The tri-component synthesis of novel chiral benzimidazole Mannich bases, by reaction between benzimidazole, aqueous 30% formaldehyde and an amine, the biological evaluation and DFT studies of the new compounds are reported here. The 1H-NMR, 13C-NMR, FTIR spectra and elemental analysis confirm the structures of the new compounds. All synthesized compounds were screened by qualitative and quantitative methods for their in vitro antibacterial activity against 4 bacterial strains. DFT studies were accomplished using GAMESS 2012 software and HOMO–LUMO analysis allowed the calculation of electronic and structural parameters of the chiral Mannich bases. The geometry of 1-methylpiperazine, the cumulated Mullikan atomic charges of the two heteroatoms and of the methyl, and the value of the global electrophilicity index (ω = 0.0527) of the M-1 molecule is correlated with its good antimicrobial activity. It was found that the presence of saturated heterocycles from the amine molecule, 1-methyl piperazine and morpholine, respectively, contributes to an increased biological activity, compared to aromatic amino analogs, diphenylamino-, 4-nitroamino- and 4-aminobenzoic acid. The planarity of the molecules, specific bond lengths and localization of HOMO–LUMO orbitals is responsible for the best biological activities of the compounds.

中文翻译：

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新型苯并咪唑曼尼希碱的合成，密度泛函理论研究和体外抗菌评估。

通过苯并咪唑，30％甲醛水溶液和胺之间的反应，合成了新型手性苯并咪唑曼尼希碱的三组分，在此报道了新化合物的生物学评估和DFT研究。1H-NMR，13C-NMR，FTIR光谱和元素分析证实了新化合物的结构。通过定性和定量方法筛选所有合成的化合物对四种细菌的体外抗菌活性。DFT研究使用GAMESS 2012软件完成，HOMO-LUMO分析允许计算手性曼尼希碱的电子和结构参数。1-甲基哌嗪的几何形状，两个杂原子和甲基的累积Mullikan原子电荷以及全局亲电指数的值（ω= 0。M-1分子的0527）与其良好的抗菌活性有关。发现与胺基氨基类似物二苯氨基-，4-硝基氨基-和4-氨基苯甲酸相比，分别来自胺分子，1-甲基哌嗪和吗啉的饱和杂环的存在有助于提高生物活性。分子的平面性，特定的键长和HOMO-LUMO轨道的位置决定了化合物的最佳生物活性。