b, 1c and 1d) were optimized and their single point energies were calculated by Density Functional Theory (DFT) B3LYP method based on the Polarized Continuum Model (PCM) in water, which shows that the most likely existed tautomer in human cells is the same in the crystal structure. Based on the optimized structure, their Wiberg bond orders, Natural Population Analysis (NPA) atomic charges, molecular electrostatic potential (MEP) maps were calculated to analyze their electronic structures, which were then compared with the corresponding values of the diprotonated metformin cation (cation 2) and the neutral metformin (compound 3). Finally, the possible tautomeric mechanism of the monoprotonated metformin cation was discussed based on the observed phenomena.

【 授权许可】

Unknown