咪唑类离子液体与酪氨酸相互作用及机理的密度泛函理论研究（英文）

离子液体的物理化学性质稳定且结构可调,被认为是潜在的新一代绿色高效生物分子溶剂。本文通过密度泛函理论研究了系列咪唑基离子液体与两性离子型氨基酸(酪氨酸)的相互作用及机理。利用对称微扰理论(SAPT)、分子中的原子理论(AIM)及约化密度梯度函数(RDG),分析了氢键作用、静电力、诱导力和色散力对离子液体-氨基酸体系相互作用的贡献。计算结果表明静电作用对于阴、阳离子与酪氨酸的相互作用占主导地位。对于系列阳离子而言,具有不同的甲基取代位点和烷基侧链长度对不同的相互作用模式会产生显著影响。其中,当甲基位于咪唑环的C2位点时,诱导力与色散力占比差别较小;当甲基取代位于咪唑环的N3位点时,诱导力与色散力占比差别较大。产生这一差异的原因在于当甲基位于C2位时,氢键、咪唑环与苯环之间的π~+–π作用为主要作用模式,而甲基取代位为N3位时,氢键和烷基链与苯环之间的C_(Alkyl)―H…π作用则成为主导。进一步获得离子对-酪氨酸的相互作用能变化趋势与阳离子-酪氨酸的变化趋势一致,阴阳离子的共同作用使其与酪氨酸结合更稳定。该研究结果阐明了离子液体中阳离子氢键位点及侧链长度差异对于离子液体-酪氨酸体系的相互作用模式的影响机制,为高效分离氨基酸的功能性离子液体的设计和筛选提供了新思路。     

碳纳米管与咪唑类离子液体相互作用机制的理论研究

离子液体(IL)与碳纳米管(CNT)形成的复合体系在许多重要领域有潜在的应用价值,然而人们对于其微观结构的理解尚不清晰,对IL与CNT相互作用机理的认识还存有争议.本文以(8,0)CNT与1-丁基-3-甲基咪唑六氟化磷IL为例研究了CNT与IL的相互作用,分别探讨了1-丁基-3-甲基咪唑阳离子([BMIM+])、六氟化...     

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.     

离子液体与生物大分子相互作用研究进展

离子液体作为一类新型绿色溶剂,因其独特的理化性质,被广泛应用于催化、有机合成、分离富集和电化学等领域。其中,离子液体在生物大分子的分离纯化、催化和降解方面显示出良好的应用前景,成为研究的热点领域之一。本文从离子液体与生物大分子的本质关系出发,对离子液体在DNA和蛋白质的分离纯化、酶的活性稳定性和天然纤维素溶解等过程中与生物大分子之间的相互作用进行了综述。     

肾上腺素与胞嘧啶相互作用的密度泛函理论研究

采用密度泛函理论（DFT）B3LYP方法和6-311＋G（d,p）基组对肾上腺素-胞嘧啶复合物进行结构优化和频率计算,得到15种稳定的复合物.研究发现,所有的复合物进行基组重叠误差（BSSE）校正后的相互作用能为-11.43^-48.96kJ/mol,符合氢键能量范围,相互作用能主要由氢键所贡献.结构和振动频率分析显示,氢键的形成使相应O（N）—H键的键长变长,对称伸缩振动频率减小,说明复合物中形成的氢键都是正常的红移型氢键.应用自然键轨道（NBO）理论和分子中的原子（AIM）理论对15种复合物的氢键性质和特征进行分析,发现氢键对于复合物的稳定性起着重要作用,当复合物形成2个或更多的氢键时,氢键的数目、类型及强度共同决定着复合物的稳定性,复合物基本符合三氢键〉二氢键〉单氢键的稳定顺序,三氢键复合物4是最稳定的,复合物3存在单氢键O—H…O,比部分二氢键复合物要稳定.     

烷基咪唑型离子液体与牛血清白蛋白的相互作用研究

应用荧光光谱、紫外吸收光谱、傅立叶变换红外光谱和核磁共振波谱研究了烷基咪唑型离子液体[bmim][PF6]及其前体物质[bmim]Cl与牛血清白蛋白(BSA)分子间的相互作用.研究表明:在生理pH值条件下,[ bmim][ PF5]和[bmim] Cl均对BSA的内源性荧光产生猝灭,其猝灭程度[bmim][ PF6]＞...     

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.     

聚合物在咪唑类离子液体中的溶解

离子液体（ILs）具有难挥发、热稳定、宽液程和高电导率等独特优点,在聚合物领域中的应用受到越来越多的关注。由于ILs内部的复杂相互作用力,ILs的溶剂化能力还不能像分子溶剂那样有定量的方法来表征,特别是ILs与聚合物的相容性没有一个统一的判据。本文从咪唑基ILs内部的四个主要相互作用力出发,简述了ILs内部的相互作用对...     

阳离子-π体系相互作用的理论研究——Ⅰ.铵离子-苯复合物构型及相互作用的密度泛函研究

运用密度泛函B3LYP/6 31G 方法对铵离子 苯复合物的 6种可能构型进行了计算研究 ,发现铵离子的 2个氢指向苯环且不具对称性的结构为能量优势结构 .根据计算得到的复合物结构特点 ,分子间作用方式及热力学参数 ,得出铵离子和苯之间的作用是氢键相互作用的结论 .     

硝仿肼离子对相互作用的密度泛函理论研究

用密度泛函理论(DFT)方法,在B3LYP/6-31+G^**水平下,求得硝仿肼离子对体系势能面上2种全优化构型.经基组叠加误差(BSSE)和零点能校正,求得离子对最大相互作用能为-420.03kJ/mol,肼和硝仿离子化所需能量可由该值得到完全补偿.离子对间键的主要贡献为库仑作用,但键鞍点上的电子密度值表明共价作用也有显著的贡献.基于统计热力学求得相关体系的热力学性质,298.2K时由自由离子形成最稳定离子对的最大焓变和最大自由能变化分别为-419.72和-376.61kJ/mol     

烷基咪唑型卤盐类离子液体的合成机理研究

用密度泛函理论考察了甲基咪唑和一系列的卤代烷烃(氯乙烷,氯丁烷,溴乙烷,溴丁烷)反应合成咪唑类离子液体的反应机理. 在B3LYP/6-31++G**//B3LYP/6-31G*基组水平上找到了两条反应路径：路径A(反应物→TS1→P1)和路径B(反应物→TS2→P2). 在路径A中, 卤素离子和咪唑环C2上的氢质子形成氢键；在路径B中, 卤素离子和咪唑环C5上的氢质子形成氢键. 计算发现, 氢键的形成在反应中起到了非常重要的作用, 特别是咪唑环C2上的氢质子在和卤素离子成氢键后形成了一个五员环结构的过渡态, 该过渡态能量较低. 经过渡态TS1的反应途径其活化能要低于经过渡态TS2的反应途径, 反应路径A为主要的反应通道. 计算结果表明, 经过渡态TS1的反应途径是一放热过程, 这和实验观察现象一致.     

The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids

[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (pK_a) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The pK_a values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (H₀) values (0.05 mol·L⁻¹) were about 4.6 in water. In addition, the pK_a values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.     

咪唑氟硼酸类离子液体熔点与分子内相互作用能的关系

运用密度泛函理论B3LYP方法及6-311++G(d,p)基组对11种咪唑氟硼酸离子液体进行了研究.选择相应化合物的离子体系{[XIM][BF4]n}(n-1)-(n=2,3)作为研究对象,即研究体系由一个烷基咪唑阳离子XIM+和2-3个BF4-阴离子构成,对其进行结构优化.在优化得到的最低能量构型的基础上计算了分子内阳离子与阴离子间的相互作用能,同时考虑了基组重叠误差的修正.结果表明所研究离子体系的离子间相互作用能与离子液体的实验熔点之间存在明确的线性关系,并且所得到的线性方程与氨基酸阳离子型离子液体中存在的线性关系相近.我们的工作为今后借助量子化学方法设计功能化离子液体提供了一定的理论基础.     

Coupling‐Reagent‐Free Synthesis of Dipeptides and Tripeptides Using Amino Acid Ionic Liquids

A general method for the synthesis of dipeptides has been developed, which does not require any coupling reagents. This method is based on the reaction of readily available HCl salts of amino acid methyl esters with tetrabutylphosphonium amino acid ionic liquids. The isolation procedure of stepwise treatment with AcOH is easy to carry out. The method was extended to the synthesis of tripeptide, tyrosyl‐glycyl‐glycine, present in IMREG‐1, also.     

A Comprehensive Study on Lyotropic Liquid–Crystalline Behavior of an Amphiphile in 20 Kinds of Amino Acid Ionic Liquids

We examined the self‐organization behavior of a designed amphiphilic molecule in 20 kinds of amino acid ionic liquids composed of 1‐butyl‐3‐methylimidazolium cation and natural amino acid anion ([C4mim][AA]). Addition of [C4mim][AA], regardless of their anion species, to the amphiphile provided homogeneous mixtures showing lyotropic liquid–crystalline (LC) behavior. Upon increasing the component ratio of [C4mim][AA] in the mixtures, a successive change of the mesophase patterns from inverted hexagonal columnar, in some case via bicontinuous cubic, to layered phases was observed. By examining the LC properties at various temperatures and component ratios, we constructed lyotropic LC phase diagrams. Interestingly, the appearance of these phase diagrams is greatly different according to the selection of [AA]. Through comparison, we found that the self‐organization behavior of an amphiphile in ionic liquids can be tuned by controlling their ability to form hydrogen‐bond, van der Waals, and π‐π interactions.     

Macrocyclic Ionic Liquids with Amino Acid Residues: Synthesis and Influence of Thiacalix[4]arene Conformation on Thermal Stability

Novel thiacalix[4]arene based ammonium ionic liquids (ILs) containing amino acid residues (glycine and L-phenylalanine) in cone, partial cone, and 1,3-alternate conformations were synthesized by alkylation of macrocyclic tertiary amines with N-bromoacetyl-amino acids ethyl ester followed by replacing bromide anions with bis(trifluoromethylsulfonyl)imide ions. The melting temperature of the obtained ILs was found in the range of 50–75 °C. The effect of macrocyclic core conformation on the synthesized ILs’ melting points was shown, i.e., the ILs in partial cone conformation have the lowest melting points. Thermal stability of the obtained macrocyclic ILs was determined via thermogravimetry and differential scanning calorimetry. The onset of decomposition of the synthesized compounds was established at 305–327 °C. The compounds with L-phenylalanine residues are less thermally stable by 3–19 °C than the same glycine-containing derivatives.     

Ionic liquids as additives in high performance liquid chromatography: Analysis of amines and the interaction mechanism of ionic liquids

As novel solvents, ionic liquids have many applications in synthesis, catalysis and analytical separation, i.e. extraction and chromatography separation. In this paper, some amines including benzidine, benzylamine, N-ethylaniline and N,N′-dimethylaniline are separated using ionic liquids as additives for the mobile phase in high performance liquid chromatography (HPLC). The effects of the length of alkyl chain or counterions on different ionic liquids and their concentrations on the separation of these analytes are performed. The differences between ionic liquids and tetrabutylammonium bromide (TBA) on the separation of o-, m-, p-phthalic acids are compared and the results show that ionic liquids are ion-pair reagents in essence, although their hydrophobicity and hydrogen bonding also play important roles.     

A Computational Analysis of the Reaction of SO2 with Amino Acid Anions: Implications for Its Chemisorption in Biobased Ionic Liquids

We report a series of calculations to elucidate one possible mechanism of SO₂ chemisorption in amino acid-based ionic liquids. Such systems have been successfully exploited as CO₂ absorbents and, since SO₂ is also a by-product of fossil fuels’ combustion, their ability in capturing SO₂ has been assessed by recent experiments. This work is exclusively focused on evaluating the efficiency of the chemical trapping of SO₂ by analyzing its reaction with the amino group of the amino acid. We have found that, overall, SO₂ is less reactive than CO₂, and that the specific amino acid side chain (either acid or basic) does not play a relevant role. We noticed that bimolecular absorption processes are quite unlikely to take place, a notable difference with CO₂. The barriers along the reaction paths are found to be non-negligible, around 7–11 kcal/mol, and the thermodynamic of the reaction appears, from our models, unfavorable.     

Interactions between a dsDNA Oligonucleotide and Imidazolium Chloride Ionic Liquids: Effect of Alkyl Chain Length,Part I

Ionic liquids (ILs) have become nearly ubiquitous solvents and their interactions with biomolecules has been a focus of study. Here, we used the fluorescence emission of DAPI, a groove binding fluorophore, coupled with molecular dynamics (MD) simulations to report on interactions between imidazolium chloride ([Im_n,1]⁺) ionic liquids and a synthetic DNA oligonucleotide composed entirely of T/A bases (7(TA)) to elucidate the effects ILs on a model DNA duplex. Spectral shifts on the order of 500–1000 cm⁻¹, spectral broadening (~1000 cm⁻¹), and excitation and emission intensity ratio changes combine to give evidence of an increased DAPI environment heterogeneity on added IL. Fluorescence lifetimes for DAPI/IL solutions yielded two time constants 0.15 ns (~80% to 60% contribution) and 2.36–2.71 ns for IL up to 250 mM. With DNA, three time constants were required that varied with added IL (0.33–0.15 ns (1–58% contribution), ~1.7–1.0 ns (~5% contribution), and 3.8–3.6 ns (94–39% contribution)). MD radial distribution functions revealed that π-π stacking interactions between the imidazolium ring were dominant at lower IL concentration and that electrostatic and hydrophobic interactions become more prominent as IL concentration increased. Alkyl chain alignment with DNA and IL-IL interactions also varied with IL. Collectively, our data showed that, at low IL concentration, IL was primarily bound to the DNA minor groove and with increased IL concentration the phosphate regions and major groove binding sites were also important contributors to the complete set of IL-DNA duplex interactions.