Interactions of simazine, metsulfuron-methyl, and tetracycline with biochars and soil as a function of molecular structure

Purpose

Biochars are increasingly recognized as effective, inexpensive, and environmentally friendly sorbents for abating organic contaminants. In this study, the sorption and competitive sorption characteristics of simazine (SZ), metsulfuron-methyl (ME), and tetracycline (TC) to corn straw biochars and soil were examined to understand the interactions of herbicides and antibiotics with biochars and the potential role of biochars as engineered sorbents.

Materials and methods

Biochars were obtained by pyrolyzing corn straw at 400, 500, and 600 °C for 6 h under oxygen-limited conditions and were characterized via elemental analysis, N₂-BET surface area determination, ¹³C nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. Soil was collected from North Tanggu Farm in Tianjin, and its organic carbon, cation exchange capacity, and particle size distribution were analyzed. The batch sorption experiments were performed to obtain the sorption isotherms of SZ, ME, and TC to biochars and soil.

Results and discussion

The biochars that were pyrolyzed at higher temperatures had higher sorption affinities for SZ, ME, and TC, which may be due to the enhancement of hydrophobic interactions, charge transfer (π–π*) interactions, and pore-filling mechanism. The sorption affinities for these compounds to all biochars decreased in the order SZ?>?TC?>?ME, indicating that the neutral molecule with a stronger hydrophobicity is more easily adsorbed by biochars. For soil, the decrease of the sorption affinities followed the order TC?>?SZ?>?ME due to the high sorption affinity of TC with clays in the soil. Moreover, the sorption affinities of TC by biochars were lower than by soil, indicating that corn straw biochars may be not an ideal sorbent for the immobilization of TC. Biochars were much more effective in sorbing SZ and ME than soil, indicating that corn straw biochars can potentially prevent transport of the herbicides to surface and ground water. Nevertheless, the presence of TC significantly hinders biochar adsorption of SZ and ME, implying that the coexisting contaminants should be considered when developing biochars as engineered sorbents.

Conclusions

The observations in this study demonstrated that the sorption of organic contaminants by biochars is dependent on the properties of the biochars and the molecular structures of the contaminants. Corn straw biochars effectively retain SZ and ME and hinder their transportation to surface and ground water; however, the coexisting contaminants should be considered. Our results will be helpful for designing biochars as engineered sorbents for environmental applications.     

A simulation model of 3D migration of Cs-137 in soils

This paper presents an algorithm and its numerical realization for a simulation model of migration of radiocesium in a certain volume of soil, including non-uniform contamination and pronounced inclination of the soil surface. The model can also be used to predict the redistribution of soil toxicants.     

番茄的结构-功能模型 Ⅰ：基于有限态自动机的3D形态构建

根据番茄的形态结构特点及其演变规则,应用有限态自动机的数学理论,研究建立了番茄动态发展的随机结构模型。该模型建立在对番茄结构的宏观抽象和生理年龄(PHYAGE)与生长年龄(GA)这两个最重要的基本概念之上,利用“事件驱动”的状态转移机制模拟了番茄生长过程、分枝过程和死亡过程,其中利用了二项随机分布模拟番茄的动态生长,离散的Markov链用于模拟番茄的分枝模式。番茄的有限态自动机模型完成了对主茎上节间长度、果实个数以及叶子结构的随机模拟。并利用试验统计分析获得的参数结果,模拟出番茄在不同生长阶段的3D结构。该动态的番茄结构模型,为与生理生态模型进行接口建立互影响、互反馈的结构-功能模型打下了基础。     

基于X3D的虚拟植物建模与可视化研究

本文在阐述X3D虚拟现实技术的基础上,介绍并分析了基于X3D虚拟植物建模的关键技术和优势,进一步探讨了基于X3D虚拟现实技术植物建模的原理与方法,最后,针对国内外应用现状,提出了应用中出现的问题,并为未来的研究方向进行了展望。     

Long-time 3D CFD modeling of sedimentation with dredging in a hydropower reservoir

Purpose

The purpose of the current study was to present a 3D computational fluid dynamics (CFD) model that can be used to predict long-term (11 years) bed changes in a reservoir due to sedimentation and dredging and that can be done with a reasonable computational time (18 h) on a desktop computer.

Materials and methods

The numerical model solved the Navier-Stokes equations on a 3D non-orthogonal unstructured grid to find the water velocities and turbulence. The convection-diffusion equation for suspended sediment transport was solved to find the sediment deposition pattern. Bed changes were computed and used to adjust the grid over time. Thereby, bed elevations over time were computed. The effect of dredging was also included in the model, and how this affected the bed elevation changes. The main feature of the numerical model enabling a reasonable computational time was implicit numerical methods giving the possibility to use long time steps.

Results and discussion

The results were compared with annually measured bed elevation changes in the reservoir over 11 years. This gave 11 figures of bed elevation changes, due to the combined effect of sedimentation and dredging. Comparing the annually computed and measured bed changes, there was a fair agreement for most of the years. The main deposition patterns were reproduced. The amount of sediments removed in three dredging campaigns were also computed numerically and compared with the measured values. Parameter tests were done for the grid size, fall velocity of the sediments, cohesion, and sediment transport formula. The deviation between computed and measured dredged sediment volumes was less than 16% for all these four parameters/formulas.

Conclusions

The 3D CFD numerical model was able to compute water flow, sediment transport, and bed elevation changes in a hydropower reservoir over a time period of 11 years. Field measurements showed reasonable agreement with the computed bed elevation changes. The results were most sensitive to the sediment particle fall velocity and cohesion of the bed material.

     

Study on the binding of propiconazole to protein by molecular modeling and a multispectroscopic method

Propiconazole (PCZ) is an N-substituted triazole used as a fungicide on fruits, grains, seeds, hardwoods, and conifers. Although the triazole fungicides have shorter half-lives and lower bioaccumulation than the organochlorine pesticides, possible detrimental effects on the aquatic ecosystem and human health also exist. To evaluate the toxicity of PCZ at the protein level, its effects on human serum albumin (HSA) were characterized by molecular modeling and multispectroscopic method. On the basis of the fluorescence spectra, PCZ exhibited remarkable fluorescence quenching, which was attributed to the formation of a complex. The thermodynamic parameters ΔH and ΔS were calculated to be -14.980 KJ/mol and 26.966 J/(mol K), respectively, according to the van't Hoff equation, which suggests hydrophobic and electrostatic interactions are the predominant intermolecular forces in stabilizing the PCZ-protein complex. Furthermore, HSA conformation was slightly altered in the presence of PCZ. These results indicated that PCZ indeed affected the conformation of HSA.     

Interactions of vitamin D3 with bovine beta-lactoglobulin A and beta-casein

It is of nutritional significance to fortify processed dairy products (e.g., cheese, yogurt, and ice cream) with vitamin D3; however, the inherent complexity of these foods may influence the stability and bioavailability of this nutrient. In the present study, the interactions of vitamin D3 with beta-lactoglobulin A and beta-casein were investigated under various environmental conditions (i.e., pH and ionic strength) using fluorescence and circular dichroism spectroscopic techniques. The results indicated that vitamin D3 was bound to both beta-lactoglobulin A and beta-casein depending on the solution conditions. The apparent dissociation constants ranged from 0.02 to 0.29 microM for beta-lactoglobulin A, whereas the beta-casein apparent dissociation constants ranged from 0.06 to 0.26 microM. The apparent mole ratios were also comparable, i.e., 0.51-2.04 and 1.16-2.05 mol of vitamin D3 were bound per mole of beta-lactoglobulin A and beta-casein, respectively. It was concluded that these interactions may strongly influence vitamin D3 stability and, hence, bioavailability in processed dairy products.     

3D simulation of the permeability tensor in a soil aggregate on basis of nanotomographic imaging and LBE solver

Purpose  

The purpose of this hydropedological work is to investigate the feasibility of a method to calculate permeability of soil peds on the matrix pore scale resolution. This paper focuses on imaging of the intra-aggregate microstructure and, based on the three-dimensional (3D) images, quantification of the pore network connectivity and permeability tensor. Finally, lattice Boltzmann equation (LBE) simulations of Navier–Stokes flow in the thus derived pore network allow to compute the heterogeneous 3D flow velocity field.     

Fulvic acids: structure and metal binding. I. A random molecular model

We have investigated a model of fulvic acid based on randomized positioning of functional groups and aromatic rings which can be used to deduce the types of metal chelating sites and provide statistical estimates of their concentrations. A FORTRAN program ‘RANDOM’ has been written which generates random molecules of fulvic acid. For each molecule generated the program also searches for and counts 14 types of binding site and calculates average concentrations over one thousand such molecules. A formula relating percentage aromatic carbon to the molar hydrogen/carbon ratio is also derived. The results show that the predominant bidentate sites are likely to be phthalate- and salicylate-type sites with a significant proportion of aromatic carboxyl and phenolic hydroxyl not participating in chelating sites.     

Tyrosine cross-links: molecular basis of gluten structure and function

The formation of the large protein structure known as "gluten" during dough-mixing and bread-making processes is extremely complex. It has been established that a specific subset of the proteins comprising gluten, the glutenin subunits, directly affects dough formation and breadmaking quality. Glutenin subunits have no definitive structural differences that can be directly correlated to their ability to form gluten and affect dough formation or breadmaking quality. Many protein structural studies, as well as mixing and baking studies, have postulated that disulfide bonds are present in the gluten structure and contribute to the process of dough formation through the process of disulfide-sulfhydryl exchange. Evidence presented here indicates that tyrosine bonds form in wheat doughs during the processes of mixing and baking, contributing to the structure of the gluten network. The relative contributions of tyrosine bonds and disulfide--sulfhydryl interchange are discussed.     

Relationship between the glass transition of soy protein and molecular structure

The change in molecular structure of the soy protein samples as a result of the microbial transglutaminase treatment was studied using solid-state (13)C NMR spectroscopy and circular dichroism (CD), and the relation to the glass transition temperature (T(g)) was examined. From NMR measurements, the structure of the local region of the C(alpha) methine was observed to change, and the region had relatively high mobility. From CD measurements, the structural change seemed to be caused by the change in the secondary structure (disintegration of the beta-structure). By comparison with the T(g) of another protein, the state of the secondary structure of a protein was suggested to be a key in determining its T(g).     

Combining genetic structure and ecological niche modeling to establish units of conservation: A case study of an imperiled salamander

Identification of conservation units below the species level has been difficult for researchers and conservation planners. Methods reliant solely on genetics to identify conservation units are widely used but have limited scope. Additionally, methods used to assess ecological distinctness are typically difficult to interpret, and hence not broadly applicable. Here, we attempt to reconcile these problems by defining conservation units utilizing both genetic and ecological methods. This study suggests a framework to evaluate discreteness and significance among populations for assessment of distinct population segments (DPSs). Specifically, we highlight a methodology that incorporates genetic analyses and niche-based distribution modeling to identify conservation units. As a case study, we sought to determine whether populations of an imperiled salamander (Notophthalmus perstriatus), appearing to exist in two regions separated by 125 km, exhibited genetic and ecological distinctness such that the regions demarcate separate conservation units. Using mtDNA (cyt-b), we found that haplotypes were shared between localities within each region but none were shared between regions. Niche-based distribution modeling revealed significant differences in the ecological setting between the two regions. In combination, the absence of evidence for recent genetic exchange and model-based support for differing ecological conditions utilized by newts between regions provides evidence that eastern and western populations are both distinct and significant. This study formalizes a method to assess DPS distinctness and significance providing general utility for this methodology as a conservation tool for many species.     

Effect of soil structure on wheat root growth, water uptake and grain yield. A computer simulation model

A model for simulation of wheat root growth under non-optimal conditions has been developed. The following influences on root growth are considered: soil temperature; soil water suction and mechanical resistance dependent on soil density and soil water content; the occurrence of soil cracks. The probability of root tips finding cracks, where unimpeded growth can occur, is given special consideration, including the effect of changes in the crack system with changes in soil water content. Water uptake is calculated, and by use of a transpiration coefficient an estimate of dry-matter production is made. This is partitioned between roots, leaves and stem and later grain. Effects of soil fertility are not yet considered in this model.A sensitivity analysis of the model was made by varying the soil density profile, the occurrence of cracks, sowing date and plant density for several years of weather data. The variability, caused by the fact that only a limited number of root axes was simulated in each run and guided by random numbers, was also investigated.The model can be used to assess the effects of compaction on wheat yield, and also the likely benefits which may be derived from sub-soiling or slit-tillage.The model is written in Digital's VAX FORTRAN language, and a run for one growing season takes less than 10 seconds of CPU-time on a VAX 11/785 computer.     

A novel black tea pigment and two new oxidation products of epigallocatechin-3-O-gallate

During tea fermentation, oxidation-reduction dismutation of a number of quinone metabolites of tea catechins yields numerous minor products, which make it difficult to separate and purify black tea polyphenols. In this study, epigallocatechin-3-O-gallate was enzymatically oxidized and then the unstable quinone metabolites in the oxidation mixture were hydrogenated with 2-mercaptoethanol to reduce production of inseparable minor dismutation products. As a result, three new oxidation products including a new black tea pigment were isolated, and their structures were determined based on chemical and spectroscopic data. Dehydrotheasinensin AQ is a new reddish-orange pigment with a 1,2-diketone structure, and its presence in commercial black tea was confirmed. In addition, a new quinone dimer with a complex caged structure and a trimer of epigallocatechin-3-O-gallate were also isolated and their production mechanisms are proposed. The presence of this trimer suggested participation of galloyl quinones in production of minor polyphenols in black tea.     

Binding of phthalate plasticizers to human serum albumin in vitro: a multispectroscopic approach and molecular modeling

As endocrine-disrupting chemicals, a few frequently used phthalate plasticizers were banned or restricted for use as additives in food in some countries. The interaction mechanisms between three phthalate plasticizers with human serum albumin (HSA) were studied by fluorescence (quenching, synchronous, and three-dimensional), UV-vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy, in combination with molecular modeling under simulative physiological conditions, respectively. The results obtained from fluorescence quenching data revealed that the plasticizers-HSA interaction altered the conformational strcture of HSA. Meanwhile, the alterations of HSA secondary structure in the presence of phthalate plasticizers were investigated. The binding distances for the plasticizers-HSA system were provided by the efficiency of fluorescence resonance energy transfer. Furthermore, the thermodynamic analysis implied that hydrophobic forces were the main interaction for the plasticizers-HSA system, which agreed well with the results from the molecular modeling study.     

Binding of the pepper alkaloid piperine to bovine beta-lactoglobulin: circular dichroism spectroscopy and molecular modeling study

The pepper alkaloid piperine is a nontoxic, natural dietary compound with a broad range of physiological activity. The present work is the first demonstration of its interaction with a mammalian protein. Circular dichroism (CD) spectroscopy was used to reveal and analyze the binding of piperine to a lipocalin protein. Induced CD spectra measured in pH 7.7 phosphate buffer at 37 degrees C demonstrated reversible, non-covalent association of piperine with bovine beta-lactoglobulin (BLG), the major whey protein in milk. The binding parameters (K(a) approximately 8 x 10(4) M(-1), n = 0.8) determined from the CD titration data showed no significant differences between the piperine binding properties of the two main genetic variants of BLG (A and B). The vanishing extrinsic CD signal obtained upon acidification of the piperine-BLG sample solution (Tanford transition) suggested that the ligand binds in the central hydrophobic cavity of the beta-barrel. The cavity binding concept was further supported by a CD displacement experiment using palmitic acid, the well-known hydrophobic ligand of BLG. Molecular docking calculations showed that piperine can be efficiently accommodated within the calyx of BLG. Additional molecular modeling calculations indicated that the beta-barrel of human tear lipocalin, human serum retinol binding protein, and human neutrophil gelatinase associated lipocalin might also accommodate a piperine molecule.