Solvent Effects on the Absorption Spectrum of the Product and the Equilibrium Constant for the Proton Transfer Reaction from 1-Phenacylquinolinium Bromide to Amines

The equilibrium constants, K ₂, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ⁺, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF) and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K ₂ value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K ₂ value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The change in the K ₂ value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of P⁻Q⁺ (the deprotonated product of PHQ⁺). The effect of THF on the K ₂ value is consistent with that of the peak wavelength of the absorption spectrum of P⁻Q⁺. The change in the K ₂ value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The effect of EtOH on the K ₂ value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities were adjusted to that of EtOH. The K ₂ value increased with increasing vol-% of EtOH because of the stabilization of P⁻Q⁺ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P⁻Q⁺ demonstrated a blue shift as the vol-% of EtOH increased.     

Double hexagonal chains with minimal total <Emphasis Type="Italic">π</Emphasis>-electron energy

The total energy of all π-electrons in a conjugated hydrocarbon (within the framework of HMO approximation) is the sum of the absolute value of all the eigenvalues of its corresponding graph. In this paper, we consider “double hexagonal chains” as benzenoids constructed by successive fusions of successive naphthalenes along a zig–zag sequence of triples of edges as appear on opposite sides of each naphthalene unit. It is shown that if the fusions are such as to give a polyaceacene then the total π-electron energy is the minimum from among all the double hexagonal chains with the same number of naphthalene units.      

Surface chemistry studies of (CdSe)ZnS quantum dots at the air-water interface

Trioctylphosphine oxide- (TOPO-) capped (CdSe)ZnS quantum dots (QDs) were prepared through a stepwise synthesis. The surface chemistry behavior of the QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherm of the Langmuir film of the QDs gave an average diameter of 4.4 nm, which matched very well with the value determined by transmission electron microscopy (TEM) measurements if the thickness of the TOPO cap was counted. The stability of the Langmuir film of the QDs was tested by two different methods, compression/decompression cycling and kinetic measurements, both of which indicated that TOPO-capped (CdSe)ZnS QDs can form stable Langmuir films at the air-water interface. Epifluorescence microscopy revealed the two-dimensional aggregation of the QDs in Langmuir films during the early stage of the compression process. However, at high surface pressures, the Langmuir film of QDs was more homogeneous and was capable of being deposited on a hydrophobic quartz slide by the Langmuir-Blodgett (LB) film technique. Photoluminescence (PL) spectroscopy was utilized to characterize the LB films. The PL intensity of the LB film of QDs at the first emission maximum was found to increase linearly with increasing number of layers deposited onto the hydrophobic quartz slide, which implied a homogeneous deposition of the Langmuir film of QDs at surface pressures greater than 20 mN.m(-1).     

New features in the catalytic cycle of cytochrome P450 during the formation of compound I from compound 0

Density functional theory (DFT) is applied to the dark section of the catalytic cycle of the enzyme cytochrome P450, namely, the formation of the active species, Compound I (Cpd I), from the ferric-hydroperoxide species (Cpd 0) by a protonation-assisted mechanism. The chosen 96-atom model includes the key functionalities deduced from experiment: Asp(251), Thr(252), Glu(366), and the water channels that relay the protons. The DFT model calculations show that (a) Cpd I is not formed spontaneously from Cpd 0 by direct protonation, nor is the process very exothermic. The process is virtually thermoneutral and involves a significant barrier such that formation of Cpd I is not facile on this route. (b) Along the protonation pathway, there exists an intermediate, a protonated Cpd 0, which is a potent oxidant since it is a ferric complex of water oxide. Preliminary quantum mechanical/molecular mechanical calculations confirm that Cpd 0 and Cpd I are of similar energy for the chosen model and that protonated Cpd 0 may exist as an unstable intermediate. The paper also addresses the essential role of Thr(252) as a hydrogen-bond acceptor (in accord with mutation studies of the OH group to OMe).     

Synthesis and characterization of complexes of UO2(II) and Th(IV) of bis-schiff bases derived from furoylpyrazolone

Four new complexes of UO₂(II) and Th(IV) with bis-Schiff bases, derived from N,N'-bis[(l-phenyl-3-methyl-5-oxo-4-pyrazolinyl)-a-furylmethylidyne]-1,2-propylenediimine [1,2-BPMOPFP-H₂] and N,N'- bis[(l-phenyl-3-methyl-5-oxo-4-pyrazolinyl)-a-furylmethylidyne]-1,3-propylenediimine [1,3-BPMOPFP-H₂], were synthesized and characterized by elemental analysis, IR, UV, ¹HNMR spectroscopy, and molar conductivity. The general formula of the complexes was confirmed to be [UO₂(BPMOPFP)], [Th(BPMOPFP)(NO₃)]NO₃. A possible structure for the complexes have been proposed.     

头发锌含量测定的应用价值评价

以114例2－5岁儿童为对象，同时取其末梢血和头发，测定锌含量。以全血锌值为标准，评价头锌测定的应用价值。结果显示，头发锌测定的灵敏度可达86．1％，特异度为52．4％，符合率为73．7％。     

Effect of the fibre-forming material structure and silica nanoparticles

The paper discusses the thermal properties of alginate fibres made from alginic acid or sodium alginate and from alginates substituted with divalent metal ions during the fibre-forming stage. Alginate fibres with an addition of silica nanoparticles have also been examined. The selection of fibre-forming parameters was intended to obtain the best either sorption or strength properties depending on the specific fibre application. Thermal curves of the fibres under investigations obtained by under air atmosphere and differential scanning calorimetry (DSC) under neutral gas atmosphere have been interpreted from the view of physical and chemical changes in the fibre-forming material. Based on thermogravimetric curves, the fibre thermal stability indices have been determined. It has been found that the addition of silica nanoparticles exerts a positive influence on the thermal properties of the examined fibres.     

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

Equimolar mixtures of 3,5-dimethylpyrazole (1) with four NH-imidazoles (2–5) have been studied by¹³C and ¹⁵N CPMAS NMR and by DSC. In three cases, the solid mixture behaves as the sum of the individual components [imidazole (2), 2-methylimidazole (3) and 2,4(5)-dimethylimidazole (5)]. In one case [4,5-dimethylimidazole (4)], the mixture corresponds to a new species in which the dynamic behavior of1 no longer exists.     

Studies on the Distribution of Phenoxyacetic Acid in Two-Phase Systems: <Emphasis Type="Italic">n</Emphasis>-Aliphatic Hydrocarbon – Water

Summary. Phenoxyacetic acid distribution in two-phase systems n-aliphatic hydrocarbon (C₅–C₈) – water and its dimerization in organic phase were investigated. The values of distribution coefficient (D _HR), distribution constant (K _D), and dimerization constant (K _dim) of acid were obtained. The empirical correlations of these quantities with Hildebrand solubility parameter of organic solvents were established. The influence of pH of the aqueous phase as well as the polarity of the applied organic solvents on phenoxyacetic acid physical chemistry in the two-phase systems was described.     

Synthesis of non-agglomerated Ba<Subscript>0.77</Subscript>Ca<Subscript>0.23</Subscript>TiO<Subscript>3</Subscript> nanopowders by a modified polymeric precursor method

In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba_0.77Ca_0.23TiO₃ nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis, morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy. In summary, Ba_0.77Ca_0.23TiO₃ nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution (30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the chelation in higher pHs.