Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

Summary 2,6-bis-(Benzimidazol-2330/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-yl)-pyridine (bzimpy = H₂ L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)₂](ClO₄)₂ (M = Fe²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H₂O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state 330/xxlarge8594.gif" alt="rarr" align="BASELINE" BORDER="0"> low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (330/xxlarge955.gif" alt="lambda" align="BASELINE" BORDER="0">_max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (330/xxlarge955.gif" alt="lambda" align="BASELINE" BORDER="0">_max=563 to 557 nm) is observed when HClO₄ is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Conformational studies of 1,2,3-trichloro- and 1,2,3-tribromopropane by nuclear magnetic resonance spectroscopy: attractive parallel (1:3) halogen-hydr

Analysis of the NMR spectra of 1,2,3-trichloropropane and 1,2,3-tribromopropane in various media shows the most stable conformer to be AG_-. The populations of several conformera have been estimated by using pure trans and gauche coupling constants obtained from closely similar molecules. The calculated populations found in non-polar solvents agree well with those obtained by electron diffraction studies in the gas phase. It is suggested that the AG_- form is stabilised relative to AG₊ by the former having two parallel (1:3) halogen-hydrogen attractions against one in the AG₊ form. Comparison is made to related molecules where the most stable conformers also have the greatest number of parallel (1:3) halogen-hydrogen interactions.     

Photochemically induced fluorescence investigation of aβ-cyclodextrin: Azure A inclusion complex and determination of analytical parameters

The photooxidation of Azure A and fluorescence properties of Azure A and its photoproduct have been investigated in aqueous media and in the presence of330h5325n6/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin (330h5325n6/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD). The fluorescence intensity of the complex formed between the photoproduct and 330h5325n6/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD was found to be three times higher than that of the uncomplexed Azure A photoproduct. A complex formation constant of 110±40 M^–1 was calculated using the Benesi-Hildebrand treatment of the fluorescence emission data. Although the stoichiometry of the Azure A photoproduct: 330h5325n6/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD complex was found to be 1: 1, it seems that the Azure A structure is only partially included. Calibration graphs were plotted for the free Azure A photoproduct and the photogenerated product included in 330h5325n6/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD. The analytical parameters and quantification limits were determined.     

Synthesis of H (type 4) trisaccharide,key structural fragment of globo-H and fucosyl-GM1 cancer-associated antigens

A convenient synthesis of Fucα1-2Galβ1-3GalNAcβ-OCH₂CH₂CH₂NH₂ (trisaccharide H type 4) is described. This glycan is the terminal part of glycosphingolipids globo-H and fucosyl-GM1 known as cancer-associated carbohydrate antigens.     

Syntheses of chiral fused 4,5-diazafluorene–bis(nopinane) derivatives

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三轴加速度计ADXL330的特点及其应用

ADXL330是美国模拟器件公司推出的完整的三轴加速度计,可以静态或者动态测量物体的加速度,测量范围是±2g.介绍了ADXL330的主要特点及其在组合导航系统中的应用.     

基于加速度计的汽车动力学参数采集平台设计

为了方便采集汽车运动中的动力学数据,设计了一种基于加速度计ADXL330的汽车动力学参数采集平台。采用集成CAN协议模块的MC9S12DJ256单片机作为控制器,可以及时、准确地对汽车运动的相关信息进行数据采集、分析和计算。在此平台基础上进行二次开发,可应用于汽车自动变速器、汽车安全气囊（Airbag）、ABS防抱死刹车系统、电子稳定程序（ESP）等方面。     

Nonlinear dynamics of the heartbeat: I. The AV junction: Passive conduit or active oscillator?

Under physiologic conditions, the AV junction is traditionally regarded as a passive conduit for the conduction of impulses from the atria to the ventricles. An alternative view, namely that subsidiary pacemakers play an active role in normal electrophysiologic dynamics during sinus rhythm, has been suggested based on nonlinear models of cardiac oscillators. A central problem has been the development of a simple but explicit mathematical model for coupled nonlinear oscillators relevant both to stable and perturbed cardiac dynamics. We use equations describing an analog electrical circuit with an external d.c. voltage source (V₀) and two nonlinear oscillators with intrinsic frequencies in the ratio of 3:2, comparable to the SA node and AV junction rates. The oscillators are coupled by means of a resistor. 1:1 (SA:AV) phase-locking of the oscillators occurs over a critical range of V₀. Externally driving the SA oscillator at increasing rates results in 3:2 AV Wenckebach periodicity and a 2:1 AV block. These findings appear with no assumptions about conduction time or refractoriness. This dynamical model is consistent with the new interpretation that normal sinus rhythm may represent 1:1 coupling of two or more active nonlinear oscillators and also accounts for the appearance of an AV block with critical changes in a single parameter such as the pacing rate.     

Infinite transition solutions for a class of Allen–Cahn model equations

This paper constructs a family of solutions that undergoes an infinite number of spatial transitions for an Allen–Cahn model equation.      

Chemoselective hydrogenation of 3-nitrostyrene over Ag/TiO2-SiO2 catalyst in a flow reactor

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