Vibrational frequencies and infrared intensities of acetonitrile coordinated with metal cations: an ab initio study

Vibrational frequencies and infrared intensities have been calculated at the 6-31G and 6-31G^** levels for acetonitrile and for the complexes of acetonitrile with Li⁺ and Na⁺ cations. The changes in the infrared characteristics from an isolated acetonitrile to acetonitrile coordinated with metal cations (Li⁺ and Na⁺) have been evaluated. The ab initio calculations predict an essential increase of the intensities of the stretching CN, C-C and deformation CH₃, CCN vibrations in the complexes of acetonitrile with Li⁺ and Na⁺ cations.     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

The structure and potentials of the interaction of complexes of polyatomic anions with Li, Na, and the molecules of aprotic solvents

The semiempiric CNDO method with the modified potential of core-core repulsion is used for quantum-chemical calculations of the potential surface cross-sections, charge distribution and the electrostatic field in complexes of the type A⁻…M⁺ (A⁻ = ClO⁻₄, NO⁻₃, SCN⁻, BF⁻₄, AsF⁻₆; M⁺ = Li⁺, Na⁺) and A⁻…M⁺…Mol (acetonitrile, pyridine, dimethylformamide, dimethylsufloxide, nitromethane, tetrahydrofuran). It is established that the anion-cation interaction potential has the form of a complex function with several minima which correspond to possible types of coordination between anions and cations. The effect of solvent molecules leads to the weakening of the interionic bond and the decrease of the potential barrier between configurations with different types of anion-cation coordination.     

Polarization-corrected molecular electrostatic potential for the cation binding problem

The molecular electrostatic potential (MESP) and polarization-corrected MESP (PMESP) minima for some small molecules are calculated on the surface generated by rolling cations (Li⁺ and Na⁺) on their van der Waals surfaces. The cation binding energies of these molecules are obtained with HF/6-31G^** level ab initio calculations. A noteworthy outcome of the present study is that the plot of these binding energies and the corresponding PMESP surface minimum values turns out to be remarkably linear with a slope close to unity. The PMESP is thus found to work as a powerful tool for unearthing the patterns of cation binding sites and energetics for molecular systems.     

Molecular orbital theory of the hydrogen bond : XXXII. The effect of H and Li association on the A---T and G---C pairs

Ab initio molecular orbital calculations have been performed to determine the structures and stabilization energies of the A---T and G---C base pairs and their complexes with H⁺ and Li⁺, H⁺ and Li⁺ association stabilizes the A---T pair except for Li⁺ association at O₄ in thymine. Protonation of thymine stabilizes the A---T pair to a greater extent than protonation of adenine. The association of H⁺ and Li⁺ with guanine stabilizes the G---C pair, but protonation of cytosine destabilizes G---C. Changes in the structures of the hydrogen bonds in the A---T and G---C pairs reflect changes in hydrogen bond strengths.     

尖晶石型LiMn2O4薄膜电极的制备及电化学性质研究──电化学石英晶体微天平(EQCM)技术研究

石英晶体微天平(QCM)作为纳克级的质量传感器,可通过测定石英晶体振动频率的变化来测定石英晶体表面微小的质量变化.近年来,电化学石英晶体微天平(EQCM)技术已广泛应用于电化学研究领域[1].在锂嵌入型电极充放电过程中,锂离子在嵌基材料中嵌入脱出会引起电极质量的微小变化,因而利用EQCM技术研究Li+的嵌入脱出过程有其独到之处.     

SCF calculations of the interactions of alkali and halide ions with the mercury surface

From extensive ab initio calculations on the interactions between mercury clusters and alkali and halide ions we have derived analytical pair-potential functions for the interaction between the ion and an extended mercury (111) surface. A novel correction scheme is proposed in order to reduce the shortcomings of cluster model. A preferred adsorption above the twofold bridge site was found for Li⁺ and Na⁺ and above the threefold hollow site for all other ions. The ab initio results have been fitted to analytical functions that can be used in computer simulations.     

Gas-phase chemistry of nitrogen trifluoride NF3: structure and stability of its M–NF3 (M=H, Li, Na, K) complexes

The stationary points characterizing the potential energy profiles of the complex processes of the M⁺(M=H, Li, Na, K) and NF₃ were investigated by QCISD and B3LYP in conjunction with the 6-311+G(2d,2p) basis set. The optimized geometries and NBO analysis indicate that the complexes of M⁺(M=Li, Na, K) and NF₃ exist as ion-dipole molecules. But for H⁺ complexes, there are two stable isomers NF₃H⁺ and NF₂⁺–HF. The interaction distances of isomers follow the sequence H⁺< Li⁺< Na⁺< K⁺. The calculated affinity energies of the most stable isomers of H⁺, Li⁺, Na⁺, and K⁺ complexes exceed 20.1 kJ/mol, and these values suggest that the M⁺–NF₃ (M=H, Li, Na, K) complexes could be observed as stable species in gas phase, which supports Fujii's proposal that Li⁺ ion attachment mass spectrometry can serve as a conceivable technique to quantify the emissions of the NF₃.     

Spectroscopic, mass spectrometry, and semiempirical investigations of a new 2-(2-methoxyethoxy)ethyl ester of Monensin A and its complexes with monovalent cations

A new 2-(2-methoxyethoxy)ethyl ester of Monensin A (MON7) has been synthesized and its capability of complex formation with Li⁺, Na⁺, and K⁺ cations has been studied by ESI MS, ¹H and ¹³C NMR, FT-IR, and PM5 semiempirical methods. ESI mass spectrometry indicates that MON7 forms complexes with Li⁺, Na⁺, and K⁺ of exclusively 1:1 stoichiometry which are stable up to cv = 70 V. The formation of complexes between MON7 and Na⁺ cations is strongly favored. Starting from about cv = 90 V fragmentation of the respective complexes is observed, primarily characterized by several dehydration steps. The structures of the MON7 complexes with Li⁺, Na⁺, and K⁺ cations are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The structures are visualized and discussed in detail. It has been proved that the formation of a pseudo crown ring structure formed by MON7 is preferred in complexes with Na⁺ cations.     

Separation and Transport of Lithium of 10-5 M in the Presence of Sodium Chloride Higher than 0.1 M

Lithium is an important element for lithium battery and clinical treatment of manic depression. Thus,rapid and accurate methods for the determination of lithium and its separation and collection of lithium in recycle are receiving a great concern. Because of the high concentrations of Na⁺ in sea water and blood, very high Li⁺/Na⁺ selectivity is required for the separation and determination of Li⁺ at concentration less than 10^-4 M (700 ppb) in a large excess of Na⁺. We report here the methods of separation, transport and determination of lithium as low as 10^-5 M (M=mol dm^-3) in the presence of Na⁺ more than 0.1 M by using a water-soluble octabromoporphyrin; H₂P^4-) synthesized in our laboratory.     

ESI MS, spectroscopic and PM5 semiempirical studies of Colchicine complexes with lithium, sodium and potassium salts

The colchicine complexes with Li⁺, Na⁺ and K⁺ cations have been synthesized and studied by ESI MS, ¹H and ¹³C NMR, FT-IR and PM5 semiempirical methods. It has been shown that colchicine forms stable complexes of 1:1 stoichiometry with monovalent metal cations. For Li⁺ cations also formation of the 2:1 stoichiometry complexes has been detected. The most stable structures of the complexes are those in which the acetamide groups are involved in the coordination process. The structures of the colchicine complexes with Li⁺, Na⁺ and K⁺ cations are visualized and discussed in details.     

Pictorial intuition of the correlation between structure and properties in liquid solutions: acetonitrile as a strongly structured solvent of dissociated ions

The self-consistent mean field hypernetted-chain (SCMF/HNC) approximation of classical statistical mechanics is used to calculate the pair distributions which define the molecular order at the two-particle level. This theory is applied to pure deuterated acetonitrile and to a 0.4 M cryptates K⁺222/ClO₄⁻ solution in deuterated acetonitrile. The cross-sections of the coherent neutron scattering are calculated for both systems and compared to experimental data. The molecular architectures in the liquid state which are predicted by theory are compared to those observed in the crystal phases or deduced from a two-particle energy minimization. The combined effects of the many-body correlations and of the shape and charge distribution anisotropies of the acetonitrile molecules are emphasized.     

Structure and stability of endohedral X@Si20H20 complexes (X = Li, Na, K, Be, Mg, Ca)

The structure and stability of endohedral X@Si₂₀H₂₀ complexes (X = Li^0/+, Na^0/+, K^0/+, Be^0/2+, Mg^0/2+, Ca^0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X = Na^0/+, K^0/+, Mg and Ca^0/2+ are energy minimum structures with X at the cage center in I_h symmetry, while those with X = Li^0/+, Be^0/2+, Mg²⁺ have off-centered structures with X towards one pentagon face in C_5v symmetry. Large electron or charge transfer between the Si₂₀H₂₀ cage and the encapsulated X has been observed.     

邻甲氧基羰基苄氧基取代杯[4]芳烃衍生物的合成及其性能研究

杯芳烃是继冠醚、环糊精之后的第三代主体分子[1].据文献[2,3]报道,在杯[4]芳烃下沿酚氧原子上连接乙酸酯得到的四取代衍生物对Na+有很高的选择性,核磁与晶体结构研究均证实这是由于羧酸酯的羰基和酚氧基参与了对Na+的配位,而且配位基团所形成的包络空间大小与钠离子相匹配.一般认为,随着包络空间改变,对金属离子的识别作用会有所变化[4].但目前对这方面的工作并没有给予更多的重视.我们发现,用2-溴甲基苯甲酸甲酯与杯[4]芳烃反应,得到了一种新的四取代杯[4]芳烃衍生物[2]萃取研究结果表明,该化合物对钾离子有较好的选择性.此外,在合成该衍生物的过程中,还得到了另一新的二取代衍生物(3).     

Raman spectroscopic study of the conformational change of 12-crown-4 due to cation capture

Raman spectra of the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ complexes of 12-crown-4 and also 12-crown-4 in various states are observed. The spectra of 12-crown-4 change remarkably by complex formation with cations. Normal vibration calculations of various conformations of 12-crown-4 are carried out. On the basis of the observed spectra and the results of the calculations, the conformation of 12-crown-4 in the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺ complexes is found to have approximate D_2d symmetry, while that in the Ca²⁺, Sr²⁺, Ba²⁺ complexes is found to have approximate C_2V symmetry.     

Ab initio study on the structures, energies, and vibrational frequencies of acetone complexes with metal monocations and dications

The structures, interaction energies, and vibrational frequencies of acetone and its complexes with proton and various metal monocations/dications such as H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, and Zn²⁺ have been investigated from the ab initio calculations. The linear or bent structure for the cation-acetone complexes has been found to be deeply influenced by the amount of charge transfer. The amount of red-shift of CO stretching frequencies of acetone is almost equivalent regardless of the kind of alkali metal monocations. This behavior can be attributed to the electrostatic nature of the interactions rather than orbital interactions. This phenomenon has been supported by the highest occupied molecular orbitals of the acetone complexes investigated, charge transfer based on natural bond orbital (NBO) atomic charges, and the inversely proportional behavior of the interaction energies to the interatomic distances r(M⁺O).     

Autoionization spectra of Li2 and the XΣg ground state of Li2: Experimental and theoretical investigations

Autoionizing Rydberg levels of Li₂ molecules in a supersonic molecular beam are populated by stepwise excitation with two tunable pulsed dye lasers. The observed autoionization spectra show severe perturbations. Based on calculations of quantum defects and a perturbation treatment of l-uncoupling a tentative assignment of Rydberg series up to n = 32 is proposed. The convergence limits of these series yield a value of IP = 41475 cm⁻¹ for the adiabatic ionization potential and a vibrational constant ω_e = 263 cm⁻¹ for the X²Σ⁺_g ground state of Li⁺₂. The experimental results are compared with ab initio calculations combined with a core polarization potential, which yield the potential curve. the dissociation energy, the quadrupole moment and the vibrational frequency for the X²Σ⁺_g ground state of Li⁺₂, in the excellent agreement with experimental findings.     

Theoretical Study of Stability and Electronic Characteristics in Various Complexes of Psoralen as an Anticancer Drug in Gas Phase,Water and CCl4 Solutions

The present research employs density functional theory(DFT) computations to analyze the structure and energy of complexes formed by psoralen drug with alkali(Li⁺, Na⁺, K⁺) and alkaline earth(Be²⁺, Mg²⁺, Ca²⁺) metal cations. The computations are conducted on M06-2X/aug-cc-pVTZ level of theory in the gas phase and solution. The Atoms in Molecules(AIM) and natural bond orbital(NBO) analyses are applied to evaluating the characterization of bonds and the atomic charge distribution, respectively. The results show that the absolute values of binding energies decrease with going from the gas phase to the solution. Furthermore, the considered complexes in the water(as a polar solvent) are more stable than the CCl₄(as a non-polar solvent). The DFT based chemical reactivity indices, such as molecular orbital energies, chemical potential, hardness and softness are also investigated. The outcomes show that the considered complexes have high chemical stability and low reactivity from the gas phase to the solution. Finally, charge density distributions and chemical reactive sites of a typical complex explored in this study are obtained by molecular electrostatic potential surface.     

Ab initio calculations of minimum-energy pathways of the nucleophilic addition of the H anion, LiH molecule and Li/H ion pair to acetylene and methylacetylene

Ab initio calculations were performed for special points of the minimal energy pathways (MEP) of the nucleophilic addition reactions of the isolated H⁻ anion, LiH molecule and Li⁺/H⁻ ion pair to acetylene (A) and methylacetylene (MA) molecules, proceeding in accordance (M) and against (aM) the Markovnikov's rule. All structural parameters were optimized using the restricted Hartree–Fock (RHF) method. For the addition of H⁻, the 6-31++G^* basis set was used and for the reactions of LiH and Li⁺/H⁻ the 6-31G^* basis set with the subsequent recalculation of single point energies, taking into account of electron correlation energy by means of the second-order Möller–Plesset perturbation theory at the MP2/6-31++G^** level. The results of calculations demonstrate, that the energy characteristics of both M- and aM-additions with H⁻ do not differ sufficiently (0.1–1.2 kcal/mol for the activation energies (ΔE_a) and the reaction heats (ΔQ)). The substitution of the H atom by the CH₃ group in A molecule results in practically the same values of ΔQ and ΔE_a. On the contrary, for the LiH molecule and Li⁺/H⁻ ionic pair, the M-addition is favorable (charge control). It is found that the presence of electrophile decreases the activation energy by 3–5 kcal/mol as compared with the addition of the isolated hydride ion H⁻.     

锂离子选择性电极的研究

根据锂的萃取化学,以1-(苯基偶氮)萘酚-2(ST-I)及氧化三辛基膦(TOPO)为载体和协萃剂制备了PVC膜锂离子选择性电极.考察了增塑剂等因素对电极响应性能的影响,并对膜组成进行优化.以含4.5mgST-I,9.0mgTOPO及180mg磷酸三丁酯的膜制备的电极在pH8.5的tris缓冲底液中对锂呈线性电位响应,斜率为51.7mV/pC,线性范围为2.0×10^-5～1.0×10^-1mol/L,检测下限为4.0×10^-6mol/L.电极用于碳酸锂片剂中锂含量测定,结果满意.