1-乙基-3-甲基咪唑阳离子与天冬酰胺阴离子的相互作用

利用密度泛函理论B3LYP方法, 在6-311+G(d,p)水平上, 对1-乙基-3-甲基咪唑阳离子Emim]+与天冬酰胺阴离子Asn]-形成的氨基酸离子液体气态阴阳离子对(Emim]Asn])进行理论研究. 通过几何结构优化和频率分析得到势能面上的五个稳定构型. Emim]+和Asn]-之间能够形成较强的氢键相互作用, 零点能校正后的能量在-373.96至-326.28 kJ·mol-1之间. 其稳定化能主要来源于Asn]-中羰基O的孤对电子lp(O)与Emim]+中C—H反键轨道σ*(C—H)之间的相互作用: lp(O)→σ*(C—H). 红外光谱特征和自然布居分析(NPA)计算表明咪唑阳离子中参与形成氢键的C—H键振动的红移值、阴阳离子间的电荷转移与氢键相互作用能成正比关系. 分子中的原子(AIM)理论分析得到Emim]+和Asn]-之间的氢键相互作用以静电作用为主. 通过计算结果初步探讨影响氨基酸离子液体玻璃化温度Tg的结构因素.

Interaction between 1-Ethyl-3-Metyl-Imidazolium Cation and Asparagine Anion

Gas phase ion pairs of the amino acid ionic liquid 1-ethyl-3-methyl-imidazolium asparagine (Emim]Asn]) was investigated with density functional theory at B3LYP/6-311+G(d,p) level. Five geometries of the Emim]Asn] complex were optimized and their geometrical parameters are discussed in detail. Theoretical results indicate that H-bond interactions of Emim] Asn] are very strong, -373.96 to -326.28 kJ·mol -1 with zero point energy (ZPE) correction, which is mainly attributed to the interaction between lone pairs of the carbonyl O atom in Asn]- and the antibonding orbital of C—H in Emim]+. Interaction H-bond energies, IR spectra, and natural population analysis (NPA) were presented and analyzed，declaring that both the red shift of the C—H stretching frequencies in the imidazolium cation and the charge transferred between cation and anion were in roughly direct proportion to the interaction energies.Atoms inmolecules (AIM) analyses indicate that theH-bond between Emim]+ and Asn]- is primarily ionic character. A preliminary analysis of cation-anion interactions provides some initial hints as to the structural factors that contribute to the experimental glass transition temperature Tg.