Multilayered Dermal Subcompartments for Modeling Chemical Absorption

Abstract

Dermal penetration of chemicals and drugs is of concern to both toxicologists and pharmacologists. Environmental professionals try to limit exposure to chemicals using protective clothing and gloves or barrier creams to trap chemicals. Drug developers try to enhance penetration of chemicals through the skin for medical purposes. Both can use predictive biologically-based mathematical models to assist in understanding the processes involved. These models are especially useful when they are based on physiological and biochemical parameters which can be measured in the laboratory. Appropriately validated models based on conservation of mass, diffusion and chemical transport by flow can be predictive of human exposures. In this paper we develop two new physiologically-based pharmacokinetic (PBPK) skin models to predict blood concentrations of dibromomethane in rats after skin-only vapor exposures. These new models improve the predictions of the blood concentrations especially at the beginning of the exposures. Sensitivity analysis shows that the permeability constants followed by partition coefficients have the most impact on blood concentration predictions. With proper validation the new models could be used to improve species, dose, and duration extrapolations of chemical or drug penetration. They could also be used to investigate and predict concentrations of drugs or chemicals in the skin.     

Modeling Heterogeneity in UO2 Nanoparticles Using X-ray Absorption Spectroscopy

EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long-range crystallinity. There is a limitation in that EXAFS provides averaged structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface-specific information from conventional EXAFS measurements collected on UO₂ NPs of varying size. Specifically, the surface terminating species of UO₂ NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user-defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure.     

A Chemical Recognition Element for Lithium Ions Based on Optical Electronic Absorption

Xerogel samples with entrapped series of four optical absorption chemosensors were prepared by sol-gel process. These materials are proposed as chemical recognition elements of an optical chemical sensor. The roles of the chemosensors play proton-dissociable chromogenic azocrown ethers bearing phenol and two azo groups as parts of macrocycles. Occurrence of the alkali ion—receptor interaction is signalled by the chemosensors changing their electronic absorption spectra. By this way chemosensor 4O-CH₃ is able to distinguish Li⁺ ions from other alkali metal ions present in aqueous solution, if the chemosensor is entrapped in Glymo-silica (1:1) xerogel matrix. The proposed recognition element for Li⁺ has been exposed to the cycles chemisorption—desorption many times. Besides DRIFT spectra of the used xerogel matrices were analyzed.     

Indirect Atomic and Molecular Absorption Spectrometric Methods for the Determination of Tungsten

Abstract

Indirect atomic absorption spectrometric and spectrophotometric methods for the determination of tungsten have been developed based on the precipitation of lead(II) tungstate and the measurement of the excess lead(II) in the supernate. The optimum Concentration ranges are approximately 3–30 ppm of tungsten on the basis of sample solution.     

Quantum Chemical Study Aimed at Modeling Efficient Aza-BODIPY NIR Dyes: Molecular and Electronic Structure,Absorption, and Emission Spectra

A comprehensive study of the molecular structure of aza-BODIPY and its derivatives, obtained by introduction of one or more substituents, was carried out. We considered the changes in the characteristics of the electronic and geometric structure of the unsubstituted aza-BODIPY introducing the following substituents into the dipyrrin core; phenyl, 2-thiophenyl, 2-furanyl, 3-pyridinyl, 4-pyridinyl, 2-pyridinyl, and ethyl groups. The ground-state geometries of the unsubstituted Aza-BODIPY and 27 derivatives were computed at the PBE/6-31G(d) and CAM-B3LYP/6-31+G(d,p) levels of theory. The time-dependent density-functional theory (TDDFT) together with FC vibronic couplings was used to investigate their absorption and emission spectra.     

Effective L-Series Mass Absorption Coefficients for EDS

 Energy dispersive X-ray spectroscopy has insufficient resolution to separate the individual lines of low energy L-series peaks. However, the mass absorption coefficients for Lα and Lβ radiation differ significantly for elements with atomic numbers between 21 and 32. Effective mass absorption coefficients for the entire L-shell emission were determined by measuring the variation of the X-ray intensities emitted from pure element standards, as a function of the accelerating voltage, and fitting the experimental data with a theoretical curve using the XMAC software. These experimentally determined mass absorption coefficients were compared with average values calculated on the basis of the theoretical line intensities, taking into account the primary vacancy generation and the radiationless Coster-Kronig transitions.     

A Simple,Robust, and Convenient HPLC Assay for Urinary Lactulose and Mannitol in the Dual Sugar Absorption Test

Background: Heterogeneous laborious analytical methodologies for the determination of urinary lactulose and mannitol limit their utility in intestinal permeability testing. Methods: We developed an assay using a Shimadzu HPLC system, an Aminex HPX87C column, and refractive index detection. The test was calibrated using a series of dilutions from standard stock solutions of lactulose and mannitol ‘spiked’ into urine samples. The utility to quantify urinary excretion during the dual sugar absorption test over 6 h was also determined. Results: Lactulose and mannitol were eluted isocratically at 5.7 and 10.1 min, respectively, with water as a mobile phase at a flow rate of 0.3 mL min⁻¹, 858 psi, 60 °C. The calibration curves for both sugars were linear up to 500 µg mL⁻¹ with a limit of detection in standard solutions at 4 µg mL⁻¹ and in ‘spiked’ urine samples at 15 µg mL⁻¹. The intra-assay and inter-assay CVs were between 2.0–5.1% and 2.0–5.1% for lactulose and 2.5–4.4% and 2.8–3.9% for mannitol. The urinary profiles of the 6 h absorption of lactulose and mannitol showed similar peak-retention times to standard solutions and were well-resolved at 5.9 and 10.4 min, respectively. Conclusions: The assay was easy to automate, using commonly available equipment and convenient requiring no prior laborious sample derivatization. The simplicity, reproducibility, and robustness of this assay facilitates its use in routine clinical settings for the quantification of intestinal permeability.     

Analysis of Tea for Metals by Flame and Graphite Furnace Atomic Absorption Spectrometry with Multivariate Analysis

The concentrations of iron, zinc, manganese, copper, chromium, nickel, lead, arsenic, and cadmium were determined using flame and graphite furnace atomic absorption spectrometry in nine herbal tea samples. Hawthorn, yarrow, elderflower, and bearberry are herbal teas for which the metal content has been rarely determined. The concentration of cadmium in St John’s wort exceeded the maximum permissible limit of 0.3?mg/kg. The metals were also determined in aqueous extracts following 5, 10, and 20?min of boiling and using different preparations, including acidification with lemon juice. The influence of these factors on metal release was demonstrated using multivariate analyses by redundancy analysis and principal component analysis. The metal release was not considerably affected by the boiling time, while the acidity of the medium was generally positively correlated. For the infusions, arsenic was detected only in acidified mint tea. The extraction efficiencies of metals were determined and classified as highly, moderately, and poorly extractable, with chromium showing largest variations.     

Modeling and Sensitivity Analysis of Particle Size Distribution and Chain Length Distribution in a Semibatch Emulsion Copolymerization Reactor

Summary: A comprehensive model is developed to predict the relationship between the particle size distribution and molecular weights of particles in an emulsion copolymerization reactor. A full population balance equation is used for the particle size distribution and extended to the model for the molecular properties using a continuous reactor approach. The numerical prediction clearly distinguishes the characteristics of molecular properties of particles by homogeneous nucleation from those by micellar nucleation with the dependence on the particle size. Sensitivity analysis of the proposed model under a variety of conditions shows that the compartmentalized feature of the emulsion system should be considered for better prediction of molecular properties, and provides information on the manipulated variables and lumped parameters which effectively decompose the correlation of both properties. Finally, a control strategy utilizing a lumped parameters tracking method is suggested for the regulation of both the particle size distribution and molecular properties.

Time evolution of number‐averaged molecular weights in the element under base conditions.     

流动注射多功能溶液处理装置在原子吸收光谱分析中的应用

使用本实验室研制的流动注射多功能溶液处理装置，通过比较流动注射在线离子交换、在线液－液萃取火焰原子吸收光谱法测定铅和资金的效果，评价了该装置的性能。     

A Simplified Method for Determining Arsenic and Antimony by the Hydride Evolution-Atomic Absorption Method

Abstract

A plastic disposable syringe hydride generator and aspirator system coupled with atomic absorption spectroscopy is shown to give results comparable to complex systems costing many times more. Details of operation, sensitivity, range of linearity and detection limits are outlined. Analyses performed on National Bureau of Standards Orchard Leaves and Bovine Liver are given and the results compared with NBS provisional values.     

化工原理填料吸收塔与板式精馏塔计算问题类比教学的探讨

Analogy teaching of calculation of packing absorption column and plate tower of distillation was studied in this paper. Firstly, a detailed analogy of the above calculation problems was studied according to the frame of calculation type, calculation basis, quantitative calculation and qualitative analysis. Secondly, the qualitative analysis of the above calculations was used as examples to illustrate the analysis methodology. Students could master very well the sameness and difference of the calculation of absorption and distillation through analogy teaching.     

用原子吸收光谱对痕量铬作价态分析

本文详细研究了鱼腥藻对Ｃｒ＾３＋和Ｃｒ＾６＋离子的选择吸附条件，发现Ｃｒ＾３＋的最佳吸附ＰＨ值为４－５；Ｃｒ＾６＋的最佳ＰＨ为７左右，一定量柠檬酸能抑制Ｃｕ＾２＋，Ｐｂ＾２＋及Ｃｄ＾２＋对Ｃｒ＾６＋的吸附干扰。建立了痕量铬的不同价态原子吸收分析方法；对金属离子与藻之间的吸附机理作了初步探讨。     

Continuous Flow Chemical Vapor Generation for the Determination of Cadmium in Foodstuffs by Atomic Absorption Spectrometry Using Derivative Signal Processing

A method has been developed for the generation of a “cold vapor” of cadmium by means of continuous flow chemical vapor generation from aqueous samples and for use in derivative atomic absorption spectrometry. Variables such as acidity, reducing agent concentration, atomization temperature, argon flow rate, reaction coil length, and other parameters were optimized. Detection limits and repeatability were measured, and cadmium was also determined in certified reference material and in tap water. The results showed that the proposed automated method is simple and accurate with a detection limit of 0.021 ng mL⁻¹ when the derivative system’s sensitivity was 2 mV min⁻¹     

在线阴离子富集-石墨炉原子吸收光谱法的研究

将流动注射在线预富集系统与石墨炉原子吸收光谱法联用,以强碱型阴离子交换纤维为柱填充材料,以浓盐酸为络合剂,以稀盐酸为洗脱液,用固定洗脱液体积方式测定了Cd,Pb和Zn,富集倍数分别为19,17和15(与直接引入40μL进样量相比),检出限(3σ,ng/L)分别为1.1,8.2和2.6.     

基于Rasch模型的化学核心概念理解测量研究

学科概念的理解程度直接决定着学习目标的达成与否,国内外科学教育标准均把培养学生科学核心概念理解能力作为提高科学素养宗旨的主要途径。在探查和诊断学生对化学核心概念理解能力上,既需要考虑具体的学科概念,也需要考虑到学生当前的认知阶段。尽管有很多工具可用来诊断学生的概念理解能力,与其他诊断工具相比,二段式诊断工具具有精确性和具体性,且可以大规模地推广和应用。同时,在对诊断方法有效性检验上,Rasch测量模型理论比经典测量理论更具针对性和有效性。以化学学科中"溶液中的离子平衡"概念为例,阐述如何利用二段式诊断方法来设计化学核心概念理解的测量工具,并进一步实证研究如何利用Rasch测量模型理论来对测量工具进行质量检验与修改。     

A Protocol for the Estimation of Parameters in Process Models: Case Studies with Polymerization Scenarios

Summary: As our understanding of chemical processes increases, the complexity of the models developed to describe them also increases. In most cases the equations are nonlinear in the inputs and parameters, and must be solved numerically. At present in estimating parameters for large process models, there are two shortcomings in the existing knowledge about (multiresponse) parameter estimation. The first is, how effective is the present parameter estimation methodology when applied to large models, and the second is, can any advantage be gained from considering the parameter estimation problem as a whole. This paper will address these questions, by revisiting the various steps of a parameter estimation protocol. There is little discussion in the literature as to how all the steps for parameter estimation are related. In the development of this protocol all of the steps for parameter estimation will be revisited: parameter sensitivity analysis, statistical design of experiments, estimation of parameters and confidence regions. By considering all these steps as a whole the overall parameter estimation procedure can be more efficient and some pitfalls, such as local optima and incorrect confidence regions, may be dealt with in an appropriate manner. To illustrate the application of the protocol, two case studies related to polymerization models are presented. These case studies illustrate some of the problems that may be encountered in the parameter estimation process and how the proposed protocol can aid in overcoming them.

Plot of conversion versus time for the copolymerization of styrene/methyl methacrylate.