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.     

质子化甜菜碱阳离子与双三氟甲磺酰亚胺阴离子相互作用的理论研究

利用密度泛函理论(DFT)方法, 在B3LYP/6-311＋G(d,p)水平下, 对质子化甜菜碱阳离子与双三氟甲磺酰亚胺阴离子形成的气态阴阳离子对([Hbet][Tf₂N])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六个稳定构型. 计算结果表明[Hbet]^＋和[Tf₂N]^－之间能够形成较强的氢键相互作用, 氢键相互作用的稳定化能主要来源于[Tf₂N]^－中O, N原子的孤对电子和[Hbet]^＋中参与形成氢键的O-H, C-H反键轨道之间的相互作用. 自然布局分析(NPA)给出气态[Hbet][Tf₂N]离子对中阴阳离子间的电荷转移比传统离子液体中电荷转移的数值小. AIM (atoms in molecules)分析得到[Hbet]^＋和[Tf₂N]^－之间的氢键相互作用以静电作用为主. 通过实验和理论结果相比较, 初步探讨影响离子液体熔点及其对金属离子选择性溶解的结构因素.     

烷基乙二胺-CF_3CO_2型质子化离子液体的分子间氢键作用

利用密度泛函理论M06-2X方法,在6-311G(d,p)水平下,对由N-烷基乙二胺阳离子[HAlkyl]~+(Alkyl=Hex,Oct,Et Hex)与三氟乙酸阴离子[TFA]~-形成的[HHex][TFA],[HOct][TFA]及[HEtHex][TFA]型质子化离子液体(PILs)的离子对进行了理论研究.通过几何优化和分子振动频率分析3种PILs均得到5种较稳定构型[HAlkyl][TFA]S1~S5.结果表明,[HAlkyl]~+与[TFA]~-间发生了质子转移形成了O—H…N型氢键.3种PILs的基组重叠误差校正后的分子间相互作用能(ΔE_(int)~(BSSE))在-449.91~-522.87 kJ/mol范围内.由于分子间形成了较强的O—H…N氢键作用,引起N—H振动频率消失,在2200~2700 cm~(-1)范围内出现了较强的O—H键振动.通过自然键轨道(NBO)及分子中原子(AIM)理论计算,研究了分子间氢键作用的相对强度及其对分子构型稳定性的影响.NBO分析结果表明,其稳定化能主要源自于[HAlkyl]的氨基中孤对电子LP(N)与[TFA]中O—H反键轨道σ*(H—O)间的相互作用,即LP(N)→σ*(H—O).并探讨了阳离子部位[HAlkyl]~+的质子化位置以及烷基链长、支链的引入对[HAlkyl]与[TFA]间氢键作用强度的影响.     

一种室温离子液体与水相互作用的密度泛函理论研究

采用量子化学计算中的密度泛函理论(DFT),在B3LYP/6-31+G(d,p)计算水平上研究了离子液体1-乙基-3-甲基咪唑四氟硼酸盐([Emim]BF4)及其与水分子形成的复合物的稳定构型和相互作用能;经振动频率分析得到了[Emim]BF4及其与水的复合物的红外光谱.计算结果表明,相对于水分子与阳离子的作用而言,水分子与阴离子的作用对离子液体结构的影响更大.与此同时,实验测得的[Emim]BF4的红外光谱与计算结果吻合.     

离子液体1-乙基-3-甲基咪唑三氟甲基磺酸盐与水之间的氢键作用(英文)

通过衰减全反射红外(ATR-IR)光谱、二维红外相关谱结合量子化学计算研究了1-乙基-3-甲基咪唑三氟甲基磺酸盐([emim][OTf])和水之间的氢键作用.结果表明,在[emim][OTf]-水体系中,当水的浓度较低时(0.1x(D2O)0.3),水分子的主要存在形式是包裹在离子液体中的没有缔合的单体.水分子优先填充到[emim][OTf]的空隙中,并且与[emim][OTf]的阴离子形成"[OTf]-…HOH…[OTf]-"结构,水分子与[emim][OTf]的阳离子的相互作用位点是烷基氢而不是芳香氢;当水分子浓度较高时,水分子倾向于自身缔合形成小团簇结构,水分子与[emim][OTf]的阳离子的相互作用位点是芳香氢而不是烷基氢.     

Zn-MOF-74负载ILs的结构稳定性和吸附研究

离子液体（ILs）作为一种新型绿色溶剂应用广泛,以多孔材料MOFs作为支撑体负载ILs,不仅有望降低离子液体的高粘性,而且有助于提高材料的吸附分离能力,但要如何选择适合MOFs体系来负载ILs是一个难点。本文采用密度泛函理论（DFT）,利用VASP和Gaussian 09 程序对负载IL（[Emim][BF4]）的Zn-MOF-74的结构稳定性进行系统研究,从几何结构、电荷分析、相互作用等方面将Zn-MOF-74@[Emim][BF4]复合体系与[Emim][BF4]和Zn-MOF-74比较分析。计算结果表明,负载[Emim][BF4]的Zn-MOF-74体系中,IL的阴离子与Zn-MOF-74的开放金属位点Zn发生强相互作用, Zn、F1原子之间因库仑力成键,造成了MOF-74配位构型的改变。IL的负载扰乱了Zn-MOF-74结构的对称性,增强了离子间相互作用。Zn-MOF-74 @[Emim][BF4]复合体系形变过程伴随着电荷转移,其吸附能为-1.032 eV,绘制的差分电荷以及相互作用图验证MOF和IL之间发生了化学吸附。进一步探讨负载离子液体的Zn-MOF-74吸附能力,研究了CO2在复合体系中吸附作用机制。     

离子液体表面活性剂1-丁基-3-甲基咪唑烷基硫酸酯的合成及其在水溶液中的聚集行为

采用离子交换法,由1-丁基-3甲基咪唑氯盐（C4mimCl）和烷基硫酸钠合成了一系列无卤素的阴离子表面活性离子液体—1-丁基-3-甲基咪唑烷基硫酸酯[C4mim][CnH2n 1SO4](n=8,12,16),利用表面张力仪、稳态荧光光谱等手段考察了表面活性离子液体在水溶液表面及体相中的聚集行为,结果表明,与传统无机反离子相比,有机咪唑阳离子[C4mim] 作为反离子的离子液体型表面活性剂具有较高的表面活性,[C4mim] 产生的氢键引起的抑制分子规则排列的作用小于其促进分子有序排列的疏水作用。长烷基链的阴离子是界面膜及胶束的主要组成成分,阴离子疏水烷基碳链的增长虽然可促进胶束的形成,但却在一定程度上抑制[C4mim] 离子参与界面或胶束的形成;阴离子所带烷基链越长,越不利于阳离子[C4mim]＋参与界面膜或胶束的形成,界面膜或胶束中表面活性剂排布越松散,即界面张力越大,体系中胶束聚集数较小。     

1-乙胺基-3-甲基咪唑四氟硼酸盐吸收CO_2的理论研究

采用密度泛函理论(DFT)对离子液体1-乙胺基-3-甲基咪唑四氟硼酸盐([NH2e-mim][BF4])吸收CO_2的反应机理进行了研究.在B3LYP/6-311++G(d,p)计算水平下,对离子液体[NH2e-mim][BF4]的结构及与CO_2反应的中间体、过渡态和产物进行了全优化,获得了优化结构的构型参数、振动频率和热力学数据.利用自然键轨道(NBO)分析了离子液体[NH2e-mim][BF4]和CO_2的自然电荷布居.计算结果表明,通过阳离子[NH2e-mim]+自偶解离产生的阳离子[NH3e-mim]2+能与阴离子[BF4]-结合形成更强的离子键.根据反应吉布斯自由能变(ΔG0—)和焓变(ΔH0—)的计算结果,判断离子液体[NH2e-mim][BF4]吸收CO_2按理论摩尔比2∶1分步进行反应,吸收过程中质子的转移需克服52.51 k J/mol的能垒.     

核磁方法研究离子液体与丙酮的相互作用

运用核磁共振手段, 研究了室温离子液体1-辛基-3-甲基咪唑四氟硼酸盐([C8mim][BF4])在不同比例的离子液体／丙酮混合体系中1H和13C的化学位移及13C的自旋-晶格弛豫时间(T1). 结果表明, 离子液体[C8mim][BF4]的阳离子芳环上的氢原子, 以及与氮原子直接相连的甲基和亚甲基上的氢原子都与丙酮羰基上的氧原子有相互作用, 从而减弱了离子液体阴阳离子间的强相互作用, 使离子液体的运动加快, 黏度降低.     

离子液体1-乙基-3-甲基咪唑三氟甲基磺酸盐与水之间的氢键作用

通过衰减全反射红外（ATR-IR）光谱、二维红外相关谱结合量子化学计算研究了1-乙基-3-甲基咪唑三氟甲基磺酸盐（[emim][OTf]）和水之间的氢键作用. 结果表明,在[emim][OTf]^-水体系中,当水的浓度较低时（0.1< x（D₂O）< 0.3）,水分子的主要存在形式是包裹在离子液体中的没有缔合的单体. 水分子优先填充到[emim][OTf]的空隙中,并且与[emim][OTf]的阴离子形成“[OTf]^-…HOH…[OTf]^-”结构,水分子与[emim][OTf]的阳离子的相互作用位点是烷基氢而不是芳香氢;当水分子浓度较高时,水分子倾向于自身缔合形成小团簇结构,水分子与[emim][OTf]的阳离子的相互作用位点是芳香氢而不是烷基氢.     

Computational studies of the structure and cation-anion interactions in 1-ethyl-3-methylimidazolium lactate ionic liquid

Quantum chemical calculations of the structures and cation-anion interaction of 1-ethyl-3-methylimidazolium lactate ([Emim][LAC]) ion pair at the B3LYP/6-31++G** theoretical level were performed. The relevant geometrical characteristics, energy properties, intermolecular H-bonds (H-bonds), and calculated IR vibrations with respect to isolated ions were systematically discussed. The natural bond orbital (NBO) and atoms in molecule (AIM) analyses were also employed to understand the nature of the interactions between cation and anion. The five most stable geometries were verified by analyzing the relative energies and interaction energies. It was found that the most of the C-H···O intermolecular H-bonds interactions in five stable conformers have some covalent character in nature. The elongation and red shift in IR spectrum of C-H bonds which involve in H-bonds is proved by electron transfers from the lone pairs of the carbonyl O atom of [LAC] to the C-H antibonding orbital of the [Emim]+. The interaction modes are more favorable when the carbonyl O atoms of [LAC] interact with the C2-H of the imidazolium ring and the C-H of the ethyl group through the formation of triple H-bonds.     

Homogeneous enzymatic reactions in ionic liquids with poly(ethylene glycol)-modified subtilisin

Subtilisin Carlsberg was covalently modified with comb-shaped poly(ethylene glycol) (PM13). PM13-modified subtilisin (PM13-Sub) was readily solubilized in three different ionic liquids (ILs), i.e., [Emim][Tf2N], [C2OC1mim][Tf2N] and [C2OHmim][Tf2N]. Analysis of homogeneous enzymatic reactions in the ILs revealed that PM13-Sub exhibited excellent catalytic performance while the native enzyme suspended in ILs showed no activity. Hydrophobicity of ILs slightly affected enzyme activity, and the relatively hydrophobic IL [Emim][Tf2N] was the preferred medium for enzymatic reactions, similar to enzymatic reactions in conventional organic solvents. Enzyme activity was much higher in [Emim][Tf2N] than in conventional organic solvents, and excellent activity was associated with unique properties of ILs such as hydrophobicity and high polarity. Furthermore, PM13-Sub showed good stability in [Emim][Tf2N], and maintained 80% of its initial activity after 60 h.     

Carbon-based ionogels: tuning the properties of the ionic liquid via carbon-ionic liquid interaction

The behavior of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium dicyanamide [Emim][DCA] and 1-ethyl-3-methylimidazolium triflate [Emim][TfO], in (meso)porous carbonaceous hosts was investigated. Prior to IL incorporation into the host, the carbon matrix was thermally annealed between 180 and 900 °C to control carbon condensation and surface chemistry. The resulting materials have an increasing "graphitic" carbon character with increasing treatment temperature, reflected in a modified behavior of the ILs when impregnated into the carbon host. The two ILs show significant changes in the thermal behavior as measured from differential scanning calorimetry; these changes can be assigned to anion-π interaction between the IL anions and the pore wall surfaces of these flexible carbonaceous support materials.     

Understanding the interactions between tris(pentafluoroethyl)-trifluorophosphate-based ionic liquid and small molecules from molecular dynamics simulation

Tris(pentafluoroethyl)trifluorophosphate ([FEP])-based ionic liquids have been widely applied in many fields. For better understanding the properties of [FEP]-based ionic liquids, the interactions between 1-hexyl-3-methylimidazolium ([hmim])[FEP] and small molecules were investigated by molecular dynamics simulations in this work. The small molecules are water, methanol and dimethyl ether. The united-atom (UA) force fields were proposed for methanol and dimethyl ether based on AMBER force field. The densities, enthalpies of vaporization, excess molar properties, and diffusion coefficients of the mixtures were calculated, as well as the microscopic structures characterized by radial distribution functions. Both of the results of the excess energies and microscopic properties show that the strongest interaction is between [hmim][FEP] and dimethyl ether, whereas the interaction between [hmim][FEP] and water is the weakest. Moreover, [hmim][FEP] is more hydrophobic than [hmim] hexafluorophosphate ([PF6]), and the three solutes are mainly distributed around [FEP] anion.     

Characterization of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N])∕TX-100∕cyclohexane ternary microemulsion: investigation of photoinduced electron transfer in this RTIL containing microemulsion

In this study we have characterized a ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl)imide containing ternary nonaqueous microemulsion ([Emim][Tf(2)N]∕∕TX-100∕cyclo- hexane). The phase behavior and dynamic light scattering study show that the [Emim][Tf(2)N]∕TX-100∕cyclohexane three component system can form microemulsion with [Emim][Tf(2)N] as polar core at suitable condition. We have investigated photoinduced electron transfer (PET) using dimethyl aniline as electron donor and several Coumarin dyes as electron acceptor molecules at two different R values (R = [ionic liquid]∕[surfactant]) to observe how the dynamics of the PET rate is affected in this type of confined microenvironment compared to that of the PET dynamics in neat ionic liquid and other pure solvent media. The plot of observed k(q) values with the free energy change (ΔG(0)) for electron transfer reaction shows an apparent inversion in the observed rate as predicted by the Marcus theory.     

Influence of halide ions on the chirality and luminescent property of ionothermally synthesized lanthanide-based metal-organic frameworks

Four lanthanide-based metal-organic frameworks, [Emim][Ln(1.5)(2,5-tdc)(2)]Cl(1.5-x)Br(x) (Ln = Nd 1, Eu 2) and [Emim][Ln(2,5-tdc)(2)] (Ln = Nd 3, Eu 4) (2,5-tdc = thiophene-2,5-dicarboxylate, Emim = 1-methyl-3-ethylimidazolium), were synthesized under ionothermal conditions. Compounds 1 and 2 crystallize in the polar space group P2(1)2(1)2, while 3 and 4 crystallize in the central symmetry space group P2(1)/c. Luminescence studies revealed a significantly higher quantum yield of 4 than that of 2, with similar lifetimes. It is clear that the coordination of the halide ions has profound effects on the structures and properties of these lanthanide-based metal-organic frameworks.     

A novel efficient medium for chromogenic catalysis of tetramethylbenzidine with horseradish peroxidase

The traditional surfactant sodium dodecyl sulfate (SDS) and ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF₄]) have been combined to create a novel efficient medium for chromogenic catalysis of 3,3',5,5'-tetramethylbenzidine with horseradish peroxidase in presence of H₂O₂. The results have shown the [Emim][BF₄] in the mediums can promote the rate of formation of the blue chromogen, the SDS is responsible for the stabilization of the blue chromogen due to the electrostatic attraction between positively charged blue chromogen and the negatively charged surfactant. The SDS/[Emim][BF₄] combination not only enhance catalytic activity of HRP remarkably but also stabilize the blue chromogen formed in the HRP oxidation of the substrate TMB compared to the conventional medium. Based on the superior combination of SDS and [Emim][BF₄], the colorimetric assay for detecting HRP activity and H₂O₂ concentration was established. This work demonstrates a novel efficient medium for chromogenic catalysis with potential applications in biosensors and clinical diagnosis.     

Electrophilic nitration of aromatics in ionic liquid solvents.

Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Hünig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.