Determination of 13 estrogenic endocrine disrupting compounds in atmospheric particulate matter by pressurised liquid extraction and liquid chromatography-tandem mass spectrometry

This paper describes the optimisation of an analytical method for the simultaneous determination of up to 13 estrogenic endocrine disrupting compounds (EDCs), including natural and synthetic estrogens, alkylphenols, bisphenol A and phthalate esters, in atmospheric particulate matter. This methodology is based on pressurised liquid extraction and liquid chromatography-tandem mass spectrometry and is the first method described for analysis of estrogens in air. Samples were collected with high-volume samplers equipped with quartz microfiber filters. Two selected reaction monitoring transitions were chosen for identification and confirmation of the target compounds. Quantitation was performed by the internal standard method with the use of deuterated surrogate standards. The analytical features of the method were satisfactory: absolute recoveries were around 45 % for all compounds, except estrogens (～29 %), because of matrix effects. Repeatability was in all cases below 15 %. Quantitation limits of the method ranged from 5 pg/m³ (for diethylphthalate) to 83 pg/m³ (for 17-α-ethynylestradiol). As a part of the validation procedure, the developed method was applied to the analysis of eight air particulate samples (fine grain-size particles, PM_2.5) collected in industrial, urban and non-polluted suburban areas of A Coruña (NW of Spain). Results evidenced the presence of dibutylphthalate, diethylhexylphthalate and nonylphenol in all samples. The highest concentration corresponded to dibutylphthalate (54.7 ng/m³) in an industrial area. Daily exposure to these EDCs in terms of estradiol equivalents (3 pg/day for toddlers and 5 pg/day for adults) is not expected to pose a risk to human health.     

Specific and nonspecific interaction forces between Escherichia coli and silicon nitride, determined by poisson statistical analysis

The nature of the physical interactions between Escherichia coli JM109 and a model surface (silicon nitride) was investigated in water via atomic force microscopy (AFM). AFM force measurements on bacteria can represent the combined effects of van der Waals and electrostatic forces, hydrogen bonding, steric interactions, and perhaps ligand-receptor type bonds. It can be difficult to decouple these forces into their individual components since both specific (chemical or short-range forces such as hydrogen bonding) and nonspecific (long-range colloidal) forces may be present in the overall profiles. An analysis is presented based on the application of Poisson statistics to AFM adhesion data, to decouple the specific and nonspecific interactions. Comparisons with classical DLVO theory and a modified form of a van der Waals expression for rough surfaces were made in order to help explain the nature of the interactions. The only specific forces in the system were due to hydrogen bonding, which from the Poisson analysis were found to be -0.125 nN. The nonspecific forces of 0.155 nN represent an overall repulsive interaction. These nonspecific forces are comparable to the forces calculated from DLVO theory, in which electrostatic-double layer interactions are added to van der Waals attractions calculated at the distance of closest approach, as long as the van der Waals model for "rough" spherical surfaces is used. Calculated electrostatic-double layer and van der Waals interactions summed to 0.116 nN. In contrast, if the classic (i.e., smooth) sphere-sphere model was used to predict the van der Waals forces, the sum of electrostatic and van der Waals forces was -7.11 nN, which appears to be a large overprediction. The Poisson statistical analysis of adhesion forces may be very useful in applications of bacterial adhesion, because it represents an easy way to determine the magnitude of hydrogen bonding in a given system and it allows the fundamental forces to be easily broken into their components.     

A spectroscopic study on the interaction between the anticancer drug erlotinib and human serum albumin

The interaction between erlotinib and human serum albumin (HSA) in simulated physiological conditions was investigated by spectroscopic methods. The results revealed that erlotinib caused the fluorescence quenching of HSA through a static quenching procedure. The binding constants at 293, 298, 303 and 308 K were obtained as 2.53 × 10⁵, 8.13 × 10⁴, 3.59 × 10⁴ and 1.93 × 10⁴ M^?1, respectively. There may be one binding site of erlotinib on HSA at 298 K. The thermodynamic parameters indicated that the interaction between erlotinib and HSA was driven mainly by hydrogen bonding or van der Waals forces. Synchronous fluorescence spectra, UV–Vis spectra, circular dichroism and Fourier Transform infrared spectroscopy results showed erlotinib binding slightly changed the conformation of HSA with secondary structural content changes. Förster resonance energy transfer study revealed high possibility of energy transfer with erlotinib-Trp-214 distance of 3.48 nm. The results of the present study may provide valuable information for studying the distribution, toxicological and pharmacological mechanisms of erlotinib in vivo.     

Self‐Sorting of Two Hydrocarbon Receptors with One Carbonaceous Ligand

Non‐directional van der Waals forces in biological and synthetic supramolecular systems play important roles in molecular assembly, particularly in determining the distances of the interacting species. The van der Waals forces are normally used in combination with other directional forces and are considered to play a secondary role in achieving specificity and fidelity in molecular recognition. Using an ideal supramolecular system consisting solely of hydrogen and carbon atoms, we found that the van der Waals interactions enable the high‐fidelity sorting of two homomeric receptors during ligand‐induced assembly. The self‐sorting occurred in a narcissistic manner by repulsion of a competing diastereoisomeric receptor from the assembly. The structure–sorting relationship study with enantiomers further revealed the dominant role of the van der Waals forces in shape recognition for high‐fidelity self‐sorting.     

Optimization of parameters for the alcoholic-assisted dispersive liquid–liquid microextraction of estrogens in water

Extraction and determination of estrogens in water samples were performed using alcoholic-assisted dispersive liquid–liquid microextraction (AA-DLLME) and high-performance liquid chromatography (UV/Vis detection). A Plackett–Burman design and a central composite design were applied to evaluate the AA-DLLME procedure. The effect of six parameters on extraction efficiency was investigated. The factors studied were volume of extraction and dispersive solvents, extraction time, pH, amount of salt and agitation rate. According to Plackett–Burman design results, the effective parameters were volume of extraction solvent and pH. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 220 μL 1-octanol as extraction solvent, 700 μL ethanol as dispersive solvent, pH 6 and 200 μL sample volume. Linearity was observed in the range of 1–500 μg L^?1 for E2 and 0.1–100 μg L^?1 for E1. Limits of detection were 0.1 μg L^?1 for E2 and 0.01 μg L^?1 for E1. The enrichment factors and extraction recoveries were 42.2, 46.4 and 80.4, 86.7, respectively. The relative standard deviations for determination of estrogens in water were in the range of 3.9–7.2 % (n = 3). The developed method was successfully applied for the determination of estrogens in environmental water samples.     

Partitioning Solvophobic and Dispersion Forces in Alkyl and Perfluoroalkyl Cohesion

Fluorocarbons often have distinct miscibility properties compared to their nonfluorinated analogues. These differences may be attributed to van der Waals dispersion forces or solvophobic effects, but their contributions are notoriously difficult to separate in molecular recognition processes. Here, molecular torsion balances were used to compare cohesive alkyl and perfluoroalkyl interactions in a range of solvents. A simple linear regression enabled the energetic partitioning of solvophobic and van der Waals forces in the self‐association of apolar chains. The contributions of dispersion interactions in apolar cohesion were found to be strongly attenuated in solution compared to the gas phase, but still play a major role in fluorous and organic solvents. In contrast, solvophobic effects were found to be dominant in driving the association of apolar chains in aqueous solution. The results are expected to assist the computational modelling of van der Waals forces in solution.     

Self-assembled organogels based on two-component system

Organogels were produced by the self-assembly of two organogelators, 3,5-bis(dodecanoylamino)benzoic acid and aromatic amines, in nonaromatic hydrocarbon solvents, through hydrogen bonding, aromatic stacking, and van der Waals interactions. 3,5-Bis(dodecanoylamino)benzoic acid has one carboxylic acid group for hydrogen bonding with amines and two alkylamide groups that can participate in interlayer hydrogen bonding and van der Waals interactions. The shape and size of the aromatic amines have a significant effect on the gel properties as well as their structures. A variety of organogels were realized by forming complexes of 3,5-bis(dodecanoylamino)benzoic acid and various amines with an aromatic group in nonaromatic hydrocarbon solvents.     

A novel class of organo- (hydro-) gelators based on ascorbic acid

A library of novel, lipid-modified derivatives of ascorbic acid was shown to exhibit highly attractive properties as surfactants, emulsifiers, oil soluble antioxidants, and highly effective gelators in organic solvents and especially water. In these systems, intermolecular hydrogen bonding and van der Waals forces act synergistically to induce gelation as confirmed by spectroscopic studies. The morphology of the formed gel has been characterized by scanning electron microscopy.     

Structural changes in the molecular sheets along (hk0) planes derived from cellulose Iβ by molecular dynamics simulations

We studied the stability of molecular sheets with four cellotetraoses in an aqueous environment by molecular dynamics simulation to identify the molecular details of first structure as one of the possibilities in the course of crystallization of cellulose I. After simulation, the molecular sheets formed by van der Waals forces along the (11?0) and (110) crystal plane did not change their structures in an aqueous environment, whereas the other ones formed by hydrogen bonds along the (100) and (200) crystal plane changed into a van der Waals associated molecular sheet, similar to the former. These simulated molecular sheets formed by van der Waals forces were structurally stable in water because of their hydrophilic exterior and hydrophobic interior. Therefore, if the molecular sheet structures are formed in the real system, the sheets formed by van der Waals forces are probably the initial structure of crystallization. A close analysis indicated that these sheets could be classified into two groups in terms of the hydrogen bonding networks, camber angle, and main and side chain conformations. One group was the molecular sheets corresponding to the (110) after simulation. This sheet is probably rigid because intramolecular hydrogen bonds of the chains in the sheet are highly developed. The other group was the molecular sheets corresponding to (200), (100), and (11?0) crystal plane: the chains in these sheets seemed to be rather flexible due to their moderately developed intramolecular hydrogen bonds.     

Matrix Effects on Water Analysis for Alkylphenols Using Solid Phase Extraction Gas Chromatography-Mass Spectrometry

Gas chromatography with mass spectrometry is frequently used for the quantification of many classes of substances, including alkylphenols. Alkylphenol polyethoxylates are nonionic surfactants used in a wide variety of industrial and consumer applications. Alkylphenol polyethoxylates can degrade to alkylphenols, which are endocrine disruptors. In analytical validation procedures, the most common parameters studied are the detection and quantification limits, linearity, and recovery; however, the matrix effects are sometimes neglected. Although some investigators have evaluated matrix effects, there is no consensus on how to evaluate them during method validation. In this study, the matrix effects of alkylphenol polyethoxylates (nonylphenol monoethoxylate, nonylphenol diethoxylate, octylphenol monoethoxylate, octylphenol diethoxylate) and alkylphenols (nonylphenol and octylphenol) were studied using solid phase extraction and gas chromatography-mass spectrometry analysis. For alkylphenol polyethoxylates, the matrix effects ranged from 16 to 4692%, whereas for alkylphenols (nonylphenol and octylphenol), the effects were insignificant. Therefore, constructing an analytical curve in the matrix for alkylphenol polyethoxylates is essential.     

Trajectory Analysis and Collision Efficiency during Microbubble Flotation

The hydrodynamic interaction between a rising bubble and a sedimenting particle during microbubble flotation is considered. The effects of attractive van der Waals forces and attractive or repulsive electrostatic forces are included. A mathematical model is presented which is used to perform a trajectory analysis and to calculate collision efficiencies between the bubble and particle. It is shown that collision efficiencies and the nature of the bubble-particle interactions are strongly dependent on the relative strengths of the van der Waals and electrostatic forces and on the lengthscales over which these forces act. It is demonstrated that optimal operating conditions can be suggested to achieve efficient microbubble flotation by correctly accounting for the interaction of van der Waals, electrostatic, and hydrodynamic forces. Copyright 1999 Academic Press.     

Determination of Estrogens in Water Samples by Ionic Liquid-Based Dispersive Liquid-Liquid Microextraction Combined with High Performance Liquid Chromatography

Using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) ionic liquid as extraction solvent, five estrogens including estrone (E₁), 17β-estradiol (E₂), estriol (E₃), 17α -ethynylestradiol (EE₂), and diethylstilbestrol (DES) in water samples were determined by dispersive liquid-liquid microextraction (DLLME) followed by high performance liquid chromatography with a photodiode array detector and a fluorescence detector (HPLC-DAD-FLD). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C₆MIM][PF₆] dispersed entirely into the sample solution with the help of a disperser solvent (acetone). Parameters including both extraction and disperser solvents and their volumes, extraction and centrifugal time, sample pH, and salt effect were investigated and optimized. Under the optimized conditions, 110–349 fold enrichment factors of analytes were obtained. The calibration curves were linear in the concentration range of 0.2–100 µg L^?1 for E₂, E₃, and EE₂ detected with FLD, and 1–100 µg L^?1 for E₁ and DES detected with DAD. The correlation coefficient of the calibration curve was between 0.9990 and 0.9997. The limits of detection (LOD, S/N = 3) for the five estrogens were in the range of 0.08–0.5 µg L^?1. The relative standard deviations (RSD) for six replication experiments at the concentration of 5.0 µg L^?1 were ≤5.7%. The proposed method was applied to the analysis of three water samples from different sources (river water, waste water, and sea water). The relative recoveries of spiked water samples are satisfied with 89.3–102.4% and 88.7–105.2% at two different concentration levels of 5.0 and 50.0 µg L^?1, respectively.     

Intermolecular Interactions and the Adhesion of Oleic Acid

The method presented by Good, van Oss, and Chaudhury was applied to characterize intermolecular interactions and the adhesion of oleic acid to selected model surfaces. Interfacial tensions of oleic acid were on the order 11–12 mJ/m² in aqueous solutions and 31–32 mJ/m² at air. The dispersive contribution to the surface tension of oleic acid against different neutral interfaces was determined to be 24–31 mJ/m² in air. Contact angles of oleic acid on selected hydrophilic and hydrophobic model surfaces were measured both in air and in aqueous solution. Van der Waals (dispersive) interactions determined the wetting properties of oleic acid in air both on nonpolar and basic surfaces. As expected, the adhesion of oleic acid to hydrophilic surfaces was much lower and to hydrophobic surfaces higher in aqueous environment than in air. The adhesion in aqueous environment is mainly governed by the cohesive and adhesive properties of water. It was concluded that the GvOC method in this case was only capable to give qualitative information about Lewis acid-base and van der Waals properties of surfaces and liquids, an important limiting factor being the asymmetry of oleic acid and the common probe liquids (diiodomethane and water).     

Evaluation of the individual hydrogen bonding energies in N-methylacetamide chains

The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction. The calculation results indicate that compared with MP2 results, B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ mol^?1 for both the terminal and central hydrogen bonds, whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds, but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol^?1 for the hydrogen bonds near the center. Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends. The weakest individual hydrogen bonding energy is about ?29.0 kJ mol^?1 found in the dimer, whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as ?62.5 kJ mol^?1 found in the N-methylacetamide decamer, showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains. The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H?O=C bond, corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital, and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.     

Can Dispersion Forces Govern Aromatic Stacking in an Organic Solvent?

Experimental support for the dominance of van der Waals dispersion forces in aromatic stacking interactions occurring in organic solution is surprisingly limited. The size‐dependence of aromatic stacking in an organic solvent was examined. The interaction energy was found to vary by about 7.5 kJ mol⁻¹ on going from a phenyl–phenyl to an anthracene–pyrene stack. Strikingly, the experimental data were highly correlated with dispersion energies determined using symmetry‐adapted perturbation theory (SAPT), while the induction, exchange, electrostatic, and solvation energy components correlated poorly. Both the experimental data and the SAPT‐dispersion energies gave high‐quality correlations with the change in solvent accessible area upon complexation. Thus, the size‐dependence of aromatic stacking interactions is consistent with the dominance of van der Waals dispersion forces even in the presence of a competing polarizable solvent.     

Can Dispersion Forces Govern Aromatic Stacking in an Organic Solvent?

Experimental support for the dominance of van der Waals dispersion forces in aromatic stacking interactions occurring in organic solution is surprisingly limited. The size‐dependence of aromatic stacking in an organic solvent was examined. The interaction energy was found to vary by about 7.5 kJ mol^?1 on going from a phenyl–phenyl to an anthracene–pyrene stack. Strikingly, the experimental data were highly correlated with dispersion energies determined using symmetry‐adapted perturbation theory (SAPT), while the induction, exchange, electrostatic, and solvation energy components correlated poorly. Both the experimental data and the SAPT‐dispersion energies gave high‐quality correlations with the change in solvent accessible area upon complexation. Thus, the size‐dependence of aromatic stacking interactions is consistent with the dominance of van der Waals dispersion forces even in the presence of a competing polarizable solvent.     

长程范德华力导向作用下胶体凝聚的计算机模拟

采用计算机模拟方法研究了长程范德华力在胶体凝聚过程中的作用, 发现由于胶粒间的范德华力是长程力, 它对胶粒或团簇运动将产生导向作用. 与不考虑导向作用的扩散控制团簇凝聚(DLCA)模型比较, 这种导向作用不仅加速了胶体的凝聚过程, 而且形成了更致密、分形维数更大的结构体. 研究还发现, 长程范德华力导向作用对胶粒的初始浓度非常敏感, 不论是在凝聚物的结构还是凝聚速率方面, 只有在胶粒初始浓度较低时, 该导向作用效应才明显. 其可能的原因是,在胶粒初始浓度较高时, 由于胶粒布朗运动的平均自由程很短而且位阻效应大, 从而使导向作用效应未能反映出来.     

Investigating the interaction of juglone (5-hydroxy-1, 4-naphthoquinone) with serum albumins using spectroscopic and in silico methods

The interaction between juglone at the concentration range of 10–110 µM and bovine serum albumin (BSA) or human serum albumin (HSA) at the constant concentration of 11 µM was investigated by fluorescence and UV absorption spectroscopy under physiological-like condition. Performing the experiments at different temperatures showed that the fluorescence intensity of BSA/HSA was decreased in the presence of juglone by a static quenching mechanism due to the formation of the juglone–protein complex. The binding constant for the interaction was in the order of 10³ M^?1, and the number of binding sites for juglone on serum albumins was determined to be equal to one. The thermodynamic parameters including enthalpy (ΔH), entropy (ΔS) and Gibb’s free energy (ΔG) changes were obtained by using the van’t Hoff equation. These results indicated that van der Waals force and hydrogen bonding were the main intermolecular forces stabilizing the complex in a spontaneous association reaction. Moreover, the interaction of BSA/HSA with juglone was verified by UV absorption spectra and molecular docking. The results of synchronous fluorescence, UV–visible and CD spectra demonstrated that the binding of juglone with BSA/HSA induces minimum conformational changes in the structure of albumins. The increased binding affinity of juglone to albumin observed in the presence of site markers (digoxin and ibuprofen) excludes IIA and IIIA sites as the binding site of juglone. This is partially in agreement with the results of molecular docking studies which suggests sub-domain IA of albumin as the binding site.     

漂浮液滴固化分散液液微萃取与高效液相色谱联用检测环境水样中的3种烷基苯酚

建立了漂浮液滴固化分散液液微萃取(DLLME-SFO)方法,以脂肪酸作为萃取剂,以甲醇作为分散剂,与高效液相色谱联用检测了环境水样中3种烷基苯酚。对影响前处理方法的因素进行了详细考察,在最佳萃取条件(60μL萃取剂辛酸、600μL分散剂甲醇、pH值为2.0~8.0、10 mL水样中加入0.5 g NaCl)下,3种烷基苯酚在20~1 500μg/L范围内具有良好的线性关系,相关系数不小于0.998 5,3种目标化合物的检出限为0.45~0.61μg/L,富集倍数为145~169,实际样品中3个水平的加标回收率为80.1%~109.9%。该方法将脂肪酸作为萃取剂,与HPLC联用实现了烷基苯酚的富集与检测,为环境水样中烷基苯酚的检测提供了对环境友好的前处理新方法。     

Force interactions of porous silica glass microspheres against mirror-polished stainless steel in nonaqueous solvents

Force interactions of porous silica particles against mirror-polished stainless steel surfaces were quantified in the presence of various solvents to facilitate processing of ceramics with less reliance on organic aids which subsequently need to be burned off. The results were compared to and found to be in good agreement to idealized models of van der Waals force interactions. Significantly, van der Waals attractive forces between steel surfaces and silica surfaces were minimized through the use of tetrahydrofuran and enhanced using methanol. The solvent selections were further extended to settling behavior and were found to follow the general trends determined by Stokes law. The methods presented herein can be extended to other real-world systems.