Laser-induced reactions of NO2 in the visible region

The reaction of NO₂ with isobutane, induced by 488 nm laser radiation, to form 2-nitro-2-methylpropane has been investigated and the results computer-modeled according to two possible reaction mechanisms. The first scheme involves the direct abstraction of H from isobutane by vibronically excited NO₂ (NO ₂ ^* ), and the second, abstraction by an intermediate NO₃ radial produced by NO ₂ ^* +NO₂. The modeling results strongly support the NO ₂ ^* scheme as the dominant reaction mechanism.     

含dppm桥的双核过渡金属配合物中金属─金属间的相互作用

应用ＥＨＭＯ法研究了一系列含ｄｐｐｍ双二苯基膦甲烷桥的双核过渡金属配合物［ＰｄＢｒ（ｄｐｐｍ）］_２，Ｍ_２Ｃｌ_２（μ－ＣＯ）（ｄｐｐｍ）_２（Ｍ＝Ｐｄ，Ｒｈ），［ＲｈＣｌ（ＣＯ）（ｄｐｐｍ）］_２，Ｍ_２－（μ－Ｃｌ）_２Ｃｌ_４（ｄｐｐｍ）_２（Ｍ＝Ｎｂ、Ｔａ、Ｒｅ、Ｒｕ）的电子结构。根据配合物的成键特征，对其金属－金属的相互作用进行了分析。计算结果可以作为解释这类配合物的某些物理化学性质的理论依据。     

自增强高性能聚合物的成型工艺同力学性能间相关性研究——1.超高分子量聚乙烯的应力诱导结晶理论和其自增强作用

本文发展了一种高分子量聚合物熔融体的应力诱导结晶结构形态模型,它是由微晶聚集体(以下简称微区)-高分子链组网和缠结网的网络结构组成。基于上述模型,把二种网中的单个链组作为独立的统计单元和形变单元,计算了二种网中单个链组的末端距分布函数,进一步计算了二种网和总网的形变自由能。在此基础上,讨论了诱导结晶结晶机理和自增强聚合物网络自由能的依赖性,并着重地研究了超拉伸高聚物的起始熔点拉伸比间的关系。用超高分子量聚乙烯膜和超取向高密度聚乙烯纤维的起始熔点和拉伸比的实验数据进行处理,得到理论予期的近似直线关系,初步验证了聚合物网应力诱导结晶理论。     

对硝基氯苄与活性亚甲基化合物的反应

对硝基苄基衍生物可以与许多阴离子起单电子转移的亲核取代反应。Kornblum等以对硝基氯苄为底物,2-乙氧羰基香豆满-3-酮的钠盐为阴离子,作了深入的研究,得出对硝基氯苄与2-乙氧羰基香豆满-3-酮钠盐的C-烷化反应机理为自由基链式亲核取代反应。同时,Russell等提出对硝基氯苄与2-     

Oxidation of dibenzothiophene catalyzed by heme-containing enzymes encapsulated in sol-gel glass

We have encapsulated several hemoproteins in the sol-gel glass to catalyze the oxidation reaction of dibenzothiophene (model for organic sulfur compounds in coal) with hydrogen peroxide. In addition to cytochrome c and myoglobin, which have previously been encapsulated in sol-gel glasses, two other hemoproteins, horseradish peroxidase and bovine blood hemoglobin, have now been successfully immobilized in sol-gel media with the retention of their spectroscopic properties. All four hemoproteins studied also demonstrate similar catalytic activities toward the oxidation of dibenzothiophene as compared with the results obtained with the proteins in solution. In the case of encapsulated cytochrome c, the more water-soluble S-oxide was obtained with much higher selectivity over the less water-soluble sulfone (S-oxide/sulfone = 7.1) as compared to what was obtained in the aqueous/organic medium (S-oxide/sulfone = 2.3). Because of the advantage of easy separation of the encapsulated proteins from the liquid reaction mixture, it is clear from these studies that the immobilization of active hemoproteins in the solid glass media could serve as more practical biocatalysts.     

Plasticization and Crystallization of Poly(ethylene Terephthalate) Induced by Water

Commercial poly(ethylene terephthalate) (PET) was treated at R. H.>80% and room temperature for a set time. The glass transition temperature (Tg) decreases with the time of exposure to high humidity. The decrease in Tg is a result of plasticization. Our data indicate that the Tg of dry PET of 76-78°C may decrease to as low a temperature as 65-67°C when it is wet. Induced crystallization of PET in the presence of water reduces the cold crystallization temperature (Tc). The structure of water-induced crystals is imperfect and can be improved in perfection by annealing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction between netropsin and double-stranded DNA in capillary zone electrophoresis and affinity capillary electrophoresis

Poor sensitivity and low phase ratio are the main drawbacks of open tubular capillary electrochromatography (OTCEC). The poor sensitivity results from the use of narrow bore size capillary, whereas the low phase ratio, which limits the separation capability, is caused by the limited surface area of conventional capillary. Two strategies may be useful to overcome these disadvantages. First, an extended light path (ELP) capillary, which has a bubble cell at the detection point, is used to improve the sensitivity. Secondly, an etched capillary of a 1,000-fold increased surface area is used to enhance the phase ratio. In this work, use of an ELP capillary and an etched capillary in OTCEC was evaluated with a chiral stationary phase of avidin prepared with the physical adsorption method. With a 20 microm I.D. ELP capillary with a 150 microm bubble cell, the peak height was enhanced by 4-10-fold and the corrected peak area was increased by 12-fold relative to a 20 microm I.D. conventional capillary. However, the peak efficiency and resolution decreased noticeably. The phase ratio on the etched capillary was slightly enhanced, by a factor of 1.64 relative to an unetched capillary. Consequently, the separation capability was slightly improved. The increase in the phase ratio was much lower than that expected from the increase in surface area, the reason for which is probably the reduced density of surface silanol group and the generation of nitrogen-containing groups due to the etching process.     

Matrix Effects and Behaviors of Elements in Oxalic Acid Medium by Inductively Coupled Plasma Mass Spectrometry

Because of its high sensitivity, wide dynamic range and relative freedom from interferences, inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the determination of trace and ultra-trace levels of elements in various fields1. Due…