Influence of pore dimension and sorption configuration on the heat of sorption of hexane on monodimensional siliceous zeolites

Sorption of n-hexane on monodimensional pure silica SSZ-35, CIT-5, ZSM-12, and ZSM-22 zeolites with different pore dimension and on recently synthesized ITQ-29 was studied by IR spectroscopic and computational chemistry methods. Heats of sorption of n-hexane on these zeolites was determined experimentally from the temperature dependence of the intensity of IR bands of sorbed hexane as well as from theoretical calculations. Calculations have shown the different orientations of sorbed hexane molecules inside zeolite channels, which depend on the type of zeolite and loading. At high loadings, ordering of hexane inside the channels is observed due to optimization of sorbate-sorbate and sorbate-zeolite interaction energies. Such ordering is responsible for the increase of the sorption energy. A decrease of the sorption energy upon increasing the pore dimension of zeolite was observed, in agreement with results previously published in the literature. Effects of pore diameter of zeolites and ordering of molecules inside zeolite channels on the sorption energy of hexane are discussed.     

Importance of clean-up for comparison of TEQ-values obtained by CALUX and chemo-analysis

This paper presents Chemically Activated LUciferine gene eXpression (CALUX) TEQ-values obtained for nine plasma samples following two different purification procedures, one of them involving fractionation. CALUX results obtained for the dioxin (DX) and dioxin + PCB (DX + PCB) fractions were then compared to the GC-HRMS TEQ-values calculated for the 17 polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (17 PCDD/F) and 17 PCDD/F + 4 cPCB congeners, respectively. The overestimation of the CALUX (DX fraction) TEQ-values in comparison with the chemo-analyses of the 17 PCDD/F is mainly explained by the presence of other AhR agonists, like brominated compounds. Otherwise, the constancy of the CALUX (DX + PCB fraction) TEQ-value which compares to increasing the GC-HRMS (17 PCDD/F + 4 cPCB) TEQ results raises questions concerning (1) the significance of CALUX results obtained without fractionation as well as (2) the toxicological effect of a cocktail of contaminants on the human health.     

A simple rule for classification of polychlorinated dibenzo-p-dioxin congeners on the basis of IR frequency patterns

The IR spectra of 76 dioxin congeners with zero to eight chlorines have been calculated by the DFT (B3LYP) method. Close inspection of the calculated spectra provides a simple rule for IR spectral analysis in polychlorinated dibenzo-p-dioxins (PCDDs). All congeners with a common structural motif of chlorine substitution in either of two benzene rings share the same main IR frequency, and the chlorination of one ring has little influence on the vibrational frequencies of the other ring. As a result, the main ring vibrational frequencies of all dioxin congeners could be classified into 10 groups according to the chlorine substitution pattern. This simplifies the complex IR spectral analysis of PCDDs to identifying two main peaks in essence, each of which corresponds to either of two chlorinated benzene rings. The systematic trend originates from the mass effect of the substituted chlorines. The C-H bending (in plane) character in the ring skeleton vibration mode is affected in quite different ways, depending on whether the chlorine is substituted on longitudinal or lateral positions. In particular, when all the lateral positions (2, 3, 7, 8) are chlorinated in PCDDs, the vibrational frequency of a b(1u) mode (or its analogues in other symmetry) gives a characteristic IR peak around 1392 cm(-1). This peak is unique to all toxic congeners and could be used as an indicator for them.     

Determination of polychlorinated dibenzofuran (PCDF) and dibenzo-p-dioxin (PCDD) levels and isomer patterns in fish, crustacea, mussel and sediment samples from a fjord region polluted by Mg-production

Summary Isomer-specific determination of polychlorinated dibenzofurans (PCDF) and dibenzo-p-dioxins (PCDD) was carried out in 37 samples of different fish species, crustaea and mussel from a fjord area contaminated by waste water from a Mg-factory. In addition 6 sediment samples were analysed. The tetra- and pentachlorodibenzofuran isomer pattern of the Mg-process is very characteristic and dominated by isomers with chlorine in the positions 1,2,3,7 and/or 8. Very similar patterns were found in sediment, crustacea and mussel samples up to 15 km from the factory. Nearly all isomers were present in crab, shrimp and mussel while fish samples contained mainly 2,3,7,8-substituted congeners. The isomer distributions and concentration levels for different species and tissues with high and low fat content are presented. The applied analysis techniques and the quality assurance procedure as well as practical problems are described in detail. The found levels varied between low ppt- and high ppb-levels for single isomers.

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Bestimmung von polychlorierten Dibenzofuranen (PCDF) und Dibenzo-p-dioxinen (PCDD) und deren Isomerenverteilung in Fisch, Crustaceen, Muscheln und Sedimenten einer durch Mg-Produktion verunreinigten Fjordregion

     

Comparison of immunoaffinity column recovery patterns of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans on columns generated with different monoclonal antibody clones and polyclonal antibodies

Evaluation of immunoaffinity columns (IACs) for dioxin serum sample clean-up requires a determination of the recovery of various dioxin congeners. We compared the IAC performance of different monoclonal and polyclonal anti-dioxin antibodies, measuring the recovery of congeners of polychlorinated dibenzo-p-dioxins (PCDDs). In addition, we measured the recovery of congeners of the structurally related polychlorinated dibenzofurans (PCDFs).The polyclonal antibody based IACs evaluated had lower recovery for highly chlorinated dioxin congeners, but were more specific toward 2,3,7,8-TCDD. The resemblance of the hapten to 2,3,7,8-TCDD appeared to play a clear role, but chlorines in the 2-, 3- and 7-positions of the hapten were essential. Recovery of 2,3,7,8-TCDD from the IAC showed some relation to the affinity for the antibody measured by either the K_a from accelerator mass spectrometry (AMS) or with 50% inhibition of color activity (IC₅₀) determined from an ELISA analysis.The IACs prepared from four monoclonal antibodies (Mabs) derived from a common hapten showed differences in their retention patterns of PCDDs/PCDFs. Comparison of IC₅₀ from ELISA with recovery from the IACs indicated that a minimum IC₅₀ of 100 ppb was required for satisfactory recovery from the IAC, but the correlation was poor, indicating other factors were involved. Mab DD3 showed the broadest spectrum of the Mabs and showed satisfactory recoveries of all of the dioxin congeners, except OCDD. In addition, DD3 showed good recovery toward 2,3,4,8-TCDF, 2,3,4,7,8-PeCDF and 2,3,4,6,7,8-HxCDF but has poor recovery when PCDFs have a chlorine substitution in the 1-position.     

Experiences on the analysis of PCDDs and PCDFs in pulp and paper industry matrices

Summary Some remarks on the analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans in pulp and paper industry matrices are presented. The way in which samples are dried and the solvent which is used for extraction can affect the results. For the separation of individual congeners, three capillary columns with different lengths and polarities have been compared. The effect of the resolution of the mass spectrometer has been tested for pulp samples.     

FTIR investigation of 2-chlorophenol chemisorption on a silica surface from 200 to 500 degrees C

The time-dependent chemisorption of 2-chlorophenol on a fumed silica surface was studied in situ from 200 to 500 degrees C using a temperature-controlled dosing cell and FTIR absorption spectroscopy. 2-Chlorophenol was found to chemisorb at isolated and geminal surface hydroxyl sites. 2-Chlorophenol chemisorption and subsequent surface oxidation resulted in a mixture of chlorophenolate and partial oxidation products, such as formates and acetates. The rates of chemisorption were measured, and the activation energy of adsorption was found to be 15 +/- 4 kJ mol(-1) for a fast, initial reaction and 22 +/- 2 kJ mol(-1) for a slower reaction at higher surface coverage. This work was motivated by the observation that combustion-generated fly ash mediates the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) at temperatures between 250 and 450 degrees C. Although transition metals such as copper are known to catalyze or mediate this reaction, silica is the major component of fly ash and chemisorption at higher concentration surface sites of silica must have a significant impact on the surface-mediated PCDD/F formation on fly ash surfaces.     

SSZ-39分子筛的合成及应用进展

近年来,小孔八元环SSZ-39分子筛因具有特殊的孔道结构和物理化学性质,在小分子择形催化反应中展现出相对优异的催化活性、抗积碳性和水热稳定性.本文概述了SSZ-39分子筛的合成历程,包括不同种类有机模板剂的使用、特定硅源铝源的选择以及凝胶组成的调控等;简要总结了SSZ-39分子筛在甲醇制低碳烯烃、氮氧化物的选择性催化还...     

Fast clean-up for polychlorinated dibenzo-p-dioxins, dibenzofurans and coplanar polychlorinated biphenyls analysis of high-fat-content biological samples

A fast clean-up procedure for the low level analysis of polychlorinated dibenzo-p-dioxins. polychlorinated dibenzofurans and coplanar polychlorinated biphenyls in highly fatty biological matrices using high capacity disposable multi-layer silica columns is presented. Results were compared with gel permeation chromatography for removal of lipids. Analytical criteria such as recovery rates, repeatability, reproducibility and robustness are evaluated through a broad range of biological matrices and reference materials analysis. The final proposed procedure for the complete analysis, including pressurized liquid extraction, Power-Prep system clean-up and GC-high-resolution MS analysis requires only 48 h, and allows the simultaneous preparation of up to 10 samples.     

Theoretical study of the reactions of 2-chlorophenol over the dehydrated and hydroxylated silica clusters

Silica is the main component of combustion-generated fly ash and is expected to have an important impact on the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in municipal waste incinerators. In this work, we theoretically studied the reactions of 2-chlorinated phenol (2-CP) over the clusters (SiO(2))(3) and (SiO(2))(3)O(2)H(4), which mimic the dehydrated and hydroxylated silica structures, respectively. The dehydrated cluster is much more active toward the attack of 2-CP to form highly stable 2-chlorophenolate than the hydroxylated silica cluster. The further dissociation of chlorophenolates to form CP radicals (CPRs) is calculated to be very difficult. The calculated energy barrier of the reaction of 2-CP over the dehydrated (SiO(2))(3) cluster and IR data are in good agreement with early experimental observations. On the basis of the calculated results, we propose that the formation of PCDD/Fs from CPs over silica surfaces may not involve CPRs, but be relevant to the further conversion of chlorophenolates over silica surfaces. This mechanism is very different from the corresponding reactions mediated by transition metal oxides. The results presented here may be helpful to understand the chemisorption mechanism of CPs on silica surfaces in real waste combustion.     

Determination of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans,and dioxin‐like polychlorinated biphenyls in human serum using programmable‐temperature vaporization gas chromatography with high‐resolution mass spectrometry

The determination of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in blood from a non‐occupational population is essential for the investigation of adverse health effects from these pollutants. In this study, a sensitive method based on programmable‐temperature vaporization with large‐volume injection coupled with gas chromatography with high‐resolution mass spectrometry was developed to determine these pollutants in 1–2 mL of human serum samples. Various key parameters of programmable‐temperature vaporization injector, including vent temperature, vent time, vent flow, transfer temperature and transfer time were optimized by factorial design. The accuracy and precision as well as applicability were assessed by determining polychlorinated dibenzo‐p‐dioxins, polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in calibration standard solutions, standard reference materials and real human serum samples from non‐occupational population. The method detection limits of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls were 1.5–9.0 and 0.005–0.02 ng/kg wet weight, respectively. By comparing with typically splitless injection, the application of programmable‐temperature vaporization injector could effectively lead to higher detectable rate of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in 1–2 mL of human serum samples.     

Understanding the congener-specific toxicity in polychlorinated dibenzo-p-dioxins: chlorination pattern and molecular quadrupole moment.

It is well known that the biological activities and toxicities of planar polychlorinated aromatic compounds are extremely sensitive to chlorination pattern. Although their toxic responses have been correlated with the relative affinity for the receptor, the origin of this congener specificity is not well understood. We present a general interpretation of the congener-specific activity in polychlorinated dibenzo-p-dioxins, which concludes that molecular electrostatics is the principal factor determining the structure-activity relationship in this highly controversial environmental pollutant even though this electrostatic interaction represents only a part of the total interaction energy. Through calculations of the molecular charge distribution in the complete set of 76 dioxin congeners, we show that all active congeners share a unique charge distribution pattern, which is quantitatively described in terms of the molecular quadrupole moment (QM). The QM of dioxins changes sensitively and systematically with chlorination pattern. The three-dimensional electrostatic interactions at the receptor-binding site, which are optimized at a specific QM pattern represented by that of 2,3,7,8-tetrachlorodibenzo-p-dioxin, could explain the congener specificity in the binding affinity and toxicity. Although the polarizability also changes systematically with chlorination, it can only account for the effect of the degree of chlorination, not the congener specificity.     

Surfacial,liquid sorption and monolayer-forming properties of hydrophilic and hydrophobic Stöber silica particles

The surface of silica spheres with a diameter of 500 nm was modified with ethoxysilane. Hydrophilic and partially hydrophobic silica spheres were obtained, suitable for the preparation of two-dimensional monoparticle films at the liquid-air interface. The tendency of these particles to self-assemble is basically dependent on surface hydrophobicity. Liquid sorption excess isotherms were studied in ethanol-cyclohexane and ethanol-chloroform mixtures with the aim of characterizing the adsorption capacity of the particles. Specific surface area and porosity were measured by nitrogen adsorption. The specific surface area determined by liquid sorption was considerably larger than determined by gas adsorption. This is ascribed to penetration of ethanol into the pores and the swelling of the silica particles in ethanol. Surface modification of hydrophilic particles changed the film-forming properties of the particles. The compressibility and the lift-off area of the monolayer films of hydrophobic particles on water were higher than for the films of hydrophilic particles.     

广义相关指数用于持久性环境污染物的定量结构-色谱保留关系研究

基于分子拓扑图形特征和顶点连接方式,通过定义广义相关函数、性质相关参数以及距离关系函数等概念,将“面向用户”实际应用的观点及对目标问题“自适应性”的思想引入到分子结构表征当中,从而得到一种新型分子拓扑性质表征方法:广义相关指数(GC I)。使用该指数对115个多氯代二苯并呋喃、41个多氯代二苯并-p-二、62个多氯代萘和210个多氯联苯在DB-5气相色谱柱上的保留行为进行了定量结构-色谱保留关系研究,所得模型复相关系数Rcum以及交叉检验复相关系数Qcum均在0.98以上。结果表明GC I指数具有较强分子结构表达能力及对化合物各类性质的优良适应性。     

High-resolution separation of polychlorinated biphenyls by comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC x GC) with micro electron-capture detection (microECD) has been optimised for the separation of polychlorinated biphenyl congeners with emphasis on the separation of 12 toxic non- and mono-ortho chlorinated biphenyls (CBs), viz. CBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189. The selection of the first- and second-dimension columns and the temperature programme optimisation were carried out with a mixture of 90 CBs and the results are compared with those of one-dimensional GC. A complete separation of all 12 priority CBs was obtained with two column combinations, HP-1-HT-8 and HP-1-SupelcoWax-10. With the HP-1-HT-8 column set, ordered structures show up in the two-dimensional plane, with the number of chlorine substituents and their position (ortho vs. non-ortho) being the main parameters of interest. This can help with congener identification. Estimated detection limits are excellent, i.e. about 10 fg. To illustrate the potential and the versatility of GC x GC-microECD, a cod liver extract and a standard mixture of the 17 most toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans together with 90 CBs were analysed as an application.     

Micropore-free surface-activated carbon for the analysis of polychlorinated dibenzo-p-dioxins-dibenzofurans and non-ortho-substituted polychlorinated biphenyls in environmental samples

2,3,7,8-Substituted polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) and non-ortho-substituted polychlorinated biphenyls (PCBs) account for almost all of the total toxic equivalents (TEQ) in environmental samples. Activated carbon columns are used to fractionate the samples for GC-MS analysis or bioassay. Micropore-free surface-activated carbon is highly selective for PCDD/Fs and non-ortho-PCBs and can improve the conventional activated carbon column clean-up. Along with sulfuric acid-coated diatomaceous earth columns, micropore-free surface-activated carbon provides a rapid, robust, and high-throughput sample preparation method for PCDD/Fs and non-ortho-PCBs analysis.     

Relationships between biological potency and electronic states of polychlorinated dibenzofurans and polychlorinated biphenyls.

It was found that the differences between the frontier molecular orbital energies (epsilon homo - epsilon lumo = delta epsilon) in polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) have a correlationship with the magnitude of the biological activity which is influenced by both the number and position of chlorine atom substituents on PCDFs and PCBs skeletons. Moreover, it was found that the delta epsilon's values of PCBs are classified into two types which coincide with the well-known classification of PCBs to types of 3-methylcholanthrene and phenobarbital according to their biological activities. The relationship between delta epsilon and biological activity in these xenobiotics suggests that the congeners having small delta epsilon values as 2,3,4,7,8-pentaCDF, 2,3,4,6,7-pentaCDF, 3,4,5,3',4'-pentaCB, and 3,4,5,3',4',5'-hexaCB form stable molecular complexes with an Ah-receptor, e.g. (2,3,4,7,8-PentaCDF-Ah-receptor), while the congeners having large delta epsilon values are strongly suggested to be unstable in a complex formation. Thus, this work presents an explanatory method to help understand the structure-activity relationship of the xenobiotics PCDFs and PCBs.     

Characteristics of major dioxin/furan congeners in melted slag of ash from municipal solid waste incinerators

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in slag of fly ash from three municipal solid waste (MSW) incinerators were analyzed to observe any changes in characteristics and distribution of their congeners by melting process. Actual concentration and Toxic Equivalent (TEQ) concentration profiles of 17 major congeners of PCDDs/PCDFs for gas, fly ash and melted slag were compared. The distributions of PCDDs/PCDFs in different streams macroscopically showed similarities with the generally known profiles for emission gas from a municipal waste incinerator. The total concentrations of PCDDs/PCDFs in off-gas and fly ash have been known to be a function of incineration conditions and of air pollution control device utilization; however, their normalized distributions were independent of such conditions. The concentrations of PCDDs/PCDFs in the melted slag of fly ash were not related to the concentrations of PCDDs/PCDFs congeners in fly ash but were rather a function of the melting furnace type and operation. The total amount of PCDDs/PCDFs in the melted slag of fly ash contained almost 150–27,000 times less dioxin than that in fly ash, however, the TEQ of dioxin in the slag was reduced by 435–43,500 times, which could enable them to be utilized as recycled construction materials. In normalized TEQ concentration profiles of 17 congeners of PCDDs/PCDFs, the ratio of PCDFs to PCDDs changed from 1.32 to 2.19 by melting, which showed relatively higher portion of furans left in melted slag than those in fly ash. By comparing reduction ratios of different congeners, PCDDs (dioxins) were relatively easier to destruct than PCDFs (furans) during melting process. The most difficult congener to destruct could be octa-chlorinated dibenzofuran (OCDF) among major congeners. For slag cooling methods, dioxin concentration in TEQ of slow cooled slag by air was four times higher than that of fast cooled slag by water. Thus cooling by water is more appropriate with the added beneficial effect of producing granules/particles, which can be utilized as roadbed materials.     

Research in environmental pollution

Summary Five non-o,o-Cl and 15 mono-o,o-Cl substituted PCB congeners were identified in Hessian human milk by GC-MS. For risk and hazard assessment the concentrations of these analysed PCB congeners were transformed into the corresponding TCDD-equivalents (TE). It was found that the concentrations of the analysed coplanar PCB congeners in human milk expressed in TE are by a factor of about 4 higher than that of the polychlorinated dibenzo-p-dioxins (PCDD's) and dibenzofurans (PCDF's).