平面五配位硅、 锗XBe5H6(X=Si,Ge)团簇

采用密度泛函理论PBE0方法, 在aug-cc-pVTZ水平上理论预测了含平面五配位硅和锗原子的XBe₅H₆ (X=Si, Ge)团簇. 势能面系统搜索及高精度量化计算表明, 它们均为全局极小结构. XBe₅H₆(X=Si, Ge)团簇整体呈完美的扇形结构: Si/Ge原子被5个金属Be原子配位; 4个H原子以桥基方式与Be原子相键连, 剩余的2个 H原子以端基方式与两端的Be原子成键. 化学键分析表明, XBe₅H₆(X=Si, Ge) 团簇中XBe₅单元具有完全离域的1个π及3个σ键, 外围铍氢间形成4个Be—H—Be 三中心二电子(3c-2e)键及2个定域的Be—H键. XBe₅单元上离域的2π及6σ电子赋予体系π和σ双重芳香性, 并使Si/Ge原子满足八隅律（或八电子规则）. 能量分解-化学价自然轨道分析揭示, Si/Ge和Be₅H₆之间主要为电子共享键.     

g-CN体系的准粒子能带结构和光学特性

利用多体格林函数理论,本文研究了二维CN体系(包括triazine和tri-s-triazine)的激发态特性。通过GW方法,我们计算了准粒子的能量。考虑电子-空穴相互作用,通过求解Bethe-Salpeter方程,我们获得了激发态能量和光谱。我们发现,在这两种CN体系的价带中,σ轨道和π轨道之间的交换作用非常强烈。由于占据的σ轨道和π轨道之间的准粒子修正量非常不同,因此,为了得到准确的带隙值和光谱,我们需要对这两种轨道开展精确的GW计算。与单层的CN体系相比,双层结构中层与层之间的范德华相互作用使带隙值降低了0.6 eV,而光吸收谱红移了0.2 eV,这是由于双层结构具有更小的激子束缚能。我们计算的吸收峰的位置与实验结果符合很好。实验中的吸收峰主要是由深能级的π轨道到π^*轨道的跃迁形成的。π→π^*跃迁和σ→π^*跃迁之间的耦合能够在长波长范围产生弱的吸收尾巴,如果调整入射光的极化方向,由σ→π^*跃迁产生的高强度的吸收峰将会在更低能量处出现。     

碰撞能对K(2S)+HF(X1Σ+)→KF(X1Σ+)+H(2S)反应的影响

基于Sayós等构建的基态势能面, 运用准经典轨线方法对原子-分子反应K(²S)+HF(X¹∑⁺)→KF(X¹∑⁺)+ H(²S)的立体动力学性质进行了研究. 计算了该反应的极化微分反应截面、 两矢量k?j'相关分布函数P(θ_r)、 三矢量k?k'?j'相关分布函数P(?_r)和空间分布函数P(θ_r,?_r). 结果表明, 产物KF的转动角动量j′不仅在垂直于反应物相对速度矢量k的方向上有强烈的取向效应, 而且还定向于y轴的负方向, 转动角动量j′敏感地依赖于碰撞能.     

1, 1, 2, 3, 4, 5-六苯基硅杂环戊二烯X射线谱的理论研究

近年来苯基硅杂环戊二烯作为一类高效的有机发光二极管材料被广泛研究。本工作利用密度泛函理论结合芯态空穴近似研究了1, 1, 2, 3, 4, 5-六苯基硅杂环戊二烯分子中碳原子K壳层和硅原子L壳层的X射线光电子能谱和近边X射线吸收精细结构谱,与实验谱线符合较好。通过理论结果对实验测量的1, 1, 2, 3, 4, 5-六苯基硅杂环戊二烯分子的X射线谱进行了分析和标定。我们发现碳原子K壳层X射线光电子能谱在低能区283.8eV处的谱峰是由于与硅原子成键的两个电负性较强的碳原子导致的。碳原子K壳层近边X射线吸收精细结构谱中最强的吸收峰与苯分子的吸收峰类似。硅原子L壳层近边X射线吸收精细结构谱两个主要吸收峰分别来自于σ_Si-C^*和π_Si-Ph^*跃迁。     

吡咯锂的合成、表征及晶体结构

Development of clean energy is an urgent requirement because of the depletion of fossil energy sources and increasingly severe environmental pollution. However, the lack of safe and efficient hydrogen storage materials is one of the bottlenecks in the implementation of hydrogen energy. Liquid organic hydrogen carriers (LOHCs) have been recognized as potential materials for the storage and transportation of hydrogen owing to their high gravimetric and volumetric hydrogen densities, reversible hydrogen absorption and desorption ability, and ease of widespread implementation with minimal modification on the existing fueling infrastructure. While some LOHCs such as cycloalkanes and N-heterocycles have been developed for hydrogen storage, they require a high hydrogen release temperature due to the large enthalpy change of dehydrogenation. In our previous work, a metallation strategy was proposed to improve the thermodynamic properties of liquid organic hydrogen carriers for hydrogen storage, and a series of metalorganic hydrides were synthesized and investigated. Among them, sodium phenoxide-cyclohexanolate pair, lithium carbazolide-perhydrocarbazolide, and sodium anilinide-cyclohexylamide pair showed promising dehydrogenation thermodynamics and improved hydrogen storage properties. Sodium pyrrolide and sodium imidazolide were also synthesized. However, pyrrolides were not well characterized, and the structure of lithium pyrrolide was not resolved. In the present study, we synthesized sodium and lithium pyrrolides by ball milling and wet chemical methods. One equivalent of hydrogen could be released from the reaction of pyrrole and metal hydrides, indicating the replacement of H by metal. The formation of pyrrolides was confirmed by nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and ultraviolet-visible spectroscopy analyses. The ¹H signals attributed to C－H in the NMR spectra of the alkali metal pyrrolides shifted upfield due to the replacement of the H of N－H with a stronger electron-donating species (Li or Na), resulting in a greater shielding environment upon metallation. The absorption peaks of lithium and sodium pyrrolides showed red shifts, and the intensities became obviously stronger in the UV-Vis spectra, suggesting an enhancement of the conjugation effect, in accordance with theoretical calculations. The structure of lithium pyrrolide was determined by the combined direct space method and first-principles calculations on XRD data and Rietveld refinement. This molecule crystallizes in the monoclinic P2₁/c (14) space group, with lattice parameters of a = 4.4364(7) Å, b = 11.969(2) Å, c = 8.192(2) Å, β = 108.789(8)°, and V = 411.8(2) ų (1 Å = 0.1 nm). Each Li⁺ cation is surrounded by three pyrrolides via cation－N σ bonding with two pyrrolides and a cation–π interaction with the third pyrrolide, where the Li⁺ is on the top of the π face. Our experimental findings are different from the theoretical prediction in the literature.     

方酸与2, 6-二苯并咪唑的超分子自组装及氢键实验与理论研究

在氘代的二甲基亚砜的溶剂中合成了方酸与2, 6-二苯并咪唑的超分子的化合物,并用X射线单晶衍射对其结构进行了表征。晶体结构分析表明:超分子是通过π-π堆积和分子之间氢键所形成的一维链状的聚合物。探讨了不同温度和不同浓度CCl₄溶剂对聚合物中氢键的影响。此外,用密度泛函理论和分子中原子理论对其进行了理论分析,计算结果表明分子间的键能分别是135.65和49.40 J·mol^-1。     

Can QTAIM topological parameters be a measure of hydrogen bonding strength?

The block-localized wave function (BLW) method, which is the simplest variant of ab initio valence bond (VB) theory, together with the quantum theory of atoms in molecules (QTAIM) approach, have been used to probe the intramolecular hydrogen bonding interactions in a series of representative systems of resonance-assisted hydrogen bonds (RAHBs). RAHB is characteristic of the cooperativity between the π-electron delocalization and hydrogen bonding interactions and is identified in many biological systems. While the deactivation of the π resonance in these RAHB systems by the use of the BLW method is expected to considerably weaken the hydrogen bonding strength, little change on the topological properties of electron densities at hydrogen bond critical points (HBCPs) is observed. This raises a question of whether the QTAIM topological parameters can be an effective measure of hydrogen bond strength.     

Research Progress of Regulation of Driving Forces in Short Peptide Supramolecular Self-Assembly北大核心CSCD

Some short peptides can spontaneously self-assemble into various nanostructures via the synergistic driving forces of non-covalent interactions. These non-covalent interactions,including electrostatic interaction,hydrogen bonding,aromatic interactions and other non-covalent interactions,are usually highly coupled together. Through rational sequence design and proper modification of short peptide molecules,the driving forces could be regulated purposively,and the nanostructures and morphologies of the self-assemblies could be controlled accordingly,and thus so as to achieve the fabrication of peptide-based supramolecular biomaterials and develop their functions. In this paper,the effects of hydrogen bonding,π-π stacking, electrostatic interaction,hydrophobic interaction,metal ion coordination and chiral center on the self-assembly behavior of peptide self-assembly have been reviewed. The driving force regulation strategies, including sequence design,pH and concentration adjustment and metal ion coordination,and the resulted nanostructures have also been discussed. We also make the outlooks on the development of peptide-based supramolecular biomaterials with specific functions in biomedicines and biocatalysis. © 2022, Science Press (China). All rights reserved.     

应用ABEEMσπ极化力场对Zn2+水溶液配位微结构和水交换反应进行分子动力学模拟研究

应用ABEEMσπ极化力场,对Zn²⁺水溶液体系进行分子动力学模拟,探讨Zn²⁺的配位微结构和配体水交换反应。水分子模型采用ABEEM-7P精细水模型。模拟后对体系结构、电荷及动力学性质进行细致分析。结构分析表明,平衡体系中Zn²⁺的第一层配位数为6,这与实验值是一致的。水交换反应过程中,溶剂水由O-Zn-O角分线斜上（下）方进攻Zn²⁺,配位水由O-Zn-O角分线斜下（上）方逐渐远离。极化力场模拟时Zn²⁺与交换水间的距离变化波动较大,而固定电荷力场的波动较小。模拟发现,极化力场的径向分布函数能精细地展示第二、三层配体的配位微结构,第二配位层存在靠近Zn²⁺的亚壳层,能与第一水合层发生水交换反应,充分体现了Zn²⁺的极化效应。本文阐明了水交换反应中,Zn²⁺位点电荷与交换水中氧原子孤对电子位点电荷的规律性变化,从电荷的角度解释了水交换反应的合理性。ABEEMσπ极化力场模拟Zn²⁺水溶液获得第一水合层的平均配位驻留时间为2.0×10^-9 s,在实验值范围内,说明ABEEMσπ极化力场可以合理地模拟Zn²⁺水溶液体系。     

八电子Pd4四面体团簇的电子结构稳定性分析

基于理论计算,我们报道了T_d对称性的[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]团簇及一系列类似物的结构与成键。成键分析表明：每个Pd原子都是sp³杂化,其10个价电子与四个配体提供的8个价电子,满足18电子规则。并且,每个Pd原子与四个桥连的SbH₃配体可以形成四个离域的四中心两电子超级σ键或八中心两电子键。一方面,根据超原子网络模型,这个钯团簇可以描述成四个2电子的超原子网络。另一方面,凝胶模型表明,它可以合理化的作为电子组态是1S²1P⁶的8电子超原子。与此同时,d¹⁰…d¹⁰闭壳层相互作用在稳定Pd₄四面体结构中起到了关键性的作用。密度泛函理论计算表明：T_d对称性[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]团簇表现出高度稳定性,具有充满的电子壳层,大的HOMO-LUMO带隙(2.84 eV)以及负的核独立化学位移(NICS)值。此外,基于[Pd₄(μ₃-SbH₃)₄(SbH₃)₄]结构与成键模式,我们设计了一系列稳定的类似物,其有可能被实验合成出来。     

确定分子中离域π键πnm的方法

A method for obtaining the delocalized π bonds π_n^m in a molecule has been discussed in this paper, and the delocalized π bonds π_n^m in linear, bent, planar trigonal, single cyclic conjugated, and polycyclic conjugated molecules have been studied. The reasons of π₃⁴ in NO₂ and 2π₃² in C₃ molecules have been proposed. The delocalized π bonds 2π₁₈¹⁸ in cyclo[18] carbon are analyzed.     

PO2X…PX3/PH2X(X=F,Cl, Br,CH3, NH2)复合物中π-hole磷键作用的电子密度拓扑分析

磷键作为一种新型的分子键合力,因在晶体工程和超分子合成等方面的重要作用而越来越多地引起科研工作者的广泛关注。本文采用量子化学从头算和电子密度拓扑分析等方法,在MP2/aug-cc-pVTZ理论水平上,对PO₂X…PX₃和PO₂X…PH₂X (X = F, Cl, Br, CH₃, NH₂) π型复合物的结构和磷键性质进行了理论研究。研究表明:π-hole磷键复合物存在A和B两种稳定构型,分别以P…P和P…X磷键作用为主。分子中原子(AIM)、非共价作用(NCI)、电子定域函数(ELF)及适应性自然密度划分(AdNDP)分析表明,不同取代基对该类磷键作用的性质产生很大影响:当取代基为给电子基(CH₃, NH₂)时,磷键具有明显的共价作用特征;当取代基为吸电子基(F, Cl, Br)时,构型和取代基不同的磷键分别表现为非共价、部分共价或共价作用特征。自然键轨道(NBO)分析指出,分子间磷键的Wiberg键级的数值越大,磷键的共价性越强,磷键的作用强度越大。构型B的电荷转移主要是PX₃/PH₂X中X原子上的孤对电子转移到PO₂X中π^*(P=O)反键空轨道。     

SiO2/聚乙二醇非牛顿流体流变性能研究

利用应力控制流变仪考察了SiO₂/聚乙二醇分散体系稳态和动态的流变性能. 实验结果表明, 该体系具有剪切变稀和可逆的剪切增稠现象. 稳态应力实验中, 当应力较小时, 体系具有剪切变稀现象, 而在剪切应力(σ)大于临界剪切应力(σ_c^s, σ_c^s=9.99 Pa)后, 体系粘度急剧增大. 在动态实验中, 剪切应力小于临界剪切应力(σ_c^o, σ_c^o=15.85 Pa)时, 储能模量G′减小, 耗能模量G″与复合粘度η*基本不变, 但σ＞15.85 Pa后, G′、G″及η*同步增大, 且在所研究的应力范围内, G″均大于G′. 同时还考察了测试频率、分散相含量以及分散介质平均分子量的差别对流变性的影响. σ_c^o随测试频率的增大而变大; SiO₂质量分数越大, σ_c^o基本不变, 但增稠现象变得更明显; 与平均分子量小的PEG200体系相比, 平均分子量大的PEG400体系, σ_c^o并未发生改变, 但在增稠之前体系的粘度较低, 增稠之后体系粘度增大的幅度较大.     

2-甲基呋喃分子激发态超快非绝热动力学

Excited-state dynamics of 2-methyl furan has been studied by femtosecond time-resolved photoelectron imaging. The molecule 2-methyl furan was simultaneously excited to the n=3 Rydberg series of S₁[¹A"(π3s)], ¹A'(π3p_x), ¹A"(π3p_y) and ¹A"(π3p_z) and the valence state of ¹A'(ππ^*) by two 400 nm photons and subsequently probed by two 800 nm photons. The average lifetime of the Rydberg series and the valence state was measured to be on the time scale of 50 fs by the time-dependent ion yield of the parent ion. Ultrafast internal conversions among these excited states were observed and extracted from the time-dependences of the photoelectron kinetic energy components of these excited states in the photoelectron kinetic energy spectra. Furthermore, it is identified that the ¹A'(ππ^*) state might play an important role in internal conversions among these excited states. The Rydberg-valence mixings, which result in numerous conical intersections, act as the driving force to accomplish such ultrafast internal conversions.     

异氰酸苯酯诱导的类胶原多肽自组装

Synthetic matrices provide powerful tools for dissecting molecular interactions involved in the organization of the extracellular matrix (ECM), establishment of cell axis polarity, and suppression of neoplasticity in pre-cancerous endothelial cells. Collagen is the most abundant protein in extracellular matrix. A de novo approach is essential for the synthesis of collagen matrices which can have a broad impact on the understanding of matrix biology and our capacity to construct safe and medically useful biomaterials. Conventionally, the ECM has been studied by an analytical "top-down" approach, where the individual components of the matrix are first isolated and then characterized to explore their biochemical and functional properties. Since native collagen is difficult to modify and can engender pathogenic and immunological side effects, its application on tissue regeneration is limited. Therefore, we attempted to synthesize artificial collagen directly through small organic molecule recognition. The collagen-like peptides possess various benefits such as being clean, programmable, and easy to modify; therefore, in recent years, they have been used as ideal substrates for the synthesis of collagen nanomaterials. The self-assembly of collagen-like peptides is mainly driven by various non-covalent interactions such as electrostatic attraction, π-π stacking, and metal coordination. This renders a difficulty in the rational design of uniform nanostructures from short synthesized peptides and demands a novel strategy. To date, small organic molecules have been rarely used for the self-assembly of collagen-like peptides. In the present study, we attempted to use the small organic molecules for the combined supramolecular self-assembly of collagen-like peptides. Initially, the collagen-like peptides, (POG)₆ and (POG)₈, synthesized by the solid-phase synthesis technique, were both modified chemically using 4, 4'-methylene bis(phenyl isocyanate) to obtain the collagen-like hybrid peptides, AP₆ and AP₈, respectively. Phenyl isocyanate contributes to the formation of potential weak forces, such as hydrogen bonds and π-π stacking at the N-terminal regions of the collagen-like hybrid peptides. The purity and molecular weight of the collagen-like hybrid peptides were analyzed using analytical high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF), respectively. The stability of AP₆ and AP₈ triple helices was analyzed by circular dichroism (CD) spectroscopy. The small organic molecule 4, 4'-methylene bis(phenyl isocyanate) promoted the unfolding of (POG)₆ and increased the melting temperature (T_m) of (POG)₈ from 37.7 to 58.8 ℃to form a triple helix. The hydrodynamic radii of collagen-like hybrid peptides were measured by dynamic light scattering (DLS). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to analyze the morphology of the aggregation states. AFM results showed that the collagen-like hybrid peptides, AP₆ and AP₈, formed nanofibers spontaneously. Consistent with the AFM results, TEM showed that the AP₆ and AP₈ collagen-like hybrid peptides also formed nanofiber structures. The formation of stable complexes was attributed to the presence of multiple weak interactions such as hydrogen bonding, π-π stacking, and hydrophobic interactions. In the present study, we demonstrated that the chemical modification of collagen-like polypeptides at the N-terminus via the small organic molecule, 4, 4'-methylene bis(phenyl isocyanate), promoted the intramolecular and intermolecular assembly of collagen-like peptides. A simple and effective strategy has been developed in this study to promote the self-assembly of collagen-like peptides.     

基于两亲性喹喔啉的超分子凝胶：手性信号反转以及多重响应手性光学开关

The regulation of supramolecular chirality has applications in various aspects including asymmetric catalysis, chiral sensing, optical materials and smart devices. Additionally, it provides opportunities for the simulation of important activities in living organisms and the clarification of their mechanisms. Herein, we synthesized a chiral gelator SQLG (styrylquinoxalinyl L-amino glutamic diamide) containing a π-conjugated headgroup by introducing the quinoxaline-derived moiety into L-glutamic diamide-based amphiphile via two simple condensation steps. SQLG self-assembled into nanofibers through multiple intermolecular interactions, including π–π stacking, hydrogen bonding and van der Waals interaction, leading to gelation of various organic solvents ranging from nonpolar to polar ones. Chirality transfer from the chiral center to the supramolecular level was observed when organogels formed, which manifested itself in circular dichroism (CD) spectra. The organogels formed in polar solvents such as N, N-dimethylformamide (DMF) and nonpolar solvents such as toluene exhibited opposite signals of supramolecular chirality, attributed to different hydrogen bonding strengths and thus two different types of gelator stacking modes of the gelators which was confirmed by infrared spectroscopy (IR) and X-ray diffraction (XRD). Circular polarized luminescence (CPL) denotes left-handed or right-handed circularly polarized light with different intensities emitted by the chiral luminescent system, and it characterizes the chirality of the excited state, which finds potential application in fields such as 3D optical displays, optical data storage, polarization-based information encryption and bioencoding. Owing to the strong fluorescence and supramolecular chirality, the toluene gel emitted right-handed circular polarized luminescence upon excitation, while the gel formed in DMF did not exhibit CPL emission because of its relatively weak fluorescence. Furthermore, the organogels responded rapidly and distinctly to the stimulus of acid due to the proton-accepting sites in the quinoxaline skeleton. Utilizing NMR spectroscopy, we found that the two nitrogen atoms in the quinoxaline moiety could be protonated upon acidification. During the process, intramolecular charge transfer (ICT) was significantly strengthened and the driving forces of self-assembly underwent remarkable changes, resulting in the collapse of the yellow transparent organogel into a red dispersion. Meanwhile, transformation from nanofibers to nanospheres was observed using a scanning electron microscope (SEM). With change in stacking modes in the supramolecular assembly, a complete inversion of the CD signal was detected. The CPL signal was found to be switched off, which along with the other changes of the system could subsequently be recovered by neutralization of the entire system. Therefore, we constructed a chiroptical switch with multiple stimuli-responsiveness through the introduction of an acid-sensitive π-conjugated moiety into the L-glutamic diamide-based chiral amphiphile.     

Benzohydrazide Derivatives: Gelation and Application in Oil Spill Recovery

The synthesis and gelation properties of a series of organogelators containing a benzohydrazide unit and two alkoxy chains(oBn) were reported herein. oBn(n=8, 10, 12) could form stable gels in commercial fuels(e.g., diesel), which were characterized by low critical gelation concentrations(CGCs) and good mechanical properties (G'>10⁵ Pa). The gelation process was further studied by field-emission scanning electron microscopy(FE-SEM), Fourier transform infrared spectroscopy(FTIR) and X-ray diffraction(XRD), etc. It was demonstrated that in these organogels, molecules self-assembled into fibrils 3D-network, where hydrogen bonding, van der Waals force and π-π interaction were confirmed as the driving forces. As compounds oBn(n=8, 10, 12) show very good gelation properties in diesel, their applications in oil spill treatment have also been tested. It was found that oBn could achieve rapid (<30 s) and effective oil removal at room temperature, being good candidates for oil spill treatment in the future. Also, the removal efficiency could be as high as 95%.     

2, 4, 6-三甲基苯甲酸与5, 5'-二甲基-2, 2'-联吡啶构筑的系列镧系超分子配合物的晶体结构、热分解机理和性能

Six ternary lanthanide complexes formulated as [Ln(2, 4, 6-TMBA)₃(5, 5'-DM-2, 2'-bipy)]₂ (Ln = Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Dy 6; 2, 4, 6-TMBA = 2, 4, 6-trimethylbenzoate; 5, 5'-DM-2, 2'-bipy = 5, 5'-dimethyl-2, 2'-bipyridine) have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, etc. The results of crystal diffraction analysis show that complexes 1–6 are binuclear units, crystallizing in the triclinic Pī space group. Complexes 1–5 are isostructural, and each of the central metal ions has a coordination number of 9. The asymmetric unit of complexes 1–5 consists of one Ln³⁺, one 5, 5'-DM-2, 2'-bipy ligand, and three 2, 4, 6-TMBA^- moieties with three coordination modes: chelation bidentate, bridging bidentate, and bridging tridentate. The coordination geometry of Ln³⁺ is distorted monocapped square antiprismatic. The binuclear units of complexes 1–5 form a one-dimensional (1D) supramolecular chain along the c-axis via π–π stacking interactions between the 2, 4, 6-trimethylbenzoic acid rings. The 1D chains are linked to form a supramolecular two-dimensional (2D) sheet in the bc plane via π–π stacking interactions between the pyridine rings. Although the molecular formulae of complex 6 and complexes 1–5 are similar, the coordination environment of the lanthanide ions is different in the two cases. The asymmetric unit of complex 6 contains a Dy³⁺ ion coordinated by a bidentate 5, 5'-DM-2, 2'-bipy and three 2, 4, 6-TMBA^- ligands adopting bidentate and bridging bidentate coordination modes. The Dy³⁺ metal center has a coordination number of 8, with distorted square antiprismatic molecular geometry. The binuclear molecule of 6 is assembled into a six-nuclear unit by π–π weak staking interactions between two 5, 5'-DM-2, 2'-bipy ligands; then, adjacent six-nuclear units form a 1D chain via offset π–π interactions between 5, 5'-DM-2, 2'-bipy ligands on different adjacent units. The adjacent 1D chains are linked by C―H···O hydrogen bonding interactions to form a 2D supramolecular structure. The thermal stability and thermal decomposition mechanism of all the complexes are investigated by the combination of thermogravimetry and infrared spectroscopy (TG/FTIR) techniques under a simulated air atmosphere in the temperature range of 298–973 K at a heating rate of 10 K·min^-1. Thermogravimetric studies show that this series of complexes have excellent thermal stability. During the thermal decomposition of the complex, the neutral ligand is lost first, followed by the acid ligand, and finally, the complex is decomposed into rare earth oxides. The three-dimensional infrared results are consistent with the thermogravimetric results. The photoluminescence spectra of complex 4 show the strong characteristic luminescence of Eu³⁺. The five typical emission peaks at 581, 591, 621, 651, and 701 nm correspond to the ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃, and ⁵D₀ → ⁷F₄ electronic transitions of Eu³⁺, respectively. The emission at 621 nm is due to the electric dipole transition ⁵D₀ → ⁷F₂, while that at 591 nm is assigned to the ⁵D₀ → ⁷F₁ the magnetic dipole transition. The lifetime (τ) of complex 4 is calculated as 1.15 ms based on the equation τ = (B₁τ₁² + B₂τ₂²))/(B₁τ₁ + B₂τ₂), and the intrinsic quantum yield is calculated to be 45.1%. Further, the magnetic properties of complex 6 in the temperature range of 2–300 K are studied under an applied magnetic field of 1000 Oe.     

方胺功能化荧光金属-有机框架材料的制备及对组氨酸的识别研究

以方胺功能化配体5,5′-[(3,4-二氧环丁-1-烯-1,2-二基)二(氮烷二基)]二间苯二甲酸(H₄L)和六水合硝酸钴为原料, 在碱性条件下通过水热反应制备了一种方胺功能化的金属-有机框架材料(Co-L). X射线单晶衍射结果显示, 该材料是由一维链通过CH…π和氢键相互作用形成的三维网络结构, 在b轴和c轴方向分别存在窗口直径为0.52和0.63 nm的一维孔道. 荧光测试结果表明, Co-L可在20种天然氨基酸中高选择性地检测组氨酸, 并对其检测机理进行了研究.     

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

Ionic liquids (ILs) are thermally and chemically stable and have adjustable structures, which gives them the potential to be used as green, efficient biomolecular solvents. Given the critical role of ILs in dissolving biomolecules, the mechanism of interaction between them deserves further study. Herein, density functional theory (DFT) calculations, using the SMD implicit water solvent model, were employed to study the interaction and mechanism between a hydrophobic zwitterionic amino acid (Tyr) and a series of imidazolium ILs with different alkyl chain lengths and methylation sites. The contributions of hydrogen bonding (H-bonding), electrostatic effects, induction, and dispersion to the intermolecular interactions were determined by combining the symmetry-adapted perturbation theory (SAPT), the atoms in molecules (AIM) theory, and reduced density gradient (RDG) analysis. The results indicate that the H-bonding between the IL cation and Tyr is stronger than that between the IL anion and Tyr; however, the binding between either ion and Tyr is dominated by electrostatic effects. By contrast, the difference between the induction and dispersion forces is small when methylation occurs on the C2 site of the imidazolium cation; whereas, it is significantly large when methylation takes place on the N3 site. This is rationalized by the interaction patterns that vary based on the methylation site. H-bonding and π⁺-π stacking interactions between the imidazole and benzene rings are dominant during C2-methylation, while H-bonding and C_Alkyl-H…π interactions between the alkyl chain and benzene ring are dominant during N3-methylation. Increasing the side alkyl chain length has different effects on the interaction energy to cations with different methylation sites. During N3-methylation, when the side alkyl chain length increases from 4 to 12, there are significant van der Waals interactions between the Tyr benzene and the side alkyl chain. However, these van der Waals interactions are inapparent when methylation takes place on the C2 site. Finally, the synergetic effect of the H-bonding and the interaction between the benzene and the side alkyl chain for C2-methylation is greater than the H-bonding and the interaction between the imidazole and benzene rings for N3-methylation, when the side alkyl chain length n > 9. Therefore, the interaction strength and mechanism in these imidazolium-Tyr complexes can be regulated by changing the methylation site and the side alkyl chain length of the cation. Further study of ion-pair and Tyr reveals that the change tendency of the interaction energy of IL-Tyr systems is consistent with that of cation-Tyr cases, and the ion pair further stabilizes the binding with Tyr. These results illustrate the interaction mechanism of IL-Tyr systems and provide a novel strategy for the design and screening of functional ILs for amino acid extraction and separation in the future.