超细AgO粉末:制备及热分解非等温动力学

采用化学沉淀法,以臭氧为氧化剂制备了超细AgO粉末,并用XRD、XPS、SEM和粒度分析仪对制备的粉末进行了表征,借助热重分析法(TG)和线性升温理论对超细AgO粉末的热分解过程和非等温热分解动力学机理进行了研究。结果表明,制备的AgO属于单斜晶系,形貌为片状,其粒径分布在45～551nm之间,大部分在200nm左右;AgO的热分解分两步,158℃开始分解,放出氧气形成Ag2O,413℃进一步分解形成Ag;其热分解反应服从核生成和核成长为控制步骤的A2机理,热分解表观活化能为90.26kJ·mol-1,反应频率因子为1.64×108s-1。     

Effect of High Order Coulombic Interaction on Radiationless Resonance Transfer of Electronic Excitation

The decay of sensitizer phosphorescence in a rigid solution modified by the electronic energy transfer by the mechanism of dipole-dipole interaction mixing with the dipole-quadrupole interaction is proposed. The rate constant for the transfer process transfer process as (equation).where (equation). Calculations are made of the yield and the decay time of the sensitizer phosphorescence as functions of the activator concentration and the mixing coefficient of dipole-dipole interaction with dipole-quadrupole interaction. It is hoped that the proposed mechanism will provide a sound, quantitative basis for analyzing experimental data in a triplet-singlet energy transfer process. As a demonstration, results indicate that about 9% of the electronic energy radiationlessly transferred from triplet triphenylene-d₁₂ to singlet Rhodamine B is induced by the electric dipole-quadrupole coulombic interaction.     

Dialkyl Peroxides Decomposition in the Presence of Quaternary Ammonium Halides

Decomposition of dicumyl peroxide and cumyl tert-butyl peroxide was studied in the presence of tetraethylammonium halides in acetonitrile, dimethylformamide, 2-propanol, and acetic acid. The tetraethylammonium halides accelerate the decomposition of dialkyl peroxides in 2-propanol and acetic acid, but do not affect the reaction velocity in dimethylformamide and acetonitrile. The decomposition products character depends on the solvent nature.     

Chemiluminescence and Bioluminescence as an Excitation Source in the Photodynamic Therapy of Cancer: A Critical Review

Photodynamic therapy (PDT) of cancer is known for its limited number of side effects, and requires light, oxygen and photosensitizer. However, PDT is limited by poor penetration of light into deeply localized tissues, and the use of external light sources is required. Thus, researchers have been studying ways to improve the effectiveness of this phototherapy and expand it for the treatment of the deepest cancers, by using chemiluminescent or bioluminescent formulations to excite the photosensitizer by intracellular generation of light. The aim of this Minireview is to give a précis of the most important general chemi‐/bioluminescence mechanisms and to analyze several studies that apply them for PDT. These studies have demonstrated the potential of utilizing chemi‐/bioluminescence as excitation source in the PDT of cancer, besides combining new approaches to overcome the limitations of this mode of treatment.     

The Mechanism of the Decomposition of Peroxides and Hydroperoxides by Mineral Fillers

The interaction of fillers and pigments with free radical initiators has been studied. Clay minerals have a marked influence on both the rate and the mechanism of the decomposition of peroxides and hydroperoxides. Kaolinite is a particularly effective catalyst and causes rapid decomposition even at room temperature. The reaction of cumene hydroperoxide with kaolinite is first-order in peroxide and the rate constant is proportional to the ratio of clay to hydroperoxide. From a study of the products of the reaction and the influence of solvent on the decomposition, a mechanism involving an intramolecular rearrangement or closely associated ion pairs has been proposed. The application of these results to polymer filler composites is discussed.     

Acid-Induced Free-Radical Decomposition of Hydroperoxides and Peroxides: New Low-Temperature Initiator Systems for Vinyl Polymerization

Evidence for an acid-induced free-radical breakdown of tert-butyl hydroperoxide and di-tert-butyl peroxide at room temperature has been obtained from polymerization experiments with methyl methacrylate and styrene.     

稀释稳定剂对有机过氧化物热分解的压力效应

小型密闭压力试验;压力行为;稀释稳定剂对有机过氧化物热分解的压力效应     

Radiationless processes in a molecular beam: Time resolved emission from benzophenone

In order to study the radiative properties of the isolated benzophenone molecule, a molecular beam of benzophenone is excited by a pulsed nitrogen laser or a pulsed tunable dye laser and the subsequent emission intensity is measured as a function of time. We find the decay to be exponential with a lifetime of about O.5μs. This value is shorter than the radiative lifetime calculated from absorption measurements. As the background pressure in the molecular beam chamber is raised from 10^?6 torr to 10^?4 torr, the decay of the emission lengthens and becomes biexponential. An explanation involving giant self-collision-induced cross sections for intersystem crossing is advanced to reconcile these observations with results from previous studies of benzophenone emission decay.     

Minireview: A Caritical Review of the Transition Metal Ions Influence on Peroxyoxalate Chemiluminescence

ABSTRACT

A detailed study and evaluation of the presence of Cr(III), Zn(II) and Pb(II) and various parameters affecting the intensity of the chemiluminescent reaction of TCPO and 2-NPO with hydrogen peroxide in the presence of 3-aminofluoranthene, as the fluorophore, and imidazole (IMI) as catalyst, is presented. Depending on the unprotonated imidazole and fluorophore concentrations, these metal ions enhance the intensity of the fluorophore at pH's higher than 8.0. At pH = 7.0, in the presence of IMI/HIMI⁺ (IMI = 1×10^?2 mol.L^?1), tris(hydroxymethyl)aminomethane or HPO₄ ^2?/H₂PO₄ ^? buffers, no effect of these metal ions was observed. A critical comparison with the data reported in the literature is presented.     

Chemiluminescence as a PDT light source for microbial control

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem? concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm2 level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.     

Semiempirical Analysis of the Homolytic Decomposition of Peresters with the Concerted Cleavage of Two Bonds

The parabolic model of a bimolecular reaction is modified to study the monomolecular decomposition of molecules into radicals by the cleavage of several bonds. Together with the oscillation model of molecule decomposition with the concerted cleavage of several bonds, this model is used to analyze the kinetic data on the decomposition of 16 peresters with the simultaneous cleavage of C–C and O–O bonds. Parameters characterizing this decomposition are obtained and multiple variants in representing such decomposition in terms of the parabolic model are discussed.     

Activation Energy and Transition State Determination of the Olefin Insertion Process of Metallocene Catalysts Using a Semiempirical Molecular Orbital Calculation

The transition state of the olefin insertion process of metallocene catalysts can be determined by adopting the semiempirical PM3 model. In computational chemistry, the computational methods most employed are the ab initio method and density functional theory, which are very time consuming. The semiempirical molecular orbital method requires much less computational resources than the above methods. However, the accuracy and reliability of the semiempirical molecular orbital method remains to be determined. The PM3 model is the most recently developed the semiempirical molecular orbital method and can also be applied to transition metal calculations. This study is intended to investigate the reliability of computational results determined using semiempirical PM3 model on metallocene catalysts through comparison with published results on the density functional theory (DFT). The saddle point finding procedure is adopted to find the transition state of the ethylene insertion process of metallocene catalysts. Results on the geometry and energy trends of the ethylene insertion process of metallocene catalysts determined using the PM3 model are in good agreement with the DFT results. In addition, the saddle point of the potential energy surface of ethylene insertion is verified in accordance with the eigenvalue of the vibrational frequency spectrum. Correct eigenvalues indicate that the correct saddle point of the potential energy surface of ethylene insertion has been successfully located. Hence, the eigenvalue of the vibrational frequency spectrum is a valuable reference in terms of saddle point justification. Computational results and vibrational frequency spectrum analysis demonstrate that the PM3 model can be used to locate the correct saddle point of the potential energy surface. The results obtained using the PM3 model confirm that the eigenvalue of the transition state lies nearly on the vibrational frequency spectrum. The eigenvalues are also analyzed, providing a valuable reference for further studies of the transition state of olefin insertion of metallocene catalysts. The activation energies for the olefin insertion reaction are also studied for evaluation of the catalyst.     

Simulation of the Glass Transition

Enthalpic relaxation has been used to model the development of the glass transition in polymers, using kinetic parameters determined separately. For this purpose the Kohlrausch-Williams-Watt stretched exponential function, relating the extent of relaxation, Φ(t), to time t and an average relaxation time, τ_a, i.e.

Thermal Decomposition and Glass Transition Temperature Study of Poly-p-isopropylstyrene

Thermal decomposition and glass transition temperature studies have been carried out on poly-p-isopropylstyrene (PpiPrS) with a differential scanning calorimeter. The un-decomposed polymer as well as its decomposition products were analyzed by gel permeation chromatography (GPC), infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). During isothermal treatments in the 25–150°C temperature range (α < 3%), the observed increase in M arose primarily from interchain linking between the longer radical-bearing chains. Beyond 315°C (α > 6%), the molecular weight increases result from crosslinking reactions between decomposed polymer and longer undecomposed chains. During interchain linking, the number of isomethyl groups (iso-CH³) increase. In the crosslinking reactions that take place at temperatures beyond 315°C, the number of iso-CH³ and terminal or α-methyl groups (α-CH³) both increase while the number of methylene groups (CH²) decreases. Activation energies of decomposition for various homologs of polystyrene (PS) obey the following order: E_PS > E_PpiPrS > E_PpiPrαMeS ≥ E_PαMeS. A comparison of the Tg_e values of PS with those of PpiPrS, poly-α-methylstyrene (PαMeS) and poly-p-isopropyl-α- methylstyrene (PpiPrαMeS) shows that the presence of the p-isopropyl groups lowers the T_g of PS as well as that of PaMeS by about 30–35° K.     

Four-Membered Ring Peroxides as Excited State Equivalents: A New Dimension in Bioorganic Chemistry

Consideration of chemiluminescent and bioluminescent processes invariably brings to mind the four-membered ring peroxides, 1,2-dioxetanes and α-peroxylactones. Nevertheless, while chemiluminescence and bioluminescence are well established fields of scientific study, isolable and characterized “high-energy” molecules such as the 1,2-dioxetanes and α-peroxylactones are of relatively recent vintage, about a decade. These intriguing compounds produce electronically excited products which manifest themselves by light emission during their thermal decay; more importantly, these transformations are involved in luminescent as well as dark enzymatic processes. It is not our intention to present a comprehensive overview in this progress report, but rather to focus on those aspects which require further study.     

Associated species of dimethylsulfoxide: Semiempirical modeling

Quantum chemical calculations have been carried to gain insight into the self-association of dimethylsulfoxide (DMSO), the interaction of DMSO with a solvent, and the protonation of DMSO. Different species that may be present in DMSO solutions have been modeled semiempirically.