Mechanistic study of stereoselective gas-phase reactions of phosphenium ions with cis- and trans-1,2-diaminocyclohexanes

The 1,3-dioxolane-2-phosphenium ion, 1,3-benzodioxole-2-phosphenium ion, and o-biphenylenephosphenium ion are reported to react in a stereoselective manner with cis- and trans-1,2-diaminocyclohexanes in the gas phase in a Fourier transform ion cyclotron resonance mass spectrometer. Elimination of NH3 from an addition product was observed only for the trans isomer. Several reaction mechanisms were experimentally and computationally examined (B3LYP/6-31G(d)//HF/6-31G(d) + ZPVE level of theory). The most plausible mechanism is initiated by addition of one of the amino groups to the electrophilic phosphorus atom followed by proton transfer between the amino groups. A change to a diaxial conformation for the trans isomer facilitates anchimeric assistance by the now nucleophilic phosphorus atom as the C-N bond breaks to release NH3. Intramolecular proton transfer competes with the conformational change and ultimately leads to ethylene glycol elimination. The transition states for the critical steps of these two reactions are calculated to be nearly equal in magnitude, which rationalizes the observation of both reactions for the trans-diamine. In contrast, the adduct of the cis isomer can eliminate NH3 via a concerted 1,2-hydride shift without a need for a conformational change. However, the barrier associated with this reaction was found to be substantially greater than for proton transfer between the N- and O-atoms. The latter reaction dominates and ultimately leads to ethylene glycol elimination.     

Mechanical properties and transition temperatures of crosslinked-oriented gelatin

 This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation and water content on the glass transition temperature T _g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin which had been room-conditioned showed two transition temperatures: the lower one was attributed to T _g of the water-plasticized gelatin, and the higher one was interpreted as T _g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T _g and melting temperatures T _m (217 and 230 ^°C, respectively) are so similar. Using water as plasticizer not only decreases T _g but produces imperfect crystallites which melt below the T _g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous phases. Received: 8 October 1996 Accepted: 2 November 1995     

Reactions of charged phenyl radicals with aliphatic amino acids in the gas phase

Gas-phase reactivity of five differently substituted positively charged phenyl radicals was examined toward six amino acids by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The reactivity of the radicals studied was determined by the electrophilicity of the radical, which can be characterized by the radical's electron affinity (EA). The larger the electron affinity of the radical, the higher the overall reaction rate. In addition to the expected H-atom abstraction, several unprecedented reaction pathways were observed, including NH2 abstraction, SH abstraction, and SCH3 abstraction. These reaction pathways dominate for the most electrophilic radicals, and they may not follow radical but rather nucleophilic addition-elimination mechanisms. Hydrogen abstraction from glycine was also investigated theoretically. The results indicate that hydrogen abstraction from alphaC of glycine is both kinetically and thermodynamically favored over the NH2 group. The ordering of transition state energies for hydrogen abstraction from the alphaC and NH2 groups was found to reflect the radicals' EA ordering.     

New Copper（Ⅱ） and Nickel（Ⅱ） Complexes of 4-Morpholinoacetophenone Thiosemicarbazone： Structural, Electrochemical and Antimicrobial Studies

4-Morpholinoacetophenone thiosemicarbazone, MAPT, and its nickel（Ⅱ） and copper（Ⅱ） complexes have been prepared and characterized by elemental analysis, magnetic susceptibility, spectral methods （FT-IR, ^1H NMR） and cyclic voltammetry. Electrochemical behaviors of the complexes have been studied by cyclic voltammetry in DMF media showing metal centered reduction processes for both of them. The redox properties, nature of the electrode processes and the stability of the complexes were discussed. [Cu（MAPT）2]Cl2 complex shows Cu（Ⅱ）/Cu（Ⅰ） couple and quasi-reversible wave associated with the Cu（Ⅲ）/Cu（Ⅱ） process. The reduction/oxidation potential values depend on the structures of complexes. Also, the antimicrobial activities of these complexes were determined against S. aureus, E. coli and B. subtilis.     

2(H)-1,4-Oxazin-2-ones as ambident azadienes

3,5-Dichloro-6-phenyl-2(H)-1,4-oxazin-2-one 3, 5-chloro-3,6-dimethyl-2(H)-1,4-oxazin-2-one 4, 5-chloro-6-methyl-3-phenyl-2(H)-1,4-oxazin-2-one 5 and 5-chloro-3,6-diphenyl-2(H)-1,4-oxazin-2-one 7, are ambident azadienes reacting efficiently and selectively with both electron rich and electron poor dienophiles.     

Engineering Multifunctional Gold Decorated Dendritic Mesoporous Silica/Tantalum Oxide Nanoparticles for Intraperitoneal Tumor‐Specific Delivery

Nonspecific high‐energy radiation for treatment of metastatic ovarian cancer is limited by damage to healthy organs, which can be mitigated by the use of radiosensitizers and image‐guided radiotherapy. Gold (Au) and tantalum oxide (TaO_x) nanoparticles (NPs), by virtue of their high atomic numbers, find utility in the design of bimetallic NP systems capable of high‐contrast computed tomography (CT) imaging as well as a potential radiosensitizing effect. These two radio‐dense metals are integrated into dendritic mesoporous silica NPs (dMSNs) with radial porous channels for high surface‐area loading of therapeutic agents. This approach results in stable, monodispersed dMSNs with a uniform distribution of Au on the surface and TaO_x in the core that exhibits CT attenuation up to seven times greater than iodine or monometallic dMSNs without either TaO_x or Au. Tumor targeting is assessed in a metastatic ovarian cancer mouse model. Ex vivo micro‐CT imaging of collected tumors shows that these NPs not only accumulate at tumor sites but also penetrate inside tumor tissues. This study demonstrates that after intraperitoneal administration, rationally designed bimetallic NPs can simultaneously serve as targeted contrast agents for imaging tumors and to enhance radiation therapy in metastatic ovarian cancer.     

Development and validation of an LC‐MS/MS method for simultaneous quantitative analysis of free and conjugated bisphenol A in human urine

Bisphenol A (BPA) is an environmental endocrine‐disrupting chemicals that is widely used in common consumer products. There is an increasing concern regarding human exposure to BPA owing to the potential adverse effects associated with its estrogenic activity. For assessing environmental exposure to BPA, it is essential to have a sensitive, accurate and selective analytical method, especially one that can detect low BPA levels in complex sample matrices. In this study, we developed and validated an accurate, sensitive, and robust liquid chromatography–tandem mass spectrometry method for simultaneous quantification of free BPA and BPA β‐d ‐glucuronide (BPA‐gluc) concentrations in human urine with only a single injection. Calibration curves were linear over a concentration range of 1–100 ng/mL for BPA and 10–1000 ng/mL for BPA‐gluc. The levels of the analytes were determined quantitatively with HPLC/ESI‐MS/MS by using negative electrospray ionization in the select ion monitoring mode and a pentaflouraphenyl propyl column. The validated method was applied to the analysis of spot urine specimens collected from randomly selected healthy human subjects. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of Hg(II) in Environmental Water Samples by Dispersive Liquid Phase Microextraction Combined with Flame Atomic Absorption Spectrometry

In this study, a method of dispersive liquid phase microextraction combined with the flame atomic absorption spectrometry was proposed for the determination of trace Hg using diphenylthiocarbazone as chelating reagent. Several factors which have effect on the microextraction efficiency of Hg, such as pH, extraction and dispersive solvent type and their volume, concentration of the chelating agent, extraction time were investigated, and the optimized experimental conditions were established. After extraction, the enrichment factor was 68. The detection limit of the method was 45 ng mL^?1, and the relative standard deviation for eight determinations of 2 μg mL^?1 Hg was 1.7%. The results for the determination of Hg in environmental water samples (tap water, well water, mineral water and Caspian sea water) have demonstrated the applicability of the proposed method.     

收缩喷嘴中的湍流Ⅰ——边界层解

应用边界层积分法,研究锥形喷嘴入口区域中湍动涡流的发展.球面坐标系中的控制方程,通过边界层的假定得到简化,并对边界层进行了积分.应用4阶Adams预测校正法求解该微分方程组.入口区域的切向和轴向速度,分别应用自由涡流和均匀速度分布来表示.由于缺乏收缩喷嘴中涡流的实验数据,需要用数值模拟对该发展模式进行逆向验证.数值模拟的结果证明,该解析模型在预测边界层参数中的能力,例如边界层的生长、剪切率和边界层厚度,以及不同锥度角时的涡流强度衰减率等.为所提出的方法引进一个简明而有效的程序,用以研究几何形状收缩设备内的边界层参数.