Molecular Structure Transformation Research Articles

Selective degradation of organic pollutants in the aquatic environment by microplastic-derived dissolved organic matter through molecular photoresponse sequence transformation

The photochemical behavior of microplastics (MPs)-dissolved organic matter (PDOM) has received considerable attention, the molecular mechanism by which it undergoes photoresponsive transformation to generate reactive oxygen species (ROS) for the removal of organic pollutants remains unclear. This study combines fluorescence, mass spectrometry, and theoretical models to analyse the differences in the molecular mechanisms of PDOM, biochar-DOM (BDOM) and soil-DOM (SDOM) photoresponsive releasing ROS for selective degradation of organic pollutants. During the photoresponse process, molecular compounds in DOMs mainly undergo demethylation, decarboxylation, deoxygenation reactions to selectively degrade organic pollutants. However, differences in DOMs’ molecular structure composition and transformation patterns lead to varying ROS production. BDOMs containing higher proportion of aromatic compounds (26.68 %) exhibit stronger photoreactivity, resulting in better degradation efficiency of pollutants (>90 %). The high selectivity of PDOM for degradation of organic pollutants stems from the interconversion mode between its high and low oxygen compounds. PDOM degrades large molecular pollutants into less biotoxic small molecular intermediates through both radical and non-radical pathways, thereby reducing environmental hazards (1.5–948 times) posed by pollutants. The results show that although MPs is harmful to aquatic environment, it plays a positive role in regulating the structure of organic carbon pool and reducing environmental risks of other pollutants.

Stereochemical Control of Redox CoII/CoIII-Cages with Switchable Cotton Effects Based on Labile-Static States.

The structural dynamics of artificial assemblies, in aspects such as molecular recognition and structural transformation, provide us with a blueprint to achieve bioinspired applications. Here, we describe the assembly of redox-switchable chiral metal-organic cages Λ8/Δ8-[Pd6(CoIIL3)8]28+ and Λ8/Δ8-[Pd6(CoIIIL3)8]36+. These isomeric cages demonstrate an on-off chirality logic gate controlled by their chemical and stereostructural dynamics tunable through redox transitions between the labile CoII-state and static CoIII-state with a distinct Cotton effect. The transition between different states is enabled by a reversible redox process and chiral recognition originating in the tris-chelate Co-centers. All cages in two states are thoroughly characterized by NMR, ESI-MS, CV, CD, and X-ray crystallographic analysis, which clarify their redox-switching behaviors upon chemical reduction/oxidation. The stereochemical lability of the CoII-center endows the Λ8/Δ8-CoII-cages with efficient chiral-induction by enantiomeric guests, leading to enantiomeric isomerization to switch between Λ8/Δ8-CoII-cages, which can be stabilized by oxidation to their chemically inert forms of Λ8/Δ8-CoIII-cages. Kinetic studies reveal that the isomerization rate of the Δ8-CoIII-cage is at least an order of magnitude slower than that of the Δ8-CoII-cage even at an elevated temperature, while its activation energy is 16 kcal mol-1 higher than that of the CoII-cage.

Targeted Stimulation of Micropores by CS2 Extraction on Molecular of Coal.

The targeted stimulation of micropores based on the transformation of coal's molecular structure is proposed due to the chemical properties and difficult-to-transform properties of micropores. Carbon disulfide (CS2) extraction is used as a targeted stimulation to reveal the internal evolution mechanism of micropore transformation. The variations of microcrystalline structures and micropores of bituminous coal and anthracite extracted by CS2 were analyzed with X-ray diffraction (XRD), low-temperature carbon dioxide (CO2) adsorption, and molecular simulation. The results show that CS2 extraction, with the broken chain effect, swelling effect, and aromatic ring rearrangement effect, can promote micropore generation of bituminous coal by transforming the microcrystalline structure. Furthermore, CS2 extraction on bituminous coal can decrease the average micropore size and increase the micropore volume and area. The aromatic layer fragmentation effect of CS2 extraction on anthracite, compared to the micropore generation effect of the broken chain effect and swelling effect, can enlarge micropores more remarkably, as it induces an enhancement in the average micropore size and a decline in the micropore volume and area. The research is expected to provide a theoretical basis for establishing reservoir stimulation technology based on CS2 extraction.

Elucidating the Changes in Molecular Structure at the Buried Interface of RTV Silicone Elastomers during Curing.

Silicone elastomers are widely used in many industrial applications, including coatings, adhesives, and sealants. Room-temperature vulcanized (RTV) silicone, a major subcategory of silicone elastomers, undergoes molecular structural transformations during condensation curing, which affect their mechanical, thermal, and chemical properties. The role of reactive hydroxyl (-OH) groups in the curing reaction of RTV silicone is crucial but not well understood, particularly when multiple sources of hydroxyl groups are present in a formulated product. This work aims to elucidate the interfacial molecular structural changes and origins of interfacial reactive hydroxyl groups in RTV silicone during curing, focusing on the methoxy groups at interfaces and their relationship to adhesion. Sum frequency generation (SFG) vibrational spectroscopy is an in situ nondestructive technique used in this study to investigate the interfacial molecular structure of select RTV formulations at the buried interface at different levels of cure. The primary sources of hydroxyl groups required for interfacial reactions in the initial curing stage are found to be those on the substrate surface rather than those from the ingress of ambient moisture. The silylation treatment of silica substrates eliminates interfacial hydroxyl groups, which greatly impact the silicone interfacial behavior and properties (e.g., adhesion). This study establishes the correlation between interfacial molecular structural changes in RTV silicones and their effect on adhesion strength. It also highlights the power of SFG spectroscopy as a unique tool for studying chemical and structural changes at RTV silicone/substrate interface in situ and in real time during curing. This work provides valuable insights into the interfacial chemistry of RTV silicone and its implications for material performance and application development, aiding in the development of improved silicone adhesives.

Shock Wave–Induced Dynamic Mechanical Behavior of Calcium Silicate Aluminate Hydrate at the Molecular Scale

Calcium silicate aluminate hydrate (C-A-S-H) is the main hydration product of cement mixed with industrial wastes. The purpose of this study is to understand the dynamic mechanical behavior and structural transformations of molecular-scale C-A-S-H induced by shock waves. Three C-A-S-H models with Al/Si ratios of 0.0, 0.1, and 0.2 are constructed and reactive molecular dynamics simulations are used to perform shock compressions with different shock velocities from 0.1 km/s to 3.6 km/s. The distributions of particle velocity, pressure, and density along the shock direction are calculated using the binning analysis method, allowing Hugoniot pressure-specific volume curves to be derived. The results reveal that shock waves may induce elastic, elastic-plastic, or shock Hugoniot responses in molecular-scale C-A-S-H, depending on the Al/Si ratio and the shock velocity. Below the Hugoniot elastic limit (HEL), higher Al/Si ratios cause the elastic wave to propagate farther due to the cross-linking effect of aluminate units. Above the HEL, higher Al/Si ratios give rise to a distinct two-wave structure characteristic comprising a plastic front and an elastic precursor. This characteristic becomes less pronounced as the shock velocity increases. Analysis of the molecular structural transformations of C-A-S-H revealed that the main atomic deformation behavior below the HEL involves a reduction of interatomic distances; above the HEL the main response is a densification of water molecules followed by a general collapse of the layered structure as the shock velocity increases.

Crystallinity effect on electron-induced molecular structure transformations in additive-free PLA

Additive-free biodegradable polylactides (PLAs) with different crystallinities from 0 to 13.3% (according to x-ray diffraction, XRD) were used as starting materials modified by the electron beam (EB) with several irradiation doses at 25 °C (below glass transition temperature, <Tg) and 80 °C (>Tg) in nitrogen. The crystallinity effects on radical decay and molecular structure transformation were investigated. After irradiation, the main stable radical remained in PLA is –O–C*(CH3)–CO–. During irradiation, radical reactions were inhibited by high crystallinity. Large amounts of EB-induced crosslinking and long-chain branching (LCB) were introduced by performing irradiation at 80 °C. An increasing crystallinity has been found that restrained crosslinking and LCB due to the poor chain mobility in the crystalline areas. An increase of crystallinity from 0 to 13.3% obviously decreased the saturated crosslink content from 65% to 43% and restrained LCB formation. This study also verified that strict moisture control combined with applying an irradiation temperature above Tg can be a universal method to introduce large amounts of crosslinking and LCB in different grades of additive-free PLA.

Understanding the membrane fouling control process at molecular level in the heated persulfate activation- membrane distillation hybrid system

Sulfate radical (SO4●−) based advanced oxidation is considered as a promising pretreatment strategy to degrade organic pollutants and thereby mitigate the membrane fouling in the membrane process. In this study, heat-activated persulfate (PS) activation was integrated with the membrane distillation (MD) process for the alleviation of membrane fouling in treatment of wastewater treatment plant (WWTP) secondary effluent and surface water. In-depth understanding of the molecular fate during membrane fouling control process was performed by using a non-targeted screening method of two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC−TOF−MS) coupling with multiple characterizations. It was found that the heat-activated PS activation pretreatment could effectively degrade the dissolved organic matter (DOM) and change its molecular conformation, wherein the relative abundance of oxygen-containing substances was remarkably increased through oxygenation reactions. Moreover, the refractory organics with higher molecular weight (MW) and unsaturation degree were more inclined to be destroyed, following by partial mineralization during pretreatment process. It was also identified that oxygen-deficient compounds and the molecular formulas featuring higher double bond equivalent (DBE) values and lower MW tended to be deposited on the membrane surface to cause the membrane fouling. In particular, the aliphatic substances were the predominant components irrespective of membrane foulant samples from secondary effluent or surface water. Meanwhile, the complexation between organic compounds and high valence cations as well as the precipitation of inorganics were restrained owing to the reduction of DOM concentration and the transformation of molecular structure, consequently leading to reduced membrane fouling. This study is believed to further provide new insight into the membrane fouling control mechanism at molecular level.

Elucidating Orbital Delocalization Effects on Boosting Electrochemiluminescence Efficiency of Carbon Nitrides

AbstractHighly efficient inter‐conversion of different types of energy is the core of science and technology. Among them, electrochemiluminescence (ECL), an emission of light excited by electrochemical reactions, has drawn attention as a powerful tool across diverse fields in addressing global energy, environment, and health challenges. Nonetheless, the ECL efficiency (ΦECL) of most luminophores in aqueous solutions is low, significantly hampering their broad applications. Along this line, developing ECL luminophores with high ΦECL and understanding the associated intrinsic factors is highly envisioned. Herein, taking carbon nitride (CN) with rigid 2D backbones as an emerging model luminophore, it is reported that the orbital delocalization is a unified and quantifiable factor for its ΦECL. Behind the complicated transformation of molecular structures of cyano‐terminal groups and triazine/heptazine basal frameworks, the orbital delocalization of CN is found to be generally improved at an elevated condensation temperature. Such intrinsic evolution in electronic structure favored the electron injection in excitation and follow‐up photon emission in ECL for CN. As a result, the cathodic ΦECL of CN is remarkably improved to a new milestone of 24‐fold greater than the previous record.

Metal‐free and One‐pot for the Synthesis of Indolo[2,1‐a]isoquinoline Aldehyde via a Free Radical Cascade Pathway followed by Direct Hydrolyzation

AbstractAs one of the most versatile intermediate group in synthetic chemistry, the introduction of an aldehyde group into a specific moiety is important for the transformation of molecular structures. Herein, we provided a metal‐free, regioselective and one‐pot formylation of the indolo[2,1‐a]isoquinoline moiety. This strategy features an oxidative coupling process using commercially available 1,3‐dioxolane as a formylated reagent followed by direct hydrolyzation without a separation process. This reaction can be carried out under common reaction conditions and displays broad functional group tolerance.

Self-assembly and cellular distribution of a series of transformable peptides.

Transformable peptides (TPs) are biomedical materials with unique structures and diverse functionalities that have drawn great interest in materials science and nanomedicine. Here, we design a series of TPs with five self-assembling sequences conjugated with the hydrophobic unit bis(pyrene) and the targeting sequence RGD, and study the transformable features induced by ligand (RGD)-receptor (integrin or Ca2+) interactions. TPs are able to self-assemble into nanoparticles or nanosheets and then transform into nano-aggregates or nanofibers induced by RGD-Ca2+ interactions in solution. When TPs are incubated with breast cancer cells expressing integrin receptors on the cell membrane, it is found that they display different cell distributions, including adhesion on the cell membrane, location in the lysosome, or escape from the lysosome to cytoplasm. This study reveals that the self-assembling sequence affects the dynamic self-assembly nanostructures of TPs and the resultant biodistribution in cells.

Nanoscale geochemical heterogeneity of organic matter in thermally-mature shales: An AFM-IR study

The composition and characteristics of organic matter within shales can reveal important information on hydrocarbon generation, migration and accumulation processes during catagenesis. It may also impact upon the chemical properties and mechanical behavior of shales acting as hydrocarbon reservoirs or caprocks/seals for carbon and subsurface energy storage. Here we apply advanced atomic force microscopy-based infrared spectroscopy (AFM-IR) to capture the in-situ chemical structure of nanoscale molecular composition of individual organic particles and map the distribution of typical functional groups nondestructively; something that cannot be achieved via conventional analysis since some methods damage the sample, some only collect bulk measurements and some do not achieve nano-scale resolution. The nanoscale geochemical characteristics of organic matter in thermally mature samples of a Baltic Basin shale, from Lithuania and the Bowland Shale, from the UK, obtained from AFM-IR, are compared in this study. Significant chemical heterogeneity can be observed in migrated solid bitumen. In contrast, graptolite, alginite and inertinite generally display homogeneous molecular composition. The potential role of laminae as barriers to the vertical migration of hydrocarbons is also apparent. This research provides insights into nanoscale geochemical information on different organic matter types in thermally-mature shales to enhance the understanding of molecular structure transformation of organic matter during hydrocarbon expulsion and migration processes, and also sheds light on implications of nanogeochemistry for enhanced gas recovery, carbon sequestration and underground hydrogen storage-related energy applications. We also characterised specific materials which have not been reported in other geological studies using AFM-IR. Some of them display similar characteristics to other organic matter particles in the samples, but the possibilities of unknown organic contaminants introduced to the sample during sample storage or preparation stages cannot be ruled out. A comprehensive analysis on this undefined organic material is provided. Standardized approaches during sample preparation and storage are required for future research to dislodge potential surface-attached contaminants.

The molecular structural transformation of jackfruit seed starch in hydrogen peroxide oxidation condition

Jackfruit (Artocarpus heterophyllus Lam.) is popularly grown in tropical countries including Vietnam. Jackfruit seeds contain high starch but usually discharged during processing produces about jackfruit. The study was carried out oxidizing the starch isolating from jackfruit seeds by hydrogen peroxide agent to increase starch value for its potential industrial applications. The optimal parameters were oxidizing agent concentration, starch/water ratio, temperature, pH and reaction time. The recovery efficiency was at 95.79%; Carbonyl content of oxidized jackfruit seed starch (OJS) products was at 1.06%; and carboxyl was at 0.29%. Scanning electron microscopy (SEM) revealed that the OJS particles remained the original structure, but the grain surface was no longer as smooth as natural starch but rough, appeared to have small pores and the edges lost definition completely. The vibrations of featured functional groups in OJS structure appeared at peak with the wavenumber of 1760 ​cm−1 related to the oscillation of the C = O group via Fourier transform infrared (FTIR) spectrum. The oxidation mainly occurred in the amorphous phase using X-ray diffraction (XRD) pattern. The structural modellings of jackfruit seed starch products related to glucose chains were shown based on evaluation for changes of microstructure via XRD and FTIR analyses Abstract Text.

Iron-catalyzed tandem oxidative coupling and acetal hydrolysis reaction to prepare formylated benzothiazoles and isoquinolines.

The aldehyde group is one of the most versatile intermediates in synthetic chemistry, and the introduction of an aldehyde group into heteroarenes is important for the transformation of molecular structure. Herein, we achieved the direct formylation of benzothiazo/les and isoquinolines. The reaction features a novel iron-catalyzed Minisci-type oxidative coupling process using commercially available 1,3-dioxolane as a formylated reagent followed by acetal hydrolysis without a separation process. The reaction can be performed under exceedingly mild reaction conditions and exhibits broad functional group tolerance.

Fatigue performance of carbon fiber reinforced epoxy resin: A molecular simulation

In this work, mechanical behavior of multilayer graphene reinforced epoxy resin during fatigue was studied by molecular dynamic method. Transversely isotropic atom based model was established to simulate the carbon fiber reinforced plastics. The reinforced phase was multilayer graphene, and the matrix phase was epoxy resin. Performance degradation in the fiber direction (axial fatigue) and the vertical fiber direction (transversal fatigue) was studied, respectively. Mean stress was considered as the performance per cycle and the power function was employed to describe the tendency of performance degradation. Evolution of energy and structure in atomic scale was used to characterize the cause of performance degradation. The results showed that performance degraded slower in the fiber direction than that in the vertical fiber direction and faster in atomic scale than that in macroscopic experiment. Transformation of molecular structure, which could be represented by the radius of gyration (Rg) of molecular fragments, was one of the reasons that caused performance degradation. Besides, it could cause a change in microscopic energy. Both bond stretch energy and non‐bond interactional energy decrease obviously in the fiber direction while only non‐bond interactional energy decrease in the vertical fiber direction. This phenomenon indicates that existence of carbon fiber effectively slows down the rate of performance degradation in the fiber direction.

Rapid degradation of ciprofloxacin over BiOCl: Insight into the molecular structure transformation and antibacterial activity elimination

Currently, the widespread usage of antibiotics brings great challenge to sustainable water environment due to the production of drug-resistant bacteria, the rapid and effective removal of antibiotics attracts more and more attention. Herein, a BiOCl microsphere prepared by a facile hydrolysis method via controlling the EG-H2O ratio was found to have unexpected photocatalytic activity for ciprofloxacin (CIP) removal. The photodegradation rate of CIP over optimal BiOCl-20 reached 92.9% in only 3 min of simulated sunlight irradiation, and the mineralization rate was 30.8% after 60 min reaction. The antibacterial tests of CIP solution under different irradiation minutes were evaluated using Escherichia coli (E. coli) as the model bacteria. The results indicated that CIP photodegradation intermediates had also certain antimicrobial potency, which could be eliminated almost completely after 3 min irradiation, although there still had some incompletely mineralized intermediates. In view of these results, the macroscopic degradation behavior of CIP over BiOCl-20 as well as the microscopic existence state and reaction behavior of the intermediates should be clarified. A ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for determination of CIP and its intermediates. Ten primary intermediates were separated and identified, and their corresponding molecular structures were elucidated. Three main photodegradation pathways were deduced, and the correlation between molecular structure transformation and antibacterial activity of CIP was established. Because of the destruction of piperazine ring and defluorination of quinolone ring, the antibacterial activity of the treated CIP solution was weakened or even eliminated. Finally, a possible photodegradation mechanism was proposed, the OVs, O2−, h+ and OH played significant roles in the CIP photodegradation. This work does have great perspective for BiOCl potential application in CIP wastewater treatment.

Fabrication of phthalonitrile-based copper-clad laminates and their application properties: Thermo-stability and dielectric properties

Abstract Various phthalonitrile-based resins were prepared and their copper clad laminates were fabricated in this work. The curing behaviors and mechanisms were investigated by Dynamic rheological analysis (DRA) and in-situ FTIR. Results indicated that all phthalonitrile-based resins possessed wide process temperature windows and exhibit good processability. However, phthalonitrile-based resins resulted to various final crosslinking network in the presence of various catalyst/curing agents. Phthalonitrile-based copper clad laminates (CCL) were fabricated with hot-press mold technology. Mechanical properties of the CCL including flexural strength/modulus and peel strength were discussed, accompanied by the investigation of fractural surface of the laminates. Glass transition temperatures of the laminates were studied by both Differential scanning calorimetric (DSC) and Dynamic mechanical analysis (DMA). Then, fractural surface of fiber-reinforced composite laminates was investigated by Scanning electron microscope (SEM) and Micro slicing image (MSI). Results confirmed the satisfactory interfacial adhesion between resin matrices and fibers, which resulted to excellent mechanical properties of composite laminates. Then, dielectric properties of various composite laminates were investigated to evaluate their applications in the field of PCB substrates. Moreover, final dielectric properties of various phthalonitrile-based composites were discussed based on the transformation of molecular structures according to the polymerization mechanisms.

In situ cell for x-ray absorption spectroscopy of low volatility compound vapors

Technologically relevant gas phase processes rely on reactants in vapor form for the production of thin films and nanoparticles. An instrument is described which enables the investigation of such vapors by x-ray absorption spectroscopy. Corresponding in situ studies provide information about gas phase precursor chemistry and optimized synthesis processes. The setup consists of a sealed vapor container heated by a hot air bath. Inert gas filling and temperature monitoring are implemented. Fluid dynamic simulations reveal a homogeneous temperature distribution without hot or cold spots. Temperature stability better than 1 K for at least 190 min allows time-dependent measurements or improved signal to noise ratios by averaging of datasets. Iron acetylacetonate is studied as a model system. X-ray absorption spectra measured by fluorescence are of high quality, allowing a detailed analysis of X-ray Absorption Near Edge Structure (XANES) and extended x-ray absorption fine structure. A molecular structure transformation is observed in XANES spectra of iron acetylacetonate vapor above 480 K probably due to the loss of one ligand. The setup allows the investigation of low volatility compounds with vapor pressures above 2 kPa at temperatures up to 520 K.

Geochemical barriers as structural components of the geochemical systems evolution

The term “geochemical barrier” (GCB) has been widely used in the Russian geochemical literature as a key concept of the distribution of elements and substances theory (incl. pollutions)although in the world research practice this term is not particularly represented. The assessment of the functional role of the geochemical barriers in relation to the properties and evolution of the geochemical systems (GCS)is demonstrated.The foundations of Haken synergy, the foundations of self-organization of systems and non-equilibrium (non-linear) thermodynamics of I. Prigogine and his school are used as a methodological framework. From the authors’ point of view, GCB are considered as self-organizing components of GCS, in which physical and chemical processes are activated, leading to the transformation of atomic and molecular structures, chemical associations and individual chemical elements under the impact of active media (processes). They can be the defining phenomenon of the emergence and evolution of GCS. The concept of geochemical barriers is the foundation for technologies that are actively implemented for cleaning and protecting soils, groundwater and surface water, and the geological environment in general.

Gas generation by coal matter in contemporary conditions

A new approach for the study of processes at the atomic-molecular level occurring in the current situation in fossil carbonized organics was proposed. A new phenomenological model of physicochemical transformations in a metastable coal substance with the emission of fluids has been developed. The proposed physic/chemical model is based on the genetic connection of coal methane with fossil organic matter and determines the conditions for the activation of structural transformations in coalmines. This model describes the possible options for the coal/gas system development in the current situation. The accumulation of thermal and mechanical energy by coal in the form of structural stresses in an amount, sufficient to activate free-radical reactions, was experimentally established. In the undisturbed coalrock massif the processes of the coal molecular structure transformation have the relaxation character. The result of relaxation of the accumulated energy in the conditions of a gas-saturated coalrock massif is the methane generation by coal. Gas generation in the process of coalification, in its essence, is the energy response of the system to the action of external geomechanical options (temperature and pressure), by the way of releasing the accumulated additional energy with the emission of gaseous products and the destruction of the solid phase in the organic matter of the coal.

Super-bandgap light stimulated reversible transformation and laser-driven mass transport at the surface of As2S3 chalcogenide nanolayers studied in situ.

The super-bandgap laser irradiation of the in situ prepared As-S chalcogenide films was found to cause drastic structural transformations and unexpected selective diffusion processes, leading to As enrichment on the nanolayer surface. Excitation energy dependent synchrotron radiation photoelectron spectroscopy showed complete reversibility of the molecular transformations and selective laser-driven mass transport during "laser irradiation"-"thermal annealing" cycles. Molecular modeling and density functional theory calculations performed on As-rich cage-like clusters built from basic structural units indicate that the underlying microscopic mechanism of laser induced transformations is connected with the realgar-pararealgar transition in the As-S structure. The detected changes in surface composition as well as the related local and molecular structural transformations are analyzed and a model is proposed and discussed in detail. It is suggested that the formation of a concentration gradient is a result of bond cleavage and molecular reorientation during transformations and anisotropic molecular diffusion.