Chemical Selectivity Research Articles

A modular mechanistic framework for estimating exposure to SVOCs: Next steps for modeling emission and partitioning of plasticizers and PFAS.

Estimates of human exposure to semi-volatile organic compounds (SVOCs) such as phthalates, phthalate alternatives, and some per- and polyfluoroalkyl substances (PFAS) are required for the risk-based evaluation of chemicals. Recently, a modular mechanistic modeling framework to rapidly predict SVOC emission and partitioning in indoor environments has been presented, in which several mechanistically consistent source emission categories (SECs) were identified. However, not all SECs have well-developed emission models. In addition, data on model parameters are missing even for frequently studied SVOCs. These knowledge gaps impede the comprehensive prediction of the fate of SVOCs indoors. In this paper, sets of high-priority phthalates, phthalate alternatives, and PFAS were identified based on chemical occurrence indoors and additional selection criteria. These high-priority chemicals served as the basis for exploring model parameter availability for existing indoor SVOC emission and partitioning models. The results reveal that additional experimental and modeling work is needed to fully understand the behavior of SVOCs indoors and to predict exposures with greater confidence and lower uncertainty. Modeling approaches to fill some of the identified gaps are proposed. The prioritized sets of chemicals and proposed new modeling approaches will help guide future research. The inclusion of polar phases in the framework will further expand its applicability and scope. IMPACT STATEMENT: This paper compiles data on high-priority chemicals commonly found indoors and information on the availability of applicable models and model parameters to predict emission, partitioning, and subsequent exposure to these chemicals. Modeling approaches for a selection of the missing SECs (source emission categories) are proposed, to illustrate the path forward. The comprehensive data set helps inform researchers, exposure assessors, and policy makers to better understand the state of the science regarding modeling of indoor exposure to semi-volatile organic compounds (SVOCs) and per- and polyfluoroalkyl substances (PFAS).

Electrochemically Controlled Switchable Copolymerization of Lactide, Carbon Dioxide, and Epoxides.

Electrochemical redox-control is an emerging strategy for the regulation of polymerization process without the addition of external oxidants and reductants, which enables the control over composition, microstructure and properties of the polymer products. In this paper, based on the chemical selectivity of heterometallic Salen-Co-Mn complexes of different valences, an electrochemically switchable strategy was developed for the copolymerization of lactide (LA), CO2 and epoxides. The switchable redox reactions endowed this system with the capability to easily synthesize a multi-block copolymer of polylactide (PLA) and polycarbonate (PC). Moreover, the multi-block copolymer could be further modified by introducing various monomers with different microstructures and functional groups.

Electrochemically Controlled Switchable Copolymerization of Lactide, Carbon Dioxide, and Epoxides

Electrochemical redox-control is an emerging strategy for the regulation of polymerization process without the addition of external oxidants and reductants, which enables the control over composition, microstructure and properties of the polymer products. In this paper, based on the chemical selectivity of heterometallic Salen-Co-Mn complexes of different valences, an electrochemically switchable strategy was developed for the copolymerization of lactide (LA), CO2 and epoxides. The switchable redox reactions endowed this system with the capability to easily synthesize a multi-block copolymer of polylactide (PLA) and polycarbonate (PC). Moreover, the multi-block copolymer could be further modified by introducing various monomers with different microstructures and functional groups.

Barrier Potential, Structure (Monomer and Dimer), Inter- and Intra-Molecular Interactions, Vibrational Analysis, Fukui Functions, MESP, NBO, UV and NMR Analysis of Pyridine-3-Carboxylic Acid Using Spectroscopic and DFT Approach

Pyridine-3-carboxylic (or nicotinic) (P3CA) acid has been recorded by using different spectroscopic tools like NMR (13C, 1H), UV–Vis, FT-IR and FT-Raman spectral analysis. The structural conformation examined by potential energy scan for the titled compound was obtained by using DFT computations through B3LYP method with 6–311++G(d,p) basis set. Using optimized monomer structure, the dimeric structures (head-to-tail and tail-to-tail) are obtained. The title compound exhibits inter-molecular as well as intra-molecular hydrogen bonding forming a supramolecular network. The geometrical parameters of both monomer and dimer are coinciding with the observed ones. Using vibrational frequencies, Infrared and Raman intensities were computed. The rms error between the experimental and scaled quantum mechanical frequencies is 9.77 cm−1 for P3CA. From the scaled quantum mechanical method, reliable vibrational assignments were made using PED. The site of chemical reactivity and selectivity of the title compound were estimated from frontier molecular orbitals and local reactivity descriptors. The reactive areas around the compound were evaluated by using MESP. The interactions of donor and acceptor are studied by NBO analysis. The 13C and 1H NMR chemical shifts of the title compound were determined using the gauge independent atomic orbital (GIAO) method in DMSO-d6 solution. By using UV–visible spectrum, the maximum absorption wavelength was obtained and compared with the TD-DFT method.

Simultaneous effects of agglomeration and interfacial defects on gas transport properties in nanocomposites: A novel modeling approach

In this study, a novel modeling approach for gas permeability predictionhas been proposed. For the first time, simultaneous effects of particle agglomeration andinterfaciallayerhave been considereddirectly in the model formula. The results show that the model fits well with the experimental data due to considering both particle agglomeration andinterfacialshell layer. For instance, average absolute relative error (AARE) has been decreased from 51% to 0.73% for O2 permeability throughpolyethersulfone(PES)/Zeolite4Amixed matrix membrane (MMM). Also,the precision ofthe proposed model is nearly more than 95% forall thestudied cases showing the great potential of this modelin the prediction ofMMMspermeability.The output of this study will help chemical engineers tofabricateMMMswith optimal permeability and selectivity and togeta better insight into particle–particle and particle-polymer interactions.

Plasmonic Photoelectrochemical Coupling Reactions of para-Aminobenzoic Acid on Nanostructured Gold Electrodes.

Surface plasmon resonance (SPR) bridges photonics and photoelectrochemistry by providing an effective interaction between absorption and confinement of light to surface electrons of plasmonic metal nanostructures (PMNs). SPR enhances the Raman intensity enormously in surface-enhanced Raman spectroscopy (SERS) and leads to the plasmon-mediated chemical reaction on the surface of nanostructured metal electrodes. To observe variations in chemical reactivity and selectivity, we studied the SPR photoelectrochemical reactions of para-aminobenzoic acid (PABA) on nanostructured gold electrodes. The head-to-tail coupling product "4-[(4-imino-2,5-cyclohexadien-1-ylidene)amino]benzoic acid (ICBA)" and the head-to-head coupling product p,p'-azodibenzoate (ADBA) were obtained from PABA adsorbed on PMN-modified gold electrodes. In particular, under acidic and neutral conditions, ICBA was obtained as the main product, and ADBA was obtained as the minor product. At the same time, under basic conditions, ADBA was obtained as the major product, and ICBA was obtained as the minor product. We have also provided sufficient evidence for the oxidation of the tail-to-tail coupling reaction product that occurred in a nonaqueous medium rather than in an aqueous medium. The above finding was validated by the cyclic voltammetry, SERS, and theoretical calculation results of possible reaction intermediates, namely, 4-aminophenlylenediamine, 4-hydroxyphenlylenediamine, and benzidine. The theoretical adsorption model and experimental results indicated that PABA has been adsorbed as para-aminobenzoate on the gold cluster in a bidentate configuration. This work offers a new view toward the modulation of selective surface catalytic coupling reactions on PMN, which benefits the hot carrier transfer efficiency at photoelectrochemical interfaces.

Differential Oligomerization of Alpha versus Beta Amino Acids and Hydroxy Acids in Abiotic Proto-Peptide Synthesis Reactions.

The origin of biopolymers is a central question in origins of life research. In extant life, proteins are coded linear polymers made of a fixed set of twenty alpha-L-amino acids. It is likely that the prebiotic forerunners of proteins, or protopeptides, were more heterogenous polymers with a greater diversity of building blocks and linkage stereochemistry. To investigate a possible chemical selection for alpha versus beta amino acids in abiotic polymerization reactions, we subjected mixtures of alpha and beta hydroxy and amino acids to single-step dry-down or wet-dry cycling conditions. The resulting model protopeptide mixtures were analyzed by a variety of analytical techniques, including mass spectrometry and NMR spectroscopy. We observed that amino acids typically exhibited a higher extent of polymerization in reactions that also contained alpha hydroxy acids over beta hydroxy acids, whereas the extent of polymerization by beta amino acids was higher compared to their alpha amino acid analogs. Our results suggest that a variety of heterogenous protopeptide backbones existed during the prebiotic epoch, and that selection towards alpha backbones occurred later as a result of polymer evolution.

Green Chemistry, Biocatalysis, and the Chemical Industry of the Future.

In the movement to decarbonize our economy and move away from fossil fuels we will need to harness the waste products of our activities, such as waste lignocellulose, methane, and carbon dioxide. Our wastes need to be integrated into a circular economy where used products are recycled into a manufacturing carbon cycle. Key to this will be the recycling of plastics at the resin and monomer levels. Biotechnology is well suited to a future chemical industry that must adapt to widely distributed and diverse biological chemical feedstocks. Our increasing mastery of biotechnology is allowing us to develop enzymes and organisms that can synthesize a widening selection of desirable bulk chemicals, including plastics, at commercially viable productivities. Integration of bioreactors with electrochemical systems will permit new production opportunities with enhanced productivities and the advantage of using a low-carbon electricity from renewable and sustainable sources.

Fabrication of ultrathin suspended membranes from atomic layer deposition films

Ultrathin films suspended as freestanding membranes are critical to many microelectronic and materials science applications. However, fabrication methods are currently limited in either their flexibility, due to material selectivity issues during the final membrane release, or their scalability. Here, we demonstrate a novel fabrication process for suspending ultrathin films with thicknesses as low as 4 nm and lateral dimensions up to 20 × 1000 μm from a variety of materials grown by atomic layer deposition. A silicon nitride membrane serves as the support for a sacrificial polymer layer and an ultrathin atomic layer deposition film which, after plasma etching, will form the membrane. The high chemical selectivity between atomic layer deposition-grown transition metal nitrides and oxides and the sacrificial polymer means that ultrathin films of a variety of materials can be released without damage using a single process. Electrically conductive titanium nitride membranes can be produced by this method and are of significant interest for electron microscopy applications. Electron transparency of titanium nitride membranes was found to be ∼14% higher than silicon nitride of the same thickness, and of similar conductivity to graphite, meaning that ultrathin, conductive, and electron transparent membranes can be fabricated at scale. These membranes are ideal supports for electron and photon characterization techniques, as well as microelectromechanical system applications that require a conductive membrane.

On the use of laser heating to detail the physical mechanisms of nanopore sensing

Measurement of the physical properties of molecules as they transit a nanopore sensor provides a route for the detailed understanding of membrane transport processes and offers prescriptive solutions for designing biosensors with molecular selectivity. Fundamental to the selective operation of a nanopore sensor are the unique molecular interactions that dictate kinetic barriers for capture and escape from the nanopore cavity. Efforts to understand the energetic contributions of direct molecular interactions (enthalpy), and polymer dynamics (entropy) allow us to disentangle the relative energetic contributions that lead to chemical selectivity in a nanopore sensor.

Surface‐Enhanced Electronic Raman Scattering at Various Metal Surfaces

Surface‐enhanced Raman scattering (SERS) has been extensively used to obtain vibrational information at metal/dielectric interfaces because of its extremely high chemical sensitivity and surface selectivity. Since the discovery of this effect in 1970s, however, the origin of the spectral background has remained questionable. Because the “background” signals dominate in the low‐frequency region, it is necessary to deeply understand this phenomenon for analyzing SERS spectra properly in the wide spectral range. Herein, scattering spectra for various metal surfaces are measured with and without excitation of plasmonic resonances in the wide frequency ranges covering both Stokes and anti‐Stokes branches, including very low‐frequency region. The comparison of the spectra between smooth surfaces and plasmonic rough surfaces of Au, Ag, and Pt and the theoretical evaluation of local fields at the metal/air interfaces indicate that electronic Raman scattering accounts for the background continuum in SERS spectra. This is also confirmed by the comparison of the spectra with and without ultrathin Ag films on a same Au surface. An analytical method of SERS spectra is demonstrated in which both contributions of electronic Raman scattering and vibrational Raman scattering are considered.

Self‐assembly of polymers from multicomponent reactions

AbstractSupramolecular assemblies from synthetic polymers have been widely used in materials science and biological applications. Developing convenient and efficient methods to tune polymer structures and architectures is important for achieving desired self‐assembly behaviors. Among various synthetic strategies, multicomponent reactions have drawn significant interest due to the high reaction efficiency, chemical selectivity, atom economy and one‐pot manner. These features make it convenient to manipulate polymer properties by varying chemical building blocks. In this review, we summarize the recent advances in the self‐assembly of polymers from multicomponent reactions. We discuss how multicomponent reactions are applied for polymerization and post‐polymerization modifications, generating polymers with specific self‐assembly behaviors for various research and application purposes. Challenges and perspectives about the development of this field are also discussed. © 2021 Society of Industrial Chemistry.

Microwave Susceptor Positional Configuration for Palm Empty Fruit Bunch and Waste Tire Co-Pyrolytic Oil Yield and Selectivity of Value-Added Chemicals

Microwave Susceptor Positional Configuration for Palm Empty Fruit Bunch and Waste Tire Co-Pyrolytic Oil Yield and Selectivity of Value-Added Chemicals

Mechanism, reactivity, and selectivity in a palladium-catalyzed organosilicon-based cross coupling reaction

A thermodynamic control mechanism unravels the unusual chemical selectivity in Pd-catalyzed cross-coupling reaction of silacycles.

International approaches to hazard assessment and classification of endocrine disruptors

Introduction. The problems of the impact of endocrine disruptors on human health and the environment are of serious concern today at the international, regional and national levels. Although the first mention about an ability of a substance to harm the endocrine system back in the 60 th of the XX century, the issues of substantiating the criteria for classifying it as endocrine disruptors, identifying potential disruptors of the endocrine system, assessing and classifying their danger to health and the environment with the purpose of further regulation. The aim of the study. To study of world experience in classifying chemical compounds as endocrine disruptors; creating a list of chemicals circulating on the territory of the Russian Federation that can potentially affect the endocrine system; selection of criteria for their classification according to the degree of hazard. The material for the analysis was literature sources from the bibliographic databases Web of Science, MedLine, EMBASE, Global Health, PubMed, Scopus, RSCI. The documents of international organizations, the European Union, the USA, Canada, Japan, India and other states on the hazard assessment, classification and regulation of endocrine disruptors have been studied and analyzed. Considering international experience, the criteria for classifying chemical compounds as endocrine disruptors have been substantiated, including three main components: an adverse effect on the body, an endocrine mechanism of action, and a biological relationship between endocrine activity and an adverse effect. A comparative analysis of the hazard classifications of endocrine disruptors developed by the EU and India showed to be based on the principles of the Globally Harmonized System of Classification and Labeling of Hazards of Chemicals and Mixtures. Considering the limited scientific knowledge about substances capable of destroying the endocrine system, it is advisable to introduce class 3 for substances with limited data obtained in “in vitro” experiments in invertebrates tests. Conclusion. International approaches to the selection, assessment and classification of chemicals that have a potential impact on the endocrine system will allow for the first time in the Russian Federation to form a national list of endocrine disruptors, to identify substances that are the priority in terms of hazard and degree of risk for making relevant management decisions.

Justification of measures to protect against exposure nicotine-containing products in enclosed spaces

Introduction. The introduction of amendments and additions to the anti-smoking Federal Law No. 15-FZ of 23.02.2013 in 2020 contributed to the cardinal revision of the name of this law and the introduction of a ban on consumption of any nicotine-containing products in public places. There are no separate, specially allocated isolated premises provided for the consumption of tobacco products and other types of nicotine-containing products by law, even though specially conducted studies have shown significantly different levels of additional inhalation risk arising from air pollution when consuming tobacco products and electronic nicotine delivery systems or heating tobacco. The aim of the study: based on experimental data, to justify the multiplicity of air exchange in unique isolated rooms designed to protect against the effects of ambient tobacco smoke, the consequences of tobacco consumption or nicotine-containing products. Materials and methods. The study was subject to 3 types of nicotine-containing products: tobacco cigarettes (cigarettes), an electronic nicotine delivery system (ENDS) and an electronic tobacco heating system (ETHS). In the course of the study were carried out: a series of experiments on the consumption of nicotine-containing products in various ways in a specially equipped indoor room, air sampling and laboratory studies were performed, the gross and specific emissions of chemicals entering the air environment from one unit of production per hour were calculated, the selection of priority chemicals for calculating the air removed from the room when using nicotine-containing products of each type was carried out, the necessary level of air exchange of premises was calculated, intended for the consumption of tobacco or nicotine. Results. The indoor air quality assessment showed that the main components of the gross intake into the air environment are suspended particles and carbon monoxide when smoking cigarettes. However, taking into account the values of the maximum permissible concentrations, the most significant contribution to the integral indicator is made by acetaldehyde and suspended particles PM10 and PM2.5. Using ENDS, the most significant pollutants were acetaldehyde and carbon monoxide, using ETHS - acetaldehyde and suspended particles PM10 and PM2.5. For all the investigation types of products, the priority substance for calculating the removed air is acetaldehyde, its share in the structure of all detected pollutants was: for cigarettes - 56.27%, for ENDS - 62.7%, for ETHS - 82.51%, in connection with which its specific values can be used to calculate the consumption of the removed air when modelling a specially allocated room intended for the consumption of tobacco products and other types of nicotine-containing products. Conclusion. The obtained findings demonstrated an obvious, more than 10-fold difference in the requirements for air exchange of premises intended for cigarette smoking and premises intended for the consumption of ENDS or ETHS, at the same intensity of consumption. Therefore, when organizing specially designated places for smoking or the consumption of nicotine-containing products, it is advisable to separate them depending on the type of products consumed: tobacco smoking separately, ENDS and ETHS consumption separately.

Study on the Influence of Physicochemical Indexes on Wine Quality

The quality of a wine is generally determined by hiring a group of qualified wine judges to taste the wine. The quality of wine grapes is directly related to the quality of wine. To explore how the physical and chemical indicators of wine and wine grapes can reflect the quality of wine and grape to a certain extent. This article is based on 2012 Chinese college students' mathematical contest in modeling A problem of data, to score as the dependent variable, wine physical and chemical indicators as independent variables, the method of using principal component analysis of physical and chemical indexes of wine grape dimension reduction, physical and chemical indexes selection of grapes, and use the decision tree regression method to establish score and wine function relation between the physical and chemical indicators. Then, after the comparison of the results of the four clustering algorithms, the hierarchical clustering method based on Agnes algorithm was used to conduct cluster analysis on the wines. Considering the rationality of classification, red and white wines were divided into four grades, and the average value of the estimated scores of each grade was used as the benchmark score for the wines of this grade.

In Situ Visualizing Nascent RNA by Exploring DNA-Templated Oxidative Amination of 4-Thiouridine.

Tracking and mapping the nascent RNA molecules in cells is essential for deciphering embryonic development and neuronal differentiation. Here, we utilized 4-thiouridine (s4U) as a metabolic tag to label nascent RNA and developed a fluorescence imaging method based on the DNA-templated oxidative amination (DTOA) reaction of s4U. The DTOA reaction occurred between amine-modified DNA and s4U-containing RNA with high sequence specificity and chemical selectivity. Target nascent mRNAs in HeLa cells, including those encoding green fluorescent proteins (GFPs) and endogenous BAG-1, were thus lit up selectively by DTOA-based fluorescence in situ hybridization (DTOA FISH). We believe the DTOA conjugation chemistry shown in this study could be generally applied to investigate the spatial distribution of nascent transcription dynamics in cellular processes.

Anchoring and Reacting On-Surface to Achieve Programmability.

On-surface synthesis has developed into a modern method to fabricate low-dimensional molecular nanostructures with atomic precision. It impresses the chemistry community mostly via its simplicity, selectivity, and programmability during the synthesis. However, an insufficient mechanistic understanding of on-surface reactions and the discriminations in methodologies block it out from the conventional cognition of reaction and catalysis, which inhibits the extensive implication of on-surface synthesis. In this Perspective, we summarize the empirical paradigms of conceptually appealing programmability in on-surface synthesis. We endeavor to deliver the message that the impressive programmability is related to chemical heterogeneity which can also be coded at the molecular level and deciphered by the catalytic surfaces in varying chemical environments as specific chemical selectivity. With the assistance of structure-sensitive techniques, it is possible to recognize the chemical heterogeneity on surfaces to provide insight into the programmable on-surface construction of molecular nanoarchitectures and to reshape the correlation between the mechanistic understanding in on-surface synthesis and conventional chemistry.

The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and Gaia eDR3

ABSTRACT Since the advent of Gaia astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, Gaia-Sausage-Enceladus (GSE), appears to be an early ‘building block’ given its virial mass $\gt 10^{10}\, \mathrm{M_\odot }$ at infall (z ∼ 1−3). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-α abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] versus [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including $30 \lt \sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} \lt 55$, we can characterize an unprecedented 24 abundances of this structure with GALAH+ DR3. With our chemical selection we characterize the dynamical properties of the GSE, for example mean $\sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} =$$26_{-14}^{+9}$. We find only $(29\pm 1){{\ \rm per\ cent}}$ of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way.