Small Molecular Fragments Research Articles

Towards realistic structural char models: Generation of stacked graphene-like layers using constrained reactive molecular dynamics simulations

For a molecular understanding of coal combustion, realistic coal and char models are pivotal. We propose a novel top-down method for the construction of char models, consisting of stacked graphene-like layers with defects. We start on the mesoscale with corrugated stacked surfaces as a template. Then the carbon atoms are pre-positioned on these surfaces and surrounded by hydrogen atoms. In a constrained reactive MD simulation the carbon atoms are then rearranged into a chemically reasonable state with dangling bonds saturated by hydrogen atoms. Importantly, the initial shape of the template is maintained to a great extent, leading to a substantial amount of defects in the graphitic planes, especially for high curvatures. In a final step, small molecular fragments and unfavorable arrangements are removed and remaining dangling bonds are saturated with hydrogen atoms. The central advantage over other approaches is the ability to choose the shape and size of the templating planes, with the possibility to use experimental input.The method is validated on single sheets with a protrusion and application examples are shown for stacked graphitic layers with up to 100 Å size and more than 20000 atoms. It represents the first step of a longer term project. In the future, heteroatoms and functional groups will be implemented, and by combining several such stacks, the approach will allow the construction of more realistic char models using the data from HRTEM images as an experimental boundary condition. On this basis important questions like the adsorption and diffusion of volatiles under high temperatures can be studied on a molecular level.

Molecular secondary recombination for pitch-derived carbon microsphere toward ultra-high sodium storage

Because the direct carbonization of low-cost pitch will form a highly graphitized soft carbon, and the soft carbon lacks a low-voltage platform to store sodium, so the sodium storage performance is poor. Therefore, in this research, by combining defect and pore engineering, the porous carbon microspheres with primary oxygen crosslinking were reorganized through secondary sulfur crosslinking to achieve the oxygen/sulfur complex crosslinked defect structure. At the same time, small molecular sulfur fragments filled the pores of the porous carbon microspheres to form the ultramicropores structure. It is worth noting that this pitch-derived carbon microsphere exhibits a new sodium storage mechanism of a new 'high-voltage platform'. Therefore, it shows stable cycle performance (220 mAh g−1 at 1 A g−1 after 2000 cycles) and excellent rate performance (101 mAh g−1 at 10 A g−1) in half cells; In addition, the structure of the ultramicropores can improve the initial coulomb efficiency of carbon microspheres. The sodium storage mechanism dominated by surface adsorption was determined by kinetic analysis and in-situ characterization techniques. This study provides a new idea for precise molecular regulation of anode materials for sodium ion batteries.

Rotational-state-selected Carbon Astrochemistry.

The addition of individual quanta of rotational excitation to a molecule has been shown to markedly change its reactivity by significantly modifying the intermolecular interactions. So far, it has only been possible to observe these rotational effects in a very limited number of systems due to lack of rotational selectivity in chemical reaction experiments. The recent development of rotationally controlled molecular beams now makes such investigations possible for a wide range of systems. This is particularly crucial in order to understand the chemistry occurring in the interstellar medium, such as exploring the formation of carbon-based astrochemical molecules and the emergence of molecular complexity in interstellar space from the reaction of small atomic and molecular fragments.

Investigation of dislocation and twinning behavior in HMX under high-velocity impact employing molecular dynamics simulations.

Under the ReaxFF/lg force field, the multiscale shock technique (MSST) was employed to investigate the decomposition behavior of perfect, dislocated, and twinned octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) at a velocity of 11 km/s. This study aimed to analyze the changes in system temperature, bond formation and breaking, variations in the number of small molecules, and the number of clusters. The results indicated that the sensitivity of dislocated HMX was the lowest, while the sensitivity of twinned and perfect HMX was comparable. Comparing the formation and breaking of bonds in HMX during the shock process, it was found that the change in the number of bonds in dislocated HMX was similar to that in perfect HMX, whereas twinning accelerated the breaking of bonds. By analyzing the changes in small molecular fragments (CO, CO2, H, H2, H2O, N2, N2H, NH2, NO, NO2, and O) during the shock process of HMX, it was found that dislocation had a relatively minor effect on the small molecular fragments, while twinning promoted the generation of CO, H, NO, and O and accelerated the decomposition of NO. A comparison of the number, weight, and atomic ratio of clusters under perfect, dislocated, and twinned conditions revealed that under the influence of shock, the number of clusters initially increased sharply and then decreased slowly. Meanwhile, compared to the perfect and dislocated explosives, the number of clusters under the twinned structure was significantly fewer, indicating that the twinned structure could reduce cluster formation. The proportion of oxygen to carbon in the twinned HMX was lower than that in the perfect and dislocated explosives, possibly due to the higher content of small molecular fragment O in twinned HMX. Different structures of HMX crystals were constructed, including twinned defect structure (with a supercell containing 6458 atoms), dislocation defect structure (with a supercell containing 2352 atoms), and perfect structure (also with a supercell containing 2352 atoms). The modeling of defect crystal structures was carried out using the Atomsk software. For the twinned defect structure, we first constructed a mirror symmetric structure of the original configuration and then merged these two structures together. For the dislocation defect structure, we shifted a segment of the originally ordered perfect crystal structure by a certain distance using Atomsk. Before conducting the simulations, we performed geometric optimization of the models using the conjugate gradient (CG) algorithm and carried out 10 ps of NVT and NPT simulations to equilibrate the energy, temperature, and other parameters within the system. Finally, a 50-ps MSST impact simulation was performed using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS).

Speeding-up the Determination of Protein-Ligand Affinities by STD NMR: The Reduced Data Set STD NMR Approach (rd-STD NMR).

STD NMR spectroscopy is a powerful ligand-observed NMR tool for screening and characterizing the interactions of small molecules and low molecular weight fragments with a given macromolecule, identifying the main intermolecular contacts in the bound state. It is also a powerful analytical technique for the accurate determination of protein-ligand dissociation constants (KD) of medium-to-weak affinity, of interest in the pharmaceutical industry. However, accurate KD determination and epitope mapping requires a long series of experiments at increasing saturation times to carry out a full analysis using the so-called STD NMR build-up curve approach and apply the "initial slopes approximation". Here, we have developed a new protocol to bypass this important limitation, which allows us to obtain initial slopes by using just two saturation times and, hence, to very quickly determine precise protein-ligand dissociation constants by STD NMR.

Intermolecular interaction potential maps from energy decomposition for interpreting reactivity and intermolecular interactions.

The electrostatic potential (ESP) has been widely used to visualize electrostatic interactions about a molecule. However, electrostatic effects are often insufficient for capturing the entirety of an interaction or a reaction of interest. In this investigation, intermolecular interaction potential maps (IMIPs), constructed from the potentials derived from energy decomposition analysis (EDA) using density functional theory, were developed and applied to provide unique insight into molecular interactions and reactivity. To this end, rather than constructing a potential map from probe point charge interactions, IMIPs were constructed from probe interactions with small molecular fragments, including CH3+, CH3-, benzene, and atomic probes including alkali metals, transition metals, and halides. The interaction potentials are further decomposed producing IMIPs for each interaction component using EDA (electrostatic, orbital, steric, etc.). The IMIPs are applied to the study of various interactions including cation-π and anion-π interactions, electrophilic and nucleophilic aromatic substitution, Lewis acid activation, π-stacking, endohedral fullerenes, and select organometallics which reveal fundamental insight into the positional preferences and physical origins of the interactions that otherwise would be difficult to uncover through other surface analyses.

Accessing the usefulness of atomic adsorption configurations in predicting the adsorption properties of molecules with machine learning.

We present a systematic study into the effect of adding atomic adsorption configurations into the training and validation dataset for a neural network's predictions of the adsorption energies of small molecules on single metal and bimetallic, single crystal surfaces. Specifically, we examine the efficacy of models trained with and without H and X atomic adsorption configurations, where X is C, N, or O, to predict XHn adsorption energies. In addition, we compare our machine learning models to traditional simple scaling relationships. We find that models trained with the atomic adsorption configurations outperform models trained with only molecular adsorption configurations, with as much as a 0.37 eV decrease in the MAE. We find that models trained with the atomic adsorption configurations slightly outperform traditional scaling relationships. In general, these results suggest it may be possible to vastly reduce the number of adsorption configurations one needs for training and validation datasets by supplementing said data with the adsorption configurations of composite atoms or smaller molecular fragments.

Robust fragment-based method of calculating hydrogen atom transfer activation barrier in complex molecules.

Dynamic processes driven by non-covalent interactions (NCI), such as conformational exchange, molecular binding, and solvation, can strongly influence the rate constants of reactions with low activation barriers, especially at low temperatures. Examples of this may include hydrogen-atom-transfer (HAT) reactions involved in the oxidative stress of an active pharmaceutical ingredient (API). Here, we develop an automated workflow to generate HAT transition-state (TS) geometries for complex and flexible APIs and then systematically evaluate the influences of NCI on the free activation energies, based on the multi-conformational transition-state theory (MC-TST) within the framework of a multi-step reaction path. The two APIs studied: fesoterodine and imipramine, display considerable conformational complexity and have multiple ways of forming hydrogen bonds with the abstracting radical-a hydroxymethyl peroxyl radical. Our results underscore the significance of considering conformational exchange and multiple activation pathways in activation calculations. We also show that structural elements and NCIs outside the reaction site minimally influence TS core geometry and covalent activation barrier, although they more strongly affect reactant binding and consequently the overall activation barrier. We further propose a robust and economical fragment-based method to obtain overall activation barriers, by combining the covalent activation barrier calculated for a small molecular fragment with the binding free energy calculated for the whole molecule.

Fragment-based drug discovery for disorders of the central nervous system: designing better drugs piece by piece.

Fragment-based drug discovery (FBDD) has emerged as a powerful strategy to confront the challenges faced by conventional drug development approaches, particularly in the context of central nervous system (CNS) disorders. FBDD involves the screening of libraries that comprise thousands of small molecular fragments, each no greater than 300Da in size. Unlike the generally larger molecules from high-throughput screening that limit customisation, fragments offer a more strategic starting point. These fragments are inherently compact, providing a strong foundation with good binding affinity for the development of drug candidates. The minimal elaboration required to transition the hit into a drug-like molecule is not only accelerated, but also it allows for precise modifications to enhance both their activity and pharmacokinetic properties. This shift towards a fragment-centric approach has seen commercial success and holds considerable promise in the continued streamlining of the drug discovery and development process. In this review, we highlight how FBDD can be integrated into the CNS drug discovery process to enhance the exploration of a target. Furthermore, we provide recent examples where FBDD has been an integral component in CNS drug discovery programs, enabling the improvement of pharmacokinetic properties that have previously proven challenging. The FBDD optimisation process provides a systematic approach to explore this vast chemical space, facilitating the discovery and design of compounds piece by piece that are capable of modulating crucial CNS targets.

ReaxFF Molecular Dynamics Study on the Microscopic Mechanism for Kerogen Pyrolysis.

Kerogen is mainly composed of carbon, hydrogen, and oxygen, which are the main components of crude oil and gas. The pyrolysis of kerogen is an efficient method to generate clean energy. In the present work, the pyrolysis reaction process of three types of kerogen is simulated using ReaxFF molecular dynamics (MD) methods to study the microscopic mechanism and the distribution of products. The results indicated that the pyrolysis products of the three types of kerogen significantly depend on the molecular structures, temperature, and reaction time. As the temperature increases, the gaseous hydrocarbon and the light and heavy oil fractions decreased, where small molecular fragments polymerized to form new molecular fragments. For an isothermal temperature, with the reaction proceeding, some component polymerization of the pyrolyzed fragments occurred, resulting in the generation of new light oils and heavy oils. Moreover, quantum chemical analysis was employed to reveal the kerogen pyrolysis mechanism. First, the weak bonds such as C-O, C-N, and C-S structures were decomposed to generate large carbon and some heavy shale oil fragments. Second, the cycloalkanes and long-chain alkanes were decomposed to generate a large amount of light shale oil and gaseous hydrocarbons. Finally, the decomposition of C═C in the aromatic ring, the secondary decomposition of light and heavy shale oils, and the further decomposition of short-chain alkanes occurred. In addition, the production of hydrogen (H2) occurred at the late stage of the pyrolysis reaction. Hydrogen radicals were formed by the decomposition of C-H bonds and subsequently collided with each other, resulting in the formation of H2 molecules. The pyrolysis and chemical analysis of kerogen can clearly determine the type and content of hydrocarbon substances, providing scientific data for exploration, development, and utilization of shale gas and shale oil.

Perspective from a Hubbard U-density corrected scheme towards a spin crossover-mediated change in gas affinity.

By employing a recently proposed Hubbard U density-corrected scheme within density functional theory, we provide design principles towards the design of materials exhibiting a spin crossover-assisted gas release. Small molecular fragments are used as case study to identify two main mechanisms behind the change in binding energy upon spin transitions. The feasibility of the proposed mechanism in porous crystals is assessed by correlating the change in binding energy of CO2, CO, N2, and H2, upon spin crossover, with the adiabatic energy difference associated with the spin state change of the square-planar metal in Hofmann-type clathrates (M = Fe, Mn, Ni). A few promising cases are identified for the adsorption of intermediate ligand field strength molecules such as N2 and H2. The latter stands out as the most original result as the strong interaction in low spin, as expected from a Kubas mechanism, results in a large change in binding energy. This work provides a general perspective towards the engineering of open-metal site frameworks exhibiting local environments designed to have a spin crossover upon adsorption of specific gas molecules.

Insight into pyrolysis mechanism of plastic waste with C-O/C-N bonds in the backbone

Pyrolysis is an important method for efficiently recovering plastic monomers, fuels and chemicals from plastic waste. The depolymerization of the backbone structure of plastic waste is a key step of the pyrolysis process. Currently, researches on the pyrolysis mechanism of plastics with C-O/C-N bonds in the backbone are still not sufficiently in-depth and also lack systematic and comprehensive investigation. Therefore, this study for the first time comprehensively investigated both macroscopic and microscopic pyrolysis processes of plastics with C-O/C-N bonds in the backbone, and evaluated the difficulty of breaking different backbone linkages via bond dissociation energy (BDE) obtained by density functional theory (DFT) calculations to deeply reveal the pyrolysis mechanism. The results indicated that polyethylene terephthalate (PET) had a higher initial pyrolysis temperature and its thermal stability was slightly stronger than nylon 6. The backbone of PET was mainly decomposed via the cleavage of Cα-O on the alkyl side, while the degradation of nylon 6 backbone began with NH2 groups at the end of the backbone. The pyrolysis products of PET were mainly derived from the small molecular fragments, which were generated by the degradation of the backbone through the cleavage of CO bonds or CC bonds, while the pyrolysis products of nylon 6 were always dominated by caprolactam. In addition, based on the results of DFT calculations, it could be inferred that the cleavage of CC bond in PET backbone and the cleavage of its adjacent Cα-O were most likely to occur, which followed a competitive reaction mechanism. However, in pyrolysis of nylon 6, the conversion to caprolactam was mainly via the concerted reaction of amide CN bonds. Compared with the concerted cleavage of amide CN bond, the cleavage of CC bond in the backbone of nylon 6 was not predominant.

Re-discussion on the essence of the ultra-bright fluorescent carbon dots synthesized by citric acid and ethylenediamine

Citric acid and ethylenediamine can synthesize ultrabright fluorescent carbon dots (super CDs, S-CDs) with photoluminescence quantum yields (PLQY) up to ∼100% by simple hydrothermal method, almost exceeding all the currently reported fluorescent carbon dots. In this work, we examined the synthesis and properties of S-CDs in details. Our observations suggest that carbonization/graphitization degree contributes little to the PLQY of S-CDs. Morphological characterization shows the S-CDs have no graphene cores. Excitation wavelength independent emission behavior implies that the S-CDs might have an exclusive emission center/fluorophore, which is independent of the quantum size effect. Dialysis experiment reveals that not only nanoparticles, small molecular fragments also have PL emission ability. All the above experimental observations suggest that the S-CDs should be not real CDs but copolymer of CA and EDA. Furthermore, a possible reaction mechanism was proposed for synthesis of the S-CDs. This work reveals the essence of S-CDs and paves the way for their large-scale industrial production and applications.

Natural gums as a novel, potent, and natural additive towards coke making: a preliminary feasibility study

ABSTRACT The present investigation entails delineating the implications of using a novel and naturally sourced additive for coke making. In particular, the focus of this study was to understand the extent to which such natural gums could induce plasticity and strength to non-coking coals without inclusion of any prime coking coal, emphasizing on the importance of thermal pre-treatment as an important parameter. Experimentally, the non-coking coal was pre-treated with xanthan gum (300°C for 1 h), followed by carbonization at 600°C for 1 h. Addition of water as an additive was deduced to be beneficial in enhancing the bulk density of the coal blend. The coal blend, including non-coking coal with natural gums (10–20%) and water (10 mL in 20 g scale), produced F grade coke when treated under low-temperature Gray King (LTGK) assay conditions at 600°C. A comparative XRD and Raman analysis of raw coal and coke demonstrated the presence of graphitic content in the resultant coke only. FTIR results showed the absence of small molecular fragments, thus substantiating semi-coke formation during the re-solidification stage. The present invention holds significant industrial viability toward production of coke from non-coking coal without inclusion of any prime coking coal.

A new biocomposite based on microbial autocrine laccase-rice straw: Preparation, characterization and application

The immobilization of laccase on crop residues is a promising way to treat water containing bisphenol A (BPA), but the high cost of commercially available solutions of this enzyme indicates a need for research into feasible cost-effective alternatives. Here, a new biocomposite was developed based on a microbial autocrine laccase process, where rice straw served as the sole carbon source and as a carrier mixed with Comamonas testosteroni FJ17 ( C. testosteroni FJ17). A laccase-rice straw biocomposite (RS-Lac) was prepared via a one-step synthesis and subsequently evaluated for the removal of BPA. A response surface methodology was used to optimize the synthesis of RS-Lac, where the subsequent removal efficiency of BPA (500 μg L −1 ) by RS-Lac biocomposite increased from 46.1 (unoptimized) to 57.0% (optimized). The molecular weight (Mw) of laccase was identified by SDS-PAGE to be 34 kDa. SEM, CLSM , FTIR, and XRD results confirmed laccase secreted by C. testosteroni FJ17 was coated with polysaccharides , and these were successfully immobilized on rice straw. The specific surface area of RS-Lac increased from 2.79 to 5.37 m 2 g −1 following synthesis optimization, and zeta potential analyzer indicated that it carried a strong negative charge. In addition, RS-Lac was also used to successfully remove estrone (E1), 17β-estradiol (E2), Cu(II), Sb(Ⅲ), As(Ⅲ), and As(Ⅴ) to varying degrees, with removal efficiencies of 68.7%, 66.4%, 77.5%, 84.0%, 83.7%, and 91.6%, respectively. This broad versatility indicated that RS-Lac has great potential as a low-cost biocomposite for treating wastewater. • A rice straw-i autocrine laccase biocomposite was prepared in one-step. • Various characterizations confirmed that crude laccase immobilized on rice straw. • The rice straw was coated with polysaccharides and immobilized laccase. • Degradation of bisphenol A (57%) to small molecular fragments in solution. • Heavy metal ions (>77.5%) and estrogen (>66.4%) were removed.

Quantification of urinary total luteinizing hormone immunoreactivity may improve the prediction of ovulation time.

ObjectivesMost of the currently available ovulation prediction kits provide a relatively rough estimation of ovulation time with a short fertility window. This is due to their focus on the maximum probability of conception occurring one day before ovulation, with no follow-up after LH surge until ovulation nor during the subsequent days thereafter. Earlier studies have shown that urine of reproductive age women contains at least 3 different molecular forms of luteinizing hormone (LH); 1) intact LH, 2) LH beta-subunit (LHβ) and a 3) small molecular weight fragment of LHβ, LHβ core fragment (LHβcf). The proportion of these LH forms in urine varies remarkably during the menstrual cycle, particularly in relation to the mid-cycle LH surge. In this exploratory study, we studied the potential implications of determining the periovulatory course of total LH immunoreactivity in urine (U-LH-ir) and intact LH immunoreactivity in serum (S-LH-ir) in the evaluation of the fertility window from a broader aspect with emphasis on the post-surge segment.MethodsWe determined total U-LH-ir in addition to intact S-LH-ir, follicle-stimulating hormone (FSH), progesterone, and estradiol in 32 consecutive samples collected daily from 10 women at reproductive age. Inference to the non-intact U-LH-ir levels was made by calculating the proportion of total U-LH-ir to intact S-LH-ir.ResultsTotal U-LH-ir increased along with LH surge and remained at statistically significantly higher levels than those in serum for 5 consecutive days after the surge in S-LH-ir. S-LH-ir returned to follicular phase levels immediately on the following day after the LH surge, whereas the same took 7 days for total U-LH-ir.ConclusionsThe current exploratory study provides preliminary evidence of the fact that U-LH-ir derived from degradation products of LH remains detectable at peak levels from the LH surge until ovulation and further during the early postovulatory period of fecundability. Thus, non-intact (or total) U-LH-ir appears to be a promising marker in the evaluation of the post-surge segment of the fertility window. Future studies are needed to unravel if this method can improve the prediction of ovulation time and higher rates of fecundability in both natural and assisted conception.

Microscopic reaction mechanism for CO2 gasification of cellulose based on reactive force field molecular dynamics simulations

Gasification is the key process of biomass conversion and utilization, which has been proved to be one of the most promising technologies. In this study, the CO2 gasification process of cellulose was explored by reactive force field molecular dynamics simulations. Firstly, the distribution of average local ionization energy was analyzed. The results showed that the oxygen and hydrogen atoms might be reactive sites. In addition, the product evolution, bond-breaking behavior and carbon conversion during CO2 gasification were investigated. It was found that the bond dissociation energy of glycosidic bond was low and the bond breaking was easy to occur. The CO2 gasification of cellulose was divided into two stages, first the cellulose molecules broke down into small molecular fragments, and then they reacted with CO2. Finally, the effects of CO2/steam ratio and CO2/O2 ratio on the gasification process were analyzed. As the CO2/steam ratio decreased, the H2 yield increased, while the CO yield decreased. With the increase of CO2/O2 ratio, the carbon conversion rate had little change, while the contribution of CO2 gasification to carbon conversion decreased from 99.07% to 50%. The research provides a reference for revealing the microscopic mechanism for CO2 gasification of biomass.

Mechanism of catalytic conversion of kerosene co-refining heavy oil to BTEXN by Py-GC/MS based on “point-line-surface-body” step by step research strategy

Kerosene co-refining heavy oil (KCR-H), KCR-H six group components (KCR-HS), six typical model compounds representing the KCR-HS and its mixed model compound were selected as raw materials. The effects of the physicochemical properties of single and bi-metallic modified HZSM-5 (Me/Z-5) on the selectivity and yield of benzene (B), toluene (T), ethylbenzene (E), xylene (X), naphthalene (N) in cracking products were investigated by pyrolysis–gas chromatograph/mass spectrometer (Py-GC/MS). The results show that Ni-Mo/Z-5 exhibits superior selectivity for light aromatic in the catalytic conversion of tetradecane, benzofuran, and KCR-H, compared with Z-5. Additionally, oxygenated and aliphatic compounds are more easily converted to light aromatics than PAHs and nitrogen-containing compounds. Using Ni-Mo/Z-5 catalytic conversion benzofuran, the selectivity of BTEXN in the cracking product is 65.01 %, which is 23.44 times higher than pyrene (2.66 %). Due to the preferential cracking of benzofuran, small molecular fragments prepared by tetradecane and methyl naphthalene promote the catalytic conversion of methyl phenol, quinoline, and pyrene. Compared with the theoretical BTEXN yield (1338.39 mg/kg), the experimental BTEXN yield obtained from mixed model compounds (MCs) increasing by 37.95 %, which is 1846.40 mg/kg. In addition, the BTEXN selectivity of saturates (Satur) over Ni-Mo/Z-5 is 62.97 %, increases by 12.97 % compared with tetradecane, which represents the components of this group, indicating that the synergistic effect between oxygenated compounds and aliphatic compounds is conducive to produce light aromatics. Furthermore, based on the structural characteristics and catalytic properties of metalmodified Z-5 and the conformational relationships between points, lines, surfaces, and bodies, possible catalytic conversion mechanisms and pathways for KCR-H and KCR-HS were proposed.

Applying the quantum chemical simulation to describe electrical conductivity in silicate-based materials

Introduction. It is confirmed that a dispersion of carbon black when it added to concrete is likely to increase its electrical conductivity. These materials are of great importance for construction for example for civil engineering, transportation and energy industries. In that branches such materials could be used as snow melting systems, protective materials for metal bars, electromagnetically shielded materials. This study is about probable reason of electrically conductive properties in silicate-based material with carbon particles.
 
 Materials and methods. Small molecular fragments which are the parts of modified concrete have been considered to investigate contact areas between carbon particles in silicate based material. Fire Fly has been chosen as software. Exchange-correlation phenomenon has been included by using B3LYP.
 
 Results. An optimum percentage of modifier in mineral binder leads to the formation of an electrically conductive grid made of carbon nanoparticles. Electrical conductivity of material is influenced by contact areas between these nanoparticles. Quantum chemical molecular models of molecular fragments and interactions between these fragments have been made. Also, the impact of these areas on electrical conductivity was estimated.
 
 Conclusions. Quantum chemical molecular models and analysis based on the optimum percentage of the modifier showed that electrical conductivity of the modified concrete depended on an electrons movement along the grid of carbon nanoparticles formed within the mineral matrix. The key role in electrical conductivity of the material plays contact areas between these particles. Electrical conductivity is increasing due to silicate-based components in molecular fragments.

Photoaging and release profile of acrylonitrile butadiene styrene microplastics under simulated solar radiation in water

Microplastics (MPs) pollution has become a major environmental problem and poses a risk to a variety of organisms. In this study, the photoaging behavior of acrylonitrile butadiene styrene microplastics (ABS-MP) in aqueous environment was investigated under simulated solar irradiation. Results showed that the long chains of ABS-MP broke under the light irradiation, and its thermal stability was reduced. ABS-MP was oxidized during photoaging and produced a large number of oxygen-containing functional groups. Structure destruction of ABS-MP decreased the formation of environmentally persistent free radicals (EPFRs) and further photoirradiation generated secondary EPFRs. Nuclear magnetic resonance (NMR) analysis of the aged leachates confirmed that ABS-MP was oxidized and some small molecular fragments were dropped during photoaging. Meanwhile, C–Br bond broke of additive tetrabromobisphenol A (TBBPA) resulting in more bromine released into water and Sb(III) of additive Sb2O3 was oxidized to Sb(V) during photoaging. These findings illustrate the necessity of considering the aging of MPs in natural environment, expand the understanding of the potential harm and fate of MPs in aqueous environment, which is important for the management of MPs.