液相色谱法测定果蔬汁中柠檬黄和日落黄方法优化

对液相色谱法测定果蔬汁中柠檬黄和日落黄进行了方法优化,对色谱条件进行了调整,采用ODS-C18型(250 mm×4.6 mm)色谱柱,流动相甲醇-0.02 mol/L乙酸铵(体积比40∶60,pH4),流速为0.6 mL/min。采用紫外检测器,柠檬黄检测波长为430 nm,日落黄检测波长为510 nm。该方法测定结果的相对标准偏差为柠檬黄1.3%(n=4)、日落黄2.3%(n=4)。柠檬黄和日落黄的平均回收率分别为84.17%、88.33%。该法满足实验要求。     

芳香寡聚酰胺大环化合物的合成

通过芳香二胺单体1和二酸酰氯单体2的一步环化反应合成了酰胺键上的氢原子被2,4-二甲氧基苄基部分取代的一系列新型的芳香酰胺八聚体大环化合物3, 这些带有不同R基团环状八聚体的结构得到了核磁、高分辨质谱和MALDI-TOF的确认.     

板式脉动热管用于LED散热研究

随着LED输入功率的不断提高,大耗散功率带来的高发热量及要求高的出光效率给LED散热提出了更高的要求。脉动热管与常规的散热技术相比,具有高效、结构简单、传热性能好等优点。本文主要通过板式脉动热管对大功率LED散热实验,对热管壁面温度及LED发光强度随时间的变化特征进行了研究。实验结果分析表明:板式脉动热管对各功率LED都会产生非常显著的冷却效果。随着LED功率的增大,脉动热管的启动时间逐渐减短,热阻也呈下降趋势。在理论方面,通过建立LED板式脉动热管水冷理论模型,发现板式脉动热管的热阻是影响LED结温高低的重要因素。     

某型双频接收机混频中放组件的研制

介绍了S、X波段带数字控制衰减器的混频中放单元设计方法,带内增益平坦度≤±0.5dB,功率输出1dB压缩点≥15dBm;介绍了放大器增益的分配思路、数控衰减器的工作原理、电路的实现方法及电路制版后装配调试和测试结果,满足设计要求。     

Na+, Mg2+, and Zn2+ binding to all tautomers of adenine, cytosine, and thymine and the eight most stable keto/enol tautomers of guanine: a correlated ab initio quantum chemical study

Interactions of adenine, cytosine, guanine, and thymine with Na(+), Mg(2+), and Zn(2+) cations were studied using an approximate resolution of identity correlated second-order MP2 (RI-MP2) method with the TZVPP ([5s3p2d1f/3s2p1d]) basis set. All existing tautomers of adenine, cytosine, and thymine and the eight most stable keto/enol tautomers of guanine were considered. Cations bind mostly in a bidentate manner, and stabilization energies of these complexes are larger than those in the case when cations bind in a unidentate manner. The cation...Y (Y equal to N or O) distances for divalent metals are shorter than those for Na(+) and for Zn(2+) are mostly shorter than the Mg(2+)...Y distance. The intermolecular distances between the cation and the base for complexes containing adenine and cytosine are systematically shorter than those for complexes containing guanine and thymine. Only for cytosine the canonical keto/amino tautomer structure with ions represents the global minimum. For guanine, the metalated canonical form is again the most stable, but its stabilization energy is within less than 5% of the stabilization energies of the two other rare tautomers, which indicates that the canonical form and these two rare tautomers could coexist. The canonical structures of adenine and thymine in the presence of ions are considerably less stable (by more than 10%) than the complexes of the rare tautomers. It can be concluded that the interaction of Na(+), Mg(2+), and Zn(2+) cations with cytosine in the gas phase will not induce the change of the canonical form to the rare tautomeric form. In the case of isolated guanine, the equilibrium of the canonical form with rare tautomers can be found. For isolated adenine and thymine the presence of rare tautomers is highly probable.     

Analysis of alkyl polyglucosides in industrial products by capillary electrophoresis with pulsed amperometric detection

Pulsed amperometric detection following micellar electrokinetic chromatography has been applied successfully to the direct detection of alkyl polyglucosides (APGs) in shampoos and other industrial products without prior conversion to highly absorbing or fluorescing derivatives. For electrochemical detection, it is necessary to dissociate the hydroxyl groups of the APGs. Thus, we used 0.1 M NaOH in the outlet vial to dissociate the APGs. The main problems associated with the combination of electrochemical detection and capillary electrophoresis are the need to isolate the detector from the electric field used in the capillary electrophoresis separation and the difficulty of aligning the working electrode with the end of the capillary. To overcome these problems, a simple capillary-electrode holder was constructed. This holder automatically aligns the capillary and the electrode in a wall-jet configuration without the aid of micropositioners and facilitates the replacement of electrodes and capillaries without reconstruction of the entire capillary/electrode setup. Special microcylindrical gold electrodes have been produced by sealing 300-μm-diameter gold wire into borosilicate-glass capillaries.     

Absolute and relative-rate kinetics experiments and direct dynamics computations for the reaction of Br atoms with CH2ClBr

Kinetics of the reaction Br + CH2ClBr <--> CHClBr + HBr (1, -1) were studied experimentally in the forward direction. The absolute reaction kinetics method of laser flash photolysis coupled with Br atom resonance fluorescence detection and three different relative-rate methods with gas-chromatographic analysis were applied to carry out the experiments. The rate constants determined were found to obey the Arrhenius law in the wide temperature range of T = 293-785 K providing the kinetic expression k1 = (2.8 +/- 0.1) x 10(13) exp[-(47.6 +/- 0.3) kJ mol(-1)/RT] cm3 mol(-1) s(-1) (the errors given refer to 1sigma precision). An ab initio direct dynamics method was used to study reaction (1, -1) theoretically. The electronic structure information including geometries, gradients, and force constants was obtained at the MP2 level of theory; and energies were improved at higher theoretical levels. Rate constants were calculated using the canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-1000 K. Theory substantially underestimates k1 compared to experiment. The agreement was found good with k(-1) reported previously predicting positive temperature dependence. The experimental kinetic parameters were utilized in thermochemical calculations yielding the recommended standard enthalpy of formation of delta(f)H degrees (298) (CHClBr) = (140 +/- 4) kJ mol(-1) (with 2sigma accuracy given).     

Synthesis and Crystal Structure of （E）2-（3′-Bromo- 5′-chloro-salicylidene amino）-4-methyl Pyridine

A new Schiff base compound, 2-bromo-4-chloro-6-[（4-methylpyridin-2-ylimino）methyl]phenol （C13H10BrClN20）, has been synthesized by the condensation of equimolar 3-bromo-5- chlorosalicylaldehyde and 4-methylpyridin-2-ylamine in a methanol solution. The compound was characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The crystal belongs to the monoclinic system, space group P21 with a = 6.048（3）, b = 14.063（7）, c = 7.623（4） A,β = 97.703（7）°, Z = 2, V = 642.5（6）A3, Dc = 1.683 g/cm3, Mr=325.59, 2（MoKa） = 0.71073A,μ = 3.395 mm^-1, F（000） = 324, R = 0.0370 and wR = 0.0662. A total of 3879 reflections were collected, of which 1970 with I 〉 2σ（I） were observed. As expected, the molecule adopts a trans configuration about the C=N double bond. The benzene and pyridine rings are nearly coplanar （mean deviation from the combined plane is 0.031（3）A）, with their dihedral angle of 3.3（3）°. The preliminary biological tests show that the compound has excellent antibacterial activities.     

COMMUTATORS OF SINGULAR INTEGRAL OPERATORS WITH NON-SMOOTH KERNELS

Let T be a singular integral operator bounded on Lp(Rn) for some p, 1 ＜ p ＜∞. The authors give a sufficient condition on the kernel of T so that when b ∈BMO, the commutator [b, T](f) = T(bf) - bT(f) is bounded on the space Lp for all p, 1 ＜ p ＜∞.The condition of this paper is weaker than the usual pointwise Hormander condition.