水化锂蒙脱石层间结构和动力特征的分子模拟

利用分子力场和分子动力学(MD)的方法研究了Li-蒙脱石的结构构型, 层间阳离子的水化行为、水分子的结构特征以及它们的扩散性质. 分子力场构型优化结果表明: Li-蒙脱石的层间距、体积和密度与层间水含量有关; MD模拟的动画轨迹显示Li-蒙脱石层间Li^＋的位置与层间电荷位置有关. 均方根位移和自扩散系数的计算结果表明: 层间阳离子、水分子在Li-蒙脱石一、二层水合物中的扩散受到上下粘土片表面的限制, 在三层水合物中开始离开粘土层面向其它方向快速扩散. 径向分布函数及其结构因子的分析结果表明Li^＋在一、二、三层水合物中有不同的水合层; 层间水分子的结构特征说明其在蒙脱石层间有水合水分子和自由水分子之分, 且它们的比值在一、二和三层水合物中有所不同.     

聚氧乙烯-粘土-碱金属离子插层复合物作用机理研究

测量了聚氧乙烯(PEO)-粘土-K^＋/Na^＋插层复合物在不同相对湿度环境中的相对吸水量, 研究了相对吸水量与粘土层间距d₀₀₁之间的关系, 并结合X射线光电子能谱的研究结果, 探讨了复合物中PEO、粘土与碱金属离子三者之间的相互作用. 在K-MMT-PEO复合物中, K^＋与PEO和粘土表面都存在配合作用, 形成稳定的三元配合物, 在不同相对湿度下, K-MMT-PEO配合物吸水能力较低, 层间距基本不变. 在Na-MMT-PEO复合物中, Na^＋与PEO形成配合物, 水分子能破坏Na^＋-PEO之间的配合作用, 使PEO和Na^＋各自形成水化层, 因此随着相对湿度的增加Na-MMT-PEO复合物的相对吸水量和层间距都增大.     

内含式化合物X@Al12P12的结构与稳定性研究

采用B3LYP/6-31G*方法, 对内含式化合物X@Al₁₂P₁₂ (X＝Li^0/＋, Na^0/＋, K^0/＋, Be^0/2＋, Mg^0/2＋, Ca^0/2＋, H和He)的不同对称性构型进行计算, 讨论其最稳定构型的几何参数、布居分析、偶极矩、电离势、包含能、频率、HOMO-LUMO能隙和自旋密度．发现X@Al₁₂P₁₂化合物中, 客体X＝Na^0/＋, K^0/＋, Mg和He几乎处在笼的中心, Be和Ca^0/2＋处在中心附近0.033 nm的半径内, Li^0/＋, Be^2＋, Mg^2＋和H很大程度上偏离笼的中心位置. 大部分金属内含式化合物的C₃对称性构型稳定．Li^0/＋, Be^0/2＋, Mg^2＋, Ca^2＋和H与其它离子相比更易嵌入笼内形成稳定的内含式化合物.     

WQD-1沸石离子交换性能的研究

测定了W_QD-1沸石在一价碱金属离子混合溶液中的分配系数、饱和交换量和在25℃时，NH⁺₄/K⁺、NH⁺₄/Na⁺交换等温线。得出该沸石一价离子选择性序列为：Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺, Na⁺/K⁺交换自由焓变ΔG(T,P)=-6.745 KJ/mol。     

双阳离子体系高通量丝光沸石膜的合成及其乙酸脱水应用

采用多种表征技术详细研究了碱金属阳离子对丝光沸石分子筛膜生长和渗透汽化性能的影响。结果表明,Li⁺、Na⁺、K⁺和Cs⁺以及Na⁺-Li⁺、Na⁺-K⁺和Na⁺-Cs⁺的不同离子组合对丝光沸石分子筛膜的形貌和性能有很大影响。研究发现,碱金属阳离子通过促进硅在初始凝胶中的溶解,在硅铝酸盐的重排过程中起到结构导向作用,进而起到构筑丝光沸石晶体骨架结构的作用。Na⁺对丝光沸石晶体的结晶有明显的促进作用,而Li⁺、K⁺和Cs⁺在相同的结晶时间内表现出较慢的结晶速率。在合成凝胶中用K⁺代替少量Na⁺可以显著改善膜表面的亲水性。特别是合成凝胶中Na⁺/K⁺比（n_Na⁺/n_K⁺）为2时,形成了更致密、更亲水的丝光沸石分子筛膜,显示出更高的渗透汽化性能。对于90℃下HAc质量分数为90%的HAc/H₂O混合物的分离,该膜显示出2.67 kg·m^-2·h^-1的高渗透通量和约为4 000的分离因子。此外,最优条件下合成的丝光沸石分子筛膜在90℃下长达240 h渗透汽化分离90%的HAc/H₂O混合物依然显示优越的酸稳定性。     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

内含式化合物X@(HBNH)12的结构与稳定性

采用B3LYP/6-31++G(d,p)方法，对内含式化合物X@(HBNH)₁₂ (X = Li^0/+, Na^0/+, K^0/+, Be^0/2+, Mg^0/2+, Ca^0/2+, H和He)的不同对称性构型进行计算，讨论其最稳定构型的几何参数、包含能、平衡常数、自然电荷、自旋密度、电离势和HOMO-LUMO能隙。发现在X@(HBNH)₁₂化合物中，客体Na^0/+, K^0/+, Mg^0/2+, Ca^0/2+, H和He几乎处在笼的中心，Li⁺处在中心附近0.021 nm的半径内，Li和Be^0/2+很大程度上偏离笼的中心位置。Li⁺, Be²⁺, Mg²⁺和Ca²⁺与其它离子相比，更易嵌入笼内形成稳定的内含式化合物。而且，M@(HBNH)₁₂ (M = Li, Na,K)的第一电离势比Cs(3.9 eV)原子小，是超碱金属。     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

五元体系Li＋, K＋//, CO32- ,SO42- , B4O72- -H2O在288 K时的介稳相平衡研究

采用等温蒸发法研究了五元体系Li^＋, K^＋//, , -H₂O 在288 K时的介稳相平衡关系, 测定了该五元体系在288 K条件下的介稳平衡的溶解度和溶液密度, 根据实验数据绘制了相应的介稳平衡相图和水图. 相平衡研究结果表明该五元体系介稳相平衡中有复盐K₂SO₄•Li₂SO₄生成, 其介稳相图(Li₂CO₃饱和)有4个共饱和点, 9条单变量曲线, 6个Li₂CO₃饱和的结晶区分别为LiBO₂•8H₂O, K₂B₄O₇•4H₂O, K₂CO₃•3/2H₂O, K₂SO₄, Li₂SO₄•H₂O和复盐 K₂SO₄•Li₂SO₄.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

Factors governing the metal coordination number in isolated group IA and IIA metal hydrates

Many of the group IA and IIA metal ions, such as Na+, K+, Mg2+, and Ca2+, play crucial roles in biological functions. Previous theoretical studies generally focus on the number of water molecules bound to a particular (as opposed to all) alkali or alkaline earth cations and could not establish a single preferred CN for the heavier alkali and alkaline earth ion-water complexes. Crystal structures of hydrated Na+, K+, and Rb+ also cannot establish the preferred number of inner-shell water molecules bound to these cations. Consequently, it is unclear if the gas-phase CNs of group IA metal hydrates increase with increasing ion size, as observed for the group IIA series from the Cambridge Structural Database, and if the same factors govern the gas-phase CNs of both group IA and IIA ion-water complexes. Thus, in this work, we determine the number of water molecules directly bound to the series of alkali (Li+, Na+, K+, and Rb+) and alkaline earth (Be2+, Mg2+, Ca2+, Sr2+, and Ba2+) metal ions in the gas phase by computing the free energy for forming an isolated metal-aqua complex as a function of the number of water molecules at 298 K. The preferred gas-phase CNs of group IA hydrates appear insensitive to the ion size; they are all 4, except for Rb+, where a CN of 6 seems as likely. In contrast, the preferred gas-phase CNs of the group IIA dications increase with increasing ion size; they are 4 for Be2+, 6 for Mg2+ and Ca2+, and 7 for Sr2+ and Ba2+. An entropic penalty disfavors a gas-phase CN greater than 4 for group IA hydrates, but it does not dictate the gas-phase CNs of group IIA hydrates. Instead, interactions between the metal ion and first-shell water molecules and between first-shell and second-shell water molecules govern the preferred gas-phase CNs of the group IIA metal hydrates.     

Organometallic ionophore for alkali metal cations

Complexes of a novel synthetic organometallic ionophore with lithium and sodium cations have been characterized by single-crystal X-ray diffraction. The crystal structure of the lithium complex consists of cation-liganddimers with a tetrahedral coordination around Li. The sodium complex reveals a different structure type consisting of cation-ligandtrimers, with water molecules being included between the trimeric entities. The coordination sphere around the Na ions has a distorted octahedral symmetry. It is anticipated that the observed structures of dinuclear Li and trinuclear Na complexes represent possible modes of aggregation of the cation-ligand entities in lipophilic media.     

Hydration of methane intercalated in Na-smectites with distinct layer charge: insights from molecular simulations

Molecular dynamic simulations have been carried out to investigate the behavior of methane hydration in Na-smectite interlayers with different layer-charge distributions and water contents under certain pressure-temperature (P-T) conditions, which is analogous to the methane hydrate-bearing marine sediments. It was found that sufficient interlayer water is necessary for coordinating with methane and forming hydrate-like structures. Methane molecules are solvated by nearly 12-13 water molecules and coordinated with six oxygen atoms from the clay surface in the interlayer of nontronite as well as in montmorillonite. The mobility of the interlayer water of smectite, which is determined by the layer-charge amount and distribution of smectite, also influences the stability of hydrate methane complexes. The tetrahedral negative charge site is closer to the surface than the octahedral charge site and is more effective in confining water than methane water molecules.     

Dehydration and dehydroxylation of reduced charge montmorillonite

Reduced charge montmorillonites (RCM) were prepared by the thermal treatment of lithiumsaturated montmorillonite. Samples prepared by mild thermal treatment with lithium contained more water sorbed than the original montmorrilonite. When RCMs were prepared, part of the lithium cations reacted with hydroxyl groups in the octahedral sheet and released protons, which reacted with the structure. Acid treatment probably enhanced the surface area. which was reflected in the amount of water sorbed. Deprotonation of hydroxyl groups was proved by the measurements of the ignition loss. The heating of lithium saturated montmorillonite at higher temperatures brough about the collapse of the interlayers and a decrease in the amount of water sorbed.     

Arrangement and mobility of water in vermiculite hydrates followed by 1H NMR spectroscopy

The arrangement of water molecules in one- and two-layer hydrates of high-charged vermiculites, saturated with alkaline (Li(+), Na(+)) and alkali-earth (Mg(2+), Ca(2+), Ba(2+)) cations, has been analyzed with (1)H NMR spectroscopy. Two different orientations for water molecules have been found, depending on the hydration state and the sites occupied by interlayer cations. As the amount of water increases, hydrogen bond interactions between water molecules increase at expenses of water-silicate interactions. This interaction favors water mobility in vermiculites. A comparison of the temperature dependence of relaxation times T(1) and T(2) for one and two-layer hydrates of Na-vermiculite shows that the rotations of water molecules around C(2)-axes and that of cation hydration shells around the c-axis is favored in the two-layer hydrate. In both hydrates, the anisotropic diffusion of water takes place at room temperature, preserving the orientation of water molecules relative to the silicate layers. Information obtained by NMR spectroscopy is compatible with that deduced by infrared spectroscopy and with structural studies carried out with X-ray and neutron diffraction techniques on single-crystals of vermiculite.     

Ion exchange in reverse micelles

The distribution and dynamics of alkali cations inside Na-AOT reverse micelles have been investigated using Monte Carlo and molecular dynamics simulations. Water is modeled using the extended simple point charge (SPC/E) model. Simulations were carried out for alkali salts of Li+, Na+, K+, and Cs+ placed into the aqueous core of the reverse micelle, for situations corresponding to one and three molecules of added salt. In all cases, we observe that the larger K+ and Cs+ ions exchange with the Na+ counterion; however, the smaller Li+ ion prefers to remains solvated within the core of the reverse micelle. Our study reveals that the oil-water interface of the Na-AOT reverse micelle has the greatest selectivity toward Cs+ followed by K+ and Li+. A model based on enthalpic contributions illustrates that the solvation energies of the different cations in water control the ion-exchange process. The hydration number of the first water shell for Li+ situated in the aqueous core of the reverse micelle with radius R = 14.1 A was similar to that observed at infinite dilution in bulk water.     

水化Na-蒙脱石和Na/Mg-蒙脱石的分子动力学模拟

利用分子动力学方法(MD)研究了Na-蒙脱石和Na/Mg-蒙脱石层间的补偿阳离子和水分子的结构及扩散性质. 模拟结果表明, 在一定水含量范围内Na-蒙脱石和Na/Mg-蒙脱石表现出不同的膨胀形式, 特别是层间水分子数目在48～72之间时, Na/Mg-蒙脱石的层间距比Na-蒙脱石有较为明显的增大. Na/Mg-蒙脱石两层水化物的层间水分子与Mg2+形成了明显的两层水合壳; 而与Na+只形成了一层平面的水合壳. 在Na/Mg-蒙脱石中, Na+和 Mg2+的扩散方式不同, Na+的扩散范围相对更广, 自扩散系数更大. Na/Mg-蒙脱石比相同水含量下的Na-蒙脱石层间水的自扩散系数小. 由于Mg2+和Na+对层间结构的强烈影响, 从而使有少量Mg2+取代Na+的Na/Mg-蒙脱石与Na-蒙脱石表现出不同的膨胀性质和层间物质的扩散性质.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.     

Non-covalent interactions of alkali metal cations with singly charged tryptic peptides

The complexes formed by alkali metal cations (Cat(+) = Li(+), Na(+), K(+), Rb(+)) and singly charged tryptic peptides were investigated by combining results from the low-energy collision-induced dissociation (CID) and ion mobility experiments with molecular dynamics and density functional theory calculations. The structure and reactivity of [M + H + Cat](2+) tryptic peptides is greatly influenced by charge repulsion as well as the ability of the peptide to solvate charge points. Charge separation between fragment ions occurs upon dissociation, i.e. b ions tend to be alkali metal cationised while y ions are protonated, suggesting the location of the cation towards the peptide N-terminus. The low-energy dissociation channels were found to be strongly dependant on the cation size. Complexes containing smaller cations (Li(+) or Na(+)) dissociate predominantly by sequence-specific cleavages, whereas the main process for complexes containing larger cations (Rb(+)) is cation expulsion and formation of [M + H](+). The obtained structural data might suggest a relationship between the peptide primary structure and the nature of the cation coordination shell. Peptides with a significant number of side chain carbonyl oxygens provide good charge solvation without the need for involving peptide bond carbonyl groups and thus forming a tight globular structure. However, due to the lack of the conformational flexibility which would allow effective solvation of both charges (the cation and the proton) peptides with seven or less amino acids are unable to form sufficiently abundant [M + H + Cat](2+) ion. Finally, the fact that [M + H + Cat](2+) peptides dissociate similarly as [M + H](+) (via sequence-specific cleavages, however, with the additional formation of alkali metal cationised b ions) offers a way for generating the low-energy CID spectra of 'singly charged' tryptic peptides.     

The effect of metal cations on the nature of the first electronic transition of liquid water as studied by attenuated total reflection far-ultraviolet spectroscopy

The first electronic transition (?←X?) of liquid water was studied from the perspective of the hydration of cations by analyzing the attenuated total reflection far-ultraviolet (ATR-FUV) spectra of the Group I, II, and XIII metal nitrate electrolyte solutions. The ?←X? transition energies of 1 M electrolyte solutions are higher (Li(+): 8.024 eV and Cs(+): 8.013 eV) than that of pure water (8.010 eV) and linearly correlate with the Gibbs energies of hydration of the cations. The increases in the ?←X? transition energies are mostly attributable to the hydrogen bond formation energies of water molecules in the ground state induced by the presence of the cations. The deviation from the linear relation was observed for the high charge density cations, H(+), Li(+), and Be(2+), which reflects that the electronic energies in the excited states are also perturbed. Quantum chemical calculations show that the ?←X? transition energies of the water-cation complexes depend on the hydration structures of the cations. The calculated ?←X? transition energies of the water molecules hydrating high charge density cations spread more widely than those of the low charge density cations. The calculated transition energy spreads of the water-cation complexes directly correlate with the widths of the ?←X? transition bands measured by ATR-FUV spectroscopy.