Structure determination of a sildenafil analogue contained in commercial herb drinks

It was found from HPLC analysis that a commercial herb drink contains a putative sildenafil analog. In order to identify the sildenafil-like compound, separation and purification were carried out. The structure determination was performed based on routine 1D and 2D NMR experiments. Unlike sildenafil, the compound contains an ethylpiperazine instead of a methylpiperazine group. In addition, the piperazine and phenyl groups are connected through an acetyl group instead of the sulfonyl group of sildenafil.     

Crystal structure of a new phosphate compound, Mg2KNa(PO4)2·14H2O

A new phosphate compound, Mg₂KNa(PO₄)₂·14H₂O, formed in the laboratory by cyanobacteria, has been identified and its crystal structure studied with single-crystal X-ray diffraction and infrared spectroscopy. The crystal is orthorhombic with the space group Pnma and unit-cell parameters a=25.1754(18) Å, b=6.9316(5) Å, c=11.2189(10) Å, V=1957.8(3) Å³. Its structure can be viewed as stacking of three types of layers along the a-axis in a sequence ABCBABCB…, where layer A is composed of Mg1(H₂O)₆ octahedra and Na(H₂O)₆ trigonal prisms, layer B of two crystallographically distinct PO₄³⁻ tetrahedra (designated as P1 and P2), and layer C of Mg2(H₂O)₆ octahedra and highly irregular K-polyhedra formed by five H₂O molecules and one O²⁻ from the P2 tetrahedron. The linkage between layers is principally achieved through hydrogen bonding, except for the K-O5 bond between layers B and C. The structure of Mg₂KNa(PO₄)₂·14H₂O has many features similar to those for the struvite analogs of MgK(PO₄)·6H₂O (Acta Crystallogr. B 35 (1979) 11) or MgNa(PO₄)·7H₂O (Acta Crystallogr. B 38 (1982) 40) and represents the first struvite-type phosphate compound that contains both K and Na as univalent cations.     

Multinuclear macromolecule metal complexes 2. Preparation and characterization of Prussian blue and its analogs bonded to pofy(vinylamine hydrochloride)

Prussian blue and its analogs bonded to poly(vinylamine hydrochloride) (PVAm · HCl) containing Fe^II or Fe^III and M²⁺ (M=Fe, Co, Cu) in a 11 molar ratio were obtained by the reaction of [Fe(CN)₆] ^n– (n=3,4) with M²⁺ ion-PVAm · HCl mixture in aqueous solution. Under a limited polymer concentration (T_VAm/T_Fe over 10), these polymer complexes thus obtained were stable and soluble in water. By casting these solutions, colored films can be produced. The formation of Prussian blue and its analogs bonded to PVAm · HCl was also investigated by the Benesi-Hildebrand method. The molar extinction coefficients of intervalence charge transfer (Fe^IIFe^III, Co^IIFe^III, Fe^IICu^II) band for MFe(CN)₆]^(n–2)– bound to PVAm · HCl (M=Fe, Co, Cu) were found to be 10,100–9601 · mol^–1 · cm^–1 at 25 C. The formation constants were found to be in the range of 10⁷ to 10¹⁰ M^–1. The changes of enthalpy (H) and entropy (S) were found to be in the range of –10.4 to –22.5 kJ · mol^–1 and 5.7 to 52.9 J · K^–1 mol^–1 respectively, at 25C.     

Polymer–polymer interactions via analog calorimetry. 2. Blends of polystyrene with bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Analog calorimetry is used as a tool to study the interaction of polystyrene, PS, with bisphenol-A polycarbonate, PC, and with tetramethyl bisphenol-A polycarbonate, TMPC. Electrostatic charge calculations were used as a guide to divide polymer repeat units and analogs into groups. A mean-field binary interaction model was used to evaluate group interaction energies. The enthalpic interaction energy obtained from this study for the PS-PC pair is 0.41 ± 0.13 cal/cm³ while that for the PS-TMPC pair is 0.19 ± 0.34 cal/cm³. The result for PS-PC blends is in good agreement with values obtained from studies using the critical molecular weight approach and the phase behavior of copolymer blends. The value for PS-TMPC does not correctly predict the phase behavior of this blend; however, its standard deviation (on both an absolute and relative basis) is large and the range of possible interaction energies includes the negative values obtained from neutron scattering. The results of this study indicate that the presence of methyl groups on the aromatic ring of TMPC repeat unit is the main factor favoring the miscibility of PS-TMPC blends. © 1997 John Wiley & Sons, Inc.     

Synthesis and Antibacterial Activity of Novel Oxazolidinone Analogs Containing Substituted Thiazole/Fused-Bicyclic Groups

IntroductionOxazolidinones, exemplified by linezolid, are anovel class of totally synthetic antibacterial agents withactivities against a variety of clinically important sus-ceptible and resistant Gram-positive pathogenic bacteriasuch as methicillin-resis…     

The reactivity of 3,5-dimethylidene-2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl and its diamagneticN-methyl analog in nucleophilic addition of amines and diels—Alder dimerization

3,5-Dimethylidene-1,2,2,6,6-pentamethyl-4-oxopiperidine was shown by the kinetic method to be less reactive than 3,5-dimethylidene-2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl in the nucleophilic addition of secondary amines and Diels—Alder dimerization. According to the quantum-chemical AM1 calculations, this is due to the difference in the structures of the activated complexes (in the reactions with amines) and to the “press” effect created by theN-methyl group that impedes the necessary cycle flattening (in the Diels—Alder reaction). Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1698–1702, October, 2000.     

µ-X-ray fluorescence and µ-X-ray diffraction investigations of sediment from the Ruprechtov nuclear waste disposal natural analog site

Results from combined µ-XRF and µ-XRD investigations of a uranium-rich tertiary sediment from a nuclear repository natural analog site in Ruprechtov, Czech Republic, are reported. The goal of the investigations is to identify arsenopyrite from diffraction patterns obtained in As-rich areas of the sample. Arsenopyrite has been revealed to be present in the sediment as thin coatings on the surface of Fe nodules from previous µ-XANES results and observed linear dependencies between Fe and As(0) distributions obtained from µ-XRF measurements. In thin sections of the sediment investigated here we find, however, neither diffraction reflections expected for arsenopyrite nor for other As-sulfides. The As(0) phase is likely present in the form of very small grains, or it is amorphous. Statistical analysis of the µ-XRD data using unsupervised classification and principle component analysis from selected sample areas also indicate that pyrite and siderite, but no arsenopyrite, are the sole diffracting phases. That pyrite and siderite are found in the same sample is an indication that the pH of the sediment environment during diagenesis must have been neutral. This allows us to refine our hypothesis for the mechanism of uranium immobilization.     

基于遗传RBF网络的惯性测量组合模拟电路故障诊断

为解决惯性测量组合模拟电路的诊断不易定位到元件级故障的问题,提出了一种基于遗传RBF网络的智能诊断方法。该方法首先利用RBF神经网络快速准确识别故障的能力,以RBF的训练均方误差为遗传算法的适应度函数,依靠遗传算法强大的全局寻优能力实现故障特征选择。在特征选择的过程中,同时记录使训练均方误差达到最小的最优RBF网络,然后直接利用特征选择过程中训练好的最优RBF网络诊断故障,而无需利用特征选择后的训练数据对RBF网络进行再训练,简化了诊断步骤,同时增强了网络的抗干扰能力。仿真结果表明,该方法能有效去除冗余特征,准确诊断惯性测量组合模拟电路的故障,并有较好的抗噪能力,证明了该方法的有效性和可行性。     

他克林二联体类似物的合成和药理研究进展

他克林二联体及其类似物是一类药效明显的乙酰胆碱酯酶抑制剂，按AnA,AnX,XnX和AnH(A)等四种类型系统地综述了其合成和药理研究进展。参考文献28篇。     

Hemicyanine-linked pyrimidine mimics as solvatochromic fluorophores with visible excitation wavelengths

The design of solvatochromic fluorescent nucleosides with visible excitation wavelengths is a goal towards the generation of modified oligonucleotides for fluorimetry-based molecular imaging. Herein, two hemicyanine-linked C5-2′-deoxyuridine nucleosides (PyI-dU and APPy-dU) have been synthesized by first generating hemicyanine-alkyne precursors that were attached via the alkyne moiety to 5-iodo-2′-deoxyuridine (5-I-dU) by Sonogashira coupling. The photophysical properties of the hemicyanine-linked dU probes have been characterized and compared to the corresponding properties of the hemicyanine-alkyne precursors. The nucleoside probe PyI-dU exhibits optical features that mimic the properties of the free hemicyanine-alkyne precursor, while the APPy-dU probe displays more favorable optical properties (longer excitation wavelength, brighter emission in water) than its precursor that is ascribed to π-stacking interactions between the hemicyanine dye with the dU nucleobase. Overall, probe APPy-dU is a superior solvatochromic fluorophore than PyI-dU suggesting its greater utility for fluorescent imaging applications.