A DFT Study on Deactivation of Triplet Excited State Riboflavin by Polyphenols

The deactivation of triplet excited state riboflavin by polyphenols, e.g. rutin and catechin, was studied on the basis of density functional theory calculations. The results show that the H-atom transfer pathway is more feasible on thermodynamic grounds in comparison with the direct energy transfer or direct electron transfer pathways involved in the triplet excited state riboflavin deactivation by rutin/catechin. The findings are helpful to understand the protective effect of polyphenols against the riboflavin induced photosensitizing damage.     

Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPS^T in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 10¹⁰ M⁻¹ s⁻¹. The CH₂C(CH₃)₂OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 10⁹ M⁻¹ s⁻¹) with ZnTPPS^T to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH₃)₂COH radical reduces both ZnTPPS (k = 1 × 10⁸ M⁻¹ s⁻¹) and ZnTPPS^T (k = 3 × 10⁹ M⁻¹ s⁻¹) to the anion radical (ZnTPPS)⁻. The radical Br⁻₂ oxidizes both states to the cation radical (ZnTPPS)⁺ with k = 8 × 10⁸ M⁻¹ s⁻¹ for the ground state and 5 × 10⁹ M⁻¹ s⁻¹ for the triplet. The transient cation Cd⁺ reduces both states with a diffusion-controlled rate (k = 1 × 10¹⁰ M⁻¹ s⁻¹) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.     

Theoretical Study on Reactions of Triplet Excited State Thioxanthone with Indole

In the present work, a theoretical study on the deactivation of triplet excited (T₁) state thioxanthone (TX) by indole (INH) was performed, based on density functional theory calculations. Three feasible pathways, namely direct electron transfer from INH to T₁ state TX, electron transfer followed by proton transfer from INH^.+ to TX^.−, and H-atom transfer from nitrogen of INH to keto oxygen of T₁ state TX, were proposed theoretically to be involved in T₁ state TX deactivation by INH.     

Triplet State Interrogation in Supersonic Beams by Surface Electron Ejection

Recently, we have developed an experimental method for the detection of triplet states generated by laser excitation in supersonic beams. It is based on electron ejection from low work-function surfaces by metastable triplet states. We have detected both directly laser-excited triplets and triplets generated via intersystem crossing from laser-excited singlet states. Here, we review the applications of this method and discuss its mechanism. By comparing the laser-induced fluorescence (LIF) spectrum and Surface Electron Ejection by Laser-Excited Metastables (SEELEM), we have measured relative triplet formation quantum yields for several aromatic compounds. By utilizing a detector mounted on a translational stage, we could vary the distance between the pulsed laser excitation and the detector and measure the decay rates of triplets in molecular beams. The major advantage of the method is in extending the measurement of triplet lifetimes to the ∼ 1-ms range. The combination of LIF, SEELEM, and fluorescence quantum yields enabled us to discriminate between intersystem crossing and internal conversion in isoquinoline. SEELEM is now being utilized in studying the spectroscopy and the dynamics of directly laser-excited triplet states. Although the oscillator strength of the lowest triplet state of pyrazine is about 10⁻⁸, we have measured the spectrum and the decay rates of its various vibronic levels. Our results support the notion that surface Penning ionization is the mechanism of SEELEM. The detector is insensitive to vibrational energy (thus enabling the distinction between intersystem crossing and internal conversion). The detection sensitivity of triplets rises with the excess electronic energy and with the lowering of the surface work-function.     

弱酸性树脂吸附低浓度游离碱行为的研究

利用电导实验技术 ,跟踪观察弱酸性树脂吸附低浓度游离碱的行为 ,研究温度对吸附的影响 ,测定吸附活化能 ( Ea)和吸附剂 -吸附质相互作用能 ( U)。实验结果表明 ,温度升高 ,吸附剂 -吸附质相互作用能增加 ,表观吸附速率常数 ( k)增大 ,而且 U与 T存在良好的线性相关 ( r=0 .995 1 )     

锆基催化剂合成乙酸十二醇酯的非等温反应动力学研究

利用锆基催化剂合成乙酸正十二醇酯 ,确定了反应条件。同时根据非等温变体积条件下的动态法液-固相反应的特点 ,导出了反应速率方程。计算结果表明 ,乙酸正十二醇酯合成反应服从二级动力学模型 ,表观活化能为 35 1.19k J· mol- 1 ,频率因子为 2 .45 0 7× 10 46 L· m ol- 1 · min- 1 ,反应服从二级动力学模型。     

丹东河蚌游离型多糖的提取

利用丹东地区河蚌-褶纹冠蚌为原料,对游离型多糖提取工艺进行了研究.结果表明,经匀浆,微波处理,透析,去蛋白质等处理步骤,在真空条件下干燥,得游离型多糖 ,纯度93.3%.收率0.83%.     

EPR and Kinetic Studies of Hydrogen Centers in Aluminoborate Glasses

Barium aluminoborate glasses containing hydrogen as an impurity, irradiated at 77 K with X rays, show the characteristic doublet of atomic hydrogen in the EPR spectra when measured at T<200 K. The hfs constant of the H^o_i center is smaller than that of free atomic hydrogen, indicating that the attractive van der Waals interaction is more important than the repulsive Pauli exclusion forces in that glassy matrix. It is suggested on the basis of isochronal and isothermal annealing experiments that there are at least three different sites for hydrogen, each one contributing with Ist-order decay kinetics. The activation energies found in 30 mol% BaO, 60 B₂O₃, 10 Al₂O₃ glass are, respectively, equal to E₁=(0.5±0.1), E₂=(0.24±0.03), and E₃=(0.16±0.03)×lO⁻¹⁹ J.     

Spin Polarization in the Photoexcitation of the Triplet State of Phenazine in a Rigid Glass

Phenazine dissolved in a rigid toluene glass is excited to its triplet state by illumination with a modulated light source. The ESR signal is modulated, the nature of the modulation depending on the kinetics of population and depopulation of the triplet sublevels. Modulation of the ESR signal varies across the spectrum because of the dependence of the kinetics on orientation.     

土曲霉固态发酵lovastatin的动力学研究

对Aspergillus terreus ATCC 20542固态发酵产lovastatin的过程进行了研究,根据发酵过程中菌体生长和产物生成等规律,建立了土曲霉固态发酵的过程动力学模型,并对模型进行了参数拟合和验证.模型在一定程度上揭示了lovastatin 发酵代谢过程的特征,可以用于分析固体发酵过程.     

玉米秸秆木质素脱除动力学研究

采用KOH在不同温度下蒸煮稀酸预水解后的玉米秸秆。确定了不同蒸煮温度下木质素脱除速率常数,木质素脱除动力学方程表达为:WL=0.0137exp(-∞t)+0.8433exp(-k2t)+0.1430exp(-k3t)。利用Arrhenius方程确定木质素在大量脱除段以及残余脱除段的活化能分别达到54.46kJ/mol和27.62kJ/mol。确定在该体系中最佳蒸煮温度为100℃,蒸煮时间为100min,木质素脱除率可达到90%以上。     

Salt‐Free Aqueous Extraction of a Cell‐Bound Biosurfactant: a Kinetic Study

A cell‐bound biosurfactant produced by Lactobacillus pentosus was obtained under eco‐friendly conditions and used directly as an emulsifying agent in order to stabilize fluorene/water emulsions. The biosurfactant was extracted from L. pentosus cells with an aqueous phosphate buffer solution in the absence of NaCl. This is important because most the cell‐bound biosurfactants are extracted in the presence of NaCl, which is considered highly phytotoxic. A pseudo‐second order kinetic model best described the batch extraction of the biosurfactant from cells. As expected, the initial extraction rate of the biosurfactant increased with the temperature. Calculation of the activation energy with the Arrhenius equation yielded a positive value, indicating that the process is endothermic. The aqueous solution containing the biosurfactant was able to stabilize fluorene/water emulsions, with relative emulsion values of 62.2 % after 7 days of emulsion formation.     

醇法生产聚乙烯醇缩丁醛的动力学研究

在醇法均相工艺中,通过正交试验,初步优选出适宜的反应温度、反应时间、物料配比等工艺参数。结果表明反应条件为：55℃,mH2SO4：mPVA=0.1：1,n丁醛：n 羟基=1.1：2,3h,在此基础上测定了反应速度,获得了动力学方程为：r=kCA^n1CB^n2=573.59e^ 5769.78/τCA^2.08CB^0.31。     

强化蒸发技术在天然碱加工中的应用研究

提高一水碱结晶质量是提高 (一水碱法 )重质纯碱质量的关键。笔者对河南桐柏安棚天然碱卤水进行了添加活性剂的蒸发试验。试验表明 :添加适宜的活性剂 ,可使一水碱结晶颗粒增大、粒度分布均匀、含水量降低、沉降时间缩短 ;不仅明显提高了重质纯碱的质量 ,而且增加了产量。强化蒸发技术是一水碱法生产重质纯碱企业提高产品质量和产量的有效、可行途径。     

自由基氧化法处理乳化油废水实验研究

乳化油废水危害巨大,文章研究二氧化铅电极处理乳化油废水的最佳pH和处理时间等,以及在此基础上进行处理实际废水的初步研究。     

硫代硫胺氧化反应动力学研究

探讨了双氧水氧化硫代硫胺反应的机理,建立了描述氢离子浓度和双氧水浓度变化的氧化动力学方程,与实验结果吻合良好。研究表明,该反应是酸的自动催化反应,氢离子初始浓度的增加可以加速反应进程,由此为实际工业生产中氧化前的加酸工序提供了原理性的指导依据。     

乙丙橡胶湿法脱挥工艺研究

采用乙丙橡胶(J-2070)胶液进行了凝聚、挤出脱挥的实验研究。采用改造后的喷嘴结构及合理的加料方式,有效地提高了胶液凝聚过程中的脱挥效率。采用改造后的Ⅱ型模头,进行乙丙橡胶水凝聚样品的挤出脱挥实验,实验结果表明:在挤出机模头压力3.6 MPa机头温度为154℃时,挤出样品的w(总挥发分)0.5%;在挤出机转速为50~120 r/min的范围内,挤出样品不发生降解,说明该脱挥工艺可行,满足乙丙橡胶脱挥的要求。     

Kinetic Study of Copper Deposition on Iron by Cementation Reaction

Abstract

Cementation of copper on iron powder was shown to be a feasible process to achieve a high degree of copper removal over a broad operational range. First-order kinetics were followed for both the copper concentration and the surface area of iron. To minimize the effect of copper-hydroxyl formation and excess iron consumption, the cementation process was found to be more practical in weak acidic conditions