Chiral separation of N-(trans-4-isopropylcyclohexylcarbonyl)-D,L-phenylalanine isomers by high performance liquid chromatography

Summary A high-performance liquid chromatographic method was developed for the chiral separation of a new anti-diabetic agent, N-(trans-4-isopropylcyclohexylcarbonyl)-D-phenylalanine, and its L-enantiomer. The separation was performed on a Sumichiral OA-3300 column. Optimized mobile phase was 0.025 mol.L⁻¹ ammonium acetate in methanol solution. UV detection was at 210 nm. Baseline chiral separation was obtained within 12 minutes. The detection limits are 80 pg for the D-enantiomer and 120 pg for the L-enantiomer. RSD of the method was below 1% (n=5).     

Synthesis and analytical application of tribromocarboxyarsenazo as a new chromogenic reagent for zirconium

A new chromogenic reagent tribromocarboxyarsenazo has been synthesized and the chromogenic reaction of this reagent with zirconium studied. In the medium of 0.5 mol/1 HCl, a blue complex is formed by the reaction of zirconium with tribromocarboxyarsenazo. The maximum absorption of the complex is at 633 nm, and the apparent molar absorptivity is 4.8 x 10(4) 1/mol/cm. Beer's law is obeyed over the zirconium concentration range 0-18, mug/25 ml. The method has been applied to the determination of zirconium in aluminum, copper and magnesium alloys with satisfactory results.     

Multinuclear NMR study of lanthanide(III) complexes of 1,2-PDTA in aqueous solution

The complexation of lanthanide(III) cations with 1,2-propanediaminetetraacetate (1,2-PDTA) in aqueous solution has been investigated by ¹⁰Na, ³⁵Cl, ²H and ¹¹O NMR shift measurements. It has been shown that the contact shifts are dominant for ¹⁷O, ¹⁶Cl and ²H (only for the heavier lanthanide series) and the pseudocontact shifts are dominant for ²⁵Na. It is suggested that the 1,2-PDTA ligand is bound pentadentately via the two nitrogens and the three carboxylates for the lighter lanthanide complexes, hexdentately via the two nitrogens and the four carboxylates for the heavier ones. The numbers of the water coordinated were determined. The small amount of chloride anion in inner coordination sphere was observed.     

Aggregate manganese Schiff base moieties by terephthalate or acetate: dinuclear manganese and trinuclear mixed metal Mn2/Na complexes

A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(H(2)O) (3), and (salen)(2)Mn(2)(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH(3)OH)(NO(3)) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H[Mn(2)Na(salpn)(2)(mu-OAc)(2)(H(2)O)(2)](OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. (1)H NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/-0.12V has been assigned to the redox of Mn(2)(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.     

Carbonyl allylation of aldehydes catalyzed by a silica-supported poly-γ-diphenylarsinopropylsiloxane palladium(0) complex

A silica-supported poly-γ-diphenylarsinopropylsiloxane palladium(0) complex has been prepared from γ-chloropropyltriethoxysilane via immobilization on fumed silica, followed by reacting with potassium diphenylarsenide and palladium chloride, and then the reduction with hydrazine hydrate. The palladium(0) complex has been found to catalyze the allylation of aldehydes via the formation of π-allylpalladium complexes, using allylic chlorides as allylating agent and SnCl₂ as reducing agent. This polymeric palladium complex can be recovered and reused.     

Concatenation of two molecular switches via a Fe(II)/Fe(III) couple

[reaction: see text] Modulation of the fluorescein fluorescence in the presence of spiropyran and ferric ion by light was observed. Such fluorescence modulation was due to the low oxidation potential of complex MC.Fe(2+), which made the electron transfer from MC.Fe(2+) to Flu(+)()(*)() thermodynamically favorable. As a result, the communication between two molecular switches based on fluorescein and spiropyan, respectively, was realized via the reversible Fe(III)/Fe(II) redox couple. The communicating behavior corresponds well to the function of an INHIBIT logic gate.     

电池热安全性表征模型及其相关技术

本文通过对Ni-MH电池充放电微量热及原位电化学等参量监测实验结果进行分析研究,建立包括可逆和不可逆过程的电池充放电电压和热耗散的模型.根据以热力学对电池体系在充放电过程的分析和目前国内不少学者从电池电极过程,充放电进程中电压和热耗散所受影响大小及其与时间的关系,获得了相关数理模型方程:E=Ef Ei,其中Ef=Eθ RT/F1n([M(H)]0 I/Ft)为理想电位,Ei=ktf为非理想电位,以及包括非电化学耗散Wch=g m×exp(k2t)的数理方程如下:     

K对Mn—Co—O的结构及氧化活性的影响

利用XRD,TPD,TFD-MS及催化氧化反应等实验技术,研究了K对Mn-Co-O的结构及氧化活性的影响。XRD结果表明,Mn-Co-O系已形成反尖晶石型的MnCo_2O_4结构;K-Mn-Co-O系中除MnCo_2O_4型结构外,还有新相KMnO_2存在。根据O_2的TPD-MS及吡啶的TPD结果,Mn-Co-O中添加适量的K能提高供氧活性和增加供氧数目,但酸中心数目减少,强度降低。K对Mn-Co—O催化剂氧化活性的影响随反应物分子结构的不同而异,对乙酸乙脂、苯甲酰氯等极性有机物的完全氧化反应,K能提高氧化活性,但对苯、正己烷等非极性有机物的完全氧化反应,K使其活性降低。     

Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis

Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.     

Electronic effects steer the mechanism of asymmetric hydrogenations of unfunctionalized aryl-substituted alkenes

Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.