固体酸催化合成4-羟基苯基-1′-O-D-吡喃葡萄糖苷

报道了一种简便易行的绿色合成4-羟基苯基-1′-O-D-吡喃葡萄糖苷(即熊果苷及其端基异构体)新方法,采用固体酸蒙脱石K-10或4A分子筛为催化剂,将四苄基保护的葡萄糖(2)或α-三氯乙酰亚胺酯糖给体(3)与氢醌直接进行糖基化反应,最高以86%的产率获得4-羟基苯基-2,′3,′4,′6′-四-O-苄基-1′-O-D-吡喃葡萄糖苷(4),进而脱除苄基保护,定量获得熊果苷及其端基异构体(1)。中间体(4)的结构经IR、MS、1H NMR及元素分析等测试技术进行了确认,化合物(1)的理化数据与文献值相同。     

Pulse radiolysis study on the mechanisms of reactions of CCl_3OO radical with quercetin, rutin and epigallocatechin gallate

The mechanisms of reactions between CCI3OO radical and quercetin, rutin and epigal-locatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is suggested that the electron transfer reaction is the main reaction between CCI3OO radical and rutin, EGCG, but there are two main pathways for the reaction of CCI3OO" radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants were determined. It is proved that quercetin and rutin are better CCI3OO radical scavengers than EGCG.     

氨基酸残基延展态可及表面积的预测

氨基酸残基的延展态可及表面积(ASA)对预测蛋白质结构和功能起着至关重要的作用.采用偏最小二乘法和多元回归法成功构建了具有较高准确率的预测氨基酸延展态ASA的模型.所得模型具有良好的预测性和可重复性,在模型中,训练集的最优Rt2r可以达到0.998 3,而测试集的Rt2e最优可以达到0.999 2.     

液体火箭发动机燃烧稳定性数值仿真

建立液体火箭发动机燃烧稳定性数值仿真模型, 对液氧/煤油, 煤油/气氧/气氢, 气氢/液氧发动机的两相燃烧稳定性进行了数值仿真. 首次得到的系列自激燃烧振荡的仿真结果与试验规律相符: 氢气有利于烃氧火焰稳定; 提高同轴式喷嘴的气相喷射速度有利于稳定. 对仿真结果的进一步分析表明, 燃烧室头部附近的预混低温区为燃烧振荡提供了能量. 根据仿真结果提出了抑制燃烧不稳定的技术措施: 在推进剂中添加催化剂降低反应活化能, 或者改进喷注器的设计以缩小喷嘴附近的预混低温区.     

乳状液膜法制备超细碳酸钙

探讨了不同流动载体的煤油、司本 - 80与碳酸钠水溶液制成的乳状液的稳定性 .考察了外相氢氧化钙水溶液中Ca2 + 浓度、膜相磷酸三丁酯的量及乳水比等因素对Ca2 + 迁移率的影响 .经TEM测定 ,破乳后的沉淀颗粒粒径不超过 10 0nm .     

放线菌素D光敏产生活性氧的EPR研究

放线菌素D是一种和双链DNA和单链DNA都能发生选择性结合的抗生素, 而这种结合作用大大增加了DNA的光敏性. 利用电子顺磁共振(EPR)和自旋捕捉技术, 对放线菌素D光动力作用过程中产生的活性氧进行了系统研究, 发现无论是在溶液中还是在与DNA形成复合物以后, ¹O₂和O₂^—. 都是重要的活性产物, 而且两者的产额存在竞争关系. 实验结果说明, 放线菌素D的光敏作用是通过能量转移(Ⅱ型机制)和电子转移(Ⅰ型机制)两种反应途径进行的. 当在溶液中氧自由存在时, 以能量转移形成¹O₂为主; 而当和DNA形成复合物时, 放线菌素D的激发态与DNA之间的电子转移反应成为主要的反应途径.     

Various Recipes of SiNx Passivated AlGaN/GaN High Electron Mobility Transistors in Correlation with Current Slump

The current slump of different recipes of SiN~ passivated AIGaN/GaN high electron mobility transistors （HEMTs） is investigated. The dc and pulsed current-voltage curves of AIGaN/GaN HEMTs using different recipes are analyzed. It is found that passivation leakage has a strong relationship with NH3 flow in the plasma-enhanced chemical vapor phase deposition process, which has impacted on the current collapse of SiNs passivated devices. We analyze the pulsed IDS -- VDS characteristics of different recipes of SiNx passivation devices for different combinations of gate and drain quiescent biases （VGso, VDSO） of （0, 0）, （-6, 0）, （-6, 15） and （0, 15）V. The possible mechanisms are the traps in SiNxpassivation capturing the electrons and the surface states at the SiNx/AIGaN interface, which can affect the channel of two-dimensional electron gas and cause the current collapse.     

辩证的运动观在数学问题解决中的运用

辩证地认识运动,并合理地将其运用于数学问题的解决中,往往能够起到意想不到的效果.……     

改良型比光谱-导数分光光度法在四元混合体系同时测定中的应用

提出了可应用于四元混合体系同时测定的比光谱-导数分光光度法，阐述了该方法的基本原理，并将其应用于氨基比林、苯巴比妥、咖啡因和非那西丁四元混合体系中各组分的同时测定。结果表明，氨基比林、笨巴比妥、咖啡因和非那西丁的回收率分别是109．3％（RSD=4．3％）、102．4％（RSD=6．6％）、108.7％（RSD=5．1％）、98．62％（RSD=3．2％）。方法的准确度和精密度都可以满足四组分同时测定的要求，方法简单、快速。     

Improved device performance of recessed-gate AlGaN/GaN HEMTs by using in-situ N2O radical treatment

The N₂O radicals in-situ treatment on gate region has been employed to improve device performance of recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). The samples after gate recess etching were treated by N₂O radicals without physical bombardment. After in-situ treatment (IST) processing, the gate leakage currents decreased by more than one order of magnitude compared to the sample without IST. The fabricated HEMTs with the IST process show a low reverse gate current of 10^-9 A/mm, high on/off current ratio of 10⁸, and high f_T×L_g of 13.44 GHz· μm. A transmission electron microscope (TEM) imaging illustrates an oxide layer with a thickness of 1.8 nm exists at the AlGaN surface. X-ray photoelectron spectroscopy (XPS) measurement shows that the content of the Al-O and Ga-O bonds elevated after IST, indicating that the Al-N and Ga-N bonds on the AlGaN surface were broken and meanwhile the Al-O and Ga-O bonds formed. The oxide formed by a chemical reaction between radicals and the surface of the AlGaN barrier layer is responsible for improved device characteristics.