Determination of the Association Constants of Macrocyclic Ethers by the Aid of 13C Dipole-dipole Relaxation Time Measurements. I.,: Li+, Mg2+ and Ca2+ complexes of 1,4,7,10-tetraoxacyclododecane

Abstract

The association constants of Li⁺, Ca⁺² and Mg⁺² ions complexing with 1, 4, 7, 10-tetraoxcyclododecane in DHO were determined by the aid of ¹³C dipole-dipole relaxation time measurements. To obtain the K_a, association constant, the T^O ₁ values of the stoichiometric complex solutions and the T₁₀ of the free molecules were applied to the equation derived, 1/K_a· A_o + 2 = 1/P + P, for the 1:1 ratio of the complexing and to the equation 1/2K_a·A_o + 3/2 = P + 1/2P for the 1:2 ratio of the complexing where P, is molar ratio of the crown complexed ions.

Accordingly we found that the binding ability of the macrocyclic ether towards to the cations is in the following order of Li⁺ < Mg⁺² ? Ca⁺² in DHO solutions.     

Determination of the Complexing Constants by the Aid of 13C Dipole-Dipole Relaxation Time Measurements. Part. III. Complexing of 15-Crown-5 and 18-Crown-6 with Na+,K+ and Ca2+ in DHOX

The association constants, K_a of KI, Nal and CaCl₂ complexing with 1,4,7,10,13-pentaoxacyclopentadecane and 1,4,7,10,13,16-hexaoxacycloocta-decane in DHO were determined by the aid of ¹³C dipole-dipole relaxation time measurements.

The mole fraction of the complexed ligand, P_C were obtained by the use of the equation of 1/T^obs ₁ - 1/T₁₀ = P_C (1/T^O ₁ - 1/T₁₀) where the T₁₀ and T^o ₁ are the relaxation times of free and complexed macrocyclic ethers respectively.

K_a values obtained from the above given equation depending on the cation concentration, [A⁺ _O] typically reflected the relation between the cationic radius and cyclic ether ring size.     

Interaction studies of cysteine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cation complexes

The coordination geometries, electronic features, metal ion affinities, entropies, and the energetics of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible conformations of cysteine complexes were studied. The complexes were optimized using density functional theory (B3LYP) and second order Moller–Plesset Perturbation (MP2) theory methods using 6‐311 + +G** basis set. The interactions of the metal cations at different nucleophilic sites of cysteine conformations were considered after a careful selection among several binding sites. All the metal cations coordinate with cysteine in a tridentate manner and also the most preferred position for the interaction. It is found that, the overall structural parameters of cysteine are not altered by metal ion substitution, but, the metal ion‐binding site has undergone a noticeable change. All the complexes were characterized by an electrostatic interaction between ligand and metal ions that appears slightly more pronounced for lithium and beryllium metal complexes. The metal ion affinity (MIA) and basis set superposition error (BSSE) corrected interaction energy were also computed for all the complexes. The effect of metal cations on the infrared (IR) stretching vibrational modes of amino N? H bond, side chain thiol group S? H bond, hydroxyl O? H bond, and Carbonyl C?O bond in cysteine molecules have also been studied. The nature of the metal ion‐ligand bond and the coordination properties were examined using natural bond order (NBO) at bond critical point (electron density and their Laplacian of electron density) through Atoms in Molecules (AIM) analyses. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and theoretical insight into the cooperativity effect in composite wax powder and ternary complex of coronene with CH4 and Mn+ (Mn+ = Li+, Na+, K+, Be2+, Mg2+ or Ca2+)

The experimental infrared (IR) spectrum of composite wax powder was investigated. The frequency shifts of the C=C anti-symmetrical stretching mode were observed and the experimental cooperativity effect involving Na⁺···π interaction was suggested. In order to further reveal the nature of cooperativity effect, the interaction energies in Mⁿ⁺···coronene···CH₄ (Mⁿ⁺ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ or Ca²⁺) as the model systems of composite wax powder were calculated by using the B3LYP, M06-2X and MP2 methods with 6-311++G^** basis set. The results show that the Mⁿ⁺···π interactions were strengthened upon the formation of ternary complexes. Although the changes of absolute values of the interactions between CH₄ and coronene were not obvious, the relative values were considerably significant upon the formation of ternary complexes. The cooperativity effect was perhaps the reason for the formation of notable advantage of composite wax powder upon the introduction of surfactant with cation into wax powder. Reduced density gradient and atoms-in-molecules analysis confirm the cooperativity effect in Mⁿ⁺···coronene···CH₄, and reveal the nature of the formation of the predominant advantage of composite wax powder.     

掺入Mg2+对CsNiCl3晶体的基态能级、零场分裂参量及Jahn-Teller效应的影响

应用不可约张量理论构造了三角对称晶场中3d2/3d8态离子的45阶可完全对角化的微扰哈密顿矩阵,在考虑了以前工作中被忽略的自旋-自旋耦合作用的基础上计算了CsNiCl3晶体和CsNiCl3:Mg2+晶体的基态能级、晶体结构、零场分裂参量和Jahn-Teller效应,研究了掺入Mg2+对CsNiCl3晶体的光谱、零场分裂参量及Jahn-Teller效应的影响和自旋单重态对基态能级的贡献,发现掺杂使得晶体结构产生畸变,从而改变晶体光谱的精细结构和零场分裂参量,不改变Jahn-Teller效应的分裂规律但改变分裂的大小.     

Li嵌入Mg2Ge的反应次序和电子结构变化

Mg2Ge有望成为新的锂离子电池负极材料.使用基于平面波展开的第一性原理赝势法,计算并得到了Li嵌入Mg2Ge负极材料时的反应次序.Li首先占据其中的间隙位置,占满间隙位置后随着嵌Li量的进一步增加,Li将逐步替位Mg2Ge中一半的Mg位置,直到生成Li2MgGe.计算结果表明,在整个嵌Li过程中主体材料的体积先膨胀后收缩.体积胀缩量很大,这是导致Mg2Ge作为锂离子电池电极材料循环性能较差的重要原因.对材料电子结构的分析表明,随着Li嵌入量的增加,主体材料发生了从半导体性到金属性、又到半金属性的转化.     

The NaCrS2 cathode for secondary Li cells. II. Effect of the temperature of synthesis on its properties and cyclic performance

By changing the conditions of synthesis and oxidation of NaCrS₂, the coulombic efficiency and cycling life of Ni_xNa_0.1CrS₂ cathodes is significantly improved. The importance of studying the main physical and structural properties of the intercalation compound during the optimization of its electrochemical performance is demonstrated. Imitating the nonexistant CrS₂ in composition and possessing the rugged crystal structure of NaCrS₂, the optimized Li_xNa_0.1CrS₂ cathodic material exhibits high coulombic efficiency, excellent cycling resistance, and moderate power capability in nonaqueous secondary Li cells. Having in mind also the simple and reproducible preparation technique and the availability of its raw materials, Li_xNa_0.1CrS₂ appears to be a serious candidate for the future secondary Li nonaqueous cell.     

The effect of Pb2+ dopant in the crystal of CsI and its application as scintillation detector: a study of alpha particles

Scintillation crystals have been used in various fields, such as high energy physics, nuclear instrumentation, radiation measurements, medical imaging, nuclear tomography, astrophysics and other fields of science and engineering. For these applications, the development of scintillation crystals with good performance is required. Scintillation crystals based on cesium iodide (CsI) matrix are matters with relatively low hygroscopicity, easy to handle and of low cost, characteristics that favor their use as radiation detectors. In this study, pure CsI crystal and lead doped CsI crystals were grown using the Bridgman vertical technique. The concentration of the lead doping element (Pb) was studied in the range of 10^?2 to 5×10^?4 M. The distribution of the doping element in the crystalline volume was determined by atomic absorption technique. The CsI:Pb crystal with nominal concentration of 10^?3 M was cut into 14 slices of 6 mm. The results show a higher concentration at the top of the crystal with a decrease in the initial phase of growth. The dopant concentration of Pb showed good uniformity from the slice 2 to the slice 12: the region is, therefore, suitable for use as a radiation detector. The luminescence emission of these crystals was measured. A predominant luminescence band near 450 nm and a single broad band around 320 nm were found with the addition of the Pb²⁺ ions in the CsI matrix. Alpha particles spectrometry measurements were carried out to evaluate the developed scintillators.The resolution of 5.6% was obtained for the CsI:Pb 5×10^?4 M crystal, when excited with alpha particles from a ²⁴¹Am source, with energy of 5.54 MeV.     

Luminescence of CuInS2: I. The broad band emission and its dependence on the defect chemistry

The emission of CuInS₂ is studied as a function of the exact composition in terms of deviations from molecularity and stoichiometry. By means of temperature-dependent (4.2–220 K) and excitation-intensity-dependent measurements, the two broad emission bands usually present are correlated with donor-acceptor transitions. In In-rich material the acceptor is located at 0.10 eV above the valence band. This acceptor is ascribed to V_Cu. In Cu-rich CuInS₂ the acceptor level is located at 0.15 eV above the valence band, which is attributed to either V_In or Cu_In. Two donor levels are identified, their ionization energies being about 35 and 72 meV. These donors are present in both In and Cu-rich samples and may originate from either intrinsic defects or impurities (Fe). Also, the influence of quenching of the crystals as well as the effect of different crystal growth methods (melt-growth and vapour-growth) on the emission is studied.     

The Effect of Shape on Intermethod Correlation of Techniques for Characterizing the Size Distribution of Powder. Part 2: Correlating the Size Distribution as Measured by Diffractometer Methods,TSI-Amherst Aerosol Spectrometer,and Coulter Counter

In an aerosol spectrometer the size of a powder grain is measured from the time-of-flight of the fineparticle between two laser beams. Due to the flow conditions, irregularly shaped fineparticles align themselves along the direction of flow of the air stream carrying them across the gap between the laser beams. The size distribution measured therefore varies with the shape of the fineparticles. This fact is demonstrated by comparing size distributions generated by image analysis, electrozone stream counter, diffractometer, and time-of-flight aerosol spectrometer.     

The d + d reactions at low energies II. Comparison of angular distributions of outgoing nucleon polarizations for the charge symmetric reactions2H(d,p)3H and2H(d,n)3He

Precision measurement of the angular distribution of polarized protons from the²H(d,p)³H reaction at about 1 MeV is compared with experimental polarization data from the mirror reaction²H(d,n)³He at the same entrance and exit channel energies. In both comparisons, differences in polarizations of outgoing nucleons from the d + d charge symmetric reactions were found to be larger than experimental uncertainties.     

Natural J coupling (NJC) analysis of the electron lone pair effect on NMR couplings: 2. The anomeric effects on 1 J (C,H) couplings and its dependence on solvent

The electronic origin of the influence of the anomeric effect (negative hyperconjugative interaction, NHI) on the Fermi contact (FC) term of ¹ J(C, H) couplings has been studied from a theoretical point of view at the DFT-B3LYP level. The HN=CH₂, molecule was chosen as the primary model compound, in which both FC ¹ J(C, H) couplings were decomposed into bond contributions with the natural J coupling dissection approach (NJC). Differences between the ¹ J (C, H)^FC couplings for C——H bonds in synperiplanar and antiperiplanar orientations with respect to the nitrogen non-bonding electron pair closely follow the experimental trend. They are made up chiefly of three NJC contributions: ‘bond’, ‘direct lone pair’ and the ‘carbon-core orbitals’. The NHI influence on these terms was studied by applying the natural bond orbital (NBO) deletion procedure to the charge transfer interaction into the antiperiplanar (C——H) antibond (n(N)→(C——H)?) prior to the NJC dissection calculation. The dielectric solvation effect on both the total FC terms and the respective NJC contributions was estimated by carrying out the calculations using the polarization continuum model. Inhibition of the anomeric effect is evident when the solvent polarity is increased. NHI saturates rapidly with increasing solvent dielectric. Specific solute-solvent interaction effects on ¹ J(C, H) couplings were estimated by evaluating molecular complex models of the form CH₂=HN…S (S = H₂O and DMSO).