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.     

一锅法从卟啉配体合成μ-氧代四苯基双核铁卟啉

A novel method for synthesis of substituted u-oxo-bis[tetraphenyl porphyrinatoiron] compotmds （[TRPPFe]20） based on the reaction among free base porphyrins （TRPPH2）, FeSO4·7H2O and H2O in one pot was proposed and investigated. Four kinds of [TRPPFe]2O were synthesized by this novel synthetic method, and their structures were characterized by elemental analysis, infrared spectra and UV-vis spectroscopy. The reaction conditions, including the effect of different iron salts on the formation of [TRPPFe]2O, the reaction time between FeSO4-7H2O and TRPPH2, the molar ratio of FeSO4-7H2O/TRPPH2 as well as the volume ratio of H2O/DMF, were investigated. The [TRPPFe]2O yield of 93% 98% could be obtained under the following optimal conditions： the reaction time of FeSOn-7H2O with TRPPH2 was about 10 h, the molar ratio of FeSOn-7H2O/TRPPH2 about 5 ： 1, and the volume ratio of H2O/DMF exceeded 2 ： 1. Further research indicated that only TRPPFeCI were formed once FeSOn-7H2O was replaced by FeCl2-4H2O, the reason of which might be that halogen ions in iron salts interfered the formation of [TRPPFe]2O, suggesting that halogen ions should be avoided in this novel synthetic method.     

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.     

Triplet EPR Dynamics of Randomly Oriented Dications and Dianions of Tetraoxaporphyrinoids

This paper deals with the photoexcited triplet state of several tetraoxaporphyrinoids studied by time-resolved electron paramagnetic resonance (EPR). The porphyrinoids studied are tetraoxa[18]porphyrin ( 1a ⁺⁺), octaethyl-tetraoxa[18]porphyrin ( 1b ⁺⁺), tetra-n-butyl tetraoxa[18]porphyrin ( 1c ⁺⁺), octaethyl-tetraoxa[26]porphyrin ( 2 ⁺⁺), and tetraoxa[18]porphycene ( 3 ⁺⁺), all of them as per-chlorate salts. To qualify as stable aromatic 18π- (or 26π-) electron systems, they must exist as dications. Analysis of the triplet EPR spectra is characterized by unique features not found in their parent porphyrins and porphycenes. While in the case of the axially-symmetric tetraphenylporphyrin, the triplet EPR spectra indicate deviation from axial symmetry, the tetraoxaporphyrin 1a ⁺⁺ exhibits, as expected, a vanishing E-term of the zero-field splitting (ZFS) tensor. A conspicuous difference is found between the triplet EPR spectra of the dications and the dianions of all tetraoxa compounds. The results are discussed in terms of the electronic structures of the porphyrinoids.     

Hyperfine Interactions in the Lowest Triplet State of Pyridine

Results are reported of nitrogen and deuterium hyperfine studies of the triplet state of pyridine-d₅ as a guest in a single crystal of benzene at 1.2 K. Through the use of electron spin echo (ESE) techniques complete hyperfine tensors have been obtained: for nitrogen from the ESE detected EPR spectra and for the para-deuterium atom from the modulations of the ESE envelope. These tensors unambiguously show that the molecule is no longer planar in the lowest triplet state T₀. Pyridine's structure considerably changes upon excitation, but the mirror plane perpendicular to the molecule is preserved. Experimental and theoretical evidence is presented for the fact that this deformation is an intrinsic property of T₀ and is not induced by the crystal field. About fourty percent of the triplet electron spin density is found to be localised in the π-orbital of nitrogen, about ten percent in the lone pair orbital of nitrogen and somewhat more than thirty percent in the π-orbital of the para-carbon atom.     

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。     

论轮胎的自由滚动力学

从轮胎稳态自由滚动的运动特点入手,通过对运动中的车辆和轮胎进行受力分析,得到自由滚动轮胎的受力与力矩平衡条件,建立用有限元方法分析轮胎稳态自由滚动的边界条件和初始条件。结合Abaqus软件所提供的子程序二次开发功能,采用Fortran语言编写求解轮胎自由滚动状态的子程序,可以实现轮胎自由滚动状态的自动求解,提高了计算精度和计算效率。仿真与轮胎试验结果对比验证了该方法的可靠性。另外,讨论了驱动、制动、自由滚动状态下轮胎接地面内的受力差异,进一步验证了该方法的有效性,为接地面内动态受力研究提供了方向。     

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.     

EPR Spectroscopy and Imaging of Free Radicals in Food

Electron Paramagnetic Resonance (EPR) is a well-known spectroscopic and imaging technique that can detect free radicals both in vitro and non-invasively in vivo, with high sensitivity. In food, free radicals can be generated by several commonly used industrial processes, such as radiosterilization or heat treatment. EPR spectroscopy has been widely used to detect radioinduced free radicals in food, but is limited to the measurement of the global response of a sample. EPR imaging (EPRI) allows the spin density distribution of free radicals to be mapped within objects. We investigated the possibility of acquiring 2D and 3D EPR images of the distribution of free radicals in various foodstuffs with naturally occurring or induced free radicals, including frogs' legs, tea leaves, coffee beans, and sunflower seeds. Our results demonstrated that the free radicals contained in foodstuffs give EPR signals with characteristics compatible with the acquisition of high-quality images. Small-size structures (e.g., frog bones, 1.0–1.5 mm width) could be delineated with accuracy. The strongest signals came from irradiated samples, but low-intensity signals from naturally occurring free radicals could also be imaged. EPRI is likely to be used when additional information is needed about the spatial distribution of unpaired electrons. The method offers the unique ability to monitor the fate of these free radicals in biological samples and in vivo.     

Generation and Electron-Transfer Reactivity of the Long-Lived Photoexcited State of a Manganese(IV)-Oxo-Scandium Nitrate Complex

Photoexcitation of a manganese(IV)-oxo-scandium nitrate complex ([(Bn-TPEN)Mn^IV(O)]²⁺−Sc(NO₃)₃) in a solvent mixture of trifluoroethanol and acetonitrile (v/v=1 : 1) resulted in generation of the long-lived photoexcited state, which is detected by nanosecond laser transient absorption measurements. The transient absorption maximum (λ_max) of the ²E excited state of [(Bn-TPEN)Mn^IV(O)]²⁺−Sc(NO₃)₃ is observed at 620 nm with lifetimes of 7.1 μs. The λ_max value is blue-shifted and the lifetime becomes longer as compared with the previously reported values of λ_max (640 nm) and lifetime (6.4 μs) of the ²E excited state of the 1 : 2 complex between [(Bn-TPEN)Mn^IV(O)]²⁺ and Sc(OTf)₃ ([(Bn-TPEN)Mn^IV(O)]²⁺−(Sc(OTf)₃)₂). The electron-transfer reactivity of the ²E excited states of [(Bn-TPEN)Mn^IV(O)]²⁺−Sc(NO₃)₃ was similar to that of [(Bn-TPEN)Mn^IV(O)]²⁺−(Sc(OTf)₃)₂. The long lifetime and the high reactivity of the ²E excited state of [(Bn-TPEN)Mn^IV(O)]²⁺−Sc(NO₃)₃ provide an excellent photooxidant for oxidation of compounds, which would otherwise be impossible to be oxidized.     

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.     

Kinetic Study of Nickel Oxide Reduction by Methane

The reduction of the nickel oxide, NiO, by methane was investigated in this work. The thermogravimetric technique was used for the determination of kinetic parameters for the reaction. The reaction was carried out in the temperature range of 600–725 °C, at atmospheric pressure with porous pellets prepared from nickel oxide powder with a mean particle size of 0.026 μm. The conversion‐time data have been interpreted by using the grain model. Complete conversion can be achieved in 11 min at 725 °C, which is shorter than the time required by carbon, i.e., ca. 120 min at 1000 °C. This faster reduction in comparison with carbonthermal reduction is attributed to the high carbon activity in methane. For the first order reaction with respect to methane concentration, the activation energy is found to be 63.9 kcal/g mol.