QALE analysis of CO dissociative kinetics of Ru(CO)4L (L = P-donor ligands): accelerating effects of hydrogen in PHnR(3 - n) ligands (n = 1-2)

Studies of CO-dissociative substitution reactions of the complexes Ru(CO)4L (L = a wide variety of P-donor ligands) have been extended and analysis of the results by the QALE methodology has been refined (QALE = quantitative analysis of ligand effects). Rates increase substantially with increasing size of L, mainly as a consequence of increasingly favourable activation entropies. These can be associated with increasing Ru-CO bond breaking that is compensated enthalpically by increasing Ru-P bond making allowed by release of steric strain. Explicit allowance for pi-acidity shows that these effects are just significant while sigma-donor and aryl effects are negligible. However, pendent hydrogen atoms, attached directly to the phosphorus atoms, have a pronounced and unique positive effect on the rates, with significant kinetic isotope effects (KIE). This is associated with the novel occurrence of direct Ru-H or incipient Ru-(eta2-P-H) agostic bond making as the CO ligand departs.     

Theoretical investigations of substituent effects in dimethyldioxirane epoxidation reactions

A detailed theoretical study of dimethyldioxirane-mediated epoxidations with a variety of differently substituted alkenes 3-21 is presented. Transition structures and activation barriers were determined in the gas phase and in acetone as solvent with the B3LYP/6-311+G(d) level of theory. Substituent effects were elucidated by frontier orbital analyses of the reacting species as well as by natural bond orbital (NBO) analysis of the transition structures. Epoxidations with alkenes carrying electron-donating groups such as OMe or NHAc commonly tend to have low activation energies and early transitions states, whereas using alkenes with electron-withdrawing moieties such as CN, SO2Me, CO2Me, CF3, CHO, and Cl higher activation barriers and late transition states are observed. In all cases a net charge transfer (CT) from the alkene to the dioxirane was observed substantiating the electrophilic character of dimethyldioxirane.     

Enhancing reactivity of carbonyl compounds via hydrogen-bond formation. A DFT study of the hetero-Diels-Alder reaction between butadiene derivative and acetone in chloroform

To examine how hydrogen-bond (HB) formation involving chloroform solvent molecules influences the chemical reactivity of ketones, the hetero-Diels-Alder reaction of N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene and acetone has been studied by using density functional theory (DFT) at the B3LYP/6-31G level. The effects of the chloroform on the activation energies have been modeled by means of discrete-continuum models. In the gas phase, the formation of specific HB between acetone and one and two chloroform molecules decreases the activation barriers from 19.3 to 13.6 and 8.5 kcal/mol, respectively. Inclusion of solvent effects by means of combined discrete and polarizable continuum models yields a change of molecular mechanism from a concerted to a two-step mechanism, and the first nucleophilic step is the rate-limiting step. The corresponding values of activation barriers in chloroform are 18.6 kcal/ mol (no HB), 13.5 kcal/mol (one HB), and 9.6 kcal/mol (two HBs). These theoretical results account for the experimental observation that chloroform accelerates the reaction more markedly than more polar aprotic solvent such as acetonitrile. A DFT analysis of the global electrophilicity power of the reagents provides a sound explanation about the catalytic effects of chloroform.     

Pomegranate fruit extract modulates UV-B-mediated phosphorylation of mitogen-activated protein kinases and activation of nuclear factor kappa B in normal human epidermal keratinocytes paragraph sign

Excessive exposure of solar ultraviolet (UV) radiation, particularly its UV-B component, to humans causes many adverse effects that include erythema, hyperplasia, hyperpigmentation, immunosuppression, photoaging and skin cancer. In recent years, there is increasing use of botanical agents in skin care products. Pomegranate derived from the tree Punica granatum contains anthocyanins (such as delphinidin, cyanidin and pelargonidin) and hydrolyzable tannins (such as punicalin, pedunculagin, punicalagin, gallagic and ellagic acid esters of glucose) and possesses strong antioxidant and anti-inflammatory properties. Recently, we have shown that pomegranate fruit extract (PFE) possesses antitumor promoting effects in a mouse model of chemical carcinogenesis. To begin to establish the effect of PFE for humans in this study, we determined its effect on UV-B-induced adverse effects in normal human epidermal keratinocytes (NHEK). We first assessed the effect of PFE on UV-B-mediated phosphorylation of mitogen-activated protein kinases (MAPK) pathway in NHEK. Immunoblot analysis demonstrated that the treatment of NHEK with PFE (10-40 microg/mL) for 24 h before UV-B (40 mJ/cm(2)) exposure dose dependently inhibited UV-B-mediated phosphorylation of ERKl/2, JNK1/2 and p38 protein. We also observed that PFE (20 microg/mL) inhibited UV-B-mediated phosphorylation of MAPK in a time-dependent manner. Furthermore, in dose- and time-dependent studies, we evaluated the effect of PFE on UV-B-mediated activation of nuclear factor kappa B (NF-kappaB) pathway. Using Western blot analysis, we found that PFE treatment of NHEK resulted in a dose- and time-dependent inhibition of UV-B-mediated degradation and phosphorylation of IkappaBalpha and activation of IKKalpha. Using immunoblot analysis, enzyme-linked immunosorbent assay and electrophoretic mobility shift assay, we found that PFE treatment to NHEK resulted in a dose- and time-dependent inhibition of UV-B-mediated nuclear translocation and phosphorylation of NF-kappaB/p65 at Ser(536). Taken together, our data shows that PFE protects against the adverse effects of UV-B radiation by inhibiting UV-B-induced modulations of NF-kappaB and MAPK pathways and provides a molecular basis for the photochemopreventive effects of PFE.     

Molecular dynamics calculation of the activation volume for water exchange on Li+

The activation volume of water exchange around Li+ (aq) was determined from reactive flux calculations using molecular dynamics simulations with a classical force field. The barrier height for exchange decreases with pressure, giving a negative activation volume, in agreement with the current paradigm for inferring exchange mechanism from activation volume. However, it is also demonstrated that pressure-dependent transmission effects make a significant contribution to the overall activation volume. These calculations indicate that small activation volumes should not be regarded as mechanistically indicative because of the potential contributions from transmission effects.     

Comparison of 14 MeV-NAA, k0-NAA and ED-XRF for air pollution bio-monitoring

In this paper the performances and the limitations of three multi-elementary analysis techniques are compared applied to a study of air pollution biomonitoring in Morocco. These techniques are: (1) 14 MeV neutron activation analysis (14 MeV-NAA), (2) thermal neutron activation analysis using the k ₀ quasi-absolute method (k ₀-NAA) and (3) energy dispersive X-ray fluorescence analysis (ED-XRF). The experimental procedures and the control of the analytical results using certified reference materials are described and discussed. The three methods were confronted for the analysis of lichens, mosses and tree-barks. The complementarity of these methods enabled us to determine 43 elements in different samples. The most suitable method for each element was selected according to the sensitivity and selectivity necessitating the minimum corrections of the matrix effects and/or the interfering reactions.     

Optimization of preparation conditions for activated carbon from palm oil fronds using response surface methodology on removal of pesticides from aqueous solution

Palm oil fronds were used to prepare activated carbon using the physiochemical activation method, which consisted of potassium hydroxide (KOH) treatment and carbon dioxide (CO₂) gasification. The effects of variable parameters activation temperature, activation time and chemical impregnation ratios (KOH: char by weight) on the preparation of the activated carbon and for the removal of pesticides: bentazon, carbofuran and 2,4-Dichlorophenoxyacetic acid (2,4-D) were investigated. Based on the central composite design (CCD), two factor interaction (2FI) and quadratic models were respectively employed to correlate the effect of variable parameters on the preparation of activated carbon used for the removal of pesticides with carbon yield. From the analysis of variance (ANOVA), the most influential factor on each experimental design response was identified. The optimum conditions for preparing the activated carbon from oil palm fronds were found as follows: activation temperature of 750 °C, activation time of 2 h and chemical impregnation ratio of 2.38. The percentage error between predicted and experimental results for the removal of bentazon, carbofuran and 2,4-D were 8.2, 1.3 and 9.2%, respectively and for the yield of the palm oil frond activated carbon was 5.6.     

La(NO3)3和Pr(NO3)3对高岭石脱羟基动力学的影响

采用热重和微商热重(TG/DTA)综合热分析技术在不同升温速率下研究了掺入La(NO₃)₃和Pr(NO₃)₃的高岭石的热分解过程, 利用Coats-Redfern积分法和Achar微分法对热分析实验数据进行动力学计算, 得到了高岭石脱羟基反应过程中的控制机理函数、 活化能和指前因子等动力学参数; 分析了2种稀土掺入对高岭石脱羟基过程动力学参数的影响, 并用Ozawa法对活化能进行了验证. 结果表明, 未掺稀土和掺入Pr(NO₃)₃的高岭石的脱羟基反应过程均受化学反应模型F₃控制, 反应的活化能分别为307.94和282.86 kJ/mol, 指前因子lnA的值分别为47.8980和44.1718; 掺入La(NO₃)₃的高岭石脱羟基反应过程控制机理函数发生改变, 受化学反应模型F₂控制, 反应活化能为196.02 kJ/mol, 指前因子lnA的值为29.5551. 与未掺稀土的高岭石对比, 掺入Pr(NO₃)₃后活化能和指前因子略有降低; 而掺入La(NO₃)₃后则显著降低, 分别降低了36.34%和38.30%. 采用Ozawa法验证得到的活化能与Coats-Redfern积分法和Achar微分法结果一致.     

不熔化沥青球在低速流化床中炭化和活化的初步研究

不熔化沥青球在低速流化床中炭化和活化的初步研究乔文明，王克温，凌立成，刘朗周承泽，王瑾，郑斌（中国科学院山西煤炭化学研究所，太原０３０００１）（上海太平洋化工（集团）公司焦化总厂，２００２４１）关键词低速流化床，活化，炭化，球形活性炭由于球形活性炭，...     

Molecular activation analysis for chemical species studies

Molecular activation analysis (MAA) refers to an activation analysis method that is able to provide information on the chemical species of elements in systems of interest, though its exact definition has yet to be assigned. Its development is strongly stimulated by the urgent need to know the chemical species of elements, because knowledge of bulk contents or concentrations is often insufficient to judge biological, environmental or geochemical effects of elements. The features, methodology and limitations of MAA are outlined, as well as the up-to-date MAA progress in our laboratory. Received: 14 August 1998 / Revised: 30 November 1998 / Accepted: 1 December 1998     

Study on thermal activated sepiolite for enhancing decoloration of crude palm oil

Thermal activated sepiolite was prepared and used as an adsorbent for efficient decoloration of crude palm oil. The effects of activation temperature on the structure of sepiolite were investigated by Fourier transform infrared spectroscopy, X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, Zeta potential and nitrogen adsorption–desorption isotherms techniques, and the decolorization efficiency for crude palm oil was systematically evaluated by Lovibond tone. The results indicate that the thermal activation of sepiolite affects its structure and decoloration efficiency. The Red value and content of phosphorus only reduced by 28.29 and 68.00 %, respectively, after decoloring with acid-treated sepiolite, but by 57.14 and 76.00 %, respectively, after thermal activation because that the thermal activation improved the porous structure and surface activity of sepiolite by releasing different kinds of waters and creating new adsorptive sites. In addition, the suitable activation temperature (400 °C) is significant to reach an optimal decoloring capacity.     

Induction of apoptosis in human promyelocytic leukemia HL60 cells by panaxynol and panaxydol

Panaxynol and panaxydol are naturally occurring polyacetylenes, isolated from the lipophilic fractions of Panax notoginseng, that exert anti-proliferative effects against malignant cells. However, to the best of our knowledge, no study concerning the inhibitory effects of the two polyacetylenes on cell growth of human promyelocytic leukemia cells has been reported. In this paper, we examined the antiproliferation and proapoptotic effects of panaxynol and panaxydol on HL60 cells and investigated their mechanism of action. Cell growth inhibition of panaxynol and panaxydol were determined by trypan blue dye exclusion assays. Apoptosis of cells was revealed by morphological observation, analysis for nuclear DNA distribution and by annexin V-FITC/ PI staining using flow cytometry. It was found that panaxynol and panaxydol markedly inhibited proliferation of HL60 cells in a time- and dose-dependent manner via an apoptotic pathway. In concern with these ?ndings, Western blot analysis showed proteolytic activation of PKCδ, caspase-3 activation and cleavage of poly (ADP [adenosine diphosphate]-ribose) polymerase in HL60 cells treated by panaxynol and panaxydol. In conclusion, panaxynol and panaxydol have profound effects on growth and apoptosis of HL60 cells, suggesting those substances are worthy of further exploration as potential anti-cancer agents.     

Preparation and gas-sensing properties of pitch-based carbon fiber prepared using a melt-electrospinning method

Pitch-based carbon fibers (PCFs) were fabricated using a melt-electrospinning method and used as a gas sensor electrode for nitric oxide (NO). The PCFs were modified through different heat-treatment temperatures (1,000, 1,650, and 2,300 °C) and activation conditions (2, 4, and 6 M KOH solutions) to investigate the effect of these processes on the structure and surface functionalities of the resultant fiber samples. Field emission scanning electron microscopy, elemental analyzer, Raman spectroscopy, and pore analysis techniques were then employed to characterize the prepared samples. As a result of these modifications, the porosity and electrical conductivity of the prepared PCFs increased, which resulted in enlarged gas adsorption sites and an improved electron transfer. The improved porosity of the PCFs was attributed to the chemical activation process, whereas the enhanced electrical conductivity was also attributed to higher heat-treatment temperature. The sensing ability of the PCFs for NO-gas was thus significantly improved based on the effects of the chemical activation and higher heat-treatment temperatures. The performance of these PCFs as an NO-gas sensor system suggests promising application of carbon fibers as a novel and highly efficient NO-gas sensing material.     

Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

The kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis. The use of the compensation effect provides an efficient way of evaluating the preexponential factor for both single- and multi-step kinetics. Many effects observed experimentally as the reaction temperature shifts usually involve changes in both activation energy and preexponential factor and, thus, are better understood by combining both parameters into the rate constant. A technique for establishing the temperature dependence of the rate constant by utilizing the isoconversional values of the activation energy and preexponential factor is explained. It is stressed that that the experimental effects that involve changes in the preexponential factor can be traced to the activation entropy changes that may help in obtaining deeper insights into the process kinetics. The arguments are illustrated by experimental examples.     

Nanoconfinement revealed in degradation and relaxation studies of two structurally different polystyrene-clay systems

Degradation and relaxation studies have been performed on two polystyrene (PS)-montmorillonite clay nanocomposites, one of which has an intercalated PS-clay structure and the other an exfoliated PS-clay brush structure. Compared to virgin PS, both nanostructured materials have demonstrated the following similarities: (a) a high yield of alpha-methylstyrene in the degradation products as measured by infrared spectroscopy; (b) larger values of the activation energy of the thermal degradation as determined by isoconversional kinetic analysis of thermogravimetric data; and (c) larger values of the activation energy for the glass transition as found from the frequency dependence of the glass transition temperature measured by multifrequency temperature-modulated differential scanning calorimetry. These effects are taken as structure independent manifestations of nanoconfinement of the PS chains in the PS-clay materials. Heat capacity measurements have been employed to evaluate the size of the cooperatively rearranging region, VCRR, that is found to be structure dependent. Compared to its value in virgin PS, VCRR has markedly increased in the exfoliated PS-clay brush system but remained practically unchanged in the intercalated PS-clay system.     

BEAMGAA: A chance for high precision analysis of big samples

Summary In activation analysis of traces in small samples, the non-equivalence of the activating radiation doses of sample and calibration material gives rise to sometimes tolerable systematic errors. Conversely, analysis of major components usually demands high trueness and precision. To meet this, beam geometry activation analysis (BEAMGAA) procedures have been developed for instrumental photon (IPAA) and neutron activation analysis (INAA) in which the activating neutron/photon beam exhibits broad, flat-topped characteristics. This results in a very low lateral activating flux gradient compared to known radiation facilities, however, at significantly lower flux density. The axial flux gradient can be accounted for by a monitor-sample-monitor assembly. As a first approach, major components were determined in high purity substances as well as selenium in a cattle fodder additive.     

Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

In situ microwave activation is applied to the electrochemical oxidation of thiourea at low surface area (polished polycrystalline) and at high surface area (electrodeposited mesoporous platinum coated) platinum microelectrodes. The one electron oxidation of thiourea to formamidine disulfide is monitored as a function of the different activation parameters. In the absence of microwaves (ambient temperature, low mass transport) increasing the surface area (roughness) increases the thiourea oxidation response predominantly due to adsorption effects. In the presence of high microwave intensities, high mass transport and thermal effects further increase the oxidation current at mesoporous platinum. The most effective thickness of the mesoporous platinum film for the thiourea oxidation process is estimated as 3 μm independent of electrode diameter, temperature, or mass transport effects.     

Performance of NAA Methods in an International Interlaboratory Reference Material Characterization Campaign

An extensive database of analytical results from a recent biological matrix Reference Material Characterization Campaign permitted an intercomparison of the performances of various methods among each other and with "true" best estimate concentration values established for these materials. Six different variants of neutron activation analysis (NAA) methods were employed including: instrumental neutron activation analysis, instrumental neutron activation analysis with acid digestion, neutron activation analysis with radiochemical separation, neutron capture prompt gamma activation analysis, epithermal instrumental neutron activation analysis, and neutron activation analysis with preconcentration. The precision and accuracy performance of NAA-based analytical methods are compared with three other major techniques, atomic absorption spectrometry (AAS), atomic emission spectrometry (AES) and mass spectrometry (MS) for 28 elements in 10 natural matrix materials.     

Comparison of elemental contents of Korean space foods using instrumental neutron activation analysis

The analysis of mineral contents in space foods is needed to obtain an information on a comprehensive elemental composition as well as the investigation on the effects of human nutrition and health based on the dietary intake of mineral elements. Recently, six items of new Korean space foods (KSFs) such as kimchi, bibimbap, bulgogi, a ramen, a mulberry beverage and a fruit punch which was developed by the KAERI, and the contents of more than 15 elements in the samples were examined by using instrumental neutron activation analysis (INAA). Five biological certified reference materials, NIST SRM were used for analytical quality control. The results were compared with those of common Korean foods reported, and these results will be applied toward the identification of irradiated foods.