Theoretical calculations of proton affinities of azines. Prediction of the relative basicities and preferred protonation sites

Theoretical calculations at the 3-21G and 3-21 + G ab initio levels and at the MNDO and AM1 semiempirical levels of several six-membered nitrogenated heterocycles and their protonated species have been carried out. The 3–21G calculated proton affinities are systematically too high, in relation to the available experimental data, and it is estimated that inclusion of electron correlation and zero-point corrections is not sufficient to reach the desired agreement; however, additional inclusion of diffuse functions (3-21 + G/3-21G calculations) lowers the calculated proton affinities by 5.4–6.8 kcal/mol, a good agreement being thus obtained, at least for 1–7 . On the other hand, semiempirical methods underestimate the repulsion between each pair of vicinal nitrogens; however, if a correction of ?9 kcal/mol is added to the AM1 results for each pair of neighboring nitrogens containing lone pairs of electrons, the corresponding proton affinities match fairly well the available exoerimental data and corrected 3-21 + G results. As expected, all methods predict that the introduction of additional nitrogens decreases the overall absolute basicity. Futhermore, comparison of the relative basicity of the isomers and of the preferred protonation site for each isomer indicates that nitrogen atoms with (only) one α-nitrogen and without a γ-nitrogen are more basic than any others. In benzazines, MNDO and AM1 suggest that the 2,3-diaza arrangement has a higher intrinsic basicity than the 1,2-diaza arrangement.     

Gas-phase molecular absorption spectrometry: Determination of sulphite with diode-array detection

A method is described for determining sulphite by SO₂ generation and UV-visible molecular absorption spectrometry with diode-array detection. The molecular absorption maximum of SO₂ appears at 198 nm. The parameters affecting generation (particularly those relating to the kinetics of the process) and determination are optimized; under the optimum conditions found, only a 30 s preconcentration time is necessary. The linear response range is between 10 and 1000 g ml^–1 of SO ₃ ^2– , the RSD is 3.5% and the detection limit is 3.2 g ml^–1. The effect of different species on the SO₂ signal is also studied. The method is applied to the determination of SO₂ in air samples.     

Flow Injection Spectrophotometric Determination of Ferbam Based on a Photochemical Reaction

A flow-injection configuration for the spectrophotometric determination of ferbam is proposed. The procedure is based on the online decomposition of ferbam and complexation of the released Fe³⁺ with oxalate. The ferrioxalate formed is decomposed upon irradiation with visible light. The Fe²⁺ produced in the photochemical reaction was monitored by measuring the absorbance after complexation with ferrozine (_max=562nm). The method shows a linear range between 1.0 and 30µgmL^–1 (2.5×10^–6–7.2×10^–5molL^–1) with a limit of detection of 0.2µgmL^–1. Repeatibility was 0.53% expressed as relative standard deviation (n=10), and reproducibility, studied on five different days, was ±1.23%. The sampling frequency was about 45samplesh^–1. The applicability of the method was tested in the determination of ferbam in waters and grains.Received December 2, 2002; accepted April 13, 2003 Published online July 16, 2003     

n-th roots of a non-negative operator. Conditions for uniqueness

In the present paper we study which restrictions must be imposed on the n-th roots of certain non-negative closed operators A on a Banach space so that these roots are unique.Counterexamples are given to show that the two results on this subject in the previous literature are incorrect.Finally, we obtain an explicit formula relating the canonical root A^1/n to another given non-negative n-th root B, and this allows us to establish the conditions for a given element to yield the same value by both roots. This point of view, which had not been considered up to now, provides simple conditions for global uniqueness that need only to be checked on the subspaces D(A)=_n1D(Aⁿ) and R(A)=_n1R(Aⁿ).     

Fe(Ⅲ)掺杂Nb2O5微纳球的水热合成及其电化学性能

采用一步水热法合成Nb_2O_5和Fe(Ⅲ)掺杂的五氧化二铌微纳米球(Fe-Nb_2O_5),并利用X射线衍射(XRD)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)等测试手段分别对其结构和形貌进行了表征。结果发现,所合成的Fe-Nb_2O_5和Nb_2O_5均为正交晶相,Nb_2O_5为尺寸分布在50~300 nm之间的形貌不规则颗粒,而Fe-Nb_2O_5是由约50 nm的一次颗粒自组装而成的直径约为1μm的均匀微纳米球,即具有多级结构,其有利于增大电极材料与电解液的接触界面。电化学测试结果表明,Fe-Nb_2O_5的循环稳定性和倍率性能得到明显改善,在50 m A·g~(-1)电流密度下,100次循环后放电容量仍保持在193.2 m Ah·g~(-1),即使在5 A·g~(-1)的电流密度下,容量仍可达到108.4 m Ah·g~(-1)。并分析了其性能改善的原因。     

新型甘露醇基凝油剂的制备及性能研究

通过甘露醇和环己酮的缩酮反应,合成了具有相选择性的新型糖基凝油剂-环己酮缩甘露醇。考察了反应时间、催化剂用量、分子筛用量、底物配比等多个因素对产物产率的影响。结果表明,分子筛用量为12g、催化剂用量为0.8g、环己酮与甘露醇摩尔比为6.2∶1的条件下反应1h,产率为52%。对所制备的环己酮缩甘露醇的凝油能力测试表明,它可以凝固汽油、硅油等多种油类,柴油、汽油和硅油凝固的最小浓度分别为0.74(wt)%、2.70(wt)%和0.39(wt)%。     

Mitochondrially Targeted Nanoparticles Based on α‐TOS for the Selective Cancer Treatment

The aim of this work is the preparation of an active nanovehicle for the effective administration of α‐tocopheryl succinate (α‐TOS). α‐TOS is loaded in the core of nanoparticles (NPs) based on amphiphilic pseudo‐block copolymers of N‐vinyl pyrrolidone and a methacrylic derivative of α‐TOS. These well‐defined spherical NPs have sizes below 165 nm and high encapsulation efficiencies. In vitro activity of NPs is tested in hypopharynx squamous carcinoma (FaDu) cells and nonmalignant epithelial cells, demonstrating that the presence of additional α‐TOS significantly enhances its antiproliferative activity; however, a range of selective concentrations is observed. These NPs induce apoptosis of FaDu cells by activating the mitochondria death pathway (via caspase‐9). Both loaded and unloaded NPs act via complex II and produce high levels of reactive oxygen species that trigger apoptosis. Additionally, these NPs effectively suppress the vascular endothelial growth factor (VEGF) expression of human umbilical vein endothelial cells (HUVECs). These results open the possibility to use this promising nanoformulation as an α‐TOS delivery system for the effective cancer treatment, effectively resolving the current limitations of free α‐TOS administration.

     

Rhombohedral-cubic transition in Li0.2Na0.3La0.5TiO3 perovskite

High-temperature behavior of the fast ionic conductor Li_0.2Na_0.3La_0.5TiO₃ has been investigated by neutron powder diffraction between 300 and 1073 K. The Rietveld analysis of diffraction patterns showed around 1000 K a change from rhombohedral () to cubic () symmetry. During the heating, the tilting of octahedra along the [111] direction of the cubic perovskite decreased and the rhombic distortion of oxygen square windows that relates contiguous A-sites of the perovskite was eliminated. The influence of the octahedral tilting on Li mobility is finally discussed.     

Molecular treatment of charge transfer cross sections in N5+ collisions with H2

We present cross sections for electron capture in N⁵⁺+H₂ collisions in the energy range 100 eV/amu≤E≤6 keV/amu. We employ a model potential aproximation to treat the interaction of the active electron with the cores, and a recently proposed method, which applies the independent particle model to evaluate the Hamiltonian matrix elements. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001